Molecular cloning of a novel member of the HSP110 family of genes, ischemia-responsive protein 94 kDa (irp94), expressed in rat brain after transientforebrain ischemia

To identify genes induced by transient forebrain ischemia, we used the mRNA differential display technique in the four-vessel occlusion model in rats. Some genes were identified as candidates that encode ischemia-responsive p rotein, and one of them was cloned as ischemia-responsive protein 94 kDa (i rp94) from the rat hippocampal cDNA library. Sequence analysis suggested th at rat irp94 was a transcriptional variant or a homologue of mouse apg-2 an d human heat shock protein (hsp) 70RY and a member of the HSP110 family, be cause IRP94 was >90% identical to APG-2 and HSP70RY and similar to 60% iden tical to the other members of the HSP110 family. Although irp94 mRNA was co nstitutively expressed in the normal hippocampus, it was clearly enhanced 4 -24 h after ischemia for 10 (1.9-fold increase) and 15 min (3.4-fold increa se). These changes mainly occurred in neuronal cells, as judged by the loca lization of irp94 mRNA using in situ hybridization histochemistry. On the o ther hand, hyperthermic stress did not enhance irp94 mRNA expression, sugge sting that irp94 expression was enhanced under ischemic stress and not rela ted to the heat shock signaling mechanism. Our study suggested that irp94, a novel member of the HSP110 family, might play an important role in the en vironment altering neuronal functions, especially after transient forebrain ischemia.