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Examining How the MAFB Transcription Factor Affects Islet β-Cell Function Postnatally.
Cyphert HA, Walker EM, Hang Y, Dhawan S, Haliyur R, Bonatakis L, Avrahami D, Brissova M, Kaestner KH, Bhushan A, Powers AC, Stein R
(2019) Diabetes 68: 337-348
MeSH Terms: Animals, Cells, Cultured, Chromatin Immunoprecipitation, Chromosomes, Artificial, Bacterial, DNA Methylation, Female, Humans, In Vitro Techniques, Insulin-Secreting Cells, Maf Transcription Factors, Large, MafB Transcription Factor, Mice, Mice, Transgenic, Pregnancy, Tryptophan Hydroxylase
Show Abstract · Added January 8, 2019
The sustained expression of the MAFB transcription factor in human islet β-cells represents a distinct difference in mice. Moreover, mRNA expression of closely related and islet β-cell-enriched MAFA does not peak in humans until after 9 years of age. We show that the MAFA protein also is weakly produced within the juvenile human islet β-cell population and that expression is postnatally restricted in mouse β-cells by de novo DNA methylation. To gain insight into how MAFB affects human β-cells, we developed a mouse model to ectopically express in adult mouse β-cells using transcriptional control sequences. Coexpression of MafB with MafA had no overt impact on mouse β-cells, suggesting that the human adult β-cell MAFA/MAFB heterodimer is functionally equivalent to the mouse MafA homodimer. However, MafB alone was unable to rescue the islet β-cell defects in a mouse mutant lacking MafA in β-cells. Of note, transgenic production of MafB in β-cells elevated tryptophan hydroxylase 1 mRNA production during pregnancy, which drives the serotonin biosynthesis critical for adaptive maternal β-cell responses. Together, these studies provide novel insight into the role of MAFB in human islet β-cells.
© 2018 by the American Diabetes Association.
1 Communities
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15 MeSH Terms
G6PC2 Modulates the Effects of Dexamethasone on Fasting Blood Glucose and Glucose Tolerance.
Boortz KA, Syring KE, Lee RA, Dai C, Oeser JK, McGuinness OP, Wang JC, O'Brien RM
(2016) Endocrinology 157: 4133-4145
MeSH Terms: Animals, Blood Glucose, Cell Line, Cell Line, Tumor, Cricetinae, Dexamethasone, Fasting, Glucose-6-Phosphatase, Maf Transcription Factors, Large, Mice, Mice, Inbred C57BL, Mice, Knockout, Polymorphism, Single Nucleotide, Promoter Regions, Genetic, Rats, Receptors, Glucocorticoid
Show Abstract · Added March 14, 2018
The glucose-6-phosphatase catalytic subunit 2 (G6PC2) gene encodes an islet-specific glucose-6-phosphatase catalytic subunit. G6PC2 forms a substrate cycle with glucokinase that determines the glucose sensitivity of insulin secretion. Consequently, deletion of G6pc2 lowers fasting blood glucose (FBG) without affecting fasting plasma insulin. Although chronic elevation of FBG is detrimental to health, glucocorticoids induce G6PC2 expression, suggesting that G6PC2 evolved to transiently modulate FBG under conditions of glucocorticoid-related stress. We show, using competition and mutagenesis experiments, that the synthetic glucocorticoid dexamethasone (Dex) induces G6PC2 promoter activity through a mechanism involving displacement of the islet-enriched transcription factor MafA by the glucocorticoid receptor. The induction of G6PC2 promoter activity by Dex is modulated by a single nucleotide polymorphism, previously linked to altered FBG in humans, that affects FOXA2 binding. A 5-day repeated injection paradigm was used to examine the chronic effect of Dex on FBG and glucose tolerance in wild-type (WT) and G6pc2 knockout mice. Acute Dex treatment only induces G6pc2 expression in 129SvEv but not C57BL/6J mice, but this chronic treatment induced G6pc2 expression in both. In 6-hour fasted C57BL/6J WT mice, Dex treatment lowered FBG and improved glucose tolerance, with G6pc2 deletion exacerbating the decrease in FBG and enhancing the improvement in glucose tolerance. In contrast, in 24-hour fasted C57BL/6J WT mice, Dex treatment raised FBG but still improved glucose tolerance, with G6pc2 deletion limiting the increase in FBG and enhancing the improvement in glucose tolerance. These observations demonstrate that G6pc2 modulates the complex effects of Dex on both FBG and glucose tolerance.
