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A Fusco

Publications and source records attributed to A Fusco.

At least 55 records · Page 3Linked to original sources
PubMed2001

RNF4 is a growth inhibitor expressed in germ cells but not in human testicular tumors.

The RING-finger protein RNF4 modulates both steroid-receptor-dependent and basal transcription and interacts with a variety of nuclear proteins involved in cell growth control. RNF4 is expressed at very high levels in testis and at much lower levels in several other tissues. We show that in germ cells RNF4 expression is strongly modulated during progression of spermatogonia to spermatids, with a peak in spermatocytes. Analysis of human testicular germ cell tumors shows that RNF4 is not expressed in all tumors analyzed including seminomas, the highly malignant embryonal carcinomas, yolk sac, and mixed germ cell tumors. We also show that the ectopically expressed RNF4 gene inhibits cell proliferation of both somatic and germ cell tumor-derived cells. Mutation of critical cysteine residues in the RING finger domain abolished the RNF4 growth inhibition activity. Our results suggest that the lack of RNF4 expression may play a role in the progression of testicular tumors.

Animals↗
PubMed2001

The RET receptor: function in development and dysfunction in congenital malformation.

Germline mutations in the RET proto-oncogene are responsible for two unrelated neural crest disorders: Hirschsprung disease, a congenital absence of the enteric nervous system in the hindgut, and multiple endocrine neoplasia type 2, a dominantly inherited cancer syndrome. Moreover, somatic rearrangements of RET are causally involved in the genesis of papillary thyroid carcinoma. The receptor tyrosine kinase encoded by the RET gene acts as the subunit of a multimolecular complex that binds four distinct ligands and activates a signalling network crucial for neural and kidney development. Over the past few years, a clearer picture of the mode of RET activation and of its multifaceted role during development has started to emerge. These findings, which provide new clues to the molecular mechanisms underlying RET signalling dysfunction in Hirschsprung disease, are summarized in this review.

Animals↗
PubMed2001

Opioid dysregulation after biliopancreatic diversion: effect of naloxone on preprandial and postprandial growth hormone (GH)-releasing hormone-induced GH release in surgically induced weight loss.

Previously, we have shown that in the opposite extremes of nutritional status (obesity and anorexia nervosa [AN]), the growth hormone (GH) response to GH-releasing hormone (GHRH) is not inhibited by the ingestion of a normal 800-kcal meal at noon. In obese subjects, GHRH-induced GH release is significantly increased (known as the "paradoxical response"). An opiate antagonist infusion (naloxone [NAL]) inhibited this postprandial meal-induced augmenting effect in obese subjects, suggesting opioid involvement in the paradoxical response. The paradoxical postprandial GH release persisted in obese subjects, who after biliopancreatic diversion (BPD) experienced a reduction in body weight, despite the elevation of fasting GH levels. We therefore tested a group of patients, before and after BPD, composed of 10 females, aged 23 to 54 years, who after surgery had experienced a significant reduction in body weight (mean body mass index [BMI], 25.78 +/- 1.01 kg/mg v 44.68 +/- 1.73 kg/mg). The subjects were studied 16 to 24 months after operation, in a phase of stabilized body weight. They underwent, in randomized order, the following tests: GHRH (1 microg/kg as an intravenous [IV] bolus) at 1:00 PM, in the fasting state; GHRH (1 microg/kg) at 1:00 PM, 45 minutes after a standard 800-kcal meal consumed between noon and 12:15 PM; and fasting state and postprandial GHRH (1 microg/kg) during NAL infusion (1.6 mg/h x 2.5 h, starting at noon). We found that NAL inhibited the paradoxical postprandial GH increase only in pre-BPD subjects (GH area under the concentration time curve [AUC] in microg/L/90 min)-before meal: after GHRH 237.54 +/- 62.28, after NAL + GHRH 699.2 +/- 271.57; after meal: after GHRH 575.46 +/- 109.68, after NAL + GHRH 156.17 +/- 24.96. On the other hand, NAL failed to have significant effects in post-BPD subjects (GH AUC in microg/L/90 min)-before meal: after GHRH 871.11 +/- 256.38, after NAL + GHRH 449.19 +/- 119.13; after meal: after GHRH 1,981.54 +/- 319.92, after NAL + GHRH 1,665.91 +/- 315.4. It could be hypothesized that the opioid system is radically modified by the surgical procedure, and that opioids are not the only mediators in the paradoxical response, which persists after BPD, despite the reversion of the hyposecretory GH state, which is a characteristic of obese subjects.

