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Zaborska KE, Jordan KL, Thorson AS, Dadi PK, Schaub CM, Nakhe AY, Dickerson MT, Lynch JC, Weiss AJ, Dobson JR, Jacobson DA. Liraglutide increases islet Ca 2+ oscillation frequency and insulin secretion by activating hyperpolarization-activated cyclic nucleotide-gated channels. Diabetes Obes Metab 2022; 24:1741-1752. [PMID: 35546791 PMCID: PMC9843726 DOI: 10.1111/dom.14747] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/06/2021] [Revised: 04/28/2022] [Accepted: 04/29/2022] [Indexed: 01/19/2023]
Abstract
AIM To determine whether hyperpolarization-activated cyclic nucleotide-gated (HCN) channels impact glucagon-like peptide-1 (GLP-1) receptor (GLP-1R) modulation of islet Ca2+ handling and insulin secretion. METHODS The impact of liraglutide (GLP-1 analogue) on islet Ca2+ handling, HCN currents and insulin secretion was monitored with fluorescence microscopy, electrophysiology and enzyme immunoassays, respectively. Furthermore, liraglutide-mediated β-to-δ-cell cross-communication was assessed following selective ablation of either mouse islet δ or β cells. RESULTS Liraglutide increased β-cell Ca2+ oscillation frequency in mouse and human islets under stimulatory glucose conditions. This was dependent in part on liraglutide activation of HCN channels, which also enhanced insulin secretion. Similarly, liraglutide activation of HCN channels also increased β-cell Ca2+ oscillation frequency in islets from rodents exposed to a diabetogenic diet. Interestingly, liraglutide accelerated Ca2+ oscillations in a majority of islet δ cells, which showed synchronized Ca2+ oscillations equivalent to β cells; therefore, we assessed if either cell type was driving this liraglutide-mediated islet Ca2+ response. Although δ-cell loss did not impact liraglutide-mediated increase in β-cell Ca2+ oscillation frequency, β-cell ablation attenuated liraglutide-facilitated acceleration of δ-cell Ca2+ oscillations. CONCLUSION The data presented here show that liraglutide-induced stimulation of islet HCN channels augments Ca2+ oscillation frequency. As insulin secretion oscillates with β-cell Ca2+ , these findings have important implications for pulsatile insulin secretion that is probably enhanced by liraglutide activation of HCN channels and therapeutics that target GLP-1Rs for treating diabetes. Furthermore, these studies suggest that liraglutide as well as GLP-1-based therapies enhance δ-cell Ca2+ oscillation frequency and somatostatin secretion kinetics in a β-cell-dependent manner.
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Affiliation(s)
- Karolina E Zaborska
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Kelli L Jordan
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Ariel S Thorson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Charles M Schaub
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Arya Y Nakhe
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Matthew T Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Joshua C Lynch
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Adam J Weiss
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - Jordyn R Dobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, Tennessee
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Dickerson MT, Dadi PK, Altman MK, Verlage KR, Thorson AS, Jordan KL, Vierra NC, Amarnath G, Jacobson DA. Glucose-mediated inhibition of calcium-activated potassium channels limits α-cell calcium influx and glucagon secretion. Am J Physiol Endocrinol Metab 2019; 316:E646-E659. [PMID: 30694690 PMCID: PMC6482666 DOI: 10.1152/ajpendo.00342.2018] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Pancreatic α-cells exhibit oscillations in cytosolic Ca2+ (Ca2+c), which control pulsatile glucagon (GCG) secretion. However, the mechanisms that modulate α-cell Ca2+c oscillations have not been elucidated. As β-cell Ca2+c oscillations are regulated in part by Ca2+-activated K+ (Kslow) currents, this work investigated the role of Kslow in α-cell Ca2+ handling and GCG secretion. α-Cells displayed Kslow currents that were dependent on Ca2+ influx through L- and P/Q-type voltage-dependent Ca2+ channels (VDCCs) as well as Ca2+ released from endoplasmic reticulum stores. α-Cell Kslow was decreased by small-conductance Ca2+-activated K+ (SK) channel inhibitors apamin and UCL 1684, large-conductance Ca2+-activated K+ (BK) channel inhibitor iberiotoxin (IbTx), and intermediate-conductance Ca2+-activated K+ (IK) channel inhibitor TRAM 