A Single Amino Acid Residue Contributes to Distinct Mechanisms of Inhibition of the Human Multidrug Transporter by Stereoisomers of the Dopamine Receptor Antagonist Flupentixol

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• 作者：Saibal Dey ; Peter Hafkemeyer ; Ira Pastan ; and Michael M. Gottesman
• 刊名：Biochemistry
• 出版年：1999
• 出版时间：May 18, 1999
• 年：1999
• 卷：38
• 期：20
• 页码：6630 - 6639
• 全文大小：216K
• 年卷期：v.38,no.20(May 18, 1999)
• ISSN：1520-4995

文摘

Both cis and trans isomers of the dopamine receptor antagonist flupentixol inhibit drug transportand reverse drug resistance mediated by the human multidrug transporter P-glycoprotein (Pgp) with astereoselective potency. The rate of ATP hydrolysis by Pgp and photoaffinity labeling of Pgp with thesubstrate analogue [¹²⁵I]iodoarylazidoprazosin ([¹²⁵I]IAAP) are modulated by each isomer in an oppositemanner, suggesting different mechanisms for the inhibitory effect on drug transport. In this study wedemonstrate that substitution of a single phenylalanine residue at position 983 (F983) with alanine (F983A)in putative transmembrane (TM) region 12 selectively affects inhibition of Pgp-mediated drug transportby both isomers of flupentixol. In F983A the stimulatory effect of cis(Z)-flupentixol and the inhibitoryeffect of trans(E)-flupentixol on ATP hydrolysis and [¹²⁵I]IAAP labeling were significantly altered. Thisindicates that F983 contributes to inhibition of drug transport by both isomers of flupentixol and plays animportant role in stimulation and inhibition of ATP hydrolysis and [¹²⁵I]IAAP labeling by cis(Z)- andtrans(E)-flupentixol, respectively. The near-wild-type level of drug transport by the F983A Pgp mutantdissociates susceptibility to inhibition by flupentixol from drug translocation, indicating the allostericnature of the flupentixol interaction. The inhibitory effects of cyclosporin A on drug transport, drug-stimulated ATP hydrolysis, and [¹²⁵I]IAAP labeling as well as the stimulatory effect of verapamil onATP hydrolysis by Pgp were minimally affected by substitution of F983, suggesting no global alterationin the structural and functional integrity of the mutant. Taken together, our data suggest that distinctmechanisms of inhibition of Pgp-mediated drug transport by the cis and trans isomers of flupentixol aremediated through a common site of interaction.