Selected Publications of Dr. Holz

Role of phospholipase C-epsilon in physiological phosphoinositide signaling networks, Cellular Signalling 2012
This review concerning PLC-epsilon was a collaboration of Drs. Alan V. Smrcka, Joan Heller Brown, and George G. Holz. Summarized are current concepts regarding how Epac signals through Rap in order to control PLC-epsilon activity, thereby influencing Ca2+ handling, excitation-contraction coupling, and exocytosis in various cell types.

cAMP Sensor Epac and Gastrointestinal Function, Physiology of the Gastrointestinal Tract, Fifth Edition 2012
Summarized in this handbook chapter are the surprisingly diverse roles Epac proteins play in gastrointestinal function. The work was a collaboration of the Holz laboratory with Dr. Xiaodong Cheng of the University of Texas Medical Branch in Galveston, TX.

Isoform-specific antagonists of exchange proteins directly activated by cAMP, Proceedings of the National Academy of Sciences 2012
A major breakthrough for the field of signal transduction research was the discovery by Dr. Xiaodong Cheng of small molecule compounds (ESI-05, ESI-07) that specifically inhibit Epac2 while leaving Epac1 and PKA unaffected. The specificity of ESI-05 and ESI-07 was validated in FRET-based assays of Epac or PKA activation, as performed in the Holz laboratory by Drs. Oleg G. Chepurny and Colin A. Leech.

Phospholipase C-epsilon links Epac2 activation to the potentiation of glucose-stimulated insulin secretion from mouse islets of Langerhans, Islets 2011
This report provided the first evidence that a novel Epac2 and Rap1 –regulated PLC-epsilon mediates the action of cAMP to potentiate glucose-stimulated insulin secretion from mouse islets. Consistent with this concept, the insulin secretagogue action of an Epac activator (8-pCPT-2’-O-Me-cAMP-AM) was found to be diminished in islets of Epac2 and PLC-epsilon KO mice. The study was a collaboration of the Holz laboratory with Dr. Youming Lu who provided the Epac2 KO mice, and Dr. Alan V. Smrcka who provided the PLC-epsilon KO mice.

Molecular physiology of glucagon-like peptide-1 insulin secretagogue action in pancreatic beta cells, Progress in Biophysics and Molecular Biology 2011
This review provided an update concerning the molecular basis for incretin hormone action, as it pertains to insulin secretion under the control of GLP-1. New findings reported in this review included the discovery of Dr. Igor Dzhura that an Epac activator (8-pCPT-2 ’-O-Me-cAMP-AM) initiated electrical “bursting” activity in mouse islets. This bursting activity was comprised of action potentials, and it occurred in synchrony with oscillations of cytosolic [Ca2+] that are known to “trigger” pulsatile insulin secretion.

PKA-dependent potentiation of glucose-stimulated insulin secretion by Epac activator 8-pCPT-2'-O-Me-cAMP-AM in human islets of Langerhans, American Journal of Physiology 2010
This paper established the efficacy of Epac activator 8-pCPT-2 ’-O-Me-cAMP-AM as a stimulator of insulin secretion from human pancreatic islets. Surprisingly, protein kinase A (PKA) activity was found to be permissive in order for the Epac activator to exert its effect. Based on this finding, our view is that Epac participates in beta-cell stimulus-secretion coupling at an “early” step upstream of PKA-dependent secretory granule exocytosis. For example, our studies demonstrate that Epac facilitates glucose-dependent K-ATP channel closure, Ca2+ influx, and Ca2+ mobilization.

Facilitation of beta-cell K-ATP channel sulfonylurea sensitivity by a cAMP analog selective for the cAMP-regulated guanine nucleotide exchange factor Epac, Islets 2010
Clinical studies demonstrate that there is an increased risk of hypoglycemia in patients administered a sulfonylurea and a GLP-1 receptor agonist. Our 2010 paper published in Islets provided evidence that this clinical observation can be explained by the synergistic interaction of sulfonylureas and GLP-1 receptor agonists to promote beta-cell K-ATP channel closure.

Epac2-dependent mobilization of intracellular Ca2+ by glucagon-like peptide-1 receptor agonist exendin-4 is disrupted in beta cells of phospholipase C-epsilon knockout mice, Journal of Physiology 2010
Epac2 is an activator of the small GTPase Rap1, and Rap1 is know to participate in the stimulation of insulin secretion by cAMP-elevating agents such as GLP-1. This 2010 paper provided the first evidence that the Ca2+ dependent exocytosis of insulin might be stimulated as a consequence of the Epac2 and Rap1 mediated activation of a novel phosphoinositide-specific phospholipase C-epsilon. The study was a collaboration of the Holz laboratory with the laboratory of Dr. Alan V. Smrcka of the University of Rochester School of Medicine.

