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D J Drucker

Publications and source records attributed to D J Drucker.

At least 109 records · Page 6Linked to original sources
PubMed1991

Differential glucocorticoid regulation of glucagon gene expression in cell lines derived from rat and hamster islet cell tumors.

Glucocorticoid regulation of peptide hormone gene expression was studied in two cell lines derived from rodent islet cell tumors. In rat RIN1056A cells, dexamethasone reduced the levels of glucagon mRNA transcripts while markedly inducing the expression of the angiotensinogen gene. In contrast, dexamethasone had no effect on the regulation of glucagon gene expression in hamster InR1-G9 cells. Wild type InR1-G9 cells did not support the induction of the murine mammary tumor virus promoter by glucocorticoids, suggesting that these cells lacked the necessary cellular factor(s) for glucocorticoid responsiveness. Introduction of the glucocorticoid receptor into wild type InR1-G9 cells restored glucocorticoid induction of the murine mammary tumor virus promoter, but not glucocorticoid regulation of glucagon gene expression. Dexamethasone treatment of Sprague-Dawley rats had no effect on the levels of pancreatic glucagon mRNA transcripts. The results of these studies demonstrate that glucocorticoid regulation of glucagon gene expression is restricted to the immortalized RIN1056A cell line, providing additional evidence for cell-specific diversity in the regulation of peptide hormone gene expression in neuroendocrine tumors.

Adenoma, Islet Cell↗
PubMed1991

Proglucagon-derived peptides in the neuroendocrine system.

Using several novel in vitro culture systems, we have examined the tissue-specific regulation of the proglucagon-derived peptides, at the levels of proglucagon gene expression and pGdp synthesis and secretion. Our studies indicate that proglucagon gene expression in intenstine, hypothalamus and pancreas is under the regulatory control of protein kinase A- but not a protein kinase C-dependent pathway. PKA and PKC stimulate secretion of the intestinal pGdp's, whereas only PKA stimulates secretion of the hypothalamic peptides. Pancreatic glucagon secretion in response to PKA is subject to further modulation by prevailing glucose concentrations. This diversity in intracellular regulation of the pGdp's may account for some of the tissue-specific differences in synthesis and secretion of the pGdp's that we have observed in diabetes and during development.

Animals↗
PubMed1991

The rat glucagon gene is regulated by a protein kinase A-dependent pathway in pancreatic islet cells.

A cAMP response element (CRE) has been identified in the proximal 5'-flanking region of the rat glucagon gene, and activation of the cAMP-dependent pathway in fetal rat intestinal cells leads to an increase in the levels of glucagon mRNA transcripts. In contrast, the human glucagon gene does not contain a similar CRE, and the results of studies using immortalized rat and hamster islet cell lines have suggested that glucagon gene expression may not be regulated by cAMP. To reconcile these observations, we have studied the control of glucagon gene expression. Incubation of primary rat islet cell cultures with forskolin in the presence of low (0.5 g/liter) or high (2.0 g/L) glucose resulted in a 2- to 3-fold increase in the levels of glucagon mRNA transcripts. Forskolin also stimulated the secretion and synthesis of immunoreactive glucagon. The importance of the protein kinase-A-dependent pathway in the regulation of glucagon gene expression was also examined in hamster islet InR1-G9 cells. Cotransfection of a glucagon-chloramphenicol acetyltransferase (CAT) fusion gene containing the glucagon CRE and a cDNA encoding the catalytic subunit of protein kinase-A resulted in stimulation of glucagon-CAT activity in hamster islet cells. Catalytic subunit cotransfection also activated somatostatin-CAT, but no activation of RSVCAT was detected. The results of these experiments suggest that the rat glucagon gene is regulated by a protein kinase-A-dependent pathway in the endocrine pancreas.

Animals↗
PubMed1991

Regulation of peptide-YY synthesis and secretion in fetal rat intestinal cultures.

