Loss of glucocorticoid regulation of plasminogen activator activity in anucleate rat hepatoma cells

Adrenal Insufficiency in the Intensive Care Setting

In the intensive care setting, the question of adrenal insufficiency arises most frequently in patients whose endogenous adrenal function may be suppressed by pre ceding glucocorticoid therapy or in patients with the acquired immunodeficiency syndrome. Less often the question arises in patients whose adrenal tissue may have been destroyed by autoimmune disease, tuber culosis, meningococcal or other infection, hemorrhage, or replacement by malignancy, or in patients whose adrenal function has been suppressed by certain drugs. Measurements of plasma adrenocorticotrophic hor mone (ACTH), cortisol, aldosterone, and renin levels and the response of cortisol and aldosterone to exoge nously administered ACTH form the basis for clinically evaluating the adequacy of a patient's adrenal function. The naturally occurring glucocorticoid, hydrocortisone, remains the cornerstone of adrenal replacement therapy along with appropriate fluid and electrolyte administra tion. In rare instances the addition of a mineralocor ticoid is necessary. A brief review of the use of mega- dose glucocorticoids in the treatment of sepsis, shock, and the adult respiratory distress syndrome is included.

Increased activity of plasminogen activators during involution of the rat ventral prostate

Plasminogen activator was measured in the ventral prostates of non-castrated, castrated, and androgen-treated rats to determine whether changes in this activity correlated with the process of glandular involution. While the activity was very low in cytosolic extracts from the prostates of non-castrated rats, 2 days following castration the plasminogen activator activity increased in a near-linear fashion such that by day 7 it was 10-fold higher in terms of specific activity (per mg of protein) and cellular concentration (per mg of DNA). During this interval there was a rapid decrease in the cell population of the prostates. Treatment of the 7-day castrated rats with the potent androgen, dihydrotestosterone, both reduced the plasminogen activator activity and restored the cell number in a dose-related manner. Gel electrophoretic analysis revealed two major bands of plasminogen activator activity in the cytosolic extracts from 4- and 7-day castrated rats, plus additional minor bands in samples from 10- and 14-day castrated rats. Approx. 10% of the cellular concentration of plasminogen activator activity was recovered in association with an 18000g pellet fraction from the prostates; this fraction showed less heterogeneity of the plasminogen activator forms as observed by gel electrophoresis. Inhibitor studies indicated that the 18000g pellet fraction from the prostates of non-castrated rats possessed some plasminogen activator inhibitor activity, but the relative concentration of the inhibitor activity was small. We conclude that the involution of the prostate is probably associated with increased synthesis of plasminogen activators through a de-repression process which may involve loss of androgen receptors.

Paradoxical effects of glucocorticoids on regulation of plasminogen activator activity. Mediation by glucocorticoid receptors

Dexamethasone, a synthetic glucocorticoid, decreases the plasminogen activator (PA) activity of HTC rat hepatoma cells in tissue culture. Paradoxically, dexamethasone enhances the cyclic nucleotide stimulation of PA activity in these cells 2-4-fold. In this report, we investigated whether this paradoxical glucocorticoids as the induction of tyrosine aminotransferase activity. We compared the concentration-dependences for several classes of steroids, previously classified as full agonists, partial agonists, antagonists or inactive steroids with respect to induction of the transaminase, for both enhancement of cyclic nucleotide stimulation of PA activity and induction of tyrosine aminotransferase activity in parallel cultures. The full agonists dexamethasone and cortisol, the partial agonists deoxycorticosterone and 11 beta-hydroxyprogesterone, the inactive steroid tetrahydrocortisol, and the antagonist 17 alpha-methyltestosterone exhibited similar potencies with respect to both phenomena. Furthermore, when cells were incubated with both dexamethasone and 17 alpha-methyltestosterone, the latter blocked enhancement by dexamethasone in a concentration-dependent fashion. We conclude that glucocorticoid enhancement of cyclic nucleotide stimulation of PA activity is mediated by the same glucocorticoid receptors which mediate direct regulatory effects.