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16 MeSH Terms
Lack of Prox1 Downregulation Disrupts the Expansion and Maturation of Postnatal Murine β-Cells.
Paul L, Walker EM, Drosos Y, Cyphert HA, Neale G, Stein R, South J, Grosveld G, Herrera PL, Sosa-Pineda B
(2016) Diabetes 65: 687-98
MeSH Terms: Animals, Animals, Newborn, Cell Differentiation, Cell Line, Cell Proliferation, Chromatin Immunoprecipitation, Computer Simulation, Down-Regulation, Enzyme-Linked Immunosorbent Assay, Gene Expression Profiling, Gene Knockdown Techniques, Glucose Tolerance Test, Homeodomain Proteins, Humans, Hyperglycemia, Insulin, Insulin-Secreting Cells, Maf Transcription Factors, Large, Mice, Mice, Transgenic, RNA, Messenger, Real-Time Polymerase Chain Reaction, Tumor Suppressor Proteins
Show Abstract · Added September 19, 2016
Transcription factor expression fluctuates during β-cell ontogeny, and disruptions in this pattern can affect the development or function of those cells. Here we uncovered that murine endocrine pancreatic progenitors express high levels of the homeodomain transcription factor Prox1, whereas both immature and mature β-cells scarcely express this protein. We also investigated if sustained Prox1 expression is incompatible with β-cell development or maintenance using transgenic mouse approaches. We discovered that Prox1 upregulation in mature β-cells has no functional consequences; in contrast, Prox1 overexpression in immature β-cells promotes acute fasting hyperglycemia. Using a combination of immunostaining and quantitative and comparative gene expression analyses, we determined that Prox1 upregulation reduces proliferation, impairs maturation, and enables apoptosis in postnatal β-cells. Also, we uncovered substantial deficiency in β-cells that overexpress Prox1 of the key regulator of β-cell maturation MafA, several MafA downstream targets required for glucose-stimulated insulin secretion, and genes encoding important components of FGF signaling. Moreover, knocking down PROX1 in human EndoC-βH1 β-cells caused increased expression of many of these same gene products. These and other results in our study indicate that reducing the expression of Prox1 is beneficial for the expansion and maturation of postnatal β-cells.
© 2016 by the American Diabetes Association. Readers may use this article as long as the work is properly cited, the use is educational and not for profit, and the work is not altered.
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23 MeSH Terms
Preserving Mafa expression in diabetic islet β-cells improves glycemic control in vivo.
Matsuoka TA, Kaneto H, Kawashima S, Miyatsuka T, Tochino Y, Yoshikawa A, Imagawa A, Miyazaki J, Gannon M, Stein R, Shimomura I
(2015) J Biol Chem 290: 7647-57
MeSH Terms: Animals, Base Sequence, Blood Glucose, DNA Primers, Diabetes Mellitus, Experimental, Humans, Islets of Langerhans, Maf Transcription Factors, Large, Mice, Mice, Inbred C57BL, Real-Time Polymerase Chain Reaction
Show Abstract · Added September 28, 2015
The murine Mafa transcription factor is a key regulator of postnatal islet β-cell activity, affecting insulin transcription, insulin secretion, and β-cell mass. Human MAFA expression is also markedly decreased in islet β-cells of type 2 diabetes mellitus (T2DM) patients. Moreover, levels are profoundly reduced in db/db islet β-cells, a mouse model of T2DM. To examine the significance of this key islet β-cell-enriched protein to glycemic control under diabetic conditions, we generated transgenic mice that conditionally and specifically produced Mafa in db/db islet β-cells. Sustained expression of Mafa resulted in significantly lower plasma glucose levels, higher plasma insulin, and augmented islet β-cell mass. In addition, there was increased expression of insulin, Slc2a2, and newly identified Mafa-regulated genes involved in reducing β-cell stress, like Gsta1 and Gckr. Importantly, the levels of human GSTA1 were also compromised in T2DM islets. Collectively, these results illustrate how consequential the reduction in Mafa activity is to islet β-cell function under pathophysiological conditions.
