Biomedical subjects

C M Townsend

Publications and source records attributed to C M Townsend.

At least 19 recordsLinked to original sources

PubMed2006

Constitutively active CCK2 receptor splice variant increases Src-dependent HIF-1 alpha expression and tumor growth.

Gastrointestinal (GI) cancers ectopically express multiple splice variants of the cholecystokinin-2 (CCK(2))/gastrin receptor; however, their relative contributions to the cancer phenotype are unknown. The aim of this study was to compare the effects of CCK(2) receptor (CCK(2)R) and CCK(2i4sv)R expression on cell growth both in vitro and in vivo using a human epithelial cell model, HEK239. In vitro, receptor variant expression did not affect cell proliferation either in the absence or presence of agonist. However, in vivo, the expression of CCK(2i4sv)R, but not CCK(2)R, increases HEK293 tumor growth in a constitutive, Src-dependent manner. Enhanced tumorigenicity of CCK(2i4sv)R is associated with an Src-dependent increase in the transcription factor, hypoxia-inducible factor-1alpha, its downstream target, vascular endothelial growth factor and tumor micro-vessel density, suggesting that CCK(2i4sv)R may contribute to the growth and spread of GI cancers through agonist-independent mechanisms that enhance tumor angiogenesis.

Alternative Splicing↗

PubMed2003

Phosphatidylinositol 3-kinase mediates proliferative signals in intestinal epithelial cells.

BACKGROUND AND AIMS: Determination of intracellular signalling pathways that mediate intestinal epithelial proliferation is fundamental to the understanding of the integrity and function of the intestinal tract under normal and diseased conditions. The phosphoinositide 3-kinase (PI3K)/Akt pathway transduces signals initiated by growth factors and is involved in cell proliferation and differentiation. In this study, we assessed the role of PI3K/Akt in transduction of proliferative signals in intestinal epithelial cells. METHODS: A rat intestinal epithelial (RIE) cell line and human colorectal cancer HCA-7 and LS-174 cell lines served as in vitro models. The Balb/cJ mouse was the in vivo model. RESULTS: PI3K activation was critical for G1 cell cycle progression of intestinal epithelial cells. Ectopic expression of either active p110alpha or Akt-1 increased RIE cell proliferation. In vivo experiments demonstrated that PI3K activation was closely associated with the proliferative activity of intestinal mucosa. Treatment of mice with PI3K inhibitors blocked induction of PI3K activity and attenuated intestinal mucosal proliferation associated with oral intake. Epidermal growth factor and transforming growth factor alpha stimulated PI3K activation which was required for growth factor induced expression of cyclin D1. CONCLUSIONS: The PI3K/Akt pathway transduces mitogenic signals from growth factor receptors to the cell cycle machinery and plays a critical role in regulation of intestinal epithelial proliferation.

Animals↗

PubMed2001

Activator protein-1 transcription factor mediates bombesin-stimulated cyclooxygenase-2 expression in intestinal epithelial cells.

Colorectal carcinogenesis is a complex, multistep process involving genetic alterations and progressive changes in signaling pathways regulating intestinal epithelial cell proliferation, differentiation, and apoptosis. Although cyclooxygenase-2 (COX-2), gastrin-releasing peptide (GRP), and its receptor, GRP-R, are not normally expressed by the epithelial cells lining the human colon, the levels of all three proteins are aberrantly overexpressed in premalignant adenomatous polyps and colorectal carcinomas of humans. Overexpression of these proteins is associated with altered epithelial cell growth, adhesion, and tumor cell invasiveness, both in vitro and in vivo; however, a mechanistic link between GRP-R-mediated signaling pathways and increased COX-2 overexpression has not been established. We report that bombesin, a homolog of GRP, potently stimulates the expression of COX-2 mRNA and protein as well as the release of prostaglandin E(2) from a rat intestinal epithelial cell line engineered to express GRP-R. Bombesin stimulation of COX-2 expression requires an increase in [Ca(2+)](i), activation of extracellular signal-regulated kinase (ERK)-1 and -2 and p38(MAPK), and increased activation and expression of the transcription factors Elk-1, ATF-2, c-Fos, and c-Jun. These data suggest that the expression of GRP-R in intestinal epithelial cells may play a role in carcinogenesis by stimulating COX-2 overexpression through an activator protein-1-dependent pathway.

