α2β1 integrin regulates lineage commitment in multipotent human colorectal cancer cells

The human colorectal epithelium is maintained by multipotent stem cells that give rise to absorptive, mucous, and endocrine lineages. Recent evidence suggests that human colorectal cancers are likewise maintained by a minority population of so-called cancer stem cells. We have previously established a human colorectal cancer cell line with multipotent characteristics (HRA-19) and developed a serum-free medium that induces endocrine, mucous and absorptive lineage commitment by HRA-19 cells in vitro. In this study, we investigate the role of the beta 1 integrin family of cell surface extracellular matrix receptors in multilineage differentiation by these multipotent human colorectal cancer cells. We show that endocrine and mucous lineage commitment is blocked in the presence of function-blocking antibodies to beta 1 integrin. Function-blocking antibodies to alpha 2 integrin also blocked both HRA-19 endocrine lineage commitment and enterocytic differentiation by Caco-2 human colon cancer cells; both effects being abrogated by the MEK inhibitor, PD98059, suggesting a role for ERK signaling in alpha 2-mediated regulation of colorectal cancer cell differentiation. To further explore the role of alpha 2 integrin in multilineage differentiation, we established multipotent cells expressing high levels of wild-type alpha 2 integrin or a non-signaling chimeric alpha 2 integrin. Overexpression of wild-type alpha 2 integrin in HRA-19 cells significantly enhanced endocrine and mucous lineage commitment, while cells expressing the non-signaling chimeric alpha 2 integrin had negligible ability for either endocrine or mucous lineage commitment. This study indicates that the collagen receptor alpha 2 beta 1 integrin is a regulator of cell fate in human multipotent colorectal cancer cells.