CD44-positive colorectal adenoma cells express the potential stem cell markers musashi antigen (msi1) and ephrin B2 receptor (EphB2)

Abstract

The majority of colorectal adenomas contain a mutation in the APC gene activating the wnt pathway. As wnt signalling preserves stem cell functions, it would be expected that stem cells would be enriched in adenomas. We have shown expression of the wnt target gene CD44, which may characterize the expanded stem cell compartment, in colorectal tumours. To investigate this possibility, we performed an immunohistological survey of CD44 expression in relation to the proliferation marker Ki67 and apoptosis in colorectal tumour tissue, and have isolated a CD44-positive subpopulation of the human colorectal adenoma cell line LT97 for cell biological analysis. In tissues, CD44 expression was not related to Ki67, but was associated with lower apoptosis in the CD44-positive areas. CD44-positive and -negative populations isolated from LT97 cultures were identical in their Ki-ras and p53 status but differed in their growth and survival characteristics. While CD44-positive cells attached and grew to reconstitute the original culture, the CD44-negative cells rapidly underwent apoptosis and were unable to resume growth. In comparison to unsorted growing LT97 cells, the CD44-positive cells had shifted beta-catenin into the nucleus and expressed beta-catenin target genes, such as ephrin B receptor (ephB2) and musashi antigen (msi1). By contrast, CD44-negative cultures contained no cells with nuclear beta-catenin. In summary, the CD44-positive cells accumulating in colorectal tumours have increased survival capacity both in vivo and in vitro. They also express markers typical of colorectal progenitor cells, msi1 and ephB2, in the premalignant progenitor population.