The regulation of intestinal peptide-YY (PYY) synthesis and secretion has not been well studied. We have used fetal rat intestinal cells in culture to examine the intra- and extracellular factors controlling the production of PYY. Immunohistochemical analysis demonstrated a distinct population of cells containing immunoreactive PYY (IR-PYY). When examined by HPLC, the IR-PYY stored and secreted by fetal rat intestinal cell cultures eluted as a single moiety with the same elution time as synthetic rat PYY. Pro-PYY mRNA transcript levels and secretion of IR-PYY into the cell medium were increased by activation of protein kinase-A with either a long-acting cAMP analog or forskolin. In contrast, IR-PYY secretion only was stimulated in a synergistic fashion through calcium- and protein kinase-C-dependent pathways (stimulated with A23187 and phorbol myristate acetate, respectively). The intestinal endocrine peptide, gastric inhibitory peptide, and the neurocrine peptide, gastrin-releasing peptide, were found to stimulate IR-PYY secretion in a dose-dependent fashion, with significant effects observed at concentrations as low as 10(-8) and 10(-12) M, respectively (P less than 0.05-0.001). Cholecystokinin and vasoactive intestinal peptide were without effect on IR-PYY secretion at doses of 10(-12)-10(-6) M. The fatty acid sodium oleate and the cholinergic agonist bethanechol were also found to stimulate IR-PYY secretion, each at a concentration of 10(-4) M (P less than 0.001). The results of the present study indicate that the synthesis and secretion of PYY by the rat intestine is under the regulatory control of a wide variety of extracellular agents, mediated by several intracellular signalling pathways.

1-Methyl-3-isobutylxanthine↗
PubMed1991

Islet cell and extrapancreatic expression of the LIM domain homeobox gene isl-1.

The phenotypically distinct cell types of the islets of Langerhans express a number of different hormone genes in a regulated and cell-specific manner. Analysis of the molecular factors important for the control of insulin gene transcription has led to the identification of a number of insulin gene-binding proteins. The cDNAs for several of these proteins have been isolated, including isl-1, a LIM domain homeobox protein reported to be preferentially expressed in islet cells. We now report that isl-1 mRNA transcripts are present not only in islet cells, but also in pheochromocytoma (PC-12) cell lines. Isl-1 mRNA transcripts were also detected in several different regions of rat brain as well as in rat kidney. Analysis of the patterns of gene expression in rat islet cell lines and human pancreatic endocrine tumors demonstrated a variable relationship between the hormonal phenotype of the tumor and expression of the isl-1 and insulin genes. Immunocytochemical studies demonstrated both cytoplasmic and nuclear staining for isl-1 in human pancreatic endocrine tumors, in normal pancreatic A, B, D, and PP cells, and in distal tubular cells of the kidney. Isl-1 immunoreactivity was also widely distributed in neurons in both the central and peripheral nervous system, pituitary, and several human pituitary tumors and pheochromocytomas. The results of these studies implicate a potential role for isl-1 outside the endocrine pancreas in the nervous system and kidney.

Animals↗
PubMed1991

Rapid induction of parathyroid hormone-like peptide gene expression by sodium butyrate in a rat islet cell line.

The PTH-like peptide (PLP) gene is expressed in a diverse number of normal and neoplastic cell types, and induction of PLP gene expression has been observed after the induction of cellular differentiation. The differentiation of islet cells can be studied in vitro, after the exposure of rat islet cell lines to sodium butyrate. The present work found that rat RIN 1056A islet cells express the PLP gene and treatment with sodium butyrate resulted in rapid (detectable by 30 min) induction of PLP gene expression. PLP gene expression was rapidly and transiently induced by serum and cycloheximide, but the butyrate induction of PLP mRNA transcripts was not dependent on serum or new protein synthesis. Dexamethasone inhibited PLP gene expression and blocked the butyrate induction of PLP mRNA transcripts. The rapid induction of PLP gene expression after the exposure of islet cells to sodium butyrate, serum, and cycloheximide suggests that PLP may be a member of a class of early response genes involved in the regulation of cellular growth or differentiation.

Animals↗
PubMed1990

Parathyroid hormone-like peptide in normal and neoplastic mesothelial cells.

Mesothelioma has not been commonly reported as a cause of hypercalcemia of malignancy. We have studied a patient with malignant mesothelioma and hypercalcemia in association with elevated plasma concentrations of parathyroid hormone-like peptide (PLP). Immunohistochemical analysis of the tumor and seven of eight other mesotheliomas that were not associated with hypercalcemia revealed the presence of PLP cytoplasmic immunopositivity. PLP immunopositivity was also detected in normal and reactive mesothelial cells. The results of these studies suggest that PLP immunoreactivity is common in normal and neoplastic mesothelial cells and raises the possibility that PLP production may play a role in the pathogenesis of hypercalcemia associated with mesothelioma.

Adult↗
PubMed1990

Ultraviolet B radiation induction of ornithine decarboxylase gene expression in mouse epidermis.

