Functional defect of variants in the adenosine triphosphate–binding sites of ABCB4 and their rescue by the cystic fibrosis transmembrane conductance regulator potentiator, ivacaftor (VX‐770)

Abstract

ABCB4 (MDR3) is an adenosine triphosphate (ATP)‐binding cassette (ABC) transporter expressed at the canalicular membrane of hepatocytes, where it mediates phosphatidylcholine (PC) secretion. Variations in the ABCB4 gene are responsible for several biliary diseases, including progressive familial intrahepatic cholestasis type 3 (PFIC3), a rare disease that can be lethal in the absence of liver transplantation. In this study, we investigated the effect and potential rescue of ABCB4 missense variations that reside in the highly conserved motifs of ABC transporters, involved in ATP binding. Five disease‐causing variations in these motifs have been identified in ABCB4 (G535D, G536R, S1076C, S1176L, and G1178S), three of which are homologous to the gating mutations of cystic fibrosis transmembrane conductance regulator (CFTR or ABCC7; i.e., G551D, S1251N, and G1349D), that were previously shown to be function defective and corrected by ivacaftor (VX‐770; Kalydeco), a clinically approved CFTR potentiator. Three‐dimensional structural modeling predicted that all five ABCB4 variants would disrupt critical interactions in the binding of ATP and thereby impair ATP‐induced nucleotide‐binding domain dimerization and ABCB4 function. This prediction was confirmed by expression in cell models, which showed that the ABCB4 mutants were normally processed and targeted to the plasma membrane, whereas their PC secretion activity was dramatically decreased. As also hypothesized on the basis of molecular modeling, PC secretion activity of the mutants was rescued by the CFTR potentiator, ivacaftor (VX‐770). Conclusion: Disease‐causing variations in the ATP‐binding sites of ABCB4 cause defects in PC secretion, which can be rescued by ivacaftor. These results provide the first experimental evidence that ivacaftor is a potential therapy for selected patients who harbor mutations in the ATP‐binding sites of ABCB4. (Hepatology 2017;65:560‐570)

ABCB4 Gene Aberrations in Human Liver Disease: An Evolving Spectrum

“…Recently, the approved treatment with the CTFR potentiator ivacaftor (efficient in carriers of CF gating mutations) was found to be able to reverse the condition in human cells with ABCB4 class III mutations (►Table 1) that affect transporter activity as well. 82 These mutations (p.G535D, p.G536R, p. S1076C, p.S1176L, p.G1178S) are localized in conserved motifs involved in ATP binding and hydrolysis, and homologous to the gating mutations of CFTR. Novel therapeutic approaches for modulating bile composition in ABCB4 deficiency were investigated in Abcb4 knockout mice.…”

Functional rescue of an ABCB11 mutant by ivacaftor: A new targeted pharmacotherapy approach in bile salt export pump deficiency

“…Model of the 3D structure of the ABCB11 NBD1/NBD2 assembly was built with Modeller v9.15 13 using as a template the experimental structure of the MJ0796 NBD1/NBD2 heterodimer in complex with ATP (pdb 1l2t), 14 solved at 1.9 Å, as described previously for the modelling of the ABCB4 NBD1/NBD2 assembly. 12 We have used this MJ0796 3D structure, rather than other 3D structures sharing higher sequence similarities with ABCB11, because of the high resolution observed within the ATP-binding sites. The sequence alignment used for modelling is given in Figure S1.…”

“…10,11 Interestingly, it has been shown that ivacaftor could also increase the function of some MDR3 (multidrug resistance protein 3, ABCB4) mutants resulting from mutations located in NBDs and responsible for PFIC3, another chronic cholestatic liver disease. 12 However, the ability of potentiators to increase the function of BSEP mutants affecting BA transport activity has not been studied. BSEP ATP-binding sites having a strong similarity with those of CFTR and MDR3, we selected the p.T463I mutation, identified in a PFIC2 patient and located in the Walker-A motif of the first BSEP nucleotide binding domain (NBD1).…”

Potentiation of ABCA3 lipid transport function by ivacaftor and genistein

“…47,48 Furthermore, ivacaftor did not overcome impaired PC secretion activity in a TMD mutant of ABCB4. 49 Residue L1580 is not directly located in the ATP binding site, however its mutation to a proline most likely breaks the helix, in which it is located. This will affect the upstream H-loop, which is also implicated in NBD dimerization and ATP binding.…”