Search PubMed⌕ Search

Biomedical subjects

R Callahan

Publications and source records attributed to R Callahan.

At least 55 records · Page 3Linked to original sources
PubMed1993

p53 alterations in non-small cell lung cancers correlate with metastatic involvement of hilar and mediastinal lymph nodes.

Alterations of p53 are one of the most common molecular changes found in all types of lung tumors, suggesting a crucial role for p53 in bronchial carcinogenesis. However, the prognostic significance of p53 abnormalities in lung cancer patients is still unclear. By using genetic and immunohistochemical methods we have found p53 alterations in 40 of 53 (75%) primary, resected non-small cell lung cancer. A strong association (P = 0.0015) was found between deletions on chromosome region 17p13.3 and p53 mutations suggesting that loss of the wild-type p53 allele might be necessary for tumorigenesis. Correlations to clinicopathological parameters showed that p53 alterations (structural aberration of the gene and/or nuclear accumulation of the protein) are significantly linked with metastatic involvement of hilar and mediastinal lymph nodes (P < 0.01). Since the latter are well established prognostic factors for non-small cell lung cancer, p53 aberrations may also be a predictor of tumor aggressiveness.

Aged↗
PubMed1993

Two distinct regions involved in 1p deletion in human primary breast cancer.

Alteration of chromosome 1 is the most consistent cytogenetic abnormality found in human breast carcinoma. Cytogenetic studies have shown independent alterations on the two arms of chromosome 1, increased copy number of the long arm and loss of the short arm of chromosome 1. These deletions are thought to coincide with the location of tumor suppressor gene(s). We carried out deletion analysis of the 1p region by using restriction fragment length polymorphism markers mapping to the long (six markers) and short arm (22 markers). Thirty-five of the 74 (47.3%) human breast tumors tested showed somatic loss of heterozygosity at one or more loci on the short arm. Two commonly deleted regions, 1p13-p21 and 1p32-pter, were identified. The latter region is frequently involved in other types of tumors, suggesting that it harbors a common tumor suppressor gene. Our findings suggest that two tumor suppressor genes involved in the development of human breast carcinoma may occur on the short arm of the chromosome 1.

Alleles↗
PubMed1993

Definition of regions of the human genome affected by loss of heterozygosity in primary human breast tumors.

We have undertaken a systematic study of primary human breast tumor DNA to identify and characterize frequently occurring somatic mutations. Loss of heterozygosity (LOH) has been the most frequent mutation in our panels of primary breast tumor DNA. It is currently thought that LOH reveals recessive mutations within the affected region of the genome. One goal of our studies has been to physically define the target genes revealed by LOH in primary breast tumors. We have focused our efforts on chromosome 17, finding five regions of the chromosome which are independently affected by LOH in breast tumors. Two apparent target loci are on chromosome 17p; one is the TP53 gene. The other is an as-yet undefined locus telomeric to the TP53 gene. Loss of expression of the nme1 gene on chromosome 17q in tumors was linked to patients with a poor prognosis (p = 0.018). Although a significant trend (p = 0.05) was found between LOH of the nme1 gene and loss of nme1 expression, no point mutations were found within the coding region of the nme1 gene by single strand conformational polymorphism (SSCP) or nucleotide sequence analysis. These and other results suggest to us that there may be potential tumor suppressor genes both centromeric and telomeric to the nme1 locus on chromosome 17q.

Breast Neoplasms↗
PubMed1993

Oncogenes, tumour suppressor genes and growth factors in breast cancer: novel targets for diagnosis, prognosis and therapy.

The complexity of growth factors and growth factor receptors that are aberrantly expressed, as well as the mutational events that either directly cause or influence the expression of these and other gene products, should provide in the near future multiple diagnostic, prognostic indicators or targets for therapeutic intervention. It seems reasonable to expect that soon the search for aberrantly expressed gene products in breast cancer cells will merge with the search and characterization of somatic mutations that are selected during tumour progression. Clearly, the current rapid development of new molecular biological methodologies aimed at detecting and cloning of RNA sequences that are aberrantly expressed in breast tumour cells, as well as molecular probes and reagents to detect and physically map mutated genes on affected chromosomes, should accelerate the effort to identify targets for therapeutic intervention. We are at the beginning of this learning curve, but already several potential target gene products have been identified. A major challenge will be to sort out those approaches and reagents that appear efficacious on the basis of results from in vitro and in vivo model systems that will actually have an impact on the treatment of the disease in the clinic. Reagents that target some of these gene products are currently in clinical trials; however, there are others such as immunotherapy against the mutated TP53 protein and human CG treatment of high risk breast cancer patients that warrant testing in this context.

Breast Neoplasms↗
PubMed1992

Somatic mutations and human breast cancer. A status report.