Bombesin↗

PubMed2001

Amino acid, glucose, and lipid kinetics after palliative resection in a patient with glucagonoma syndrome.

Glucagon excess causes catabolic changes, including enhanced glucose production, lipolysis, and amino acid oxidation. In this study, we evaluate the metabolic effects of debulking surgery on a patient with glucagon-producing tumor. Stable isotope tracer methods were used to measure glucose, glycerol, and alpha-ketoisocaproic acid (alpha KICA) rates of appearance (Ra) into plasma. Measurements were obtained 25 days after surgery in the basal state and during hormonal suppression of glucagon production by infusing somatostatin with insulin replacement. Basal plasma glucagon concentration (14,100 pg/mL) remained high after debulking surgery. Somatostatin infusion decreased plasma glucagon concentration to 6,735 pg/mL and basal substrate kinetics (alpha-KICA Ra from 1.97 to 1.48 micromol/kg/min; glucose Ra from 16.89 to 11.56 micromol/kg/min; and glycerol Ra from 3.33 to 2.74 micromol/kg/min). We conclude that debulking surgery fails to adequately suppress glucagon production and the alterations in substrate metabolism associated with excess glucagon. In these patients, somatostatin therapy can be an effective method to suppress secretion of glucagon and help attenuate its catabolic effects.

Amino Acids↗

PubMed2001

The role of caspases in methotrexate-induced gastrointestinal toxicity.

BACKGROUND: Enterocolitis is the major toxicity of methotrexate-based cancer chemotherapy, which limits its clinical applications. Methotrexate induces gut mucosal apoptosis in vivo; however, little is known about the molecular mechanism involved. The effectors of apoptosis include the caspase family of proteases, which are selectively activated in a stimulus-specific and tissue-specific fashion. The aims of this study were (1) to establish an in vitro model of methotrexate-induced gut apoptosis and (2) to determine the role of caspases in methotrexate-induced apoptosis in intestinal epithelial cells. METHODS: Rat intestinal epithelial cells (RIE-1) were treated with methotrexate in the absence or presence of ZVAD-fluoromethyl ketone, a general caspase inhibitor. Apoptosis was quantified by means of deoxyribonucleic acid (DNA) fragmentation assays and Hoechst nuclear staining. Caspase activation was measured with the use of fluorogenic substrates. RESULTS: Methotrexate induced apoptosis and decreased cell number in RIE-1 cells. DNA fragmentation was preceded by the sequential activation of caspases 9, 2, and 3, whereas caspases 1 and 8 remained inactive. ZVAD-fluoromethyl ketone inhibited methotrexate-induced caspase activation, DNA fragmentation, and nuclear condensation. CONCLUSIONS: These results indicate that methotrexate activates specific caspases and induces apoptosis in RIE-1 cells. Furthermore, caspases may play an important role in methotrexate-induced apoptosis in RIE-1 cells and may be potential therapeutic targets to attenuate methotrexate-induced enterocolitis.

Amino Acid Chloromethyl Ketones↗

PubMed2000

Human colorectal cancers express a constitutively active cholecystokinin-B/gastrin receptor that stimulates cell growth.

