Impact of uncoupling protein-2 overexpression on proinsulin processing.
Hyperproinsulinemia is observed in type 2 diabetic patients. We hypothesized that the induction of uncoupling protein-2 (UCP2) would impair processing of proinsulin to mature insulin and potentially contribute to hyperproinsulinemia, based on the evidence that hormone processing is an ATP-dependent process and UCP2 up-regulation can suppress cellular ATP production. UCP2 was overexpressed (UCP2-OE) by twofold in INS-1 cells by means of plasmid transfection. Although UCP2-OE reduced glucose-stimulated insulin secretion and cellular ATP content, no effects on proinsulin processing, as measured by western blotting, were observed. To increase the demand for insulin, we then cultured UCP2-OE and control INS-1 cells in medium containing 20 mM KCl for 24 h. High K(+) markedly reduced glucose-stimulated insulin secretion from control cells, indicating inability of cells to meet secretory demand. Independent of UCP2 expression, high K(+) reduced preproinsulin mRNA expression but had no effect on ATP content despite increasing ATP synthase expression. In UCP2-OE cells, high K(+)decreased total cellular insulin species content and increased the ratio of proinsulin to insulin, indicating an impairment of processing. We conclude that UCP2-OE can negatively impact proinsulin processing, possibly by ATP-dependent alteration of the granule environment or reduction of Ca(2+)availability, particularly when cells are chronically stimulated to secrete insulin.
Kashemsant
Narudee
N
Department of Biomedical Sciences, University of Prince Edward Island, 550 University Avenue, Charlottetown, Prince Edward Island, Canada C1A 4P3.
Chan
Catherine B
CB
D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D002460:Cell Line; D015870:Gene Expression; D005947:Glucose / Q000494:pharmacology; D015699:HIV Envelope Protein gp120 / Q000378:metabolism; D006801:Humans; D007473:Ion Channels / Q000235:genetics / Q000378:metabolism*; D024101:Mitochondrial Proteins / Q000235:genetics / Q000378:metabolism*; D009840:Oligomycins / Q000494:pharmacology; D011384:Proinsulin / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics; D000071246:Uncoupling Protein 2
D015699:HIV Envelope Protein gp120; D007473:Ion Channels; D024101:Mitochondrial Proteins; D009840:Oligomycins; D012333:RNA, Messenger; D011994:Recombinant Proteins; C098257:SPC3 peptide; C000604389:UCP2 protein, human; C000604391:Ucp2 protein, rat; D000071246:Uncoupling Protein 2; D000255:Adenosine Triphosphate; D011384:Proinsulin; D005947:Glucose