¹This work was supported by Grants-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan, the Takeda Science Foundation, and the Nagase Science and Technology Foundation. N.T., M.M., and Y.Y. are Research Fellows of the Japan Society for the Promotion of Science (JSPS).

²To whom correspondence should be addressed. Tel/Fax: +81-86-251-7958, E-mail: mizushima@pharm.okayama-u.ac.jp