34. Moreover, partial inhibition of α-cell Kslow with apamin depolarized membrane potential ( Vm) (3.8 ± 0.7 mV) and reduced action potential (AP) amplitude (10.4 ± 1.9 mV). Although apamin transiently increased Ca2+ influx into α-cells at low glucose (42.9 ± 10.6%), sustained SK (38.5 ± 10.4%) or BK channel inhibition (31.0 ± 11.7%) decreased α-cell Ca2+ influx. Total α-cell Ca2+c was similarly reduced (28.3 ± 11.1%) following prolonged treatment with high glucose, but it was not decreased further by SK or BK channel inhibition. Consistent with reduced α-cell Ca2+c following prolonged Kslow inhibition, apamin decreased GCG secretion from mouse (20.4 ± 4.2%) and human (27.7 ± 13.1%) islets at low glucose. These data demonstrate that Kslow activation provides a hyperpolarizing influence on α-cell Vm that sustains Ca2+ entry during hypoglycemic conditions, presumably by preventing voltage-dependent inactivation of P/Q-type VDCCs. Thus, when α-cell Ca2+c is elevated during secretagogue stimulation, Kslow activation helps to preserve GCG secretion.
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Affiliation(s)
- Matthew T Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Molly K Altman
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Kenneth R Verlage
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
- School of Medicine, Texas Tech University Health Sciences Center , Lubbock, Texas
- Department of Urology, Oregon Health and Science University , Portland, Oregon
| | - Ariel S Thorson
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Kelli L Jordan
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
| | - Nicholas C Vierra
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
- Department of Neurobiology, Physiology and Behavior University of California , Davis, California
| | - Gautami Amarnath
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
- Experimental and Clinical Neurosciences, University of Regensburg , Regensburg , Germany
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University , Nashville, Tennessee
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Vierra NC, Dickerson MT, Jordan KL, Dadi PK, Katdare KA, Altman MK, Milian SC, Jacobson DA. TALK-1 reduces delta-cell endoplasmic reticulum and cytoplasmic calcium levels limiting somatostatin secretion. Mol Metab 2018; 9:84-97. [PMID: 29402588 PMCID: PMC5870147 DOI: 10.1016/j.molmet.2018.01.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/22/2017] [Accepted: 01/19/2018] [Indexed: 01/17/2023] Open
Abstract
OBJECTIVE Single-cell RNA sequencing studies have revealed that the type-2 diabetes associated two-pore domain K+ (K2P) channel TALK-1 is abundantly expressed in somatostatin-secreting δ-cells. However, a physiological role for TALK-1 in δ-cells remains unknown. We previously determined that in β-cells, K+ flux through endoplasmic reticulum (ER)-localized TALK-1 channels enhances ER Ca2+ leak, modulating Ca2+ handling and insulin secretion. As glucose amplification of islet somatostatin release relies on Ca2+-induced Ca2+ release (CICR) from the δ-cell ER, we investigated whether TALK-1 modulates δ-cell Ca2+ handling and somatostatin secretion. METHODS To define the functions of islet δ-cell TALK-1 channels, we generated control and TALK-1 channel-deficient (TALK-1 KO) mice expressing fluorescent reporters specifically in δ- and α-cells to facilitate cell type identification. Using immunofluorescence, patch clamp electrophysiology, Ca2+ imaging, and hormone secretion assays, we assessed how TALK-1 channel activity impacts δ- and α-cell function. RESULTS TALK-1 channels are expressed in both mouse and human δ-cells, where they modulate glucose-stimulated changes in cytosolic Ca2+ and somatostatin secretion. Measurement of cytosolic Ca2+ levels in response to membrane potential depolarization revealed enhanced CICR in TALK-1 KO δ-cells that could be abolished by depleting ER Ca2+ with sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) inhibitors. Consistent with elevated somatostatin inhibitory tone, we observed significantly reduced glucagon secretion and α-cell Ca2+ oscillations in TALK-1 KO islets, and found that blockade of α-cell somatostatin signaling with a somatostatin receptor 2 (SSTR2) antagonist restored glucagon secretion in TALK-1 KO islets. CONCLUSIONS These data indicate that TALK-1 reduces δ-cell cytosolic Ca2+ elevations and somatostatin release by limiting δ-cell CICR, modulating the intraislet paracrine signaling mechanisms that control glucagon secretion.
