UVB irradiation induces changes in cellular localization and phosphorylation of mouse HSP27.

We investigated the induction, cellular localization and phosphorylation of a low-molecular weight stress protein (heat shock protein 27, HSP27) by UVB (290-320 nm, max. 312 nm) irradiation stress using immunoblot and indirect immunofluorescence analysis in in vivo and in vitro experiments. The HSP27 was constitutively expressed and distributed in the cytoplasmic fraction of Pam 212 cells (mouse keratinocyte line) or dorsal skin. The increase in the cytoplasm HSP27 level induced by UVB irradiation was less than two-fold that in nonirradiated controls. On the other hand, the translocation of HSP27 from cytoplasm to the nucleus or perinuclear area was time- and dose-dependently induced by UVB irradiation. After UVB irradiation, three isoforms having different isoelectric points were detected in nucleic HSP27 by two-dimensional immunoblotting. The most basic isoform was the unphosphorylated type and the two acidic isoforms were phosphorylated, suggesting that HSP27 is phosphorylated in response to UVB irradiation and accumulates in or around the nucleus as a phosphorylated isoform. These results suggest that the translocation and phosphorylation of HSP27 are induced in response to UVB-irradiation stress.