CSF-1

24 Pages·0.556 MB·English

by  Stanley E.R.

CSF-1
E. Richard Stanley*
Department of Developmental and Molecular Biology, Albert Einstein College of Medicine,
Bronx, NY 10461, USA
*corresponding author tel: [phone], fax: [phone], e-mail: [email protected]
DOI: 10.1006/rwcy.2000.09005.
SUMMARY was shown to stimulate the formation of colonies of
macrophages (Stanley et al., 1978). Specific antibody
Colony-stimulating factor 1 (CSF-1) is the primary neutralizationstudiesandthedevelopmentofspecific
regulator of the survival, proliferation, and differ- radioimmunoassays and radioreceptor assays
entiation of mononuclear phagocytes and also regu- (Stanley, 1979; Das et al., 1980, 1981), indicated that
lates cells of the female reproductive tract. Produced it was distinct from the other CSFs (Stanley, 1985).
by a wide variety of cell types, CSF-1 acts humorally
and locally. It is secreted into the circulation as a
glycoprotein or chondroitin sulfate-containing pro- Alternative names
teoglycan and expressed on the surface of CSF-1-
producing cells. CSF-1 effects are mediated by the PriortothedelineationoftheCSFsubclasses,CSF-1
CSF-1receptortyrosinekinasethatisencodedbythe was referred to as CSF, macrophage and granulocyte
c-fms protooncogene product. Osteopetrotic Csf1op/ inducer IM (MGI-IM) or alternatively, macrophage
Csf1op mice possess an inactivating mutation in the growth factor (MGF), which was assayed by its
CSF-1 gene and besides striking reductions in num- ability to stimulate the proliferation of activated
bers of osteoclasts and certain tissue macrophages, peritoneal macrophages (Stanley, 1994). Currently, it
they exhibit a pleiotropic phenotype. This pleiotropic is also known as macrophage colony stimulating
phenotype may be due to trophic and/or scavenger factor (M-CSF), although its action is not restricted
actionsofmacrophagesandothercelltypesregulated tomacrophages.Proteoglycan-100hasbeenshownto
by CSF-1, that control such characteristics as dermal be the proteoglycan form of CSF-1 (Partenheimer
thickness, male and female fertility, and neural et al., 1995).
processing. CSF-1 appears to play an autocrine and/
orparacrineroleincancersofthefemalereproductive
tract and the myeloid system. Structure
Through alternative mRNA splicing and differential
BACKGROUND
posttranslational proteolytic processing, mouse and
human CSF-1 can either be secreted into the
Discovery
circulation as an 80–100 kDa glycoprotein or 130–
160kDachondroitinsulfate-containingproteoglycan,
Colony-stimulating factors (CSFs) were so named or expressed as a membrane-spanning 68–86kDa
because of their ability to stimulate the formation of glycoprotein on the surface of CSF-1-producing
coloniesofmaturemyeloidcellsfromsingleimmature cells. All biologically active forms are dimeric and
hematopoietic precursor cells plated in semisolid contain the N-terminal 150 amino acids of the full-
medium. The homodimeric glycoprotein colony- length (cid:24)520 amino acid CSF-1 precursor that are
stimulating factor 1 (CSF-1) was the first of these requiredforinvitrobiologicalactivity(Stanley,1994)
factors to be purified (Stanley and Heard, 1977) and (Figure 1).
Figure 1 CSF-1 genomic organization, expression, and structure. The CSF-1
gene is localized to human chromosome 1p13-p21 and mouse chromosome 3.
The bottom half of the diagram shows the intron–exon structure and four
representative human cDNA clones that have been sequenced. Similar mouse
clones have been isolated. Exons (1–10) and the transmembranedomain (TM,
cross-hatched), are indicated. The 4kb and 2.1kb mRNAs arise from
alternativeusageofuntranslatedregionsencodedbyexons9and10,thelatter
exon encoding putative mRNA instability sequences (AU). The 1.6kb and
3.1kb mRNAs are products of a splicing reaction that results in the use of a
short form of exon 6. The approximate intracellular proteolytic cleavage sites
(arrowheads) and the chondroitin sulfate glycosaminoglycan addition site
(GAG) are also shown. The top half of the diagram shows the processing of
CSF-1 homodimers encoded by both the short and long coding regions.
Hatched regions represent those present in the mature secreted or released
glycoprotein forms while both hatched and filled regions are present in the
major secreted proteoglycan form. N-Linked (filled arrowheads) and O-linked
(open circles) glycosylation sites, the chondroitin sulfate chain (linked, open
hexagons) and the transmembrane domain (filled region) are shown.
Reproduced from Stanley (1998).
