Breast cancer-associated fibroblast-derived exosomal miR-1290 promotes triple-negative breast cancer cell proliferation.

Breast cancer is a major cause of cancer-associated mortality in females. Although therapeutic strategies targeting subtype-specific receptors have been developed for various breast cancer subtypes, effective targeted therapies for triple-negative breast cancer (TNBC) are lacking. Recently, the role of the tumor microenvironment (TME), particularly cancer-associated fibroblasts (CAFs), in the progression and metastasis of breast cancer, especially TNBC, has attracted increasing attention. However, the role of exosomes secreted by CAFs in TNBC cell proliferation is poorly understood. Thus, in this study, we analyzed exosomes derived from both CAFs and MDA-MB-231 cells and identified exosomal miR-1290 as a key component. When delivered to TNBC cells (BT-549 and Hs578T), exosomal miR-1290 directly suppressed the expression of the putative tumor suppressor TBC1D4, which was accompanied by reduced TSC1 expression and activation of the mTOR pathway. The promotion of TNBC cell growth by miR-1290 through direct targeting of TBC1D4 was validated using 2D culture models, 3D spheroid models, and in vivo xenograft models. Furthermore, we demonstrated that treatment with the mTOR inhibitor rapamycin and the FDA-approved rapamycin analog everolimus effectively suppressed miR-1290-induced TNBC cell proliferation, suggesting a potential therapeutic strategy for TNBC. Moreover, in patient cohorts, elevated levels of circulating miR-1290 significantly distinguished patients with breast cancer from healthy individuals and correlated with poor survival outcomes. Therefore, miR-1290 and its direct target TBC1D4 have potential value in both targeted treatment and diagnosis of TNBC.