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D J Drucker

Publications and source records attributed to D J Drucker.

At least 73 records · Page 4Linked to original sources
PubMed1997

Biological determinants of intestinotrophic properties of GLP-2 in vivo.

Glucagon-like peptide 2 (GLP-2) appears to regulate growth of the small bowel epithelium. The importance of dose, vehicle, and route of administration for GLP-2 bioactivity was examined in vivo. Mouse small bowel weight increased following subcutaneous injection of GLP-2, 0.25 to 5.0 microg twice daily, with an increment in jejunal crypt plus villus height detected with only 250 ng GLP-2 twice daily for 14 days (1.35-fold greater than control, P < 0.05). Small bowel weight was increased by 6 days of GLP-2 administration (1.4-fold greater than control, P < 0.05) and further increased after up to 14 days of GLP-2 treatment (P < 0.001, GLP-2 vs. control). GLP-2 increased small bowel weight in either 12% gelatin or phosphate-buffered saline (PBS) formulations (P < 0.01 vs. P < 0.05, gelatin vs. PBS, respectively), and GLP-2 was intestinotrophic following either intramuscular, intraperitoneal, or subcutaneous administration (P < 0.05 for im and ip, P < 0.001 for sc, GLP-2 vs. control). GLP-2 also induced bowel growth when administered daily or every other day. These results define important biological parameters for the activity of GLP-2 in vivo.

Animals↗
PubMed1997

Intestinal response to growth factors administered alone or in combination with human [Gly2]glucagon-like peptide 2.

The control of intestinal epithelial growth is regulated by interactions of growth factors in various cellular compartments of the small and large bowel. Little information is available on the intestinal growth response to combinations of growth factors. We studied the intestinotrophic properties of a dipeptidyl peptidase IV resistant glucagon-like peptide 2 (GLP-2) analog, human [Gly2]GLP-2 (h[Gly2]GLP-2), as well as of epidermal growth factor (EGF), long [Arg3]insulin-like growth factor I (LR3IGF-I), [Gly1]IGF-II, and human growth hormone (hGH), administered by subcutaneous injection alone or in combination in mice. At the doses tested, h[Gly2]GLP-2 was the most potent agent for increasing small and large bowel mass. Mice treated with h[Gly2]GLP-2 and either GH or IGF-I exhibited greater increases in histological parameters of small intestinal growth than did mice treated with h[Gly2]GLP-2 alone. Administration of all five growth factors together induced significant increases in crypt plus villus height and in small and large bowel length and weight. The results of these experiments define regional differences in both the cellular targets and relative activities of intestinotrophic molecules and raise the possibility that selective growth factor combinations may be useful for enhancement of intestinal adaptation in vivo.

Animals↗
PubMed1997

Circulating and tissue forms of the intestinal growth factor, glucagon-like peptide-2.

Glucagon-like peptide-2 (GLP-2) has recently been identified as a stimulator of intestinal epithelial growth, prompting the development of RIA and HPLC methodologies to study this peptide in more detail. A GLP-2-specific antiserum (UTTH-7) was developed that recognizes amino acids 25-30 of human and rat GLP-2-(1-33). UTTH-7 cross-reacts with N- and C-terminally modified forms of GLP-2, proglucagon, and the major proglucagon fragment. Analysis of rat ileal extracts demonstrated the presence of GLP-2-(1-33) as well as significant amounts of GLP-2-(3-33) (16 +/- 7% of total GLP-2). The level of total immunoreactive GLP-2 in plasma from fasted rats was 700 +/- 71 pg/ml, and this increased 3.6-fold (P < 0.001) in 24-h fed rats. HPLC analysis demonstrated the presence of both GLP-2-(1-33) and GLP-2-(3-33) in plasma from fasted rats, with increments in both peptides in plasma from fed rats. Immunoreactive GLP-2 increased in plasma from human subjects 2 h after a meal, rising from 851 +/- 230 to 1106 +/- 211 pg/ml (P < 0.05); 15 +/- 4% of this immunoreactivity was accounted for by the presence of intact GLP-2. HPLC showed the presence of both GLP-2-(1-33) and GLP-2-(3-33) in plasma from fed humans. Incubation of human GLP-2-(1-33) with the enzyme dipeptidylpeptidase IV resulted in liberation of GLP-2-(3-33), whereas replacement of Ala2 with Gly2 prevented this cleavage. Thus, while GLP-2-(1-33) is a major circulating and tissue form of GLP-2, GLP-2-(3-33) is a significant component ofimmunoreactive GLP-2 in both intestine and plasma.

