Alpha‐1 adrenergic receptor transactivates signal transducer and activator of transcription‐3 (Stat3) through activation of Src and epidermal growth factor receptor (EGFR) in hepatocytes

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Abstract
Hepatocytes express adrenergic receptors (ARs) that modulate several functions, including liver regeneration, hepatocyte proliferation, glycogenolysis, gluconeogenesis, synthesis of urea and fatty acid metabolism. Adrenergic hepatic function in adults is mainly under the control of α1‐ARs; however, the mechanism through which they influence diverse processes remains incompletely understood. This study describes a novel α1‐AR‐mediated transactivation of signal transducer and activator of transcription‐3 (Stat3) in primary and transformed hepatocytes. Treatment of primary rat hepatocytes with the α1‐AR agonist, phenylephrine (PE), induced a rapid phosphorylation of Stat3. PE also increased Stat3 phosphorylation, DNA binding and transcription activity in transformed human hepatocellular carcinoma cells (Hep3B). The PE‐induced Stat3 phosphorylation, DNA binding and reporter activity were completely blocked by the selective α1‐AR antagonist, prazosin. In addition, transfection of Hep3B cells with human α1B‐AR expression vector also enhanced Stat3 phosphorylation and reporter activity. Moreover, overexpression of RGS2, a protein inhibitor of Gq/11signaling, blocked PE‐induced Stat3 phosphorylation and reporter activity. The observations that PE induced the formation of c‐Src‐Stat3 binding complex and phosphorylation of epidermal growth factor receptor (EGFR) and that inhibiting Src and EGFR prevented PE‐induced Stat3 activation indicate the involvement of Src and EGFR. Taken together, these observations demonstrate a novel α1‐AR‐mediated Stat3 activation that involves Gq/11, Src, and EGFR in hepatic cells. J. Cell. Physiol. 216: 486–497, 2008.