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Affiliation(s)
- Nicholas C Vierra
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Matthew T Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Kelli L Jordan
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Ketaki A Katdare
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Molly K Altman
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Sarah C Milian
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA.
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Dickerson MT, Bogart AM, Altman MK, Milian SC, Jordan KL, Dadi PK, Jacobson DA. Cytokine-mediated changes in K + channel activity promotes an adaptive Ca 2+ response that sustains β-cell insulin secretion during inflammation. Sci Rep 2018; 8:1158. [PMID: 29348619 PMCID: PMC5773563 DOI: 10.1038/s41598-018-19600-x] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2017] [Accepted: 01/04/2018] [Indexed: 12/13/2022] Open
Abstract
Cytokines present during low-grade inflammation contribute to β-cell dysfunction and diabetes. Cytokine signaling disrupts β-cell glucose-stimulated Ca2+ influx (GSCI) and endoplasmic reticulum (ER) Ca2+ ([Ca2+]ER) handling, leading to diminished glucose-stimulated insulin secretion (GSIS). However, cytokine-mediated changes in ion channel activity that alter β-cell Ca2+ handling remain unknown. Here we investigated the role of K+ currents in cytokine-mediated β-cell dysfunction. Kslow currents, which control the termination of intracellular Ca2+ ([Ca2+]i) oscillations, were reduced following cytokine exposure. As a consequence, [Ca2+]i and electrical oscillations were accelerated. Cytokine exposure also increased basal islet [Ca2+]i and decreased GSCI. The effect of cytokines on TALK-1 K+ currents were also examined as TALK-1 mediates Kslow by facilitating [Ca2+]ER release. Cytokine exposure decreased KCNK16 transcript abundance and associated TALK-1 protein expression, increasing [Ca2+]ER storage while maintaining 2nd phase GSCI and GSIS. This adaptive Ca2+ response was absent in TALK-1 KO islets, which exhibited decreased 2nd phase GSCI and diminished GSIS. These findings suggest that Kslow and TALK-1 currents play important roles in altered β-cell Ca2+ handling and electrical activity during low-grade inflammation. These results also reveal that a cytokine-mediated reduction in TALK-1 serves an acute protective role in β-cells by facilitating increased Ca2+ content to maintain GSIS.
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Affiliation(s)
- Matthew T Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Avery M Bogart
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA.,Department of Biological Sciences, Ohio University, Athens, OH, USA
| | - Molly K Altman
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Sarah C Milian
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Kelli L Jordan
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN, USA.