CSF-1 913
Main activities and Bovine:
CSF-1522: D87917 (Yoshihara et al., 1998)
pathophysiological roles
CSF-1225: D87918 (Yoshihara et al., 1998)
CSF-1 is the primary regulator of the survival,
proliferation, and differentiation of mononuclear
Chromosome location
phagocytes, including tissue macrophages and osteo-
clasts. It has also been shown to stimulate CD5(cid:135) B
lymphocytes to develop into biphenotypic B/macro- The human CSF-1 gene is approximately 21kb
phage cells (Borrello and Phipps, 1999). CSF-1 acts in length, comprising 10 exons (Ladner et al., 1987;
locally and humorally, preferentially regulating the KawasakiandLadner,1990)(Figure1).Itislocalized
development of macrophages found in tissues under- to human chromosome 1p13-p21. The mouse CSF-1
goingactivemorphogenesisand/ortissueremodeling. gene (Csf1) is localized to chromosome 3F3 at
Cells requiring CSF-1 for their development may what was formerly known as the op locus (Stanley,
regulate,viatrophicand/orscavengerfunctions,bone 1994).
resorption, male fertility, the thickness of the dermis, Exon 1 encodes the 50 UTR and a portion of the
and neural processing. In the female reproductive signal sequence, exons 2–6 encode the CSF-1 pre-
system, CSF-1 regulates the development of macro- cursor domain expressed on the luminal side of the
phages and the function of nonmononuclear phago- endoplasmic reticulum, the entire transmembrane
cytic, CSF-1 receptor-expressing cells. Mice bearing domain and a portion of the cytoplasmic domain,
the mutation osteopetrotic (Csf1op) possess an inacti- exon 6 spanning the transmembrane domain and
vating mutation in the CSF-1 gene and exhibit a portions of the other two domains. Exons 7 and 8
pleiotropic phenotype that reflects the roles of the encodetheremainderofthecytoplasmicdomain,exon
cells regulated by CSF-1. CSF-1 appears to play an 8also encodingasmall portionofthe30 UTR,which
autocrine and/or paracrine role in cancers of the ispredominantlyencodedbyexons9or10(Figure1).
ovary, endometrium, breast, and myeloid tissues The most abundant mRNA transcripts are those
(Janowska-Wieczorek et al., 1991; Kacinski, 1995; resultingfromthealternativeuseofdifferent30 UTRs
Pollard and Stanley, 1996; Scholl et al., 1996; Haran- encoded by exons 9 (0.68kb) and 10 (2kb) (Ladner
Ghera et al., 1997; Sapi and Kacinski, 1999). et al., 1987; Wong et al., 1987). The 30 UTR encoded
by exon 10 contains AU-rich sequences, which may
confermRNAinstability.AlternativemRNAsplicing
GENE AND GENE REGULATION in exon 6 can result in shortened coding regions in
CSF-1mRNAsthataffecttheprocessingoftheCSF-
Accession numbers 1 protein precursors they encode (Kawasaki et al.,
1985; Ladner et al., 1987; Wong et al., 1987; Cerretti
CSF-1 cDNAs have been cloned from several species etal.,1988).Theabundanceofthesemessages,which
and are listed below with their GenBank accession encode the relatively stably expressed cell surface
numbers. form of CSF-1, is less. Additional species of CSF-1
Human: mRNA have been described in specific cell lines.
CSF-1522: M37435 (Wong et al., 1987); X05825
(Ladner et al., 1987); NM_000757 (Takahashi et al.,
1989) Regulatory sites and corresponding
CSF-1406: U22385 (Cerretti et al., 1988)
transcription factors
CSF-1224: M21149 (Kawasaki et al., 1985; Pampfer
et al., 1991)
Mouse: The 50 promoter regions of the human (Ladner et al.,
CSF-1520 exon 9 30 UTR: M21149 (Ladner et al., 1987) and mouse (Harrington et al., 1991) CSF-1
1988); X05010 (DeLamarter et al., 1987) genes have been cloned. They exhibit 80% sequence
CSF-1520 exon 10 30 UTR: M21952 (Ladner et al., similarity in the region 450bp upstream of the tran-
1988) scription start site. Several elements, involved in the
CSF-1520: M15692 (Rajavashisth et al., 1987) regulation of CSF-1 gene expression, are located
Rat: within this region and the control of gene expression
CSF-1520: M84361 (Borycki et al., 1993) in monocytesandfibroblastsis mediatedby common
Rabbit: and cell type-specific trans-acting factors (Konicek
CSF-1: E14817 et al., 1998).
914 E. Richard Stanley
Cells and tissues that express Ladner, 1990). The cysteine residues involved in
intrachain (Cys7–Cys90, Cys48–Cys139, Cys102–
the gene
Cys146) and interchain, (Cys31–Cys31, Cys157–
Cys157, Cys159–Cys159) disulfide bonding in human
See Cellular sources and tissue expression. CSF-1 (Glocker et al., 1993; Wilkins et al., 1993) are
highly conserved in published CSF-1 sequences from
all species.