© 2015 by The American Society for Biochemistry and Molecular Biology, Inc.
1 Communities
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11 MeSH Terms
The MafA transcription factor becomes essential to islet β-cells soon after birth.
Hang Y, Yamamoto T, Benninger RK, Brissova M, Guo M, Bush W, Piston DW, Powers AC, Magnuson M, Thurmond DC, Stein R
(2014) Diabetes 63: 1994-2005
MeSH Terms: Animals, Cell Differentiation, Cell Proliferation, Gene Expression Regulation, Developmental, Glucose Tolerance Test, Immunohistochemistry, Insulin, Insulin Secretion, Insulin-Secreting Cells, Maf Transcription Factors, Large, Mice, RNA, Messenger, Real-Time Polymerase Chain Reaction
Show Abstract · Added March 10, 2014
The large Maf transcription factors, MafA and MafB, are expressed with distinct spatial-temporal patterns in rodent islet cells. Analysis of Mafa(-/-) and pancreas-specific Mafa(∆panc) deletion mutant mice demonstrated a primary role for MafA in adult β-cell activity, different from the embryonic importance of MafB. Our interests here were to precisely define when MafA became functionally significant to β-cells, to determine how this was affected by the brief period of postnatal MafB production, and to identify genes regulated by MafA during this period. We found that islet cell organization, β-cell mass, and β-cell function were influenced by 3 weeks of age in Mafa(Δpanc) mice and compromised earlier in Mafa(Δpanc);Mafb(+/-) mice. A combination of genome-wide microarray profiling, electron microscopy, and metabolic assays were used to reveal mechanisms of MafA control. For example, β-cell replication was produced by actions on cyclin D2 regulation, while effects on granule docking affected first-phase insulin secretion. Moreover, notable differences in the genes regulated by embryonic MafB and postnatal MafA gene expression were found. These results not only clearly define why MafA is an essential transcriptional regulator of islet β-cells, but also why cell maturation involves coordinated actions with MafB.
© 2014 by the American Diabetes Association.
1 Communities
4 Members
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13 MeSH Terms
PDX1 in ducts is not required for postnatal formation of β-cells but is necessary for their subsequent maturation.
Guo L, Inada A, Aguayo-Mazzucato C, Hollister-Lock J, Fujitani Y, Weir GC, Wright CV, Sharma A, Bonner-Weir S
(2013) Diabetes 62: 3459-68
MeSH Terms: Animals, Blood Glucose, Cell Growth Processes, Cell Survival, Cells, Cultured, Diabetes Mellitus, Experimental, Gene Expression Regulation, Developmental, Homeodomain Proteins, Insulin, Insulin Secretion, Insulin-Secreting Cells, Maf Transcription Factors, Large, Mice, Mice, Transgenic, Trans-Activators
Show Abstract · Added March 7, 2014
Pancreatic duodenal homeobox-1 (Pdx1), a transcription factor required for pancreatic development and maintenance of β-cell function, was assessed for a possible role in postnatal β-cell formation from progenitors in the pancreatic ducts by selectively deleting Pdx1 from the ducts. Carbonic anhydrase II (CAII)(Cre);Pdx1(Fl) mice were euglycemic for the first 2 postnatal weeks but showed moderate hyperglycemia from 3 to 7 weeks of age. By 10 weeks, they had near-normal morning fed glucose levels but showed severely impaired glucose tolerance and insulin secretion. Yet the loss of Pdx1 did not result in decreased islet and β-cell mass at 4 and 10 weeks of age. Within the same pancreas, there was a mixed population of islets, with PDX1 and MAFA protein expression normal in some cells and severely diminished in others. Even at 10 weeks, islets expressed immaturity markers. Thus, we conclude that Pdx1 is not necessary for the postnatal formation of β-cells but is essential for their full maturation to glucose-responsive β-cells.
1 Communities
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15 MeSH Terms
Nkx6.1 controls a gene regulatory network required for establishing and maintaining pancreatic Beta cell identity.
