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. 2007 Feb 23;366(3):756-67.
doi: 10.1016/j.jmb.2006.12.012. Epub 2006 Dec 8.

Association of alphaB-crystallin, a small heat shock protein, with actin: role in modulating actin filament dynamics in vivo

Bhairab N Singh  1 , K Sridhar Rao, Tangirala Ramakrishna, Nandini Rangaraj, Ch Mohan Rao
Affiliations

Association of alphaB-crystallin, a small heat shock protein, with actin: role in modulating actin filament dynamics in vivo

Bhairab N Singh et al. J Mol Biol. .

Abstract

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. alphaB-crystallin, a small heat shock protein, has been shown to associate with cytoskeletal proteins under normal and stress conditions. Earlier reports suggest that alphaB-crystallin could prevent stress-induced aggregation of actin in vitro. However, the molecular mechanisms by which alphaB-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, alphaB-crystallin preferentially partitions from the soluble cytosolic fraction to the insoluble cytoskeletal protein-rich fraction. Confocal microscopic analysis shows that alphaB-crystallin associates with actin filaments during heat stress and the extent of association increases with time. Further, immunoprecipitation experiments show that alphaB-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 alphaB-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 alphaB-crystallin regulates actin filament dynamics in vivo and protects cells from stress-induced death. Further, our studies suggest that the association of alphaB-crystallin with actin helps maintenance of pinocytosis, a physiological function essential for survival of cells.

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