Effects of trypsin on the cyclic AMP system of the pig skin

Trypsin inhibitors inhibit induction by interferon-gamma of HLA-DR antigen expression on human skin cells

Serine protease inhibitors with a specificity for trypsin inhibit interferon-gamma (INF-gamma)-induced HLA-DR expression on a hybrid human epidermal cell line (H12), dermal fibroblasts, and primary keratinocytes. Protease inhibitors with a specificity for chymotrypsin or papain fail to inhibit IFN-gamma. The inhibitory effect of the trypsin inhibitors is similar to that of glucocorticoids in that it is a transient event, fading with length of exposure to IFN-gamma, and is reversed by the addition of dibutyryl cyclic AMP (dbcAMP) and phospholipase C(PLC) from Clostridium perfringens. In H12 cells, dbcAMP and PLC enhance the IFN-gamma induction of HLA-DR, but do not induce in the absence of INF-gamma. Evidence suggests that the protease inhibitors, as well as dbcAMP and PLC, may modulate HLA-DR expression at a post-translational site as well as during IFN-gamma signal transduction. These results suggest that trypsin-like protease activity may be required for cellular HLA-DR antigen expression following exposure to IFN-gamma.

Glucocorticoid-induced alteration of beta-adrenergic adenylate cyclase response of epidermis

It has been reported that the beta-adrenergic adenylate cyclase system of the pig epidermis is regulated by glucocorticoids, resulting in the augmentation of epinephrine-induced cyclic-AMP accumulations. Using this phenomenon, we compared the glucocorticoidal potency of three typical glucocorticoids: hydrocortisone, prednisolone and dexamethasone. There was a considerable variation in the magnitude of the glucocorticoid-induced augmentation of the beta-adrenergic response when pig skin that had been obtained on different occasions was used. In each experimental series (using the same pig skin), however, the maximal augmentation effects obtained with these glucocorticoids were approximately the same. The potent glucocorticoid, dexamethasone, demonstrated its effect at lower concentrations than were required for prednisolone, while hydrocortisone required a much higher concentration before its effect was detectable. Thus, despite considerable variations in the magnitude of the glucocorticoid effects, the concentrations required for the glucocorticoid effect were closely associated with the established glucocorticoidal potency which has previously been described.

Colchicine-induced alteration of hormone-stimulated cyclic AMP synthesis in pig skin (epidermis)

Effects of colchicine on the epidermal adenylate cyclase systems were investigated. When pig skin (epidermis) was incubated in RPMI 1640 medium without the addition of serum, the beta-adrenergic adenylate cyclase response (epinephrine-induced cyclic AMP accumulations) gradually decreased, whereas adenosine and histamine responses remained high or increased during the long-term (up to 48 h) incubation period. The addition of colchicine (1 mumol/liter) in the incubation medium resulted in an increase in the beta-adrenergic responsiveness and a decrease in adenosine and histamine responsivenesses. The effects of colchicine were both time- and concentration-dependent; they could be observed after 9-12 h incubation, and the maximal effect was obtained at a concentration of 0.1 mumol/liter. Similar effects were observed by the addition of another microtubule-disruptive agent, vinblastine. On the other hand, cytochalasin B, which affects the microfilament system, apparently decreased the beta-adrenergic response and increased adenosine and histamine responses during the long-term incubation period. The addition of serum in the incubation medium resulted in essentially the same effect as that of colchicine; in the presence of serum, colchicine-treated skin responded much more markedly to epinephrine (and much less to adenosine and histamine) than the control skin after 24- and 48-h incubation. Previously we reported that hydrocortisone has similar potentiating effects on the beta-adrenergic system of epidermis. The comparison of the effects of both compounds revealed that colchicine had a stronger effect than hydrocortisone, and furthermore, the simultaneous addition of both compounds (colchicine and hydrocortisone) in the incubation medium resulted in the more marked increase of beta-adrenergic response than the single addition of each chemical. Our overall results, coupled with the finding that hydrocortisone has no toxic effects on the adenosine- or histamine-adenylate cyclase system of epidermis, suggest that colchicine affects epidermal adenylate cyclase systems probably through a mechanism that is independent of glucocorticoid (hydrocortisone) effect.