Hormonal regulation of plasminogen activator in rat hepatoma cells

Plasminogen activators are membrane-associated, arginine-specific serine proteases which convert the inactive plasma zymogen plasminogen to plasmin, an active, broad-spectrum serine protease. Plasmin, the major fibrinolytic enzyme in blood, also participates in a number of physiologic functions involving protein processing and tissue remodelling, and may play an important role in tumor invasion and metastasis. In HTC rat hepatoma cells in tissue culture, glucocorticoids rapidly decrease plasminogen activator (PA) activity. We have shown that this decrease is mediated by induction of a soluble inhibitor of PA activity rather than modulation of the amount of PA. The hormonally-induced inhibitor is a cellular product which specifically inhibits PA but not plasmin. We have isolated variant lines of HTC cells which are selectively resistant to the glucocorticoid inhibition of PA but retain other glucocorticoid responses. These variants lack the hormonally-induced inhibitor; PA from these variants is fully sensitive to inhibition by inhibitor from steroid-treated wild-type cells. Cyclic nucleotides dramatically stimulate PA activity in HTC cells in a time- and concentration-dependent manner. Paradoxically, glucocorticoids further enhance this stimulation. Thus glucocorticoids exert two separate and opposite effects on PA activity. The availability of glucocorticoid-resistant variant cell lines, together with the unique regulatory interactions of steroids and cyclic nucleotides, make HTC cells a useful experimental system in which to study the multihormonal regulation of plasminogen activator.

Paradoxical effects of glucocorticoids on regulation of plasminogen activator activity of rat hepatoma cells

Incubation of rat hepatoma cells with cAMP derivatives stimulates cell-associated plasminogen activator activity 8- to 22-fold and extracellular plasminogen activator activity 30- to 1300-fold. This time- and concentration-dependent increase is enhanced by phosphodiesterase inhibitors. Dexamethasone, a synthetic glucocorticoid, decreases the plasminogen activator activity of these cells, probably through induction of an inhibitor. Paradoxically, dexamethasone, added simultaneously with cAMP derivatives causes a further 4-fold enhancement of the cAMP-mediated stimulation of plasminogen activator activity. Dexamethasone also alters the time course of cAMP-mediated enhancement of plasminogen activator activity: increased protease activity is detected at 4 hr in cells incubated with 8-bromoadenosine-3':5'-cyclic monophosphoric acid and 1-methyl-3-isobutylxanthine but not until 12 hr in cells incubated with dexamethasone as well. Glucocorticoids thus exert two separate and opposite effects on plasminogen activator activity: induction of an inhibitor and amplification of cyclic nucleotide action. Although permissive and synergistic effects of dexamethasone on cyclic nucleotide action have been reported previously, glucocorticoid regulation of plasminogen activator activity is unique in that the amplification of cyclic nucleotide effects by dexamethasone opposes its regulatory action toward a specific enzyme.

Plasminogen activator activity in human prostate and breast tumors: relationship to steroid receptors

Using a fluorometric assay based on the activation of human plasminogen, plasminogen activator (PA) activity was measured in cytosolic and lysosomal extracts prepared from normal, benign hyperplastic (BPH), and carcinomatous human prostates. In all three types of prostatic tissue, the lysosomal extracts had much higher concentrations of PA activity than did the cytosolic extracts. The mean PA activity in lysosomal extracts of the carcinomatous prostates was 170% and 85% higher than that measured in normal and BPH prostates, respectively (Student's t-test, p less than .05). With prostatic carcinoma and BPH specimens there was an inverse (negative) relationship between lysosomal PA activity and the nuclear concentration of androgen-receptors (correlation coefficient, -0.84). By comparison in specimens of human breast tumors, there were weakly positive correlations between PA activity and either estrogen (ER) or progestin (PR) receptors (correlation coefficients of + 0.23 and + 0.54, respectively). While as a group ER+, PR+ breast tumors had higher PA activity that ER+, PR- or ER-, PR- tumors, the differences were not statistically significant (Student's t-test, p greater than .05). Thus in breast tumors, it is uncertain whether high levels of PA activity are indicative of hormonal dependence. However, our findings with prostatic tumors infer that in contrast, high concentrations of this enzyme may reflect a malignant phenotype characterized by a decrease in both androgen responsiveness and differentiation.

Glucocorticoid regulation of amino acid transport in anucleate rat hepatoma (HTC) cells

The transport of alpha-aminoisobutyric acid (AIB) by rat hepatoma tissue culture (HTC) cells is rapidly and reversibly inhibited by dexamethasone and other glucocorticoids. To investigate the role of the nucleus in the regulation of transport and to determine whether steroid hormones or steroid-receptor complexes may have direct effects on cytoplasmic or membrane functions, we have examined the regulation of transport by dexamethasone in anucleate HTC cells. Cytoplasts prepared from suspension cultures of HTC cells fully retain active transport of AIB with the same kinetic properties as intact cells. However, the uptake of AIB is not inhibited by dexamethasone or other corticosteroids. Neither is the inhibited rate of transport, manifested by cytoplasts prepared from dexamethasone-treated cells, restored to normal upon removal of the hormone. Anucleate cells exhibit specific, saturable binding of [3H]dexamethasone; however, the binding is reduced compared with that of intact cells. The nucleus is thus required for the glucocorticoid regulation of amino acid transport in HTC cells.