Pancreatic beta cells cultured from individual preneoplastic foci in a multistage tumorigenesis pathway: a potentially general technique for isolating physiologically representative cell lines. Mol Cell Biol. 1993;13:4223-4232. [PMID: 8391634 DOI: 10.1128/mcb.13.7.4223]

(Re-)Viewing Role of Intracellular Glucose Beyond Extracellular Regulation of Glucose-Stimulated Insulin Secretion by Pancreatic Cells

For glucose-stimulated insulin secretion (GSIS) by pancreatic β-cells in animals, it is believed that ATP generated from glucose metabolism is primarily responsible. However, this ignores two well-established aspects in literature: (a) intracellular ATP generation from other sources resulting in an overall pool of ATP, regardless of the original source, and (b) that intracellular glucose transport is 10- to 100-fold higher than intracellular glucose phosphorylation in β-cells. The latter especially provides an earlier unaddressed, but highly appealing, observation pertaining to (at least transient) the presence of intracellular glucose molecules. Could these intracellular glucose molecules be responsible for the specificity of GSIS to glucose (instead of the widely believed ATP production from its metabolism)? In this work, we provide a comprehensive compilation of literature on glucose and GSIS using various cellular systems - all studies focus only on the extracellular role of glucose in GSIS. Further, we carried out a comprehensive analysis of differential gene expression in Mouse Insulinoma 6 (MIN6) cells, exposed to low and high extracellular glucose concentrations (EGC), from the existing whole transcriptome data. The expression of other genes involved in glycolysis, Krebs cycle, and electron transport chain was found to be unaffected by EGC, except Gapdh, Atp6v0a4, and Cox20. Remarkably, 3 upregulated genes (Atp6v0a4, Cacnb4, Kif11) in high EGC were identified to have an association with cellular secretion. Using glucose as a possible ligand for the 3 proteins, computational investigations were carried out (that will require future 'wet validation', both in vitro and in vivo, e.g., using primary islets and animal models). The glucose-affinity/binding scores (in kcal/mol) obtained were also compared with glucose binding scores for positive controls (GCK and GLUT2), along with negative controls (RPA1, KU70-80, POLA1, ACAA1A, POLR1A). The binding affinity scores of glucose molecules for the 3 proteins were found to be closer to positive controls. Therefore, we report the glucose binding ability of 3 secretion-related proteins and a possible direct role of intracellular glucose molecules in GSIS.

Formation of βTC3 and MIN6 Pseudoislets Changes the Expression Pattern of Gpr40, Gpr55, and Gpr119 Receptors and Improves Lysophosphatidylcholines-Potentiated Glucose-Stimulated Insulin Secretion

The impaired spatial arrangement and connections between cells creating islets of Langerhans as well as altered expression of G protein-coupled receptors (GPCRs) often lead to dysfunction of insulin-secreting pancreatic β cells and can significantly contribute to the development of diabetes. Differences in glucose-stimulated insulin secretion (GSIS) are noticeable not only in diabetic individuals but also in model pancreatic β cells, e.g., βTC3 and MIN6 β cell lines with impaired and normal insulin secretion, respectively. Now, we compare the ability of GPCR agonists (lysophosphatidylcholines bearing fatty acid chains of different lengths) to potentiate GSIS in βTC3 and MIN6 β cell models, cultured as adherent monolayers and in a form of pseudoislets (PIs) with pancreatic MS1 endothelial cells. Our aim was also to investigate differences in expression of the GPCRs responsive to LPCs in these experimental systems. Aggregation of β cells into islet-like structures greatly enhanced the expression of Gpr40, Gpr55, and Gpr119 receptors. In contrast, the co-culture of βTC3 cells with endothelial cells converted the GPCR expression pattern closer to the pattern observed in MIN6 cells. Additionally, the efficiencies of various LPC species in βTC3-MS1 PIs also shifted toward the MIN6 cell model.

Characterization of a mouse model of islet transplantation using MIN-6 cells

Immortalized beta cells are an abundant source of insulin-producing cells. Although MIN-6 cells have similar characteristics as normal islets in vitro, the in vivo use of MIN-6 cells has not been fully described. This study characterizes in vivo mouse models of MIN-6 transplantation and rejection. Subcutaneous (sc) transplantation of MIN-6 cells in either Matrigel or HyStem-C hydrogels reduced blood sugars in nude mice and thus are good matrices for MIN-6 cells in vivo. NOD mice are good transplant recipients since they best rejected MIN-6 cells. MLR responses from BalbC, Black Webster, Swiss Black, C3H, and NOD mice correlated with mean blood glucose response suggesting the importance of allogeneic differences in the rejection of cells. Three days of cyclosporine administration caused no inhibition of MIN-6 cell rejection and 6 days resulted in a transient decrease in blood glucose, while daily administration inhibited rejection long term. Kinetic glucose tolerance (GTT) studies in nude mice demonstrated transplanted MIN-6 cells are close but not as effective as normal islets in controlling blood glucose and blood glucose set point for insulin release in MIN-6 cells decreases to hypoglycemic levels over time. To avoid hypoglycemia, the effect of MIN-6 cell irradiation was assessed. However, irradiation only delayed the development of hypoglycemia, not altering the final glucose set point for insulin release. In conclusion, we have characterized a mouse model for beta-cell transplantation using subcutaneous MIN-6 cells that can be used as a tool to study approaches to mitigate immune rejection.

Cellular models for beta-cell function and diabetes gene therapy

Diabetes is characterized by the destruction and/or relative dysfunction of insulin-secreting beta-cells in the pancreatic islets of Langerhans. Consequently, considerable effort has been made to understand the physiological processes governing insulin production and secretion in these cells and to elucidate the mechanisms involved in their deterioration in the pathogenesis of diabetes. To date, considerable research has exploited clonal beta-cell lines derived from rodent insulinomas. Such cell lines have proven to be a great asset in diabetes research, in vitro drug testing, and studies of beta-cell physiology and provide a sustainable, and in many cases, more practical alternative to the use of animals or primary tissue. However, selection of the most appropriate rodent beta cell line is often challenging and no single cell line entirely recapitulates the properties of human beta-cells. The generation of stable human beta-cell lines would provide a much more suitable model for studies of human beta-cell physiology and pathology and could potentially be used as a readily available source of implantable insulin-releasing tissue for cell-based therapies of diabetes. In this review, we discuss the history, development, functional characteristics and use of available clonal rodent beta-cell lines, as well as reflecting on recent advances in the generation of human-derived beta-cell lines, their use in research studies and their potential for cell therapy of diabetes.

Isolation and Characterization of a Cell Line from the Epithelial Cells of the Human Fetal Pancreas

Pancreatic cell lines are useful for basic studies of pancreatic biology and for possible application to cell transplantation therapies for diabetes. A retroviral vector expressing simian virus 40 (SV40) T antigen and H-rasval12 was used to infect a monolayer culture of epithelial cells from an 18-wk human fetal pancreas. Infected cells gave rise to a clonal epithelial cell line, designated TRM-1. This cell line expresses epithelial markers as well as glut2 and small amounts of insulin and glucagon. TRM-1 is the first cell line to be generated from the human fetal pancreas and also the first cell line derived directly from the fetal pancreas of any species. The approach that we have used to develop TRM-1 should be applicable to isolating cell lines from other stages of human pancreatic development. Copyright © 1997 Elsevier Science, Inc.

Implanting 1.1B4 human β-cell pseudoislets improves glycaemic control in diabetic severe combined immune deficient mice

AIM

To investigate the potential of implanting pseudoislets formed from human insulin-releasing β-cell lines as an alternative to islet transplantation.

METHODS

In this study, the anti-diabetic potential of novel human insulin releasing 1.1B4 β-cells was evaluated by implanting the cells, either as free cell suspensions, or as three-dimensional pseudoislets, into the subscapular region of severe combined immune deficient mice rendered diabetic by single high-dose administration of streptozotocin. Metabolic parameters including food and fluid intake, bodyweight and blood glucose were monitored throughout the study. At the end of the study animals were given an intraperitoneal glucose tolerance test. Animals were then culled and blood and tissues were collected for analysis. Insulin and glucagon contents of plasma and tissues were measured by insulin radioimmunoassay and chemiluminescent enzyme-linked immunosorbance assay respectively. Histological analyses of pancreatic islets were carried out by quantitative fluorescence immunohistochemistry staining.