PROTEIN
Accession numbers Description of protein
Human: ThesecretedformsofmouseCSF-1arehomodimeric
CSF-1522:AAA52117(Wongetal.,1987);FQHUMP glycoproteinandproteoglycanmolecules(Priceetal.,
(Kawasaki et al., 1985; Ladner et al., 1987; Wong 1992). Reinterpretation of earlier data on the bio-
et al., 1987); AAA59573 (Takahashi et al., 1989) synthesis and secretion of human CSF-1 (Price et al.,
CSF-1406: AAA59572 (Cerretti et al., 1988) 1992; Stanley, 1994) together with other studies
CSF-1224: AAA52120 (Kawasaki et al., 1985; (Suzuet al., 1992),indicatethat the secreted forms of
Pampfer et al., 1991) human CSF-1, previously thought to be exclusively
Mouse: glycoprotein, are predominantly proteoglycan. As
CSF-1520: P07141 (Ladner et al., 1988); A31401 (Ben shown in Figure 1, the membrane-spanning CSF-1
Avram et al., 1985); CAA28660 (DeLamarter et al., precursor encoded by the full-length mRNA is
1987) cotranslationally N-glycosylated in the endoplasmic
Rat: reticulum. It rapidly undergoes a dimerization that
CSF-1520: AAA03032 (Borycki et al., 1993) involves the formation of interchain disulfide bonds
Bovine: (Price et al., 1992) and the resulting homodimeric
CSF-1522: BAA31556 (Yoshihara et al., 1998) precursor moves to the Golgi, where the N-linked
CSF-1225: BAA31557 (Yoshihara et al., 1998) oligosaccharidesare convertedfrom highmannoseto
complex type and O-linked oligosaccharides are
added. Among these O-linked oligosaccharides is an
Sequence
18,000kDa chondroitin sulfate chain that is added to
Ser277 (human) or Ser276 (mouse) within the
cDNAs encoding CSF-1 have been isolated from consensus sequence for glycosaminoglycan addition
several species and sequenced. A comparison of the (Price et al., 1992; Suzu et al., 1992). Once in the
aminoacidsequencesforhumanandmouseCSF-1is secretory vesicle, the secreted forms of the mature
shown in Figure 2. The coding region of the full- CSF-1 are cleaved from the precursor. Depending
lengthhumanCSF-1precursorcomprisesa32amino on whether the proteolytic cleavage takes place on
acid signal sequence, followed by 522 additional the amino terminal side or the carboxyl terminal side
residues which contain four potential N-linked glyco- of the glycosaminoglycan addition site, they are
sylation sites, a single consensus sequence for secreted as either the 80–100kDa glycoprotein or
glycosaminoglycan addition (acidic residues -Ser- 130–160kDa proteoglycan. Both forms rapidly accu-
Gly-X-Gly/Ala) at Ser277 and a hydrophobic stretch mulate in the extracellular medium with a half-time
of 23 amino acids at residues 464–486 that encodes of 40 minutes (Price et al., 1992) and have similar
the transmembrane domain and is followed by a receptor binding and in vitro biological activities
sequence of charged amino acids (Arg-Trp-Arg-Arg- (Price et al., 1992; Suzu et al., 1997).
Arg) that apparently functions as a ‘stop transfer’ Three sequenced human CSF-1 cDNAs possess
sequence (Kawasaki et al., 1985; Ladner et al., shorter than full-length coding regions due to
1987; Wong et al., 1987). Without its 32 amino acid alternative splicing in exon 6 (Kawasaki et al., 1985;
signal sequence, the full-length coding region of the Cerretti et al., 1988; Pampfer et al., 1991). These
mouse transcript predicts a precursor of 520 amino clones encode precursors of 224 (CSF-1224)
acidswith59.6%sequencesimilaritytohumanCSF-1 (Kawasaki et al., 1985; Pampfer et al., 1991) or 406
and all of the features of human CSF-1 mentioned (CSF-1406)(Cerrettietal.,1988)aminoacidsinwhich
above (Ladner et al., 1988). The highest degree of the amino acids 150–447 and 332–447 respectively,
sequence similarity (80.5%) occurs for the amino have been spliced out (Figure 1 and Figure 2). CSF-
terminalresidues1–149,whichhavebeenshowntobe 1224, also found in the mouse (Pollard and Stanley,
requiredforinvitrobiologicalactivity(Kawasakiand 1996), encodes a precursor in which the region
CSF-1 915
Figure 2 Amino acid sequences of the human CSF-1522 and mouse CSF-1520
precursors.InmouseCSF-1520,aminoacididentitywiththehumansequenceis
indicated by an asterisk. Maximal alignment of sequences was achieved by
introducing four gaps, each indicated by a dash. Signal peptide and
transmembrane domains are indicated respectively by large open and filled
boxes, N-linked glycosylation sites by the heavy-lined open boxes and cysteines
involved in the disulfide bonds by light-lined open boxes. The consensus
sequence for glycosaminoglycan addition (heavy underline) and the four (cid:11)
helical and two (cid:12) pleatedregions(overlined) are also shown. Amino acids 150–
447(betweenarrowsnumbered1)and332–447(betweenarrowsnumbered2)are
deleted in truncated forms that are derived from alternatively spliced mRNAs.
