Rat Hsp20 confers thermoresistance in a clonal survival assay, but fails to protect coexpressed luciferase in Chinese hamster ovary cells.

Hsp20 is a mammalian small heat shock protein with some deviating in vitro characteristics. We now compare the in vivo cellular thermoprotective abilities of Hsp20 with those of its direct relative, alphaB-crystallin. In a clonal survival assay Chinese hamster ovary (CHO) cells stably overexpressing Hsp20 survive equally well as alphaB-crystallin-expressing cells, after a heat shock. In a transient assay, however, overexpression of Hsp20 did not result in an enhanced recovery of coexpressed firefly luciferase after heat shock, in contrast to alphaB-crystallin. This might indicate that these highly homologous stress proteins are involved in at least partially distinct protective activities in cultured cells.