Interclonal Mutually Beneficial Cooperation Mediated by TGF-β1 Enhances Invasion of Breast Cancer Cells

Intratumour heterogeneity is often associated with poor response to treatment and bad prognosis. In addition to genetic and epigenetic sources, phenotypic heterogeneity can also reflect plastic responses to signals from other cells. The latter can be mediated by various cell-cell interactions, from antagonistic (i.e., competition) to commensalistic or cooperative (mutually beneficial or altruistic). Positive exchanges can increase the fitness of clones and contribute to tumour growth, resistance to drugs and metastasis. Consequently, understanding the pathways involved in such interactions is of great significance for cancer treatment. This study used two breast cancer cell lines with different aggressiveness levels and very different secretome profiles (i.e., MDA-MB-231 and MCF7) to address the nature and mechanistic basis of interclonal crosstalk through paracrine signalling involving soluble factors during the early stages of metastasis. Our data show that MDA-MB-231 is able to recruit MCF7, through TGFβ1-mediated paracrine signalling, into expressing mesenchymal features and increased migration. On the other hand, MCF7 has no effect on the migration of MDA, suggesting a passive/commensalistic interaction. However, we found that the invasive potentials of both lines are enhanced when they are co-cultured, indicating that the two lines act synergistically and that such interclonal interactions can be mutually beneficial in vivo. Taking into account the negative impact that metastasis has on cancer prognosis and the lack of therapies to directly affect this process, interfering with the specific cooperative behaviours that tumour cells engage in during tumour progression should provide an additional strategy to increase patient survival.