| Signal transduction is a process which cells employ to convert intra- and extracellular stimuli into changes in gene expression programs. These stimuli include growth factors, cytokines, osmolarity, heat, pH, redox, radiation, and mechanical stress. They induce cellular responses such as differentiation, proliferation, migration, apoptosis. There are groups of proteins, called scaffolding proteins, which maintain signaling specificity, efficiency and integrity through specific protein-protein interactions with signaling components. JLP has been shown as scaffolding protein involved in MAPK pathways.; To date, the biological function of JLP in neuronal system remains unknown. To identify novel JLP-interacting proteins, we performed a yeast two-hybrid screen with the carboxyl-terminal domain of JLP as bait and identified a novel JLP-interacting group of proteins: SCG10 and SCLIP. An immunoprecipitation assay showed that endogenous JLP associates with endogenous SCG10/SCLIP in NGF-treated PC12 cells. Because SCG10/SCLIP are neuronal specific proteins that are critical for neuronal differentiation including neurite outgrowth, we investigated the role of JLP in regulating neuronal differentiation. Inhibition of endogenous JLP expression using siRNA methodology strongly enhanced NGF-induced neurite outgrowth in PC12 cells, indicating JLP negatively regulates NGF-induced neurite outgrowth by decreasing the level of phosphorylated SCG10. Furthermore, use of a JNK inhibitor demonstrated that JNK is required for NGF-induced neurite outgrowth by mediating the phosphorylation of SCG10. As there is a ternary protein complex formed between JLP and JNK and SCG10, we conclude that scaffolding protein JLP negatively regulates NGF-induced neurite outgrowth by sequestering the JNK-dependent phosphorylation of SCG10. As the NGF signaling pathway is associated with neurodegenerative disorders of the human brain, our discoveries provide a clue that could help identify novel therapeutic agents that could be used to treat human neurodegenerative disorders, such as Alzheimer's disease. |
