Regulation of Akt/PKB activity by P21-activated kinase in cardiomyocytes

Abstract

Akt/PKB is a critical regulator of cardiac function and morphology, and its activity is governed by dual phosphorylation at active loop (Thr308) by phosphoinositide-dependent protein kinase-1 (PDK1) and at carboxyl-terminal hydrophobic motif (Ser473) by a putative PDK2. P21-activated kinase-1 (Pak1) is a serine/threonine protein kinase implicated in the regulation of cardiac hypertrophy and contractility, and was shown previously to activate Akt through an undefined mechanism. Here we report Pak1 as a potential PDK2 that is essential for Akt activity in cardiomyocytes. Both Pak1 and Akt can be activated by multiple hypertrophic stimuli or growth factors in a phosphatidylinositol-3-kinase (PI3K)-dependent manner. Pak1 overexpression induces Akt phosphorylation at both Ser473 and Thr308 in cardiomyocytes. Conversely, silencing or inactivating Pak1 gene diminishes Akt phosphorylation in vitro and in vivo. Purified Pak1 can directly phosphorylate Akt only at Ser473, suggesting that Pak1 may be a relevant PDK2 responsible for AKT Ser473 phosphorylation in cardiomyocytes. In addition, Pak1 protects cardiomyocytes from cell death, which is blocked by Akt inhibition. Our results connect two important regulators of cellular physiological functions and provide a potential mechanism for Pak1 signaling in cardiomyocytes.

Cytoskeletal role in protection of the failing heart by β-adrenergic blockade

“…The fact that increased ␤-adrenergic activity is regularly seen in pathological cardiac hypertrophy, including this model of severe RV pressure overloading (14), together with the recent observation that ␤-adrenergic agonists cause Pak1 activation (33), and that adenosine inhibits the cardiac hypertrophy-dependent microtubule changes (19), likely through its antiadrenergic effects (12), led to the present study; that is, in the setting of this knowledge, we hypothesized and then showed here that chronic ␤-adrenergic blockade would prevent the abnormal microtubule network from forming during pathological cardiac hypertrophy.…”

“…Over a MOI range of 1-100 plaque forming units/cell of Ad-␤-Gal, there was after 48 h 90% cardiomyocyte infection as determined by immunofluorescence microscopy using a ␤-Gal antibody; there was no observable cytotoxicity. For the feline cardiomyocyte studies here, cells were infected 48 h earlier at an MOI of 1 either with Ad-␤-Gal, an adenovirus encoding bacterial ␤-galactosidase as a control or with AdKDPak1, an adenovirus encoding kinase-dead Pak1-K299R as a competitive inhibitor of Pak1 activity; AdKDPak1 was a generous gift from Q. Liang (33).…”

“…Of interest in this context, it would appear that Pak1 activation is protective against short-term toxic effects of doxorubicin on isolated neonatal cardiomyocytes (33). Although the following potential etiology for this Pak1 protective effect was not investigated in that study, doxorubicin has striking microtubule disrupting effects in isolated neonatal cardiomyocytes (40), and this microtubule disruption may be acting through effects on MAP4 (3,20).…”

“…Thus, a hallmark of deteriorating intrinsic myocardial function, even well before the onset of overt heart failure, is the increased circulating norepinephrine levels and depleted myocardial norepinephrine content that result from continuous activation of the sympathetic nervous system (9), as well as cardiomyocyte ␤ 1 -adrenergic receptor downregulation (5), including that caused by MAP4 decoration of microtubules (6). This common pathophysiological setting for both microtubule network densification and increased circulating norepineph-rine, coupled with the recent observation of ␤-agonist activation of cardiac Pak1 (33), led to the hypothesis tested in the present study. This hypothesis is that persistent adrenergic overdrive is the root cause of the microtubule network abnormality and its maladaptive effects and that ␤-adrenergic blockade would prevent or reverse its occurrence.…”

PAK1 is a therapeutic target in acute myeloid leukemia and myelodysplastic syndrome

“…To confirm PAK1 inhibition by both IPA-3 and FRAX-597 in AML cell lines, we evaluated levels of phosphorylated AKT at Ser473, an established PAK1 target. 16,18,19 Treatment with either drug resulted in decreased phosphorylation of AKT at Ser473 in a dose-dependent manner (supplemental Figure 1D-E).…”