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-PC R) detection of MUC1 transcripts has been proposed for the detection of mic rometastases from breast cancers. MUC1 expression in hematopoietic tissues has been reported but not confirmed. Our preliminary RT-PCR studies confirm ed 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, w ith an additional high molecular weight (HMW) band in blots stained with an ti-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 an d anti-EMA in 2 peripheral blood samples and all bone marrow samples. Weste rn blots from all lymph node samples stained positively with anti-EMA for t he HMW product, but the 68-kd product was less prominent. Separated periphe ral blood lymphocytes and granulocytes showed similar levels of MUC1 expres sion. RT-PCR studies demonstrated MUC1 expression in various hematopoietic cell lines. Western blots showed the 68-kd and HMW products in a granulopoi etic line, with only the 68-kd product in 3 lymphoblastoid lines. MUC1 is e xpressed ubiquitously in hematopoietic tissues and is unsuitable for use as a marker for epithelial micrometastases.