Exosomal EPHA2 transfers metastatic potential by stabilizing TGF-βRI and activating the TGF-β/SMAD3 signaling pathway in breast cancer

Intratumoral heterogeneity refers to the presence of distinct subpopulations of cancer cells within a single tumor, which exhibits variations in phenotypic traits, such as proliferation rate, drug sensitivity, and metastatic potential. Dynamic interactions among heterogeneous cell populations have a critical role in tumor progression. Increasing evidence underscores the importance of intercellular communication among heterogeneous cancer cell subpopulations in driving malignancy. However, the molecular mechanisms governing such cancer cell-to-cancer cell interactions are poorly understood.

Exosomes were isolated from highly metastatic breast cancer cells (HM-BCCs) and low metastatic breast cancer cells (LM-BCCs). The role of exosome-mediated intercellular communication on metastatic behavior was assessed using wound healing and Transwell assays. Gene knockdown and overexpression strategies, small-molecule inhibitors, and xenograft mouse models were used to elucidate the role of exosomal EPHA2.

Exosomes derived from HM-BCCs considerably enhanced the migratory and invasive capabilities of LM-BCCs in vitro and increased the metastatic potential in vivo. Mechanistically, EPHA2 was identified as a key protein enriched in exosomes from HM-BCCs and was shown to be transferred to LM-BCCs by these vesicles. Exosomal EPHA2 promoted epithelial-to-mesenchymal transition in LM-BCCs when internalized by stabilizing TGF-βRI and activating the transforming growth factor-β/mothers against decapentaplegic homolog 3 (TGF-β/SMAD3) signaling pathway, thereby facilitating the acquisition of a metastatic phenotype.

The results underscore the pivotal function of exosomal EPHA2 in mediating the transfer of metastatic potential among heterogeneous breast cancer cell populations. Targeting the EPHA2-TGF-βRI signaling axis may provide a novel therapeutic approach for preventing or limiting breast cancer metastasis.