Coordinate and independent regulation of αB‐crystallin and HSP27 expression in response to physiological stress

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Abstract
α‐Crystallins share structural and functional properties with the stress protein hsp27. These polypeptides are expressed at low constitutive levels in many tissues including brain, and αB‐crystallin and hsp27 can accumulate in central nervous system glia in a variety of neurological conditions. We report here that heat shock and exposure to transition metals result in an increase in the steady state mRNA level of αB‐crystallin and hsp27 in primary cultures of rat forebrain astrocytes. Both exposure to tumour necrosis factor‐α and hypertonic conditions result in αB‐crystallin mRNA accumulation but no change in the hsp27 mRNA level. Under some of these conditions increased synthesis and accumulation of αB‐crystallin and hsp27 protein are also evident. We are unable to detect αA‐crystallin mRNA in resting or stressed astrocytes. A novel phenomenon involving a transitory change in stress protein mRNA mobility in Northern blots during induction is reported, which is stress type and cell type independent. The results demonstrate multiple stress regulation of αB‐crystallin and hsp27 in cultured astrocytes, suggesting that they can legitimately be regarded as stress proteins in the central nervous system.