miR-193b Regulates Mcl-1 in Melanoma

MicroRNAs (miRNAs) have important roles in gene regulation. Dysregulation of miRNAs has been associated with tumorigenesis. Recent studies suggest miR-193b is a tumor suppressor gene. In a previous study, we reported that miR-193b represses cell proliferation and regulates cyclin D1 (CCND1) in melanoma. Now we demonstrate that miR-193b regulates myeloid cell leukemia sequence 1 (Mcl-1) in melanoma cells. miRNA microarray profiling revealed the miR-193b level in malignant melanomas was significantly downregulated compared to benign nevi, while a tissue microarray demonstrated overexpression of Mcl-1 in malignant melanoma. The Mcl-1 expressions were inversely correlated with the miR-193b levels in melanoma tissue samples, suggesting a potential regulatory role of miR-193b. Overexpression of miR-193b repressed Mcl-1 in melanoma cell lines. It is well known that Mcl-1 knockdown confers cell sensitivity to ABT-737, a small molecular inhibitor of Bcl-2, Bcl-XL and Bcl-w. We found miR-193b, through repressing Mcl-1 expression, could also sensitize melanoma cells that were refractory to ABT-737. Furthermore, miR-193b directly regulates Mcl-1 by targeting the 3’ untranslated region (3’UTR) of Mcl-1 mRNA. Interestingly, miR-193b may recognize sequences on the 3’UTR that do not base pair with its seed region. In conclusion, our study suggests the downregulation of miR-193b could be an early event during melanoma progression, and demonstrates miR-193b directly regulates Mcl-1 by targeting both seed and seedless sequences of the 3’ UTR. 15 primary melanoma samples, 8 metastatic melanomas and 8 benign nevi samples were profiled on Agilent miRNA array platform微小RNA（MicroRNAs，miRNAs）在基因调控中发挥关键作用，其表达失调与肿瘤发生密切相关。近期研究表明，miR-193b属于肿瘤抑制基因。在既往研究中，我们曾报道miR-193b可抑制黑色素瘤细胞增殖，并调控细胞周期蛋白D1（cyclin D1，CCND1）的表达。本研究证实，miR-193b可在黑色素瘤细胞中调控髓系细胞白血病序列1（myeloid cell leukemia sequence 1，Mcl-1）的表达。 通过miRNA芯片分析发现，相较于良性痣组织，恶性黑色素瘤组织中的miR-193b表达水平显著下调；而组织芯片检测结果显示，恶性黑色素瘤组织中Mcl-1呈现过表达状态。黑色素瘤组织样本中，Mcl-1的表达水平与miR-193b的表达水平呈负相关，提示miR-193b可能发挥调控作用。在黑色素瘤细胞系中，过表达miR-193b可抑制Mcl-1的表达。 众所周知，敲低Mcl-1可使细胞对ABT-737敏感——ABT-737是一种靶向Bcl-2、Bcl-XL及Bcl-w的小分子抑制剂。我们发现，miR-193b可通过抑制Mcl-1的表达，使原本对ABT-737耐药的黑色素瘤细胞恢复敏感性。此外，miR-193b可通过靶向结合Mcl-1 mRNA的3'非翻译区（3' untranslated region，3'UTR）直接调控Mcl-1的表达。值得注意的是，miR-193b可识别3'UTR上与其种子区（seed region）无法形成碱基配对的序列。 综上，本研究表明miR-193b的表达下调可能是黑色素瘤进展过程中的早期事件，同时证实miR-193b可通过靶向3'UTR上的种子区及非种子序列，直接调控Mcl-1的表达。本研究采用安捷伦（Agilent）miRNA芯片平台，对15例原发性黑色素瘤样本、8例转移性黑色素瘤样本及8例良性痣样本进行了芯片分析。