Angiotensin II induces phosphatidic acid formation in neonatal rat cardiac fibroblasts: evaluation of the roles of phospholipases C and D.
Phosphatidic acid has been proposed to contribute to the mitogenic actions of various growth factors. In 32P-labeled neonatal rat cardiac fibroblasts, 100 nM [Sar1]angiotensin II was shown to rapidly induce formation of 32P-phosphatidic acid. Levels peaked at 5 min (1.5-fold above control), but were partially sustained over 2 h. Phospholipase D contributed in part to phosphatidic acid formation, as 32P- or 3H-phosphatidylethanol was produced when cells labeled with [32P]H3PO4 or 1-O-[1,2- 3H]hexadecyl-2-lyso-sn-glycero-3-phosphocholine were stimulated in the presence of 1% ethanol. [Sar1]angiotensin II-induced phospholipase D activity was transient and mainly mediated through protein kinase C (PKC), since PKC downregulation reduced phosphatidylethanol formation by 68%. Residual activity may have been due to increased intracellular Ca2+, as ionomycin also activated phospholipase D in PKC-depleted cells. Phospholipase D did not fully account for [Sar1]angiotensin II-induced phosphatidic acid: 1) compared to PMA, a potent activator of phospholipase D, [Sar1]angiotensin II produced more phosphatidic acid relative to phosphatidylethanol, and 2) PKC downregulation did not affect [Sar1]angiotensin II-induced phosphatidic acid formation. The diacylglycerol kinase inhibitor R59949 depressed [Sar1]angiotensin II-induced phosphatidic acid formation by only 21%, indicating that activation of a phospholipase C and diacylglycerol kinase also can not account for the bulk of phosphatidic acid. Thus, additional pathways not involving phospholipases C and D, such as de novo synthesis, may contribute to [Sar1]angiotensin II-induced phosphatidic acid in these cells. Finally, as previously shown for [Sar1]angiotensin II, phosphatidic acid stimulated mitogen activated protein (MAP) kinase activity.(ABSTRACT TRUNCATED AT 250 WORDS)
Booz
G W
GW
Weis Center for Research, Geisinger Clinic, Danville, PA 17822.
Taher
M M
MM
Baker
K M
KM
Singer
H A
HA
D000804:Angiotensin II / Q000378:metabolism / Q000494:pharmacology*; D000818:Animals; D002478:Cells, Cultured; D019852:Diacylglycerol Kinase; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism; D006321:Heart / Q000187:drug effects*; D009206:Myocardium / Q000166:cytology / Q000378:metabolism; D010712:Phosphatidic Acids / Q000096:biosynthesis*; D010713:Phosphatidylcholines / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism*; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism*
D010712:Phosphatidic Acids; D010713:Phosphatidylcholines; D010716:Phosphatidylinositols; D000804:Angiotensin II; D017853:Phosphotransferases (Alcohol Group Acceptor); D019852:Diacylglycerol Kinase; D010738:Type C Phospholipases; D010739:Phospholipase D