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Characterization of PHLPP1 in adult mouse ventricular myocytes


The fastest growing cardiovascular disease subclass is heart failure, brought about by factors such as cardiac hypertrophy. The serine/threonine kinase Akt is involved in many cellular processes including cell growth, metabolism, protein synthesis, angiogenesis, and studies have implicated Akt in regulating cardiac hypertrophy depending on Akt intensity, duration, and localization. Growth factors, hormones, and cytokines activate Akt by phosphorylating its activation loop (Thr308) and hydrophobic motif (Ser473). Though extensive research focuses on Akt activation by upstream kinases, the mechanism of inactivation by phosphatases are poorly understood. Our project focuses on the role of the newly discovered Akt phosphatase PHLPP (PH domain leucine-rich repeat protein phosphatase) in adult mouse ventricular myocytes (AMVM). We hypothesized that removal of PHLPP1 will result in increased Akt phosphorylation at Ser473 after agonist stimulation in AMVM. We generated viable PHLPP1-/- mice to investigate physiological activation of Akt. PHLPP1 null AMVM had no overt phenotype differences at baseline compared to wild-type (WT) cells. Myocytes stimulated with the cytokine LIF displayed increased Akt Ser473 phosphorylation with no change at Thr308. Increased phosphorylation at Ser473 corresponded with increased activity as demonstrated by kinase assay, but there was no apparent changes in downstream GSK3 or MDM2 phosphorylation. Lastly, we found earlier Akt phosphorylation at Ser473 in PHLPP1 KO myocytes in cytosolic and nuclear fractions. Our data suggests PHLPP is an important regulator of Akt signaling in AMVM and ultimately the heart where it may be an important regulator of cardiac hypertrophy

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