Although ectopic expression of the cholecystokinin B/gastrin receptor (CCK-BR) is widely reported in human colorectal cancers, its role in mediating the proliferative effects of gastrin1-17 (G-17) on these cancers is unknown. Here we report the isolation of a novel splice variant of CCK-BR that exhibits constitutive (ligand-independent) activation of pathways regulating intracellular free Ca(2+) ([Ca(2+)](i)) and cell growth. The splice variant (designated CCK-BRi4sv for intron 4-containing splice variant) is expressed in colorectal cancers but not in normal colonic mucosa adjacent to the cancer. Balb3T3 cells expressing CCK-BRi4sv exhibited spontaneous, ligand-independent, oscillatory increases in [Ca(2+)](i), whereas cells expressing wild-type CCK-BR did not. Primary cultures of cells isolated from resected colorectal cancers also exhibited a similar pattern of spontaneous [Ca(2+)](i) oscillations. For both Balb3T3 and primary tumor cells, application of G-17 (10 and 200 nm, respectively) caused an increase in [Ca(2+)](i). Selective CCK-BR antagonists blocked the G-17-stimulated Ca(2+) responses but not the spontaneous [Ca(2+)](i) oscillations. Cells expressing CCK-BRi4sv exhibited an increased growth rate ( approximately 2.5-fold), in the absence of G-17, compared with cells expressing wild-type CCK-BR. The selective pattern of expression, constitutive activity, and trophic action associated with CCK-BRi4sv suggest that this variant may regulate colorectal cancer cell proliferation though a gastrin-independent mechanism.

3T3 Cells↗

PubMed2000

Roles of gastrointestinal hormones in pancreatic cancer.

Several gastrointestinal (GI) hormones, such as gastrin, cholecystokinin, and bombesin, have been reported to affect the development of pancreatic cancer. The receptors for these hormones are found in normal and neoplastic pancreatic cells. Activation of these receptors enhances pancreatic carcinogenesis and promotes the growth of established pancreatic carcinoma either in vitro or in vivo. On the other hand, some studies have shown that these GI hormones may have no effect or may play an inhibitory role in the development of pancreatic cancer. The reasons for the apparent discrepancies in the published literature are discussed in this review. In recent years, increasing emphasis has been placed on the effects of GI hormones on cancer invasion and metastasis. As the transition from noninvasion to the invasive state is the crucial event in cancer development, further investigation of the way in which GI hormones affect the invasion and metastasis of pancreatic cancer may be important for the development of new therapeutic approaches with eventual clinical utility.

Animals↗

PubMed2000

Gut peptide receptor expression in human pancreatic cancers.

OBJECTIVE: To determine the prevalence of gastrointestinal (GI) peptide receptor expression in pancreatic cancers, and to further assess signaling mechanisms regulating neurotensin (NT)-mediated pancreatic cancer growth. SUMMARY BACKGROUND DATA: Pancreatic cancer remains one of the leading causes of GI cancer death; novel strategies for the early detection and treatment of these cancers is required. Previously, the authors have shown that NT, an important GI hormone, stimulates the proliferation of an NT receptor (NTR)-positive pancreatic cancer. METHODS: A total of 26 human pancreatic adenocarcinomas, obtained after resection, and 5 pancreatic cancer xenografts were analyzed for expression of NTR, vasoactive intestinal peptide receptor (VIPR), substance P receptor (SPR), and gastrin-releasing peptide receptor (GRPR). In addition, NTR expression, [Ca2+]i mobilization, and growth in response to NT was determined in L3.6, a metastatic pancreatic cancer cell line. RESULTS: Neurotensin receptor was expressed in 88% of the surgical specimens examined and all five of the pancreatic cancer xenografts. In contrast, VIPR, SPR, and GRPR expression was detected in 31%, 27%, and 8% of pancreatic cancers examined, respectively. Expression of NTR, functionally coupled to the Ca2+ signaling pathway, was identified in L3.6 cells; treatment with NT (10 micromol/L) stimulated proliferation of these cells. CONCLUSIONS: The authors demonstrated NTR expression in most of the pancreatic adenocarcinomas examined. In contrast, VIPR, SPR, and GRPR expression was detected in fewer of the pancreatic cancers. The expression of NTR and other peptide receptors suggests the potential role of endocrine manipulation in the treatment of these cancers. Further, the presence of GI receptors may provide for targeted chemotherapy or radiation therapy or in vivo scintigraphy for early detection.

