Diacylglycerol kinase theta and zeta isoforms: regulation of activity, protein binding partners and physiological functions

Abstract

Diacylglycerol kinases (DGKs) phosphorylate the second messenger diacylglycerol (DAG) yielding phosphatidic acid (PA). In this thesis, we investigated which structural domains of DGKtheta are required for DGK activity. Furthermore, we showed that DGKzeta binds to and is activated by the Retinoblastoma tumour suppressor protein (pRB) and the pRB-related proteins p107 and p130, key regulators of the cell-cycle, differentiation and apoptosis. The interaction between pRB and DGKzeta is regulated by protein kinase C. We also found a physiological function of DGKzeta in pRB signalling. Mouse embryonic fibroblasts (MEFs) derived from pRB knock-out mice are unable to arrest in G1 phase of the cell-cycle after gamma-irradiation, whereas wild-type MEFs stop cycling to repair their DNA. DGKzeta overexpression in pRB knock-out MEFs, however, reconstituted a gamma-irradiation-induced cell-cycle arrest in a DGK activity-dependent way. As pRB is known to regulate muscle differentiation, we studied the role of DGKzeta in this process. DGKzeta was found to stimulate muscle differentiation in a DGK activity-dependent fashion and enhanced the expression of early- and late muscle-specific genes. Our results suggest that DGKthata and DGKzeta play a crucial role in determining the correct balance between DAG and PA signalling pathways to regulate physiological functions.