Mechanism of the lack of induction of UDP-glucuronosyltransferase activity in Gunn rats by 3-methylcholanthrene. Identification of a truncated enzyme.
Gunn rats lack UDP-glucuronosyltransferase (UDPGT) activity toward bilirubin. 4-Nitrophenol glucuronidation is mediated by several UDPGT isoforms that are distinct from bilirubin-UDPGT, one of which is induced after 3-methylcholanthrene (3-MC) administration in normal, but not in Gunn rats. In normal rats, 3-MC-inducible UDPGT mRNA concentration increased 15-fold in the liver and 3-fold in kidney after 3-MC (140 mg/kg) administration. Concentration of this mRNA is much lower in Gunn rat liver and kidney compared to normal. However, this mRNA was normally induced after 3-MC administration. By RNA blot hybridization, the mRNA in Gunn rat liver and kidney appeared to be of normal size. Nuclear run-on studies showed that the transcription rate for 3-MC-inducible UDPGT was 3-fold higher in Gunn rat liver and kidney than in normal and increased 3- to 5-fold after 3-MC administration. Immunotransblot studies revealed an Mr = 56,000 3-MC-inducible UDPGT in liver and kidney of normal, but not in Gunn rats. However, a new immunoreactive UDPGT band (Mr = 43,000) was present in Gunn, but not in normal rats. Cell-free translation of kidney mRNA from 3-MC-treated Gunn rats showed that the Mr = 43,000 UDPGT is synthesized as an Mr = 45,000 protein. Prior hybridization of the mRNA with an isoform-specific oligonucleotide spanning the initiation codon abolishes synthesis of this protein. These results suggest that a sequence abnormality in the 3-MC-inducible UDPGT mRNA in Gunn rats results in reduced mRNA concentration and synthesis of a truncated, enzymically inactive UDPGT.
elAwady
M
M
Department of Medicine, Albert Einstein College of Medicine, Bronx, New York 10461.
Chowdhury
J R
JR
Kesari
K
K
van Es
H
H
Jansen
P L
PL
Lederstein
M
M
Arias
I M
IM
Chowdhury
N R
NR
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism; D004790:Enzyme Induction; D014453:Glucuronosyltransferase / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D007668:Kidney / Q000201:enzymology*; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D008748:Methylcholanthrene / Q000494:pharmacology*; D008970:Molecular Weight; D014176:Protein Biosynthesis; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011911:Rats, Gunn / Q000378:metabolism*; D011919:Rats, Inbred Strains / Q000378:metabolism; D011922:Rats, Mutant Strains / Q000378:metabolism*; D013045:Species Specificity; D014158:Transcription, Genetic
D012333:RNA, Messenger; D008748:Methylcholanthrene; D014453:Glucuronosyltransferase