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5
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Vierra NC, Dadi PK, Milian SC, Dickerson MT, Jordan KL, Gilon P, Jacobson DA. TALK-1 channels control β cell endoplasmic reticulum Ca 2+ homeostasis. Sci Signal 2017; 10:10/497/eaan2883. [PMID: 28928238 DOI: 10.1126/scisignal.aan2883] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Ca2+ handling by the endoplasmic reticulum (ER) serves critical roles in controlling pancreatic β cell function and becomes perturbed during the pathogenesis of diabetes. ER Ca2+ homeostasis is determined by ion movements across the ER membrane, including K+ flux through K+ channels. We demonstrated that K+ flux through ER-localized TALK-1 channels facilitated Ca2+ release from the ER in mouse and human β cells. We found that β cells from mice lacking TALK-1 exhibited reduced basal cytosolic Ca2+ and increased ER Ca2+ concentrations, suggesting reduced ER Ca2+ leak. These changes in Ca2+ homeostasis were presumably due to TALK-1-mediated ER K+ flux, because we recorded K+ currents mediated by functional TALK-1 channels on the nuclear membrane, which is continuous with the ER. Moreover, overexpression of K+-impermeable TALK-1 channels in HEK293 cells did not reduce ER Ca2+ stores. Reduced ER Ca2+ content in β cells is associated with ER stress and islet dysfunction in diabetes, and islets from TALK-1-deficient mice fed a high-fat diet showed reduced signs of ER stress, suggesting that TALK-1 activity exacerbated ER stress. Our data establish TALK-1 channels as key regulators of β cell ER Ca2+ and suggest that TALK-1 may be a therapeutic target to reduce ER Ca2+ handling defects in β cells during the pathogenesis of diabetes.
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Affiliation(s)
- Nicholas C Vierra
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Prasanna K Dadi
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Sarah C Milian
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Matthew T Dickerson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Kelli L Jordan
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA
| | - Patrick Gilon
- Pôle d'endocrinologie, diabète et nutrition, Institut de recherche expérimentale et clinique, Université catholique de Louvain, Brussels 1200, Belgium
| | - David A Jacobson
- Department of Molecular Physiology and Biophysics, Vanderbilt University, Nashville, TN 37232, USA.
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Lu CJ, Du H, Wu J, Jansen DA, Jordan KL, Xu N, Sieck GC, Qian Q. Non-random distribution and sensory functions of primary cilia in vascular smooth muscle cells. Kidney Blood Press Res 2008; 31:171-84. [PMID: 18483460 DOI: 10.1159/000132462] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2008] [Accepted: 03/10/2008] [Indexed: 12/16/2022] Open
Abstract
Although primary cilia are increasingly recognized to play sensory roles in several cellular systems, their role in vascular smooth muscle cells (VSMCs) has not been defined. We examined in situ position/orientation of primary cilia and ciliary proteins in VSMCs and tested the hypothesis that primary cilia of VSMCs exert sensory functions. By immunofluorescence and electron microscopic imaging, primary cilia of VSMCs were positioned with their long axis aligned at 58.3 degrees angle in relation to the cross-sectional plane of the artery, projecting into the extracellular matrix (ECM). Polycystin-1, polycystin-2 and alpha 3- and beta1-integrins are present in cilia. In scratch wound experiments, the majority of cilia were repositioned to the cell-wound interface. Such repositioning was largely abolished by a beta1-integrin blocker. Moreover, compared to non-ciliated/deciliated cells, ciliated VSMCs showed more efficient migration in wound repair. Lastly, when directly stimulated with collagen (an ECM component and cognate ligand for alpha 3beta1-integrins) or induced ciliary deflection, VSMCs responded with a rise in [Ca(2+)](i) that is dependent on the presence of cilia. Taken together, primary cilia of VSMCs are preferentially oriented, possess proteins critical for cell-ECM interaction and mechanosensing and respond to ECM protein and mechanical stimulations. These observations suggest a role for primary cilia in mechanochemical sensing in vasculature.
