Since the crystal structure analysis of NIK was clarified (24, 25), selective inhibitors of NIK have been developed, and in addition to regulating cell proliferation and differentiation, they are effective against liver inflammation/steatosis, rheumatoid arthritis, lupus, osteoporosis, metabolic disorder, and cancer in animal models (26, 27). The gene discussed is MAP3K14; the disease is rheumatoid arthritis.