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The Journal of Biological Chemistry
Year: 2009  |  Volume: 284  |  Issue: 24  |  Page No.: 16633 - 16647

Aldosterone Stimulates Elastogenesis in Cardiac Fibroblasts via Mineralocorticoid Receptor-independent Action Involving the Consecutive Activation of G{alpha}13, c-Src, the Insulin-like Growth Factor-I Receptor, and Phosphatidylinositol 3-Kinase/Akt

S Bunda, Y Wang, T. F Mitts, P Liu, S Arab, M Arabkhari and A. Hinek    

Abstract:

We previously demonstrated that aldosterone, which stimulates collagen production through the mineralocorticoid receptor (MR)-dependent pathway, also induces elastogenesis via a parallel MR-independent mechanism involving insulin-like growth factor-I receptor (IGF-IR) signaling. The present study provides a more detailed explanation of this signaling pathway. Our data demonstrate that small interfering RNA-driven elimination of MR in cardiac fibroblasts does not inhibit aldosterone-induced IGF-IR phosphorylation and subsequent increase in elastin production. These results exclude the involvement of the MR in aldosterone-induced increases in elastin production. Results of further experiments aimed at identifying the upstream signaling component(s) that might be activated by aldosterone also eliminate the putative involvement of pertussis toxin-sensitive Gi proteins, which have previously been shown to be responsible for some MR-independent effects of aldosterone. Instead, we found that small interfering RNA-dependent elimination of another heterotrimeric G protein, G13, eliminates aldosterone-induced elastogenesis. We further demonstrate that aldosterone first engages G13 and then promotes its transient interaction with c-Src, which constitutes a prerequisite step for aldosterone-dependent activation of the IGF-IR and propagation of consecutive downstream elastogenic signaling involving phosphatidylinositol 3-kinase/Akt. In summary, the data we present reveal new details of an MR-independent cellular signaling pathway through which aldosterone stimulates elastogenesis in human cardiac fibroblasts.

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