Protein Kinase C Delta Inhibits Notch-Dependent Transcription by Inhibition of Proper Nuclear Targetting of Notch Intracellular Domain

Abstract

Protein kinase C delta (PKCδ) is a serine/threonine kinase that plays significant roles in the regulation of growth, apoptosis, and differentiation of a diversity of cell types. In this study, we investigated the effect of PKCδ on Notch intracellular domain (NICD)-mediated transcription by transient transfection studies with 6ⅩNRE luciferase reporter construct. The results indicated that co-expression of PKCδ significantly down-regulated NICD-dependent transcription. Co-expression of kinase-dead dominant negative PKCδ (K376R) could also slightly down-regulated NICD-dependent transcription and treatment with PKCδ inhibitor Rottlerin could partially rescue PKCδ-induced down-regulation of NICD transcriptional activity, suggesting that PKCδ could exert its inhibitory effect on NICD-dependent transcription via kinase activity-dependent and independent mechanism(s). When the subcellular distribution of NICD was investigated by both subcellular fractionation and immunocytochemistry, PKCδ could effectively impair proper nuclear localization of NICD whereas PKCδK376R failed to exert inhibitory effect on NICD nuclear localization. Taken together, these data might indicate that PKCδ can induce down-regulation of NICD transcriptional activity via kinase activity-dependent regulation of NICD nuclear localization and kinase activity-independent mechanism that remains to be verified.