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Biomedical subjects

M Tavassoli

Publications and source records attributed to M Tavassoli.

At least 37 records · Page 2Linked to original sources
PubMed1997

The expression of p185(HER-2/neu) correlates with the stage of disease and survival in colorectal cancer.

BACKGROUND & AIMS: HER-2/neu oncogene encodes a transmembrane tyrosine kinase receptor that is amplified and/or overexpressed predominantly in adenocarcinomas. This phenomenon has been most intensively studied in breast carcinoma where its amplification and overexpression correlate with the overall course of disease and poor prognosis. This study was designed to investigate HER-2/neu gene expression in benign and malignant colorectal lesions and to evaluate its prognostic importance in colorectal cancer. METHODS: Two hundred twenty-one samples of normal colon, benign lesions, and colorectal adenocarcinomas were studied for expression of HER-2/neu oncoprotein. Immunohistochemical staining of formalin-fixed, paraffin-embedded tissue sections of primary tumor and lymph nodes was performed. Immunoprecipitation followed by Western blotting of freshly frozen samples of the same tumors were also performed. RESULTS: Normal colon mucosa, benign lesions, and adenocarcinomas clearly differed in the expression levels and histological distribution of p185(HER-2/neu). Normal mucosa was mostly negative, but significant number of benign lesions and adenocarcinomas overexpressed HER-2/neu protein. Adenocarcinomas were significantly more positive than benign lesions. The results show significant correlation with the epithelial abnormality degree and clinical parameters including Dukes' classification and relapse-free and postoperative survival period. CONCLUSIONS: The p185(HER-2/neu) rate expression could serve as an independent prognostic factor in patients with p185(HER-2/neu)-positive colorectal malignancies.

Adenocarcinoma↗
PubMed1996

Loss of heterozygosity on chromosome 5q in ovarian cancer is frequently accompanied by TP53 mutation and identifies a tumour suppressor gene locus at 5q13.1-21.

Forty-nine ovarian tumours were examined for loss of heterozygosity (LOH) on chromosome 5 using eight microsatellite markers spanning both arms, including one at the APC locus. LOH on 5q was a frequent event, detectable in 23 of 49 (47%) tumours, whereas 5p LOH was detected in only 1 of 22 tumours (5%). Six tumours showed partial LOH on 5q, enabling the candidate region to be localised to a 22 cM region proximal to APC, flanked by D5S424 and D5S644. An association was found between 5q LOH and TP53 mutation, with 18 of 23 (78%) tumours with LOH on 5q also harbouring a TP53 mutation. LOH on 5q was observed in 6 of 18 (33%) stage I tumours, suggesting that it may be an early event in the molecular pathogenesis of certain ovarian carcinomas.

Base Sequence↗
PubMed1996

Efficient retroviral infection of mammalian cells is blocked by inhibition of poly(ADP-ribose) polymerase activity.

Integration of proviral DNA into the host cell genome is a characteristic feature of the retroviral life cycle. This process involves coordinate DNA strand break formation and rejoining reactions. The full details of the integration process are not yet fully understood. However, the endonuclease and DNA strand-joining activities of the virus-encoded integrase protein (IN) are thought to act in concert with other, as-yet-unidentified, endogenous nuclear components which are involved in the DNA repair process. The nuclear enzyme poly(ADP-ribose) polymerase (PARP), which is dependent on DNA strand breaks for its activity, is involved in the efficient repair of DNA strand breaks, and maintenance of genomic integrity, in nucleated eukaryotic cells. In the present work, we examine the possible involvement of PARP in the retroviral life cycle and demonstrate that inhibition of PARP activity, by any one of three independent mechanisms, blocks the infection of mammalian cells by recombinant retroviral vectors. This requirement for PARP activity appears to be restricted to processes involved in the integration of provirus into the host cell DNA. PARP inhibition does not affect viral entry into the host cell, reverse transcription of the viral RNA genome, postintegration synthesis of viral gene products, synthesis of the viral RNA genome, or the generation of infective virions. Therefore, efficient retroviral infection of mammalian cells is blocked by inhibition or PARP activity.