Adult↗
PubMed2001

Role of the high mobility group A proteins in human lipomas.

The HMGA family is comprised of four proteins: HMGA1a, HMGA1b, HMGA1c and HMGA2. The first three proteins are products of the same gene, HMGA1, generated through an alternative splicing mechanism. The HMGA proteins are involved in the regulation of chromatin structure and HMGA DNA-binding sites have been identified in functional regions of many gene promoters. Rearrangements of the HMGA2 gene have been frequently detected in human benign tumors of mesenchymal origin including lipomas. 12q13-15 chromosomal translocations involving the HMGA2 gene locus, account for these rearrangements. The HMGA proteins have three AT-hook domains and an acidic C-terminal tail. The HMGA2 modifications consist in the loss of the C-terminal tail and fusion with ectopic sequences. A pivotal role of the HMGA2 rearrangements in the process of lipomagenesis is suggested by experiments showing that transgenic mice carrying a truncated HMGA2 gene showed a giant phenotype together with abdominal/pelvic lipomatosis. As HMGA2 null mice showed a great reduction in fat tissue, a positive role of the HMGA2 gene in adipocytic cell proliferation is proposed. More recently, similar alterations of the HMGA1 gene have been described. As the block of the HMGA1 protein synthesis induces an increase in growth rate of the pre-adipocytic cell line 3T3-L1, we suggest a negative role of the HMGA1 proteins in adipocytic cell growth and, therefore, we propose that adipocytic cell growth derives from the balance of the HMGA1 and HMGA2 protein functions.

Adipocytes↗
PubMed2001

HMGI-C gene expression is not required for in vivo thyroid cell transformation.

We have previously demonstrated that HMGI proteins are required for the transformation of rat thyroid cells by v-mos and v-ras-Ki oncogenes. To determine whether HMGI proteins are also required for in vivo thyroid carcinogenesis, mice carrying a disrupted HMGI-C gene (pygmy mice) were either treated with radioactive iodine or crossed with transgenic mice carrying the E7 papilloma virus oncogene under the transcriptional control of thyroglobulin gene promoter. The pygmy mice developed thyroid carcinomas with the same frequency as occurred in wild-type mice without significant macroscopic and microscopic differences. Therefore, these results indicate that HMGI-C gene expression is not required in in vivo thyroid cell malignant transformation.

Animals↗
PubMed2001

Docking protein FRS2 links the protein tyrosine kinase RET and its oncogenic forms with the mitogen-activated protein kinase signaling cascade.

The receptor tyrosine kinase RET functions as the signal transducing receptor for the GDNF (for "glial cell-derived neurotrophic factors") family of ligands. Mutations in the RET gene were implicated in Hirschsprung disease (HSCR), multiple endocrine neoplasia type 2 (MEN 2), and thyroid carcinomas. In this report we demonstrate that the docking protein FRS2 is tyrosine phosphorylated by ligand-stimulated and by constitutively activated oncogenic forms of RET. Complex formation between RET and FRS2 is mediated by binding of the phosphotyrosine-binding domain of FRS2 to pY1062, a residue in RET that also functions as a binding site for Shc. However, overexpression of FRS2 but not Shc potentiates mitogen-activated protein (MAP) kinase activation by RET oncoproteins. We demonstrate that oncogenic RET-PTC proteins are associated with FRS2 constitutively, leading to tyrosine phosphorylation of FRS2, MAP kinase stimulation, and cell proliferation. However, loss-of-function HSCR-associated RET mutants exhibit impaired FRS2 binding and reduced MAP kinase activation. These experiments demonstrate that FRS2 couples both ligand-regulated and oncogenic forms of RET, with the MAP kinase signaling cascade as part of the response of RET under normal biological conditions and pathological conditions, such as MEN 2 and papillary thyroid carcinomas.

Adaptor Proteins, Signal Transducing↗
PubMed2001

Critical role of the HMGI(Y) proteins in adipocytic cell growth and differentiation.

