MUC1 expression in hematopoietic tissues

The MUC1 gene encodes the core protein of episialin, which is recognized by several antibodies. Reverse transcription-polymerase chain reaction (RT-PCR) detection of MUC1 transcripts has been proposed for the detection of micrometastases from breast cancers. MUC1 expression in hematopoietic tissues has been reported but not confirmed. Our preliminary RT-PCR studies confirmed MUC1 expression by MDA-231 breast cancer cells. Western blots of MDA-231 proteins stained with anti-MUC1 core gave one 68-kd (core protein) band, with an additional high molecular weight (HMW) band in blots stained with anti-epithelial membrane antigen (EMA). MUC1 expression was detectable by RT-PCR in 4 samples each of peripheral blood, bone marrow, and lymph node. MUC1 expression was detectable by Western blot analysis using anti-MUC1 core and anti-EMA in 2 peripheral blood samples and all bone marrow samples. Western blots from all lymph node samples stained positively with anti-EMA for the HMW product, but the 68-kd product was less prominent. Separated peripheral blood lymphocytes and granulocytes showed similar levels of MUC1 expression. RT-PCR studies demonstrated MUC1 expression in various hematopoietic cell lines. Western blots showed the 68-kd and HMW products in a granulopoietic line, with only the 68-kd product in 3 lymphoblastoid lines. MUC1 is expressed ubiquitously in hematopoietic tissues and is unsuitable for use as a marker for epithelial micrometastases.