3T3 Cells↗
PubMed1996

Hereditary and environmental risk factors; clinical and laboratory risk matters for head and neck, especially oral, cancer and precancer.

The continuing high incidence and mortality of squamous cell carcinoma of the upper aerodigestive tract in South Asia, parts of France and central Europe, together with a rising incidence and mortality from a lower base elsewhere in the Western world, stimulates continuing research on risk factors and risk markers. Tobaccos (smoked and smokeless), heavy alcohol consumption, and areca nut remain the dominant risk factors, with confirmation of the protective effects of diets rich in antioxidants. There is emerging evidence of a small, but real, risk associated with occupational and other air pollution, and with family, part of which may be hereditary. Markers in peripheral blood and saliva are underexploited. Clinical staging and histological grading methods continue to be refined, with improved prognostic value, much aided by newer and simpler methods for estimating cell proliferation and apoptosis. Data on the significance of viral genes are still inadequate, but there is good progress describing the epidemiology of chromosomal abnormalities and abberations of a growing list of oncogenes and tumour suppressor genes. Unfortunately, as yet, these have only limited longitudinal or prognostic data.

Alcohol Drinking↗
PubMed1995

Cloning and characterisation of the Schizosaccharomyces pombe rad32 gene: a gene required for repair of double strand breaks and recombination.

A new Schizosaccharomyces pombe mutant (rad32) which is sensitive to gamma and UV irradiation is described. Pulsed field gel electrophoresis of DNA from irradiated cells indicates that the rad32 mutant, in comparison to wild type cells, has decreased ability to repair DNA double strand breaks. The mutant also undergoes decreased meiotic recombination and displays reduced stability of minichromosomes. The rad32 gene has been cloned by complementation of the UV sensitive phenotype. The gene, which is not essential for cell viability and is expressed at a moderate level in mitotically dividing cells, has significant homology to the meiotic recombination gene MRE11 of Saccharomyces cerevisiae. Epistasis analysis indicates that rad32 functions in a pathway which includes the rhp51 gene (the S.pombe homologue to S.cerevisiae RAD51) and that cells deleted for the rad32 gene in conjunction with either the rad3 deletion (a G2 checkpoint mutation) or the rad2 deletion (a chromosome stability and potential nucleotide excision repair mutation) are not viable.

Amino Acid Sequence↗
PubMed1995

Enhancement of human hematopoiesis by mast cell growth factor in human-sheep chimeras created by the in utero transplantation of human fetal hematopoietic cells.

We have previously described a unique model of long-term, multilineage, human hematopoietic chimerism in sheep created by the in utero transplantation of human hematopoietic stem cells (HSC) into pre-immune fetal lambs. In this study, we examined the effect of chronic administration of recombinant human mast cell growth factor (rhMGF) on 1) human cell engraftment in pre-immune sheep and 2) human cell expression in human-sheep chimeras at 2-years posttransplant. rhMGF (25 micrograms/kg) or saline was administered in utero via chronic intraperitoneal (IP) catheters to three separate sets of twin fetuses on alternate days for 10 doses following transplantation of human HSC. Flow-cytometric and karyotype analyses of peripheral blood from two sets of twins at 45-days posttransplant and of peripheral blood from the remaining set of twins at birth revealed a significant increase in percentages of donor (human) progenitors and cells in rhMGF-treated lambs. rhMGF (60 micrograms/kg/day) was also administered by IP injection to two, 2 year-old, human-sheep chimeras for 18 consecutive days. Flow-cytometric analysis of peripheral blood and bone marrow revealed a six- to seven-fold increase in human cell expression. The effect on early human progenitors (i.e., colony-forming unit-mix [CFU-Mix], CFU granulocyte/macrophage [CFU-GM], and burst-forming unit-erythroid [BFU-E]) was determined by karyotype analysis of individual colonies grown under conditions favoring human cell growth. A three- to five-fold increase in human CFU-Mix and BFU-E occurred with a minimal increase in CFU-GM. This in vivo study supports in vitro data suggesting that MGF is a powerful regulator of human hematopoiesis and preferentially stimulates early hematopoietic progenitors. It also supports the potential value of the human-sheep model for the in vivo study of normal and abnormal human hematopoiesis.