Epac2-dependent Rap1 activation and the control of islet insulin secretion by glucagon-like peptide-1, Vitamins and Hormones 2010
This review summarized current concepts regarding the relative contributions of Epac2 and PKA to the control of islet insulin secretion by GLP-1 receptor agonists. An overview was provided concerning which steps of beta-cell stimulus-secretion coupling are under the control of Epac2 and/or PKA.

Enhanced Rap1 activation and insulin secretagogue properties of an acetoxymethyl ester of an Epac-selective cyclic AMP analog in rat INS-1 cells: studies with 8-pCPT-2'-O-Me-cAMP-AM, The Journal of Biological Chemistry 2009
Soon after the Holz laboratory moved from NYU School of Medicine to SUNY Upstate Medical University, we collaborated with the BIOLOG Life Science Institute in order to demonstrate the potent insulin secretagogue action of a novel AM-ester of an Epac-selective cAMP analog (ESCA). Such AM-esters of ESCAs are powerful new tools with which to study Epac signal transduction since these compounds have especially high membrane permeability.

Glucose-dependent potentiation of mouse islet insulin secretion by Epac activator 8-pCPT-2'-O-Me-cAMP-AM, Islets 2009
Working with Dr. Grant G. Kelley of SUNY Upstate, the Holz laboratory was the first to document that the AM-ester of 8-pCPT-2 ’-O-Me-cAMP exerted a powerful stimulatory action in mouse islets to potentiate first and second phase glucose-stimulated insulin secretion (GSIS). These findings resolved a long-standing discrepancy in the literature in which the non-AM ester of this Epac activator was reported to either stimulate, or not stimulate, islet insulin secretion.

Glucagon-like peptide-1 induced signaling and insulin secretion do not drive fuel and energy metabolism in primary rodent pancreatic beta-cells, PLoS One 2009
This collaborative study of the Holz (SUNY), Prentki (University of Montreal), and Heart (MBL) labs re-examined whether GLP-1 renders beta-cells “glucose competent” by upregulating oxidative glucose metabolism in the beta cells. Surprisingly, and in contrast to findings of Tsuboi et al. 2003 for insulin-secreting MIN6 cells, no such action of GLP-1 was measurable in isolated human or mouse islets.

Role of the cAMP sensor Epac as a determinant of K-ATP channel ATP-sensitivity in human pancreatic beta cells and rat INS-1 cells, Journal of Physiology 2008
This paper was the first to demonstrate that an Epac-selective cAMP analog has the capacity to render beta-cell K-ATP channels more sensitive to the inhibitory action of ATP. This finding provides one possible explanation for how cAMP-elevating hormone GLP-1 acts as a beta-cell glucose sensitizer to enhance insulin secretion.

Cytosolic adenylate kinases regulate K-ATP channel activity in human beta-cells, Biochemical and Biophysical Research Communications 2008
Reported in this paper are new findings concerning the role of adenylate kinases as intermediaries linking intracellular glucose metabolism to the closure of K-ATP channels in human beta cells.

Epac-selective cAMP analogs: New tools with which to evaluate the signal transduction properties of cAMP-regulated guanine nucleotide exchange factors, Cellular Signalling 2008
This review constitutes a collaboration of the Holz lab with Dr. Frank Schwede of the BIOLOG Life Science Institute. Summarized is an account of research that led to the generation of Epac-selective cAMP analogs (ESCAs). Also summarized are the structural and pharmacological properties of these ESCAs.

Synchronizing Ca²⁺ and cAMP oscillations in pancreatic beta cells: a role for glucose metabolism and GLP-1 receptors? American Journal of Physiology, Cell Physiology 2008
This commentary provides a summary of our understanding as to how beta-cell glucose metabolism and GLP-1 signal transduction interact to generate oscillations of Ca2+ and cAMP that are in-phase, and that stimulate pulsatile insulin secretion. The paper represents a collaboration of the Holz lab with Dr. Emma Heart of the Marine Biological Laboratory, Woods Hole, MA.

A novel cyclic adenosine monophosphate-responsive luciferase reporter incorporating a nonpalindromic cyclic adenosine monophosphate response element provides optimal performance for use in G protein-coupled receptor drug discovery efforts, Journal of Biomolecular Screening 2007
This paper describes the invention of a luciferase reporter that is cAMP responsive, and that is useful for screening of cell lines that express G protein-coupled receptors. New ligands that activate these receptors can be identified, or ligands with known structures can be evaluated in order to determine their efficacies or potencies.

