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L J Helman

Publications and source records attributed to L J Helman.

At least 37 records · Page 2Linked to original sources
PubMed1996

Regulation of insulin-like growth factor II P3 promotor by p53: a potential mechanism for tumorigenesis.

Human insulin-like growth factor (IGF)-II mRNA has been shown to be expressed at high levels in a variety of tumors, including rhabdomyosarcomas. In addition, many tumors have alterations in p53 expression. To investigate whether p53 regulates IGF-II gene expression, we transfected wild-type p53 expression vectors and luciferase constructs driven by IGF-II P3 promotors into multiple cell lines. We found that p53 reduced, in a dose-dependent manner, both endogenous IGF-II P3 transcripts and transfected P3 luciferase expression. The inhibition of P3 luciferase expression by p53 was more pronounced in the two cell lines that expressed mutant p53 protein, RD, and HTB114. The element responsible for this inhibition was mapped to the minimal promoter region. We also transfected an HPV-16 E6 expression plasmid into CCL13 cells containing functional p53 and found that E6 up-regulated IGF-II P3 activity. Wild-type, but not mutant, p53 interfered with the binding of TATA-binding protein to the TATA motif of P3, although both could directly associate with human TATA-binding protein. Our results suggest that p53 may play a role in regulation of IGF-II gene expression.

Gene Expression Regulation, Neoplastic↗
PubMed1996

Tumorigenic and mitogenic capacities are reduced in transfected fibroblasts expressing mutant insulin-like growth factor (IGF)-I receptors. The role of tyrosine residues 1250, 1251, and 1316 in the carboxy-terminus of the IGF-I receptor.

Regulation of ligand-mediated signal transduction through transmembrane tyrosine kinase growth factor receptors involves phosphorylation of tyrosine residues in the intracellular domain of the receptor. The insulin-like growth factor-I (IGF-I) receptor contains three tyrosine residues in the carboxy-terminal domain at positions 1250, 1251, and 1316. Of these, only the tyrosine at position 1316 is conserved in the homologous position of the insulin receptor. Mutational analysis was used to study the role of these tyrosines in specific outcomes of IGF-I-mediated signal transduction. Mutations in the human IGF-I receptor were either replacement of tyrosines 1250 and 1251 with phenylalanine and histidine (yyFH), respectively, or replacement of the conserved distal tyrosine (position 1316) with phenylalanine (yCF). The yyFH mutation results in an IGF-I receptor with the amino acids found in the homologous position of the human insulin receptor. Cells overexpressing mutated IGF-I receptors were compared with cells expressing only endogenous IGF-I receptors or overexpressing wild-type IGF-I receptors. The ability of yyFH mutant IGF-I receptors to autophosphorylate the beta-subunit or phosphorylate insulin receptor substrate-1 was not significantly different from wild-type type IGF-I receptors. However, one or both of the proximal tyrosine residues (positions 1250 and 1251) in the carboxy-terminus of the IGF-I receptor are essential for IGF-I-stimulation of mitogenic and tumorigenic pathways. IGF-I-induced mitogenesis, measured as thymidine incorporation and cellular proliferation, was abrogated in cells overexpressing mutant IGF-I receptors with replacement of the proximal double tyrosines (positions 1250 and 1251). Fibroblasts expressing this mutant IGF-I receptor formed fewer tumors than the negative control cells, whereas cells expressing wild-type IGF-I receptors formed large tumors in all recipient mice injected. Conversely, cells expressing mutant IGF-I receptors with only the conserved distal tyrosine (position 1316) replaced had slightly reduced IGF-I-stimulated beta-subunit autophosphorylation, thymidine incorporation, and cellular proliferation when compared with cells expressing wild-type receptors. Phosphorylation of insulin receptor substrate-1 by the yCF mutant receptors was not impaired. Despite the ability of these mutant receptors to stimulate mitogenic growth, fibroblasts expressing this mutant receptor were also incapable of forming tumors in recipient nude mice. The distal tyrosine (position 1316) of the IGF-I receptor is crucial for tumor formation but is not essential for IGF-I stimulated mitogenesis. Thus, the tyrosine moieties in the carboxy-terminus of the IGF-I receptor participate in the signal transduction pathways that affect the mitogenic and tumorigenic potentials of cells expressing mutant IGF-I receptors.

