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 (PKC eta) is a unique member of the PKC family since its regulation is distinct from other PKC isozymes. PKC eta was shown to regulate cell proliferation, differentiation and cell death. It was also shown to contribute to chemoresistance in several cancers. PKC eta 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 PKC eta were more susceptible to tumor formation in a two-stage carcinogenesis model, and it is downregulated in hepatocellular carcinoma. Thus, the role of PKC eta in cancer remains controversial. The purpose of this review article is to discuss how PKC eta regulates various cellular processes that may contribute to its contrasting roles in cancer.