Influence of proteinase inhibitors on glucocorticoid receptor binding.

The influence of several proteinase inhibitors on rat liver cytosolic glucocorticoid receptor binding to [3H]triamcinolone acetonide has been investigated. E-64 (36 microM), an active-site directed cysteine proteinase inhibitor, significantly (about 40%) inhibited receptor binding. Tos-Lys-CH2Cl (1-2 mM) and Tos-Phe-CH2Cl (1-2 mM) also depressed receptor binding (20-67%). Interestingly, 5 mM dithiothreitol was able to prevent Tos-Lys-CH2Cl and Tos-Phe-CH2Cl effects, but had no apparent influence on E-64 action. A degree of proteinase inhibitor specificity was indicated by the lack of effect of several other proteinase inhibitors such as diisopropylfluorophosphate (1 mM), phenylmethylsulfonyl fluoride (1-2 mM), soybean trypsin inhibitor (1-2 mg/ml), tissue inhibitor of metalloproteinase (3.8 U/ml), cystatin (4-8 microM), and phosphoramidon (20-40 microM). These results suggest that thiol reactive proteinase inhibitors block glucocorticoid receptor binding, and that E-64 may prove to be a useful chemical probe in studying glucocorticoid receptor interaction.