SRSF1 promotes the inclusion of exon 3 of SRA1 and the invasion of hepatocellular carcinoma cells by interacting with exon 3 of SRA1pre-mRNA

• Main Authors: Sijia Lei, Bin Zhang, Luyuan Huang, Ziyou Zheng, Shaohan Xie, Lianghua Shen, Mason Breitzig, Alexander Czachor, Hongtao Liu, Huiru Luo, Yanxia Chen, Kangshou Liu, Hanxiao Sun, Qing Zheng, Qiang Li, Feng Wang
• Format: Article
• Language: English
• Published: Nature Publishing Group 2021-05-01
• Series: Cell Death Discovery
• Online Access: https://doi.org/10.1038/s41420-021-00498-w

Abstract Steroid receptor RNA activator 1 (SRA1) has been described as a novel transcriptional co-activator that affects the migration of cancer cells. Through RT-PCR, we identified that skipping exon 3 of SRA1 produces two isoforms, including the truncated short isoform, SRA1-S, and the long isoform, SRA1-L. However, the effect of these two isomers on the migration of HCC cells, as well as the specific mechanism of exon 3 skipping remain unclear. In this study, we found up regulated expression of SRSF1 and SRA1-L in highly metastatic HCCLM3, as well as in HCCs with SRSF1 demonstrating the strongest correlation with SRA1-L. In contrast, we observed a constitutively low expression of SRA1-S and SRSF1 in lowly metastatic HepG2 cells. Overexpression of SRSF1 or SRA1-L promoted migration and invasion by increasing the expression of CD44, while SRA1-S reversed the effect of SRSF1 and SRA1-L in vitro. In addition, lung metastasis in mice revealed that, knockdown of SRSF1 or SRA1-L inhibited the migration of HCC cells, while SRA1-L overexpression abolished the effect of SRSF1 knockout and instead promoted HCC cells migration in vivo. More importantly, RNA immunoprecipitation and Cross-link immunoprecipitation analyses showed that SRSF1 interacts with exon 3 of SRA1 to up regulate the expression of SRA1-L in HCC cells. RNA pull-down results indicated that SRSF1 could also bind to exon 3 of SRA1 in vitro. Finally, minigene -MS2 mutation experiments showed that mutation of the SRA1 exon 3 binding site for SRSF1 prevented the binding of SRA1 pre-mRNA. In summary, our results provide experimental evidence that SRA1 exon 3 inclusion is up regulated by SRSF1 to promote tumor invasion and metastasis in hepatocellular carcinoma.