alpha-crystallin stabilizes actin filaments and prevents cytochalasin-induced depolymerization in a phosphorylation-dependent manner.
alpha-crystallin, a major lens protein of approximately 800 kDa with subunits of about 20 kDa has previously been shown to act as a chaperone protecting other proteins from stress-induced damage and to share sequence similarity with small heat-shock proteins, sHsp. It is now demonstrated that this chaperone effect extends to protection of the intracellular matrix component actin. It was found that the powerful depolymerization effect of cytochalasin D could be almost completely blocked by alpha-crystallin, alpha A-crystallin or alpha B-crystallin. However, phosphorylation of alpha-crystallin markedly decreased its protective effect. It is suggested that phosphorylation of alpha-crystallin may contribute to changes in actin structure observed during cellular remodeling that occurs with the terminal differentiation of a lens epithelial cell to a fiber cell and contributes to cellular remodeling in other cell types that contain alpha-crystallin species. This communication presents biochemical evidence clearly demonstrating that alpha-crystallin is involved in actin polymerization-depolymerization dynamics. It is also shown that alpha-crystallin prevented heat-induced aggregation of actin filaments. alpha-crystallin was found to stabilize actin polymers decreasing dilution-induced depolymerization rates up to twofold while slightly decreasing the critical concentration from 0.23 microM to 0.18 microM. Similar results were found with either alpha-crystallin or its purified subunits alpha A-crystallin and alpha B-crystallin. In contrast to the experiments with cytochalasin D, phosphorylation had no effect. There does not appear to be an interaction between alpha-crystallin and actin monomers since the effect of alpha-crystallin in enhancing actin polymerization does not become apparent until some polymerization has occurred. Examination of the stoichiometry of the alpha-crystallin effect indicates that 2-3 alpha-crystallin monomers/actin monomer give maximum actin polymer stabilization.
Wang
K
K
Department of Ophthalmology, Columbia University, New York, NY 10032, USA.
Spector
A
A
D000199:Actins / Q000378:metabolism*; D000818:Animals; D003459:Crystallins / Q000378:metabolism*; D015638:Cytochalasin D / Q000378:metabolism*; D008970:Molecular Weight; D018482:Muscle, Skeletal / Q000737:chemistry / Q000378:metabolism; D010766:Phosphorylation; D011817:Rabbits; D013050:Spectrometry, Fluorescence
D000199:Actins; D003459:Crystallins; D015638:Cytochalasin D