Bcl-2 dependent modulation of Hippo pathway in cancer cells

Introduction: Bcl-2 and Bcl-xL are the most studied anti-apoptotic members of Bcl-2 Family proteins. We previously characterized both of them, not only for their role in regulating Apoptosis and resistance to therapy in Cancer cells, but also for their non-canonical functions, mainly including promotion of Cancer progression, metastatization, angiogenesis, and involvement in the crosstalk among Cancer cells and components of the tumor microenvironment. Our goal was to identify transcriptional signature and novel cellular pathways specifically modulated by Bcl-2.

Methods: We performed RNAseq analysis of siRNA-mediated transient knockdown of Bcl-2 or Bcl-xL in human melanoma cells and gene ontology analysis to identify a specific Bcl-2 transcriptional signature. Expression of genes modulated by Bcl-2 and associated to Hippo pathway were validated in human melanoma, breast adenocarcinoma and non-small cell lung Cancer cell lines by qRT-PCR. Western blotting analysis were performed to analyse protein expression of upstream regulators of YAP and in relation to different level of Bcl-2 protein. The effects of YAP silencing in Bcl-2 overexpressing Cancer cells were evaluated in migration and cell viability assays in relation to different stiffness conditions. In vitro wound healing assays and co-cultures were used to evaluate cancer-specific Bcl-2 ability to activate fibroblasts.

Results: We demonstrated the Bcl-2-dependent modulation of Hippo Pathway in Cancer cell lines from different tumor types by acting on upstream YAP regulators. YAP inhibition abolished the ability of Bcl-2 to increase tumor cell migration and proliferation on high stiffness condition of culture, to stimulate in vitro fibroblasts migration and to induce fibroblasts activation.

Conclusions: We discovered that Bcl-2 regulates the Hippo pathway in different tumor types, promoting cell migration, adaptation to higher stiffness culture condition and fibroblast activation. Our data indicate that Bcl-2 inhibitors should be further investigated to counteract cancer-promoting mechanisms.

Bcl-2; Breast cancer; Hippo Pathway; Melanoma.