OSMOTIC-STRESS PROTEIN-94 (OSP94) - A NEW MEMBER OF THE HSP110 SSE GENE SUBFAMILY/

Preservation of cell viability and function in the hyperosmolar enviro nment of the renal medulla is a complex process that requires selectiv e gene expression. We have identified a new member of the heat shock p rotein (hsp) 70 superfamily that is up regulated in renal inner medull ary collecting duct cells (mIMCD3 cells) during exposure to hyperosmot ic NaCl stress. Known as osmotic stress protein 94, or Osp94, this 293 5-base pair cDNA encodes an 838-amino acid protein that shows greatest homology to the recently discovered hsp110/SSE gene subfamily. Like t he hsps, Osp94 has a putative amino-terminal ATP-binding domain and a putative carboxyl-terminal peptide-binding domain. The in vitro transl ated Osp94 product migrated as a 105-110-kDa protein on SDS-polyacryla mide gel electrophoresis. In mIMCD3 cells, Osp94 mRNA expression was g reatly upregulated by hyperosmotic NaCl or heat stress. In mouse kidne y, Osp94 mRNA expression paralleled the known corticomedullary osmolal ity gradient showing highest expression in the inner medulla. Moreover , inner medullary Osp94 expression was increased during water restrict ion when osmolality is known to increase. Thus, Osp94 is a new member of the hsp110/SSE stress protein subfamily and likely acts as a molecu lar chaperone.