泛素连接酶UBE3C泛素化降解E-cadherin促进黑色素瘤侵袭转移的机制研究

The ubiquitin proteasome pathway performs a critical role in the promotion of invasion and metastasis of melanoma. The ubiquitin ligase is a crucial regulator in this process through the selective recognizing and degrading the substrate protein. Experimental results show that the ubiquitin ligase UBE3C can promote the process of invasion and metastasis of melanoma, but the specific mechanism of this process remains unclear. Further studies demonstrate that UBE3C is closely correlated with E-cadherin: (1) Melanoma tissues with high expression of UBE3C exhibit low expression of E-cadherin; (2) UBE3C knockdown can up-regulate E-cadherin expression in melanoma cells; (3) Co-immunoprecipitation results show that UBE3C and E-cadherin have direct interaction; (4) UBE3C is associated with the process of epithelial-mesenchymal transition (EMT) of melanoma. Thus, UBE3C possibly targets the epithelial phenotype marker E-cadherin for ubiquitin-mediated degradation, making melanoma cells lose epithelial cell polarity, trigger EMT, and then promote invasion and metastasis of melanoma. Accordingly, in this study, we aim to unmask the specific mechanisms of UBE3C promoting melanoma invasion and metastasis by targeting E-cadherin for ubiquitin-mediated degradation, inducing EMT, and therefore promoting melanoma invasion and metastasis. It will contribute to reveal new mechanisms of the ubiquitin proteasome pathway promoting melanoma invasion and metastasis and provide new therapeutic targets for early blocking the process of melanoma invasion and metastasis.

泛素化途径是促进黑色素瘤侵袭转移的重要机制，泛素连接酶识别、降解底物蛋白是其关键步骤。泛素连接酶UBE3C可促进黑色素瘤的侵袭转移，然而其发生的具体机制仍不清楚。研究发现，UBE3C与E-cadherin关系密切：（1）UBE3C表达较高的黑色素瘤组织E-cadherin 表达往往较低；（2）抑制UBE3C表达可显著上调黑色素瘤细胞的E-cadherin表达；（3）免疫共沉淀结果显示UBE3C与E-cadherin有直接相互作用；（4）UBE3C与黑色素瘤的上皮间质转化有关。因此，我们设想：UBE3C可能通过泛素化降解E-cadherin，使黑色素瘤细胞丧失上皮细胞极性，触发上皮间质转化，从而促进黑色素瘤的侵袭转移。为证明这一设想，本项目拟通过系列研究UBE3C促进黑色素瘤侵袭转移的过程和机制，为揭示泛素化途径促进黑色素瘤侵袭转移提供新的依据，并为早期阻断黑色素瘤的侵袭转移提供新的靶点。

近年来，泛素连接酶UBE3C在肿瘤中的作用受到很大关注。我们前期研究发现：（1）UBE3C在原发性和转移性黑色素瘤组织中的表达水平较高，而在正常皮肤组织中则表达较低；（2）抑制UBE3C表达可显著减弱黑色素瘤细胞A375的生长、增殖、迁移和侵袭能力。本课题在前期工作基础上，进一步证实：（1）UBE3C与E-cadherin表达水平显著负相关：UBE3C表达水平较高的黑色素瘤组织上皮标志E-cadherin 表达水平往往较低、间质标志 Vimentin 表达较高；反之亦然。（2）抑制UBE3C表达能够显著减弱黑色素瘤细胞A375、SK-MEL-24的生长、增殖、迁移和侵袭能力；（3）动物实验结果显示抑制UBE3C表达可以显著抑制黑色素瘤的生长；（4）抑制UBE3C表达能够显著上调黑色素瘤细胞A375、SK-MEL-24的上皮表型蛋白如E-cadherin的表达，并显著下调A375、SK-MEL-24的间质表型蛋白如Vimentin、Snail1的表达。通过这一系列实验，证实了UBE3C通过调控黑色素瘤细胞上皮间质转化过程进而促进黑色素瘤侵袭转移。