The cellular effects of u.v. radiation have been studied by using a hairless-mouse model in vivo. U.v. B radiation (u.v.B) induced the activity of the enzyme ornithine decarboxylase (ODC) in mouse epidermis. Maximal induction was noted after radiation with 90 mJ/cm2, and increased ODC activity was first detected 2 h after u.v.B exposure. U.v.B. also induced the expression of the ODC gene in a time- and dose-dependent manner, but did not induce the levels of actin mRNA transcripts. Cycloheximide treatment did not alter basal levels of ODC mRNA transcripts and had no effect on the u.v.B induction of ODC-gene expression. The results of these experiments demonstrate that u.v.B radiation induces both the expression of the ODC gene and the activity of the enzyme, and provides a useful 'in vivo' paradigm for the analysis of the molecular effects of u.v.B radiation.

Animals↗
PubMed1990

Ultraviolet radiation induction of ornithine decarboxylase in rat keratinocytes.

UV radiation plays an important role in the induction of cutaneous malignancy, including basal cell and squamous cell carcinomas and malignant melanoma. In addition to its effects on DNA damage and repair mechanisms, UV radiation has been shown to modulate the expression of specific genes, altering the levels of their mRNAs and the synthesis of their corresponding proteins. In order to gain further information about the molecular effects of UV radiation, we have studied the regulation of ornithine decarboxylase (ODC) gene expression in response to UVB radiation. ODC is the rate-limiting enzyme in polyamine biosynthesis, is involved in growth and differentiation, and has been implicated in carcinogenesis. Keratinocytes grown in culture were either sham-irradiated or exposed to increasing doses of UVB (1-5 mJ/cm2). Northern blot analysis of keratinocyte RNA under basal conditions demonstrated the presence of two ODC mRNA transcripts. Increasing exposure to UVB resulted in a dose-dependent increase in the levels of both ODC mRNA transcripts. The induction of ODC gene expression following UVB was noted 2 h after UVB exposure, and ODC mRNA levels continued to increase up to 24 h after UVB exposure. The UVB-induced increase in ODC gene expression was not serum dependent, despite the ability of serum alone to induce ODC gene expression. The mRNA transcripts for actin and hexosaminidase A were not induced after UVB exposure. These studies show that the UVB-induced increase in ODC activity is due, at least in part, to an increase in ODC gene expression and they provide a useful model for the analysis of the molecular effects of UVB radiation.

Animals↗
PubMed1990

Molecular and cellular analysis of a neoplastic pancreatic A cell tumor.

Endocrine tumors of the pancreas may produce characteristic syndromes attributable to the increased secretion of one or more hormones. These tumors provide valuable opportunities for the analysis of hormone biosynthesis and secretion in the neoplastic human endocrine cell. The authors studied a pancreatic endocrine tumor obtained from a patient with classical glucagonoma syndrome. Characterization of plasma and tumor glucagon-like immunoreactivity (GLI) by high-performance liquid chromatography and radioimmunoassay for GLI showed different chromatographic profiles, with glucagon the major molecular form in the tumor, and glicentin and oxyntomodulin predominating in plasma. Although immunocytochemical staining of the tumor showed only focal weak positivity for glucagon, tumor extracts contained large amounts of immunoreactive GLI peptide. Northern blot analysis of tumor RNA demonstrated that abundant glucagon mRNA transcripts were present, just slightly larger in size than those detected in normal pancreas and intestine. Electron microscopic analysis of the tumor cellular ultrastructure revealed only occasional small electron dense secretory granules. A large number of complex lysosome-like structures of variable size and electron density were detected throughout the cytoplasm and ringing the nucleus of most cells, a feature atypical of endocrine tumors of the pancreas. Primary cultures of dispersed tumor cells were established and, in contrast to previous results, were obtained using normal or neoplastic islet cell models, GLI secretion was found to be stimulated eightfold by incubation with 5 mM dibutyryl cyclic adenosine monophosphate. Phorbol myristate acetate, the calcium ionophore A23187, and sodium butyrate had no effect on GLI secretion in vitro. These observations indicate that neoplastic human A cells may have abnormalities at different points in the biosynthesis and secretion of glucagon.

Adenoma, Islet Cell↗
PubMed1990

Glucagon and the glucagon-like peptides.