Adenocarcinoma↗

PubMed2000

Signaling mechanisms regulating bombesin-mediated AP-1 gene induction in the human gastric cancer SIIA.

The hormone bombesin (BBS) and its mammalian equivalent gastrin-releasing peptide (GRP) act through specific GRP receptors (GRP-R) to affect multiple cellular functions in the gastrointestinal tract; the intracellular signaling pathways leading to these effects are not clearly defined. Previously, we demonstrated that the human gastric cancer SIIA possesses GRP-R and that BBS stimulates activator protein-1 (AP-1) gene expression. The purpose of our present study was to determine the signaling pathways leading to AP-1 induction in SIIA cells. A rapid induction of c-jun and jun-B gene expression was noted after BBS treatment; this effect was blocked by specific GRP-R antagonists, indicating that BBS is acting through the GRP-R. The signaling pathways leading to increased AP-1 gene expression were delineated using phorbol 12-myristate 13-acetate (PMA), which stimulates protein kinase C (PKC)-dependent pathways, by forskolin (FSK), which stimulates protein kinase A (PKA)-dependent pathways, and by the use of various protein kinase inhibitors. Treatment with PMA stimulated AP-1 gene expression and DNA binding activity similar to the effects noted with BBS; FSK stimulated jun-B expression but produced only minimal increases of c-jun mRNA and AP-1 binding activity. Pretreatment of SIIA cells with either H-7 or H-8 (primarily PKC inhibitors) inhibited the induction of c-jun and jun-B mRNAs in response to BBS, whereas H-89 (PKA inhibitor) exhibited only minimal effects. Pretreatment with tyrphostin-25, a protein tyrosine kinase (PTK) inhibitor, attenuated the BBS-mediated induction of c-jun and jun-B, but the effect was not as pronounced as with H-7. Collectively, our results demonstrate that BBS acts through its receptor to produce a rapid induction of both c-jun and jun-B mRNA and AP-1 DNA binding activity in the SIIA human gastric cancer. Moreover, this induction of AP-1, in response to BBS, is mediated through both PKC- and PTK-dependent signal transduction pathways with only minimal involvement of PKA.

Bombesin↗

PubMed1999

Multiple protein kinase pathways are involved in gastrin-releasing peptide receptor-regulated secretion.

Gastrin-releasing peptide (GRP) and its amphibian homolog, bombesin, are potent secretogogues in mammals. We determined the roles of intracellular free Ca(2+) ([Ca(2+)](i)), protein kinase C (PKC), and mitogen-activated protein kinases (MAPK) in GRP receptor (GRP-R)-regulated secretion. Bombesin induced either [Ca(2+)](i) oscillations or a biphasic elevation in [Ca(2+)](i). The biphasic response was associated with peptide secretion. Receptor-activated secretion was blocked by removal of extracellular Ca(2+), by chelation of [Ca(2+)](i), and by treatment with inhibitors of phospholipase C, conventional PKC isozymes, and MAPK kinase (MEK). Agonist-induced increases in [Ca(2+)](i) were also inhibited by dominant negative MEK-1 and the MEK inhibitor, PD89059, but not by an inhibitor of PKC. Direct activation of PKC by a phorbol ester activated MAPK and stimulated peptide secretion without a concomitant increase in [Ca(2+)](i). Inhibition of MEK blocked both bombesin- and phorbol 12-myristate 13-acetate-induced secretion. GRP-R-regulated secretion is initiated by an increase in [Ca(2+)](i); however, elevated [Ca(2+)](i) is insufficient to stimulate secretion in the absence of activation of PKC and the downstream MEK/MAPK pathways. We demonstrated that the activity of MEK is important for maintaining elevated [Ca(2+)](i) levels induced by GRP-R activation, suggesting that MEK may affect receptor-regulated secretion by modulating the activity of Ca(2+)-sensitive PKC.