Cell physiology of cAMP sensor Epac, The Journal of Physiology Topical Review 2006
This Topical review highlights the emerging role of cAMP sensor Epac as a central player in multiple aspects of cell physiology. The novel pharmacological properties and physiological actions of Epac-selective cAMP analogs (ESCAs) are also updated.

Simultaneous Optical Measurements of Cytosolic Ca²⁺ and cAMP in Single Cells, Science's STKE 2006
Our collaboration with the laboratory of Dr. Michael W. Roe at the University of Chicago has generated this ground-breaking technology that allows for the very first time, the simultaneous digital imaging of cAMP and calcium concentrations in single living cells. The detailed protocols described here are an extension of the prior study of the Roe, Lohse, and Holz labs (Landa et al. 2005, see below).

cAMP sensor Epac as a determinant of ATP-sensitive potassium channel activity in human pancreatic β cells and rat INS-1 cells, Journal of Physiology 2006
This research paper describes a novel form of ion channel modulation in which the activity of pancreatic beta cell ATP-sensitive potassium channels is shown to be be inhibited by Epac-selective cAMP analogs. The significance of this finding is that it establishes Epac, a cAMP-regulated guanine nucleotide exchange factor (cAMP-GEF), to be a likely target for pharmacological intervention in the treatment of type 2 diabetes mellitus.

Diabetes Outfoxed by GLP-1?, Science's STKE 2005
This perspective published originally at Science magazine's STKE web site provides our view of how GLP-1 influences pancreatic beta cell growth and differentiation.

A cAMP and Ca²⁺ coincidence detector in support of Ca²⁺-induced Ca²⁺ release in mouse pancreatic β cells, Journal of Physiology 2005
This research paper is the first to establish the phenomenon of Second Messenger Coincidence Detection as a key cellular signaling event underlying the ability of a GLP-1 receptor agonist (Exendin-4, also known as Byetta) to stimulate pancreatic beta cell function.

Interplay of Ca²⁺ and cAMP Signaling in the Insulin-secreting MIN6 β-Cell Line, Journal of Biological Chemistry 2005
This research paper is the first to demonstrate that a newly-developed Epac-based FRET reporter can be activated as a consequence of GLP-1 receptor stimulation in pancreatic beta cells. The significance of this finding is that it establishes the cAMP-binding domain of Epac to be sensitive to the increase of cytosolic cAMP concentration that results upon stimulation of beta cells with Exendin-4. This report is an outgrowth of collaborative studies with the laboratory of Dr. Michael Roe of the University of Chicago.

New Insights Concerning the Glucose-dependent Insulin Secretagogue Action of Glucagon-like Peptide-1 in Pancreatic β-Cells, Hormone and Metabolic Research 2004
This review summarizes our view of how GLP-1 and glucose metabolism interact to stimulate the secretion of insulin from pancreatic beta cells.

Epac: A New cAMP-Binding Protein in Support of Glucagon-Like Peptide-1 Receptor-Mediated Signal Transduction in the Pancreatic β-Cell, Diabetes 2004
This perspective highlights the potential role of cAMP-binding protein Epac as a determinant of GLP-1 signal transduction in the pancreatic beta cell.

Glucagon-Like Peptide-1 Synthetic Analogs: New Therapeutic Agents for Use in the Treatment of Diabetes Mellitus, Current Medicinal Chemistry 2003
This review summarizes current efforts directed at the generation of GLP-1 analogs that have an extended duration of action and which are useful for treatment of type 2 diabetes mellitus.

Epac-selective cAMP Analog 8-pCPT-2'-O-Me-cAMP as a Stimulus for Ca²⁺-induced Ca²⁺ Release and Exocytosis in Pancreatic β-Cells, Journal of Biological Chemistry 2003
This paper describes the pharmacological properties of a newly developed cAMP analog that activates Epac and which stimulates calcium signaling and exocytosis in pancreatic beta cells.

Glucagon-like peptide-1 mobilizes intracellular Ca²⁺ and stimulates mitochondrial ATP synthesis in pancreatic MIN6 β-cells, Biochemical Journal 2003
This paper describes collaborative studies with the laboratory of Dr. G. Rutter in which stimulatory effects of GLP-1 on mitochondrial ATP production were documented.