RESULTS

Both pseudoislet and cell suspension implants yielded well vascularised β-cell masses of similar insulin content. This was associated with progressive amelioration of hyperphagia (P < 0.05), polydipsia (P < 0.05), body weight loss (P < 0.05), hypoinsulinaemia (P < 0.05), hyperglycaemia (P < 0.05 - P < 0.001) and glucose tolerance (P < 0.01). Islet morphology was also significantly improved in both groups of transplanted mice, with increased β-cell (P < 0.05 - P < 0.001) and decreased alpha cell (P < 0.05 - P < 0.001) areas. Whereas mice receiving 1.1B4 cell suspensions eventually exhibited hypoglycaemic complications, pseudoislet recipients displayed a more gradual amelioration of diabetes, and achieved stable blood glucose control similar to non-diabetic mice at the end of the study.

CONCLUSION

Although further work is needed to address safety issues, these results provide proof of concept for possible therapeutic applicability of human β-cell line pseudoislets in diabetes.

Granuphilin exclusively mediates functional granule docking to the plasma membrane

In regulated exocytosis, it is generally assumed that vesicles must stably “dock” at the plasma membrane before they are primed to become fusion-competent. However, recent biophysical analyses in living cells that visualize fluorescent secretory granules have revealed that exocytic behaviors are not necessarily uniform: some granules beneath the plasma membrane are resistant to Ca²⁺ -triggered release, while others are accelerated to fuse without a pause for stable docking. These findings suggest that stable docking is unnecessary, and can even be inhibitory or nonfunctional, for fusion. Consistently, pancreatic β cells deficient in the Rab27 effector, granuphilin, lack insulin granules directly attached to the plasma membrane in electron micrographs but nevertheless exhibit augmented exocytosis. Here we directly compare the exocytic behaviors between granuphilin-positive and -negative insulin granules. Although granuphilin makes granules immobile and fusion-reluctant beneath the plasma membrane, those granuphilin-positive, docked granules release a portion of granuphilin upon fusion, and fuse at a frequency and time course similar to those of granuphilin-negative undocked granules. Furthermore, granuphilin forms a 180-nm cluster at the site of each docked granule, along with granuphilin-interacting Rab27a and Munc18-1 clusters. These findings indicate that granuphilin is an exclusive component of the functional and fusion-inhibitory docking machinery of secretory granules.

Insm1 cooperates with Neurod1 and Foxa2 to maintain mature pancreatic β-cell function

Key transcription factors control the gene expression program in mature pancreatic β-cells, but their integration into regulatory networks is little understood. Here, we show that Insm1, Neurod1 and Foxa2 directly interact and together bind regulatory sequences in the genome of mature pancreatic β-cells. We used Insm1 ablation in mature β-cells in mice and found pronounced deficits in insulin secretion and gene expression. Insm1-dependent genes identified previously in developing β-cells markedly differ from the ones identified in the adult. In particular, adult mutant β-cells resemble immature β-cells of newborn mice in gene expression and functional properties. We defined Insm1, Neurod1 and Foxa2 binding sites associated with genes deregulated in Insm1 mutant β-cells. Remarkably, combinatorial binding of Insm1, Neurod1 and Foxa2 but not binding of Insm1 alone explained a significant fraction of gene expression changes. Human genomic sequences corresponding to the murine sites occupied by Insm1/Neurod1/Foxa2 were enriched in single nucleotide polymorphisms associated with glycolytic traits. Thus, our data explain part of the mechanisms by which β-cells maintain maturity: Combinatorial Insm1/Neurod1/Foxa2 binding identifies regulatory sequences that maintain the mature gene expression program in β-cells, and disruption of this network results in functional failure.

GATA factors promote ER integrity and β-cell survival and contribute to type 1 diabetes risk

Pancreatic β-cell survival remains poorly understood despite decades of research. GATA transcription factors broadly regulate embryogenesis and influence survival of several cell types, but their role in adult β-cells remains undefined. To investigate the role of GATA factors in adult β-cells, we derived β-cell-inducible Gata4- and Gata6-knockout mice, along with whole-body inducible Gata4 knockouts. β-Cell Gata4 deletion modestly increased the proportion of dying β-cells in situ with ultrastructural abnormalities suggesting endoplasmic reticulum (ER) stress. Notably, glucose homeostasis was not grossly altered in Gata4- and Gata6-knockout mice, suggesting that GATA factors do not have essential roles in β-cells. Several ER stress signals were up-regulated in Gata4 and Gata6 knockouts, most notably CHOP, a known regulator of ER stress-induced apoptosis. However, ER stress signals were not elevated to levels observed after acute thapsigargin administration, suggesting that GATA deficiency only caused mild ER stress. Simultaneous deletion of Gata4 and CHOP partially restored β-cell survival. In contrast, whole-body inducible Gata4 knockouts displayed no evidence of ER stress in other GATA4-enriched tissues, such as heart. Indeed, distinct GATA transcriptional targets were differentially expressed in islets compared with heart. Such β-cell-specific findings prompted study of a large meta-analysis dataset to investigate single nucleotide polymorphisms harbored within the human GATA4 locus, revealing several variants significantly associated with type 1 diabetes mellitus. We conclude that GATA factors have important but nonessential roles to promote ER integrity and β-cell survival in a tissue-specific manner and that GATA factors likely contribute to type 1 diabetes mellitus pathogenesis.

A novel dual-color reporter for identifying insulin-producing beta-cells and classifying heterogeneity of insulinoma cell lines

Many research studies use immortalized cell lines as surrogates for primary beta- cells. We describe the production and use of a novel "indirect" dual-fluorescent reporter system that leads to mutually exclusive expression of EGFP in insulin-producing (INS(+)) beta-cells or mCherry in non-beta-cells. Our system uses the human insulin promoter to initiate a Cre-mediated shift in reporter color within a single transgene construct and is useful for FACS selection of cells from single cultures for further analysis. Application of our reporter to presumably clonal HIT-T15 insulinoma cells, as well as other presumably clonal lines, indicates that these cultures are in fact heterogeneous with respect to INS(+) phenotype. Our strategy could be easily applied to other cell- or tissue-specific promoters. We anticipate its utility for FACS purification of INS(+) and glucose-responsive beta-like-cells from primary human islet cell isolates or in vitro differentiated pluripotent stem cells.

Survival benefit with proapoptotic molecular and pathologic responses from dual targeting of mammalian target of rapamycin and epidermal growth factor receptor in a preclinical model of pancreatic neuroendocrine carcinogenesis

PURPOSE

Pancreatic neuroendocrine tumors (PNETs), although rare, often metastasize, such that surgery, the only potentially curative therapy, is not possible. There is no effective systemic therapy for patients with advanced PNETs. Therefore, new strategies are needed. Toward that end, we investigated the potential benefit of dual therapeutic targeting of the epidermal growth factor receptor (EGFR) and mammalian target of rapamycin (mTOR) kinases, using a preclinical mouse model of PNET.

MATERIALS AND METHODS

Rapamycin and erlotinib, inhibitors of mTOR and EGFR, respectively, were used to treat RIP-Tag2 transgenic mice bearing advanced multifocal PNET. Tumor growth and survival were monitored, and tumors were surveyed for potential biomarkers of response to the therapeutics.

RESULTS

Rapamycin monotherapy was notably efficacious, prolonging survival concomitant with tumor stasis (stable disease). However, the tumors developed resistance, as evidenced by eventual relapse to progressive tumor growth. Erlotinib monotherapy slowed tumor growth and elicited a marginal survival benefit. In combination, there was an unprecedented survival benefit in the face of this aggressive multifocal cancer and, in contrast to either monotherapy, the development of adaptive resistance was not apparent. Additionally, the antiapoptotic protein survivin was implicated as a biomarker of sensitivity and beneficial responses to the dual targeted therapy.

CONCLUSION

Preclinical trials in a mouse model of endogenous PNET suggest that combined targeting of the mTOR and EGFR signaling pathways could have potential clinical benefit in treating PNET. These results have encouraged development of an ongoing phase II clinical trial aimed to evaluate the efficacy of this treatment regimen in human neuroendocrine tumors.

Menin interacts with IQGAP1 to enhance intercellular adhesion of beta-cells

Multiple endocrine neoplasia type 1 (MEN1) is a dominantly inherited tumor syndrome that results from the mutation of the MEN1 gene that encodes protein menin. Stable overexpression of MEN1 has been shown to partially suppress the RAS-mediated morphological changes of NH3 fibroblast cells. Little is known about the molecular mechanisms by which menin decreases the oncogenic effects on cell morphology and other phenotypes. Here we showed that ectopic expression of menin in pretumor beta cells increases islet cell adhesion and reduces cell migration. Our further studies revealed that menin interacts with the scaffold protein, IQGAP1, reduces GTP-Rac1 interaction with IQGAP1 but increases E-cadherin/ß-catenin interaction with IQGAP1. Consistent with an essential role for menin in regulating ß cell adhesion in vivo, accumulations of β-catenin and E-cadherin are reduced at cell junctions in the islets from Men1-excised mice. Together, these results define a novel menin-IQGAP1 pathway that controls cell migration and cell-cell adhesion in endocrine cells.

