A Novel hsp110-related Gene, apg-1, That Is Abundantly Expressed in the Testis Responds to a Low Temperature Heat Shock Rather than the Traditional Elevated Temperatures*

We isolated a novel hsp110-related gene, apg-1, from a testis cDNA library. The apg-1 transcripts were constitutively expressed in the testicular germ cells and, in some degree, most tissues examined. In a mouse TAMA26 Sertoli cell line, apg-1 transcripts were induced in 2 h by a temperature shift from 32 to 39°C, but not by a shift from 37 to 42°C, the traditional heat stress, or a shift from 32 to 42°C. The heat response pattern of hsp110 expression was similar to that of apg-1. Although induction of a hsp70 transcript was observed in 2 h by a shift from 32 to 39°C, the induction was more apparent by a shift from 37 to 42°C or from 32 to 42°C. Essentially similar differential response patterns were observed among these genes in NIH/3T3 fibroblasts as well. The nuclear run-on assay and the native gel mobility shift assay demonstrated that, by the 32 to 39°C temperature shift, the apg-1 gene was transcriptionally activated, and heat shock factor 1 bound to the heat shock elements in the 5′-flanking region of the apg-1 gene. These results demonstrated that expressions of apg-1, hsp110, and hsp70 could be heat-induced at a temperature lower than the traditional elevated temperatures in somatic cells of both testis and nontestis origin and suggest that the mechanisms regulating the transcript levels of apg-1 and hsp110 are different from those of hsp70. Furthermore, the constitutive expression in germ cells suggests that APG-1 plays a specific role in spermatogenesis as well as in stress response.