Amplification of exocytosis by Ca²⁺-induced Ca²⁺ release in INS-1 pancreatic β cells, Journal of Physiology 2003
This paper was the first to demonstrate that GLP-1 receptor agonist Exendin-4 stimulates exocytosis by mobilizing an intracellular source of calcium.

Exendin-4 as a Stimulator of Rat Insulin I Gene Promoter Activity via bZIP/CRE Interactions Sensitive to Serine/Threonine Protein Kinase Inhibitor Ro 31-8220, Endocrinology 2002
This paper describes our studies of regulatory elements in the rat insulin 1 gene promoter that mediate stimulatory actions of Exendin-4 on insulin gene expression.

Over-expression of the glucagon-like peptide-1 receptor on INS-1 cells confers autocrine stimulation of insulin gene promoter activity: a strategy for production of pancreatic β-cell lines for use in transplantation, Cell and Tissue Research 2002
This paper describes a strategy for the generation of insulin-secreting cell lines that overexpress GLP-1 receptors and which exhibit robust glucose-dependent insulin gene expression.

cAMP-regulated guanine nucleotide exchange factor II (Epac2) mediates Ca²⁺-induced Ca²⁺ release in INS-1 pancreatic β-cells, Journal of Physiology 2001
This paper was the first to establish a link between GLP-1 receptors, activation of Epac, and the mobilization of intracellular calcium.

Glucagon-Like Peptide 1 Stimulates Insulin Gene Promoter Activity by Protein Kinase A-Independent Activation of the Rat Insulin I Gene cAMP Response Element, Diabetes 2000
This paper was the first to demonstrate that protein kinase A-independent signaling pathways mediate stimulatory actions of GLP-1 at the insulin gene promoter.

cAMP-dependent Mobilization of Intracellular Ca²⁺ Stores by Activation of Ryanodine Receptors in Pancreatic β-Cells, Journal of Biological Chemistry 1999
This paper established a link between GLP-1, cAMP production, and the release of calcium from intracellular calcium stores in beta-cells.

Leptin Suppression of Insulin Secretion and Gene Expression in Human Pancreatic Islets: Implications for the Development of Adipogenic Diabetes Mellitus, Journal of Clinical Endocrinology and Metabolism 1999
This study examined the action of Leptin - a newly described "obesity hormone" that was found to inhibit pancreatic beta cell insulin gene expression. The findings were generated at Massachusetts General Hospital through the collaboration of Dr. Holz with Dr. Jochen Seufert while working in the laboratory of Dr. Joel F. Habener.

Leptin Suppression of Insulin Secretion by the Activation of ATP-Sensitive K⁺ Channels in Pancreatic β-Cells, Diabetes 1997
This was the first published study to demonstrate that the "obesity hormone" Leptin stimulates the function of ATP-sensitive potassium channels. Leptin receptors on pancreatic beta cells were characterized, and the inhibitory action of leptin on beta cell insulin secretion was established. The findings were generated through a collaboration of Dr. Holz with Dr. Timothy Kieffer while working in the laboratory of Dr. Joel F. Habener at Massachusetts General Hospital.

Signal transduction of PACAP and GLP-1 in pancreatic beta cells, Annals of the New York Academy of Sciences 1996
This review summarized our laboratory's findings concerning the cAMP-mediated actions of PACAP and GLP-1 to activate non-selective cation channels in pancreatic beta cells. These findings were presented by Drs. George Holz and Colin Leech at a meeting of the New York Academy of Sciences in New Orleans, LA.

Activation of a cAMP-regulated Ca²⁺-Sgnaling Pathway in Pancreatic β-Cells by the Insulinotropic Hormone Glucagon-like Peptide-1, Journal of Biological Chemistry 1995
This paper established a role for non-selective cation channels as targets of cAMP signaling in pancreatic beta cells. In addition to its inhibitory effect at ATP-sensitive potassium channels, GLP-1 promotes sodium-dependent depolarization of beta cells, thereby increasing levels of cytosolic calcium. The study was a collaboration with Dr. Colin A. Leech of Massachusetts General Hospital while working in the laboratory of Dr. Joel F. Habener.

Pituitary Adenylate Cyclase-Activating Polypeptide Induces the Voltage-Independent Activation of Inward Membrane Currents and Elevation of Intracellular Calcium in HIT-T15 Insulinoma Cells, Endocrinology 1995
This paper describes the stimulatory action of the neuropeptide PACAP on beta cell function. PACAP is structurally-related to GLP-1, and the PACAP receptor bears resemblence to the GLP-1 receptor. The study was a collaboration with Dr. Colin A. Leech of Massachusetts General Hospital while working in the laboratory of Dr. Joel F. Habener.