A systematic study of primary human breast tumor DNA demonstrated that three proto-oncogenes or regions of the genome (c-myc, int-2, and c-erbB2) are frequently amplified and that there is loss of heterozygosity (LOH) on chromosomes 1p(37%), 1q(20%), 3p(30%), 7(41%), 11p(20%), 13q(30%), 17p(49%), 17q(29%), and 18q(34%). Specific subsets of tumors can be defined based on the particular collection of mutations they contain. For instance, LOH on chromosomes 11p, 17p, and 18q frequently occurs in the same tumor. A search for putative tumor suppressor genes within the regions of the genome affected by LOH has been started. In a comprehensive molecular analysis of the p53 gene on chromosome 17p, 46% of the tumors contained a point mutation in the p53 gene.

Breast Neoplasms↗
PubMed1992

Loss of heterozygosity on chromosome 7q and aggressive primary breast cancer.

Genetic alterations are believed to be important in the origin and dissemination of breast cancer. Cytogenetic rearrangements on chromosome 7 are common in breast tumours. We used the c-met proto-oncogene probe, which detects sequences on chromosome 7q31, to analyse tumour and blood leucocyte DNA samples from 245 patients with primary breast cancers. The pmetH polymorphic probe detected a high frequency of allele loss (40.5%) among the 121 informative (heterozygous) patients. This genetic alteration was not significantly associated with standard prognostic features including tumour size, histopathological grade, and lymph-node or steroid receptor status. However, patients with loss of heterozygosity on chromosome 7q31 in primary tumour DNA had significantly shorter metastasis-free survival (p = 0.00022) and overall survival (p = 0.0036) after surgery than patients without this alteration. These findings indicate that this region of chromosome 7 might be the site of a breast tumour or metastasis suppressor gene.

Alleles↗
PubMed1992

Effect of heta-starch colloidal solutions on reticuloendothelial phagocytic system (RES) function in burned and infected rats.

The biodistribution of the plasma expander colloidal solution, heta-starch (HES), has been examined in rats, subjected to thermal injury or sepsis. The ability of these solutions to alter RES phagocytic function of [99mTc]-sulphur colloid ([99mTc]SC) uptake in vivo has been examined. The biodistribution of radiolabelled HES has been determined in normal rats. The HES colloidal solution has no deleterious effect upon RES function in vivo in the thermally injured animals or the septic animals as compared to sham controls. In addition, the HES colloidal solution seemed to be distributed primarily within the liver, spleen and kidney, with a small amount residing in the lung. Thermal injury did not increase the uptake of this material by the lung. These results suggest that the use of HES in thermally injured and septic individuals has no deleterious effects on RES function, nor does it accumulate in the lungs, and hence, should be advocated for use in these situations.

Animals↗
PubMed1992

Expression of an activated Notch-related int-3 transgene interferes with cell differentiation and induces neoplastic transformation in mammary and salivary glands.

Expression of the int-3 locus is activated in mouse mammary tumors as a consequence of insertional mutagenesis by the mouse mammary tumor virus (MMTV). Integration of the MMTV provirus into the int-3 locus promotes the transcription and translation of flanking cellular int-3 sequences sharing significant homology with the intracellular domain of the neurogenic Notch gene of Drosophila, and with the yeast cell cycle regulatory genes cdc10 and SWI6. To determine the in vivo consequences of activated int-3 expression, transgenic mice were generated harboring a genomic tumor DNA fragment consisting of the MMTV LTR and the flanking cellular int-3 sequences. All six int-3 founder transgenic mice and the progeny of one established line exhibited similar dramatic phenotypic abnormalities in tissues in which the transgene was expressed. Focal and often multiple poorly differentiated mammary and salivary adenocarcinomas appeared in the majority of transgenic mice between 2 and 7 months of age. Significantly, mammary glands were arrested in development and were lactation deficient in all female int-3 mice. The salivary glands, glands of the nasal mucosa and maxillary sinus, the extraorbital lacrimal glands, and the Harderian glands of juvenile and adult transgenic mice all contained proliferating immature ductule cells and were incompletely differentiated. In addition, all male int-3 transgenic mice were sterile, apparently the result of severe hyperplasia of the epididymis. These findings demonstrate in vivo that expression of the activated Notch-related int-3 gene causes deregulation of normal developmental controls and hyperproliferation of glandular epithelia.

Adenocarcinoma↗
PubMed1992

Mouse mammary tumor gene int-3: a member of the notch gene family transforms mammary epithelial cells.

Expression of a 2.3-kb RNA species is induced in mammary tumors as a consequence of insertional mutagenesis at the int-3 locus by the mouse mammary tumor virus. The nucleotide sequence and biological activity of this mammary tumor-specific int-3 RNA species were determined. It contains an open reading frame which encodes a 57-kDa protein. The translated protein possesses six nearly contiguous 32-amino-acid repeats which are related to a similar motif in the Saccharomyces cerevisiae cdc-10-encoded cell cycle protein. In addition, the int-3 cdc-10 repeats are bounded by the PEST amino acid sequence motif which is commonly found in proteins having a rapid turnover and may represent sites for phosphorylation. The int-3 cdc-10 repeat sequences are 50% identical to a portion of the intracellular domain of the neurogenic Drosophila notch gene product. Activation of expression of a recombinant int-3 genomic DNA fragment encoding the 2.3-kb RNA species in HC11 mouse mammary epithelial cells in vitro induces anchorage-independent growth in soft agar.

