Laboratory of Cancer Biology, China-Japan Union Hospital of Jilin University, Jilin University, Changchun, Jilin 130033, China.
School of Life Sciences, Jilin University, Changchun, Jilin 130012, China.
J Biochem. 2021 Sep 22;170(1):69-77. doi: 10.1093/jb/mvab023.
SF3B1, an essential RNA splicing factor, is frequently mutated in various types of cancers, and the cancer-associated SF3B1 mutation causes aberrant RNA splicing. The aberrant splicing of several transcripts, including MAP3K7, promotes tumorigenesis. Here, we identify a premature termination codon in the aberrantly spliced transcript of MAP3K7. Treatment of HEK293T cells transfected with the K700E-mutated SF3B1 with cycloheximide leads to increased accumulation of the aberrant spliced transcript of MAP3K7, demonstrating that the aberrantly spliced transcript of MAP3K7 is targeted by nonsense-mediated decay. The aberrantly spliced MAP3K7 transcript uses an aberrant 3' splice sites and an alternative branchpoint sequence. In addition, the aberrant splicing of MAP3K7 requires not only the polypyrimidine tract associated with normal splicing but also an alternative polypyrimidine tract upstream of the aberrant 3' splice site. Other cancer-associated SF3B1 mutations also cause the aberrant splicing of MAP3K7, which depends on the same sequence features. Our data provide a further understanding of the mechanisms underlying aberrant splicing induced by cancer-associated SF3B1 mutation, and reveal an important role of alternative polypyrimidine tract in diseases.
SF3B1 是一种必需的 RNA 剪接因子，在各种类型的癌症中经常发生突变，而与癌症相关的 SF3B1 突变会导致异常的 RNA 剪接。几种转录本的异常剪接，包括 MAP3K7，促进了肿瘤的发生。在这里，我们在 MAP3K7 的异常剪接转录本中鉴定出一个过早终止密码子。用环己酰亚胺处理转染了 K700E 突变 SF3B1 的 HEK293T 细胞，导致 MAP3K7 的异常剪接转录本积累增加，表明 MAP3K7 的异常剪接转录本被无意义介导的衰变所靶向。MAP3K7 的异常剪接转录本使用异常的 3' 剪接位点和替代分支点序列。此外，MAP3K7 的异常剪接不仅需要与正常剪接相关的多嘧啶tract，还需要异常 3' 剪接位点上游的替代多嘧啶 tract。其他与癌症相关的 SF3B1 突变也会导致 MAP3K7 的异常剪接，这取决于相同的序列特征。我们的数据提供了对癌症相关 SF3B1 突变诱导的异常剪接机制的进一步理解，并揭示了替代多嘧啶 tract 在疾病中的重要作用。
