title: Association of alphaB-crystallin, a small heat shock protein, with actin: role in modulating actin filament dynamics in vivo.
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.
authors.affiliation: Centre for Cellular and Molecular Biology, Hyderabad, India.
authors.forename: Bhairab N
authors.initials: BN
authors.lastname: Singh
authors.forename: K Sridhar
authors.initials: KS
authors.lastname: Rao
authors.forename: Tangirala
authors.initials: T
authors.lastname: Ramakrishna
authors.forename: Nandini
authors.initials: N
authors.lastname: Rangaraj
authors.forename: Ch Mohan
authors.initials: ChM
authors.lastname: Rao
mesh_terms: D008841:Actin Cytoskeleton / Q000737:chemistry / Q000187:drug effects / Q000378:metabolism*; D000199:Actins / Q000378:metabolism*; D000818:Animals; D015153:Blotting, Western; D003571:Cytochalasin B / Q000494:pharmacology; D003911:Dextrans / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016650:Fluorescein-5-isothiocyanate; D050888:Heat-Shock Proteins, Small / Q000378:metabolism*; D018869:Heat-Shock Response / Q000502:physiology; D006358:Hot Temperature; D006979:Hyperthermia, Induced; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors; D010766:Phosphorylation / Q000187:drug effects; D010873:Pinocytosis / Q000187:drug effects; D011485:Protein Binding / Q000187:drug effects; D021381:Protein Transport / Q000187:drug effects; D051381:Rats; D012995:Solubility / Q000187:drug effects; D038203:alpha-Crystallin B Chain / Q000378:metabolism*
chemical_list: D000199:Actins; D003911:Dextrans; D004791:Enzyme Inhibitors; D050888:Heat-Shock Proteins, Small; D038203:alpha-Crystallin B Chain; D003571:Cytochalasin B; D020928:Mitogen-Activated Protein Kinases; D016650:Fluorescein-5-isothiocyanate