“Ubiquitin-dependent mechanisms have emerged as essential regulatory elements controlling cellular levels of Smads and TGFβ-dependent biological outputs such as epithelial–mesenchymal transition (EMT).
In this study, we identify a HECT E3 ubiquitin ligase known as WWP2 (Full-length WWP2-FL), together with two WWP2 isoforms (N-terminal, WWP2-N; C-terminal WWP2-C), as novel Smad-binding partners. We show that WWP2-FL interacts exclusively with Smad2, Smad3 and Smad7 in the TGFβ pathway.
Interestingly, the WWP2-N isoform interacts with Smad2 and Smad3, whereas WWP2-C interacts only with Smad7. In addition, WWP2-FL and WWP2-C have a preference for Smad7 based on protein turnover and ubiquitination studies. Unexpectedly, we also find that WWP2-N, which lacks the HECT ubiquitin ligase domain, can also interact with WWP2-FL in a TGFβ-regulated manner and activate endogenous WWP2 ubiquitin ligase activity causing degradation of unstimulated Smad2 and Smad3.
Consistent with our protein interaction data, overexpression and knockdown approaches reveal that WWP2 isoforms differentially modulate TGFβ-dependent transcription and EMT.
Finally, we show that selective disruption of WWP2 interactions with inhibitory Smad7 can stabilise Smad7 protein levels and prevent TGFβ-induced EMT.
Collectively, our data suggest that WWP2-N can stimulate WWP2-FL leading to increased activity against unstimulated Smad2 and Smad3, and that Smad7 is a preferred substrate for WWP2-FL and WWP2-C following prolonged TGFβ stimulation.
Significantly, this is the first report of an interdependent biological role for distinct HECT E3 ubiquitin ligase isoforms, and highlights an entirely novel regulatory paradigm that selectively limits the level of inhibitory and activating Smads.”
That was an abstract I was browsing over coffee in my oncology RSS feeds and while it was a bit heavy for early in the day, I was intrigued because Smads have been cropping up in GI sessions at meetings over the last six months or so. Smads are signal transducers for members of the transforming growth factor-beta (TGF-beta) superfamily, so they occupy a key role in transcription of proteins:
In addition, I’ve included a link to an open access article on the biology of Smads in the references below.
Essentially, the translational research from Soond and Chantry (2011) is suggesting that blocking the WWP2 gene could prevent metastasis, ie cancers from spreading to other organs of the body. Many of you will remember the post on Norton and Massague’s cancer cell seeding theory and this new finding could well have implications for that research too.
Overall, the latest findings mean that if we have a valid target, we can design a drug to target the rogue gene sending signals.
Of course, these are still very early days yet, but it will be interesting to see if the basic science can be translated into R&D and eventually, a real clinical impact in the long run.
For those of you wanting a simpler version of the abstract, BBC Health did a nice job of putting the research into plain English. Do check out their short report with pretty pictures here.
Soond, S., & Chantry, A. (2011). Selective targeting of activating and inhibitory Smads by distinct WWP2 ubiquitin ligase isoforms differentially modulates TGFβ signalling and EMT Oncogene DOI: 10.1038/onc.2010.617
Attisano, L., & Tuen Lee-Hoeflich, S. (2001). The Smads Genome Biology, 2 (8) DOI: 10.1186/gb-2001-2-8-reviews3010
Izzi, L., & Attisano, L. (2004). Regulation of the TGFβ signalling pathway by ubiquitin-mediated degradation Oncogene, 23 (11), 2071-2078 DOI: 10.1038/sj.onc.1207412