Differential expression of two stress-inducible hsp70 genes by various stressors.

Inducible HSP70s encoded by two almost identical hsp70 genes, known as hsp70.1 and hsp70.3 are located in a tandem array on mouse chromosome 17. Duplication of this gene has been found in various higher organisms. However, the role of two almost identical hsp70 genes is still unclear. To elucidate the ambiguity of expression pattern between hsp70.1 and hsp70.3, we investigated the induction of each hsp70 isoforms by several HSP70-inducible stressors in wild type (hsp70.1+/+ and hsp70.3+/+) and the hsp70.1-/- (hsp70.1-/- and hsp70.3+/+) murine embryo fibroblast (MEF) cells, and the M-1 mouse cortical collecting duct cell line. Each induced hsp70 isoforms by heat shock were very similar at transcriptional and translational levels in wild type and hsp70.1-/- MEF cells. The mRNA stabilities of both hsp70.1 and hsp70.3, even in two kinds of hsp70.3 transcripts, were also very similar. L-azetidine-2-carboxylic acid, sodium arsenite, CdCl2 and ZnCI2 caused induction of both isoforms of the hsp70 genes, even though their expression levels were variable. NaCl caused induction of just hsp70.1 gene expression. H2O2 failed to induce the expression of either hsp70 genes in MEF cells, caused induction of hsp70.1 gene expression in the M-1 cell line. Hsp70 accumulation by H2O2 and NaCl treatment was mainly due to hsp70.1 expression. Our studies demonstrated that two hsp70 genes respond differentially to types of stress.