The high-mobility group I (HMGI) nonhistone chromosomal proteins HMGI(Y) and HMGI-C have been implicated in defining chromatin structure and in regulating the transcription of several genes. These proteins have been implicated in adipocyte homeostasis: a severe deficiency of fat tissue is found in mice with targeted disruption of the HMGI-C locus, and lipomagenesis in humans is frequently associated with somatic mutations of HMGI genes. The aim of this study was to examine the role of HMGI(Y) proteins in adipocytic cell growth and differentiation. First, we found that differentiation of the preadipocytic 3T3-L1 cell line caused early induction of HMGI(Y) gene expression. Suppression of HMGI(Y) expression by antisense technology dramatically increased the growth rate and impaired adipocytic differentiation in these cells. The process of adipogenic differentiation involves the interplay of several transcription factors, among which is the CCAAT/enhancer-binding protein (C/EBP) family of proteins. These factors are required for the transcriptional activation of adipocyte-specific genes. We also tested the hypothesis that HMGI(Y) might participate in transcriptional control of adipocyte-specific promoters. We found that HMGI(Y) proteins bind C/EBPbeta in vivo and in vitro. Furthermore, we show that HMGI(Y) strongly potentiates the capacity of C/EBPbeta to transactivate the leptin promoter, an adipose-specific promoter. Taken together, these results indicate that the HMGI(Y) proteins play a critical role in adipocytic cell growth and differentiation.

3T3 Cells↗
PubMed2001

Regulation of thyroid cell proliferation by TSH and other factors: a critical evaluation of in vitro models.

TSH via cAMP, and various growth factors, in cooperation with insulin or IGF-I stimulate cell cycle progression and proliferation in various thyrocyte culture systems, including rat thyroid cell lines (FRTL-5, WRT, PC Cl3) and primary cultures of rat, dog, sheep and human thyroid. The available data on cell signaling cascades, cell cycle kinetics, and cell cycle-regulatory proteins are thoroughly and critically reviewed in these experimental systems. In most FRTL-5 cells, TSH (cAMP) merely acts as a priming/competence factor amplifying PI3K and MAPK pathway activation and DNA synthesis elicited by insulin/IGF-I. In WRT cells, TSH and insulin/IGF-I can independently activate Ras and PI3K pathways and DNA synthesis. In dog thyroid primary cultures, TSH (cAMP) does not activate Ras and PI3K, and cAMP must be continuously elevated by TSH to directly control the progression through G(1) phase. This effect is exerted, at least in part, via the cAMP-dependent activation of the required cyclin D3, itself synthesized in response to insulin/IGF-I. This and other discrepancies show that the mechanistic logics of cell cycle stimulation by cAMP profoundly diverge in these different in vitro models of the same cell. Therefore, although these different thyrocyte systems constitute interesting models of the wide diversity of possible mechanisms of cAMP-dependent proliferation in various cell types, extrapolation of in vitro mechanistic data to TSH-dependent goitrogenesis in man can only be accepted in the cases where independent validation is provided.

Animals↗
PubMed2001

The activation of the phosphotyrosine phosphatase eta (r-PTP eta) is responsible for the somatostatin inhibition of PC Cl3 thyroid cell proliferation.

The aim of this study was the characterization of the intracellular effectors of the antiproliferative activity of somatostatin in PC Cl3 thyroid cells. Somatostatin inhibited PC Cl3 cell proliferation through the activation of a membrane phosphotyrosine phosphatase. Conversely, PC Cl3 cells stably expressing the v-mos oncogene (PC mos) were completely insensitive to the somatostatin antiproliferative effects since somatostatin was unable to stimulate a phosphotyrosine phosphatase activity. In PC mos cells basal phosphotyrosine phosphatase activity was also reduced, suggesting that the expression of a specific phosphotyrosine phosphatase was impaired in these transformed cells. We suggested that this phosphotyrosine phosphatase could be r-PTP eta whose expression was abolished in the PC mos cells. To directly prove the involvement of r-PTP eta in somatostatin's effect, we stably transfected this phosphatase in PC mos cells. This new cell line (PC mos/PTP eta) recovered somatostatin's ability to inhibit cell proliferation, showing dose-dependence and time course similar to those observed in PC Cl3 cells. Conversely, the transfection of a catalytically inactive mutant of r-PTP eta did not restore the antiproliferative effects of somatostatin. PC mos/PTP eta cells showed a high basal phosphotyrosine phosphatase activity which, similarly to PC Cl3 cells, was further increased after somatostatin treatment. The specificity of the role of r-PTP eta in somatostatin receptor signal transduction was demonstrated by measuring its specific activity after somatostatin treatment in an immunocomplex assay. Somatostatin highly increased r-PTP eta activity in PCCl3 and PC mos/PTP eta (+300%, P < 0.01) but not in PCmos cells. Conversely, no differences in somatostatin-stimulated SHP-2 activity, (approximately +50%, P < 0.05), were observed among all the cell lines. The activation of r-PTP eta by somatostatin caused, acting downstream of MAPK kinase, an inhibition of insulin-induced ERK1/2 activation with the subsequent blockade of the phosphorylation, ubiquitination, and proteasome degradation of the cyclin-dependent kinase inhibitor p27(kip1). Ultimately, high levels of p27(kip1) lead to cell proliferation arrest. In conclusion, somatostatin inhibition of PC Cl3 cell proliferation requires the activation of r-PTP eta which, through the inhibition of MAPK activity, causes the stabilization of the cell cycle inhibitor p27(kip1).

