Steroid–Cell Interactions

446 Pages·1974·23.902 MB·English

by  R. J. B. King and W. I. P. Mainwaring (Auth.)

THIS BOOK IS DEDICATED TO ANNE AND VERONICA
Prosperity's the very bond of love.
Whose fresh complexion and whose heart together
Affliction alters.
The Winters Tale:
William Shakespeare
Interactions are set up that lead to strong attraction and
the formation of a chemical bond.
The Nature of the Chemical Bond:
Linus Pauling
This book essentially concerns the latter type of bond.
Fortunately for the authors, however, their long
suffering wives sustained their faith in the more poetic
definition of a bond during the vicissitudes of writing.
S T E R O I D - C E LL
I N T E R A C T I O NS
R. J. B. KING, M.Sc. Ph.D.
and
W.I.P. MAINWARING, Ph.D.
Imperial Cancer Research Fund
LONDON
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First published in 1974
©Butterworth b Co (Publishers) Ltd, 1974
ISBN 0 408 70539 6
Filmset by Keyspools Ltd, Golborne, Lancashire
Printed in England by Hazell Watson b Viney Ltd, Aylesbury, Bucks.
Preface
The main purpose of this book is to describe the processes involved
in the intracellular binding of steroids (and related compounds) in
mammalian cells but, for the sake of completeness, brief comments
have been included on serum binding proteins and steroid-immuno-
globulin interaction. At the time of writing this book, the main
unanswered question concerns the relationship of these binding
processes to the biological action of the steroid. For this reason a
chapter on this topic has been included which, of necessity, is rather
vague but which we hope will be of use to the reader.
The fact that the book has been written at all is due to an original
naivety on the part of the two authors, coupled with a rapidly
developing obstinacy that it was going to be finished, come what
may. As the latter stages were accomplished when the authors were
eight thousand miles apart in Israel and California respectively, a
great deal of the credit for the book goes to the 'referee' who was
centrally placed in London, namely our secretary, Mrs Margaret
Barker. There is no doubt that, without her, the book would still be
being written. Our appreciation is also extended to Mrs Doonie
Swales who coped with the translation from handwritten scribble
to typescript and to one of our (R.J.B.K.'s) mothers-in-law who,
naively, offered to put many of the references into alphabetical order.
Sincere thanks are also extended to the staff's of the Hormone
Biochemistry and Androgen Physiology Departments of the Imperial
Cancer Research Fund, London, the Biodynamics Department of the
Weizmann Institute, Israel, the Cardiovascular Research Unit,
University of California, San Francisco and to the many authors
who sent us preprints or unpublished data. Finally, we would like to
thank our publisher, Butterworths.
Introduction
Steroid + receptor steroid-receptor complex ^nucleus.
This equation is almost the sine qua non of any discussion of steroid
hormone action today but, with one exception, it is only in the last
decade that the components of this equation have been formulated.
The exception is the receptor, the concept of which was formulated
at the end of the nineteenth century by Paul Ehrlich (The collected
papers of Paul Ehrlich, vol. 3, 1960, edited by F. Himmelweit;
London: Academic Press). He considered that ligands had two
components in their structure, the haptophore which combined
with the receptor so that the ergo- or toxiphore region could initiate
the biological events. This view has been superseded by the theories
of allostery and induced-fit so that as far as steroids are concerned
it now seems likely that the ergophore is part of the receptor rather
than of the ligand. Nevertheless, Ehrlich's view is still valid that the
selective affinity of ligands for certain organs is determined by the
presence of receptors and the chemical composition of the ligand.
He even carried out cellular distribution studies by injecting a
quinoline derivative, thallin, which was detected by ferric chloride
staining. The analogy to many of the experiments described in this
book is obvious. The concept of receptor-drug interaction was
refined by Clark (Clark, A. J., The mode of action of drugs on cells,
1933, London: Arnold) who related dose-response phenomena to
drug-receptor interaction by proposing that the intensity of response
is related to the number of receptor sites and that there is an all-or-
none response elicited by the drug at each receptor. These proposi­
tions have been modified as it is now known that all receptors need
not be occupied in order to get a biological response and that there
is not a strict relationship between receptor occupancy and biologi­
cal response (reviewed in Molecular Pharmacology, vol 1, 1964,
edited by E. J. Ariens; New York: Academic Press; and in Molecular
orbital theory in drug research, L. B. Kier, 1971, New York: Academic
Press). These relatively recent views are certainly in harmony with
the data on steroid-receptor interaction in which there often seems
to be a surplus of cytoplasmic receptor and, in some cases, the
hormone will bind to the receptor without initiating a biological
response.
We shall unashamedly use the word 'receptor' throughout this
book to describe the intracellular macromolecular entity to w4iich
the steroid or related ligand attaches. Strictly speaking, this is not
justified as the usual definition of a receptor is a macromolecule
with which a drug combines to produce its characteristic biological
eñ*ect. The biological eñ*ectiveness of steroid (or related compound)-
macromolecular interaction has not yet been convincingly proven
but we hope that, after reading Chapter 9, you will agree with us that
the circumstantial evidence permits the use of the word 'receptor'.
Of course, the serum proteins do not come into this category.
Early attempts to demonstrate specific steroid-receptor inter
actions were unsuccessful because of the pharmacologic rather than
