Focal Adhesion Kinase-mediated Phosphorylation of Beclin1 Protein Suppresses Cardiomyocyte Autophagy and Initiates Hypertrophic Growth

Abstract

Autophagy is an evolutionarily conserved intracellular degradation/recycling system that is essential for cellular homeostasis but is dysregulated in a number of diseases, including myocardial hypertrophy. Although it is clear that limiting or accelerating autophagic flux can result in pathological cardiac remodeling, the physiological signaling pathways that fine-tune cardiac autophagy are poorly understood. Herein, we demonstrated that stimulation of cardiomyocytes with phenylephrine (PE), a well known hypertrophic agonist, suppresses autophagy and that activation of focal adhesion kinase (FAK) is necessary for PE-stimulated autophagy suppression and subsequent initiation of hypertrophic growth. Mechanistically, we showed that FAK phosphorylates Beclin1, a core autophagy protein, on Tyr-233 and that this post-translational modification limits Beclin1 association with Atg14L and reduces Beclin1-dependent autophagosome formation. Remarkably, although ectopic expression of wild-type Beclin1 promoted cardiomyocyte atrophy, expression of a Y233E phosphomimetic variant of Beclin1 failed to affect cardiomyocyte size. Moreover, genetic depletion of Beclin1 attenuated PE-mediated/FAK-dependent initiation of myocyte hypertrophy in vivo. Collectively, these findings identify FAK as a novel negative regulator of Beclin1-mediated autophagy and indicate that this pathway can facilitate the promotion of compensatory hypertrophic growth. This novel mechanism to limit Beclin1 activity has important implications for treating a variety of pathologies associated with altered autophagic flux.Macroautophagy is an evolutionarily conserved intracellular degradation/recycling process in which cytoplasmic cargo is non-selectively enveloped within double-membraned vesicles called autophagosomes that are transported to and fuse with lysosomes. Within these so-called autolysosomes, cytoplasmic cargo and the inner membrane are degraded so that the amino acids, fatty acids, and glucose released can be used to support cellular metabolism or to synthesize new proteins. Cardiomyocytes are both highly metabolically active cells and long-lived cells and as such are particularly dependent on macroautophagy (hereafter referred to as autophagy) for energy production and removal of damaged organelles or misfolded proteins. However, in some cases up-regulation of autophagy (or failure of autophagy suppression) can lead to detrimental cardiac remodeling.Autophagy is regulated in a stepwise fashion that involves the formation of distinct protein complexes composed of autophagy-related genes (Atg proteins) and their enzymatic binding partners. Nutrient deprivation-induced activation of the AMP kinase/Unc-51-like autophagy-activating kinase 1 (ULK) kinase cascade leads to the recruitment of core proteins VPS34, VPS15, and Beclin1 (complex I) to endoplasmic reticulum exit sites to form phosphatidylinositol 1,4,5-phosphate 3-kinase-dependent double membrane autophagosome precursors. Complex I then facilitates the recruitment of additional proteins, includi...

PRKAR1A deficiency impedes hypertrophy and reduces heart size

“…Immunostaining was performed as described previously (Cheng et al, 2017), with the following primary antibodies: mouse anti‐cardiac troponin T (MS‐295‐P, Thermo Scientific, 1:100), mouse anti‐COX IV (#11967, Cell Signaling, 1:100), or rabbit anti‐Drp1 (#8570, Cell Signaling, 1:100). Cardiomyocyte cell surface area was measured using ImageJ.…”

ATM ‐ CHK 2‐Beclin 1 axis promotes autophagy to maintain ROS homeostasis under oxidative stress

“…For instance, ULK1, AMPK, MAPKAPK2/3, DAPK, CaMKII, and PGK1 can phosphorylate Beclin 1 to promote autophagy (Zalckvar et al , ; Kim et al , ; Russell et al , ; Wei et al , ; Fujiwara et al , ; Zhang et al , 2016a; Li et al , ; Qian et al , ). In contrast, AKT1, EGFR, FAK, HER2, and MST1 phosphorylate Beclin 1 to inhibit autophagy (Wang et al , ; Maejima et al , ; Wei et al , ; Cheng et al , ; Vega‐Rubin‐de‐Celis et al , ). Beclin 1 phosphorylation is also precisely regulated by diverse signals including glucose starvation, serum starvation, amino acid deprivation, glutamine deprivation, ionomycin treatment, and hypoxia (Kim et al , ; Russell et al , ; Wei et al , ; Zhang et al , 2016a; Li et al , ; Qian et al , ).…”

Osteoprotegerin prompts cardiomyocyte hypertrophy via FAK/BECLIN1 mediated autophagy inhibition

“…Indeed, in this study, we observed that FAK mediated the OPG induced Belcin1-Tyr-233 phosphorylation. It has been reported that phosphorylation of Beclin1 at Tyr-233 can restrain its binding ability to complex I (Atg14L/Vps15/Vps34) as well as complex II (UVRAG/Vps15/Vps34), which are essential steps for autophagosome formation and autophagosome-lysosomal fusion, respectively [5]. So it is plausible to reason that OPG activates FAK, which in turn phosphorylates Belcin1-Tyr-233, causing inability to form complex I and II, thus hinders autophagy activation.…”

“…Beclin1 is a Core Protein regulating autophagy. It has been demonstrated that phosphorylation of Beclin1 at Tyr233 limit its binding with the complex I and complex II, a necessary step for autophagy activation [5]. As shown in Fig.…”