Phosphorylation of alphaB-crystallin and HSP27 is induced by similar stressors in HeLa cells.

Three members of the small heat shock protein family, alphaA-, alphaB-crystallin, and HSP27, confer thermoresistance upon their overexpression in mammalian cells. Phosphorylation, in conjunction with the molecular chaperone-like activity of these small HSPs, is believed to be important for this in situ functional property. We here report the influence of heat shock and other kinds of stress on the phosphorylation of alphaA-, alphaB-crystallin, and HSP27 in stably transfected HeLa cells. It is observed that alphaB-crystallin becomes phosphorylated upon exposure to the same inducers as is HSP27, although to a lesser extent. In contrast, phosphorylation of alphaA-crystallin is very low upon heat stress and even absent when other stressors are used. This indicates that phosphorylation is not in all instances essential for the stress protective functioning of the various small HSPs.