Alpha B crystallin expression in response to hormone, oncogenes and stress.

alpha B crystallin is one of the major eye lens proteins and it is abundantly expressed in many non-lenticular tissues as well. The alpha B crystallin protein sequence is similar to that of small heat shock proteins and we could demonstrate that alpha B crystallin does indeed accumulate in response to heat shock and other forms of stress. Moreover, ectopic expression of alpha B crystallin establishes a state of thermotolerance. Glucocorticoid hormones activate the alpha B crystallin gene with a delayed kinetics. Induced expression of the Ha-ras oncogene accelerates hormone-mediated gene induction. A shorter promoter sequence is required for the ras supported hormone response. However, sustained Ha-ras oncogene expression attenuates glucocorticoid-triggered induction of the alpha B crystallin gene completely. Whereas the small heat shock protein Hsp27 is overexpressed in many human mammary carcinomas, we observed the frequent absence of alpha B crystallin in these tumors but not in the normal breast tissue. In contrast, overexpression of alpha B crystallin has been frequently observed in non-neuronal brain tumors.