THE CATALYTIC DOMAIN OF PKC-EPSILON, IN RECIPROCAL PKC-DELTA AND PKC-EPSILON CHIMERAS, IS RESPONSIBLE FOR CONFERRING TUMORGENICITY TO NIH3T3 CELLS, WHEREAS BOTH REGULATORY AND CATALYTIC DOMAINS OF PKC-EPSILON CONTRIBUTE TO IN-VITRO TRANSFORMATION

Protein kinase C-epsilon (PKC-epsilon) has been shown to increase grow th and cause malignant transformation when overexpressed in NIH3T3 cel ls, whereas PKC-delta reduced fibroblast growth, Two reciprocal chimer ic proteins (PKC-epsilon delta and PKC-delta epsilon were constructed by exchanging the regulatory and catalytic domains of PKC-delta and -e psilon and were stably overexpressed in NIH3T3 cells, Fibroblasts that overexpressed either chimera showed maximum cell density and morpholo gy that were intermediate between cells overexpressing PKC-delta and t hose that overexpressed PKC-epsilon, Moreover, all lines that expresse d chimeras were capable of anchorage-independent growth in the presenc e of TPA, which indicated that both the regulatory and catalytic domai ns of PKC-epsilon could independently induce NIH3T3 transformation, al though the combination of both domains, as found in PKC-epsilon, was t he most active form, In contrast, the translocation pattern and abilit y to induce tumors in nude mice was attributable to the catalytic doma ins exclusively, In particular, cells that expressed PKC-delta epsilon retained PKC-epsilon's full potency of tumorgenicity when injected in to 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 distinguish able events of transformation and tumorgenesis.