3T3 Cells↗
PubMed1996

1 alpha, 25-dihydroxy-16-ene-23-yne-26,27-hexafluorocholecalciferol (Ro24-5531) modulation of insulin-like growth factor-binding protein-3 and induction of differentiation and growth arrest in a human osteosarcoma cell line.

1 alpha,25-Dihydroxycholecalciferol [1,25-(OH)2D3] is a potent differentiating agent in a variety of tumor cell lines. However, the induction of severe hypercalcemia has limited its clinical use. Several analogs have been synthesized that retain the antiproliferative differentiating effects of 1,25-(OH)2D3, but do not have the calcitropic effect of the parent compound. One such analog, 1 alpha,25(OH)2-16-ene-23-yne-26,27-hexafluorocholecalciferol (Ro24-5531), can induce differentiation in HL-60 cells and does not induce hypercalcemia in animal models. We, therefore, evaluated the effect of Ro24-5531 on a human osteosarcoma cell line, MG-63. Compared with 1,25-(OH)2D3, the analog Ro24-5531 is 10-100 times more potent as an inhibitor of MG-63 cell proliferation, as determined by [3H]thymidine incorporation and/or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. The inhibition in cell growth is accompanied by a decrease in the expression of p34cdc2 (> 4-fold), a protein critically involved in cell cycle regulation. Ro24-5531 treatment of MG-63, at a concentration of 10(-8) mol/L, induced expression of the bone differentiation markers biglycan and osteocalcin, as determined by Northern analysis. These data suggest that Ro24-5531 treatment induces growth arrest coupled with differentiation. To begin to evaluate the mechanisms by which Ro24-5531 may exert an effect, we evaluated the effect of Ro24-5531 on components of the insulin-like growth factor I (IGF-I) signaling pathway, an important regulator of normal bone growth and differentiation. The expression of IGF-binding protein (IGFBP), IGFBP-3 messenger ribonucleic acid, and protein levels are increased 20-fold after 72 h of treatment with Ro24-5531 and are associated with a marked increase in detectable binding of ligand to binding protein, as measured by RRA. These data suggest an association between Ro24-5531-induced growth arrest and increased expression of IGFBP-3.

Bone Development↗
PubMed1996

Involvement of IGF-II in human cancer.

IGF-II is a regulatory peptide which appears to be involved significantly in the progression of many tumors, while minimally involved in post-fetal non-tumor tissue. Interruption of IGF-II pathways therefore offers the possibility of tumor control with a high therapeutic index. Investigators should continue to evaluate tumors for the involvement of IGF-II as well as investigate clinically relevant means of disrupting those pathways.

Cell Membrane↗
PubMed1996

Metastatic human rhabdomyosarcoma: molecular, cellular and cytogenetic analysis of a novel cellular model.

A new human metastatic rhabdomyosarcoma (RMS) model was established and analyzed for a number of biologic, cytogenetic and molecular parameters. Consistent with previous studies, the metastatic capacity of different RMS cell variants did not correlate with their tumorigenic or proliferative capacities. Interestingly, a highly metastatic variant was diploid, while a nonmetastatic variant was tetraploid, which parallels previous clinical observations. Genes whose expression had been found to be associated with either low- or high-metastatic capacity in carcinoma or melanoma did not show a similar association with different metastatic variants of RMS, derived from a mesenchymal tumor. We also found, in transient reporter gene assays, that several promoters had higher transcriptional activity in highly metastatic than in nonmetastatic RMS cell variants. This novel human RMS metastatic model may be instrumental for a better understanding of the regulatory pathways that control the metastatic phenotype of tumors of mesenchymal origin.

Animals↗
PubMed1995

Loss of imprinting of IGF2 in Ewing's sarcoma.

Insulin-like Growth Factor 2 (IGF2) has recently been demonstrated to be maternally imprinted in both mice and humans. We previously reported loss of imprinting (LOI) of IGF2 in rhabdomyosarcoma (RMS) where IGF2 has been shown to act as an autocrine growth factor and play an important role in pathogenesis. Since IGF2 does not appear to play a role in the pathogenesis of Ewing's sarcoma, we sought to determine whether normal IGF2 imprinting was maintained in these tumors. Of 32 Ewing's tumors examined for imprinting of IGF2, 10 were informative heterozygotes and three of these expressed IGF2 biallelically. Furthermore, all three tumors with LOI and five of seven tumors with normal imprinting transcribed IGF2 mRNA at lower levels while relatively higher levels of IGF2 expression was observed in the remaining two tumors with normal imprinting. These data demonstrate altered imprinting of IGF2 occurs in some Ewing's sarcomas. However, LOI of IGF2 in Ewing's sarcoma was not associated with increased expression of IGF2 mRNA, suggesting that LOI may not be involved in the regulation of IGF2 expression and may be related to genetic or epigenetic abnormalities in tumors independent of IGF2 expression.

