A micropeptide XBP1SBM encoded by lncRNA promotes angiogenesis and metastasis of TNBC via XBP1s pathway

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer (BC) with a poor prognosis. To date, the mechanism of TNBC's aggressive phenotype is still unclear. Based on metabolome analysis, we found that glutamine (Gln) metabolism plays a key role in the difference between TNBC and non-TNBC. We identified a 21-amino-acid survival-associated micropeptide XBP1SBM, encoded by the lncRNA MLLT4-AS1, which was upregulated in TNBC tissues and Gln-deprived TNBC cell lines. We showed that XBP1SBM expression was upregulated by Gln-deprivation-induced XBP1s transcriptional promotion, and in turn retained XBP1s in the nuclear to enhance the expression of VEGF. Using human endothelial cells, mouse xenograft models and mouse spontaneous BC models, we found that XBP1SBM improved Gln levels and promoted angiogenesis and metastasis in TNBC. Our study showed that a TNBC-specific nutrient deficiency adaption results in aggressive TNBC, and this mechanism provides a novel potential prognostic biomarker and therapeutic target in TNBC.