Schaffer AE, Taylor BL, Benthuysen JR, Liu J, Thorel F, Yuan W, Jiao Y, Kaestner KH, Herrera PL, Magnuson MA, May CL, Sander M
(2013) PLoS Genet 9: e1003274
MeSH Terms: Animals, Cell Differentiation, Cell Lineage, Cell- and Tissue-Based Therapy, Endocrine Cells, Gene Expression Regulation, Developmental, Gene Regulatory Networks, Homeodomain Proteins, Humans, Insulin, Insulin Secretion, Insulin-Secreting Cells, Maf Transcription Factors, Large, Mice, Pancreas, Stem Cells, Trans-Activators, Transcription Factors
Show Abstract · Added November 26, 2013
All pancreatic endocrine cell types arise from a common endocrine precursor cell population, yet the molecular mechanisms that establish and maintain the unique gene expression programs of each endocrine cell lineage have remained largely elusive. Such knowledge would improve our ability to correctly program or reprogram cells to adopt specific endocrine fates. Here, we show that the transcription factor Nkx6.1 is both necessary and sufficient to specify insulin-producing beta cells. Heritable expression of Nkx6.1 in endocrine precursors of mice is sufficient to respecify non-beta endocrine precursors towards the beta cell lineage, while endocrine precursor- or beta cell-specific inactivation of Nkx6.1 converts beta cells to alternative endocrine lineages. Remaining insulin(+) cells in conditional Nkx6.1 mutants fail to express the beta cell transcription factors Pdx1 and MafA and ectopically express genes found in non-beta endocrine cells. By showing that Nkx6.1 binds to and represses the alpha cell determinant Arx, we identify Arx as a direct target of Nkx6.1. Moreover, we demonstrate that Nkx6.1 and the Arx activator Isl1 regulate Arx transcription antagonistically, thus establishing competition between Isl1 and Nkx6.1 as a critical mechanism for determining alpha versus beta cell identity. Our findings establish Nkx6.1 as a beta cell programming factor and demonstrate that repression of alternative lineage programs is a fundamental principle by which beta cells are specified and maintained. Given the lack of Nkx6.1 expression and aberrant activation of non-beta endocrine hormones in human embryonic stem cell (hESC)-derived insulin(+) cells, our study has significant implications for developing cell replacement therapies.
2 Communities
1 Members
0 Resources
18 MeSH Terms
Characterization of an apparently novel β-cell line-enriched 80-88 kDa transcriptional activator of the MafA and Pdx1 genes.
Hunter CS, Stein R
(2013) J Biol Chem 288: 3795-803
MeSH Terms: Animals, Cell Line, Gene Expression Regulation, Homeodomain Proteins, Insulin-Secreting Cells, Maf Transcription Factors, Large, Mice, Response Elements, Trans-Activators
Show Abstract · Added March 7, 2014
MafA and Pdx1 represent critical transcriptional regulators required for the maintenance of pancreatic islet β-cell function. The in vivo β-cell-enriched expression pattern of these genes is principally directed by islet transcription factors binding within conserved Region 3 (base pairs (bp) -8118/-7750) of MafA and Area II (bp -2153/-1923) of the Pdx1 gene. Comprehensive mutational analysis of conserved MafA Region 3 revealed two new β-cell line-specific cis-activation elements, termed Site 4 (bp -7997 to -7988) and Site 12 (bp -7835 to -7826). Gel mobility and antibody super-shift analysis identified Pdx1 as the Site 4 binding factor, while an 80-88 kilodalton (kDa) β-cell line-enriched protein complex bound Site 12 and similar aligned nucleotides within Pdx1 Area II. The 80-88 kDa activator was also found in adult mouse islet extract. Strikingly, the molecular weight, DNA binding, and antibody recognition properties of this activator were unique when compared with all other key islet transcription factors tested, including Prox1 (83 kDa), Hnf1α (67 kDa), FoxA2 (48 kDa), MafA (46 kDa), Isl1 (44 kDa), Pdx1 (42 kDa), and Nkx2.2 (30 kDa). Collectively, these data define an apparently novel MafA Region 3 and Pdx1 Area II activator contributing to expression in β-cells.
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9 MeSH Terms
Hnf1α (MODY3) regulates β-cell-enriched MafA transcription factor expression.
