Disease relevance of UGT1A4

• Insect cells were co-infected with mixtures containing different combinations of recombinant baculoviruses encoding either UGT1A4 or 1A9Sol [1].

High impact information on UGT1A4

• UGT1A4 P24T and L48V exhibited reduced glucuronidation activities: beta-naphthylamine 30% and 50%, and dihydrotestosterone 50% and 0%, respectively [2].
• These data suggest that the UGT1A4 codon 24 and UGT2B7 codon 268 polymorphisms may be associated with altered rates glucuronidation and detoxification of NNAL in vivo [3].
• However, maternal liver UGT1A4 and UGT1A6 were dramatically elevated and maintained after birth, indicating that these proteins may play a critical role in maternal metabolism during lactation [4].
• Pharmacophore, two-dimensional (2D), and three-dimensional (3D) quantitative structure-activity relationship (QSAR) modeling techniques were used to develop and test models capable of rationalizing and predicting human UDP-glucuronosyltransferase 1A4 (UGT1A4) substrate selectivity and binding affinity (as K(m,app)) [5].
• Incubations containing PhIP as substrate formed direct PhIP-glucuronides in microsomes expressing UGT1A1, UGT1A4 and UGT1A9 but at levels averaging 53-fold lower than when N-hydroxy-PhIP was used as the substrate [6].

Biological context of UGT1A4

• In comparing rabbit and human, it is evident that the UGT1A4 and UGT1A6 gene clusters in rabbit have undergone gene duplication [7].
• The kinetics of imipramine N-glucuronidation in UGT1A4 Supersomes did not fit the Michaelis-Menten plot, showing a K(m) of >1 mM [8].
• UGT1A3 is 93% identical to UGT1A4 in primary amino acid sequence [9].
• Of the compounds screened as inhibitors, hecogenin, alone, was selective; significant inhibition was observed only for UGT1A4 (IC50 1.5 microM) [10].
• A similar strategy but using probes which correspond to the unique regions of human UDPGT-Br1 and human UDPGT-Br2 showed that the exon 1 of UGT1A and UGT1D encodes the unique region of human UDPGT-Br1, and human UDPGT-Br2 and is located 5.6 and 49 Kb, respectively, upstream of the 4 common exons [11].

Anatomical context of UGT1A4

• Apparent K(m) values for TAM N-glucuronidation by human liver microsomes and recombinant UGT1A4 were 35.8 and 32.4 microM, respectively [12].
• A third previously undefined glucuronide accounted for 31% of the total glucuronides formed from the UGT1A4 expressing microsomes [6].
• However, the UGT1A3 and UGT1A4 promoters exhibit low activity in the human embryonic kidney cell line HEK293, unless coexpressed with hepatocyte nuclear factor (HNF) 1alpha [13].
• The formation of AFQ N-glucuronidation by human liver, jejunum, and recombinant UGT1A4 microsomes was effectively inhibited by trifluoperazine, a known specific substrate for UGT1A4 [14].

Associations of UGT1A4 with chemical compounds

• None of the UGTs examined catalyzed the N-glucuronidation of S(-)-nicotine, R(+)-nicotine, and S(-)-cotinine, including UGT1A3 and UGT1A4, the only isoforms known to catalyze many substrates at a tertiary amine [15].
• Also, neither S(-)-nicotine or S(-)-cotinine affected enzyme inhibition of trifluoperazine, a UGT1A4 substrate [15].
• UGT1A4 Supersomes also catalyzed cotinine N-glucuronidation, but at one-tenth the rate of nicotine glucuronidation [16].
• Taken together, these data support a role for both UGT1A9 and UGT1A4 in the catalysis of nicotine and cotinine N-glucuronidation [16].
• The 4'-HPPH O-glucuronidation in pooled human liver microsomes was inhibited by beta-estradiol as a typical substrate for UGT1A1 (IC(50) = 21.1 microM) and imipramine as a typical substrate for UGT1A4 (IC(50) = 57.7 microM) [17].

Other interactions of UGT1A4

• In contrast, all UGT isoforms, except for UGT1A3 and UGT1A4, catalyzed O-glucuronidation of 4-HO-TAM [18].
• Both propofol, a UGT1A9 substrate, and imipramine, a UGT1A4 substrate, inhibited the glucuronidation of nicotine and cotinine by human liver microsomes [16].
• However, replacing the first 110 amino acids of UGT1A5, a region that may be involved in substrate binding, with the counterpart segment from UGT1A4 did not increase the 4-aminobiphenyl glucuronidation activity [19].
• Characterization of rabbit UDP-glucuronosyltransferase UGT1A7: tertiary amine glucuronidation is catalyzed by UGT1A7 and UGT1A4 [20].
• We directly sequenced polymerase chain reaction-amplified fragments of the UGT1A4 gene from 100 healthy adult Japanese volunteers and calculated their mutation frequency [21].

Analytical, diagnostic and therapeutic context of UGT1A4

• METHODS: HPLC was used to detect glucuronide conjugates in microsomes from UGT1A4-overexpressing HK293 cells [22].
• The Vmax/Km ratio for the UGT1A424Pro/48Val variant was significantly (P < or = 0.005) higher than that observed for the wild-type UGT1A4 isoform for both the trans and cis isomers of 4-OH-TAM after normalization for UGT1A4 expression by western blotting [22].
• The UGT1A4 wild-type cDNA was synthesized by RT-PCR using normal human liver total RNA [22].

References