A 3′‐pre‐tRNA‐derived small RNA tRF‐1‐Ser regulated by 25(OH)D promotes proliferation and stemness by inhibiting the function of MBNL1 in breast cancer

Abstract Background We explored the potential novel anticancer mechanisms of 25‐hydroxyvitamin D (25(OH)D), a vitamin D metabolite with antitumour effects in breast cancer. It is stable in serum and is used to assess vitamin D levels in clinical practice. Transfer RNA‐derived small RNAs are small noncoding RNAs that generate various distinct biological functions, but more research is needed on their role in breast cancer. Methods Small RNA microarrays were used to explore the novel regulatory mechanism of 25(OH)D. High‐throughput RNA‐sequencing technology was used to detect transcriptome changes after 25(OH)D treatment and tRF‐1‐Ser knockdown. RNA pull‐down and high‐performance liquid chromatography–mass spectrometry/mass spectrometry were used to explore the proteins bound to tRF‐1‐Ser . In vitro and in vivo functional experiments were conducted to assess the influence of 25(OH)D and tRF‐1‐Ser on breast cancer. Semi‐quantitative PCR was performed to detect alternative splicing events. Western blot assay and qPCR were used to assess protein and mRNA expression. Results The expression of tRF‐1‐Ser is negatively regulated by 25(OH)D. In our breast cancer (BRCA) clinical samples, we found that the expression of tRF‐1‐Ser was higher in cancer tissues than in paired normal tissues, and was significantly associated with tumour invasion. Moreover, tRF‐1‐Ser inhibits the function of MBNL1 by hindering its nuclear translocation. Functional experiments and transcriptome data revealed that the downregulation of tRF‐1‐Ser plays a vital role in the anticancer effect of 25(OH)D. Conclusions In brief, our research revealed a novel anticancer mechanism of 25(OH)D, unveiled the vital function of tRF‐1‐Ser in BRCA progression, and suggested that tRF‐1‐Ser could emerge as a new therapeutic target for BRCA.