Adult↗
PubMed1997

The caudal homeobox protein cdx-2/3 activates endogenous proglucagon gene expression in InR1-G9 islet cells.

The proglucagon gene is expressed in a highly cell-specific manner in islet and enteroendocrine cells. DNA sequences within the proximal proglucagon G1 promoter region bind the homeobox protein cdx-2/3, and cdx-2/3 activates the proglucagon promoter in fibroblasts. We show here that cdx-2/3 activates the proglucagon promoter in both islet (InR1-G9) and enteroendocrine (STC-1 and GLUTag) cell lines. Furthermore, transfected cdx-2/3 increased the levels of endogenous proglucagon mRNA transcripts in both transient and stable transfections of InR1-G9 islet cells. The cdx-2/3-dependent induction of endogenous proglucagon mRNA transcripts in stable islet lines was associated with a corresponding increase in the transcriptional activity of proglucagon promoter-luciferase plasmids. An amino-terminally truncated cdx-2/3 derivative containing the homeodomain and carboxy-terminal region of the molecule inhibited both the cdx-2/3 activation of the proglucagon promoter and the induction of endogenous proglucagon mRNA transcripts. These observations demonstrate that cdx-2/3, acting through the proximal G1 element, is a major transcriptional determinant of cell-specific proglucagon gene expression in pancreatic islet cells.

Animals↗
PubMed1997

Leptin sensitivity in nonobese glucagon-like peptide I receptor -/- mice.

Glucagon-like peptide I (GLP-I) stimulates glucose-dependent insulin secretion and inhibits food intake in the central nervous system. Because leptin reduces food intake but inhibits insulin secretion, we examined leptin action in mice with a null mutation in the GLP-I receptor. Intracerebroventricular leptin administration inhibited food intake in both wild-type and GLP-I receptor (GLP-IR) -/- mice, and daily intraperitoneal administration of leptin for 2 weeks produced comparable reductions in food intake and body weight in control and GLP-IR -/- mice. Glucose tolerance was improved in both wild-type and GLP-IR -/- mice, whether pair fed or leptin treated; however, blood sugars were significantly lower in the leptin-treated GLP-IR -/- mice following oral glucose challenge (P < 0.01). Glucose-stimulated insulin was reduced in both pair-fed and leptin-treated mice (P < 0.01-0.001); however, insulin levels were significantly lower in leptin-treated versus pair-fed GLP-IR -/- mice (P < 0.01). A single leptin injection had no effect on glucose tolerance in GLP-IR -/- mice, but decreased hepatic PEPCK mRNA in both wild-type and GLP-IR -/- mice. The improvement in blood glucose excursion, despite lower levels of glucose-stimulated insulin in lean leptin-treated GLP-IR -/- mice, suggests that leptin may have beneficial effects on control of blood glucose in the absence of obesity. Furthermore, the greater effects of leptin on glucose and insulin in leptin-treated versus pair-fed GLP-IR -/- mice raises the possibility that disruption of GLP-I signaling modifies the sensitivity to leptin in vivo.

Animals↗
PubMed1996

Induction of intestinal epithelial proliferation by glucagon-like peptide 2.

Injury, inflammation, or resection of the small intestine results in severe compromise of intestinal function. Nevertheless, therapeutic strategies for enhancing growth and repair of the intestinal mucosal epithelium are currently not available. We demonstrate that nude mice bearing subcutaneous proglucagon-producing tumors exhibit marked proliferation of the small intestinal epithelium. The factor responsible for inducing intestinal proliferation was identified as glucagon-like peptide 2 (GLP-2), a 33-aa peptide with no previously ascribed biological function. GLP-2 stimulated crypt cell proliferation and consistently induced a marked increase in bowel weight and villus growth of the jejunum and ileum that was evident within 4 days after initiation of GLP-2 administration. These observations define a novel biological role for GLP-2 as an intestinal-derived peptide stimulator of small bowel epithelial proliferation.

Animals↗
PubMed1996

UVB radiation induces p21Cip1/WAF1 and mediates G1 and S phase checkpoints.

