Rj. Damato et al., 2-METHOXYESTRADIOL, AN ENDOGENOUS MAMMALIAN METABOLITE, INHIBITS TUBULIN POLYMERIZATION BY INTERACTING AT THE COLCHICINE SITE, Proceedings of the National Academy of Sciences of the United Statesof America, 91(9), 1994, pp. 3964-3968
A metabolite of estradiol, 2-methoxyestradiol (2ME), inhibits angiogen
esis in the chicken embryo chorioallantoic membrane assay. Since 2ME c
auses mitotic perturbations, we examined its interactions with tubulin
. In our standard 1.0 M glutamate system (plus 1.0 mM MgCl2 at 37 degr
ees C), superstoichiometric concentrations (relative to tubulin) of 2M
E inhibited the nucleation and propagation phases of tubulin assembly
but did not affect the reaction extent. Although polymer formed in the
presence of 2ME was more cold-stable than control polymer, morphology
was little changed. Under suboptimal reaction conditions (0.8 M gluta
mate/no MgCl2 at 26 degrees C), substoichiometric 2ME totally inhibite
d polymerization. No other estrogenic compound was as effective as 2ME
as an inhibitor of polymerization or of the binding of colchicine to
tubulin. Inhibition of colchicine binding was competitive (K-i, 22 mu
M). Thus, a mammalian metabolite of estradiol binds to the colchicine
site of tubulin and, depending on reaction conditions, either inhibits
assembly or seems to be incorporated into a polymer with altered stab
ility properties.