BMI-1: a protein expressed in stem cells, specialized cells and tumors of the gastrointestinal tract.

Recently, BMI-1 was identified as a protein downregulating p16ink4a and mandatory for the continued existence of several stem cell compartments like hematopoietic and neural stem cells. In this study we investigated BMI-1 expression as a potential stem cell marker of the gastrointestinal tract. We found weak expression in the isthmus region of the stomach, and moderate expression in crypts of the intestines, whereas intestinal surface epithelial cells were weakly positive or negative for BMI-1. In addition, a variety of highly differentiated cells such as parietal cells, neuroendocrine cells of the pylorus, Paneth cells and a subset of goblet cells were moderately to strongly positive for BMI-1. Furthermore, we detected strong expression in gastrointestinal neoplasias. This expression pattern indicates a correlation of BMI-1 expression with gastrointestinal stem cells as well as numerous specialized cell types and points to a role of this protein in cellular differentiation in addition to that of stem cell maintenance. Besides, our results imply a role for BMI-1 in the tumorigenesis of gastrointestinal cancer.