Blotting, Northern↗
PubMed2001

RET protein expression has no prognostic impact on the long-term outcome of papillary thyroid carcinoma.

BACKGROUND: RET proto-oncogene rearrangements (RET/PTC) are causative events in the pathogenesis of a subset of papillary thyroid cancer (PTC). The prevalence of RET/PTC varies in different countries and according to specific clinical features: it is higher after radiation exposure and it is claimed to be higher in young patients. Conflicting results are reported regarding the prognostic role of RET/PTC activation. OBJECTIVE: To investigate the prognostic meaning of RET/PTC rearrangement on the long term outcome of PTC. METHODS: We have studied the expression of the RET encoded protein in 127 papillary thyroid carcinomas by immunohistochemistry using a polyclonal antibody against the tyrosine-kinase domain of the RET protein. These cases have been collected during 1970-1985, and have a mean (+/-S.D.) period of follow-up of 18.6+/-3.7 years (range 12-27 years). The results have been compared with the patients' outcome. RESULTS: The tyrosine-kinase domain of RET was expressed in 82 (64.6%) papillary carcinomas. Among them, RET was highly expressed in 65 (51.2%) cases and moderately expressed in 17 (13.4%). RET expression was absent in 45 (35.4%) cases. No correlation was found between RET expression and other parameters such as sex, age at diagnosis, tumor class and histological variant. Follow-up analysis showed no influence of RET expression on patients' outcome. By multivariate analysis, age (>45 years) and tumor class IV, but not sex and RET expression were adverse prognostic indicators of death. CONCLUSION: In conclusion, our analysis indicates that RET expression is frequently found in PTC, and has no influence on tumor outcome.

Adolescent↗
PubMed2001

Human papilloma virus 16 E7 oncogene does not cooperate with RET/PTC 3 oncogene in the neoplastic transformation of thyroid cells in transgenic mice.

We have previously reported that the thyroid-targeted expression of the RET/PTC3 oncogene (Tg-RET/PTC3) in transgenic mice induces follicular hyperplasia with papillary architecture, resulting in a modest increase of the thyroid gland volume, followed by the appearance of papillary carcinomas in approximately 1-year-old animals. In order to analyze the genetic alterations that may cooperate with RET/PTC3 in the development or progression of thyroid tumors, we interbred Tg-RET/PTC3 mice with Tg-E7 transgenic mice, which express the E7 oncogene of the human papilloma virus 16 in thyroid cells. Tg-E7 mice develop large colloid goiters with small papillae and well-differentiated thyroid carcinomas in older animals. Here we show that thyroid lesions in Tg-RET/PTC3-Tg-E7 double transgenics were morphologically different from those occurring in Tg-RET/PTC3 mice, while they were virtually indistinguishable from those occurring in Tg-E7 mice. In addition, the coexpression of RET/PTC3 and E7 oncogenes neither enhanced the malignant phenotype nor reduced the latency period of thyroid lesions with respect to parental transgenic lines. We conclude that the coexpression of RET/PTC3 and E7 lacks any cooperative effect in the neoplastic transformation of thyroid cells and that the E7-induced thyroid phenotype is dominant with respect to the RET/PTC3 one.

