150-kDa oxygen-regulated protein (ORP150) functions as a novel molecular chaperone in MDCK cells

To assess the participation of the 150-kDa oxygen-regulated protein (ORP150 ) in protein transport, its function in Madin-Darby canine kidney (MDCK) ce lls was studied. Exposure of MDCK cells to hypoxia resulted in an increase of ORP150 antigen and increased binding of ORP150 to GP80/clusterin (80-kDa glycoprotein), a natural secretory protein in this cell line. In ORP150 an tisense transformant MDCK cells, GP80 was retained within the endoplasmic r eticulum after exposure to hypoxia. Metabolic labeling showed the delay of GP80 maturation in antisense transformants in hypoxia, whereas its matured form was detected in wild-type cells, indicating a role of ORP150 in protei n transport, especially in hypoxia. The affinity chromatographic analysis o f ORP150 suggested its ability to bind to ATP-agarose. Furthermore, the ATP hydrolysis analysis showed that ORP150 can release GP80 at a lower ATP con centration. These data indicate that ORP150 may function as a unique molecu lar chaperone in renal epithelial cells by facilitating protein transport/m aturation in an environment where less ATP is accessible.