LAUSR

The Smoothened receptor (SMO) belongs to the frizzled-class-G-protein coupled receptor and its activity can be classified in the canonical and the non-canonical pathway. The canonical pathway concludes in the transcriptional activation of the Hedgehog target genes through the GLI family of transcription factors whereas the non-canonical pathway leads to the recruitment and activation of trimeric G proteins. Recently, we have reported two novel roles of SMO with relevance to cell survival and drug resistance in DLBCL. In the first, SMO promotes a shift in the ubiquitination pattern for TNF receptor-associated factor 6 (TRAF6) from degradation inducing K48-ubiquitin branching towards K63-ubiquitination. TRAF6 is a K63-Ub E3 ubiquitin ligase for AKT and K63-ubiquitination of AKT increases membrane recruitment, activation and stability. Evidently, SMO promotes the formation of a scaffold-like protein complex including the de-ubiquitinating enzyme Ubiquitin specific peptidase 8 (USP8) and TRAF6. In its second novel role, SMO influences the vesicular sorting of IGF1R and other receptor tyrosine kinases. Loss of SMO leads to increased IGF1R lysosomal degradation and reduced IGF1R recycling, while overexpression increases IGF1R levels and AKT signaling. These observations indicate SMO receptor biology outside of the established canonical and non-canonical pathway functions. We have set out to use BioID to investigate the SMO interactome that contributes to these novel functionalities using a fusion protein of SMO and the reengineered E. coli biotinyl transferase BirA (Turbo) as bait. Preliminary BioID using SMO-Turbo returned a list of candidates which will require further data filtering approaches, but thus far shows a marked enrichment for proteins involved in vesicular trafficking. Citation Format: Samantha Manuel, Nitin Agarwal, Daniel Bilbao, Francisco Vega, Ralf Landgraf. Exploring novel roles of the GPCR Smoothened in AKT signaling and drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 2567.