IL-6 and IL-8, secreted by myofibroblasts in the tumor microenvironment, activate HES1 to expand the cancer stem cell population in early colorectal tumor

Abstract

Interaction between a tumor and its microenvironment is important for tumor initiation and progression. Cancer stem cells (CSCs) within the tumor interact with a microenvironmental niche that controls their maintenance and differentiation. We investigated the CSC-promoting effect of factors released from myofibroblasts into the microenvironment of early colorectal cancer tumors and its molecular mechanism. By messenger RNA microarray analysis, expression of HES1, a Notch signaling target, significantly increased in Caco-2 cells cocultured with 18Co cells (pericryptal myofibroblasts), compared to its expression in Caco-2 cells cultured alone. Caco-2 cells cultured in 18Co-conditioned media (CM) showed a significant increase in CD133+CD44+ cells and HES1 expression compared to that in Caco-2 cells cultured in regular media. Significant amounts of interleukin-6 (IL-6) and IL-8 were detected in 18Co-CM compared to levels in regular media. The 18Co-CM-induced increase in CD133+CD44+ cells was attenuated by IL-6- and IL-8-neutralizing antibodies. Furthermore, these neutralizing antibodies and inhibitors of STAT3 and gamma-secretase reduced the expression of HES1 induced in Caco-2 cells cultured in 18Co-CM. Immunohistochemical analysis of human tissues revealed that IL-6, IL-8, and HES1 expression increased from normal to adenoma, and from adenoma to cancer tissues. In addition, IL-6 and HES1 expression was positively correlated in early colorectal cancer tissues. In conclusion, the increase of CSCs by myofibroblasts could be mediated by IL-6/IL-8-induced HES1 activation in the tumor microenvironment. Based on these data, the IL-6/IL-8-mediated Notch/HES1 and STAT3 pathway, through which CSCs interact with their microenvironment, might be a potential target for the prevention and treatment of colorectal tumors.