Non-small cell lung cancer (NSCLC) is a major form of lung cancer and is the leading cause of cancer mortality in the western world. Transforming growth factor β (TGFβ) deregulation leads to many human diseases: TGFβ is a tumor suppressor in normal lung epithelium; however, it switches roles and promotes lung cancer metastasis in cancer cells. TGFβ induces cell proliferation, migration and invasion in NSCLC cells.
The canonical pathway of TGFβ is initiated through binding of TGFβ ligand to transmembrane Ser/Thr kinase receptors, which propagate their signaling via receptor regulated R-Smads; proteins that function as intracellular effectors in the TGFβ pathway. Once activated, R-Smads form a complex with common (Co)-Smads that translocates into the nucleus to regulate transcriptional responses. Access of R-Smads to the activated receptor complex is regulated by an adaptor protein called Smad anchor for receptor activation (SARA). SARA facilitates the activation of Smads and allow efficient Smad signalling.
In addition to R-Smads and Co-Smads, inhibitory Smads (I-Smads) regulate TGFβ signalling. I-Smads block the signalling by competing against R-Smads for the association with TβR complex or by targeting receptors for ubiquitin-mediate degradation. I-Smads recruit the E3 ubiquitin ligases, Smad ubiquitination regulatory factors (Smurfs), to catalyze degradation of the receptor complex. The overall aim of the project is to characterize SARA in TGFβ receptor signalling and study the interaction of SARA with different proteins involved in the pathway, such as Smurf2 and Smad7.
We first examined how SARA, Smurf2 and Smad7 influence each other by performing a multi-combination transfection study. We also examined the interaction between SARA and Smurf2 through co-immunoprecipitation. We observed that the level of SARA decrease in the presence of Smurf2 and Smad7. In the presence of Smurf2 ligase inactive mutant and Smad7, the level of SARA is somewhat recovered. However, SARA does not directly interact with Smurf2. These data together suggest that SARA and Smurf2 influence each other in a very close manner. It also suggest that it could be a transient interaction. Characterizing SARA in TGFβ receptor signalling will provide us with possible drug targets for NSCLC.
Citation Format: Sanghyun Lee, John M. Di Guglielmo. Role of Smurf2 in regulation of Smad anchor necessary for receptor activation (SARA) in TGFβ-receptor signaling. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4427.