Search

The small heat shock protein αB-Crystallin (CryAB, HspB5) and SH2 domain-containing tyrosine phosphatase 2 (Shp2) are important molecules in heart response to pathophysiological stress. Here we show that CryAB interacts with and potentially regulates Shp2 catalytic activity in stretched cardiomyocytes. Such an interaction requires CryAB oligomer to attenuate Shp2 activation. Stretched cardiomyocytes show a robust CryAB/Shp2 association accompanied by a reduction in the Shp2 phosphatase activity. Accordingly, CryAB knock-down in cardiomyocytes enhances Shp2 activity induced by mechanical stress. These results revealed a new role for CryAB, as a modulator of Shp2 phosphatase activity during a functionally relevant stimulus in cardiomyocytes.

Small heat shock proteins (sHSPs) play a central role in protein homeostasis under conditions of stress by binding partly unfolded, aggregate‐prone proteins and keeping them soluble. Like many sHSPs, the widely expressed human sHSP, αB‐crystallin (‘αB’), forms large polydisperse multimeric assemblies. Molecular interactions involved in both sHSP function and oligomer formation remain to be delineated. A growing database of structural information reveals that a central conserved α‐crystallin domain (ACD) forms dimeric building blocks, while flanking N‐ and C‐termini direct the formation of larger sHSP oligomers. The most commonly observed inter‐subunit interaction involves a highly conserved C‐terminal ‘IxI/V’ motif and a groove in the ACD that is also implicated in client binding. To investigate the inherent properties of this interaction, peptides mimicking the IxI/V motif of αB and other human sHSPs were tested for binding to dimeric αB‐ACD. IxI‐mimicking peptides bind the isolated ACD at 22°C in a manner similar to interactions observed in the oligomer at low temperature, confirming these interactions are likely to exist in functional αB oligomers.

Tsang J Y S, Lai M W H, Wong K H Y, Chan S-K, Lam C C F, Tsang A K H, Yu A M C, Tan P-H & Tse G M (2012) Histopathology 61, 378–386 αB-crystallin is a useful marker for triple negative and basal breast cancers Aims: Basal-like breast cancers (BLBCs), a breast cancer subtype with triple-negative status, pose significant problems in clinical management because of their aggressive behaviour. Recently, an association between αΒ-crystallin expression and BLBCs has been suggested, and we therefore investigated whether αΒ-crystallin could be a putative marker allowing BLBCs to be identified more accurately. Methods and results: We evaluated the expression of αB-crystallin and other biomarkers in 395 cases of breast carcinoma by immunohistochemistry, analysed the correlation of their expression with different breast cancer subtypes, and compared their sensitivity as well as specificity in identifying BLBCs. αΒ-crystallin expression was found to be correlated positively with basal markers and histological subtypes associated with BLBCs. A significant positive correlation of αΒ-crystallin expression was also found with triple-negative breast cancers (TNBC) (C = 0.409, P

A major stress protein, α-crystallin, functions as a chaperone. Site-directed mutagenesis has been used to identify regions of the protein necessary for chaperone function. In this work we have taken some of the previously described mutants produced and assessed their chaperone function by both a traditional heat-induced aggregation method at elevated temperature and using enzyme methods at 37 °C. In general the different assays gave parallel results indicating that the same property is being measured. Discrepancies were explicable by the heat lability of some mutants. Most mutants had full chaperone function showing the robust nature of α-crystallin. A mutant corresponding to a minor component of rodent αA-crystallin, αAins-crystallin, had decreased chaperone function. Decreased chaperone function was also found for human Ser139 Arg, Thr144Arg, Ser59Ala mutants of αB-crystallin and double mutants Ser45Ala/Ser59Ala, Lys103 Leu/His104Ile, and Glu110His/His111Glu. A mutant Phe27Arg that was the subject of previous controversy was shown to be fully active at physiological temperatures.

Photoincorporation of the fluorescent probe 4,4'-bis(1-anilino-8-naphthalene sulfonic acid) (bis-ANS) can be used to locate solvent-exposed hydrophobic regions in proteins. We show that bis-ANS is specifically incorporated into the putative N-terminal domain of alpha B-crystallin. This incorporation diminishes the chaperone-like activity of alpha B-crystallin, suggesting that hydrophobic surfaces in the N-terminal domain are involved in the binding of unfolding proteins.

Introduction: Ambient particulate matter (PM) can increase cardiac arrhythmias via oxidative stress. This study was performed to reveal that the heat shock protein, α B-crystallin, could prevent the arrhythmogenic effect of PM.Methods: Using optical mapping, arrhythmic mechanism were evaluated in Langendorff-perfused Adult Sprague-Dawley rat heart after infusion of diesel exhaust product (DEP) and αB-crystallin.Results: In neonatal rat cardiomyocytes, DEP provoked cell death and ROS generation in dose dependant manner. In Langendorff-perfused rat hearts, DEP infusion of 12.5 mg/L (n=12) prolonged action potential duration (APD90) at only the base of left ventricle (LV) from 101±14 ms to 152±22 ms (p=0.001) increasing apicobasal APD differences from 4±8 ms to 54±25 ms (p=0.003). Pretreatment of αB-crystallin (1 mg/kg, n=9) with a delivery system (TAT-protein transduction domain) prevented the DEP-induced APD prolongation (106±10 ms, p=0.83) and apicobasal APD differences (1.5±15.5 ms, p=0.83). Compared with DEP alone, pretreatment of αB-crystallin decreased triggered activity (67% vs. 11%, p=0.02) and apicobasal reentry (82% vs. 0%, p=0.001). The ventricular tachyarrhythmia (VT) was observed in 9 (75%) and 4 (44%) hearts after DEP alone and pretreatment of αB-crystallin (p=0.04), respectively.Conclusions: Heat shock protein, αB-crystallin, can prevent arrhythmogenic effect of PM by suppressing apicobasal repolarization gradient and triggered activity.