physiologic amount of hormone required for subsequent detection
purposes. The pioneering synthesis of tritiated steroids and hexoes
trol derivatives by R. F. Glascock, W. H. Pearlman and E. V. Jensen
overcame this difficulty and lead to the publication of the now
classical paper by the latter worker in 1962 (E. V. Jensen and H. I.
Jacobsen (1962), Recent Prog. Hormone Res., 18, 387). This opened
the way for the experiments reported and discussed in this book..
From this body of scholarship, a fairly general picture is emerging
of the way in which steroidal hormones enter responsive cells and
are transported to the site where they initiate their characteristic
biological responses. At least part of this basic process has been
detected in plants, arthropods and several vertebrate orders. Al
though there are exceptions, this common mechanism suggests that
it is an efficient process which evolved early in evolutionary time.
1
Physico-Chemical Considerations
of Steroid-Receptor Interactions
The two aims of receptor experiments are to determine their bio
logical function and to unravel the mechanism whereby the two
molecules react. As the latter aspect must be explicable in physico-
chemical terms, this chapter will present an elementary account of
the factors contributing to the interaction between a steroid hormone
and another molecule. As the majority of the relevant steroid inter
actions are non-covalent, only this type of reaction will be considered
here. A diverse range of molecules including amino acids,^ purines,^^
lipids^'and nucleic acids'^'^'^^ will bind steroids but the vast
majority of the interactions relevant to this book involve proteins.
STEROID STRUCTURE
Two features of the steroid molecule contribute to the specific inter
action of a steroid and macromolecule: the type of reactant groups
possessed by the steroid and the spatial arrangement of these groups.
This is illustrated by comparing non-specific and specific steroid-
protein interactions. The former usually follow the polarity rule
whereby increasing the number of polar substituents in the steroid
decreases the protein binding potential. The interaction is
obviously of a hydrophobic type. The spatial arrangement of the
substituents influences binding but not to the same extent as in the
specific type of binding. With the latter type of interaction, the
polarity rule is not applicable and the spatial arrangement of sub
stituents is of major importance. These are discussed in the chapters
dealing with the ciiñ"erent steroids.
1
2 Physico-chemical Considerations
REACTANT GROUPS
Most steroids do not have many functional groups and are therefore
limited in the ways in which they can react with other molecules.
Figure 1.1 gives examples of each of the main classes of steroids as
expressed by conventional chemical formulae.
CHjOH
C=0
Cortisol Aldosterone
[Glucocorticoid ] iMineralocorticoid 1
Progesterone
IProgestinl
Oestradiol Testosterone
[Oestrogen 1 [ Androgen ]
Figure 1.1
It is evident that only certain types of interaction are possible
between free steroids and other molecules. Except for the phenolic
OH group in the oestrogens there are no possibilities of true ionic
bonds. Even with the oestrogens it is most unlikely that ionic inter-
Physico-chemical Considerations 3
actions are important as the phenoHc hydroxyl group has a pK of
10 to 10-5. All of the steroids have at least one oxygen function which
usually takes the form of a primary or secondary alcohol or a ketone.
Aldosterone is exceptional in having an aldol group. All these groups
are capable of forming hydrogen bonds with suitably placed adjacent
groups but, with that exception, they are limited to covalent and
induced dipole interactions. Covalent attachment to macromole-
cules is rare but does occur between steroids and small molecules
such as sulphuric and glucuronic acids. They are water-soluble
derivatives which, as they carry a net negative charge at pH 7-4, are
capable of forming ionic bonds.
CONFORMATION
The picture of a steroid given by the type of structure shown in
Figure LI does not give a true pattern of the shape of the molecule.
Each of rings A, Β and C are capable of existing in either the boat or
chair form (Figure 1.2) of which the latter is the most stable. The
cyclopentane structure of ring D can exist in either the envelope or
Chair Boat
Figure 1.2
half-chair form. Fortunately for steroid chemists, the naturally
occurring, hormonally active molecules all have rings B, C and D in
the chair form with the ß:C and C.D functions in the trans con­
figuration. In certain toad poisons the C injunction is eis. With the
exception of the planar aromatic ring in the oestrogens, the A ring
is also in the boat form.
A Δ"^ double bond slightly increases the planarity of the molecule
but its reduction leads to two isomers of very different conformation.
Formation of the 5a (trans) compound slightly decreases the
planarity of the A :ß junction but the Sß conformation produces a
bend in the molecule {Figure 1.3). This difiference in conformation
markedly influences the biological properties of the molecule; 5a
reduced compounds usually have at least some of the biological
properties of the parent compound whereas 5^ isomers lose or
change their properties. This will be amplified in the chapters dealing
with the individual steroids.
4 Physico-chemical Considerations
Scott^^ has pointed out that the free energy for the association of
steroids with purines is near to the stabiHsation energy of the chair
form of cyclohexane (about 25*2 kJ/mole). Hence it is possible that
steroid-receptor interaction might result in a change in conforma­
tion of the steroid.
CH3 OH
CH,
Testosterone
Η CH3 OH
Y
Η
5 α Androstan -17 ^ - ol - 3 - one 5j3 androstan-17jS-ol-3-one
I Dihydrotestosterone ]
Figure 1.3
Figure 1.4. Model of testosterone. The approximate cross-sectional areas (± 10%) are
represented by the rectangular parallelepiped. The same approximate dimensions
apply to progesterone, deoxycorticosterone and hydrocortisone. This figure is
based on Munck^^