αB-crystallin interacts with and prevents stress-activated proteolysis of focal adhesion kinase by calpain in cardiomyocytes

Abstract

Focal adhesion kinase (FAK) contributes to cellular homeostasis under stress conditions. Here we show that aB-crystallin interacts with and confers protection to FAK against calpainmediated proteolysis in cardiomyocytes. A hydrophobic patch mapped between helices 1 and 4 of the FAK FAT domain was found to bind to the b4-b8 groove of aB-crystallin. Such an interaction requires FAK tyrosine 925 and is enhanced following its phosphorylation by Src, which occurs upon FAK stimulation. aB-crystallin silencing results in calpain-dependent FAK depletion and in the increased apoptosis of cardiomyocytes in response to mechanical stress. FAK overexpression protects cardiomyocytes depleted of aB-crystallin against the stretch-induced apoptosis. Consistently, load-induced apoptosis is blunted in the hearts from cardiac-specific FAK transgenic mice transiently depleted of aB-crystallin by RNA interference. These studies define a role for aB-crystallin in controlling FAK function and cardiomyocyte survival through the prevention of calpain-mediated degradation of FAK.

αB-crystallin: Portrait of a malignant chaperone as a cancer therapeutic target

“…Intriguingly, αB-crystallin inhibits activation of this key cell death protease that lies at the convergence of both apoptotic pathways, thereby conferring protection against a broad range of apoptotic stimuli, including chemotherapy and other cytotoxic drugs, tumor necrosis factor (TNF)-α, TNF-related apoptosis-inducing ligand (TRAIL), growth factor deprivation, matrix detachment-induced apoptosis, hypoxia, hypertonic and oxidative stress, ultraviolet radiation and others (Kegel et al, 1996; Mehlen et al, 1996; Andley et al, 2000; Kamradt et al, 2001, 2002, 2005; Stegh et al, 2008; Ruan et al, 2011; Dou et al, 2012; Petrovic et al, 2013; van de Schootbrugge et al, 2014; Malin et al, 2015). Conversely, silencing αB-crystallin confers sensitivity to cell death stimuli (Kamradt et al, 2005; Moyano et al, 2006; Lee et al, 2012; Petrovic et al, 2013; Pereira et al, 2014; Malin et al, 2015). Procaspase-3 is activated by a two-step mechanism in which initiator caspases (caspase-9 in the intrinsic pathway or caspases-8 or -10 in the extrinsic pathway) cleave procaspase-3 between its large and small subunits to generate a p24 intermediate, which subsequently undergoes autoproteolytic cleavage to remove its N-terminal domain (Cryns & Yuan, 1998; Logue & Martin, 2008).…”

“…In addition, αB-crystallin regulates invasion in human hepatocellular carcinoma cells (Huang et al, 2013). Although the mechanisms underlying these effects on cell migration/invasion have not been clearly defined, the ability of αB-crystallin to interact with and stabilize the focal adhesion kinase (FAK), intermediate filaments and microtubules may contribute to its promigratory actions (Djabali et al, 1997, 1999; Ghosh et al, 2007a; Pereira et al, 2014). …”

Small Heat Shock Protein αB-Crystallin Controls Shape and Adhesion of Glioma and Myoblast Cells in the Absence of Stress

“…Immunostaining shows that αB-crystallin colocalizes with several cytoskeletal [11] and focal adhesion proteins in muscle [12]. In muscle cells, αB-crystallin is preferentially expressed in slow-twitch muscle compared to fast-twitch muscle [9, 13] and this may be correlated with higher mitochondrial numbers and elevated oxidative stress and protein turnover rate in type I fibers [14].…”

“…αB-crystallin localizes to the wide z-band of the sarcomere where mechanical contractile tension is exerted by the actomyosin system [10, 16], and it may protect cytoskeletal proteins from mechanical stress [12, 16]. Muscle atrophy and hypertrophy have been studied for many years using myoblast cells as a model system [17, 18].…”

“…During muscle contraction, it is well known that cells are exposed to oxidative stress, but no study has focused on cell shape and migration as related to tubulin/microtubules in the cytoskeleton. Heart muscle contracts at a slow frequency, which is thus more stressful compared to skeletal muscle and αB-crystallin seems to play an important protective role not only for FAK degradation by calpain [12] but also for tubulin cytoskeleton (Ohoto-Fujita and Atomi, manuscript in preparation). In this study we focused on the physiological function of αB-crystallin, as a ubiquitously expressed protein [26], in the absence of stress.…”