Animals↗
PubMed1994

Microenvironmental factors involved in the establishment of erythropoiesis in bone marrow.

Human erythropoiesis is focused near the venous sinuses of the bone marrow in EBI that are comprised of erythroblasts in intimate contact with supportive CM. The surface molecules and secreted products of fibroblastic reticular cells support the adhesion of erythroblasts and CM, and sequester growth factors near their surfaces. Cohesiveness within the EBI decreases as its associated erythroid cells mature, and the erythroblasts cease to express certain cytoadhesive molecules. Finally, the erythroblasts enucleate and separate from the EBI. Transiently motile reticulocytes enter the circulation through intracellular pores of venous sinus endothelial cells, and their nuclear remnants are ingested by CM or perisinal macrophages.

Animals↗
PubMed1994

5-Fluorouracil, adriamycin, and mitomycin C in adenocarcinoma of the esophagus or gastroesophageal junction tumors.

We reviewed our results with chemotherapy for adenocarcinoma of the esophagus or gastroesophageal junction tumors in patients treated with 5-fluorouracil, Adriamycin, and mitomycin C (FAM) regimen as developed by MacDonald and colleagues for adenocarcinoma of the stomach. Sixteen patients were treated, 12 with metastatic and 4 with locoregional disease. Responses were seen in 6 of 16 patients (all partial responses), for an overall response rate of 37.5%. The sites of response include liver (3), lung (1), bone (1), and lymph nodes (1). Median duration of response was 7 months. These results with FAM in adenocarcinoma of the esophagus suggest activity similar to that seen in gastric carcinoma. The second-generation chemotherapy combinations effective in gastric carcinoma merit evaluation in this tumor to see if the remission rates could be further improved.

Adenocarcinoma↗
PubMed1994

Structural and functional conservation of the human homolog of the Schizosaccharomyces pombe rad2 gene, which is required for chromosome segregation and recovery from DNA damage.

The rad2 mutant of Schizosaccharomyces pombe is sensitive to UV irradiation and deficient in the repair of UV damage. In addition, it has a very high degree of chromosome loss and/or nondisjunction. We have cloned the rad2 gene and have shown it to be a member of the Saccharomyces cerevisiae RAD2/S. pombe rad13/human XPG family. Using degenerate PCR, we have cloned the human homolog of the rad2 gene. Human cDNA has 55% amino acid sequence identity to the rad2 gene and is able to complement the UV sensitivity of the rad2 null mutant. We have thus isolated a novel human gene which is likely to be involved both in controlling the fidelity of chromosome segregation and in the repair of UV-induced DNA damage. Its involvement in two fundamental processes for maintaining chromosomal integrity suggests that it is likely to be an important component of cancer avoidance mechanisms.

Amino Acid Sequence↗
PubMed1994

Transplantation in utero of fetal human hematopoietic stem cells into mice results in hematopoietic chimerism.

Allogeneic and xenogeneic hematolymphoid chimerism has been achieved in large and small animals using varied techniques to circumvent immune mediated graft rejection by the recipient. We show here the establishment of long-term chimerism in normal mice transplanted in utero with human fetal hematopoietic stem cells (HSC). HSCs from fetal (13-20 weeks' gestation) human livers were injected into fetal mouse peritoneal cavities on days 11-13 of gestation. Histologic examination demonstrated human chimerism in 29% of 38 live born mice using fluorescein conjugated antibodies to both the CD45 and CD14 antigens present on human peripheral blood (PB) cells. Further investigation using flow cytometric analysis of cells from 70 mice transplanted in utero revealed 28% of mice greater than 16 weeks of age contained human cells in at least one organ at the following frequencies: 14% PB, 8% bone marrow, 8% spleen and 12% thymus. These data indicate that human fetal HSC can be engrafted into mouse fetuses. Additionally, the identification of circulating human cells 18 months following transplantation supports the engraftment and proliferation of a primitive hematopoietic progenitor.

Animals↗
PubMed1994

Long-term repopulating ability of xenogeneic transplanted human fetal liver hematopoietic stem cells in sheep.

