Recognizes a protein of 104kDa-110kDa, characterized as major vault protein (MVP). Vaults are large ribonucleoprotein particles (RNPs) present in all eukaryotic cells. They 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.