Increased transforming growth factor‐α levels in human colon carcinoma cell lines over‐expressing protein kinase C

Abstract

Transforming growth factor-α (TGF-α) is synthesized as a membrane-bound precursor protein, pro-TGF-α, that is converted to a soluble form by 2 endoproteolytic cleavages. Several factors have been implicated in the regulation of the second rate-limiting step, including protein kinase C (PKC). Earlier results indicated a potential role for the conventional class of PKC isozymes in the observed increase in TGF-α in the conditioned media of 2 human colon carcinoma cell lines. The present study addresses the potential role of specific PKC isozymes in this process using sense and anti-sense expression vectors for PKC isozymes. Two human colon carcinoma cell lines, HCT 116 and GEO, were transfected with plasmids, leading to the over-expression of PKC-α, -βI or -βII; and the secretion of TGF-α into the conditioned medium was determined. Over-expression of either PKC-βI or PKC-βII in these cell lines enhanced the levels of TGF-α in the media 2- to 5-fold. Over-expression of PKC-α did not alter the amount of TGF-α in the media to a significant extent. Transfection of HCT 116 cells with the anti-sense PKC-βI cDNA resulted in a reduction in PKC-βI protein expression. This was accompanied by a decrease in the amount of TGF-α in the conditioned media. Our results indicate that modulation of PKC-β protein levels alters the amount of TGF-α found in the conditioned media from these colon carcinoma cells. Int. J. Cancer 80:72–77, 1999. © 1999 Wiley-Liss, Inc.