Identification of molecular determinants for protein kinase c isotype-specific functions in human leukemia cell proliferation and differentiation

Protein kinase C is involved in the proliferation and differentiation of many cells types. Human erythrolenkemia (K562) cells express the α, β_II and ÇPKC isotypes. Using overexpression and antisense techniques we have determined that Q PKC is involved in phorbol 12-myristate 13-acetate (PMA)-induced cytostasis while βn PKC is required for cell proliferation. To identify regions within a and βjj PKC that allow participation in these divergent pathways, we constructed chimera in which the regulatory and catalytic domains of a and β_II PKC were exchanged. These PKC chimeras can be stably expressed, exhibit enzymatic properties similar to native a and β_II PKC in vitro, and participate in Q and βn PKC isotype-specific signalling pathways in whole cells. Using these chimera we have demonstrated that the catalytic domains of Q and β_II PKC contain determinants important for PKC isotype-selective function. These results suggest that the catalytic domain represents a poten-tial target for modulating PKC isotype activity in vivo.