encodingtheproteolyticcleavagesites,thesitesforO- it is cotranslationally glycosylated in the endoplasmic
linked oligosaccharide addition (including the glyco- reticulum, rapidly dimerizes there and then moves to
saminoglycan site), and half of the potential the Golgi, where its N-linked oligosaccharides are
N-linked glycosylation sites have been deleted. It dif- converted to complex type. However, it is not pro-
fers significantly from the full-length precursor CSF- teolytically cleaved in the secretory vesicle. Instead,
1522 in its processing and expression. Like CSF-1522, uponfusionofthevesiclewiththeplasmamembrane,
916 E. Richard Stanley
itisexpressedasamembrane-spanningproteinonthe Important homologies
cell surface (Rettenmier et al., 1987) (Figure 1). In
contrast to the cells expressing CSF-1522, which
The membrane-spanning, cell surface form of CSF-1
secrete soluble CSF-1, fixed cell layers expressing (CSF-1224), stem cell factor, and Flt-3 ligand all have
CSF-1224 stimulate the proliferation of overlayered
short intracellular domains and share significant
macrophages, indicating that the membrane-span-
sequencesimilarityintheextracellulardomain(Bazan,
ning, cell surface form is biologically active (Stein
1991). The human CSF-1 Cys7–Cys90 and Cys48–
etal.,1990).StudiesinmouseLcellsindicatethatthis
Cys139intrachaindisulfidebondsareconservedinall
form of CSF-1 is stably expressed at the cell surface
three, while CSF-1 possesses an extra intrachain
(t (cid:136)7 hours) (Price et al., 1992). However, release
1/2 disulfide bond and an additional Cys involved in the
of CSF-1 by proteolysis from CSF-1224 at the cell
interchain disufide that links the monomers.
surface is greatly stimulated by activation of protein
kinase C (Stein and Rettenmier, 1991). Multiple
factors determine the selection of the ectodomain
Posttranslational modifications
cleavage site for the release of bioactive CSF-1 from
CSF224 (Deng et al., 1998). It is not clear how the
processing of CSF-1406 occurs. It is possible that it is All forms of CSF-1 are highly glycosylated with N-
andO-linkedoligosaccharides.Thesecretedformsare
both expressed on the cell surface and secreted.
more glycosylated than the cell surface form. The
Expressionoftranscriptsencodingthecellsurfaceand
most glycosylated form is the secreted proteoglycan
secreted forms of CSF-1 can be differentially regu-
which may possess one or two (cid:24)18,000 molecular
lated by sex steroid hormones (Lea et al., 1999).
weight chondroitin sulfate chains per dimer (Price
et al., 1992; Suzu et al., 1992). Two different types of
glycosaminoglycan that differ in their ability to bind
Discussion of crystal structure low density lipoproteins have been identified in the
proteoglycan CSF-1 (Chang et al., 1998).
The first 149 amino acids are conserved in all bio-
logically active forms of CSF-1 and are required for
in vitro biological activity (Stanley, 1994).The crystal CELLULAR SOURCES AND
structure of this region (amino acids 4–158) has been
determinedat2.5A˚ (Panditetal.,1992)anddespiteits TISSUE EXPRESSION
lack of sequence similarity with members of the cyto-
Cellular sources that produce
kine family, it also possesses a similar four (cid:11) helical
bundle/anti-parallel (cid:12) ribbon structure. The mono-
mer is an antiparallel four (cid:11) helical bundle in which CSF-1 is found and synthesized in most tissues,
the helices run up-up-down-down, similar to the con- including submaxillary gland, lung, spleen, kidney,
nectivity observed in GM-CSF and growth hormone. lymph nodes, brain, liver, testis, and ovary (Bartocci
However, the relative lengths of the helices and the et al., 1986; Roth et al., 1997). A variety of different
connecting loops differ and there are differences in types of normal cells synthesize CSF-1, including
the disulfide bonds in all three proteins (Pandit et al., fibroblasts, endothelial cells, bone marrow stromal
1992). The exon–intron junctions occur at nearly the cells,osteoblasts,thymicepithelialcells,keratinocytes,
same positions in the three-dimensional structure of astrocytes, myoblasts, mesothelial cells, liver paren-
all three, at the end of helix A, at the beginning of chymal cells (Stanley, 1994), thyrocytes (Matsumura
helix B, at the end of helix C, and the end of helix D. et al., 1999), and adipocytes (Levine et al., 1998).
ThedimerisformedbylinkingtwoCSF-1monomers CSF-1 is synthesized by ovarian granulosa cells,
end-to-end, yielding a very flat, elongated structure oviduct epithelium and in large amounts by uterine
with dimensions of approximately 80(cid:2)30(cid:2)20A˚ epithelialcellsduringpregnancy(Bartoccietal.,1986;
(Pandit et al., 1992). There are three intrachain disul- Pollardetal.,1987;PollardandStanley,1996;Cohen
fide bonds per monomer and an interchain disulfide et al., 1999). Cells from many neoplastic cell lines,
bond that maintain the dimeric state (Glocker et al., including leukemic, lymphoma, and pancreatic cell
1993; Wilkins et al., 1993). The interchain disulfide lines, and from adenocarcinomas of the lung, breast,
bond of the truncated biologically active form is not ovary,andendometriumsynthesizeCSF-1.Inseveral
necessary for activity, provided that the intrachain cases proliferation of these neoplastic cells is under
disulfide bonds remain intact (Krautwald and CSF-1 autocrine control (Roth and Stanley, 1992;
Baccarini, 1993). Stanley, 1994).
