J. steroid B iochem . Vol. 21 , No. 6, pp. 633-637, 1984 0@22-4731 /84 $3.00 + 0.00 Printed in Great Britain. All rights reserved Copyright 0 1984 Pergamon Press Ltd MURINE GLUCOCORTICOID RECEPTORS AND THE H-2 LOCUS-A REAPPRAISAL SHARON L. Lru, JOSEPH F. GRIPPO*, ROBERT P. ERICKSON and WILLIAM B. PRATT*? Departments of Human Genetics and *Pharmacology, University of Michigan Medical School, Ann Arbor, MI 48109, U.S.A. (Received 30 April 1984) Summary-It has been demonstrated that susceptibility to glucocorticoid-induced formation of cleft palate is regulated by the mouse histocompatibility complex (H-Z). This has encouraged us to examine H-Z effects on glucocorticoid binding in tissues of adult animals which would provide sufficient material with which to study the biochemical mechanism of the H-Zeffect. Although it has been reported that cytosol prepared from lungs of adult mice with a high susceptibility to steroid-induced cleft palate formation have a higher level of glucocorticoid binding than lung cytosol prepared from a low-susceptibility strain, we are unable to demonstrate any influence of H-Zon binding capacity in this tissue from adult animals when glucocorticoid receptors are assayed in the presence of receptor reducing and stabilizing agents that maximize binding capacity. Cytosol prepared from rat liver contains an endogenous receptor-reducing system composed of NADPH and thioredoxin. It has also been reported that the murine H-2 complex contains a gene(s) that regulates the level of a modifier(s) in fetal hepatic cytosol that affects the binding of glucocorticoids to the receptor. Of two known low molecular weight modifiers that could account for this effect, we have previously established that the heat-stable, steroid receptor “modulator” is not regulated by the H-2 complex. In the present work we have assayed thioredoxin, a second potential modifier, in liver cytosols prepared from adults of two pairs of two H-2 congenic mouse strains. Our results show that the amount of thioredoxin is the same in all four mouse strains and that it is not regulated by the H-2 locus. At this time, we are unable to identify a system in adult mice in which the widely reported regulation of glucocorticoid binding by the mouse histocompatibility locus can be submitted to definitive biochemical study. INTRODUCTION Several years ago, it was established that various strains of hamsters exhibit different degrees of sus- ceptibility to glucocorticoid-induced cleft palate [l]. In mice, the different susceptibilities to glucocorticoid-induced cleft palate are partially con- trolled by the H-2locus, the major histocompatibility locus in this species [2,3]. Subsequently, it was reported [4] that facial mesenchyme cells cultured from fetuses of a mouse strain that is highly susceptible to glucocorticoid-induced cleft palate (A/J) have twice the specific glucocorticoid binding capacity as cells from a low susceptibility strain (C57BL/6J). Higher levels of specific glucocorticoid binding capacity have also been measured in fetal palatal tissue obtained from highly susceptible strains when compared to palatal tissue from less susceptible strains [5-71. Studies of binding capacity in congenic mouse strains that differ primarily at the H-Z locus have led to the proposal that glucocorticoid binding capacity, like glucocorticoid-induction of cleft palate, is regulated in part by the H-2 haplotype [5-71. tTo whom correspondence should be addressed. Address correspondence to: W. B. Pratt, Department of Pharmacology, 6448, Medical Science Bldg I, The University of Michigan Medical School, Ann Arbor, MI 48109-0010, U.S.A. As mouse strains with defined H-2 haplotypes could prove to be powerful experimental tools with which to investigate the factors that control specific glucocorticoid binding capacity, we examined the effect of the H-Z locus on steroid binding capacity in mouse liver [8]. Mouse liver was chosen because it is a large organ that is a well characterized target of glucocorticoid action and because H-Zis expressed in liver [9]. Specific glucocorticoid binding capacity was assayed in liver cytosols prepared from four mouse strains: A/J (high susceptibility), C57BL/6J (low sus- ceptibility), and the two H-2congenic lines A.BY and BIO.A. We found that the level of specific glu- cocorticoid binding activity in liver cytosol is not mediated by the H-2 locus [8]. Katsumata et al. [7] have directly compared the glucocorticoid binding capacity of fetal palate and maternal liver in four mouse strains and found that the H-Z locus affects total specific glucocorticoid binding capacity in the former but not in the latter. Although the total glucocorticoid binding capacity in liver is not regulated by H-2, there is evidence that the H-2 complex contains a gene(s) that regulates the level of a modifier(s) in hepatic cytosol that affects the binding of glucocorticoids to the receptor. The evi- dence was obtained by Katsumata et al.[lO] who found that plots of dexamethasone binding versus concentration of fetal liver cytosol were linear for 633