| Summary: | Ubiquitination is a post-translational modification involving the attachment of ubiquitin molecules onto target substrates. The most common function of ubiquitination is proteasomal degradation, which is commonly facilitated by the ubiquitination of target proteins at Lys-48. E3 ligases are crucial to the process of ubiquitination, and include WWP2 ubiquitin Ligase, an E3 enzyme that has been shown to interact with Smad mediators of the TGF family and might subsequently have a role in TGFβ-dependent oncogenic processes such as EMT. To elucidate the function of WWP2 in TGFβ-signalling and increase our understanding of this protein, is therefore the forefront of our research. Here, we found that the overexpression of WWP2 WW3-4 recognition domain led to an increase in Smad3-dependent TGF gene expression, providing strong evidence that in the absence of TGF , WW3-4 binds to the Smad3 mediator. We also predicted and validated the expression of two novel WWP2 isoforms, WWP2-ΔHECT and WWP2-N-ΔC2. Results suggest that the incomplete HECT domain within WWP2-ΔHECT is catalytically non-functional. Furthermore, the transcription of WWP2-ΔHECT has been linked to a 2kb region within intron 9/10 with its expression positively regulated by EGF stimulation. On the contrary, when the transcriptional mechanism of the existing WWP2-C isoform was investigated, a 0.5kb region at the end of intron 10/11 was identified to enhance promoter activity responsible for expression, which was negatively regulated by the SOX9 transcription factor. It was also found that ESRP splicing factor is involved in the negative regulation of not only the existing isoform WWP2-N, but also the novel WWP2-ΔHECT isoform. Using expression studies, we found that WWP2-N and ΔHECT were expressed at higher levels in epithelial cells, therefore suggesting their role as guardians of the epithelial phenotype during EMT. Overall, the data provided here can help clarify the role of WWP2 in TGFβ-dependent oncogenic signalling.
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