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 1H-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 1H-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.