Age Factors↗
PubMed2001

[The activation of the phosphotyrosine phosphatase eta is responsible for the somatostatin inhibition of PCCl3 thyroid cell proliferation].

BACKGROUND: This study was aimed to identify possible intracellular effectors of the somatostatin (SST) antiproliferative activity, in PCCl3 thyroid cells. METHODS: To prove the involvement of r-PTPeta in SST's effect, we studied th proliferative activity of subclones of PCCl3 cells that do or do not express this PTP. RESULTS: SST inhibited PCCl3 TSH+insulin-dependent cell proliferation through the induction of a phosphotyrosine phosphatase (PTP) activity, detected using the synthetic substrate pNPP (+150%, p<0.01). Conversely, PCCl3 cells stably expressing the v-mos oncogene (PCmos) were completely insensitive to SST antiproliferative effects due to the incapability of SST to increase PTP activity, that correlated with the abolishment of the expression of the receptor-like PTP, r-PTPeta. In the cells in which r-PTPeta was transfected (PCmos/ PTPeta) SST inhibited cell proliferation showing a dose-dependence similar to that observed in PCCl3 cells. Conversely, the transfection of a catalytically inactive mutant of r-PTPeta did not restore the responsivity to SST. Also in PCmos/PTPeta cells SST, treatment increased membrane PTP activity. CONCLUSIONS: SST inhibition of PCC13 cell proliferation requires the activation of r-PTPeta.

Animals↗
PubMed2000

The TRK-T1 fusion protein induces neoplastic transformation of thyroid epithelium.

Genetic analysis of human papillary thyroid carcinomas (PTC) has revealed unique chromosomal translocations that form oncogenic fusion proteins and promote thyroid tumorigenesis in up to 60% of tumors examined. Although, the majority of thyroid specific translocations involve the growth factor receptor c-RET, variant rearrangements of the receptor for nerve growth factor, NTRK1 have also been described. One such translocation, TRK-T1, forms a fusion protein composed of the carboxyl terminal tyrosine kinase domain of NTRK1 and the amino terminal portion of TPR (Translocated Promoter Region). To determine if TRK-T1 expression can cause thyroid cancer in vivo, we developed transgenic mice that express the human TRK-T1 fusion protein in the thyroid. Immunohistochemical analysis of TRK-T1 transgenic mouse thyroids revealed TRK-T1 staining within the thyroid follicular epithelium. In contrast to nontransgenic littermates, 54% of transgenic mice developed thyroid abnormalities that included follicular hyperplasia and papillary carcinoma. Furthermore, all transgenic mice examined greater than 7 months of age developed thyroid hyperplasia and/or carcinoma. These data support the conclusion that TRK-T1 is oncogenic in vivo and contributes to the neoplastic transformation of the thyroid.

Animals↗
PubMed2000

Pivotal role of the RB family proteins in in vitro thyroid cell transformation.

Rat thyroid differentiated cells (PC Cl 3) are an excellent model system with which to study the interaction between differentiation and cell transformation. We previously demonstrated that PC Cl 3 cells expressing the adenovirus E1A gene no longer depend on thyrotropin for growth and do not express thyroid differentiation markers. Here we show that an E1A mutant unable to bind the RB protein failed to transform the PC Cl 3 cells. Conversely, mutations in the E1A p300 interacting region did not affect its transforming ability. The pivotal role of RB family proteins in the thyroid cell transformation is supported by the thyrotropin independence induced by the E7 gene of human papilloma virus type 16, but not by a mutated form in the RB-binding region.

Adenovirus E1A Proteins↗
PubMed2000

Tyrosine 1062 of RET-MEN2A mediates activation of Akt (protein kinase B) and mitogen-activated protein kinase pathways leading to PC12 cell survival.