Stem/Progenitor cell sources of insulin-producing cells for the treatment of diabetes

Patients with diabetes experience decreased insulin secretion that is linked to a significant reduction in the number of islet cells. Reversal of diabetes can be achieved through islet transplantation, but the scarcity of donor islets severely hinders wide application of this therapeutic modality. Toward that end, embryonic stem cells, adult tissue-residing progenitor cells, and regenerating native beta-cells may serve as sources of islet cell surrogates. Insulin-producing cells generated from stem or progenitor cells display subsets of native beta-cell attributes, indicating the need for further development of methods for differentiation to completely functional beta-cells. Pharmacological approaches aiming at stimulating the in vivo/ex vivo regeneration of beta-cells have also been proposed as a way of augmenting islet cell mass. We review the current state of the generation of insulin-producing cells from different sources with emphasis on embryonic stem cells and adult progenitor cells. Challenges for the clinical use of these sources are also discussed.

The a3 isoform of V-ATPase regulates insulin secretion from pancreatic beta-cells

Vacuolar-type H(+)-ATPase (V-ATPase) is a multi-subunit enzyme that has important roles in the acidification of a variety of intracellular compartments and some extracellular milieus. Four isoforms for the membrane-intrinsic subunit (subunit a) of the V-ATPase have been identified in mammals, and they confer distinct cellular localizations and activities on the proton pump. We found that V-ATPase with the a3 isoform is highly expressed in pancreatic islets, and is localized to membranes of insulin-containing secretory granules in beta-cells. oc/oc mice, which have a null mutation at the a3 locus, exhibited a reduced level of insulin in the blood, even with high glucose administration. However, islet lysates contained mature insulin, and the ratio of the amount of insulin to proinsulin in oc/oc islets was similar to that of wild-type islets, indicating that processing of insulin was normal even in the absence of the a3 function. The insulin contents of oc/oc islets were reduced slightly, but this was not significant enough to explain the reduced levels of the blood insulin. The secretion of insulin from isolated islets in response to glucose or depolarizing stimulation was impaired. These results suggest that the a3 isoform of V-ATPase has a regulatory function in the exocytosis of insulin secretion.

Tumor progression induced by the loss of E-cadherin independent of beta-catenin/Tcf-mediated Wnt signaling

E-cadherin-mediated cell-cell adhesion is frequently lost during the development of malignant epithelial cancers. Employing a transgenic mouse model of beta-cell carcinogenesis (Rip1Tag2) we have previously shown that the loss of E-cadherin is a rate-limiting step in the progression from adenoma to carcinoma. However, the mere loss of cell adhesion may not be sufficient and additional signals are required to cause tumor cells to permeate the basal membrane and to invade surrounding tissue. Besides being an important component of the E-cadherin cell-adhesion complex, beta-catenin plays a critical role in canonical Wnt signaling. We report here that beta-catenin-mediated Wnt signaling does not contribute to tumor progression in Rip1Tag2 mice. E-cadherin downregulates beta-catenin/Tcf-mediated transcriptional activity by sequestrating beta-catenin into E-cadherin cell-adhesion complexes even in the presence of activated Wnt signaling. Upon loss of E-cadherin expression, beta-catenin is degraded and Tcf/beta-catenin-mediated transcriptional activity is not induced. Moreover, forced expression of constitutive-active beta-catenin or genetic ablation of Tcf/beta-catenin transcriptional activity in tumor cells of Rip1Tag2 transgenic mice does not affect tumor progression. Together, the data indicate that signals other than beta-catenin/Tcf-mediated Wnt signaling are induced by the loss of E-cadherin during tumor progression in Rip1Tag2 transgenic mice.

Early Immunization Induces Persistent Tumor-Infiltrating CD8+T Cells against an Immunodominant Epitope and Promotes Lifelong Control of Pancreatic Tumor Progression in SV40 Tumor Antigen Transgenic Mice

The ability to recruit the host's CD8+ T lymphocytes (T(CD8)) against cancer is often limited by the development of peripheral tolerance toward the dominant tumor-associated Ags. Because multiple epitopes derived from a given tumor Ag (T Ag) can be targeted by T(CD8), vaccine approaches should be directed toward those T(CD8) that are more likely to survive under conditions of persistent Ag expression. In this study, we investigated the effect of peripheral tolerance on the endogenous T(CD8) response toward two epitopes, designated epitopes I and IV, from the SV40 large T Ag. Using rat insulin promoter (RIP) 1-Tag4 transgenic mice that express T Ag from the RIP and develop pancreatic insulinomas, we demonstrate that epitope IV- but not epitope I-specific T(CD8) are maintained long term in tumor-bearing RIP1-Tag4 mice. Even large numbers of TCR-transgenic T cells specific for epitope I were rapidly eliminated from RIP1-Tag4 mice after adoptive transfer and recognition of the endogenous T Ag. Importantly, immunization of RIP1-Tag4 mice at 5 wk of age against epitope IV resulted in complete protection from tumor progression over a 2-year period despite continued expression of T Ag in the pancreas. This extensive control of tumor progression was associated with the persistence of functional epitope IV-specific T(CD8) within the pancreas for the lifetime of the mice without the development of diabetes. This study indicates that an equilibrium is reached in which immune surveillance for spontaneous cancer can be achieved for the lifespan of the host while maintaining normal organ function.

Oncogenic properties of the mutated forms of fibroblast growth factor receptor 3b

Germinal activating mutations of FGFR3 are responsible for several forms of dwarfism due to the inhibitory effect of FGFR3 on bone growth. Surprisingly, identical somatic activating mutations have been found at the somatic level in tumours: at high frequency in benign epithelial tumours (seborrheic keratosis, urothelial papilloma) and in low-grade, low-stage urothelial carcinomas, and at a lower frequency in other types of urothelial carcinoma, in cervix carcinoma, and in haematological cancer, multiple myeloma. FGFR3 exists as two isoforms, FGFR3b and FGFR3c, differs in ligand specificity and tissue expression. FGFR3b is the main form in epithelial cells and derived tumours, whereas FGFR3c is the main form in mesenchyme-derived cells and multiple myeloma. Several lines of evidence suggest that mutated FGFR3c has transforming properties. Although mutated FGFR3b is mostly found in benign epithelial tumours or carcinomas of low malignant potential, we present evidence here that mutated FGFR3b is oncogenic. All bladder tumours presenting FGFR3 mutations expressed this receptor more strongly than normal urothelium or non-mutated tumours. NIH-3T3 cells transfected with a mutated form of FGFR3b--FGFR3b-S249C, the most common mutation in bladder tumours--presented a spindle-cell morphology, grew in soft agar and gave rise to tumours when xenografted into nude mice. We identified one line of 17 bladder cell lines tested (MGH-U3) that expressed a mutated form of FGFR3b, FGFR3b-Y375C. We showed using siRNA and SU5402, an FGFR inhibitor, that the tumour properties of MGH-U3 depended on mutated receptor activity. Thus, in two different models, mutated FGFR3b presents oncogenic properties.

PDGFRbeta+ perivascular progenitor cells in tumours regulate pericyte differentiation and vascular survival

The microvasculature consists of endothelial cells and their surrounding pericytes. Few studies on the regulatory mechanisms of tumour angiogenesis have focused on pericytes. Here we report the identification of tumour-derived PDGFRbeta (+) (platelet-derived growth factor receptor beta) progenitor perivascular cells (PPCs) that have the ability to differentiate into pericytes and regulate vessel stability and vascular survival in tumours. A subset of PDGFRbeta (+) PPCs is recruited from bone marrow to perivascular sites in tumours. Specific inhibition of PDGFRbeta signalling eliminates PDGFRbeta (+) PPCs and mature pericytes around tumour vessels, leading to vascular hyperdilation and endothelial cell apoptosis in pancreatic islet tumours of transgenic Rip1Tag2 mice.

Cell lines derived from pancreatic islets

The islets of Langerhans play a major role in control of metabolic fuel homeostasis. The rapid increase in incidence of diabetes worldwide has spurred renewed interest in islet cell biology. However, gaining a detailed understanding of islet function at a molecular and biochemical level has been complicated by the difficulty and high cost associated with isolation of pancreatic islets. Until recently, islet-derived cell lines have represented sub-optimal surrogates for primary cells for functional studies due to their undifferentiated or unstable phenotypic features. New approaches have resulted in isolation and characterization of rodent insulinoma cell lines that retain many key functional attributes of normal islets and have become useful tools in the study of islet cell biology.

