雌激素对乳腺癌1号基因（GREB1）的生长调控与激素依赖性和非依赖性肿瘤发展（如肝芽肿瘤）有关。本研究发现一种GREB1剪接变体，即异构体4（Is4），通过小眼灵长类结合蛋白相关转录因子（MITF）在黑色素瘤中特异性表达，它编码了全长GREB1的C端一半内容。同时，发现GREB1第19外显子上游区域存在两个MITF结合的E-box CANNTG基序，这对于GREB1 Is4的转录是必需的。 MITF和GREB1 Is4在近20%的黑色素瘤样本中（17/89个病例）强烈共表达，并且它们的表达与肿瘤厚度相关。体外实验证明，GREB1 Is4沉默导致黑色素瘤细胞增殖减少，并伴随细胞增殖相关基因表达的改变。此外，通过反义寡核苷酸（ASO）靶向GREB1 Is4，能够降低黑色素瘤异种移植瘤的形成，并促进BRAFV600E；PTENflox黑色素瘤小鼠模型中黑色素瘤的形成，从而证明了GREB1 Is4在体内对黑色素瘤增殖的关键作用。GREB1 Is4与嘧啶代谢的限速酶CAD结合，并通过代谢通量分析揭示了GREB1 Is4对嘧啶合成的必需性。这些结果表明MITF依赖的GREB1 Is4表达导致黑色素瘤增殖，并且GREB1 Is4在黑色素瘤中代表了一个新的分子靶点。© 2023.作者（们）。

Growth regulation by estrogen in breast cancer 1 (GREB1) is involved in hormone-dependent and -independent tumor development (e.g., hepatoblastoma). In this study, we found that a GREB1 splicing variant, isoform 4 (Is4), which encodes C-terminal half of full-length GREB1, is specifically expressed via microphthalmia-associated transcription factor (MITF) in melanocytic melanoma, and that two MITF-binding E-box CANNTG motifs at the 5'-upstream region of GREB1 exon 19 are necessary for GREB1 Is4 transcription. MITF and GREB1 Is4 were strongly co-expressed in approximately 20% of the melanoma specimens evaluated (17/89 cases) and their expression was associated with tumor thickness. GREB1 Is4 silencing reduced melanoma cell proliferation in association with altered expression of cell proliferation-related genes in vitro. In addition, GREB1 Is4 targeting by antisense oligonucleotide (ASO) decreased melanoma xenograft tumor formation and GREB1 Is4 expression in a BRAFV600E; PTENflox melanoma mouse model promoted melanoma formation, demonstrating the crucial role of GREB1 Is4 for melanoma proliferation in vivo. GREB1 Is4 bound to CAD, the rate-limiting enzyme of pyrimidine metabolism, and metabolic flux analysis revealed that GREBI Is4 is necessary for pyrimidine synthesis. These results suggest that MITF-dependent GREB1 Is4 expression leads to melanoma proliferation and GREB1 Is4 represents a new molecular target in melanoma.© 2023. The Author(s).