Angiotensin stimulates phosphatidylcholine synthesis via a pathway involving diacylglycerol, protein kinase C, ERK1/2, and CTP:phosphocholine cytidylyltransferase

We are probing the regulation of phosphatidylcholine (PC) synthesis by angiotensin II. In the accompanying paper, we showed that manipulation of the lipid second messengers, arachidonic acid or hydroxyeicosatetraenoic acid, produced downstream of the angiotensin AT1a receptor did not affect the PC synthesis rates in a manner consistent with direct activation of the rate limiting enzyme in the pathway, CTP:phosphocholine cytidylyltransferase (CCT). However, suppression of diacylglycerol (DAG) production with an inhibitor of phospholipase C-β reduced angiotensin-dependent PC synthesis as well as ERK1/2 phosphorylation. Here, we show that the stimulation of PC synthesis and activation of CCT by angiotensin requires a signaling pathway that involves protein kinase C and ERK1/2. The inhibitors bis-indolylmaleimide I and PD98059 blocked ERK1/2 phosphorylation and completely eliminated angiotensin stimulation of the CCT-catalyzed reaction and PC synthesis. Exogenous addition of DAG using a lipid vesicle delivery system exactly mimicked the kinetics of angiotensin-promoted PC synthesis, suggesting that this mode of DAG delivery can effectively substitute for the DAG generated downstream of the activated AT1a receptor. Moreover, exogenous DAG activated ERK1/2, and the activation of PC synthesis by DAG was blocked by inhibition of protein kinase C and MEK. These data suggest that angiotensin-dependent DAG and the exogenously supplied DAG stimulate PC synthesis, not solely by direct action on CCT, but via a signaling pathway involving protein kinase C and ERK1/2. Angiotensin did not alter the net phosphorylation state of CCT as probed by immunoprecipitation of 32P-labeled CCT. Angiotensin stimulation of ERK1/2 likely mediates effects on CCT via a process other than CCT dephosphorylation.