Growth, differentiation and senescence of normal human urothelium in an organ-like culture

OBJECTIVE

To examine the kinetics of growth, differentiation and senescence of normal human urothelium in an organoid-like culture model.

MATERIALS AND METHODS

Micro-dissected normal human urothelium explants were grown on porous membranes pretreated with various matrix components. Between 5 and 30 days of culture, cell proliferation was assessed by BrdU incorporation. Differentiation was evaluated on the basis of cytokeratin (Ck) and uroplakin (UP) expression. Epidermal growth factor family mRNA expression was monitored during explant outgrowth. Senescence was assessed by measuring endogenous beta-galactosidase activity and p16(INK4a) mRNA expression.

RESULTS

Collagen IV was the most efficient matrix component for urothelial cell expansion. BrdU incorporation by urothelial cells was 5% between 15 and 30 days, corresponding to steady-state urothelium in vivo. Heparin-binding EGF (HB-EGF), Amphiregulin (AR) and Transforming Growth Factor alpha (TGF alpha) expression correlated with increased cell proliferation. UPII expression was stable throughout culture. P16(INK4a) mRNA expression and beta-galactosidase activity increased on day 25, giving signs of senescence.

CONCLUSIONS

This model retains many characteristics of the urothelium in vivo. It can be used for pharmacological studies between 15 to 25 days and to study mechanisms such as wound healing, proliferation and senescence.

Regulation of insulin secretion: insights from engineered beta-cell lines

Abnormalities in insulin secretion are involved in a number of diseases, including type 1 and type 2 diabetes, persistent hyperinsulinemic hypoglycemia of infancy, and insulinoma. Understanding the mechanisms that regulate insulin secretion may allow the development of new therapies for these diseases as well as contribute to our ability to engineer insulin-producing cells for cell replacement therapy of type 1 diabetes. Glucose phosphorylation in beta-cells has been viewed as a key regulatory event in coupling insulin secretion to extracellular glucose concentrations. Work with transformed rodent beta-cell lines as well as recent findings from human progenitor cells induced to differentiate into insulin-producing cells has provided new insights into the role of glucose phosphorylating enzymes in the regulation of insulin secretion.

Epidermal growth factor receptor regulates normal urothelial regeneration

Members of the epidermal growth factor (EGF) family and their receptors are involved in many cellular processes, including proliferation, migration, and differentiation. We have previously reported that these growth factors are expressed and have specific regulatory functions in an organ-like culture model of normal human urothelial cells. Here, we used this model to investigate the involvement of EGF receptor (EGFR) in human urothelial regeneration. Three 4-mm-diameter damaged areas were made in confluent normal human urothelial cell cultures with a biopsy punch. Regeneration was measured, on fixed stained cultures, with an image analyzer, at 4, 24, and 48 hours after injury. Cell proliferation was assessed by 5-bromo-2-deoxyuridine incorporation. To identify EGF family factors potentially involved in the healing process, we studied the effect of these factors on damaged confluent cultures and the level of expression of mRNAs extracted from these cultures. EGFR inhibition of the proliferation and migration of urothelial cells was tested with (1). a specific tyrosine kinase inhibitor (AG1478) and (2). a blocking anti-EGFR antibody (LA22). Exogenously added amphiregulin, EGF, transforming growth factor-alpha and heparin-binding EGF (HB-EGF) stimulated urothelial regeneration. The damaged areas were repaired by regrowth within 48 hours. Both AG1478 and LA22 inhibited the repair (by 50% and 30%, respectively), as well as proliferation and migration. This regeneration was accompanied by increased HB-EGF mRNA expression in cultures of cells from four of six subjects, but no corresponding change in EGFR protein level was observed. These results indicate that the EGFR signaling pathway is involved in urothelial regeneration. Our data support an autocrine role of HB-EGF in this process and suggest that the EGFR pathway is a potential therapeutic target for modulating urothelial cell proliferation.

Switch to anaerobic glucose metabolism with NADH accumulation in the beta-cell model of mitochondrial diabetes. Characteristics of betaHC9 cells deficient in mitochondrial DNA transcription

To elucidate the mechanism underlying diabetes caused by mitochondrial gene mutations, we created a model by applying 0.4 microg/ml ethidium bromide (EtBr) to the murine pancreatic beta cell line betaHC9; in this model, transcription of mitochondrial DNA, but not that of nuclear DNA, was suppressed in association with impairment of glucose-stimulated insulin release (Hayakawa, T., Noda, M., Yasuda, K., Yorifuji, H., Taniguchi, S., Miwa, I., Sakura, H., Terauchi, Y., Hayashi, J.-I., Sharp, G. W. G., Kanazawa, Y., Akanuma, Y., Yazaki, Y., and Kadowaki, T. (1998) J. Biol. Chem. 273, 20300-20307). To elucidate fully the metabolism-secretion coupling in these cells, we measured glucose oxidation, utilization, and lactate production. We also evaluated NADH autofluorescence in betaHC9 cells using two-photon excitation laser microscopy. In addition, we recorded the membrane potential and determined the ATP and ADP contents of the cells. The results indicated 22.2 mm glucose oxidation to be severely decreased by EtBr treatment compared with control cells (by 63% on day 4 and by 78% on day 6; both p < 0.01). By contrast, glucose utilization was only marginally decreased. Lactate production under 22.2 mm glucose was increased by 2.9- and 3.5-fold by EtBr treatment on days 4 and 6, respectively (both p < 0.01). Cellular NADH at 2.8 mm glucose was increased by 35 and 43% by EtBr on days 4 and 6 (both p < 0.01). These data suggest that reduced expression of the mitochondrial electron transport system causes NADH accumulation in beta cells, thereby halting the tricarboxylic acid cycle on one hand, and on the other hand facilitating anaerobic glucose metabolism. Glucose-induced insulin secretion was lost rapidly along with the EtBr treatment with concomitant losses of membrane potential depolarization and the [Ca(2+)](i) increase, whereas glibenclamide-induced changes persisted. This is the first report to demonstrate the connection between metabolic alteration of electron transport system and that of tricarboxylic acid cycle and its impact on insulin secretion.

Soluble Eph A receptors inhibit tumor angiogenesis and progression in vivo

The Eph family of receptor tyrosine kinases and their ligands, known as ephrins, play a crucial role in vascular development during embryogenesis. The function of these molecules in adult angiogenesis has not been well characterized. Here, we report that blocking Eph A class receptor activation inhibits angiogenesis in two independent tumor types, the RIP-Tag transgenic model of angiogenesis-dependent pancreatic islet cell carcinoma and the 4T1 model of metastatic mammary adenocarcinoma. Ephrin-A1 ligand was expressed in both tumor and endothelial cells, and EphA2 receptor was localized primarily in tumor-associated vascular endothelial cells. Soluble EphA2-Fc or EphA3-Fc receptors inhibited tumor angiogenesis in cutaneous window assays, and tumor growth in vivo. EphA2-Fc or EphA3-Fc treatment resulted in decreased tumor vascular density, tumor volume, and cell proliferation, but increased cell apoptosis. However, EphA2-Fc had no direct effect on tumor cell growth or apoptosis in culture, yet inhibited migration of endothelial cells in response to tumor cells, suggesting that the soluble receptor inhibited blood vessel recruitment by the tumor. These data provide the first functional evidence for Eph A class receptor regulation of pathogenic angiogenesis induced by tumors and support the function of A class Eph receptors in tumor progression.

Cyotomedical therapy for insulinopenic diabetes using microencapsulated pancreatic beta cell lines

Current therapy for type 1 diabetes mellitus involves a daily regimen of multiple subcutaneous or intramuscular injections of recombinant human insulin. To achieve long-term insulin delivery in vivo, we investigated the applicability of cytomedical therapy using beta TC6 cells or MIN6 cells, both of which are murine pancreatic beta cell lines that secrete insulin in a subphysiologically or physiologically regulated manner, respectively. We examined this therapy in the insulinopenic diabetic mice intraperitoneally injected with beta TC6 cells or MIN6 cells microencapsulated within alginate-poly(L)lysine-alginate membranes (APA-beta TC6 cells or APA-MIN6 cells). The diabetic mice treated with APA-beta TC6 cells fell into hypoglycemia, whereas those injected with APA-MIN6 cells maintained normal blood glucose concentrations for over 2 months without developing hypoglycemia. In addition, we also conducted an oral glucose tolerance test using these mice. The blood glucose concentrations of normal and of diabetic mice injected with APA-MIN6 cells similarly changed over time, although the blood insulin concentration increased later in the injected diabetic mice than in the former. These results suggest that cytomedicine utilizing microencapsulated pancreatic beta cell lines with a physiological glucose sensor may be a beneficial and safe therapy with which to treat diabetes mellitus.

