1032 Is specific for the major vault protein, a 104-kDa highly conserved protein interacting with estrogen receptor. It is one of a series of four mAbs which recognize different epitopes of the protein. Major vault proteins have a complex morphology, including several small molecules of RNA, but a single protein species. The MVP accounts for >70% of their mass. Their shape is reminiscent of the nucleopore central plug. Treatment of cells with estradiol increases the amount of MVP in nuclear extract. The hormone-dependent interaction of vaults with ER is prevented in vitro by sodium molybdate. Antibodies to estrogen, progesterone and glucocorticoid receptors are able to co-immunoprecipitate the MVP. MVP is overexpressed in many neoplastic tissues and cell lines. Expression of MVP predicts a poor response to chemotherapy. Positive control: MCF-7 or HeLa cells. Breast cancer.