title: IKP104-induced decay of tubulin: role of the A-ring binding site of colchicine.
abstract: Tubulin, the major subunit protein of microtubules, has a tendency to lose its ability to assemble or to interact with ligands in a time-dependent process known as decay. Decay involves the increase in exposure of sulfhydryl groups and hydrophobic areas. The antimitotic drug IKP104 [2-(4-fluorophenyl)-1-(2-chloro-3, 5-dimethoxyphenyl)-3-methyl-6-phenyl-4(1H)-pyridinone] accelerates the decay of tubulin [Ludueña et al. (1995) Biochemistry 34, 15751-15759]. In the presence of colchicine, however, IKP104 stabilizes tubulin against decay. We have shown that the stability and the acceleration of the decay of tubulin are mediated respectively by the high- and low-affinity binding site(s) of IKP104 [Chaudhuri et al. (1998) J. Protein Chem. 17, 303-309]. To better understand the mechanism by which colchicine protects tubulin from IKP104-induced decay, we examined the effect of colchicine and its analogues on this process. We found that IKP104 unfolds tubulin in a process involving a specific domain where colchicine interacts, although the binding sites of these two drugs are distinctly different. 2-Methoxy-5-(2',3',4'-trimethoxyphenyl) tropolone (MTPT), the bicyclic analogue of colchicine that lacks the B-ring, can also protect tubulin from IKP104-induced decay. An A-ring analogue of colchicine, 3,4,5-trimethoxybenzaldehyde (TMB), can also stop IKP104-induced unfolding of tubulin significantly. Interestingly, the C-ring analogue of colchicine, tropolone methyl ether (TME), does not prevent this process. Our results thus suggest that neither the B-ring nor the C-ring binding regions of colchicine are involved in the IKP104-induced decay and that the A-ring binding site of colchicine on tubulin plays a crucial role in IKP104-induced decay.
authors.affiliation: Department of Biochemistry, University of Texas Health Science Center, San Antonio 78284, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Chaudhuri
authors.forename: I
authors.initials: I
authors.lastname: Tomita
authors.forename: F
authors.initials: F
authors.lastname: Mizuhashi
authors.forename: K
authors.initials: K
authors.lastname: Murata
authors.forename: J L
authors.initials: JL
authors.lastname: Potenziano
authors.forename: R F
authors.initials: RF
authors.lastname: Ludueña
mesh_terms: D000478:Alkylation / Q000187:drug effects; D000818:Animals; D001547:Benzaldehydes / Q000494:pharmacology; D001665:Binding Sites / Q000187:drug effects; D002417:Cattle; D003078:Colchicine / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism*; D011487:Protein Conformation / Q000187:drug effects; D011728:Pyridones / Q000378:metabolism / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence; D014334:Tropolone / Q000031:analogs & derivatives / Q000494:pharmacology; D014404:Tubulin / Q000737:chemistry / Q000378:metabolism*; D050257:Tubulin Modulators
chemical_list: D001547:Benzaldehydes; D011728:Pyridones; D014404:Tubulin; D050257:Tubulin Modulators; C067096:IKP 104; C037100:2-methoxytropolone; C034031:2,4,5-trimethoxybenzaldehyde; C030370:2-methoxy-5-(2',3',4'-trimethoxyphenyl)tropone; D014334:Tropolone; D003078:Colchicine