A novel monoclonal anti-rabbit hsp90 antibody: usefulness for studies on hsp90-steroid receptor interaction

The M(r) 90,000 protein associated with steroid receptors in their non-transformed state has been identified as a heat shock protein (hsp90) but the relationship between hsp90 binding and receptor function is still poorly understood. In this work, we have obtained and characterized one monoclonal anti-rabbit hsp90 antibody (7C10), among more than 2000 wells plated. This antibody was able to complex both free and rabbit uterine progesterone receptor-associated hsp90 as demonstrated by sedimentation analysis on sucrose gradients. As assessed by ELISA, 7C10 displayed a high binding affinity for hsp90 (approximately 4 nM). A standardized and specific competitive binding assay was developed for accurate quantification of hsp90 in rabbit tissues including reticulocyte lysate. 7C10 also permitted immunolocalization of hsp90 in various rabbit tissues. In Western blot, the monoclonal antibody recognized a single polypeptide band of M(r) approximately 90,000 in crude or purified rabbit preparations but failed to cross-react with any other mammalian or avian hsp90. These findings suggest that hsp90, a highly conserved protein, is a weak immunogen and elicits a strict species specific immunological response. Owing to its high affinity and specificity for rabbit hsp90, the monoclonal antibody 7C10 was used for purification and total depletion of hsp90 from the reticulocyte lysate, an efficient system for in vitro receptor translation and reconstitution studies. Thus, 7C10 represents a new powerful tool to further investigate the importance of hsp90 in steroid hormone receptor function.