Abstract
Histamine N-methyltransferase (HNMT) catalyzes a major pathway in histamine metabolism. Levels of HNMT activity in humans are regulated by inheritance. We set out to study the molecular basis for this genetic regulation. Northern blot analysis showed that HNMT is highly expressed in the kidney, so we determined levels of enzyme activity and thermal stability in 127 human renal biopsy samples. DNA was isolated from 12 kidney samples with widely different HNMT phenotypes, and exons of the HNMT gene were amplified with the polymerase chain reaction. In these 12 samples, we observed a C314T transition that resulted in a Thr105Ile change in encoded amino acid, as well as an A939G transition within the 3′-untranslated region. All remaining renal biopsy samples then were genotyped for these two variant sequences. Frequencies of the alleles encoding Thr105 and Ile105 in the 114 samples studied were 0.90 and 0.10, respectively, whereas frequencies for the nucleotide A939 and G alleles were 0.79 and 0.21, respectively. Kidney samples with the allele encoding Ile105 had significantly lower levels of HNMT activity and thermal stability than did those with the allele that encoded Thr105. These observations were confirmed by transient expression in COS-1 cells of constructs that contained all four alleles for these two polymorphisms. COS-1 cells transfected with the Ile105 allele had significantly lower HNMT activity and immunoreactive HNMT protein than did those transfected with the Thr105 allele. These observations will make it possible to test the hypothesis that genetic polymorphisms for HNMT may play a role in the pathophysiology of human disease.
Footnotes
- Received September 16, 1997.
- Accepted January 7, 1998.
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Send reprint requests to: Dr. Richard Weinshilboum, Department of Pharmacology, Mayo Medical School, Mayo Clinic, Mayo Foundation, 200 First Street S.W., Rochester, MN 55905. E-mail:weinshilboum.richard{at}mayo.edu
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↵1 Current affiliation: Department of Drug Metabolism, Schering-Plough Research Institute, Kenilworth, NJ 07033.
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This work was supported in part by National Institutes of Health Grants RO1-GM28157 (R.M.W.) and RO1-GM35720 (R.M.W.), by a supplement to Grant RO1-GM35720 supported by the Office of Research on Women’s Health (R.M.W.), and by a National Research Scientist Award (National Institutes of Health) Individual Postdoctoral Fellowship (R.B.R.).
- The American Society for Pharmacology and Experimental Therapeutics
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