Regulation of beta-adrenergic adenylate cyclase responsiveness of pig skin epidermis by suboptimal concentrations of epinephrine

Although receptor-specific refractoriness has been suggested to be one of the regulatory mechanisms of epidermal adenylate cyclase systems, its physiologic significance has been a subject of controversy because of the requirement of unusually high concentrations of agonists to induce refractoriness. In order to determine whether the epidermal adenylate cyclase system is regulated through a refractoriness mechanism by suboptimal concentrations of receptor agonists, this study was undertaken using pig skin epidermal adenylate cyclase systems. Pretreatment of pig skin with 0.1-1 microM epinephrine in vitro resulted in the reduction of the maximal epinephrine response (epinephrine-induced cyclic AMP accumulations) to various degrees without alterations in either low or high Km cyclic AMP phosphodiesterase activities. Repeated pretreatments were shown to be more effective in inducing refractoriness than a single pretreatment. Apparently there was no change in the Km value for epinephrine, suggesting that the decrease in epinephrine response represents a reduction in the number but not in the affinity of functional beta-adrenergic adenylate cyclase receptor sites. This refractoriness by low concentrations of catecholamine pretreatment was specific to the beta-adrenergic system, since there was no reduction in histamine response after the epinephrine pretreatment. These results indicate that the epidermal beta-adrenergic adenylate cyclase system is regulated by much lower concentrations of catecholamine than were previously described. It was suggested that physiologic fluctuations of plasma catecholamine levels might have a profound effect on epidermal beta-adrenergic adenylate cyclase responsiveness, resulting in the alteration of the minimal catecholamine level required for the successive activation of cyclic AMP-dependent protein kinase, which is the predominant target of cyclic AMP in epidermis.

Effects of glucocorticoids on the beta-adrenergic adenylate cyclase system of pig skin

Effects of glucocorticoids on the epidermal beta-adrenergic adenylate cyclase system were investigated. Long-term incubation of pig skin slices in RPMI 1640 medium resulted in the gradual decrease in the epinephrine-induced cyclic AMP accumulations of skin. The addition of hydrocortisone (100 microM) in the incubation medium prevented this decrease, and after 24- and 48-h incubation, there was a marked difference in beta-adrenergic responsiveness between control and hydrocortisone-treated skin. The study using other steroid hormones revealed that this effect on the beta-adrenergic system was relatively specific for glucocorticoids. Hydrocortisone, prednisolone, dexamethasone, and beta-methasone-17-valerate were shown to have marked effects on the beta-adrenergic system, while androstenedione, testosterone, dihydrotestosterone, progesterone, estrone, and beta-estradiol had no effect. Cortisone and estriol were shown to have similar but weaker effects than hydrocortisone. The effect of glucocorticoids was also relatively specific to the beta-adrenergic system, since there was no significant difference in adenosine-or histamine-induced cyclic AMP accumulations of skin after long-term incubation with and without hydrocortisone. The mechanism of this glucocorticoid action does not seem to be through the simple protection of the beta-adrenergic system of the skin, since the addition of hydrocortisone in the incubation medium at 24 or 48 h incubation time, when the epinephrine-induced cyclic AMP accumulation was considerably decreased, reversed the epinephrine unresponsiveness of the skin, after the additional 24-h incubation. Furthermore, the effect of hydrocortisone was inhibited by 3 different kinds of inhibitors: (a) progesterone, an inhibitor of intracytoplasmic glucocorticoid receptor binding; (b) actinomycin D, an inhibitor of messenger RNA (mRNA) synthesis; and (c) cycloheximide, an inhibitor of protein synthesis at the translation step. These results are in accordance with the view that glucocorticoids affect the beta-adrenergic system of epidermis by a mechanism requiring mRNA and protein synthesis possibly through the intracytoplasmic glucocorticoid receptor system of epidermis.