Base Sequence↗
PubMed1995

Concordant loss of imprinting of the human insulin-like growth factor II gene promoters in cancer.

The human insulin-like growth factor II (IGFII) gene has been shown to be imprinted for the promoters P2, P3, and P4 but not for the promoter P1 in liver and chondrocytes. Loss of imprinting of the IGFII gene has been found in a variety of human tumors including rhabdomyosarcoma and lung cancer. In this report, we determined whether loss of imprinting in tumors displays a promoter-specific pattern. We examined allelic expression of all four IGFII promoters in rhabdomyosarcoma, lung cancer, and normal skeletal muscle. We demonstrate that the imprinting of all IGFII promoters is relaxed in rhabdomyosarcoma and lung cancer. These data suggest that loss of imprinting of IGFII gene promoters may be regulated coordinately by a common mechanism in these tumors. Unexpectedly, we also found that P1, in addition to P2, P3, and P4 is monoallelically expressed in three informative adult skeletal muscle tissues. This indicates that imprinting of the IGFII promoter P1 occurs in a tissue-specific manner.

Adult↗
PubMed1995

Retinoic acid and cAMP differentially regulate human chromogranin A promoter activity during differentiation of neuroblastoma cells.

We report the first evidence that differential transcriptional regulation of human chromogranin A (CHGA) gene expression occurs during in vitro treatment of tumorigenic neuroblastoma (NB) cells with retinoic acid (5 microM) and/or dibutyryl-cAMP (1 mM). The CHGA gene encodes a tissue specific protein restricted to cells of the diffuse neuroendocrine system, but also widely expressed among NB tumours. We previously reported that CHGA as well as other neuroendocrine markers are modulated during NB differentiation in vitro. To investigate, at the molecular level, the mechanisms leading to NB tumour cell differentiation during the treatment with biologically active compounds, we sequenced and functionally characterised 2169 bp of a genomic DNA clone encompassing the 5' flanking region of the human CHGA gene. Computer-assisted analysis of the sequence revealed the presence of a cAMP responsive element at positions -56 to -49, and Sp1 binding sites at positions -181 to -176 and -216 to -210. Two novel 9 bp motifs, located at position -462 to -454 and -91 to -83 of the CHGA promoter were identified in the regulatory regions of two other neuroendocrine genes encoding for tyrosine hydroxylase and neuropeptide Y. In addition, in the first 1000 bp of the untranslated 5' region, we found the presence of several putative DNA binding sites of bHLH molecules, a protein family regulating tissue specific differentiation. Transient transfection experiments of chloramphenicol acetyltransferase (CAT) deletion constructs, showed the presence of an active promoter within the first 455 bp upstream from the start site. This region conferred tissue specific expression to a CAT reporter gene. In addition, the transcriptional activity of this fragment was modulated during the induction of differentiation of NB cells treated by retinoic acid and/or dibutyryl-cAMP. These observations provide preliminary data regarding CHGA transcriptional regulation in NB cells, and indicate that retinoic acid and cAMP activate distinct, apparently competitive, transcriptional pathways during NB cell differentiation. The molecular characterisation of the mechanisms regulating CHGA expression in tumour and normal neuroendocrine tissue could lead to the identification of novel molecules potentially relevant for future gene therapy of NB tumours.

Base Sequence↗
PubMed1995

Insulin-like growth factor II overexpression in myoblasts induces phenotypic changes typical of the malignant phenotype.

