PO-148 Activin a upregulation mediated by P63 promotes migration and invasion of oral cancer cells

Introduction TGF-β family proteins, Activins are homo/heterodimers of β subunits βA, βB, βC and βE, while Inhibins are αβ heterodimers. Relative abundance of each monomer dictates which dimer is predominantly formed. Activins bind to typeII receptor on cell membrane and trigger their tetramerization with typeI receptor, ALK4 phosphorylating SMAD 2/3 which translocate to nucleus and regulate transcription. Activins are reported to be up regulated in various cancers including HNSCC; however, these are transcriptome-scale studies that have indicated altered βA expression, without considering other subunits’ expression or their dimerization. An oncogenic role for Activins has been demonstrated in cancer; albeit, the precise mechanisms downstream of Activin or molecules regulating its expression/function are vaguely understood. This study evaluated the expression of Activins and phenotypes that are affected by its altered expression in oral cancer; with emphasis on Activin-SMAD 2/3 signalling as the downstream mechanism. We also tested the possible role of p53 family proteins in regulating Activin gene expression and functions. Material and methods Activin subunits’ expression was assessed in oral cancer celllines and tissues by qRT-PCR, IHC and Western blot. Wound healing, Matrigel Invasion, and MTT assays were performed post knockdown of Activin βA and SMAD 2/3 using siRNA and post treatment with recombinant Activin A. We tested the regulation of Activin βA expression by p53 and p63 using ChIP assay and analysed the effect of p63 knockdown in context of Activin expression on oral cancer cells. Results and discussions Activin βA was significantly overexpressed in oral cancer cells and tissues compared to normal counterparts at transcript and protein level. Knockdown of βA resulted in decreased, while treatment with recombinant Activin A resulted in increased migration and invasion of oral cancer cells. Knockdown of SMAD 2/3 also led to similar effects, indicating that Activin A contributes to these phenotypes through SMAD2/3 signalling pathway. The ChIP experiments demonstrated that βA promoter could be bound by p63, a p53 family member with established oncogenic functions. Recombinant Activin A treatment could rescue the loss of migration upon p63 knockdown suggesting that p63 could be an upstream regulator of Activin expression and function in oral cancer. Conclusion The study revealed a novel role of p63 in regulating Activin A expression. We also deciphered the mechanism downstream of p63-Activin A axis that contributes to migration and invasion of oral cancer.