The Enigmatic Protein Kinase C-eta

Protein kinase C (PKC), a multi-gene family, plays critical roles in signal transduction and cell regulation. Protein kinase C-eta (PKCeta) is a unique member of the PKC family since its regulation is distinct from other PKC isozymes. PKCeta was shown to regulate cell proliferation, differentiation and cell death. It was also shown to contribute to chemoresistance in several cancers. PKCeta has been associated with several cancers, including renal cell carcinoma, glioblastoma, breast cancer, non-small cell lung cancer, and acute myeloid leukemia. However, mice lacking PKCeta were more susceptible to tumor formation in a two-stage carcinogenesis model, and it is downregulated in hepatocellular carcinoma. Thus, the role of PKCeta in cancer remains controversial. The purpose of this review article is to discuss how PKCeta regulates various cellular processes that may contribute to its contrasting roles in cancer.