The objective of this study was to examine the role of insulin-like growth factor II (IGF-II) in the pathogenesis of human rhabdomyosarcomas (RMS). We have demonstrated previously that RMS express high levels of IGF-II mRNA, secrete IGF-II peptide, and express both IGF-I and IGF-II receptors. Moreover, we showed that IGF-II functions as an autocrine growth and motility factor in RMS. Since IGF-II is expressed at high levels in fetal muscle cells and RMS are tumors thought to derive from skeletal myoblasts arrested along the normal myogenic pathway, autocrine production of IGF-II by RMS may be an etiological event in the development of this tumor. We have developed a model system which enabled us to study the effects of endogenous IGF-II overprotection in muscle myoblasts. Human cDNA for pre-prohormone IGF-II was transfected into mouse myoblasts in order to achieve high, constant expression of this growth factor, which is normally down-regulated at the end of the differentiation process. Expression of high IGF-II levels resulted in: (a) an increased proliferative rate; (b) impairment of the ability to differentiate into myoblasts; and (c) acquisition of the capability of anchorage-independent growth. No changes in the expression of IGF-I receptors were noted. We conclude that IGF-II overexpression in muscle myoblasts induces morphological and biological changes typical of the malignant phenotype and represents a fundamental event in the pathogenesis of RMS and possibly of other embryonal tumors.

Animals↗
PubMed1994

In vivo treatment with antibody against IGF-1 receptor suppresses growth of human rhabdomyosarcoma and down-regulates p34cdc2.

In a previous study, we have shown that insulin-like growth factor type 2 (IGF-2) functions as an autocrine growth factor in human rhabdomyosarcoma (RMS) cell lines. In addition, we demonstrated that the inhibition of binding of IGF-2 to the IGF-1 receptor, mediated by suramin, blocked the growth of RMS cells in vitro. We now report that, in vivo, a specific IGF-1 receptor blocking antibody (alpha IR-3), but not suramin, suppresses RMS tumor growth. Both progression of tumor growth in tumor-bearing animals and formation of newly established tumors were suppressed by treatment with alpha IR-3. Histological analysis of tumors from treated animals did not reveal necrotic lesions, implying that the treatments had no cytotoxic effect. The decrease in tumor growth was associated with a decrease of p34cdc2, a cellular protein involved in cell cycle regulation, suggesting that treatment resulted in the arrest of cellular proliferation. We speculate, therefore, that agents which block the IGF signaling pathway may find application in treatment of RMS.

Animals↗
PubMed1994

Human osteosarcoma cell lines are dependent on insulin-like growth factor I for in vitro growth.

Osteogenic sarcoma is the most common bone tumor of childhood and typically occurs during the adolescent growth spurt when growth hormone and insulin-like growth factor I (IGF-I) may be at their lifetime highest levels. Since IGF-I is involved in normal bone growth and differentiation, we have evaluated the possible role of IGF-I signaling in the growth of human osteogenic sarcoma cell lines. In this study, we demonstrate that in vitro survival of cells is dependent on exogenously supplied IGF-I. Furthermore, we show that these cells display functional IGF-I receptors on their surface and that in vitro growth is inhibited by blocking these receptors either by monoclonal antibodies or by antisense oligonucleotides. These data demonstrate that human osteogenic sarcoma cell lines are dependent on signaling through the IGF-I receptor for in vitro survival and proliferation. Furthermore, they suggest that modulation of the growth hormone/IGF-I axis may affect the growth of these tumors in vivo.

Cell Division↗
PubMed1994

Insulin-like growth factors stimulate growth and L-cysteine uptake by the intestinal parasite Giardia lamblia.

Giardia lamblia, a parasitic protozoan responsible for diarrhea and malabsorption in humans, grows axenically only in media that contain serum and a high concentration of L-cysteine. During our attempts to grow Giardia in the absence of serum, we found that: (a) human insulin-like growth factors (especially IGF-II), but not insulin, promote the growth and L-cysteine uptake by G. lamblia trophozoites; (b) the growth stimulation was inhibited by alpha IR3, an anti-type 1 IGF receptor monoclonal antibody, but an anti-type 2 IGF receptor antibody had no effect; and (c) IGFs act on Giardia through a type 1 IGF receptor-like protein, which can bind IGF-II with higher affinity than IGF-I, and most likely possesses intrinsic phosphotyrosine kinase activity.

Animals↗
PubMed1994

Specific expression of insulin-like growth factor-II in rhabdomyosarcoma tumor cells.