Intracellular calcium ion response to glucose in beta-cells of calbindin-D28k nullmutant mice and in betaHC13 cells overexpressing calbindin-D28k

This article describes studies on the glucose-induced responses of intracellular Ca2+ concentration ([Ca2+]i), insulin release, and redistribution of calbindin-D28k, a calcium-binding regulatory protein, in beta-cells of pancreatic islets of calbindin-D28k knockout (KO) and wild-type mice (C57BL6) as well as in betaHC-13 control cells and betaHC-13 CaBP40 cells (beta-cell line overexpressing calbindin-D28k). Upon increasing the glucose concentration from 2.8 to 30 mM, islets of KO mice showed a significantly greater increase in [Ca2+]i (mean increase in [Ca2+]i, i.e., delta[Ca2+]i, was 296 nM) compared with wild-type mice (delta[Ca2+]i = 97 nM). betaHC-13 CaBP40 cells showed little change in [Ca2+]i upon elevation of glucose from 5.5 to 32.7 mM, whereas betaHC-13 control cells exhibited significant increases in [Ca2+]i, (delta[Ca2+]i = 510 nM). Similarly, upon addition of 30 mM glucose, the rate of insulin release increased from 25.2 (basal rate) to 145.2 pg/mL/min in betaHC-13 control cells, whereas in betaHC-13 CaBP40 cells the rate of insulin release was only 27.5 pg/mL/min in high glucose. Thus, levels of calbindin-D28k in beta-cells affect both [Ca2+]i and insulin secretion in response to glucose. The three-dimensional reconstruct of confocal immunofluorescent images showed that glucose caused redistribution of calbindin-D28k resulting in co-localization in the region of L-type voltage-dependent calcium channels (VDCC). This co-localization may be an important regulatory function concerning Ca2+ influx via L-type VDCC and exocytosis of insulin granules.

Pancreatic cell lines: a review

Pancreatic cancer has an extremely poor prognosis and lacks early diagnostic and therapeutic possibilities, mainly because of its silent course and explosive fatal outcome. The histogenesis of the disease and early biochemical and genetic alterations surrounding carcinogenesis are still controversial. In vitro studies offer a useful tool to study physiologic, pathophysiologic, differentiation, and transformation processes of cells and to understand some of these shortcomings. The extreme difficulties in isolating individual pancreatic cells and their purification by maintaining their native characteristics have limited research in this area. This review is intended to present and discuss the current availability of rodent and pancreatic cell lines, their differences as well as the difficulties, limitations, and characteristics of these cultured cells. Discussed are in vitro models; ductal, islet, and acinar cell culture; cell differentiation; cell transformation, including genetic and chromosomal alterations; as well as tumor cell markers. Also addressed are the advantages and problems associated with the cell culture in humans and rodents. Advancements in tissue culture technique and molecular biology offer steady progress in this important line of research. The improved methods not only promise the establishment of beta-cell cultures for the treatment of diabetes, but also for studying sequential genetic alterations during pancreatic carcinogenesis and in understanding the tumor cell origin.

Non-Invasive monitoring of a bioartificial pancreas in vitro and in vivo

Monitoring biochemical processes relevant to the function, survival, and longevity of tissue-engineered pancreatic constructs is important for the development of an optimum construct design as well as patient care management after implantation. In this report we demonstrate the ability of nuclear magnetic resonance (NMR) techniques to monitor aspects of intracellular metabolism, overall morphology, and distribution of a microencapsulation based bioartificial pancreas in vitro and in vivo.

Unbalanced expression of 11p15 imprinted genes in focal forms of congenital hyperinsulinism: association with a reduction to homozygosity of a mutation in ABCC8 or KCNJ11

Congenital hyperinsulinism (CHI), previously named persistent hyperinsulinemic hypoglycemia of infancy, is characterized by profound hypoglycemia because of excessive insulin secretion. CHI presents as two different morphological forms: a diffuse form with functional abnormality of islets throughout the pancreas and a focal form with focal islet cell adenomatous hyperplasia, which can be cured by partial pancreatectomy. Recently, we have shown that focal adenomatous hyperplasia involves the specific loss of the maternal 11p15 region and a constitutional mutation of a paternally inherited allele of the gene encoding the regulating subunit of the K(+)(ATP) channel, the sulfonylurea receptor (ABCC8 or SUR1). In the present study on a large series of 31 patients, describing both morphological features and molecular data, we report that 61% of cases (19 out of 31) carried a paternally inherited mutation not only in the ABCC8 gene as previously described but also in the second gene encoding the K(+)(ATP) channel, the inward rectifying potassium channel (KCNJ11 or KIR6.2), in 15 cases and 4 cases, respectively. Moreover our results are consistent with the presence of a duplicated paternal 11p15 allele probably because of mitotic recombination or reduplication of the paternal chromosome after somatic loss of the maternal chromosome. In agreement with the loss of the maternal chromosome, the level of expression of a maternally expressed tumor suppressor gene, H19, was greatly reduced compared to the level of expression of the paternally expressed growth promoter gene, IGF2. The expression of IGF2 was on average only moderately increased. Thus, focal forms of CHI can be considered to be a recessive somatic disease, associating an imbalance in the expression of imprinted genes in the 11p15.5 region to a somatic reduction to homozygosity of an ABCC8- or KCNJ11-recessive mutation. The former is responsible for the abnormal growth rate, as in embryonic tumors, whereas the latter leads to unregulated secretion of insulin.

Inosine-5'-monophosphate dehydrogenase is required for mitogenic competence of transformed pancreatic beta cells

The relation of inosine-5'-monophosphate dehydrogenase (IMPDH; the rate-limiting enzyme in GTP synthesis) to mitogenesis was studied by enzymatic assay, immunoblots, and RT-PCR in several dissimilar transformed pancreatic ss-cell lines, using intact cells. Both of the two isoforms of IMPDH (constitutive type 1 and inducible type 2) were identified using RT-PCR in transformed beta cells or in intact islets. IMPDH 2 messenger RNA (mRNA) and IMPDH protein were both regulated reciprocally by changes in levels of their end-products. Flux through IMPDH was greatest in rapidly growing cells, due mostly to increased uptake of precursor. Glucose (but not 3-0-methylglucose, L-glucose, or fructose) further augmented substrate uptake and also increased IMPDH enzymatic activity after either 4 or 21 h of stimulation. Serum or ketoisocaproate also increased IMPDH activity (but not uptake). Two selective IMPDH inhibitors (mycophenolic acid and mizoribine) reduced IMPDH activity in all cell lines, and, with virtually identical concentration-response curves, inhibited DNA synthesis (assessed as bromodeoxyuridine incorporation) in response to glucose, serum, or ketoisocaproate. Inhibition of DNA synthesis was reversible, completely prevented by repletion of cellular guanine (but not adenine) nucleotides, and could not be attributed to toxic effects. Despite the fact that modulation of IMPDH expression by guanine nucleotides was readily detectable, glucose and/or serum failed to alter IMPDH mRNA or protein, indicating that their effects on IMPDH activity were largely at the enzyme level. Precursors of guanine nucleotides failed, by themselves, to induce mitogenesis. Thus, adequate IMPDH activity (and thereby, availability of GTP) is a critical requirement for beta-cell proliferation. Although it is unlikely that further increases in GTP can, by themselves, initiate DNA synthesis, such increments may be needed to sustain mitogenesis.

Isolation, maintenance, and characterization of human pancreatic islet tumor cells expressing vasoactive intestinal peptide

Tissue from a vasoactive intestinal peptide (VIP)-secreting human tumor has been used to establish and characterize human neuroendocrine primary cell cultures from which permanent, clone-derived cell lines have been established. Viable cells were obtained by enzymatic and mechanical dissociation of freshly resected pancreatic islet tumor and hepatic metastatic tumor tissues. Aliquots of tumor cells were established ex vivo under culture conditions including porous substrata coated with type IV collagen and laminin and a low serum, hormonally defined culture medium. The small (<10 microm) rounded, grape-like cells had a very slow growth rate of doubling times estimated at several weeks or more. After several passages, morphologically uniform cells were derived that strongly expressed neuroendocrine markers of synaptophysin and synaptobrevin. Although chromogranin A and VIP had somewhat weaker expression, both demonstrated phorbol ester-stimulated secretion. The morphologic and secretory properties were maintained by the cells for nearly 2 years in culture. The establishment of this novel VIP-secreting human neuroendocrine cell line (HuNET) makes available a culture model with which to study a transformed version of this pancreatic islet cell type and offers approaches by which to establish islet tumor cell lines.