The RET tyrosine kinase is a functional receptor for neurotrophic ligands of the glial cell line-derived neurotrophic factor (GDNF) family. Loss of function of RET is associated with congenital megacolon or Hirschsprung's disease, whereas germ-line point mutations causing RET activation are responsible for multiple endocrine neoplasia type 2 (MEN2A, MEN2B, and familial medullary thyroid carcinoma) syndromes. Here we show that the expression of a constitutively active RET-MEN2A oncogene promotes survival of rat pheochromocytoma PC12 cells upon growth factor withdrawal. Moreover, we show that the RET-MEN2A-mediated survival depends on signals transduced by the phosphoinositide 3-kinase (PI3K) and mitogen-activated protein kinase (MAPK) cascades. Thus, in PC12 cells, RET-MEN2A associates with the PI3K regulatory subunit p85 and promotes activation of Akt (also referred to as protein kinase B) in a PI3K-dependent fashion; in addition, RET-MEN2A promotes MAPK activation. PI3K recruitment and Akt activation as well as MAPK activation depend on RET-MEN2A tyrosine residue 1062. As a result, tyrosine 1062 of RET-MEN2A is essential for RET-MEN2A-mediated survival of PC12 cells cultured in growth factor-depleted media.

Animals↗
PubMed2000

Akt/protein kinase B promotes survival and hormone-independent proliferation of thyroid cells in the absence of dedifferentiating and transforming effects.

The Akt/protein kinase B serine/threonine kinase is a downstream effector of phosphoinositide 3-kinase (PI3K). Akt is an important component of mitogenic and antiapoptotic signaling pathways and is implicated in neoplastic transformation. Thyroid cells in culture retain a differentiated phenotype consisting of epithelial cell morphology and the expression of several tissue-specific genes. The survival and proliferation of these cells depend on thyrotropin and a mixture of five additional hormones that includes insulin. The regulation of proliferation and the expression of the thyroid differentiation program are intimately connected processes. As a result, oncogenes that induce hormone-independent proliferation invariably impair the expression of the thyroid-specific differentiation markers. Given that thyrotropin and insulin stimulate Akt activation in thyroid cells, we set out to determine the effects of Akt on thyroid cell proliferation, survival, and differentiation. To this end, we expressed constitutively active myristylated Akt (myrAkt) in PC Cl 3 thyroid cells. The myrAkt-expressing cells continued to proliferate, even in the absence of hormones, and they were resistant to programmed cell death induced by starvation. These effects were paralleled by the induction of the G1 cyclins D3 and E and by the inhibition of induction of the proapoptotic Fas, Fas ligand, and BAD genes in starved cells. However, in marked contrast with several other oncogenes, myrAkt did not interfere with the expression of thyroid differentiation functions. These results unveil the existence of an Akt-triggered thyroid cell pathway that modulates proliferation and survival without affecting the expression of the thyroid cell differentiated phenotype.

Animals↗
PubMed2000

PTEN expression is reduced in a subset of sporadic thyroid carcinomas: evidence that PTEN-growth suppressing activity in thyroid cancer cells mediated by p27kip1.

The dual-specificity phosphatase PTEN/MMAC1/TEP1 has recently been identified as the tumor suppressor gene most frequently mutated and/or deleted in human tumors. Germline mutations of PTEN give rise to Cowden Disease (CD), an autosomal dominantly-inherited cancer syndrome which predisposes to increased risk of developing breast and thyroid tumors. However, PTEN mutations have rarely been detected in sporadic thyroid carcinomas. In this study, we confirm that PTEN mutations in sporadic thyroid cancer are infrequent as we found one point mutation and one heterozygous deletion of PTEN gene in 26 tumors and eight cell lines screened. However, we report that PTEN expression is reduced both at the mRNA and at the protein level - in five out of eight tumor-derived cell lines and in 24 out of 61 primary tumors. In most cases, decreased PTEN expression is correlated with increased phosphorylation of the PTEN-regulated protein kinase Akt/PKB. Moreover, we demonstrate that PTEN may act as a suppressor of thyroid cancerogenesis as the constitutive re-expression of PTEN into two different thyroid tumor cell lines markedly inhibits cell growth. PTEN-dependent inhibition of BrdU incorporation is accompanied by enhanced expression of the cyclin-dependent kinase inhibitor p27kip1 and can be overcome by simultaneous co-transfection of an excess p27kip1 antisense plasmid. Accordingly, in a subset of thyroid primary carcinomas and tumor-derived cell lines, a striking correlation between PTEN expression and the level of p27kip1 protein was observed. In conclusion, our findings demonstrate that inactivation of PTEN may play a role in the development of sporadic thyroid carcinomas and that one key target of PTEN suppressor activity is represented by the cyclin-dependent kinase inhibitor p27kip1.

Blotting, Northern↗