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Affiliation(s)
- C J Lu
- Division of Nephrology and Hypertension, Mayo Clinic College of Medicine and Mayo Graduate School, Rochester, MN 55905, USA
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Affiliation(s)
- K L Jordan
- Department of Biochemistry and Molecular Pharmacology, Thomas Jefferson University, Philadelphia, PA, USA
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Logan TJ, Jordan KL, Evans DL, Hall DJ. Altered cell shape is linked to increased p34cdc2 gene expression in fibroblasts expressing a mutant E2F-1 transcription factor. J Cell Biochem 1997; 65:83-94. [PMID: 9138083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The E2F1 transcription factor or an amino terminal deletion mutant termed E2F1d87 was constitutively expressed in NIH3T3 fibroblasts. Cells expressing wild-type E2F1 display a morphology indistinguishable from that of normal fibroblasts. However, the E2F1d87-expressing cells exhibited a distinct rounding during culture in media containing 10% calf serum. The morphology change was most pronounced during S phase, which was considerably lengthened in the E2F1d87-expressing cells. Consistent with this rounded shape, the E2F1d87-expressing cells have significantly increased levels of both p34cdc2 mRNA and protein. Also observed was an increase in active p34cdc2 in immunoprecipitates from extracts of the E2F1d87 cell line, as assayed by histone H1 kinase assay. The upregulation of p34cdc2 expression occurs at the transcriptional level and requires ectopic E2F1d87 along with serum growth factor stimulation, since culture of these cells in low serum media results in a flattened shape and a drop in p34cdc2 expression compared to that of the control cells.
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Affiliation(s)
- T J Logan
- Department of Biochemistry and Molecular Pharmacology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA
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Jordan KL, Evans DL, Steelman S, Hall DJ. Isolation of two novel cDNAs whose products associate with the amino terminus of the E2F1 transcription factor. Biochemistry 1996; 35:12320-8. [PMID: 8823166 DOI: 10.1021/bi9611927] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The amino terminus of the E2F1 transcription factor is a protein-protein interaction domain since it associates with cyclin A/cdk2. Here, the two-hybrid yeast screen was used to clone genes whose products associate with the amino terminus of E2F1. The amino-terminal 121 amino acids of E2F1 were fused to the Lex A binding domain while a partial length cDNA library from the embryo of a 12 day old mouse was fused to the VP16 activation domain. Following coexpression of these fusions in yeast, two novel genes were cloned that code for proteins that associate with E2F1. In an in vitro assay, these E2F1 Binding Proteins (EBP1 and EBP2) associate with residues 1-121 of E2F1 or with the full-length protein; however, they do not associate with its carboxy terminus (residues 88-437). When EBP1 or EBP2 were expressed in COS cells along with E2F1 and the target promoter DNA polymerase alpha, repression of transcription was observed. However, no repression of DNA polymerase alpha was seen if the cells expressed a nonassociating mutant E2F1 (residues 88-437), along with EBP1 or EBP2. Finally, expression of the EBP2 gene is up-regulated in growing NIH3T3 fibroblasts, relative to serum-starved cells. However, this up-regulation of EBP2 expression is not seen in fibroblasts constitutively expressing E2F1.
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Affiliation(s)
- K L Jordan
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107-5541, USA
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Logan TJ, Jordan KL, Hall DJ. Constitutive expression of the E2F1 transcription factor in fibroblasts alters G0 and S phase transit following serum stimulation. Biochem Cell Biol 1996; 74:21-8. [PMID: 9035687 DOI: 10.1139/o96-003] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The E2F1 transcription factor was constitutively expressed in NIH3T3 fibroblasts to determine its effect on the cell cycle. These E2F1 cell lines were not tightly synchronized in G0 phase of the cell cycle following serum starvation, as are normal fibroblasts. Instead, the cells are spread throughout G0 and G1 phase with a portion of the population initiating DNA synthesis. Upon serum stimulation, the remaining cells in G0/G1 begin to enter S phase immediately but with a reduced rate. Constitutive expression of E2F1 appears to primarily affect the G0 phase, since transit of proliferating E2F1 cell lines through G1 phase is the same as control cells. Consistent with a shortened G0 phase, the E2F1 cell lines have a significantly reduced cellular volume. Additionally, the first S phase after serum stimulation, but not subsequent S phases, is nearly doubled in the E2F1 cell lines compared with control cells. Cell lines expressing a deletion mutant of E2F1 (termed E2F1d87), known to significantly affect cell shape, have cell cycle and volume characteristics similar to the E2F1 expressing cells. However, all S phase durations are considerably lengthened and the cells demonstrate delayed growth after plating.