CSF-1 917
Eliciting and inhibitory stimuli, IN VITRO ACTIVITIES
including exogenous and
In vitro findings
endogenous modulators
In vitro CSF-1 synthesis is stimulated following the CSF-1 was initially defined as a macrophage colony-
activation of monocytes, endothelial cells, T lympho- stimulating factor or macrophage growth factor.
cytes, B lymphocytes, fibroblasts, and mesangial cells While its action is now clearly not limited to mono-
(Roth and Stanley, 1992). Stimulatory cytokines for nuclear phagocytes (hematopoietic macrophage
human monocytes, mouse macrophages, and several colony-forming cell!monoblast!promonocyte!
other cell types reportedly include bacterial lipopoly- monocyte!macrophage) these cells, including
saccharide (LPS), IgG complexes, IL-1, IFN(cid:13), osteoclast precursors, are stimulated to survive,
TNF(cid:11), IL-4, IL-6, and GM-CSF. However, caution proliferate, and differentiate in response to CSF-1.
must be used in interpreting some of these reports as Apart from their production via the mononuclear
indicated by Hamilton (1993). Various stimuli have phagocytic lineage, CSF-1 can also stimulate
also been reported to increase CSF-1 synthesis and macrophage development from CD5(cid:135) B lympho-
secretion by retinal pigment epithelial cells, chon- cytes (Borrello and Phipps, 1999). In addition,
drocytes, thymic epithelial cells, osteoblasts, endo- antisense experiments indicate that there is auto-
metrial stromal cells, keratinocytes, and thyroid crine regulation by CSF-1 during the early
follicular cells. In several cell types other agents proliferative step following induction of myogenic
regulate CSF-1 expression as well. For example, in differentiation in L6 (cid:11)1 rat myoblasts (Borycki
osteoblasts, synthesis is increased by IL-4 (Lacey et al., 1995a, 1995b, 1995c). Other cells, including
et al., 1994), TNF(cid:11) (Kaplan et al., 1996), PTH, trophoblastic and decidual cells are apparently
PTHrP (Weir et al., 1993), 1(cid:11),25-dihydroxyvitamin regulated by CSF-1, but CSF-1 does not appear to
D3 (Rubin et al., 1996), histamine (Takamatsu and regulate their proliferation. Circulating monocytes
Nakano, 1998), and dexamethasone (Rubin et al., are noncycling cells in vivo. However, in the mouse,
1998) and inhibited by estrogen (Srivastava et al., monocytes and their precursors, hematopoietic
1998). Endometrial stromal cell synthesis is stimu- macrophage colony-forming cells, monoblasts, and
lated by progesterone, testosterone (Kanzaki et al., promonocytes, are all capable of forming macro-
1995), IFN(cid:13), and platelet-activating factor (Nasu phage colonies in the presence of CSF-1 with very
et al., 1999), while endothelial and mesangial cell high plating efficiency. Macrophages that are
synthesis is stimulated by oxidized LDL (Pai et al., recently derived from monocytes possess a slightly
1995; Rajavashisth et al., 1995) and inhibited by NO reduced plating efficiency, while resident tissue
(Peng et al., 1995). Human thyroid follicular cell macrophage populations have relatively poor
synthesis is stimulated by IL-6 and inhibited by plating efficiencies, containing many macrophages
TGF(cid:12) (Matsumura et al., 1999). that are incapable of proliferating in response to
LPS,eitherdirectly,orindirectlythroughTNF(cid:11)or CSF-1 (Stanley et al., 1978, 1983). Human mono-
IL-1, potently stimulates mouse CSF-1 synthesis by nuclear phagocytes, in contrast to mouse mono-
many tissues in vivo, resulting in an increase of up to nuclear phagocytes, generally exhibit a poorer
7-fold in the circulating CSF-1 concentration proliferative response to CSF-1 (Das et al., 1981)
approximately 4 hours after administration (Roth and the proliferative response of monocytes and
et al., 1997). Modified LDL increased serum CSF macrophages is virtually nonexistent (Bennett et al.,
activity7-to26-foldfollowinginjectioninmice(Liao 1992).
