Effect of pericytes on melanoma development.

Abstract

83 Background: Melanoma-associated stroma cells regulate tumor establishment, invasion, and dissemination through paracrine and heterotypic cell-cell interactions with cancer cells. Pericytes constitute a major noninflammatory component of the melanoma-associated stroma. Our study is designed to evaluate the role of pericytes in melanoma development. Methods: Tumors induced in GFP+/SCID mice with GFP-B16 cells were harvested after 14 days, enzyme digested, labeled against mesenchymal markers, and analyzed by flow cytometry (FC). The distribution of stromal subpopulations in tumors was investigated by immunofluorescence microscopy (IFM). Stromal pericytes from tumors and adipose tissue were FACS sorted, mixed with B16 cells at a 3:1 ratio, and injected into SCID mice. Tumor diameters were taken periodically with a scientific caliper, and used to determine tumor volumes using the ellipsoid formula. Results: FC analysis showed that the melanoma stroma was composed of CD45+ inflammatory cells, CD31+ endothelial cells, FAP+ myofibroblasts and CD146+ cells. IFM analysis showed that the CD146+ cells are perivascular CD31-/CD34-/α-SMA+ stromal pericytes that associated with TGF-β immunoreactive CD271+/CD146+B16 cells in perivascular tumor niches. Co-induction experiments were performed to investigate the effect of pericytes on melanoma development. We observed faster growth rates in the size of tumors co-induced with pericytes, compared with tumors induced with B16 cells alone. These co-induced tumors had bigger masses, more volume, were hypercellular, and had increase vascularization compared with control tumors. In addition, pericytes increased the B16 cell proliferation rate, as determined by higher expression of Ki-67 in the tumor fraction of co-induced tumors. Conclusions: Pericytes promote melanoma development by inducing angiogenesis and melanoma cell proliferation. Our results suggest that pericytes could be utilized as a therapeutic target for melanoma treatment.