In a search for effectors and targets of UVB signaling in mammalian cells, we screened a keratinocyte cDNA library with differentially subtracted UVB-enriched cDNA probes. One of the UVB induced cDNA clones proved to be the rat p21Cip1/WAF1 homologue. UVB irradiation caused a rise in p53 protein levels, in association with induction of p21Cip1/WAF1 and cyclin G expression. The effects of UVB irradiation induced p21Cip1/WAF1 on the cell cycle were examined. In contrast to gamma irradiation, which caused G2 arrest, UVB treatment of asynchronous neonatal rat keratinocytes (NK) led to a marked inhibition of replicative DNA synthesis and prolonged G1 and S phase arrests, persisting to 18-24 h, with recovery of cycling by 36 h post-UVB. G1 arrest was accompanied by inhibition of cyclin D-, E- and A-associated kinases. Kinase inhibition was not due to reduction in cyclin or cdk proteins. While the association of cyclin E with Cdk2 was moderately reduced, cyclin D1/Cdk4 and cyclin A/Cdk2 complexes were not disrupted. The activating threonine 160 phosphorylation of Cdk2 in cyclin complexes was not inhibited. An incremental binding of p21 with Cdk4 paralleled the inhibition of cyclin D1/Cdk4 kinase and a similar rise in Cdk2 binding to p21 was associated with inhibition of cyclin E and cyclin A dependent kinases. Furthermore, a rise in measurable p21Cip1/WAF1-Cdk2 inhibitory activity paralleled the loss of G1 cyclin-dependent kinase activity, supporting a role for p21Cip1/WAF1 in the UVB-induced checkpoints.

Amino Acid Sequence↗
PubMed1996

Development of colonic and pancreatic endocrine tumours in mice expressing a glucagon-SV40 T antigen transgene.

We report the histological, immunohistochemical and ultrastructural changes in mice containing a chimeric glucagon-simian virus 40 T antigen (SV40Tag) gene. Transgene expression was detected in endocrine cells of pancreas, small and large intestine. Hyperplasia of glucagon-containing cells developed in pancreas and large bowel by gestational day 19. In large bowel, hyperplastic cells increased in number postnatally and invasive carcinomas were identified at 4 weeks; several animals had lymph node metastases. In contrast, no pathology was detected in the small bowel in any of the transgenic mice. Colonic tumours expressed SV40Tag, proglucagon-derived peptides and peptide YY (PYY); scattered cells contained cholecystokinin or glycoprotein hormone alpha-subunit. Somatostatin or serotonin was also detected in some tumours. By electron microscopy, the colonic tumours retained features of endocrine differentiation, but secretory granules were smaller than those of non-tumorous intestinal glucagon-producing L cells. In postnatal pancreas, atypical cells containing SV40Tag and glucagon were initially clustered at the periphery of islets; this atypical hyperplasia progressed to neoplasia by 11-12 weeks. Some neoplastic pancreatic cells contained glucagon, PYY or vasoactive intestinal peptide immunopositivity, but most were negative for all peptides; they contained immunoreactivity for tyrosine hydroxylase and by electron microscopy, pancreatic tumour cells had neuronal features. Pancreatic polypeptide was not detected in the non-tumorous islets of transgenic animals. This line of transgenic mice provides a model for the analysis of endocrine tumour progression in the gut and pancreas.

Adenoma, Islet Cell↗
PubMed1996

Glucose intolerance but normal satiety in mice with a null mutation in the glucagon-like peptide 1 receptor gene.

Glucagon-like peptide 1 (GLP1) is postulated to regulate blood glucose and satiety, but the biological importance of GLP1 as an incretin and neuropeptide remains controversal. The regulation of nutrient-induced insulin secretion is dependent on the secretion of incretins, gut-derived peptides that potentiate insulin secretion from the pancreatic islets. To ascertain the relative physiological importance of GLP1 as a regulator of feeding behavior and insulin secretion, we have generated mice with a targeted disruption of the GLP1 receptor gene (GLP1R). These GLP1R-/- mice are viable, develop normally but exhibit increased levels of blood glucose following oral glucose challenge in association with diminished levels of circulating insulin. It is surprising that they also exhibit abnormal levels of blood glucose following intraperitoneal glucose challenge. Intracerebroventricular administration of GLP1 inhibited feeding in wild-type mice but not in GLP1R-/- mice; however, no evidence for abnormal body weight or feeding behavior was observed in GLP1R-/- mice. These observations demonstrate that GLP1 plays a central role in the regulation of glycemia; however, disruption of GLP1/GLP1R signaling in the central nervous system is not associated with perturbation of feeding behavior or obesity in vivo.