et al., 1991) and increased CSF-1 synthesis by In vitro experiments with very primitive hemato-
endothelial cells and smooth muscle cells in vitro poietic cells from the bone marrow of mice recover-
(Rajavashisth et al., 1990; Clinton et al., 1992). ing from treatment with 5-fluorouracil resulted in
the purification and description of hematopoietin
1, a cytokine that synergized with CSF-1 and
other hematopoietic growth factors in stimulating
RECEPTOR UTILIZATION
the proliferation and differentiation of these cells
along multiple hematopoietic lineages (Bartelmez
The CSF-1 receptor (CSF-1R), encoded by the c-fms and Stanley, 1985; Jubinsky, 1985; Stanley et al.,
protooncogene(Sherretal.,1985),isamemberofthe 1986). Hematopoietin 1 was subsequently shown to
type III receptor tyrosine kinase family that includes be IL-1(cid:11) (Mochizuki et al., 1986). Very primitive
the PDGF, SCF, and Flk-2/Flt-3 receptors. hematopoietic precursor cells cannot proliferate in
918 E. Richard Stanley
response to CSF-1 alone, but the combination of Regulatory molecules: Inhibitors
CSF-1 with other hematopoietic cytokines, such as
and enhancers
IL-1,IL-3,andSCF,dramaticallyincreasesboththeir
plating efficiency and colony size (Bartelmez et al.,
1989; Williams et al., 1992). Recently, combined IL-1, IL-3, SCF (Bartelmez et al., 1989; Williams
treatment of mice with IL-1 and CSF-1 has been et al., 1992), GM-CSF (McNiece et al., 1988), IL-6
shown to be particularly effective in accelerating (Botetal.,1989),IL-2(Lietal.,1989),IL-7(Jacobsen
recovery from drug-induced myelosuppression in et al., 1994), and TNF(cid:11) (Guilbert et al., 1993)
mice (Kovacs et al., 1998). synergizewithCSF-1toregulatetheproliferationand
Several systems have been used to demonstrate differentiation of primitive hematopoietic cells to
that CSF-1 is required for the generation of macrophages. CSF-1 also synergizes with osteopro-
osteoclasts from precursor cells in vitro (Felix et al., tegerin ligand (OPGL)/osteoclast differentiation fac-
1994; Pollard and Stanley, 1996). Astrocytes from tor (ODF)/TNF-related activation-induced cytokine
brain have been shown to produce CSF-1 and (TRANCE) to stimulate osteoclastogenesis from
cultured microglia to express the CSF-1R and hematopoietic cells (Lacey et al., 1998; Yasuda et al.,
proliferate in response to CSF-1. In addition, CSF- 1998). CSF-1-induced macrophage colony formation
1 in serum-free primary embryonic brain cultures or macrophage proliferation has been shown to be
derived from the hippocampus, cerebellum, cortex inhibited by prostaglandin E (Williams, 1979), IFN(cid:13),
or hypothalamus stimulated increased cell numbers TNF(cid:11), LPS (Vairo et al., 1991), glucocorticoids
and process outgrowth of the vast majority of (Hamilton, 1983), and opioids (Roy et al., 1996).
neurons in all brain regions, with networks of
processes extending between almost all cells in the
Bioassays used
cortical cultures. These neurotropic effects of
CSF-1 are likely to be mediated via its action on
microglia (Michaelson et al., 1996; Pollard and The colony-stimulating factor bioassay is based on
Stanley, 1996). the CSF-dependent stimulation of bone marrow cells
Although CSF-1 has been claimed to stimulate toformcoloniesofgranulocytesand/ormacrophages
macrophages and monocytes to produce prosta- in semisolid culture media. A limitation of this assay
glandin E, plasminogen activator, IL-1, IFN(cid:13), isthatitcannotbeusedtospecificallyassayCSF-1in
and oxygen metabolites, many of these findings preparations that contain other CSFs. However,
have been questioned. CSF-1 appears to play an CSF-1-specific competitive binding assays have been
important role in priming macrophages to respond developed that are based on the ability of CSF-1 in
to other stimuli, such as LPS, by releasing cyto- assay samples to complete for the binding of labeled
kines such as TNF(cid:11), IL-1, and IL-6 (Hamilton, CSF-1 with either anti-CSF-1 antibody or the CSF-1
1993). CSF-1 has minor effects in promoting receptor on intact cells (Stanley, 1979; Das et al.,
phagocytosis, tumor cytotoxicity, and resistance to 1980,1981;Stanley,1981).Theseassaysarerelatively
viral infections (Ralph et al., 1986; Hamilton, 1993). species-specific, but all have the advantage of only
It stimulates the synthesis and surface expression of detecting biologically active CSF-1. Several non-
macrophage scavenger receptor (De Villiers et al., radioactive competitive immunoassays with similar
1994) and maintains the expression of CD36, an properties have recently been developed. Table 1
oxidized LDL lipoprotein scavenger receptor (Huh summarizesthesensitivityandspecificityofassaysfor
et al., 1996). CSF-1.
CSF-1 stimulation of macrophages causes
rapid morphological changes, including cell spread-
ing, extension of lamellopodia, and formation of IN VIVO BIOLOGICAL
ruffles on the cell surface (Boocock et al., 1989),
ACTIVITIES OF LIGANDS IN
followed by cell polarization and increased
ANIMAL MODELS
motility (Webb et al., 1996; Allen et al., 1998). It
hasbeenshowntostimulateinvasivenessofCSF-1R-
Normal physiological roles
expressing macrophage and carcinoma cell lines in a
human amniotic basement membrane invasion assay
(Filderman et al., 1992). CSF-1 enhances phagocy- Administration of CSF-1 increases blood monocyte
tosis, but not bactericidal activity of the intracellular and tissue macrophage numbers (Hume et al., 1988;
bacterium Listeria monocytogenes (Cheers et al., Munn et al., 1990), although some populations, e.g.
