YAP (Yes-associated protein) is a transcriptional co-factor regulating a number of genes involved in several cellular processes, including proliferation, stemness and Epithelial-to-Mesenchymal Transition. Although the current model postulates that YAP activity is largely dependent on the transcriptional factors belonging to TEAD family, mounting evidence indicates that YAP may use other DNA-binding partners and that formation of specific transcriptional complexes and their regulation can be cell- and context- dependent and drive specific cellular outcomes. This is relevant in cancer, where the dynamics of the genome occupancy and the specific gene expression could differently influence tumor progression. Our published and preliminary data suggest that STAT3 could be a new transcriptional partner of YAP and that ERK5 represents a new YAP regulator. We have demonstrated in liver cells a physical interaction between YAP and STAT3 and their co-occupancy of promoter of Snail, master gene of EMT. Moreover, we found that ERK5 activity is required for this interaction. Starting from these data and from our analysis of publicly available ChIP-seq datasets for YAP and STAT3 obtained from a cell model of Triple Negative Breast Cancer enforcing our working hypothesis, this project aims to characterize the activity and the regulation of YAP/STAT3 complex in TNBC, a tumor resistant to therapy and with an overall bad prognosis.
Therefore, we will analyze: i) the cooperation of YAP and STAT3 in DNA-binding and in driving specific gene expression in TNBC cells, ii) the role of the YAP/STAT3 complex in cell motility and tumor progression, iii) the regulation of its activity by ERK5 and the molecular mechanisms involved. These studies will allow to clarify the molecular mechanisms underlying the different YAP-induced cellular outcomes and to provide new insights in the regulation of YAP activity in TNBC, in the attempt to suggest new molecular targets for therapeutic treatments.
Despite several reports highlighted the pivotal role of YAP in cancer, a number of questions still remain open. In particular, how YAP can mediate tissue- and cell context- dependent gene expression and determine different tumorigenic processes needs to be clarified.
Growing evidence indicates that the composition and genome occupancy of transcriptional YAP/TAZ/TF complexes may be tissue- and cell context-dependent, thus driving specific gene expression and functional outcome. This is relevant in cancer where the specificity of the transcriptional YAP/TAZ/TF complexes and of their regulation in cells from histotype-specific cancers can represent an important limitation in the application of the therapy developed for tumors of different origin.
Therefore, the identification of the DNA-binding partners of YAP that drive specific oncogenic activities of YAP and their regulation in different cancer histotypes can provide both basic knowledge on the mechanisms involved in the regulation of YAP oncogenic activity, and the possibility to identify new and tumor-specific therapeutic targets.
Our previous data showed a physical interaction between YAP and the transcription factor STAT3, their DNA co-occupancy and transcriptional regulation of the EMT master gene Snail. This agrees with the literature reports indicating functional cooperation between the two proteins in various cellular models. Starting from these observations, we plan to investigate the role played by the YAP/STAT3 complex in tumor progression, through the analysis of its DNA binding and transcriptional activity in a cellular model of TNBC.
Our analysis will focus on a set of genes, selected by a genome-wide analysis of the publicly available ChIP-seq data of the YAP and STAT3 binding to DNA in TNBC cells revealing a significant overlap between the respective chromatin occupancy peaks on gene regulatory regions, and all included in the GO category of "regulation of locomotion".
Furthermore, starting from our preliminary results showing the regulation of YAP transcriptional activity by ERK5/MAPK and the requirement of ERK5 activity for the YAP/STAT3 physical interaction, we aim at evaluating the role of this kinase in regulation of YAP/STAT3 transcriptional activity and the mechanisms involved.
Therefore, the results obtained in this proposal will provide new knowledge of how specific DNA binding partners of YAP and kinases regulating the complex formation and activity can dictate the selection of the its target genes in cancer. Furthermore, these studies will provide new translational insights into the mechanisms that regulate YAP activity and tumorigenesis in TNBC, a clinically very aggressive and invasive subtype of breast cancer, suggesting new possible molecular targets for its treatment.
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