Glucagon and the glucagon-like peptides are encoded within a larger precursor, proglucagon. The proglucagon gene is expressed in the pancreas, intestine, and brain, giving rise to a single proglucagon mRNA transcript that is identical in all tissues. Tissue-specific posttranslational processing of proglucagon accounts for the different molecular forms of the glucagon-related peptides present in each tissue. Glucagon-like peptide I has been demonstrated to have potent insulinotropic properties, but the biological importance of other glucagon-related peptides remains unclear. The recent advances that have increased our understanding of the biology of glucagon and the glucagon-like peptides are reviewed.

Animals↗
PubMed1990

Synthesis and secretion of somatostatin-28 and -14 by fetal rat intestinal cells in culture.

A fetal rat intestinal cell (FRIC) culture model was established to investigate the factors controlling synthesis and secretion of somatostatin-28 (S-28) by the intestine. Immunohistochemical analysis demonstrated the presence of cells containing somatostatin-like immunoreactivity (SLI), many of which emitted long processes toward neighboring cells. Gel chromatography of SLI stored and secreted by nonstimulated FRIC cultures demonstrated a predominance of S-28 (59%), lesser amounts of S-14 (31%), and a minor peak of large molecular weight SLI (10%). Secretion of SLI was stimulated by treatment of cells for 2 h with 5 mM dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP; P less than 0.01) or 2 microM phorbol ester (P less than 0.05), but was unaffected by the calcium ionophore A23187 (2 micrograms/ml). Concomitant treatment with all three agents increased SLI secretion in an additive fashion to 254 +/- 25% of controls (P less than 0.0001). DBcAMP treatment did not alter the distribution of stored or secreted S-28 (59%) and S-14 (33%). After 24 h of exposure to DBcAMP, but not after treatment with phorbol ester, a threefold increment in prosomatostatin mRNA transcript levels was observed. FRIC cultures therefore synthesize and secrete a predominance of S-28 in a regulated manner, making them a promising model for future studies on the biosynthesis and secretion of intestinal somatostatin.

1-Methyl-3-isobutylxanthine↗
PubMed1990

Glucagon and related peptides in fetal rat hypothalamus in vivo and in vitro.

Proglucagon-derived peptides are localized in pancreas, intestine, and the nervous system. We have examined the ontogeny of glucagon and related peptides in developing rat hypothalamus and have developed a fetal rat hypothalamic cell culture model to study the synthesis and secretion of these peptides in cells of neural origin. Fetal rat hypothalamus (19-21 day gestation) was found to contain glucagon-like immunoreactive (GLI) peptides including glucagon. The relative amounts of two of the GLI peptides (glicentin and oxyntomodulin) increased with development such that adult hypothalamus contained a predominance of these peptides over glucagon. The ratio of GLI peptides to glucagon increased from 2.6 +/- 0.5 in fetus to 46 +/- 11 in adult (P less than 0.001). When fetal rat hypothalamic cells (FRHC) were placed into primary culture for 7 days, the presence of neurons, glial cells, and glucagon-containing cells was detected by immunohistochemical staining. Analysis of proglucagon gene expression in FRHC cultures by Northern blotting demonstrated the presence of a single proglucagon messenger RNA (mRNA) transcript identical in size and sequence to that detected in fetal pancreas and intestine. RNase protection analysis of RNA from FRHC cultures, brainstem, and intestine confirmed that the proglucagon mRNA transcripts present in these three tissues were identical. Analysis of FRHC content of GLI peptides and immunoreactive glucagon demonstrated that peptide levels were not significantly different from those of whole fetal rat hypothalamus, and did not vary significantly throughout 2 weeks in culture. FRHC cultures were found to contain substantial amounts of glucagon after 1 week of culture. Release of the GLI peptides on day 7 of culture was increased 3-fold (P less than 0.001) by treatment of FRHC for 1 h with 5 mM (Bu)2cAMP. Rat hypothalamus therefore appears to undergo unique changes in posttranslational processing of proglucagon during development. Primary cultures of FRHC thus provide a promising in vitro model to study the molecular control of proglucagon biosynthesis and GLI peptide secretion in the brain.

Animals↗
PubMed1990

Developmental and tissue-specific regulation of proglucagon gene expression.