Animals↗
PubMed1996

Activation of proglucagon gene transcription through a novel promoter element by the caudal-related homeodomain protein cdx-2/3.

The proglucagon gene is expressed in a highly restricted tissue-specific manner in the A cells of the pancreatic islet and the L cells of the small and large intestines. The results of previous experiments indicate that cell-specific expression of the proglucagon gene is mediated by proteins that interact with the proximal G1 promoter element. We show here that the G1 element contains several AT-rich subdomains that bind proteins present in islet and enteroendocrine cell extracts. Electrophoretic mobility shift assay experiments using specific antisera identified the homeobox protein cdx-2/3 (which designates the same homeobox protein called cdx-2 for mice and cdx-3 for hamsters) as a major component of the G1-Gc2 complex in islet and intestinal cells. Mutations of the Gc element that decreased cdx-2/3 binding also resulted in decreased proglucagon promoter activity in islet and intestinal cell lines. The finding that cdx-2/3 mediates activation of the proglucagon promoter in both islet and enteroendocrine cells is consistent with the common endodermal lineage of these tissues and provides new insight into the coordinate regulation of genes expressed in both pancreatic and intestinal endocrine cell types.

Animals↗
PubMed1996

Glucagon response to hypoglycemia is improved by insulin-independent restoration of normoglycemia in diabetic rats.

The aim of this study was to determine whether the impaired glucagon response to insulin-induced hypoglycemia in the diabetic rat can be improved by correction of hyperglycemia independent of insulin. Four groups of age-matched male Sprague-Dawley rats (246 +/- 13 g BW) were studied: 1) normal controls (NC; n = 7); 2) diabetic, untreated (DU; n = 6); 3) diabetic, treated for 5-7 days using sustained release (2-3 U/day) insulin implants (DI; n = 6); and 4) diabetic, treated for 3-4 days with phlorizin (0.4 g/kg), given sc twice daily (DP; n = 7). Diabetes was induced by a single injection of streptozotocin (65 mg/kg). Basal plasma glucose was 7.4 +/- 0.3 mM in NC, but rose to 14.5 +/- 2.2 mM in DU. Basal hyperglycemia was corrected with phlorizin and insulin treatments (5.5 +/- 0.5 and 6.7 +/- 0.8 mM, respectively). NC rats responded to insulin-induced hypoglycemia with a rapid and marked increase in glucagon (peak, 2059 +/- 311 pg/ml). The glucagon response was blunted in DU (635 +/- 180 pg/ml) and was partially improved by prolonged normalization of glycemia in DP (1335 +/- 295 pg/ml; P < 0.05). Plasma somatostatin levels in all diabetic groups were 2- to 3-fold higher in the basal state, but were not different during hypoglycemia, than those in NC rats. Compared to levels in NC rats, diabetes resulted in decreased insulin, but elevated glucagon and somatostatin concentrations in the pancreatic tissue. Treatment with both insulin and phlorizin reversed the changes in the pancreatic content of both glucagon and somatostatin. Pancreatic proglucagon messenger RNA did not show significant differences among the four groups in either state. Insulin treatment in the DI group resulted in a delayed and much smaller increase in the glucagon response (740 +/- 138 pg/ml) to hypoglycemia despite normalization of glycemia. We, therefore, conclude that in streptozotocin-diabetic rats, the impaired glucagon responsiveness to hypoglycemia is significantly improved by insulin-independent correction of hyperglycemia, suggesting the importance of normoglycemia per se in maintaining, at least in part, the glucose sensitivity of pancreatic alpha-cells.

Animals↗
PubMed1996

Proglucagon gene expression is induced by gastrin-releasing peptide in a mouse enteroendocrine cell line.

The proglucagon gene is expressed in a cell-specific manner in the A cells of the islets and the L cells of the intestine; however, the physiological factors that regulate proglucagon gene expression are not well understood. Although insulin inhibits proglucagon gene transcription in the islets, peptides that stimulate proglucagon gene expression have not been identified. We show here that gastrin-releasing peptide (GRP) induces proglucagon messenger RNA transcripts in STC-1 enteroendocrine cells. The GRP induction of proglucagon gene expression was dose dependent, detectable by 4 h after GRP treatment, and sustained, i.e. detectable after a 24-h GRP incubation. GRP also induced the transcriptional activity of rat proglucagon promoter-luciferase plasmids in transfected STC-1 cells. The GRP induction of proglucagon promoter activity was attenuated, but not eliminated, after deletion of 5'-flanking sequences containing the proglucagon gene cAMP response element (CRE). A mutation in the CRE previously shown to abrogate cAMP responsiveness and CRE-binding protein binding was associated with a reduction in the transcriptional response to GRP. The proglucagon CRE also conferred GRP responsiveness to a truncated proglucagon promoter in STC-1 cells. These observations identify GRP as a peptide activator of proglucagon gene expression and provide evidence linking the proglucagon gene CRE to the physiological control of proglucagon gene expression.