Insulin-secreting pituitary GH3 cells: a potential beta-cell surrogate for diabetes cell therapy

In a companion article, we describe the engineering and characterization of pituitary GH3 cell clones stably transfected with a furin-cleavable human insulin cDNA (InsGH3 cells). This article describes the performance of InsGH3 (clones 1 and 7) cell grafts into streptozotocin (STZ)-induced diabetic nude mice. Subcutaneous implantation of 2 x 10(6) InsGH3 cells resulted in the progressive reversal of hyperglycemia and diabetic symptoms, even though the progressive growth of the transplanted cells (clone 7) eventually led to glycemic levels below the normal mouse range. Proinsulin transgene expression was maintained in harvested InsGH3 grafts that, conversely, lose the expression of the prolactin (PRL) gene. Elevated concentrations of circulating mature human insulin were detected in graft recipients, demonstrating that proinsulin processing by InsGH3 cells did occur in vivo. Histologic analysis showed that transplanted InsGH3 grew in forms of encapsulated tumors composed of cells with small cytoplasms weakly stained for the presence of insulin. Conversely, intense insulin immunoreactivity was detected in graft-draining venules. Compared to pancreatic betaTC3 cells, InsGH3 cells showed in vitro a higher rate of replication, an elevate resistance to apoptosis induced by serum deprivation and proinflammatory cytokines, and significantly higher antiapoptotic Bcl-2 protein levels. Moreover, InsGH3 cells were resistant to the streptozotocin toxicity that, in contrast, reduced betaTC3 cell viability to 50-60% of controls. In conclusion, proinsulin gene expression and mature insulin secretion persisted in transplanted InsGH3 cells that reversed hyperglycemia in vivo. InsGH3 cells might represent a potential beta-cell surrogate because they are more resistant than pancreatic beta cells to different apoptotic insults and might therefore be particularly suitable for encapsulation.

Development and characterization of pituitary GH3 cell clones stably transfected with a human proinsulin cDNA

Successful beta-cell replacement therapy in insulin-dependent (type I) diabetes is hindered by the scarcity of human donor tissue and by the recurrence of autoimmune destruction of transplanted beta cells. Availability of non-beta cells, capable of releasing insulin and escaping autoimmune recognition, would therefore be important for diabetes cell therapy. We developed rat pituitary GH3 cells stably transfected with a furin-cleavable human proinsulin cDNA linked to the rat PRL promoter. Two clones (InsGH3/clone 1 and 7) were characterized in vitro with regard to basal and stimulated insulin release and proinsulin transgene expression. Mature insulin secretion was obtained in both clones, accounting for about 40% of total released (pro)insulin-like products. Immunocytochemistry of InsGH3 cells showed a cytoplasmic granular insulin staining that colocalized with secretogranin II (SGII) immunoreactivity. InsGH3 cells/clone 7 contained and released in vitro significantly more insulin than clone 1. Secretagogue-stimulated insulin secretion was observed in both InsGH3 clones either under static or dynamic conditions, indicating that insulin was targeted also to the regulated secretory pathway. Proinsulin mRNA levels were elevated in InsGH3 cells, being significantly higher than in betaTC3 cells. Moreover, proinsulin gene expression increased in response to various stimuli, thereby showing the regulation of the transfected gene at the transcriptional level. In conclusion, these data point to InsGH3 cells as a potential beta-cell surrogate even though additional engineering is required to instruct them to release insulin in response to physiologic stimulations.

Tumour suppressive properties of fibroblast growth factor receptor 2-IIIb in human bladder cancer

FGFRs (fibroblast growth factor receptors) are encoded by four genes (FGFR1-4). Alternative splicing results in various receptor isoforms. The FGFR2-IIIb variant is present in a wide variety of epithelia, including the bladder epithelium. Recently, we have shown that FGFR2-IIIb is downregulated in a subset of transitional cell carcinomas of the bladder, and that this downregulation is associated with a poor prognosis. We investigated possible tumour suppressive properties of FGFR2-IIIb by transfecting two human bladder tumour cell lines, J82 and T24, which have no endogenous FGFR2-IIIb expression, with FGFR2-IIIb cDNA. No stable clones expressing FGFR2-IIIb were isolated with the J82 cell line. For the T24 cell line, stable transfectants expressing FGFR2-IIIb had reduced growth in vitro and formed fewer tumours in nude mice which, in addition, grew more slowly. The potential mechanisms leading to decreased FGFR2-IIIb mRNA levels were also investigated. The 5' region of the human FGFR2 gene was isolated and found to contain a CpG island which was partially methylated in more than half the cell lines and tumours which do not express FGFR2-IIIb. No homozygous deletion was identified in any of the tumours or cell lines with reduced levels of FGFR2-IIIb. Mutational analysis of the entire coding region of FGFR2-IIIb at the transcript level was performed in 33 bladder tumours. In addition to normal FGFR2-IIIb mRNA, abnormal transcripts were detected in two tumour samples. These abnormal mRNAs resulted from exon skipping which affected the region encoding the kinase domain. Altogether, these results show that FGFR2-IIIb has tumour growth suppressive properties in bladder carcinomas and suggest possible mechanisms of FGFR2 gene inactivation.

Calbindin-D(28k) controls [Ca(2+)](i) and insulin release. Evidence obtained from calbindin-d(28k) knockout mice and beta cell lines

The role of the calcium-binding protein, calbindin-D(28k) in potassium/depolarization-stimulated increases in the cytosolic free Ca(2+) concentration ([Ca(2+)](i)) and insulin release was investigated in pancreatic islets from calbindin-D(28k) nullmutant mice (knockouts; KO) or wild type mice and beta cell lines stably transfected and overexpressing calbindin. Using single islets from KO mice and stimulation with 45 mM KCl, the peak of [Ca(2+)](i) was 3.5-fold greater in islets from KO mice compared with wild type islets (p < 0.01) and [Ca(2+)](i) remained higher during the plateau phase. In addition to the increase in [Ca(2+)](i) in response to KCl there was also a significant increase in insulin release in islets isolated from KO mice. Evidence for modulation by calbindin of [Ca(2+)](i) and insulin release was also noted using beta cell lines. Rat calbindin was stably expressed in betaTC-3 and betaHC-13 cells. In response to depolarizing concentrations of K(+), insulin release was decreased by 45-47% in calbindin expressing betaTC cells and was decreased by 70-80% in calbindin expressing betaHC cells compared with insulin release from vector transfected betaTC or betaHC cells (p < 0.01). In addition, the K(+)-stimulated intracellular calcium peak was markedly inhibited in calbindin expressing betaHC cells compared with vector transfected cells (225 nM versus 1,100 nM, respectively). Buffering of the depolarization-induced rise in [Ca(2+)](i) was also observed in calbindin expressing betaTC cells. In summary, our findings, using both isolated islets from calbindin-D(28k) KO mice and beta cell lines, establish a role for calbindin in the modulation of depolarization-stimulated insulin release and suggest that calbindin can control the rate of insulin release via regulation of [Ca(2+)](i).

Luminometric assays of ATP, phosphocreatine, and creatine for estimation of free ADP and free AMP

We present methods to measure ATP, phosphocreatine, and total creatine (the sum of creatine and phosphocreatine) in alkaline cell extracts. Knowledge of these parameters, together with the known equilibrium constants for the creatine kinase and adenylate kinase-catalyzed reactions, allows one to estimate the levels of free ADP and free AMP inside cells. The enzymatic assays for the above-mentioned metabolites all lead up to the production of ATP, which is measured luminometrically with the ATP-dependent oxidation of luciferin catalyzed by firefly luciferase. To determine phosphocreatine, endogenous ATP is first destroyed, and phosphocreatine is then quantitatively reacted with exogenous ADP to form ATP. Total creatine is measured after quantitative conversion of creatine to phosphocreatine with a large excess of exogenous ATP, conversion of all ATP to ADP, and final reaction of phosphocreatine with ADP to form ATP. We used 5-microl samples in 0.5-ml microcentrifuge tubes and subsequent 5-microl additions of analytical reagents. We expect that the volumes can be changed easily. We tested the methods with glucagon- and insulin-secreting cells. Estimates of free ADP and AMP are expected to be useful in many different areas of research, such as cellular energy metabolism, purine nucleotide metabolism, adenine nucleotide gating of ion channels, and release of vasoactive or angiogenic factors.

