Protein Kinase C-eta Signalling in Breast Cancer

Pal, Deepanwita, Protein kinase C-eta signaling in breast cancer. Doctor of Philosophy (Biochemistry and Molecular Biology), November, 2013, 117 pp, 14 illustrations, 260 References Protein kinase C-eta (PKCη) is a novel member of the PKC family that is important for several cellular processes. PKCη is overexpressed in breast cancer and has been associated with chemotherapeutic resistance. PKCη is the only phorbol ester-sensitive PKC isozyme that resists downregulation upon prolonged treatment with tumorpromoting phorbol esters suggesting its unique regulation. The purpose of this dissertation is to elucidate the mechanism of PKCη regulation and its functional relevance in breast cancer. We have shown that PKCη is upregulated by several structurally and functionally distinct PKC activators in contrast to other PKC isozymes. Activator-induced upregulation of PKCη was associated with its phosphorylation. Our results indicate that novel PKCs are involved in the upregulation of PKCη by PKC activators. We also made a novel observation that PKCη is downregulated via two distinct mechanisms. While inhibition of PKC caused the downregulation of PKCη via proteasome-independent pathway, inhibition of PDK1 led to PKCη downregulation via proteasome-dependent pathway. We further demonstrated that PKCη is important for the growth and survival of breast cancer cells. The unique regulation of PKCη and its implications on breast cancer growth and survival suggests that this pathway could be selectively exploited for targeted therapies for breast cancer.