P. Maruvada et Ae. Levine, INCREASED TRANSFORMING GROWTH-FACTOR-ALPHA LEVELS IN HUMAN COLON-CARCINOMA CELL-LINES OVER-EXPRESSING PROTEIN-KINASE-C, International journal of cancer, 80(1), 1999, pp. 72-77
Transforming growth factor-alpha (TGF-alpha) is synthesized as a membr
ane-bound precursor protein, pro-TGF-alpha, that is converted to a sol
uble form by 2 endoproteolytic cleavages. Several factors have been im
plicated in the regulation of the second rate-limiting step, including
protein kinase C (PKC). Earlier results indicated a potential role fo
r the conventional class of PKC isozymes in the observed increase in T
GF-alpha in the conditioned media of 2 human colon carcinoma cell line
s. The present study addresses the potential role of specific PKC isoz
ymes 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-
alpha, -beta I or -beta II; and the secretion of TGF-alpha into the co
nditioned medium was determined. Over-expression of either PKC-PI or P
KC-beta II in these cell lines enhanced the levels of TGF-alpha in the
media 2- to 5-fold. Over-expression of PKC-alpha did not alter the am
ount of TGF-alpha in the media to a significant extent. Transfection o
f HCT 116 cells with the anti-sense PKC-beta I cDNA resulted in a redu
ction in PKC-beta I protein expression. This was accompanied by a decr
ease in the amount of TGF-alpha in the conditioned media. Our results
indicate that modulation of PKC-beta protein levels alters the amount
of TGF-alpha found in the conditioned media from these colon carcinoma
cells. (C) 1999 Wiley-Liss, Inc.