Atrial natriuretic peptide promotes cardiomyocyte survival by cGMP-dependent nuclear accumulation of zyxin and Akt

Abstract

This study delineates a mechanism for antiapoptotic signaling initiated by atrial natriuretic peptide (ANP) stimulation leading to elevation of cGMP levels and subsequent nuclear accumulation of Akt kinase associated with zyxin, a cytoskeletal LIM-domain protein. Nuclear targeting of zyxin induces resistance to cell death coincident with nuclear accumulation of activated Akt. Nuclear translocation of zyxin triggered by cGMP also promotes nuclear Akt accumulation. Additional supportive evidence for nuclear accumulation of zyxin-enhancing cardiomyocyte survival includes the following: (a) promotion of zyxin nuclear localization by cardioprotective stimuli; (b) zyxin association with phospho-Akt 473 induced by cardioprotective stimuli; and (c) recruitment of zyxin to the nucleus by activated nuclear-targeted Akt as well as recruitment of Akt by nuclear-targeted zyxin. Nuclear accumulation of zyxin requires both Akt activation and nuclear localization. Potentiation of cell survival is sensitive to stimulation intensity with high-level induction by ANP or cGMP signaling leading to apoptotic cell death rather than enhancing resistance to apoptotic stimuli. Myocardial nuclear accumulation of zyxin and Akt responds similarly in vivo following treatment of mice with ANP or cGMP. Thus, zyxin and activated Akt participate in a cGMP-dependent signaling cascade leading from ANP receptors to nuclear accumulation of both molecules. Nuclear accumulation of zyxin and activated Akt may represent a fundamental mechanism that facilitates nuclear-signal transduction and potentiates cell survival.

Akt phosphorylation of zyxin mediates its interaction with acinus-S and prevents acinus-triggered chromatin condensation

“…25 This time course is consistent with ANP-elicited zyxin nuclear accumulation in cardiomyocyte, which occurs at about 3.5 h treatment. 18 It is also in alignment with our finding that zyxin binds to acinus after 3 h growth factor stimulation Previous study reveals that Akt activity is required for zyxin nuclear translocation. 18 However, how Akt mediates zyxin nuclear import remains elusive.…”

“…Further, zyxin nuclear translocation requires both activation and nuclear localization of Akt, suggesting that these two molecules might mutually regulate each other's residence in the nucleus. 18 In the current report, we show that zyxin is a physiological substrate of Akt. Akt phosphorylates zyxin on S142 and regulates its association with acinus-S. Nuclear zyxin prevents acinus apoptotic cleavage and abolishes chromatin condensation.…”

“…Wild-type zyxin robustly bound to phosphorylated but KD Akt-*KD (T308DS473DK179A), followed by Akt-CA and KD in affinity, fitting with previous observation that zyxin specifically interacts with activated Akt. 18 Interestingly, zyxin did not bind to wild-type Akt (Figure 4c). Zyxin phosphorylation mimetic mutant, S142D, strongly associated with both Akt-CA and Akt-*KD, but neither Akt wild type or KD.…”

“…Furthermore, overexpression of nuclear-targeted zyxin substantially decreased VP16-STS-induced chromatin condensation (Figure 7f), fitting with previous report that nuclear zyxin protects cardiomyocyte from apoptosis. 18 To further investigate whether zyxin is required for repressing chromatin condensation, we eliminated endogenous zyxin with siRNA. Depletion of endogenous zyxin did not affect acinus apoptotic degradation or chromatin condensation in HEK293 cells (data not shown).…”

“…These data provide a possible mechanistic explanation for the antiapoptotic function of zyxin reported previously. 18 Zyxin is a LIM protein found prominently at sites of cell adhesion and transiently in cell nuclei. The nuclear accumulation of zyxin occurs within 2.3 h of nuclear export inhibition initiating by leptomycin B treatment.…”