E3ANDTGFBINCANCER · Role of E3 Ub-ligases in TGF-beta signaling and tumorigenesis

Role of E3 Ub-ligases in TGF-beta signaling and tumorigenesis

In living organism, cells communicate by secreting molecules. These molecules can bind to receptors at the surface of neighbour cells and this event triggers a series of signals in the cell that leads to modification of the genetic program of the cell and subsequently changes its behaviour. TGF-b is one of these molecules and the signal it generates inside the cell orders it to stop dividing. TGF-b signal act therefore to prevent anarchical cell division and protect the cell from tumour formation. In cancer, the genes that are involved in the transmission of the TGF-b signal are sometime mutated and this leads to the inability for the cell to respond to the anti-proliferative signal of the TGF-b. Such cells will then start to proliferate anarchically and form tumours. Surprisingly, TGF-b pathway also has a tumour promoter function. Indeed in the late stage of tumourigenesis TGF-b switches its effect to a tumour promoter by inducing metastasis. TGF-b signal pathway plays therefore a critical 2-step role in cancer and identifying genes that are able to modulate this signal in the cell is therefore a crucial step to understand how TGF-b is involved in tumourigenic process. Recently we were able to characterise that the gene coding for a protein called Arkadia is absolutely required for the cell to respond to the TGF-b signal. We were able to unravel the mechanism by which Arkadia acts. Arkadia contains a RING domain that gives E3 Ub-ligase activity, meaning that it can ubiquitinate and degrade its substrate. Indeed, we found that Arkadia ubiquitinates and degrades SnoN, a natural repressor of the TGF-b transduction pathway, and therefore act as an activator of the TGF-b signal. We analysed 14 lung carcinoma cell lines and found mutation of Arkadia in one out of these 14 cell lines. This mutation is a stop mutation that generates a truncated protein that has lost its functional RING domain. Restoring Arkadia in this tumour cell line restores SnoN degradation and the TGF-b response. Moreover, our results indicate that Arkadia is essential for TGF-b to induce metastasis. In order to better understand the mechanism of action and regulation of Arkadia we have sought to identify new modulators or substrates of Arkadia. Candidate approach enables us to show that Arkadia interacts with FHL2 an adaptator protein that regulates different signalling pathway such as the wnt/b-catenin pathway. We have found that FHL2 stabilises and therefore potentiates Arkadia function. In parallel, we performed a two-hybrid screen that revealed new interesting partners of Arkadia. Surprisingly the strongest interactant observed is UBE2i an enzyme involved in the sumoylation of protein, a modification of protein that is related to ubiquitination. We are therefore currently investigating the role of Arkadia in sumoylation. We have shown that Arkadia is mutated in lung cancer but is also required for metastasis and we would like to carry on this study by determining if Arkadia is overexpressed in advanced tumour and is associated to a bad prognosis. We are also very excited by our finding that Arkadia might have a role in sumoylation and we are currently testing the hypothesis that Arkadia might degrade specifically sumoylated substrate. By deciphering the mechanism of action of this E3 Ub-ligase crucial for TGF-b signalling, we hope that we will contribute to the development of new potential therapeutic target that will enable to tame tumour metastasis associated with TGF-b.

Текст от CORDIS, на английски · Данни: CORDIS, © Европейски съюз