Relationship between E-cadherin and fibroblast growth factor receptor 2b expression in bladder carcinomas

E-cadherin is a cell-cell adhesion molecule expressed predominantly by epithelial cells. Reduction or loss of E-cadherin immunoreactivity has been associated with tumour progression in many epithelial cancers, including bladder carcinomas. The fibroblast growth factor receptor 2b (FGFR2b) recognized specifically by FGF7 is expressed only by epithelial cells. Recently, decreased expression of FGFR2b protein and mRNA was found to be associated with tumour progression in bladder carcinomas. The purpose of this investigation was to look for a possible relationship between E-cadherin and FGFR2b expression in bladder carcinomas. As decreased E-cadherin immunoreactivity was found to correlate directly with decreased expression at the mRNA level, the possible relationship between E-cadherin and FGFR2b was investigated at the mRNA level using semi-quantitative RT - PCR in 92 transitional cell carcinomas (TCCs) and four lymph node metastases. All tumours with low E-cadherin expression had low expression of FGFR2b, whereas tumours with low FGFR2b mRNA could express any level of E-cadherin mRNA. The same observation was equally valid for bladder and colon cancer cell lines suggesting that, besides bladder tumours, this relationship could apply to other carcinomas types. These results suggest that a relationship exists between the transcription of the E-cadherin and FGFR2b genes preventing high expression of FGFR2b where expression of E-cadherin is low. We suggest that reduced expression of FGFR2b in conjunction with decreased expression of E-cadherin may contribute to the aggressive behaviour attributable to high grade TCCs.

Novel rabphilin-3-like protein associates with insulin-containing granules in pancreatic beta cells

A novel rabphilin-3-like gene, granuphilin, has been identified in pancreatic beta cells by comparing genes expressed in pancreatic alpha and beta cell lines using mRNA differential display. The domain structure of the protein products of the granuphilin gene contains an amino-terminal zinc-finger motif and carboxyl-terminal C(2)-domains, similar to that of the rabphilin-3 gene. There are two isoforms: the larger isoform, granuphilin-a, has two C(2)-domains, whereas the smaller one, granuphilin-b, contains only the first C(2)-domain. Granuphilin is specifically expressed in pancreatic beta cells and the pituitary gland, but not in pancreatic alpha cells, the adrenal gland, or other major organs such as the brain. A portion of granuphilin associates with insulin-containing dense-core granules, but not with synaptic-like microvesicles in beta cells. Thus, its distribution pattern presents a striking contrast with that of rabphilin-3, which associates with small synaptic vesicles in neurons. The first C(2)-domain of granuphilin binds phospholipids in a Ca(2+)-independent manner, whereas the second one does not. These distinctive characteristics of granuphilin suggest that it is not a simple counterpart of rabphilin-3 in endocrine cells and that it has a unique role in the regulated exocytosis of dense-core granules in endocrine tissues.

Cell-biological assessment of human glucokinase mutants causing maturity-onset diabetes of the young type 2 (MODY-2) or glucokinase-linked hyperinsulinaemia (GK-HI)

Mutations in the glucokinase (GK) gene cause type-2 maturity-onset diabetes of the young type 2 (MODY-2) and GK-linked hyperinsulinaemia (GK-HI). Recombinant adenoviruses expressing the human wild-type islet GK or one of four mutant forms of GK, (the MODY-2 mutants E70K, E300K and V203A and the GK-HI mutant V455M) were transduced into glucose-responsive insulin-secreting beta-HC9 cells and tested functionally in order to initiate the first analysis in vivo of recombinant wild-type and mutant human islet GK. Kinetic analysis of wild-type human GK showed that the glucose S(0. 5) and Hill coefficient were similar to previously published data in vitro (S(0.5) is the glucose level at the half-maximal rate). E70K had half the glucose affinity of wild-type, but similar enzyme activity. V203A demonstrated decreased catalytic activity and an 8-fold increase in glucose S(0.5) when compared with wild-type human islet GK. E300K had a glucose S(0.5) similar to wild-type but a 10-fold reduction in enzyme activity. E300K mRNA levels were comparable with wild-type GK mRNA levels, but Western-blot analyses demonstrated markedly reduced levels of immunologically detectable protein, consistent with an instability mutation. V455M was just as active as wild-type GK, but with a markedly reduced S(0.5). The effects of the different GK mutants on glucose-stimulated insulin release support the kinetic and expression data. These experiments show the utility of a combined genetic, biochemical and cell-biological approach to the quantification of functional and structural changes of human GK that result from MODY-2 and GK-HI mutations.

The TATA-less rat GAD65 promoter can be activated by Sp1 through non-consensus elements

Glutamic acid decarboxylase (GAD) 65 is one of two homologous proteins responsible for the synthesis of gamma-aminobutyric acid, the most ubiquitous inhibitory neurotransmitter. In order to characterize the DNA elements responsible for controlling GAD65 expression, we cloned the 5' flanking region of the rat GAD65 gene. A major, proximal and a minor, distal region of transcription initiation were located by RACE experiments. Sequence analysis revealed that the initiation sites are located within a region devoid of TATA boxes. We investigated the functional organization of the promoter by measuring the ability of 5' deletion mutants to drive the expression of a luciferase reporter gene. The major promoter was found to be located in the region encompassing the 100bp immediately upstream of the proximal transcription initiation site. A number of near consensus GC boxes and initiator elements are found in this region, but gel-shift assays suggest that they play only a minor role in transcription initiation. However, gel-shift assays and reporter gene assays suggest that Sp1 can bind to a region devoid of consensus Sp1 binding sites.

A protective role for heme oxygenase expression in pancreatic islets exposed to interleukin-1beta

Heme oxygenase (HO)-1 expression was investigated in rat isolated pancreatic islets. Freshly isolated islets showed no evidence of HO-1 expression. After a 20-h culture, there was a small increase in HO-1 in control islets, and interleukin-1beta (IL-1beta) induced HO-1 expression above control levels. N(G)-monomethyl-L-arginine inhibited the IL-1beta-induced increase in HO-1. Sodium nitroprusside-generated nitric oxide also increased HO-1 expression. CoCl2 induced a concentration- and time-dependent increase in HO-1, but not heat shock protein 70, expression. Cobalt chloride (CoCl2) protected islets from the inhibitory effects of IL-1beta on glucose-stimulated insulin release and glucose oxidation. Nickel chloride did not mimic the effects of CoCl2. An inhibitor of HO-1 activity, zinc-protoporphyrin IX (ZnPP), prevented the protective effect of CoCl2 on insulin release with IL-1beta but did not affect HO-1 expression or the inhibitory response to IL-1beta alone. ZnPP also inhibited the protective effect of hemin in IL-1beta-treated islets. CoCl2 inhibited the marked increase in islet nitrite production in response to IL-1beta. Cobalt-protoporphyrin IX (CoPP), which increased HO expression and activity, also protected islets from the inhibitory effects of IL-1beta, even though IL-1beta largely blocked the CoPP-induced increase in HO-1 expression. In betaHC9 cells, CoCl2 increased HO-1 expression and HO activity, whereas CoPP directly activated HO. ZnPP inhibited basal and CoCl2-stimulated HO activity. Thus, increased HO-1 expression and/or HO activity in response to CoCl2, CoPP, and hemin, seems to mediate protective responses of pancreatic islets against IL-1beta. HO-1 may be protective of beta-cells because of the scavenging of free heme, the antioxidant effects of the end-product bilirubin, or the generation of carbon monoxide, which might have insulin secretion-promoting effects and inhibitory effects on nitric oxide synthase.