We previously reported on the successful engraftment and long-term multilineage expression (erythroid, myeloid, lymphoid) of human fetal liver hematopoietic stem cells in sheep after transplantation in utero. That the engraftment of long-term repopulating pluripotent stem cells occurred in these animals was shown here by the fact that transplantation of human CD45+ cells isolated from bone marrow of these chimeric animals into preimmune fetal sheep resulted in engraftment and expression of human cells. Marrow cells were obtained from three chimeric sheep at 3.2-3.6 yr after transplant. The relative percentage of human CD45+ cells present in these marrows was 3.3 +/- 0.32%. A total of 29 x 10(6) CD45+ cells were isolated by panning, pooled, and transplanted into six preimmune sheep fetuses (4.8 x 10(6) cells/fetus). All six recipients were born alive. Hematopoietic progenitors exhibiting human karyotype were detected in marrows of two lambs soon after birth. Cells expressing human CD45 antigen were also detected in blood and marrow of both lambs. Human cell expression has been multilineage and has persisted for > 1 yr. These results demonstrate that the expression of human cells in this large animal model resulted from engraftment of long-term repopulating pluripotent human stem cells.

Animals↗
PubMed1993

Adhesive interaction of hemopoietic progenitor cell membrane with the RGD domain of fibronectin.

The binding of two cloned hemopoietic progenitor cell lines, B6Sut (multipotential) and FDCP-1 (bipotential) to dishes coated with fibronectin or its chymotryptic fragments was studied by labeling the cells with 51Cr or [35S]methionine. Intact fibronectin molecule and its 120 kDa fragment, containing the Arg-Gly-Asp (RGD) sequence motif, as well as a synthetic RGD-containing peptide Peptite 2000 all bound progenitor cells. However, the 40 or 45 kDa fragments, containing the heparin-binding and CS-1 domains, failed to bind the cells in a comparable magnitude. The binding of intact fibronectin and its 120 kDa fragment was inhibited in a dose-dependent fashion with increasing concentration of RGD-containing Gly-Arg-Gly-Asp-Ser peptide, but not with Gly-Arg-Gly-Glu-Ser control peptide that does not contain the RGD sequence motif. To explore the nature of the receptor for this fragment of fibronectin, membrane proteins were labeled with 125I and subjected to affinity chromatography using a matrix to which the 120 kDa fragment of fibronectin was covalently bound. Specific competitive elution with RGD yielded two bands with molecular masses of 160 and 110 kDa, corresponding, respectively, to those of alpha 5 and beta 1 chains of integrin molecule. Western blotting of whole-cell-lysate proteins with a monospecific, polyclonal serum specific for vertebrate beta 1 integrins identified a beta 1 integrin in these cells. Thus, it appears that an interaction involving alpha 5 beta 1 integrin with 120 kDa fragment of fibronectin may be involved between hemopoietic progenitor cells and the fibronectin component of extracellular matrix.

3T3 Cells↗
PubMed1993

A novel 37-Kd adhesive membrane protein from cloned murine bone marrow stromal cells and cloned murine hematopoietic progenitor cells.

The adhesion of hematopoietic progenitor cells to bone marrow stromal cells is critical to hematopoiesis and involves multiple effector molecules. Stromal cell molecules that participate in this interaction were sought by analyzing the detergent-soluble membrane proteins of GBI/6 stromal cells that could be adsorbed by intact FDCP-1 progenitor cells. A single-chain protein from GBI/6 cells having an apparent molecular weight of 37 Kd was selectively adsorbed by FDCP-1 cells. This protein, designated p37, could be surface-radiolabeled and thus appeared to be exposed on the cell membrane. An apparently identical 37-Kd protein was expressed by three stromal cell lines, by Swiss 3T3 fibroblastic cells, and by FDCP-1 and FDCP-2 progenitor cells. p37 was selectively adsorbed from membrane lysates by a variety of murine hematopoietic cells, including erythrocytes, but not by human erythrocytes. Binding of p37 to cells was calcium-dependent, and was not affected by inhibitors of the hematopoietic homing receptor or the cell-binding or heparin-binding functions of fibronectin. It is proposed that p37 may be a novel adhesive molecule expressed on the surface of a variety of hematopoietic cells that could participate in both homotypic and heterotypic interactions of stromal and progenitor cells.

