Pancreatic beta-cell-type-specific transcription of the insulin gene is mediated by basic helix-loop-helix DNA-binding proteins.

Cordle, Susan R.; Henderson, Eva; Masuoka, Howard C.; Weil, P A; Stein, Roland

doi:10.1128/mcb.11.3.1734

Cited by 144 publications

(115 citation statements)

References 42 publications

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“…The two elements contain identical sequences that can function as binding sites for bHLH proteins. In ␤TC3 cells, these sites bind a heterodimer of two bHLH proteins, a ubiquitous class A bHLH protein such as E47 (31)(32)(33)(34)44) and the neuroendocrine-specific class B bHLH protein neuroD1/BETA2 (35). In the developing pancreas, neurogenin3 may replace neuroD1/BETA2 in the heterodimer binding to this sequence.…”

Section: Discussionmentioning

confidence: 99%

Autoregulation and Maturity Onset Diabetes of the Young Transcription Factors Control the Human PAX4 Promoter

Smith¹,

Watada²,

Scheel³

et al. 2000

Journal of Biological Chemistry

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During pancreatic development, the paired homeodomain transcription factor PAX4 is required for the differentiation of the insulin-producing beta cells and somatostatin-producing delta cells. To establish the position of PAX4 in the hierarchy of factors controlling islet cell development, we examined the control of the human PAX4 gene promoter. In both cell lines and transgenic animals, a 4.9-kilobase pair region directly upstream of the human PAX4 gene transcriptional start site acts as a potent pancreas-specific promoter. Deletion mapping experiments demonstrate that a 118-base pair region lying approximately 1.9 kilobase pairs upstream of the transcription start site is both necessary and sufficient to direct pancreas-specific expression. Serial deletions through this region reveal the presence of positive elements that bind several pancreatic transcription factors as follows: the POU homeodomain factor HNF1␣, the orphan nuclear receptor HNF4␣, the homeodomain factor PDX1, and a heterodimer composed of two basic helix-loop-helix factors. Interestingly, mutations in the genes encoding four of these factors cause a dominantly inherited form of human diabetes called Maturity Onset Diabetes of the Young. In addition, PAX4 itself has at least two high affinity binding sites within the promoter through which it exerts a strong negative autoregulatory effect. Together, these results suggest a model in which PAX4 expression is activated during pancreatic development by a combination of pancreas-specific factors but is then switched off once PAX4 protein reaches sufficient levels.Organogenesis of the mammalian pancreas and its differentiation into discrete populations of endocrine and exocrine cells depends on the tightly regulated temporal and spatial expression of an array of transcription factors (for reviews see Refs. 1-3). Some of these factors, such as HNF3␤ (4, 5), PDX1 (6, 7), and HLXb9 (8, 9), are involved in the formation and outgrowth of the dorsal and ventral pancreatic buds. Within the forming pancreas, the basic helix-loop-helix transcription factor neurogenin3 functions as a pro-endocrine gene, initiating the program of endocrine differentiation in selected cells (10, 11). The complete differentiation and maturation of the endocrine cells requires additional factors, including neuroD1/BETA2 (12), NKX2.2 (13), ISL1 (14), and PAX6 (2, 15).Once neurogenin3 expression sets a progenitor cell on a course of endocrine differentiation, additional factors are necessary to determine which of the four endocrine cell types it will become. One of these islet cell-type determination factors is the paired homeodomain transcription factor PAX4. PAX4 functions as a potent transcriptional repressor and is expressed only transiently in the fetal pancreas, peaking during the period of beta and delta cell differentiation (16). Mice with a targeted disruption of the pax4 gene have a marked decrease in beta and delta cells with a commensurate increase in alpha cells (17), suggesting that PAX4 functions by repressing the alpha...

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Section: Discussionmentioning

confidence: 99%

Autoregulation and Maturity Onset Diabetes of the Young Transcription Factors Control the Human PAX4 Promoter

Smith¹,

Watada²,

Scheel³

et al. 2000

Journal of Biological Chemistry

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“…An inhibitory role for Id has been postulated in skeletal muscle, B cell maturation, and neural development based on tissue culture models and genetic studies in Drosophila (Benezra et al, 1990;Pongubala and Atchinson, 1991;Cordle et al, 1991;Ellis et al, 1990;Garrell and Modolell, 1990). The ability to follow both the temporal and spatial patterns of gene transcription during embryogenesis provides a descriptive picture for which subsequent functional experiments can be designed.…”

