SUPPRESSION OF MITOGENIC ACTIVITY BY STABLE EXPRESSION OF THE REGULATORY DOMAIN OF PKC-BETA

The amino-terminal regulatory domain portion of each protein kinase C (PKC) family member (which in the case of PKC beta 1 includes the pseu dosubstrate, C1, V1 and C2 domains) plays an important role in regulat ing the kinase activity of the carboxyl-terminal catalytic domain. To examine the possibility that this regulatory domain region (designated 'PAT') might have biological functions independent of the catalytic d omain, we have developed derivatives of R6 cells which stably express a truncated PKC beta 1 cDNA that encodes the amino-terminal 317 amino acids, including the entire regulatory domain. These R6-plPAT cells ex press abundant amounts of a 38 kDa protein which binds a labeled phorb ol ester, but lacks protein kinase activity. In contrast to the 79 kDa PKC beta 1 holoenzyme which, when overexpressed in R6 cells, is found mostly in the cytosol, the 38 kDa PAT protein is predominantly associ ated with the particulate subcellular fraction. Furthermore, the PAT p rotein fails to show down-regulation following treatment of R6-plPAT c ells with 12-O-tetradecanoylphorbol-13-acetate (TPA). Evidence is also presented that TPA-stimulated growth is suppressed in R6-plPAT cells. These findings suggest that the PKC beta 1 regulatory domain could be involved in the suppression of mitogenic signaling.