Insulin-like growth factor II (IGF-II) acts as autocrine growth and motility factor in human rhabdomyosarcoma cell lines, and Northern blot analysis of tumor biopsy specimens from both alveolar and embryonal rhabdomyosarcoma demonstrates high levels of IGF-II mRNA expression. To determine the frequency and site of expression of IGF-II in these tumors, the authors performed in situ hybridization. All tumor specimens examined expressed the gene for IGF-II, and this expression was localized to the tumor cells themselves and not to the surrounding stroma. These data suggest that the IGF-II autocrine loop may be operating not only in vitro but also in vivo.

Adolescent↗
PubMed1994

Activation of an imprinted allele of the insulin-like growth factor II gene implicated in rhabdomyosarcoma.

The insulin-like growth factor II (IGF2) gene is exclusively silent at the maternal allele in the mouse as well as in normal human tissues and is expressed at a high level in rhabdomyosarcoma (RMS). We report here that the normally imprinted allele of the IGF2 gene is activated in RMS tumors as well as in one RMS cell line. Since overexpression of IGF2 has been shown to be important in the pathogenesis of RMS, our data suggest that loss of imprinting (LOI) may lead to overexpression of IGF2 and play an important role in the onset of RMS. Furthermore, embryonal RMS usually has loss of heterozygosity (LOH) with paternal disomy of the IGF2 locus. One informative embryonal RMS tumor evaluated in this study was heterozygous at the IGF2 allele and had LOI, raising the possibility that LOI may be the functional equivalent of LOH in this tumor with both events leading to overexpression of IGF2.

Alleles↗
PubMed1993

Ara-C treatment leads to differentiation and reverses the transformed phenotype in a human rhabdomyosarcoma cell line.

Rhabdomyosarcoma (RMS) is an embryonal tumor of childhood that arises from primitive skeletal muscle-forming cells (rhabdomyoblasts) probably arrested and transformed along the normal myogenic pathway to maturation. Since Ara-C is an antitumor agent known to induce differentiation in human acute myelogenous leukemia, also presumably a disorder of cellular maturation, we treated RD, a human embryonal RMS cell line, with Ara-C and evaluated its effect on growth and differentiation. Ara-C treatment of RD cells in vitro caused a dose-dependent growth inhibition in the absence of cytotoxicity. Interestingly, RD cells treated with 5 x 10(-7) M Ara-C for 4 days were able to recover logarithmic growth after the removal of the drug from the media. A reexposure of these cells to Ara-C led to morphological and biochemical changes related to differentiation, including the appearance of an increased number of multinucleated cells that expressed muscle-specific actin and skeletal muscle myosin heavy chain (MHC) (fast). In vivo studies demonstrated that RD cells pretreated with 5 x 10(-7) M Ara-C lost their ability to form tumors in nude mice. We conclude that treatment of this human embryonal RMS cell line with Ara-C results in marked growth inhibition in vitro, loss of tumorigenicity in vivo, and the expression of biochemical markers present in a more differentiated phenotype. These data suggest a potential role for differentiation therapy as a therapeutic approach in RMS.

Animals↗
PubMed1993

Secretory protein traffic. Chromogranin A contains a dominant targeting signal for the regulated pathway.

Secretory proteins are targeted into either constitutive (secreted upon synthesis) or regulated (stored in vesicles and released in response to a secretagogue) pathways. To investigate mechanisms of protein targeting into catecholamine storage vesicles (CSV), we stably expressed human chromogranin A (CgA), the major soluble protein in human CSV, in the rat pheochromocytoma PC-12 cell line. Chromaffin cell secretagogues (0.1 mM nicotinic cholinergic agonist, 55 mM K+, or 2 mM Ba++) caused cosecretion of human CgA and catecholamines from human CgA-expressing cells. Sucrose gradients colocalized human CgA and catecholamines to subcellular particles of the same buoyant density. Chimeric proteins, in which human CgA (either full-length [457 amino acids] or truncated [amino-terminal 226 amino acids]) was fused in-frame to the ordinarily nonsecreted protein chloramphenicol acetyltransferase (CAT), were expressed transiently in PC-12 cells. Both constructs directed CAT activity into regulated secretory vesicles, as judged by secretagogue-stimulated release. These data demonstrate that human CgA expressed in PC-12 cells is targeted to regulated secretory vesicles. In addition, human CgA can divert an ordinarily non-secreted protein into the regulated secretory pathway, consistent with the operation of a dominant targeting signal for the regulated pathway within the peptide sequence of CgA.

Amino Acid Sequence↗