1989). alveolar and peritoneal macrophages, are not
CSF-1 919
Table 1 CSF-1 assay methods
Assay method a CSF specificity CSF-1 dose-response Assay
range (ng) time (days)
Bone marrow colony formation None 0.1–1.5 7–14
Peritoneal exudate macrophage colony formation CSF-1, GM-CSF 0.4–6.0 14–28
3HTdR uptake by peritoneal exudate macrophages CSF-1, GM-CSF 0.4–6.0 7
3HTdR uptake by bone marrow cells All 0.2–3.0 4
Radioimmunoassay
Mouse Mouse CSF-1 0.025–1.2 1–2
Human Human CSF-1 0.025–1.2 1–2
Radioreceptor assay (mouse) Mouse CSF-1 0.025–1.2 1
and human CSF-1
0.040–1.2 1
aStanley(1981).
increased (Asakura et al., 1997). In contrast, the induces osteoclastogenesis (Morohashi et al., 1994).
absence of CSF-1 in the Csf1op/Csf1op mouse is CSF-1 supports osteoclast differentiation in coopera-
associated with a large decrease in the concentration tion with OPGL/ODF/TRANCE and the combina-
of mononuclear phagocytes in blood, bone marrow, tion of both factors overcomes the requirement for
and major macrophage-containing tissues (Marks osteoblastic cells in co-cultures with hematopoietic
andLane,1976;Wiktor-Jedrzejczaketal.,1982,1991; cells. CSF-1 alone causes the development of small
Naito et al., 1991; Cecchini et al., 1994). These mononuclear cells, whereas OPGL stimulates the
observations clearly indicate that CSF-1 is the development of active osteoclasts in a CSF-1-depen-
primaryregulatorofmononuclearphagocyteproduc- dent fashion. This synergy may in part be explained
tion. In addition, other studies have demonstrated by CSF-1-induced OPGL receptor expression on
that while circulating CSF-1 regulates the develop- osteoclastprecursors(Laceyetal.,1998;Yasudaetal.,
ment and maintenance of certain tissue macrophage 1998). Of particular interest is the difference between
populations, e.g. Kupffer cells, other populations the CSF-1 requirement for osteoclast differentiation
are regulated by locally produced CSF-1 (Wiktor- and for maintenance of tissue macrophage popula-
Jedrzejczak et al., 1991; Cecchini et al., 1994; Roth tions. For example, a single injection of CSF-1 in a
et al., 1998). Csfmop/Csfmop mouse is sufficient to differentiate
The osteopetrotic phenotype of the CSF-1-null osteoclast Csf1op/Csf1op progenitors and correct the
Csf1op/Csf1op mouse clearly demonstrates the essen- osteopetrotic condition (Kodama et al., 1993),
tial osteoclastogenic role of CSF-1. Wild-type splenic whereas repeated injections are required to maintain
hematopoietic precursor cells proliferate and differ- tissue macrophage populations after their develop-
entiate to tartrate-resistant acid phosphatase-positive ment (Cecchini et al., 1994; Pollard and Stanley,
osteoclastswhenco-culturedwithstromalosteoblasts 1996).
fromwild-typemice,orCsf1op/Csf1oposteoblastsand Apart from its role in the proliferation and
CSF-1, but not with Csf1op/Csf1op osteoblasts alone, differentiation of osteoclast progenitors (Felix et al.,
demonstrating that osteoblast-derived CSF-1 is 1994; Pollard and Stanley, 1996), CSF-1 also appears
required for osteoclast formation (Felix et al., 1994; toplayaroleinregulatingosteoclastfunction.CSF-1
Pollard and Stanley, 1996). In cultured embryonic stimulates increases in osteoclast survival, size, and
mouse metatarsals, CSF-1 mRNA is locally and multinucleation(Jimietal.,1995;LeesandHeersche,
temporally expressed during the period of osteoclast 1999). It also stimulates the migration, chemotaxis,
development, and osteoclasts as well as their pre- spreading, and survival of isolated osteoclasts, inhib-
cursorsexpresstheCSF-1R(Felixetal.,1994;Pollard iting their resorptive activity by reducing the pro-
and Stanley, 1996)). Consistent with an action of portion of bone resorbing cells (Felix et al., 1994;
CSF-1 on proliferating osteoclast precursor cells, cul- Pollard and Stanley, 1996). The bone resorptive and
ture of Csf1op/Csf1op mouse metatarsals with CSF-1 migratory states of the osteoclast may be mutually
920 E. Richard Stanley
exclusive so that CSF-1 production by the osteoblast hypersensitivity,andnormalTandBcellresponsesto
may be important in regulating the distribution of ovalbumin or sheep red blood cells (Wiktor-
osteoclasts (Fuller et al., 1993). Here the cell surface Jedrzejczak et al., 1992; Chang et al., 1995). In fact,
and proteoglycan forms of CSF-1 could play impor- many of the effects of CSF-1, including the
tant and different roles. The osteoblast cell surface enhancement of the killing of Candida albicans and
form may be involved in direct cell–cell interaction Listeria monocytogenes (Roth and Stanley, 1992), as
with osteoclasts or be released locally by cell well as the impaired ability of Csf1op/Csf1op mice to
surface proteolysis. The proteoglycan form may be release TNF(cid:11) and G-CSF into the circulation in
differentially localized to bone via its chondroitin response to bacterial endotoxin, and to form granu-
sulfate chains after its secretion from osteoblasts or lomatous lesions (Stanley, 1994; Pollard and Stanley,
recruitment from the circulation (Felix et al., 1994; 1996), might be explained by the chemotactic role or
Pollard and Stanley, 1996). macrophage growth-promoting activities of CSF-1.