Amino Acid Sequence↗
PubMed1992

The int-2 gene product acts as a growth factor and substitutes for basic fibroblast growth factor in promoting the differentiation of a normal mouse mammary epithelial cell line.

We have investigated the effect of basic fibroblast growth factor (bFGF) and the related int-2 gene on the growth, transformation, and differentiation of HC11 mouse mammary epithelial cells. We show that in HC11 cells infected with int-2 retroviral expression vectors, the int-2 protein can function as a bFGF-like growth factor in stimulating: (a) HC11 cell proliferation in monolayer, (b) anchorage-independent growth in soft agar, and (c) soft agar growth of the bFGF-responsive SW13 tumor cell line. These effects are observed irrespective of whether the int-2 protein is expressed in its wild-type form or is linked to a signal peptide. A candidate bFGF receptor, which is the product of the flg gene and which may recognize the int-2 protein, is expressed at high levels in HC11 cells. Following epidermal growth factor or bFGF priming and subsequent treatment with lactogenic hormones, all of the int-2 infected and the parental HC11 cells synthesize similar levels of beta-casein. However, the autocrine expression of int-2 in HC11 cells abrogates their requirement for either exogenous epidermal growth factor or bFGF priming. These data suggest that, in HC11 cells, the growth factor activity of the int-2 gene is indistinguishable from that of bFGF and does not interfere with the mammary cell differentiation program associated with lactogenesis.

Agar↗
PubMed1992

Loss of heterozygosity on chromosome 17p13 in breast carcinomas identifies tumors with high proliferation index.

The capacity of breast tumor cells to proliferate is considered a potential prognostic factor together with other histopathologic parameters. The authors determined the proliferation index on a large panel of human primary breast tumors by measuring the levels of incorporation of bromodeoxyuridine (BrdU) by fresh tumor specimens in culture. Previous analysis showed that the percentage of cells entering the S-phase of the cell cycle strongly correlates with tumor grade, tumor size, and estrogen and progesterone receptor status. The capacity of tumor cells to proliferate might be associated with specific genetic mutations in primary tumors. To test this hypothesis, a panel of 96 human breast carcinomas, for which the BrdU labeling index (LI) was known, were tested for loss of heterozygosity (LOH) or increased copy number (ICN) at chromosomes 1q, 3p, 13q, 17p, and 18q. On chromosome 17p, LOH and ICN were observed in 27% and 12%, respectively, of the informative breast tumors. The LOH on chromosome 17p was significantly associated with tumors having an elevated BrdU proliferation index (P = 0.022). No association (P = 0.45) was observed between BrdU LI and tumor size (T2 + T3 compared with T1), tumor grade, and lymph node status. Increased copy number on chromosome 17p, LOH or ICN on 1q, and LOH on 13q14, 18q, and 3p also showed no significant correlation with cell kinetic parameters. These data are consistent with the presence of a gene or genes on chromosome 17p13 near the YNZ22.1 locus whose normal functioning is necessary for controlling breast tumor cells proliferation in vivo.

Blotting, Southern↗
PubMed1991

Mutations in the p53 gene in primary human breast cancers.

Twenty-six primary breast tumors were examined for mutations in the p53 tumor suppressor gene by an RNase protection assay and nucleotide sequence analysis of PCR-amplified p53 complementary DNAs. Each method detected p53 mutations in the same three tumors (12%). One tumor contained two mutations in the same allele. Single strand conformation polymorphism analysis of genomic DNA and complementary DNA proved more sensitive in the detection of mutations. Combining this technique with the other two a total of 12 mutations in the p53 gene were demonstrated in 11 tumors (46%), and a polymorphism at codon 213 was detected in another tumor. Loss of heterozygosity on chromosome 17p was detected by Southern blot analysis in 30% of the tumor DNAs. Not all of the tumors containing a point mutation in p53 also had loss of heterozygosity of the remaining allele, suggesting that loss of heterozygosity may represent a later event.

Base Sequence↗
PubMed1991

Somatic allelic deletion of nm23 in human cancer.

Tumor progression to the metastatic phenotype is accompanied in certain cell types by reduced expression of the nm23 gene. We have localized human nm23-H1 to chromosome 17 by somatic cell hybrid analysis. Regional localization in the CEPH database and in situ hybridization is reported. Somatic allelic deletion of nm23-H1 was observed in human breast, renal, colorectal, and lung carcinoma DNA samples, as compared to DNA from matched normal tissues. A homozygous deletion of nm23-H1 was observed in a lymph node metastasis of a colorectal carcinoma, indicating that nm23-H1 can be recessively inactivated. The data identify nm23-H1 as a novel, independent locus for allelic deletion in human cancer, a characteristic shared with previously described suppressor genes.

Alleles↗