J. Biochem, 2003, Vol. 133, No. 4 541-552
© 2003 Japanese Biochemical Society
BIOCHEMISTRY |
Molecular Action Mode of Hippospongic Acid A, an Inhibitor of Gastrulation of Starfish Embryos
1 Laboratory of Food & Nutritional Sciences, Department of Nutritional Science, Kobe-Gakuin University, Nishi-ku, Kobe, Hyogo 651-2180; 2 High Technology Research Center, Kobe-Gakuin University, Nishi-ku, Kobe, Hyogo 651-2180; 3 Department of Biofunctional Chemistry, Faculty of Agriculture, Kobe University, Nada-ku, Kobe, Hyogo 657-8501; 4 Department of Applied Biological Science, Tokyo University of Science, Noda, Chiba 278-8510; 5 Department of Chemistry, Faculty of Science, Tokyo University of Science, Shinjuku-ku, Tokyo 162-8601; 6 Frontier Research Center for Genomic & Drug Discovery, Tokyo University of Science, Noda, Chiba 278-8510; and 7 Department of Biological Science, Teikyo University of Science and Technology, Yamanashi 409-0193
Hippospongic acid A (HA-A) is a novel natural triterpene metabolite that exhibits inhibitory activity against the gastrulation of starfish embryos isolated from a marine sponge, Hippospongia sp. We succeeded in chemically synthesizing the natural enantiomer and the racemate HA-A. In this study, we examined its action mode in vitro. HA-A was a rare compound that could selectively but uniformly inhibit the activities of all the vertebrate DNA polymerases tested such as 
, ß, 
, 
, 
, 
, and 
, in the IC50 range of 5.9–17.6 µM, and interestingly also those of human DNA topoisomerases I and II (IC50 = 15–25 µM). HA-A exhibited no inhibitory effect on DNA polymerases from insects, plants and prokaryotes, or on many other DNA metabolic enzymes. HA-A was an inhibitor specific to DNA polymerases and DNA topoisomerases from vertebrates, but not selective as to a subclass species among the enzymes. Since DNA polymerase ß is the smallest, we used it to analyze the biochemical relationship with HA-A. Biochemical, BIAcore and computer modeling analyses demonstrated that HA-A bound selectively to the N-terminal 8 kDa DNA template-binding domain of DNA polymerase ß, and HA-A inhibited the ssDNA binding activity. HA-A could prevent the growth of NUGC-3 cancer cells at both the G1 and G2/M phases, and induce apoptosis in the cells. The LD50 value was 9.5 µM, i.e. in the same range as for the enzyme inhibition. Therefore, we concluded that one molecular basis of the gastrulation of starfish embryos is a process that requires DNA polymerases and DNA topoisomerases, and subsequently the gastrulation was inhibited by HA-A. We also discussed the in vivo role of HA-A.
+ To whom correspondence should be addressed: Tel: +81-78-974-1551 (Ext. 3232), Fax: +81-78-974-5689, E-mail: mizushin{at}nutr.kobegakuin.ac.jp