title: Normal human melanocytes exposed to chronic insulin and glucose supplementation undergo oncogenic changes and methyl group metabolism cellular redistribution.
abstract: Recent epidemiological studies have suggested a link between cancer and pathophysiological conditions associated with hyperinsulinemia. In this report, we address the possible role of insulin exposure in melanocyte transformation. To this aim, normal melanocytes were exposed to chronic insulin and glucose supplementation (twice the standard medium concentration) for at least 3 wk. After 3-wk treatment, melanocytes increased proliferation (doubling time: 2.7 vs. 5.6 days, P < 0.01). After 3-wk treatment or after 3-wk treatment followed by 4-wk reculture in standard medium, melanocytes were able to grow in soft agar colonies. Treated melanocytes had increased DNA content (+8%, P < 0.05), chromosomal aberrations, and modified oncoprotein profile: p-Akt expression increased (+32%, P < 0.01), Akt decreased, and c-Myc increased (+40%, P < 0.05). PP2A protein expression increased (+42, P < 0.05), while PP2A methylation decreased (-42%, P < 0.05), and PP2A activity was reduced (-27%, P < 0.05). PP2A transcription level was increased (ppp2r1a, PP2A subunit A, +44%, P < 0.05). Also, transcriptomic data revealed modifications in insr (insulin receptors, +10%, P < 0.05) and Il8 (inflammation protein, +99%, P < 0.01). Glycolysis was modified with increased transcription of Pgk1 and Hif1a (P < 0.05), decreased transcription of Pfkfb3 (P < 0.05), decreased activity of pyruvate kinase (P < 0.01), and decreased pyruvate cell content as assessed by (1)H-NMR spectroscopy. In addition, methyl group metabolism was altered with decreased global DNA methylation (-51%, P < 0.01), increased cytosolic protein methylation (+18%, P < 0.05), and consistent changes in methylated species on (1)H-NMR spectra. In conclusion, exposure to chronic insulin and glucose supplementation induces oncogenic changes and methyl group metabolism redistribution, which may be a biomarker of transformation.
authors.affiliation: Centre INRA de Clermont-Ferrand, 63122 Saint Genes Champanelle, France.
authors.forename: Daniel
authors.initials: D
authors.lastname: Morvan
authors.forename: Jean Marc
authors.initials: JM
authors.lastname: Steyaert
authors.forename: Laurent
authors.initials: L
authors.lastname: Schwartz
authors.forename: Maurice
authors.initials: M
authors.lastname: Israel
authors.forename: Aicha
authors.initials: A
authors.lastname: Demidem
mesh_terms: D015153:Blotting, Western; D002453:Cell Cycle / Q000187:drug effects; D002458:Cell Fractionation; D002471:Cell Transformation, Neoplastic / Q000187:drug effects*; D002648:Child; D002675:Child, Preschool; D003470:Culture Media; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005947:Glucose / Q000494:pharmacology*; D006019:Glycolysis / Q000187:drug effects; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007553:Isotope Labeling; D007621:Karyotyping; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D008544:Melanocytes / Q000187:drug effects*; D008745:Methylation; D011230:Precancerous Conditions / Q000139:chemically induced / Q000473:pathology; D054648:Protein Phosphatase 2 / Q000378:metabolism*; D011770:Pyruvate Kinase / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D013234:Stem Cells
chemical_list: D003470:Culture Media; D007004:Hypoglycemic Agents; D007328:Insulin; D004247:DNA; D011770:Pyruvate Kinase; D054648:Protein Phosphatase 2; D005947:Glucose