Metastasis the spread of cancer cells to distant organs, is the main cause of death for cancer patients. Metastasis is often mediated by lymphatic vessels that invade the primary tumor, and an early sign of metastasis is the presence of cancer cells in the regional lymph node (the first lymph node colonized by metastasizing cancer cells from a primary tumor). Understanding the interplay between tumorigenesis and lymphangiogenesis (the formation of lymphatic vessels associated with tumor growth) will provide us with new insights into mechanisms that modulate metastatic spread. In the long term, these insights will help to define new molecular targets that could be used to block lymphatic vessel-mediated metastasis and increase patient survival. Here, we review the molecular mechanisms of embryonic lymphangiogenesis and those that are recapitulated in tumor lymphangiogenesis, with a view to identifying potential targets for therapies designed to suppress tumor lymphangiogenesis and hence metastasis.

Key Points• Haploinsufficiency of Sox18 reveals an important role for VEGFD in regulating blood vascular development in vivo in vertebrates.• VEGFD acts through mitogenactivated protein kinase kinaseextracellular signal-regulated kinase to modulate the activity and nuclear concentration of endothelial-specific transcription factor SOX18.Vascular endothelial growth factor-D (VEGFD) is a potent pro-lymphangiogenic molecule during tumor growth and is considered a key therapeutic target to modulate metastasis. Despite roles in pathological neo-lymphangiogenesis, the characterization of an endogenous role for VEGFD in vascular development has remained elusive. Here, we used zebrafish to assay for genetic interactions between the Vegf/Vegf-receptor pathway and SoxF transcription factors and identified a specific interaction between Vegfd and Sox18. Double knockdown zebrafish embryos for Sox18/Vegfd and Sox7/Vegfd exhibit defects in arteriovenous differentiation. Supporting this observation, we found that Sox18/Vegfd double but not single knockout mice displayed dramatic vascular development defects. We find that VEGFD-mitogen-activated protein kinase kinase-extracellular signal-regulated kinase signaling modulates SOX18-mediated transcription, functioning at least in part by enhancing nuclear concentration and transcriptional activity in vascular endothelial cells. This work suggests that VEGFD-mediated pathologies include or involve an underlying dysregulation of SOXF-mediated transcriptional networks. (Blood. 2014;123(7):1102-1112)

The lymphatic vasculature provides a major route for tumor metastasis and inhibiting neolymphangiogenesis induced by tumors can reduce metastasis in animal models. Developmental biology studies have identified the transcription factor SOX18 as a critical switch for lymphangiogenesis in the mouse embryo. Here, we show that SOX18 is also critical for tumor-induced lymphangiogenesis, and we show that suppressing SOX18 function is sufficient to impede tumor metastasis. Immunofluorescence analysis of murine tumor xenografts showed that SOX18 is reexpressed during tumor-induced neolymphangiogenesis. Tumors generated by implantation of firefly luciferase-expressing B16-F10 melanoma cells exhibited a reduced rate of metastasis to the regional draining lymph node in Sox18-deficient mice, as assessed by live bioluminescence imaging. Lower metastatic rates correlated with reduced tumoral lymphatic vessel density and diameter and with impaired drainage of peritumoral injected liposomes specific for lymph vessels from the sentinel lymph nodes. Overall, our findings suggested that SOX18 induction is a key step in mediating tumor lymphangiogenesis and metastasis, and they identify SOX18 as a potential therapeutic target for metastatic blockade. Cancer Res; 72(12);

Caveolae are specialized plasma membrane subdomains implicated in cellular functions such as migration, signalling and trafficking. Caveolin-1 and polymerase I and transcript release factor (PTRF)/cavin-1 are essential for caveola formation. Caveolin-1 is overexpressed and secreted in prostate tumors and promotes aggressiveness and angiogenesis. In contrast, a lack of PTRF expression is reported in prostate cancer, and ectopic PTRF expression in prostate cancer cells inhibits tumor growth and metastasis. We experimentally manipulated PTRF expression in three prostate cancer cell lines, namely the caveolin-1 positive cells PC3 and DU145 and the caveolin-1-negative LNCaP cells, to evaluate angiogenesis- and lymphangiogenesis-regulating functions of PTRF. We show that the conditioned medium of PTRF-expressing prostate cancer cells decreases ECs proliferation, migration and differentiation in vitro and ex vivo. This can occur independently from caveolin-1 expression and secretion or caveola formation, since the anti-angiogenic effects of PTRF were detected in caveolin-1-negative LNCaP cells. Additionally, PTRF expression in PC3 cells significantly decreased blood and lymphatic vessel densities in orthotopic tumors in mice. Our results suggest that the absence of PTRF in prostate cancer cells contributes significantly to tumour progression and metastasis by promoting the angiogenesis and lymphangiogenesis potential of the cancer cells, and this could be exploited for therapy.