O-glycosylation of Sp1 and transcriptional regulation of the calmodulin gene by insulin and glucagon

Gipsy Majumdar, Ashley Harmon, Rosalind Candelaria, Antonio Martinez-Hernandez, Rajendra Raghow, Solomon S. Solomon

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Abstract

Both insulin and glucagon stimulate steady-state levels of Sp1 transcription factor, but only insulin stimulates transcription of the calmodulin (CaM) gene in liver. Because O-glycosylation of Sp1 by O-linked N-acetylglucosamine (O-GlcNAc) is thought to regulate its ability to activate transcription, we assayed the levels of Sp1 with anti-Sp1 and anti-O-GlcNAc antibodies in Western blots by use of extracts of H-411E liver cells treated with insulin (10,000 μU/ml) or glucagon (1.5 × 10-5 M). We also assessed subcellular localization of the native and glycosylated Sp1 in H411E cells treated with either hormone in the presence of deoxynorleucine (DON, an indirect inhibitor of O-glycosylation) or streptozotocin (STZ, an indirect stimulator of O-glycosylation). Insulin stimulated both total and O-GlcNAc-modified Sp1 primarily in the nucleus and induced CaM gene transcription (P < 0.0001). In contrast, glucagon promoted accumulation of Sp1 in the cytoplasm but not the nucleus, without significantly stimulating (P = not significant) either its O-glycosylation or transcription of the CaM gene. DON inhibited O-glycosylation of Sp1 and its ability to migrate to the nucleus and transactivate CaM gene transcription. In contrast, cotreatment of cells with STZ and glucagon enhanced O-glycosylation of Sp1, promoting its migration to the nucleus and resulting in increased CaM gene transcription. Thus O-glycosylation of Sp1 by insulin, but not glucagon, apparently enhances its (Sp1) nuclear recruitment and results in activation of CaM gene transcription.

Original languageEnglish (US)
JournalAmerican Journal of Physiology - Endocrinology and Metabolism
Volume285
Issue number3 48-3
StatePublished - Sep 1 2003

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Calmodulin
Glucagon
Glycosylation
Insulin
Genes
Sp1 Transcription Factor
Acetylglucosamine
Liver
Streptozocin
Transcriptional Activation
Cytoplasm
Western Blotting
Hormones
Antibodies

All Science Journal Classification (ASJC) codes

  • Endocrinology, Diabetes and Metabolism
  • Physiology
  • Physiology (medical)

Cite this

O-glycosylation of Sp1 and transcriptional regulation of the calmodulin gene by insulin and glucagon. / Majumdar, Gipsy; Harmon, Ashley; Candelaria, Rosalind; Martinez-Hernandez, Antonio; Raghow, Rajendra; Solomon, Solomon S.

In: American Journal of Physiology - Endocrinology and Metabolism, Vol. 285, No. 3 48-3, 01.09.2003.

Research output: Contribution to journalArticle

Majumdar, Gipsy ; Harmon, Ashley ; Candelaria, Rosalind ; Martinez-Hernandez, Antonio ; Raghow, Rajendra ; Solomon, Solomon S. / O-glycosylation of Sp1 and transcriptional regulation of the calmodulin gene by insulin and glucagon. In: American Journal of Physiology - Endocrinology and Metabolism. 2003 ; Vol. 285, No. 3 48-3.
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