DEPDC1B promotes melanoma angiogenesis and metastasis through sequestration of ubiquitin ligase CDC16 to stabilize secreted SCUBE3

Abstract

Angiogenesis, the formation of new blood vessels from pre-existing vasculature, is pivotal to melanoma progression and metastasis that contributes to melanoma lethality. Triggered by various oncogenic factors, angiogenesis can be inhibited by targeting secreted molecules and their specific signaling transduction pathways, which have been clinically proven as effective therapeutic interventions with cancer metastasis. However, the single-targeted anti-vascular endothelial growth factor (VEGF) therapy has limited efficacy on melanoma and induces rapid resistance, suggesting the existence of other key drivers governing the blood vessel formation in melanoma. Therefore, identification of the mechanisms underlying melanoma angiogenesis for the development of novel druggable targets is in urgent need. Here, I found that a SRY-related HMG-box 10 (SOX10)-regulated oncogenic DEP domain-containing protein 1B (DEPDC1B) is critical in melanoma growth and metastasis through promoting angiogenesis. Skin cutaneous melanoma (SKCM) patient samples revealed higher expression of DEPDC1B is associated with poor survival. Tissue microarray immunostaining demonstrates a positive correlation between DEPDC1B and SOX10 protein expression in different stages of melanoma. As a result, depletion of DEPDC1B leads to a significant reduction of melanoma cell proliferation, colony formation, invasion, xenograft tumorigenesis and lung metastasis. Conversely, overexpression (OE) of DEPDC1B promotes the corresponding phenotypes. In addition, the dual-luciferase reporter assay, chromatin immunoprecipitation (ChIP) assay and epistasis analysis validated DEPDC1B as a direct downstream target of SOX10 to partly mediate its oncogenic activity. Furthermore, I have observed extensive vascular distribution in mouse lung nodules induced by DEPDC1B OE and enhanced formation of human umbilical vein endothelial cell (HUVEC) tubular network upon treatment of DEPDC1B OE conditioned medium (CM), indicating that DEPDC1B is sufficient and required for promoting angiogenesis. Importantly, mass spectrometry identifies a secreted protein SCUBE3 in the CM and cycloheximide chase analysis suggested SCUBD3 can be stabilized by DEPDC1B. Functional studies showed that SCUBE3 exhibits oncogenic properties in melanoma and is pro-angiogenic both in vitro and in vivo. Mechanistically, DEPDC1B regulates SCUBE3 protein stability through the competitive association with ubiquitin ligase CDC16 to inhibit the interaction of SCUBE3 with CDC16, thereby preventing SCUBE3 from undergoing degradation via the ubiquitin-proteasome pathway. Notably, expression of SOX10, DEPDC1B, and SCUBE3 are positively correlated with higher microvessel density in the advanced stage of metastatic melanomas in tissue microarray. In conclusion, I revealed a SOX10-DEPDC1B-SCUBE3 regulatory axis that promotes melanoma angiogenesis and metastasis, which suggests targeting secreted SCUBE3 can be a therapeutic strategy against metastatic melanoma.