GLP-1 could also directly induce pre-adipocyte proliferation through the RTK-Ras-Raf-MEK-ERK (extracellular signal-related kinase) pathway, the PKC (IP3-DAG-Ca2+ pathway), and the AKT signaling pathway to increase the incidence of obesity [144]. The gene discussed is GCG; the disease is obesity due to melanocortin 4 receptor deficiency.