CD44 is a marker of cancer stem cell (CSC) in many types of tumors. Alternative splicing of its 20 exons generates various CD44 isoforms that have different tissue specific expression and functions, including the CD44 standard isoform (CD44s) encoded by the constant exons and the CD44 variant isoforms (CD44v) with variant exon insertions. Switching between the CD44v and CD44s isoforms plays pivotal roles in tumor progression. Here we reported a novel mechanism of CD44 alternative splicing induced by TGF-β1 and its connection to enhanced epithelial-to-mesenchymal transition (EMT) and stemness in human prostate cancer cells. TGF-β1 treatment increased the expression of CD44s and N-cadherin while decreased the expression of CD44v and E-cadherin in DU-145 prostate cancer cells. Other EMT markers and cancer stem cell markers were also upregulated after TGF-β1 treatment. RNAi knockdown of CD44 reversed the phenotype, which could be rescued by overexpressing CD44s but not CD44v, indicating the alternatively spliced isoform CD44s mediated the activity of TGF-β1 treatment. Mechanistically, TGF-β1 treatment induced the phosphorylation, poly-ubiquitination, and degradation of PCBP1, a well-characterized RNA binding protein known to regulate CD44 splicing. RNAi knockdown of PCBP1 was able to mimic TGF-β1 treatment to increase the expression of CD44s, as well as the EMT and cancer stem cell markers. In vitro and in vivo experiments were performed to show that CD44s promoted prostate cancer cell migration, invasion, and tumor initiation. Taken together, we defined a mechanism by which TGF-β1 induces CD44 alternative splicing and promotes prostate cancer progression.

中文翻译：

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TGF-β1 通过诱导 PCBP1 降解和 CD44 选择性剪接来促进前列腺癌细胞的上皮间质转化和干性。


CD44 是多种肿瘤中癌症干细胞 (CSC) 的标志物。其 20 个外显子的选择性剪接产生具有不同组织特异性表达和功能的各种 CD44 同种型，包括由恒定外显子编码的 CD44 标准同种型 (CD44s) 和具有变异外显子插入的 CD44 变异同种型 (CD44v)。 CD44v 和 CD44s 亚型之间的转换在肿瘤进展中发挥着关键作用。在这里，我们报道了 TGF-β1 诱导的 CD44 选择性剪接的新机制及其与增强的上皮间质转化 (EMT) 和人前列腺癌细胞干性的联系。 TGF-β1处理增加了DU-145前列腺癌细胞中CD44s和N-钙粘蛋白的表达，同时降低了CD44v和E-钙粘蛋白的表达。其他 EMT 标志物和癌症干细胞标志物在 TGF-β1 治疗后也上调。 CD44的RNAi敲低逆转了表型，这可以通过过表达CD44而不是CD44v来挽救，表明选择性剪接的亚型CD44介导了TGF-β1治疗的活性。从机制上讲，TGF-β1 处理诱导 PCBP1 的磷酸化、多聚泛素化和降解，PCBP1 是一种已知可调节 CD44 剪接的充分表征的 RNA 结合蛋白。 PCBP1 的 RNAi 敲低能够模拟 TGF-β1 治疗，增加 CD44 以及 EMT 和癌症干细胞标记物的表达。体外和体内实验表明 CD44 促进前列腺癌细胞迁移、侵袭和肿瘤发生。总之，我们定义了 TGF-β1 诱导 CD44 选择性剪接并促进前列腺癌进展的机制。