The catalytic domain of PKC-epsilon, in reciprocal PKC-delta and -epsilon chimeras, is responsible for conferring tumorgenicity to NIH3T3 cells, whereas both regulatory and catalytic domains of PKC-epsilon contribute to in vitro transformation

Abstract

Protein kinase C-epsilon (PKC-epsilon) has been shown to increase growth and cause malignant transformation when overexpressed in NIH3T3 cells, whereas PKC-delta reduced fibroblast growth. Two reciprocal chimeric proteins (PKC-epsilondelta and PKC-deltaepsilon were constructed by exchanging the regulatory and catalytic domains of PKC-delta and -epsilon and were stably overexpressed in NIH3T3 cells. Fibroblasts that overexpressed either chimera showed maximum cell density and morphology that were intermediate between cells overexpressing PKC-delta and those that overexpressed PKC-epsilon. Moreover, all lines that expressed chimeras were capable of anchorage-independent growth in the presence of TPA, which indicated that both the regulatory and catalytic domains of PKC-epsilon could independently induce NIH3T3 transformation, although the combination of both domains, as found in PKC-epsilon, was the most active form. In contrast, the translocation pattern and ability to induce tumors in nude mice was attributable to the catalytic domains exclusively. In particular, cells that expressed PKC-deltaepsilon retained PKC-epsilon's full potency of tumorgenicity when injected into nude mice. In sum, our findings not only reinforce the concept that only certain PKC isozymes contribute to carcinogenesis but also show that different domains of PKCs mediate the physiologically distinguishable events of transformation and tumorgenesis.