Adsorption↗
PubMed1993

Liver-derived fetal hematopoietic stem cells selectively and preferentially home to the fetal bone marrow.

In the course of ontogeny, the homing site for the hematopoietic stem cells (HSC) moves with certain predictability from the yolk sac to the liver/spleen and then to the marrow. The pattern of this migration has thus far been established mostly on a morphologic basis. To delineate further the course of this migration and to gain insight into its possible mechanism, we used in utero transplantation of allogeneic or xenogeneic HSC in preimmune sheep fetuses. Sex chromosome, type of hemoglobin, and species-specific surface markers were used to follow the path of transplanted cells in the fetus. Before the development of the bone marrow, transplanted HSC (liver- or marrow-derived) homed exclusively to the liver/spleen. With the development of marrow, around day 60 of gestation (term, 145 days), homing occurred also in the nascent marrow and by day 80 transplanted cells homed exclusively to the marrow. This suggests that there may be a hierarchy in homing sites, with those of the marrow having higher affinity than those of liver/spleen. Interestingly, despite a change in homing that was followed by the expansion of the marrow compartment of HSC (ie, HSC proliferation), these cells did not participate actively in blood cell formation during most of the prenatal period. Liver remained the major hematopoietic organ throughout the gestation. It was only during the perinatal period that this organ assumed the function of hematopoiesis from the liver. This lack of expression of HSC in fetal marrow can possibly be attributable to the immaturity of marrow stroma required for differentiation and maturation of progenitors and the orderly egress of mature cells into the blood stream. The availability of this model allows us to begin studies in the molecular mechanism of stem cell homing in vivo during ontogeny.

Animals↗
PubMed1993

Whole chromosome 17 loss in ovarian cancer.

Chromosomal deletions, associated with the loss of normal function of tumour suppressor genes, have been identified in a variety of both familial and sporadic human cancers. Although the molecular pathology of ovarian cancer is not understood, several studies have reported deletions in chromosome 17 in ovarian tumours. We have used 13 restriction site polymorphic, microsatellite, and variable number tandem repeat markers to make a detailed analysis of chromosome 17 deletions in 12 benign and 19 malignant ovarian tumours. Two benign and 11 malignant tumours were informative for at least one marker on each arm of the chromosome. Loss of heterozygosity (LOH) was detected in both arms (by all informative markers) in 5 malignant tumours from four women (three with the disease at FIGO stage Ia). In a further bilateral ovarian tumour a partial LOH affecting 17q22-q25 was present in one ovary only. By contrast to a number of previous studies, none of the 19 malignant and 12 benign tumours showed ERBB2 (17q12-22) amplification. The data presented show that the loss of a whole copy of chromosome 17 is a frequent and relatively early event in the development of some ovarian cancers. This suggests the possible involvement of multiple chromosome 17 loci in the pathogenesis of ovarian cancer. Equally plausible is that the loss of a whole chromosome copy could be the product of chromosomal instabilities induced by loss of the normal allele of tumour suppressors, such as TP53, located on this chromosome.

Adenofibroma↗
PubMed1993

Ethanol enhances desialylation of transferrin by liver endothelial cells in the rat.

Desialylated transferrin is emerging as a reliable index of alcoholism, and liver endothelial cells are known to partially desialylate transferrin. The effect of a single intraperitoneal injection of ethanol on the desialylation of transferrin in the rat was studied. In pulse-chase experiments, fully sialylated diferric transferrin labeled with 125I (protein moiety) or 3H (sialyl residues) was incubated with isolated, fractionated liver endothelial cells from rats that were given ethanol. The supernatants then were subjected to column chromatography using RCA120-agarose to separate and quantify the desialylated fraction of transferrin. Saline-treated animals served as controls. Incubation of the endothelial cells derived from the liver of ethanol-treated rats resulted in a 263% increase in desialylation level of transferrin. Our data indicate that administering ethanol in rats enhances the desialylation of transferrin by rat liver endothelial cells.

Animals↗