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 3ʹ 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 3ʹ 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.

中文翻译：

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癌症相关 SF3B1 突变诱导的 MAP3K7 异常剪接的表征

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，而癌症相关的 SF3B1 突变会导致异常的 RNA 剪接。包括 MAP3K7 在内的几种转录物的异常剪接促进了肿瘤发生。在这里，我们在 MAP3K7 的异常剪接转录本中发现了一个提前终止密码子。用放线菌酮处理用 K700E 突变的 SF3B1 转染的 HEK293T 细胞导致 MAP3K7 异常剪接转录物的积累增加，表明 MAP3K7 的异常剪接转录物是无义介导的衰变的目标。异常剪接的 MAP3K7 转录本使用异常的 3ʹ 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束，而且还需要异常 3' 剪接位点上游的替代多嘧啶束。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束在疾病中的重要作用。