Contextual niche signals towards colorectal tumor progression by mesenchymal stem cell in the mouse xenograft model.

Abstract

The role of mesenchymal stem/stromal cells (MSCs) in tumorigenesis remains controversial. This study aimed to determine whether heterotypic interactions between MSCs and colon cancer cells can supply contextual signals towards tumor progression. Xenografts consisting of co-implanted human colorectal cancer cells with rat MSCs in immunodeficient mice were evaluated by tumor progression, angiogenic profiles, and MSC fate. Furthermore, we investigated how MSCs function as a cancer cell niche by co-culture experiments in vitro. Tumor growth progressed in two ways, either independent of or dependent on MSCs. Such cell line-specific dependency could not be explained by host immune competency. COLO 320 xenograft angiogenesis was MSC-dependent, but less dependent on vascular endothelial growth factor (VEGF), whereas HT-29 angiogenesis was not MSC-dependent, but was VEGF-dependent. MSCs and COLO 320 cells established a functional positive feedback loop that triggered formation of a cancer cell niche, leading to AKT activation. Subsequently, MSCs differentiated into pericytes that enhanced angiogenesis as a perivascular niche. In contrast, the MSC niche conferred an anti-proliferative property to HT-29 cells, through mesenchymal-epithelial transition resulting in p38 activation. In conclusion, MSCs demonstrate pleiotropic capabilities as a cancer cell or perivascular niche to modulate colorectal cancer cell fate in a cell line-dependent manner in a xenogeneic context.