Studies of the postnatal development of tissue The dramatic elevation of uterine CSF-1 concen-
macrophage populations using Csf1op/Csf1op mice tration during pregnancy (Bartocci et al., 1986;
indicate that several tissue macrophage populations Pollard et al., 1991) and the detection of CSF-1R
are partially or completely dependent on CSF-1 for mRNA in the placenta (Pollard and Stanley, 1996)
their development and maintenance, while the suggested non-mononuclear phagocytic actions of
development and maintenance of others are largely CSF-1duringpregnancy.Beforeimplantation,CSF-1
unaffected by its absence (Table 2). In many of the mRNA and protein are detected in the oviduct
‘CSF-1-dependent’ tissues, the macrophage density is (Arcecietal.,1992).CSF-1mRNAisalsoelevatedin
normally highest at birth and the requirement for the uterus at estrus during the estrous cycle (Sanford
CSF-1 therefore appears to be prenatal. In general, et al., 1992). During pregnancy, uterine epithelial
the ‘CSF-1-dependent’ macrophages are in tissues CSF-1 synthesis, stimulated by progesterone and
which undergo significant perinatal remodeling and estradiol-17(cid:12), increases exponentially from day 3 of
morphogenesis and are believed to play significant pregnancy so that uterine concentrations are
roles in these processes by producing trophic factors increased (cid:24)5-fold at implantation and (cid:24)1000-fold
oractingasscavengers.Inseveralofthesetissues,the atterm.Thisincreaseislocal,sincecirculatingCSF-1
absence of the ‘CSF-1-dependent’ macrophages is is only increased by (cid:24)1.4-fold (Bartocci et al., 1986;
correlated with altered function of the tissue Pollard et al., 1987; Arceci et al., 1989). The uterine
(Cecchini et al., 1994; Pollard and Stanley, 1996). CSF-1 mRNA is predominantly the 2.3kb, exon 9-
CSF-1 is either synthesized locally, or the proteogly- containing species encoding the secreted forms of
can form specifically sequestered, in the regulation of CSF-1, although mRNA encoding the cell surface
macrophages of muscle, tendon, periosteum, syno- form is also present, so that juxtacrine as well as
vium,bladder,salivarygland,gut,adrenals,andbone paracrine interactions of CSF-1 may occur during
marrow (Cecchini et al., 1994). Irrespective of pregnancy. There is reciprocity in the expression of
whether the tissue macrophage requirement is for the CSF-1R. Maternal CSF-1R mRNA is first found
circulating or locally produced CSF-1, the require- in developing follicles and persists in the growing
ment is, in many cases, prenatal as well as postnatal oocyte to ovulation (Arceci et al., 1992). Zygotic
(Table 2). mRNAappearsatthelatetwo-cellstageandremains
Incontrasttothe‘CSF-1-dependent’macrophages, (Arceci et al., 1992). After decidualization com-
the development of macrophages of the epidermis mences, the primary decidual cells surrounding the
(Langerhanscells),thymus,andlymphnode(withthe invading embryo express high levels of CSF-1R
exceptionofthoseofthesubcapsularsinus) (Witmer- mRNA (Arceci et al., 1989, 1992; Regenstreif and
Packet al., 1993)is largely unalteredinCsf1op/Csf1op Rossant, 1989) and there are low intra-embryonic
mice (Takahashi et al., 1992., 1993; Witmer-Pack levels.Afterplacentation,thereisstrongexpressionin
et al., 1993; Cecchini et al., 1994). The macrophages thevariouslayersofthetrophoblastandexpressionin
of this group are believed to be important for immu- decidual cells persists at low levels in the decidua
nologicalandinflammatoryresponsesandrepresenta basalis (Arceci et al., 1989; Regenstreif and Rossant,
small proportion of total body macrophages, most of 1989). A similar pattern of CSF-1 and CSF-1R
whicharefoundintheliver,gut,andbrain.Sincethey expression is found in the human reproductive tract,
express the CSF-1R, they are possibly regulated in except that CSF-1 is also expressed by trophoblast
somewaybyCSF-1intheadult(Cecchinietal.,1994). and decidual cells (Pollard and Stanley, 1996). These
CSF-1 does not seem to have a major immuno- temporal-spatial patterns of CSF-1/CSF-1R expres-
logical role. It does not have a significant role in sion,togetherwiththesexsteroidhormoneregulation
in vivo phagocytic function, normal delayed-type of CSF-1 expression, strongly implicate CSF-1 in the