1. Department of Preventive Medicine and AIDS Research and Department of Internal Medicine, Institute of Tropical Medicine, Nagasaki University, 1-12-4 Sakamoto, Nagasaki 852-8523, Department of Pharmacology, Cancer Research Institute, Kanazawa University, 13-1 Takaramachi, Kanazawa 920-0934, and Department of Molecular Preventive Medicine, School of Medicine, University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo 113-0033, Japan