Application of patch clamp methods to the study of calcium currents and calcium channels, Methods in Cell Biology 1994
This review concerning patch clamp electrophysiology was published in Volume 40 pgs. 135-151 of Methods in Cell Biology for the issue "A Practical Guide to the Study of Calcium in Living Cells".

Voltage-Independent Calcium Channels Mediate Slow Oscillations of Cytosolic Calcium That Are Glucose Dependent in Pancreatic β-Cells, Endocrinology 1994
This study demonstrated that spontaneous oscillations of intracellular calcium concentration can occur in beta cells, a phenomenon not necessarily linked to membrane depolarization. The findings are of interest in view of the role of intracellular calcium stores as determinants of beta cell stimulus-secretion coupling and regulated gene expression. The study was a collaboration with Dr. Colin A. Leech of Massachusetts General Hospital while working in the laboratory of Dr. Joel F. Habener.

Pancreatic beta-cells are rendered glucose-competent by the insulinotropic hormone glucagon-like peptide-1(7-37), Nature 1993
This letter to Nature was the first published study in support of the Glucose Competence Concept. Our view is that GLP-1 restores the ability of compromised beta cells to metabolize glucose and to secrete insulin. The induction of glucose competence is measurable as the synergistic interaction of GLP-1 and glucose to inhibit ATP-sensitive potassium channels in beta cells. The study was a collaboration with Dr. Willem M. Khutreiber of Massachusetts General Hospital while working in the laboratory of Dr. Joel F. Habener.

Signal transduction crosstalk in the endocrine system: pancreatic β-cells and the glucose competence concept, Trends In Biochemical Sciences 1992
This review concerning the Glucose Competence Concept was published in a thematic issue of Trends in Biochemical Sciences. This issue signified the emergence of Signal Transduction as a dominant theme in contemporary biology. It was also the first formal publication generated by Dr. Holz as a consequence of his collaboration with Dr. Joel F. Habener, co-discoverer of GLP-1.

G Proteins Couple α-Adrenergic and GABA_b Receptors to Inhibition of Peptide Secretion from Peripheral Sensory Neurons, Journal of Neuroscience 1989
This research report is the culmination of postdoctoral studies performed by Dr. Holz while working in the laboratory of Dr. Kathleen Dunlap at Tufts University School of Medicine. The findings demonstrate that alpha-adrenergic receptors, GABA-B receptors, Pertussis Toxin-Sensitive G proteins, and Voltage-Dependent Calcium Channels constitute a "signaling module" which when activated, generates presynaptic inhibition of neuropeptide secretion from peripheral sensory neurons.

Characterization of the Electrically Evoked Release of Substance P from Dorsal Root Ganglion Neurons: Methods and Dihydropyridine Sensitivity, Journal of Neuroscience 1988
The role of L-type and N-type Voltage-Dependent Calcium Channels as determinants of neuropeptide secretion was first established in this study examining the exocytosis of Substance P from peripheral sensory neurons. This is the first study to demonstrate that the electrically-evoked release of a neuropeptide results from depolarization-induced activation of omega-conotoxin GVIA-sensitive N-type Calcium channels.

G proteins as regulators of ion channel function, Trends In Neuroscience 1987
This review provided the impetus for numerous studies examining the role of heterotrimeric G proteins as signaling intermediaries linking G protein-coupled receptors to the modulation of Calcium and Potassium channels in excitable cells.

Modifying channel function, Nature 1986 News and Views
This is the News and Views article which accompanied our 1986 report in Nature concering G protein regulation of voltage-dependent calcium channels.

GTP-binding proteins mediate transmitter inhibition of voltage-dependent calcium channels, Nature 1986
This is the paper that established a link between activation of G proteins and the inhibition of voltage-dependent calcium channels. It was the most highly cited paper in the field of Neuroscience for the year 1986 according to the ISI. Publication of this study was facilitated by the generosity of Dr. Ronald D. Sekura of the NIH who provided Dr. Holz purified preparations of Bordetella pertussis toxin, which at that time were not commercially available.

Serotonin Decreases the Duration of Action Potentials Recorded from Tetraethylammonium-Treated Bullfrog Dorsal Root Ganglion Cells, Journal of Neuroscience 1986
This research report summarizes the Ph.D. studies of Dr. Holz performed while working in the laboratory of Dr. Edmund G. Anderson, Chairman of Pharmacology at the University of Illinois in Chicago. The role of serotonin receptors in the generation of presynaptic inhibition was investigated in electrophysiological studies of primary sensory neurons.