Lens epithelial cells derived from alpha B-crystallin knockout mice demonstrate hyperproliferation and genomic instability

alphaB-crystallin is a member of the small heat shock protein family and ca n act as a molecular chaperone preventing the in vitro aggregation of other proteins denatured by heat or other stress conditions. Expression of alpha B-crystallin increases in cells exposed to stress and enhanced in tumors of neuroectodermal origin and in many neurodegenerative diseases. In the pres ent study, we examined the properties of lens epithelial cells derived from mice in which the alphaB-crystallin gene had been knocked out. Primary rod ent cells immortalize spontaneously in tissue culture with a frequency of 1 0(-5) to 10(-6). Primary lens epithelial cells derived from alphaB-crystall in(-/-) mice produced hyperproliferative clones at a frequency of 7.6 x 10( -2), four orders of magnitude greater than predicted by spontaneous immorta lization (1), Hyperproliferative alphaB-crystallin(-/-) cells were shown to be truly immortal since they have been passaged for more than 100 populati on doublings without any diminution in growth potential. In striking contra st to the wild-type cells, which were diploid, the alphaB-crystallin(-/-) c ultures had a high proportion of tetraploid and higher ploidy cells, indica ting that the loss of alphaB-crystallin is associated with an increase in g enomic instability. Further evidence of genomic instability of alphaB-cryst allin(-/-) cells was observed when primary cultures were infected with Ad12 SV40 hybrid virus. In striking contrast to wild-type cells, alphaB-crystall in(-/-) cells expressing SV40 T antigen exhibited a widespread cytocidal re sponse 2 to 3 days after attaining confluence, indicating that SV40 T antig en enhanced the intrinsic genomic instability of alphaB-crystallin(-/-) len s epithelial cells. These observations suggest that the widely distributed molecular chaperone alphaB-crystallin may play an important nuclear role in maintaining genomic integrity.