Enzymes in Tissues Responsive to Corticosteroids* FRED ROSEN (Departmeni of Experimental Therapeuiies, Roawell Park Memorial institute. New York State Departmentof Health, Buffalo, New York) SUMMARY The biochemical reactions which mediate the physiological effects exerted by the adrenal cortical hormones remain to be determined. It has been euggested that the @ hormonal control of cellular functions is accomplished by altering the activity of specific enzymes. This report concerns the induction of several enzymes by cortisol in tissues (liver, thymus, transplantable tumors) which are responsive to the glucocorti coids. Also, some factors involved in studies on the actions of hormones are considered. The problem of resistance to comtisol and the technics being used to evaluate the physiological significance of enzyme induction by cortisol in target tissues is dis cussed. The various dietary and physiological conditions which influence the level of the inducible enzymes are considered in regard to an explanation of the manner in which glucocorticoids alter the activity of the adaptive enzymes. Several recent articles on the adrenal corticoids action of the adrenal corticoids. This is a relative have emphasized the disparity between the de ly new area of investigation that has revealed tailed knowledge available on the chemistry and interesting facts concerning glucocorticoid action the biosynthesis or degradation of these hormones at the biochemical level. and the relative lack of information about bio The difficulties in determining the biochemical chemical events which underlie their modes of basis for certain physiological effects exerted by action (15, 925,46). Although the physiological ef the adrenal cortical hormones are apparent from fects elicited by large doses of the glucocorticoids the many different methods which have been used are well known, it is not yet clear whether such to study this subject in recent years (7, 41). Most effects are related to the major role these hormones of the studies are predicated on the basis that the fulfill under normal physiological conditions. hormonal control of cellular functions is mediated These gaps in our knowledge are not limited to the by altering the activity of specific enzymes (920, glucocorticoids. The same difficulty has been en 31). Attractive as this concept may be, it has not countered in elucidating the action at the molecu yet provided us with a clear-cut relationship be lam level of many other hormones (60). tween a biochemical event and a physiological ef Clinically the glucocorticoids have been shown feet produced by the glucocorticoids. There has to be of value in the treatment of leukemias and been renewed interest in the possibility that lymphomas (492). In this regard, the comticosteroids hormones, in general, may act to facilitate the deserve study with respect to the changes they entry of metabolites into cells, mainly because of produce in the metabolism of responsive tumors. the recent work on insulin (59) and antidiuretic In keeping with the objectives of this symposium, hormone(1,9). I do not intend to review in this paper the various Although much of the content of this paper is an mechanisms which have been proposed to explain account of studies on the action of corticosteroids the action of the glucocorticoids. Emphasis will be on intracellular enzymes, there is at present no placed almost entirely on the effects of the definitive evidence that this type of effect will glucocorticoids on the induction of certain en turn out to be the basis of their cellular actions. zymes in those tissues which are targets of the More important at this time is that such studies S This investigation was supported in part by research grants (AM-04389 and CA-05671) from the U.S. Public Health reveal the need for new information and indicate Service. areas of investigation that deserve attention. 1447 Downloaded from cancerres.aacrjournals.org on September 30, 2021. © 1963 American Association for Cancer Research. 1448 Cancer Research Vol. 923, September 1968 SoME FA@rORS To BE CONSIDERED IN STUDIES glucocorticoids has not been cleanly demonstrated ON THE Ac'nIoNS OF Hoit@&o@zs in liver slices (19) but does occur in liver perfused Target tiastses.—Mostof the experiments under with cortisol (3, 19). taken to gain information concerning metabolic Amount of hormone and it. specr@ficttyof action.