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  • 1
    Publication Date: 2018-08-17
    Description: Shuang Li, Yong Suk Cho, Bing Wang, Shuangxi Li, and Jin Jiang Hedgehog (Hh) transduces signals by promoting cell surface accumulation and activation of the G-protein-coupled receptor (GPCR)-family protein Smoothened (Smo) in Drosophila , but the molecular mechanism underlying the regulation of Smo trafficking remains poorly understood. Here, we identified the Cul4–DDB1 E3 ubiquitin ligase complex as being essential for Smo ubiquitylation and cell surface clearance. We found that the C-terminal intracellular domain of Smo recruits Cul4–DDB1 through the β subunit of trimeric G protein (Gβ), and that Cul4–DDB1–Gβ promotes the ubiquitylation of both Smo and its binding partner G-protein-coupled-receptor kinase 2 (Gprk2) and induces the internalization and degradation of Smo. Hh dissociates Cul4–DDB1 from Smo by recruiting the catalytic subunit of protein kinase A (PKA) to phosphorylate DDB1, which disrupts its interaction with Gβ. Inactivation of the Cul4–DDB1 complex resulted in elevated Smo cell surface expression, whereas an excessive amount of Cul4–DDB1 blocked Smo accumulation and attenuated Hh pathway activation. Taken together, our study identifies an E3 ubiquitin ligase complex targeting Smo for ubiquitylation and provides new insight into how Hh signaling regulates Smo trafficking and cell surface expression.
    Keywords: Ubiquitin
    Print ISSN: 0021-9533
    Electronic ISSN: 1477-9137
    Topics: Biology , Medicine
    Published by Company of Biologists
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  • 2
    Publication Date: 2018-03-06
    Description: High-grade glioma (HGG) is highly angiogenic, but antiangiogenic therapy has transient clinical benefit in only a fraction of patients. Vascular regulators of these heterogeneous responses remain undetermined. We found up-regulation of Sox7 and down-regulation of Sox17 in tumor endothelial cells (tECs) in mouse HGG. Sox7 deletion suppressed VEGFR2 expression, vascular abnormality, hypoxia-driven invasion, regulatory T cell infiltration, and tumor growth. Conversely, Sox17 deletion exacerbated these phenotypes by up-regulating Sox7 in tECs. Anti-VEGFR2 antibody treatment delayed tumor growth by normalizing Sox17 -deficient abnormal vessels with high Sox7 levels but promoted it by regressing Sox7 -deficient vessels, recapitulating variable therapeutic responses to antiangiogenic therapy in HGG patients. Our findings establish that Sox7 promotes tumor growth via vessel abnormalization, and its level determines the therapeutic outcome of VEGFR2 inhibition in HGG. In 189 HGG patients, Sox7 expression was heterogeneous in tumor vessels, and high Sox7 levels correlated with poor survival, early recurrence, and impaired vascular function, emphasizing the clinical relevance of Sox7 in HGG.
    Keywords: Solid Tumors
    Print ISSN: 0022-1007
    Electronic ISSN: 1540-9538
    Topics: Medicine
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