A vascular niche and a VEGF–Nrp1 loop regulate the initiation and stemness of skin tumours

Abstract

Angiogenesis is critical during tumour initiation and malignant progression. Different strategies aimed at blocking vascular endothelial growth factor (VEGF) and its receptors have been developed to inhibit angiogenesis in cancer patients. It has become increasingly clear that in addition to its effect on angiogenesis, other mechanisms including a direct effect of VEGF on tumour cells may account for the efficiency of VEGF-blockade therapies. Cancer stem cells (CSCs) have been described in various cancers including squamous tumours of the skin. Here we use a mouse model of skin tumours to investigate the impact of the vascular niche and VEGF signalling on controlling the stemness (the ability to self renew and differentiate) of squamous skin tumours during the early stages of tumour progression. We show that CSCs of skin papillomas are localized in a perivascular niche, in the immediate vicinity of endothelial cells. Furthermore, blocking VEGFR2 caused tumour regression not only by decreasing the microvascular density, but also by reducing CSC pool size and impairing CSC renewal properties. Conditional deletion of Vegfa in tumour epithelial cells caused tumours to regress, whereas VEGF overexpression by tumour epithelial cells accelerated tumour growth. In addition to its well-known effect on angiogenesis, VEGF affected skin tumour growth by promoting cancer stemness and symmetric CSC division, leading to CSC expansion. Moreover, deletion of neuropilin-1 (Nrp1), a VEGF co-receptor expressed in cutaneous CSCs, blocked VEGF's ability to promote cancer stemness and renewal. Our results identify a dual role for tumour-cell-derived VEGF in promoting cancer stemness: by stimulating angiogenesis in a paracrine manner, VEGF creates a perivascular niche for CSCs, and by directly affecting CSCs through Nrp1 in an autocrine loop, VEGF stimulates cancer stemness and renewal. Finally, deletion of Nrp1 in normal epidermis prevents skin tumour initiation. These results may have important implications for the prevention and treatment of skin cancers.

Autocrine Platelet-derived Growth Factor-Vascular Endothelial Growth Factor Receptor-related (Pvr) Pathway Activity Controls Intestinal Stem Cell Proliferation in the Adult Drosophila Midgut

“…For example, nearly all glioblastomas express a multitude of PDGFs and PDGFRs that establish an autocrine PDGF/ PDGFR signal loop (61)(62)(63). More recently, autocrine VEGF/ VGFR signals have been directly implicated in cancer progression through the increased renewal of cancer stem cells (64,65). Given the similarities between Pvr and the established roles of autocrine feedback loop activation of VEGF and PDGF families in cancer progression, we feel that further studies in the genetic regulation of Pvr signals in posterior midgut ISCs provides a fruitful model to study how these pathways promote disease.…”

Stemming CSCs

“…1 The results provide additional mechanistic validation for existing VEGF-based therapeutic approaches in cancer and for neuropilin 1-targeting strategies in development. The findings also suggest the potential to combine both approaches.…”

Immunological and Clinical Impact of Cancer Stem Cells in Vulvar Cancer: Role of CD133/CD24/ABCG2-Expressing Cells

“…two cell populations. VEGF signaling is in fact involved in the regulation of CSC stemness and expansion and in the recruitment of Tregs in the tumour microenvironment (5,6). Recently, several reports have demonstrated that the administration of a monoclonal antibody to VEGF (bevacizumab) as an anti-angiogenesis factor, significantly inhibited the proliferation of CSCs and concurrently the level of Tregs in the tumour microenvironment (31)(32).…”

“…Regulatory T-cells (Tregs) influence the stemness, progress and control of CSCs through regulating angiogenesis influenced by vascular endothelial growth factor (VEGF) (5,6). CSCs impact on Tregs mainly through their recruitment and induction (7).…”