Upregulation and overexpression of human X-box binding protein 1 (hXBP-1) gene in primary breast cancers.

BACKGROUND: Human X-box binding protein 1 (hXBP-1) is a transcription factor essential for hepatocyte growth as well as for plasma cell differentiation. hXBP-1 also binds to cis-elements of human T cell leukemia virus and human major histocompatibility complex genes. In order to clarify the role of XBP-1 in breast cancer, here we investigated the expression of XBP-1 in 11 primary breast cancers and 5 breast cancer cell lines.
MATERIALS AND METHODS: The study population consisted of eleven patients who were underwent surgery for breast cancer from 2000 to 2002. Five breast cancer cell lines (MDA-MB-453, CRL1500, YMB-1-E, MCF7 and HBL100) were analyzed for XBP-1 expression. Reverse transcription polymerase chain reaction was performed on 6 primary breast cancers. Then we investigated XBP-1 expression by immunohistochemically on archived paraffin-embedded sections.
RESULTS: hXBP-1 mRNA expression was increased in all 11 primary breast cancers we examined, as well as 5 breast cancer cell lines, but hardly detectable in non-cancerous breast tissue. Immunohistochemical staining demonstrated that hXBP-1 protein stained strongly in the cytoplasm of cancer cells but was unreactive in the normal breast ductal epithelial and myoepithelial cells.
CONCLUSIONS: These data indicate that increased expression of the hXBP-1 gene may play some role in human breast carcinogenesis through impairment of cell differentiation regulation.