The novel endogenous micropeptide XLH-36 binds Gemin4 to promote triple-negative breast cancer metastasis

Triple-negative breast cancer (TNBC) is the most malignant breast cancer subtype. The 5-year overall survival rate of TNBC patients is 77%, but once cancer metastasis occurs, this rate drops to 12%. To date, the discovery of biomarkers associated with TNBC metastasis remains a major challenge. In this study, we identified a novel translated product, XLH-36 micropeptide, encoded by lncRNA (long non-coding RNA) C5orf66-AS1, which acts as an "oncogenic driver" in TNBC. Through conservation analyses across 101 species, we found that XLH-36 is highly conserved in humans and primates. Analysis of RNA-seq data from 1295 breast cancer patients, including 165 TNBC patients from different cohorts, revealed significantly elevated XLH-36 expression levels in breast cancer and TNBC. Specifically, TNBC patients with low C5orf66-AS1 (encoding XLH-36) expression demonstrated a 20% higher overall survival rate compared to those with high C5orf66-AS1 expression over a 50-month follow-up. XLH-36 knockout inhibited the growth and metastasis of TNBC xenografts in mice. Furthermore, we found that XLH-36 directly binds Gemin4, causing it to remain in the cytoplasm and preventing it from carrying out its role in promoting S100A4 mRNA splicing in the nucleus. This leads to a compensatory increase in ICAM1 levels, ultimately resulting in the promotion of epithelial-to-mesenchymal transition (EMT) in TNBC cells and an increase in tumor metastasis. In summary, our findings highlight the crucial role of XLH-36 in TNBC metastasis, which could be exploited in the development of therapeutic and diagnostic strategies for TNBC patients.