— changes which underlie the physiological effects Bush (7) has recently commented in detail on one of the glucocorticoids have been carried out in of the difficulties encountered in studies in vitro liver. There are only a few reports on changes in namely, the choice of a reasonable concentration adaptive enzymes produced by adrenal corticoids of adrenal hormone. Frequently, in such studies, in lymphoid tissues and certain neoplasms that are amounts of the steroid far in excess of a reasonable so remarkably responsive to these steroids. How physiological concentration are required to pro ever, there are many studies on the metabolism of duce a significant effect. For the same reason, the glucocorticoids by target cells (11). Tissues of this high dosage used in many in vivo studies has been type which show such a rapid and demonstrable subject to criticism. Probably undue criticism has response to corticosteroid therapy are capable of been given to the use of large amounts of a hom yielding important biochemical information re mone in these different systems. Many examples lated to the effects exerted by these hormones. A can be cited in which the use of “unphysiological― major objective of our work is to determine the amounts of a compound has contributed sig basis for the selective action of glucocorticoids on nificantly to an understanding of its mechanism of lymphoid neoplasms. The manner whereby ad action and pathways of metabolism. renal corticoids impair the growth of lymphoid Other criteria must also be kept in mind when tumors may bear certain similarities to the assessing hormone experiments. The intenpreta processes underlying thymic involution or the tion of the data is difficult when the effect pro catabolism of protein. duced is not specific for a given class of hormones In vitro vs. in vivo 8tUdies.—The choice be or when an effect is obtained with an analog that tween in vitro and in vivo experiments is often is inactive in the animal. Numerous studies can determined by the problem under investigation be cited in which a variety of hormones with dif and by the technics familiar to the investigatOr. ferent structures and physiological properties act Engel (15), Villee (63), and Bush (7) have recently. similarly in their effect on a biochemical reaction emphasized the importance of the in vitro expeni (5, 14, 923, 68). Also, to be of significance in an ment to obtain unequivocal evidence for a hor in vitro system, the effects observed should bear monal effect. This approach is often justified on some discernible relationship to the effects of the the basis that it permits adequate control of many hormone in vivo, with allowances being made for of the variables that make it difficult to interpret differences in metabolism in the two systems. studies in the whole animal. However, it is not yet ENZYMES RESPONSIVE TO GLUCOCORTICOIDS clear whether the physiological or pharmacological effects of a hormone are entirely mediated by a di It is probable that alterations in the activity of certain enzymes underlie the pronounced effects rect effect of the hormone on responsive tissues. In view of our limited knowledge about hor of glucocorticoids on carbohydrate and protein mone action, it would seem that the experiment in metabolism. In this regard, it is of interest that which the test substance is administered to the most enzymes which show an increase in activity animal and the tissues subsequently examined for after glucocorticoid treatment are involved in the certain biochemical changes be given preference metabolism of glucose or amino acids (592). at this time oven the experiments involving addi Enzyme studies in different tissues of adrenal tion of the hormone to an in vitro system. The in ectomized animals have been carried out in an effort to reveal metabolic functions which are in vivo experiment is likely to provide us initially fluenced, at least in part, by adrenal hormones with the important leads concerning metabolic (30). A drop in enzyme activity following adrenal changes related to glucocorticoid action. There ap ectomy has in many instances provided cimcum pear to be few examples of any substantial effect of stantial evidence that the enzyme is under the glucocorticoids in low concentration on slices or control of the adrenal hormones. Whereas many homogenates of liver. The findings of Chiu and of the adaptive enzymes involved in amino acid Needham (8) that adrenal cortical extract in metabolism show a decrease in level after adrenal creased liver glycogen of surviving liver slices in ectomy, a number of the carbohydnate-metaboliz vitro have only recently been confirmed (924). The ing enzymes that respond to glucocorticoids do not induction of certain enzymes that can be readily undergo any significant change in activity (65). shown to occur in the liver of rats treated with The factor(s) which maintain normal hepatic Downloaded from cancerres.aacrjournals.org on September 30, 2021. © 1963 American Association for Cancer Research. ROSEN—Tissue Enzymes Responsive to Corticosteroids 1449 levels of certain glucocorticoid-inducible enzymes those previously noted for tryptophan pyrrolase, in the liver of adrenalectomized animals are not there were also certain notable differences. Ad known. renalectomy alone did not lower the level of this Carbohydrate-metabolizing enzymes.—The ad enzyme in liven, and when tyrosine was ad ministration of cortisol to rats for 5—7days in ministered to adrenalectomized rats, the activity creased the hepatic activity of glucose-6-phos of the enzyme was not increased.