Bombesin↗

PubMed1999

Characterization of two novel proabsorptive peptide YY analogs, BIM-43073D and BIM-43004C.

Effective clinical therapy to augment intestinal absorption of water and electrolytes does not exist; the gut hormone, peptide YY (PYY), is a potent proabsorptive agent in animal models. The purpose of our study was to evaluate the effects of two novel PYY analogs, BIM-43073D and BIM-43004C, on intestinal absorption. Dogs with ileal Thiry-Vella fistulae (TVF) were treated with either PYY, BIM-43073D, or BIM-43004C. Administration of BIM-43073D significantly increased water and sodium absorption over baseline and maintained this level of increased absorption for a longer duration than an equimolar dose of PYY. Administration of BIM-43004C significantly increased sodium and water absorption over baseline at a level equal to that of PYY. The novel PYY analogs, BIM-43073D and BIM-43004C, are effective proabsorptive agents with BIM-43073D producing more sustained effects than PYY. These compounds may be clinically useful in the treatment of gut malabsorption in conditions such as cholera, Crohn's disease, and the short-bowel syndrome.

Animals↗

PubMed1999

Inhibition of gastric cancer by camptothecin involves apoptosis and multiple cellular pathways.

BACKGROUND: The prognosis for gastric cancer remains dismal; novel agents that target specific molecular pathways are needed as adjuvant therapy. Camptothecin (CPT), on inhibitor of topoisomerase I, is effective in the treatment of certain solid tumors; its effects on gastric cancer are largely undefined. The purpose of this study was to (1) characterize the effects of CPT on the growth of a human gastric cancer and (2) assess potential cellular mechanisms responsible for CPT-mediated growth inhibition. METHODS: The human gastric cancer SIIA was transplanted subcutaneously into athymic nude mice. After tumors reached approximately 100 mm2, mice were randomized into 3 groups to receive either CPT (5 or 10 mg/kg) or vehicle (control) intraperitoneally 3 days per week for 3 weeks; tumor size was measured biweekly. To assess potential mechanisms of CPT-mediated inhibition, SIIA cells were treated with CPT (20 mumol/L) and cells were counted over a time course; apoptosis was assessed by Hoechst stain and DNA laddering. Expression of p53 (a tumor suppressor), p21Waf1 and p27Kip1 (cell cycle inhibitors), and Bcl-2 and Bcl-XL (antiapoptotic proteins) was determined. RESULTS: CPT (5 and 10 mg/kg) significantly inhibited tumor growth of SIIA gastric cancers compared with controls. CPT-mediated inhibition of SIIA cell proliferation was associated with an increase in apoptosis. Moreover, CPT treatment resulted in induction of p53, p21Waf1, and p27Kip1 and a decrease in Bcl-2 and Bcl-XL RNA and protein levels. CONCLUSIONS: Treatment with CPT effectively inhibited the growth of the human gastric cancer SIIA; the mechanism involved was induction of apoptosis mediated by up-regulation of p53, p21Waf1/Cip1, and p27Kip1 and the down-regulation of Bcl-2 and Bcl-XL. Novel agents such as CPT, which target specific molecular pathways, may prove clinically useful in the adjuvant treatment of gastric cancers.

Adenocarcinoma↗

PubMed1998

Stimulation of prohormone convertase-1 mRNA expression by second messenger signaling systems.

The purpose of this study was to investigate the effects of activation of various second messenger signaling systems on gene expression (i.e. mRNA levels) of a peptide hormone processing enzyme called prohormone convertase-1 (PC-1, also called PC-3) in a human pancreatic carcinoid cell line (BON) that expresses several endocrine peptides (chromogranin A, pancreastatin, neurotensin). Pharmacologic activation of adenylate cyclase-cAMP, protein kinase-C and Ca2+ mobilization pathways increased PC-1 mRNA levels and neurotensin secretion. Elevations in PC-1 mRNA levels were dose and time-related. Secretagogue-induced cellular depletion of neurotensin was followed by a replenishment of cellular neurotensin stores and an upregulation of PC-1 mRNA levels. Together, these data indicate that PC-1 mRNA expression is increased with peptide secretion and coordinated with maintenance of cellular stores of peptides.