Ethidium bromide-induced inhibition of mitochondrial gene transcription suppresses glucose-stimulated insulin release in the mouse pancreatic beta-cell line betaHC9

Recently, a mitochondrial mutation was found to be associated with maternally inherited diabetes mellitus (Kadowaki, T., Kadowaki, H., Mori, Y., Tobe, K., Sakuta, R., Suzuki, Y., Tanabe, Y, Sakura, H., Awata, T., Goto, Y., Hayakawa, T., Matsuoka, K., Kawamori, R., Kamada, T., Horai, S., Nonaka, I., Hagura, R., Akanuma, Y., and Yazaki, Y. (1994) N. Engl. J. Med. 330, 962-968). In order to elucidate its etiology, we have investigated the involvement of mitochondrial function in insulin secretion. Culture of the pancreatic beta-cell line, betaHC9, with low dose ethidium bromide (EB) (0.4 microg/ml) for 2-6 days resulted in a substantial decrease in the transcription level of mitochondrial DNA (to 10-20% of the control cells) without changing its copy number, whereas the transcription of nuclear genes was grossly unaffected. Electron microscopic analysis revealed that treatment by EB caused morphological changes only in mitochondria and not in other organelles such as nuclei, endoplasmic reticula, Golgi bodies, or secretory granules. When the cells were treated with EB for 6 days, glucose (20 mM) could no longer stimulate insulin secretion, while glibenclamide (1 microM) still did. When EB was removed after 3- or 6-day treatment, mitochondrial gene transcription recovered within 2 days, and the profiles of insulin secretion returned to normal within 7 days. Studies with fura-2 indicated that in EB-treated cells, glucose (20 mM) failed to increase intracellular Ca2+, while the effect of glibenclamide (1 microM) was maintained. Our system provides a unique way to investigate the relationship between mitochondrial function and insulin secretion.

Generation and characterization of monoclonal antibodies to alveolar type II cell lamellar body membrane

Monoclonal antibodies against the limiting membrane of alveolar type II cell lamellar bodies were obtained after immunization of mice with a membrane fraction prepared from lamellar bodies isolated from rat lungs. The specificity of the antibodies was investigated with Western blot analysis, indirect immunofluorescence, and electron-microscopic immunogold studies of freshly isolated or cultured alveolar type II cells, alveolar macrophages, and rat lung tissue. One of the monoclonal antibodies identified, MAb 3C9, recognized a 180-kDa lamellar body membrane (lbm180) protein. Immunogold labeling of rat lung tissue with MAb 3C9 demonstrated that lbm180 protein is primarily localized at the lamellar body limiting membrane and is not found in the lamellar body contents. Most multivesicular bodies of type II cells were also labeled, as were some small cytoplasmic vesicles. Golgi complex labeling and plasma membrane labeling were weak. The appearance of lbm180 protein by immunofluorescence in fetal rat lung cryosections correlated with the biogenesis of lamellar bodies. The lbm180 protein decreased with time in type II cells cultured on plastic. The lbm180 protein is an integral membrane protein of lamellar bodies and was also found in the pancreas and the pancreatic betaHC9 cell line but not in the rat brain, liver, kidney, stomach, or intestine. The present study provides evidence that the lbm180 protein is a lung lamellar body and/or multivesicular body membrane protein and that its antibody, MAb 3C9, will be a valuable reagent in further investigations of the biogenesis and trafficking of type II cell organelles.

Xenopus cadherin-11 is expressed in different populations of migrating neural crest cells

We cloned the Xenopus homologue of cadherin-11 and studied its spatiotemporal expression pattern during early development. The messenger RNA is present from the mid-gastrulation through embryo development. It is expressed in different neural crest cell populations, during their migration and differentiation. This pattern, unexpected for an adhesion molecule, reinforces the idea of novel functions for type II cadherins.

In vitro and in vivo evaluation of insulin-producing beta TC6-F7 cells in microcapsules

In the present study, the insulin secretory capacity of beta TC6-F7 cells in microcapsules was evaluated. The cell mass within capsules was found to expand in a three-dimensional fashion, in contrast to cells seeded on plates that grew as a monolayer. In in vitro studies, both free and encapsulated cells were found to secrete insulin in the absence of glucose, at 13.6 +/- 1.1 and 14.5 +/- 0.9 ng.10(6) cells-1.60 min-1, respectively, with the response rising to a maximum of 26.0 +/- 0.8 and 31 +/- 2.3 ng.10(6) cells-1.60 min-1 in the presence of 16.8 mM glucose. Encapsulated cells were able to produce Ca2+ responses in the presence of KCl (50 mM) and BAY K 8644 (100 microM). In in vivo studies, intraperitoneal transplantation of 3.0 x 10(6) microencapsulated cells into mice (n = 5) with streptozotocin-induced diabetes resulted in the restoration of normoglycemia up to 57 days. Insulin concentrations rose from 0.4 +/- 0.1 ng/ml before the graft administration to 2.2 +/- 0.8 ng/ml after the transplantation in the normoglycemic recipients. An oral glucose challenge in transplant recipients demonstrated a flat glucose response, suggesting extremely high glucose clearance rates. These data demonstrate the potential use of the immunoisolated beta-cell lines for the treatment of diabetes.

Regulated production of mature insulin by non-beta-cells

Rat hepatoma cells were engineered to express, in a regulated manner, mature human insulin as an approach to the development of artificial beta-cells for insulin-dependent diabetes mellitus (IDDM) gene therapy. A chimeric gene obtained by linking a 2.4-kb fragment of the P-enolpyruvate carboxykinase (PEPCK) gene promoter to a human proinsulin gene (PEPCK/Insm), containing genetically engineered furin endoprotease cleavage sites, was stably transfected into FTO-2B rat hepatoma cells. The FTOInsm cells expressed high levels of insulin mRNA and protein after Northern blot or immunocytochemical analysis. High-performance liquid chromatography (HPLC) fractionation of culture medium and cell extracts revealed that about 90% of the proinsulin was processed to mature insulin. Insulin secretion was very fast, and 15 min after induction with dibutyryl cyclic AMP (Bt2cAMP) plus dexamethasone significant amounts of the hormone were released. Moreover, during the first hour, the rise in insulin concentration in the medium was 10-fold that detected in nontreated FTOInsm cells. Insulin produced by FTOInsm cells was biologically active because it blocked endogenous PEPCK gene expression and induced glucose uptake and lactate production. Thus, our results showed that genetically engineered FTOInsm hepatoma cells synthesized, processed, and secreted active insulin. The implantation of encapsulated engineered FTOInsm cells might provide a safe and practical therapeutic approach for IDDM treatment.

Glucose-induced tyrosine phosphorylation of p125 in beta cells and pancreatic islets. A novel proximal signal in insulin secretion

In this study, we demonstrate that stimulation of beta cells with carbachol and glucose causes increased tyrosine phosphorylation of a 125-kDa protein concurrently with increased insulin secretion. The effect was observed in two different insulin-secreting cell lines and in rat pancreatic islets. Tyrosine phosphorylation was largely calcium independent and occurred within 2 min after stimulation of beta cells with glucose and the muscarinic agonist carbachol. In islets, the effect of glucose was greatly diminished by the addition of mannoheptulose, a seven-carbon sugar that inhibits glucokinase, suggesting that glucose metabolism is required for tyrosine phosphorylation of the protein to occur. Neither insulin nor insulin-like growth factor I significantly increased tyrosine phosphorylation of the 125-kDa protein, suggesting that it was not an autocrine effect. Depolarization of beta cells with glyburide or 50 m potassium dramatically increased insulin secretion but had no significant effect on tyrosine phosphorylation. Addition of phorbol ester caused a less than 2-fold increase in tyrosine phosphorylation, whereas the calcium ionophore A23187 had no effect. Among the various fuel secretagogues tested, only -glucose stimulated tyrosine phosphorylation, both alone and in combination with carbachol. Finally, the tyrosine kinase inhibitor AG879 inhibited both tyrosine phosphorylation and insulin secretion in a dose-dependent manner. Taken together, these data demonstrate the presence of a novel signaling pathway in glucose-induced insulin secretion: tyrosine phosphorylation of beta cell p125, which is a proximal step in insulin secretion. Our current working hypothesis is that glucose stimulation of beta cell p125 tyrosine phosphorylation is an essential step for insulin secretion.

Function of the human insulin promoter in primary cultured islet cells

Pancreatic islet beta cells regulate the rate of insulin gene transcription in response to a number of nutrients, the most potent of which is glucose. To test for its regulation by glucose, the promoter sequence was isolated from the human insulin gene. When linked to chloramphenicol acetyltransferase and transfected into primary islet cultures, the human insulin promoter is activated by glucose. In parallel islet transfections, glucose also activates the L-pyruvate kinase and islet amyloid chain ketoacid dehydrogenase E1a promoter, but it does not affect the beta cell glucose kinase promoter. Using deletion and substitution mutations of the proximal human insulin promoter, we mapped a metabolic response element to the E box, E1, at -100 base pairs relative to the transcription start site. Although the isolated E1 element responds to glucose, inclusion of either of two AT-rich sequences, A1 or A2/C1 on either side of E1, results in dramatic synergistic activation. Inclusion of A2/C1 also increases the response to glucose. The A2-E1-A1 region alone, however, does not explain all of the activity of the human insulin promoter in cultured islets, and other transcriptionally important elements likely to contribute to the glucose response as well.