The pattern of glucagon gene expression and the posttranslational processing of proglucagon was studied in the fetal and neonatal rat. Pancreatic immunoreactive glucagon (IRG) and glucagon-like immunoreactivity (GLI) were low in both fetal pancreas and intestine, respectively. Immediately after birth, pancreatic IRG rose markedly and reached a peak concentration at postnatal day 7, followed by a gradual return to its adult level. Intestinal GLI was low until postnatal day 7 and rose steadily thereafter to adult levels. The levels of GLI in the hypothalamus were much lower than in intestine, yet the developmental accumulation of hypothalamic GLI resembled the pattern observed in intestine. In contrast, the levels of GLI and IRG in the brain stem were higher in the fetus and neonate, and decreased to adult levels. Proglucagon mRNA transcripts, uniform in size, were detected in RNA isolated from fetal or adult brainstem, pancreas, and intestine. However, fetal proglucagon mRNA transcripts were larger than adult proglucagon mRNA transcripts in pancreas and intestine, but not brainstem. The results of RNAse mapping studies, including analysis of both the 5'- and 3'-ends of the mRNA transcripts, demonstrated that the larger fetal mRNA transcripts could be accounted for by an increase in the length of the polyadenylate tail in the fetal tissues. These observations demonstrate that the developing rat exhibits tissue-specific differences in both proglucagon gene expression and the pattern of posttranslational processing of the prohormone.

Animals↗
PubMed1990

Parathyroid hormone-like peptide in normal and neoplastic human endocrine tissues.

PTH-like peptide (PLP) is produced by tumors commonly associated with hypercalcemia as well as nonneoplastic tissues and several endocrine glands and tumors. To characterize the distribution of PLP in human endocrine tissues and tumors, we localized PLP in formalin-fixed paraffin-embedded material using the avidin-biotin-peroxidase technique with polyclonal antisera. Among peptide hormone-producing tissues, PLP was identified in nontumorous adenohypophysis and pituitary adenomas; medullary thyroid carcinomas; normal, hyperplastic, and adenomatous parathyroids; adrenal medulla and pheochromocytomas; normal pancreatic islets; and endocrine tumors of pancreas, gut, and lung, including small cell carcinomas. In other endocrine tissues PLP was identified in nontumorous thyroid follicular epithelium, colloid nodules, and follicular neoplasms; normal adrenal cortex, adrenocortical adenomas, and carcinomas; nontumorous testicular Leydig cells; normal ovarian granulosa and thecal cells; an ovarian thecoma and a granulosa cell tumor; placental trophoblast; and decidua. These results demonstrate that PLP is localized in many normal and neoplastic endocrine cells, including those not known to influence extracellular calcium homeostasis. The presence of PLP in a variety of endocrine tissues suggests that it may play a local physiological role in the growth or function of endocrine cells.

Adrenal Cortex Neoplasms↗
PubMed1990

Thyroiditis as the presenting manifestation of disseminated extrapulmonary Pneumocystis carinii infection.

A 38-yr-old male with acquired immunodeficiency syndrome developed neck pain in association with mild hyperthyroidism and a diffusely enlarged thyroid gland. Radioactive iodine scanning was consistent with thyroiditis, and biopsy of the thyroid demonstrated the presence of pneumocystis carinii in thyroid tissue. Treatment with pentamidine followed by trimethoprim sulfamethoxazole led to rapid normalization of thyroid size in association with the development of hypothyroidism. This case illustrates the natural history of pneumocystis carinii thyroiditis and suggests that thyroid disease be added to the spectrum of human immunodeficiency virus-associated endocrine dysfunction.

Acquired Immunodeficiency Syndrome↗
PubMed1990

Glucagon gene 3'-flanking sequences direct formation of proglucagon messenger RNA 3'-ends in islet and nonislet cells lines.

Glucagon and the glucagon-like peptides are encoded within a larger precursor, proglucagon. Transcription of the glucagon gene in pancreas, intestine, and brain gives rise to identical proglucagon mRNA transcripts, after which tissue-specific post-translational processing produces different profiles of proglucagon-derived peptides in each tissue. The importance of glucagon gene 3'-untranslated and 3'-flanking sequences in the control of glucagon mRNA production was studied by transfecting a series of 3'-deleted glucagon genes into fibroblast and islet cell lines. Glucagon genes containing 2 kilobases of 3'-flanking sequences gave rise to accurately processed mRNA transcripts in both baby hamster kidney fibroblasts and InR1-G9 islet cell lines. Deletion of all but 50 basepairs of 3'-flanking sequence had no effect on glucagon mRNA 3'-end formation. In contrast, additional deletion of 3'-flanking and 3'-untranslated sequences resulted in the production of read-through mRNA transcripts with aberrant 3'-ends. The results of these studies define a 50-basepair region in the 3'-flanking sequence of the glucagon gene important for the accurate processing of proglucagon mRNA transcripts.

Animals↗