ERK1/2 Dually Influence c‐fos Transcription and Cell Proliferation through Cytoplasmic Phosphorylation of RSK2 and Nuclear Phosphorylation of elk1 in Response to Angiotensin II

(AT 1 R) has been shown to promote aberrant cell proliferation during disease, and these events are in part mediated by ERK1/2. Both Protein Kinase C and Src kinases have separately been implicated in Ang II‐induced ERK1/2 activation. However, the outcomes associated with the activation of ERK1/2 though either mechanism are unclear. Here, we utilized mouse embryonic fibroblast (MEF) cells deficient in c‐Src, Yes, and Fyn (SYF/AT 1 ) and wild type MEF cells stably transfected with the AT 1 R. Utilizing chemical compounds and siRNA, we showed that 50% of Ang II‐induced ERK1/2 activation was mediated by c‐Src/Yes/Fyn and 50% by PKCζ‐dependent signaling. Ang II‐induced cell proliferation was markedly reduced in SYF/AT 1 cells or by PKCζ inhibition (p< 0.001). ERK1/2 nuclear accumulation was influenced solely by PKCζ whereas RSK2 nuclear phosphorylation was blocked in SYF/AT 1 cells but unaffected by PKCζ inhibition. C‐fos transcription and activity were reduced in SYF/AT 1 cells (p<0.001). Serum response factor (SRF) or ternary complex factor (TCF) binding of the c‐fos SRE both contribute to c‐fos transcription as demonstrated by transfection of SRE‐luciferase or mutated SRE‐luciferase plasmids. SRF phosphorylation was attenuated in SYF/AT 1 cells, whereas the nuclear phosphorylation of elk1 was blocked by PKCζ inhibition only. In summary, we identify the ERK1/2‐driven events leading to cell proliferation in response to Ang II. NIH K01‐DK60471, R01‐HL67277 and AHA Pre‐Doctoral Fellowship (0515138B)