Neudesin modulates <scp>IGF1</scp> and insulin signaling pathways by regulating the surface expression of <scp>IGF1R</scp> through a conserved <scp>WPE</scp> motif

Neudesin, a secreted protein implicated in diverse physiological processes, such as metabolism and immunity, lacks an identified receptor, which has prevented a detailed understanding of its molecular mechanisms. In this study, we aimed to elucidate the function of neudesin by identifying its cognate receptor and investigating its effects on cellular signaling. Using a combination of phage display, bioinformatics, and biochemical analysis, we identified insulin-like growth factor 1 receptor (IGF1R) as a high-affinity receptor for neudesin, with a binding affinity of 1.78 ± 1.87 nm. This interaction was mediated by a conserved tryptophan-proline-glutamic acid (WPE) motif in the IGF1R extracellular domain. Our cellular assays revealed that, while neudesin binding to IGF1R induces basal phosphorylation of the downstream signaling molecules extracellular signal-regulated kinase (ERK) and AKT (also known as Protein Kinase B, or PKB) in a cell-line-specific manner, it consistently acts as a negative modulator, attenuating both IGF1- and insulin-induced signaling. Mechanistically, neudesin promoted the downregulation of cell surface IGF1R, thereby reducing the receptor pool available for ligand stimulation. Furthermore, neudesin inhibited insulin signaling, likely through the co-internalization of IGF1R/insulin receptor (INSR) hybrid complexes. The physiological significance of this role was underscored in 3 T3-L1 adipocytes, where neudesin knockdown enhanced insulin-induced signaling and accelerated triglyceride accumulation. These results establish a novel molecular link between neudesin and the IGF1/insulin signaling axis, suggesting that neudesin may serve as an endogenous modulator of IGF1R/insulin activity, with potential implications for metabolic and growth-related diseases.