Signal transduction pathways of angiotensin II--induced c-fos gene expression in cardiac myocytes in vitro. Roles of phospholipid-derived second messengers.
Angiotensin II (Ang II) causes a rapid induction of immediate-early genes and hypertrophy in the cardiac myocyte. However, the signaling mechanism of Ang II-induced immediate-early gene expression in cardiac myocytes has not been characterized. Therefore, we examined signal transduction of Ang II in neonatal rat cardiac myocytes, using c-fos gene expression as a model system. Transient transfection of c-fos reporter gene constructs indicated that the serum response element is not only required but also sufficient for Ang II-induced activation of the c-fos promoter. Ang II is known to cause an increase in [Ca2+]i. We found that Ang II also causes a small increase in cAMP in cardiac myocytes. However, the Ca2+/cAMP response element of the c-fos gene was not sufficient to confer Ang II responsiveness to the c-fos promoter, and inhibitors of protein kinase A had no effects on Ang II-induced c-fos expression. On the other hand, chelating intracellular Ca2+ with BAPTA-AM inhibited Ang II-induced c-fos expression in a dose-dependent manner, suggesting that Ca2+ is required for Ang II-induced signaling. Measurements of phospholipid-derived second messengers revealed that Ang II increased production of inositol trisphosphate, diacylglycerol, phosphatidic acid, and arachidonic acids, resulting in a sustained increase in protein kinase C activity. This and other evidence suggest that Ang II activates phospholipase C, phospholipase D, and possibly phospholipase A2. All of these second-messenger systems are activated through the AT1 receptor. Pharmacological inhibition of phospholipase C or downregulation of protein kinase C significantly suppressed Ang II-induced c-fos expression. In conclusion, Ang II activates multiple phospholipid-derived second-messenger systems via the AT1 receptor in cardiac myocytes. Among these second-messenger systems, phospholipase C and protein kinase C seem essential for Ang II-induced c-fos gene expression, whereas Ca2+ may play a permissive role. Finally, the "Ang II response element" of the c-fos gene maps to the protein kinase C-dependent portion of the serum response element.
Sadoshima
J
J
Molecular Medicine Division, Beth Israel Hospital, Boston, Mass. 02215.
Izumo
S
S
D000262:Adenylyl Cyclases / Q000378:metabolism; D000595:Amino Acid Sequence; D000804:Angiotensin II / Q000494:pharmacology*; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002118:Calcium / Q000502:physiology; D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000187:drug effects*; D016762:Genes, fos; D008969:Molecular Sequence Data; D010739:Phospholipase D / Q000378:metabolism; D010743:Phospholipids / Q000502:physiology*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D011945:Receptors, Angiotensin / Q000502:physiology; D015290:Second Messenger Systems / Q000502:physiology*; D015398:Signal Transduction; D010738:Type C Phospholipases / Q000378:metabolism
D010743:Phospholipids; D011945:Receptors, Angiotensin; D000804:Angiotensin II; D016718:Arachidonic Acid; D011493:Protein Kinase C; D010738:Type C Phospholipases; D010739:Phospholipase D; D000262:Adenylyl Cyclases; D002118:Calcium