Animals↗
PubMed1996

Activation of amylin gene transcription by LIM domain homeobox gene isl-1.

The amylin (IAPP) and insulin genes are coexpressed in the pancreatic beta-cell and share related promoter elements that may bind similar islet transcription factors. The observation that these promoter elements contain AT-rich subdomains suggests that homeobox proteins may be important for the regulation of both insulin and amylin gene transcription. We show here that the LIM domain homeobox protein isl-1 activates the rat amylin promoter in both fibroblast and islet cell lines. Mutation of the rAMY promoter TAAT motifs was associated with a marked reduction in both basal and isl-1 -dependent transcriptional activity. The isl-1 homeodomain binds to the AT-rich AMY element (-156 to -137) in the human amylin (hAMY) gene promoter, and electrophoretic mobility shift assay experiments using isl-1 specific antiserum detected the formation of an hAMY-isl-1 complex using nuclear extract from InR1 -G9 islet cells. Although isl-1 binds to both the insulin and amylin gene promoter elements in vitro, these sequences display marked differences in their relative transcriptional properties when ligated adjacent to a heterologous promoter and transfected into InR1 -G9 islet cells. The insulin gene E2 sequence that binds isl-1 (-230 to -208) functions as a negative element, whereas the hAMY sequence activates the thymidine kinase promoter in islet, but not nonislet, cell lines. Transfection of isl-1-depleted isl-1 (AS)InR1 -G9 cell lines demonstrated that the E2 element continued to repress thymidine kinase promoter activity, whereas the positive transcriptional activity mediated by the AMY element was considerably reduced in isl-1 (AS)-InR1-G9 cell lines. These dat2 demonstrate that highly similar elements in islet hormone gene promoters display differential functional properties and support a role for the isl-1 homeodomain protein in the regulation of amylin, but not insulin, gene transcription.

Amyloid↗
PubMed1995

The LIM domain homeobox gene isl-1 is a positive regulator of islet cell-specific proglucagon gene transcription.

The LIM domain homeobox gene islet 1 (isl-1) is expressed in the embryonic nervous system and may be an early marker of motor neuron specification. isl-1 is expressed in all 4 islet cell types, but a role for isl-1 in the regulation of insulin gene expression has not been demonstrated, and the genetic targets for isl-1 in the pancreas remain unknown. We show here that the proximal rat proglucagon gene promoter binds an amino-terminally truncated Trp-E-isl-1 fusion protein that lacks the LIM domains. The proglucagon gene promoter also binds full-length in vitro translated isl-1 containing the intact LIM domains. isl-1 antisera detects binding of proglucagon gene sequences to isl-1 present in a slowly-migrating complex in nuclear extracts from InR1-G9 islet cells. The transcriptional properties of the proglucagon gene promoter sequences that bind isl-1 (designated Ga, Gb, and Gc) were assessed after transfection of reporter genes into wild type and isl-1-antisense (isl-1(AS)) InR1-G9 islet cells. The proximal proglucagon gene (Ga) promoter sequence reduced TK-CAT activity by approximately 50%, but no change in the activity of the Ga-TK-CAT plasmid was seen after transfection of isl-1(AS) InR1-G9 cells. In contrast, the Gb/Gc sites activated transcription 2-3 fold in wild type InR1-G9 cells, and the isl-1-dependent activation of gene transcription through the Gb/Gc element was eliminated following transfection of isl-1(AS) InR1-G9 cells. These data demonstrate that the LIM domain homeobox gene isl-1 1) is not constrained from DNA binding by its LIM domains and 2) functions as a positive regulator of proglucagon gene transcription in the endocrine pancreas.

Animals↗
PubMed1995

UVB radiation-activated genes induced by transcriptional and posttranscriptional mechanisms in rat keratinocytes.