8-Bromo Cyclic Adenosine Monophosphate↗

PubMed1998

Insulin-like growth factor-I promotes multidrug resistance in MCLM colon cancer cells.

Insulin-like growth factor-I (IGF-I) is known as a potent mitogen for a variety of cell types, including colon cancer cell lines. The objective of this study was to determine the effect of IGF-I on cell death induced by cytotoxic agents actinomycin D (Act-D), lovastatin (LOV), and doxorubicin (DOX) in the MCLM mouse colon cancer cell line, and the mechanisms involved. Subconfluent monolayer MCLM cells were treated with IGF-I (25 ng/ml) for 12 h in serum-free media. Various concentrations of cytotoxic agents then were added to the cells that were incubated continually at 37 degrees C for 24 h. Cell survival was determined with the MTT (3-[4-5-dimenthylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) assay, which assesses mitochondrial function in living cells. The mRNA expression for multidrug resistance gene-1 (mdr-1), c-H-ras, and manganese superoxide dismutase (MnSOD) in cells treated with IGF-I was examined by Northern blot or RNase protection assays. The levels of p-glycoprotein, a drug efflux pump encoded by the mdr-1 gene, were assessed by Western immunoblotting. Results demonstrated that 1) IGF-I significantly inhibited the cell death and apoptosis of MCLM cells treated with Act-D, LOV, or DOX; 2) IGF-I increased mRNA expression for mdr-1, c-H-ras, and MnSOD; 3) the p-glycoproteins in cells treated with IGF-I or stably transfected with c-H-ras were elevated when compared with control. These results suggest that IGF-I protects MCLM cells against death induced by cytotoxic agents; this acquired drug resistance may be mediated by multiple mechanisms, including promoting expression of mdr-1, c-H-ras, and MnSOD; whereas, the p-glycoprotein level stimulated by IGF-I may result partly from the increase of c-H-ras in the cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed1998

Novel expression and regulation of gastrin gene in human ovarian cancer cell line, SW626.

Gastrin-secreting tumors have been identified in ectopic locations including the ovary; the mechanisms regulating gastrin gene expression, its distribution, and signaling pathways in these ectopic tissues are not known. The purpose of our present study was to determine: (1) whether the gastrin gene and peptide could be detected in ovarian cancer cell lines, (2) if functional gastrin releasing peptide receptors (GRP-R) are present, and (3) whether gastrin gene expression is altered by GRP. Five ovarian cancer cell lines (SW626, OVCA 420, OVCA 429, OVCA 432, and OVCA 433) were analyzed. We identified gastrin gene and peptide expression in the SW626 cell line but not in the OVCA lines. SW626 cells express a functional GRP-R that is correctly coupled to the Ca2+ signaling pathway. Treatment of SW626 cells with bombesin, the amphibian equivalent of GRP, inhibited expression of the gastrin gene in a time- and dose-dependent fashion. The SW626 ovarian cancer cell line will provide a useful model to further define regulation and expression of both the gastrin gene and peptide in ectopic (nongastrointestinal) tissues.

Blotting, Northern↗

PubMed1998

A novel cytotoxic agent for human carcinoid tumors.

