CLONING OF RAT GRP75, AN HSP70-FAMILY MEMBER, AND ITS EXPRESSION IN NORMAL AND ISCHEMIC BRAIN

Following metabolic stress a variety of gene products are induced in c ells in the brain, some of which may protect the tissue from subsequen t stresses. The heat shock proteins (hsps), in particular hsp70, have been widely studied in this context, but evidence for the involvement of known hsps in protection of the CNS is inconclusive. We have theref ore undertaken the search for other stress-induced proteins which may mitigate ischemic injury. Beginning with degenerate RT-PCR, we have is olated a rat-brain cDNA encoding a protein highly similar to human grp 75, a mitochondrial member of the hsp70-family of stress proteins. It is also highly similar to two non-mitochondrial proteins; mortalin, a senescence-related gene product, and pbp74, a protein implicated in B- cell peptide processing, Sequence structure and phylogenetic analyses predict mitochondrial localization and induction by a calcium ionophor e and glucose deprivation in PC12 cells support its identification as rat grp75. In situ analysis of normal brain reveals an unusual distrib ution, with very high expression in neurons of the basal forebrain, re ticular and subthalamic nuclei, globus pallidus, amygdala and elsewher e, grp75-mRNA is upregulated following focal brain ischemia in a disti nctive fashion. When the degree of injury is small, induction occurs i n the area of injury, similar to the pattern observed for hsp70. Howev er, when the injury is extensive, hsr is upregulated in neurons outsid e the ischemic area. The induction of grp75 may represent a sensitive marker of metabolically compromised tissue. (C) 1995 Wiley-Liss, Inc.