The mechanisms utilized by ultraviolet B (UVB) radiation in the regulation of gene expression, as well as the genetic targets for transmission of the UVB signal, remain incompletely understood. To elucidate the mechanisms and targets for UVB activation in mammalian cells, we screened a keratinocyte cDNA library with differentially subtracted UVB-enriched cDNA probes. Twenty-three UVB-induced cDNA clones were isolated, including cDNAs for keratin, elongation factor-1 alpha, ferritin heavy chain, thioltransferase, cyclin G, cornifin, cellubrevin, poly(A) binding protein, and the surfeit locus. The temporal kinetics of maximal RNA induction following UVB exposure were heterogeneous, varying from 1 to 24 h post-UVB radiation. Analysis of the regulation of gene expression demonstrated that the levels of most UVB-induced mRNAs were also independently induced by serum and cycloheximide, features previously described for genes induced by DNA damage and members of the immediate early gene family. In contrast to results from studies of immediate early genes, treatment of keratinocytes with both serum and cycloheximide resulted in superinduction of only one mRNA transcript. Nuclear run-on assays demonstrated that UVB radiation increased the transcription rate in 8 of 23 genes, suggesting that UVB radiation utilizes both transcriptional and posttranscriptional mechanisms for the modulation of keratinocyte gene expression. The identification of a group of UVB-inducible keratinocyte genes should prove useful for the characterization of the genomic response to UVB radiation and the analysis of the molecular mechanisms underlying the UVB regulation of gene expression.

Animals↗
PubMed1995

The proglucagon gene upstream enhancer contains positive and negative domains important for tissue-specific proglucagon gene transcription.

The gene encoding proglucagon is restricted in expression to the central nervous system, endocrine pancreas, and intestine. Transgenic experiments indicate that the proglucagon gene upstream enhancer (GUE) element is a principal determinant of both the tissue specificity and the relative level of proglucagon gene transcription. We have now sequenced the rat proglucagon GUE and analyzed the transcriptional properties of proglucagon-luciferase fusion genes (that contain 5'- and 3'-deletions in the GUE) after transfection of islet (InR1-G9) and enteroendocrine (STC-1 and GLUTag) cell lines. The GUE contains both positive and negative elements that are recognized differentially in islet vs. intestinal cell lines. The transcriptional properties of the GUE sequences were more similar in cell lines of intestinal (STC-1 and GLUTag) compared with islet (InR1-G9) phenotypes. The electrophoretic mobility shift assay was used to identify specific domains of the GUE that interacted with nuclear proteins from islet and intestinal cells. Several GUE sequences recognized proteins present in both fibroblast and endocrine cell lines. In contrast, electrophoretic mobility shift assay experiments also identified 1) GUE-protein complexes common to both islet and intestinal cell lines and 2) GUE-protein complexes specific to either islet or intestinal lineages. One of the GUE subdomains, designated GLUE1, displayed enhancer-like activity in InR1-G9 and GLUTag, but not BHK, cell lines. Taken together, these observations demonstrate that the proglucagon GUE is comprised of multiple positive and negative domains that likely function in a combinatorial fashion to regulate islet and intestinal-specific proglucagon gene transcription.

Animals↗
PubMed1994

Parathyroid hormone-related peptide is a downstream target for ras and src activation.

Neoplastic transformation may be associated with the development of paraneoplastic syndromes that complicate the management of patients with malignant disease. One of these syndromes, humoral hypercalcemia of malignancy, has been shown to be attributable to increased secretion of a parathyroid hormone-related peptide (PTHrP). The gene encoding PTHrP is expressed at low levels in a growth factor-dependent manner in normal tissues, and the mechanisms underlying selective tumor-associated induction of PTHrP gene expression remain unclear. Here we show that cellular transformation by the EJ-Ha-ras and v-src oncogenes is associated with a marked increase in PTHrP gene expression. Ha-ras- and v-src-transfected NRK 49F cells and ras-transfected RCB 2.2 cell lines secreted increased amounts of immunoreactive PTHrP. Northern blot analysis also demonstrated increased levels of PTHrP mRNA transcripts in oncogene-transfected stable cell lines. No significant change in the half-life of PTHrP mRNA transcripts was detected in Ha-ras- and v-src-transformed cells. In contrast, nuclear run-on assays demonstrated an increased rate of PTHrP gene transcription in oncogene-transformed cells. These observations demonstrate that the gene encoding PTHrP is a downstream target for ras and src, potentially providing a molecular basis for understanding the activation of PTHrP gene expression in malignancy-associated hypercalcemia.

Animals↗