Human hydroxyindole-O-methyltransferase in pineal gland, retina and Y79 retinoblastoma cells.
Hydroxyindole-O-methyltransferase (HIOMT, EC 2.1.1.4) was studied in extracts of human pineal gland, retina and Y79 retinoblastoma cells. HIOMT enzyme activity and immunoreactive protein (approximately 42 kDa) were undetectable in the human retina; very low levels of HIOMT mRNA were detected using a highly sensitive RT-PCR/Southern blot method, as has been reported. Analysis of extracts of Y79 cells indicated that HIOMT enzyme activity, immunoreactivity (approximately 42 kDa) and mRNA (approximately 1.3 kb) were detectable at approximately 1/5-1/40 the levels found in the pineal gland. This unambiguously establishes that the HIOMT gene is expressed in Y79 cells. Kinetic analysis of Y79- and pineal-derived HIOMT indicates that the enzyme is generally similar in both tissues; one difference, however, is that substrate inhibition by N-acetylserotonin is greater with the Y79-derived enzyme. These studies show that Y79 cells represent a valid model to study the regulation of human HIOMT protein and mRNA; the differences detected may reflect the existence of tissue-specific regulatory mechanisms or differential patterns of expression of HIOMT isoforms.
Bernard
M
M
Section on Neuroendocrinology, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA.
Donohue
S J
SJ
Klein
D C
DC
D000121:Acetylserotonin O-Methyltransferase / Q000378:metabolism*; D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D000818:Animals; D001483:Base Sequence; D015342:DNA Probes; D004273:DNA, Neoplasm / Q000096:biosynthesis; D005134:Eye Neoplasms / Q000201:enzymology*; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000378:metabolism; D010870:Pineal Gland / Q000201:enzymology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000201:enzymology*; D012175:Retinoblastoma / Q000201:enzymology*; D012436:S-Adenosylmethionine / Q000378:metabolism; D014407:Tumor Cells, Cultured
D015342:DNA Probes; D004273:DNA, Neoplasm; D009419:Nerve Tissue Proteins; D012436:S-Adenosylmethionine; D000121:Acetylserotonin O-Methyltransferase