INVOLVEMENT OF PROTEIN-KINASE-C AND AN ELASTASE-LIKE ENZYME IN THE PROCESSING OF TRANSFORMING GROWTH-FACTOR-ALPHA IN HUMAN COLON-CARCINOMA CELL-LINES

Human colon carcinoma cell lines secrete transforming growth factor-al pha (TGF-alpha). Previous work indicated that the apparent m.w. of the TGF-alpha secreted by these cells ranged between 5 and 25 kDa. The mo re differentiated GEO cell line secreted a higher percentage of high m .w. TGF-alpha than did the poorly differentiated HCT 116 cell line. In addition, the HCT 116 cells secreted 5-fold more TGF-alpha. Treatment of HCT 116 and GEO cells with a phorbol ester (TPA) resulted in a 4-f old increase in TGF-alpha in the conditioned media of both cell types. The TPA-induced release of TGF-alpha was blocked by an inhibitor of e lastase-like enzymes. This suggested a role for protein kinase C (PKC) in TGF-alpha processing in colon carcinoma cells. Direct measurement of PKC activity indicated that the HCT 116 cells (which secrete more f ully processed TGF-alpha) had 10-fold more PKC activity than GEO cells . The presence of an elastase-like activity in detergent extracts and the ability of an elastase inhibitor to block the TPA-induced secretio n of TGF-alpha suggests that PKC and an elastase-like enzyme are invol ved in the processing and secretion of TGF-alpha by human colon carcin oma cell lines. (C) 1994 Wiley-Liss, Inc.