High glucose activates pituitary proopiomelanocortin gene expression: possible role of free radical-sensitive transcription factors.
BACKGROUND
Hyperglycemia is recognized as a metabolic stress, and indeed it is known to stimulate hypothalamo-pituitary-adrenal (HPA) axis, a representative anti-stress system, in patients with diabetes mellitus or in animal models of hyperglycemia. Thus, we tried to clarify the molecular mechanism of glucose-induced HPA axis activation.


METHODS
We studied the effect of high glucose on the transcriptional regulation of proopiomelanocortin (POMC) gene that encodes adrenocorticotropic hormone, a central mediator of HPA axis, using AtT20 corticotroph cell line in vitro.


RESULTS
We found that high glucose concentration (24 mM) significantly stimulated the 5'-promoter activity of POMC gene. The effect was promoter-specific, and was mimicked by nuclear factor-kappaB (NF-kappaB)- or AP1-responsive promoters but not by cAMP-responsive element or serum-response element-containing promoters. Furthermore, the stimulatory effect of high glucose on POMC gene was eliminated by NF-kappaB and AP1 inhibitors, suggesting the involvement of the transcriptional factors. The POMC 5'-promoter has the canonical NF-kappaB consensus sequence, and gel shift assay showed the binding of NF-kappaB to the element. Finally, the effect of high glucose was completely abolished by treatment with a radical quencher 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPOL).


CONCLUSIONS
Our data suggest that hyperglycemia activates POMC gene expression, at least partly, via NF-kappaB/AP1, and that high-glucose-induced free radical generation may mediate the activation of these transcription factors, which in turn stimulates the transcription of POMC gene.
Asaba
Koichi
K
Department of Endocrinology, Metabolism, and Nephrology, Kochi Medical School, Kochi University, Japan.
Iwasaki
Yasumasa
Y
Asai
Masato
M
Yoshida
Masanori
M
Nigawara
Takeshi
T
Kambayashi
Machiko
M
Hashimoto
Kozo
K
D000818:Animals; D000975:Antioxidants / Q000494:pharmacology; D001483:Base Sequence; D002460:Cell Line; D016384:Consensus Sequence; D003497:Cyclic N-Oxides / Q000494:pharmacology; D004247:DNA / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005609:Free Radicals / Q000378:metabolism*; D015870:Gene Expression / Q000187:drug effects*; D005947:Glucose / Q000008:administration & dosage* / Q000494:pharmacology; D008969:Molecular Sequence Data; D016328:NF-kappa B / Q000235:genetics / Q000378:metabolism; D010902:Pituitary Gland / Q000378:metabolism*; D011333:Pro-Opiomelanocortin / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000502:physiology; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D013113:Spin Labels; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014157:Transcription Factors / Q000502:physiology*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
D000975:Antioxidants; D003497:Cyclic N-Oxides; D005609:Free Radicals; D016328:NF-kappa B; D013113:Spin Labels; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D011333:Pro-Opiomelanocortin; D004247:DNA; D005947:Glucose; C001803:tempol