alpha B-crystallin protects glial cells from hypertonic stress

alpha B-crystallin and the small stress protein, heat shock protein of 27 kDa (HSP27), share structural similarities and are coordinately induced by classical stress stimuli. We have recently observed that hypertonic stress produced by high NaCl concentrations selectively induces alpha B-crystallin in glial cells. To examine divergence of the functional properties of these two related proteins, we have constructed stable, alpha B-crystallin-expressing glial cell lines from the U-251 MCT glioma cells, which are normally deficient in alpha B-crystallin expression but constitutively express HSP27. These transfected cells lines are more resistant to acute hypertonic stress than the parental line from which they were derived. Moreover, the parental line acclimates to stepwise increases in hypertonicity and upregulates endogenous alpha B-crystallin in the process but not HSP27. The overexpression of HSP27 and alpha B-crystallin in NIH/3T3 fibroblasts, a cell line that normally expresses little alpha B-crystallin and no HSP27, does not result in increased survival. This suggests that alpha B-crystallin interacts with cell-type specific mechanisms to aid in protection from hypertonic stress.