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.

The tyrosine phosphatase SHP2 has a dual role in cancer initiation and progression in a tissue type-dependent manner. Several studies have linked SHP2 to the aggressive behavior of breast cancer cells and poorer outcomes in people with cancer. Nevertheless, the mechanistic details of how SHP2 promotes breast cancer progression remain largely undefined.

The relationship between SHP2 expression and the prognosis of patients with breast cancer was investigated by using the TCGA and GEO databases. The expression of SHP2 in breast cancer tissues was analyzed by immunohistochemistry. CRISPR/Cas9 technology was used to generate SHP2-knockout breast cancer cells. Cell-counting kit-8, colony formation, cell cycle, and EdU incorporation assays, as well as a tumor xenograft model were used to examine the function of SHP2 in breast cancer proliferation. Quantitative RT-PCR, western blotting, immunofluorescence staining, and ubiquitination assays were used to explore the molecular mechanism through which SHP2 regulates breast cancer proliferation.

High SHP2 expression is correlated with poor prognosis in patients with breast cancer. SHP2 is required for the proliferation of breast cancer cells in vitro and tumor growth in vivo through regulation of Cyclin D1 abundance, thereby accelerating cell cycle progression. Notably, SHP2 modulates the ubiquitin–proteasome-dependent degradation of Cyclin D1 via the PI3K/AKT/GSK3β signaling pathway. SHP2 knockout attenuates the activation of PI3K/AKT signaling and causes the dephosphorylation and resultant activation of GSK3β. GSK3β then mediates phosphorylation of Cyclin D1 at threonine 286, thereby promoting the translocation of Cyclin D1 from the nucleus to the cytoplasm and facilitating Cyclin D1 degradation through the ubiquitin–proteasome system.

Our study uncovered the mechanism through which SHP2 regulates breast cancer proliferation. SHP2 may therefore potentially serve as a therapeutic target for breast cancer.