Hunter CS, Maestro MA, Raum JC, Guo M, Thompson FH, Ferrer J, Stein R
(2011) Mol Endocrinol 25: 339-47
MeSH Terms: Animals, Animals, Genetically Modified, Blotting, Western, Chromatin Immunoprecipitation, DNA-Binding Proteins, Diabetes Mellitus, Type 2, Electrophoretic Mobility Shift Assay, Gene Expression, Hepatocyte Nuclear Factor 1-alpha, Humans, Insulin-Secreting Cells, Maf Transcription Factors, Large, Mice, Promoter Regions, Genetic, Regulatory Sequences, Nucleic Acid
Show Abstract · Added December 5, 2013
The expression pattern of genes important for pancreatic islet cell function requires the actions of cell-enriched transcription factors. Musculoaponeurotic fibrosarcoma homolog A (MafA) is a β-cell-specific transcriptional activator critical to adult islet β-cell function, with MafA mutant mice manifesting symptoms associated with human type 2 diabetes. Here, we describe that MafA expression is controlled by hepatocyte nuclear factor 1-α (Hnf1α), the transcription factor gene mutated in the most common monoallelic form of maturity onset diabetes of the young. There are six conserved sequence domains in the 5'-flanking MafA promoter, of which one, region 3 (R3) [base pair (bp) -8118/-7750] is principally involved in controlling the unique developmental and adult islet β-cell-specific expression pattern. Chromatin immunoprecipitation analysis demonstrated that Hnf1α bound specifically within R3. Furthermore, in vitro DNA-binding experiments localized an Hnf1α regulatory element between bp -7822 and -7793, an area previously associated with stimulation by the islet developmental regulator, Islet1. However, site-directed mutational studies showed that Hnf1α was essential to R3-driven reporter activation through bp -7816/-7811. Significantly, MafA levels were dramatically reduced in the insulin(+) cell population remaining in embryonic and adult Hnf1α(-/-) pancreata. Our results demonstrate that Hnf1α regulates MafA in β-cells and suggests that compromised MafA expression contributes to β-cell dysfunction in maturity onset diabetes of the young.
2 Communities
0 Members
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15 MeSH Terms
MafA and MafB regulate genes critical to beta-cells in a unique temporal manner.
Artner I, Hang Y, Mazur M, Yamamoto T, Guo M, Lindner J, Magnuson MA, Stein R
(2010) Diabetes 59: 2530-9
MeSH Terms: Aging, Animals, Embryonic Development, Gene Expression Regulation, Developmental, Glucagon, Glucose-6-Phosphatase, Insulin, Insulin-Secreting Cells, Maf Transcription Factors, Large, MafB Transcription Factor, Mice, Oligonucleotide Array Sequence Analysis, Proteins, RNA, RNA, Messenger, Retinol-Binding Proteins, Plasma, Reverse Transcriptase Polymerase Chain Reaction, Up-Regulation
Show Abstract · Added January 12, 2012
OBJECTIVE - Several transcription factors are essential to pancreatic islet β-cell development, proliferation, and activity, including MafA and MafB. However, MafA and MafB are distinct from others in regard to temporal and islet cell expression pattern, with β-cells affected by MafB only during development and exclusively by MafA in the adult. Our aim was to define the functional relationship between these closely related activators to the β-cell.
RESEARCH DESIGN AND METHODS - The distribution of MafA and MafB in the β-cell population was determined immunohistochemically at various developmental and perinatal stages in mice. To identify genes regulated by MafB, microarray profiling was performed on wild-type and MafB(-/-) pancreata at embryonic day 18.5, with candidates evaluated by quantitative RT-PCR and in situ hybridization. The potential role of MafA in the expression of verified targets was next analyzed in adult islets of a pancreas-wide MafA mutant (termed MafA(ΔPanc)).
RESULTS - MafB was produced in a larger fraction of β-cells than MafA during development and found to regulate potential effectors of glucose sensing, hormone processing, vesicle formation, and insulin secretion. Notably, expression from many of these genes was compromised in MafA(ΔPanc) islets, suggesting that MafA is required to sustain expression in adults.
CONCLUSIONS - Our results provide insight into the sequential manner by which MafA and MafB regulate islet β-cell formation and maturation.
3 Communities
2 Members
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18 MeSH Terms