Glucocorticoid regulation of two serine hydrolases in rat splenic lymphocytes in vitro

A quantitative assay employing binding of [³H]diisopropylfluorophosphate ([³H]DFP) and SDS-polyacrylamide gel electrophoresis was used to measure serine hydrolases in cell-free extracts from rat splenic lymphocytes. After labeling with [³H]DFP at pH 7, six major serine hydrolases are detected on 10% gels, having molecular weights of 78, 55, 34, 30, 28 and 17 (· 10^-3). When labeled at pH 4, only four activities are measured, with M_r or 79, 55, 33 and 17 (· 10^-3). Incubation of splenic lymphocytes for 8 h in vitro with 1 μM dexamethasone followed by [³H]DFP labeling at pH 7 produces a 91% increase in the 17000 [³H]DFP. Hormone treatment for 8 h with subsequent labeling at pH 4 results in a 15% increase in the largest (78000) species, as well as 73% increase in the 17000 enzyme, compared with lysates from cells incubated without steroid. These effects are not observed after only 4 h of glucocorticoid exposure. Dexamethasone treatment for 8 h does not produce a decrease in any of these serine hydrolases, nor is there an apparent induction of new enzymes (i.e., having a molecular weight different from the preexisting species). Studies examining the effect of protease inhibitors on the [³H]DFP capacity of these proteins, show that the 17000 enzyme is sensitive to the protease inhibitor, pepstatin A, as well as the sulfhydryl reagents dithiothreitol and N-ethylmaleimide. These result suggest that this dexamethasone-responsive enzyme is a protease which requires a free thiol group for optimal activity. These findings are discussed with regard to the mechanism of glucocorticoid action in lymphocytes.