No abstract

Rad9 is conserved from yeast to humans and plays roles in DNA repair (homologous recombination repair, and base-pair excision repair) and cell cycle checkpoint controls. It has not previously been reported whether Rad9 is involved in DNA mismatch repair (MMR). In this study, we have demonstrated that both human and mouse Rad9 interacts physically with the MMR protein MLH1. Disruption of the interaction by a single-point mutation in Rad9 leads to significantly reduced MMR activity. This disruption does not affect S/M checkpoint control and the first round of G2/M checkpoint control, nor does it alter cell sensitivity to UV light, gamma rays or hydroxyurea. Our data indicate that Rad9 is an important factor in MMR and carries out its MMR function specifically through interaction with MLH1.

Summary Purpose:  Antiepileptic drugs (AEDs) are widely used not only in the treatment of epilepsy but also as treatments for psychiatric disorders. Pharmacoresistance of AEDs in the treatment of epilepsy and psychiatric disorders is a serious problem. Transport of antiepileptic drugs by P‐glycoprotein (Pgp, ABCB1, or MDR1), which is overexpressed in the blood–brain barrier, may be a mechanism for resistance of AEDs. For most AEDs, conflicting evidence precludes consensus on whether they are substrates of Pgp. The objective of this study was to evaluate whether analogs and metabolites of the AED carbamazepine are substrates of human Pgp. Methods:  Polarized cell lines MDCKII and LLC transfected with the human MDR1 gene were used in the bidirectional transport assay and concentration equilibrium transport assay. The expression of Pgp was detected by real‐time polymerase chain reaction (PCR) and immunofluorescent staining. Rhodamine‐123 uptake was also determined. Key Findings:  Pgp did not transport carbamazepine, but it did transport its active metabolite carbamazepine‐10,11‐epoxide. Pgp also pumped eslicarbazepine acetate and oxcarbazepine, as well as their active metabolite (S)‐licarbazepine. Transport of the drugs was in the order of ESL>OXC>S‐LC>CBZ‐E in concentration equilibrium conditions. The transport of these drugs was blocked by Pgp inhibitors tariquidar and verapamil. Significance:  All carbamazepine analogs or metabolites tested are Pgp substrates, except for carbamazepine. These data suggest that resistance to carbamazepine, oxcarbazepine, or eslicarbazepine acetate may be attributed to increased efflux function of Pgp because they or their active metabolites are Pgp substrates.