Estrogen-induced 24K protein in MCF-7 breast cancer cells is localized in granules.
We have previously reported the production of monoclonal antibodies which detect, by immunohistochemistry, an estrogen-induced protein of molecular weight 24,000 daltons (24K). This protein, of unknown function, has been detected in: a) estrogen receptor-positive breast cancer cell lines but not in receptor-negative lines; b) several human normal estrogen target organs; and c) certain human carcinomas, including breast tumors. To examine the subcellular localization of this 24K estrogen-induced protein, we have done immunohistochemical studies at light and electron microscopic levels using a human breast tumor cell line (MCF-7) grown in vitro and also in nude mice in vivo. MCF-7 cells grown in the ascites fluid of nude mice and processed for paraffin sections showed a defined polarity, and the 24K protein was localized in the apical cytoplasm of the cells. After cytocentrifugation, MCF-7 cells grown in vitro displayed 24K protein mainly confined to large cytoplasmic granules. The presence of 24K protein in cytoplasmic granules was also seen by immunoelectronmicroscopy in MCF-7 cells grown both in vitro and in vivo. The granules had different sizes, shapes, and 24K immunostaining intensity. The morphological evidence suggests that the 24K estrogen-induced protein is secreted from the cells.
D000818:Animals; D001943:Breast Neoplasms / Q000032:analysis* / Q000648:ultrastructure; D002460:Cell Line; D003594:Cytoplasmic Granules / Q000032:analysis*; D004967:Estrogens / Q000494:pharmacology*; D055551:HSP27 Heat-Shock Proteins; D006360:Heat-Shock Proteins; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D018832:Molecular Chaperones; D009363:Neoplasm Proteins / Q000032:analysis*
D004967:Estrogens; D055551:HSP27 Heat-Shock Proteins; C057725:HSPB1 protein, human; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D009363:Neoplasm Proteins; C038865:estrogen regulated protein