Involvement of protein kinase C epsilon (PKC epsilon) in thyroid cell death - A truncated chimeric PKC epsilon cloned from a thyroid cancer cell lineprotects thyroid cells from apoptosis

The protein kinase C (PKC) family has been implicated in the regulation of apoptosis. However, the contribution of individual PKC isozymes to this pro cess is not well understood. We reported amplification of the chromosome 2p 21 locus in 28% of thyroid neoplasms, and in the WRO thyroid carcinoma cell line. By positional cloning we identified a rearrangement and amplificatio n of the PKC epsilon gene, that maps to 2p21, in WRO cells. This resulted i n the overexpression of a chimeric/ truncated PKC epsilon (Tr-PKC epsilon) mRNA, coding for N-terminal amino acids 1-116 of the isozyme fused to an un related sequence. Expression of the Tr-PKC epsilon protein in PCCL3 cells i nhibited activation-induced translocation of endogenous PKC epsilon, but it s kinase activity was unaffected, consistent with a dominant negative effec t of the mutant protein on activation-induced translocation of wild-type PK C epsilon and/or displacement of the isozyme to an aberrant subcellular loc ation. Cell lines expressing Tr-PKC epsilon grew to a higher saturation den sity than controls. Moreover, cells expressing Tr-PKC epsilon were resistan t to apoptosis, which was associated with higher Bcl-2 levels, a marked imp airment in p53 stabilization, and dampened expression of Bar. These finding s point to a role for PKC epsilon in apoptosis-signaling pathways in thyroi d cells, and indicate that a naturally occurring PKC epsilon mutant that fu nctions as a dominant negative can block cell death triggered by a variety of stimuli.