<i>O</i>-glycosylation of Sp1 and transcriptional regulation of the calmodulin gene by insulin and glucagon

American Journal of Physiology - Endocrinology and Metabolism - Tập 285 Số 3 - Trang E584-E591 - 2003
Gipsy Majumdar1, Ashley Harmon, Rosalind P. Candelaria, Antonio Martinez-Hernandez, Rajendra Raghow, Solomon S. Solomon
1Research Services, Veterans Affairs Medical Center, Memphis, TN 38104, USA.

Tóm tắt

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 × 10-5M). 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.

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Thông tin
Thông tin xuất bản

American Journal of Physiology - Endocrinology and Metabolism

Tập 285 Số 3

E584-E591

Thông tin tác giả