Section: Id and The Hlh Myogenic Factors Are Not Coexpressedmentioning

confidence: 99%

Id expression during mouse development: A role in morphogenesis

Wang

Benezra

Sassoon

1992

Developmental Dynamics

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We have characterized the spatial and temporal pattern of Id transcription during mouse embryogenesis. The Id gene encodes a helix-loophelix (HLH) protein which can heterodimerize with the ubiquitously expressed HLH protein products of the E2A gene, and prevent them from binding DNA either alone or as a heterodimer with tissue specific HLH transcription factors such as the muscle determination gene, MyoDl (Benezra et al., 1990 Cell 61:49-59). SinceId has been shown to be down-regulated during induced differentiation in several cell lines, it has been postulated that Id plays a general inhibitory role in cell differentiation (Benezra et al., 1990). In situ analysis of Id mRNA expression in the mouse embryo was performed in order to determine whether the pattern of Id expression is consistent with this postulate. A detailed study throughout the entirety of mouse postimplantation development reveals that Id is expressed upon gastrulation at very high levels in almost all regions of the mouse embryo and expression declines as embryogenesis proceeds. In skeletal muscle, in which the inhibitory action of Id has been established in tissue culture models (Benezra et al., 19901, Id and the HLH myogenic factors are expressed in a mutually exclusive manner suggesting that myogenic precursors do not express both types of HLH gene products. In addition, Id colocalizes both spatially and temporally with Hox-7.1, a murine homeobox gene which is associated with regions of high cell proliferation and positional fate assignment. 0 1992 Wiley-Liss, Inc.

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“…Alternatively, proteins interfering with positive regulators may facilitate the down-regulation of the insulin gene (29). Beta cells exposed to high glucose levels have increased gene expression of Id-1 and Id-3 (30) and up-regulated CCAAT/enhancerbinding protein/␤ levels (31), all of which can negatively affect insulin gene expression (31,32). This inhibition is likely due to their interference with E47 homodimer or heterodimer formation (29).…”

Section: Western and Northern Analyses Formentioning

confidence: 99%

Oxidative Stress-mediated, Post-translational Loss of MafA Protein as a Contributing Mechanism to Loss of Insulin Gene Expression in Glucotoxic Beta Cells

Harmon

Stein

Robertson

2005

Journal of Biological Chemistry

213

166

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After the onset of type 2 diabetes, chronic hyperglycemia causes glucotoxic changes in many tissues (1, 2). Glucose toxicity in the pancreatic islet beta cell secondarily leads to further defects in beta cell function, including decreases in insulin reporter activity, gene expression, content, and secretion (3). Antioxidants have been shown to prevent these adverse changes in experimental models (4, 5). We previously observed that loss of insulin gene expression is accompanied by decreased binding to the promoter region of two important transcription factors, PDX-1 1 (STF-1, IDX-1, IPF-1) and RIPE-3b1 activator (6 -8). PDX-1 is required for pancreatic development and is a key regulator of insulin gene expression. Mutations within the RIPE-3b1/C1 element of the insulin promoter markedly reduce glucose-responsive insulin gene expression (7). We also reported that loss of RIPE-3b1 binding precedes the loss of PDX-1 binding to the insulin promoter as glucotoxicity develops (8). The chronology of these losses is likely to be important in light of a recent report that RIPE-3b1/MafA directly activates PDX-1 transcription (9).The work in this study features the use of HIT-T15 cells, a glucose-responsive beta cell line that has proven over the past decade to reproduce the molecular changes in gene expression that are caused by glucose toxicity in vivo in animal models. Since isolated islets cannot be chronically cultured to study the adverse effects of high glucose concentrations over many months, this cell line is a valuable surrogate. In our previous work, reconstitution of late passage glucotoxic HIT-T15 cells by transient transfection with PDX-1 partially restored insulin promoter activity (8). Since RIPE-3b1 had not yet been cloned, we were unable to extend our studies with this transcription factor but hypothesized that reconstitution of the cells with both PDX-1 and RIPE-3b1 activator would lead to greater recovery of insulin promoter activity. With the recent cloning and identification of RIPE-3b1 activator as MafA (10 -12), we have been able to perform new studies to examine 1) whether levels of MafA mRNA and protein are decreased in glucotoxic beta cells; 2) the mechanism of MafA protein degradation; 3) whether the antioxidant, N-acetylcysteine, can prevent glucotoxicity-induced loss of MafA protein and binding to the insulin promoter; and 4) whether overexpression of MafA and PDX-1 together can restore insulin promoter activity and mRNA levels more fully than PDX-1 alone. MATERIALS AND METHODSCell Culture-HIT-T15 cells were maintained in RPMI 1640 media containing 10% fetal bovine serum and 11.1 mM glucose as described previously (13). Cells were categorized as early passage (p71-75) or late passage (p123-128), with each passage occurring weekly. Chronic culturing of HIT-T15 cells with N-acetyl-L-cysteine (Sigma; 0.5, 1, or 5 mM) added to the media was begun at p70.

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Pancreatic beta-cell-type-specific transcription of the insulin gene is mediated by basic helix-loop-helix DNA-binding proteins.

Cited by 144 publications

References 42 publications

Autoregulation and Maturity Onset Diabetes of the Young Transcription Factors Control the Human PAX4 Promoter

Autoregulation and Maturity Onset Diabetes of the Young Transcription Factors Control the Human PAX4 Promoter

Id expression during mouse development: A role in morphogenesis

Oxidative Stress-mediated, Post-translational Loss of MafA Protein as a Contributing Mechanism to Loss of Insulin Gene Expression in Glucotoxic Beta Cells

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