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Affiliation(s)
- T J Logan
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, PA 19107, USA
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11
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Abstract
To gain an understanding of the role the E2F1 transcription factor plays in cell physiology, the full length protein (E2F1) and an amino terminal deletion of 87 amino acids (E2F1d87) were constitutively expressed in NIH3T3 fibroblasts. Multiple cell lines were generated for each construct. These cells do not proliferate in media containing low serum and do not proliferate in soft agar, indicating that they are likely not transformed. However, both sets of cell lines show increased DNA synthesis and increased numbers of cells in S phase when cultured in media containing low serum, compared to the control cell lines. Cells expressing E2F1d87 (but not E2F1) have an extremely rounded morphology when cultured in 10% serum-containing media. These rounded cells lack detectable microfilaments, microtubules, and focal contacts. However, when these cells are cultured in low serum-containing media (0.5%), they attain the flattened morphology and cytoskeletal structure of normal NIH3T3 cells.
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Affiliation(s)
- T J Logan
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
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Jordan KL, Haas AR, Logan TJ, Hall DJ. Detailed analysis of the basic domain of the E2F1 transcription factor indicates that it is unique among bHLH proteins. Oncogene 1994; 9:1177-85. [PMID: 8134120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
The E2F1 transcription factor binds to sites within the promoters of a number of cell cycle regulated genes through a basic-helix-loop-helix motif (bHLH). It is shown here that the basic region of E2F1 is distinct from that of all other bHLH proteins. The center of the basic region contains a helix breaking proline-glycine pair, (P122, G123), implying a turn within this region. This is in contrast to the known bHLH containing proteins where the basic region is alpha-helical. Substitution of P122 and G123 with alanines results in a significant reduction in DNA binding levels, with the predicted formation of an alpha-helix. Also in contrast to other bHLH proteins, mutations generated in conserved basic residues of E2F1 do not effect DNA binding. In addition, a single leucine (191) between helix no. 2 and the leucine zipper is required for DNA binding while the leucine zipper itself is not necessary. Finally, E2F1 interacts with all of the G-residues in the sequence GGCGGGAAA while the A-residues are not required for DNA binding. The uniqueness of the E2F1 DNA binding domain is likely to play a role in its binding a DNA site that is distinct from that of all other bHLH proteins (CACGTG).
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Affiliation(s)
- K L Jordan
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, PA 19107
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Jordan KL, Berk SH, Berk SL. A comparison of serum bactericidal activity and phenotypic characteristics of bacteremic, pneumonia-causing strains, and colonizing strains of Branhamella catarrhalis. Am J Med 1990; 88:28S-32S. [PMID: 2111090 DOI: 10.1016/0002-9343(90)90258-f] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/30/2022]
Abstract
Four blood isolates, 12 pneumonia isolates, and seven colonizing isolates of Branhamella catarrhalis were compared with respect to their ability to grow in normal human serum and in convalescent serum of a patient with B. catarrhalis bacteremia. Disease-causing isolates showed seven of 16 serum-resistant strains (43 percent) compared with one of seven (13 percent) colonizing strains. Bacteremic strains were not more serum-resistant than pneumonia-causing strains. Trypsin zones of inhibition were higher for disease-causing strains. There was no correlation between source of isolation and colistin sensitivity or ability to hemagglutinate red blood cells.
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Affiliation(s)
- K L Jordan
- Department of Internal Medicine, East Tennessee State University, James H. Quillen College of Medicine, Johnson City 37614
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