BACKGROUND: Conventional adjuvant therapy for advanced carcinoid tumors remains disappointing; novel therapeutic agents are needed. We have shown previously that inhibiting polyamine biosynthesis with alpha-difluoromethylornithine (DFMO) slows the growth of carcinoid tumors. However, the clinical utility of DFMO has been limited by its cytostatic property. Synthetic polyamine analogs such as 1,19-bis(ethylamino)-5,10,15-triazanonadecane (BE-4-4-4-4) appear to be cytotoxic against several human tumors. The purpose of our study was to determine whether BE-4-4-4-4 is a more effective antiproliferative and cytotoxic agent than DFMO on human carcinoid (BON) cells in vitro. METHODS: BON cells were treated with either 5 mmol/L DFMO, 0.5 to 10 mumol/L BE-4-4-4-4, or vehicle (control). Ornithine decarboxylase activity was determined by the rate of 14CO2 production, and intracellular polyamine levels were determined by chromatography. Cell number and viability were determined by Coulter counter and trypan blue exclusion, respectively. RESULTS: BE-4-4-4-4 inhibited ornithine decarboxylase activity and depleted all 3 polyamines. BE-4-4-4-4 decreased cell numbers by 81% compared with control and 27% compared with DFMO. BE-4-4-4-4 also induced a 2-fold increase in cell death compared with control or DFMO. CONCLUSIONS: BE-4-4-4-4 is cytotoxic and more effective than DFMO in inhibiting growth of BON cells. Polyamine analogs such as BE-4-4-4-4 may be effective adjuvant therapeutic agents for advanced carcinoid tumors.

Antineoplastic Agents↗

PubMed1998

DNA methylation contributes to expression of the human neurotensin/neuromedin N gene.

The gut and liver share a common embryological origin. The gene encoding the gut hormone neurotensin/neuromedin N (NT/N) is expressed in the adult small bowel, and NT/N is transiently expressed in the fetal liver, suppressed in the adult liver, and reexpressed in certain liver cancers. In our present study, we found that the NT/N gene was expressed at high levels in the human hepatoma cell line Hep 3B but was not expressed in Hep G2 cells. To further determine the mechanisms regulating NT/N expression, we performed Southern blotting and gene cloning techniques. Neither alteration nor mutation of the NT/N gene was responsible for this differential NT/N expression pattern. Human NT/N promoter constructs were transfected into either Hep 3B or Hep G2. Both cell lines supported NT/N transcription, indicating that the absence of NT/N expression in Hep G2 cells was due to mechanisms other than the absence of positive transcription factors. The role of DNA methylation was next assessed. Methylation of NT/N promoter constructs in vitro resulted in a 67-fold reduction in promoter activity, whereas treatment with the demethylating agent 5-azacytidine induced NT/N expression in Hep G2 cells, thus suggesting that DNA methylation plays a role in the expression of the gut endocrine gene NT/N. Defining the mechanisms regulating NT/N expression in these hepatic-derived cell lines will provide not only a better understanding of cell-specific and developmental regulation of a gut endocrine gene but also possible insight into liver cell lineage patterns and the derivation of certain hepatocellular cancers.

Adult↗

PubMed1998

A human gastric cancer cell line possesses a functional receptor for gastrin-releasing peptide.

Bombesin (BBS) exhibits diverse biological functions including those of neurotransmitter, regulator of gastrointestinal hormone release, and mitogen. Gastrin-releasing peptide (GRP, the mammalian equivalent of BBS) is found in mucosal cells of the gastric fundus and antrum. We determined whether a human gastric cancer cell line (SIIA) expresses a functional GRP-receptor (GRP-R). BBS increased intracellular calcium ([Ca2+]i), and a specific GRP-R antagonist, ([D-Phe6, Des-Met14]-BBS (6-14)-ethylamide), blocked BBS-induced increase in [Ca2+]i. SIIA cells possess GRP-R mRNA by reverse transcriptase-PCR. Furthermore, these cells possess an 80-kDa cell surface protein that specifically binds BBS with two high-binding affinities (Kd1 = 0.6 nM, Kd2 = 6.7 nM). These findings indicate that SIIA cells possess a GRP-R that is capable of physiological signal transduction, though the cellular response remains unknown.

Adenocarcinoma↗