Disruption of cytoskeletal assembly is one of the early effects of any stress that can ultimately lead to cell death. Stabilization of cytoskeletal assembly, therefore, is a critical event that regulates cell survival under stress. αB-crystallin, a small heat shock protein, has been shown to associate with cytoskeletal proteins under normal and stress conditions. Earlier reports suggest that αB-crystallin could prevent stress-induced aggregation of actin in vitro. However, the molecular mechanisms by which αB-crystallin stabilizes actin filaments in vivo are not known. Using the H9C2 rat cardiomyoblast cell line as a model system, we show that upon heat stress, αB-crystallin preferentially partitions from the soluble cytosolic fraction to the insoluble cytoskeletal protein-rich fraction. Confocal microscopic analysis shows that αB-crystallin associates with actin filaments during heat stress and the extent of association increases with time. Further, immunoprecipitation experiments show that αB-crystallin interacts directly with actin. Treatment of heat-stressed H9C2 cells with the actin depolymerzing agent, cytochalasin B, failed to disorganize actin. We show that this association of αB-crystallin with actin is dependent on its phosphorylation status, as treatment of cells with MAPK inhibitors SB202190 or PD98059 results in abrogation of this association. Our results indicate that αB-crystallin regulates actin filament dynamics in vivo and protects cells from stress-induced death. Further, our studies suggest that the association of αB-crystallin with actin helps maintenance of pinocytosis, a physiological function essential for survival of cells.
Bibliographical noteFunding Information:
We thank Dr C. C. Glembotski, San Diego State University, USA, for kindly providing us the plasmid for the 3A-αB-crystallin mutant. B.N.S. acknowledges the Council of Scientific and Industrial Research, New Delhi, India for the grant of a Senior Research Fellowship.
- cytoskeletal stabilization
- heat stress