PubMed Health⌕ Search

Biomedical subjects

B A Ponder

Publications and source records attributed to B A Ponder.

At least 19 recordsLinked to original sources
PubMed1998

Full activation of MEN2B mutant RET by an additional MEN2A mutation or by ligand GDNF stimulation.

Germline mutations of RET gene, encoding a receptor tyrosine kinase, have been associated with the MEN2A and MEN2B inherited cancer syndromes. In MEN2A mutations affecting cysteine residues in the extracellular domain of the receptor cause constitutive activation of the tyrosine kinase by the formation of disulfide-bonded homodimers. In MEN2B a single mutation in the tyrosine kinase domain (Met918Thr) has been identified. This mutation does not lead to dimer formation, but has been shown (both biologically and biochemically) to cause ligand-independent activation of the Ret protein, but to a lesser extent than MEN2A mutations. Intramolecular activation by cis-autophosphorylation of RetMEN2B monomers has been proposed as a model for activation, although alternative mechanisms can be envisaged. Here we show that the activity of RetMEN2B can be increased by stable dimerization of the receptor. Dimerization was achieved experimentally by constructing a double mutant receptor with a MEN2A mutation (Cys634Arg) in addition to the MEN2B mutation, and by chronic exposure of RetMEN2B-expressing cells to the Ret ligand GDNF. In both cases full activation of RetMEN2B, measured by 'in vitro' transfection assays and biochemical parameters, was seen. These results indicate that the MEN2B phenotype could be influenced by the tissue distribution or concentration of Ret ligand(s).

3T3 Cells↗
PubMed1998

Thymic lymphomas in mice with a truncating mutation in Brca2.

Inherited mutations in the BRCA2 gene predispose women to breast and ovarian cancer. We created a mutation in the mouse Brca2 gene that terminates translation in exon 11 at 45% of the normal transcript length. Ninety % of Brca2(tm1Cam) homozygous mutant mice die prenatally or perinatally. The location of the Brca2(tm1Cam) mutation differs from those reported previously, and this phenotype suggests a correlation with genotype analogous to that previously reported in humans. Although heterozygote mice have remained free of tumors for 10 months, Brca2(tm1Cam) homozygous mutants that survived to adulthood died with thymic lymphomas between 12 and 14 weeks of age.

Alleles↗
PubMed1998

Expression of E-cadherin, alpha-catenin and beta-catenin in normal ovarian surface epithelium and epithelial ovarian cancers.

AIMS: To study the expression of the epithelial adhesion molecule E-cadherin and its associated proteins alpha and beta catenin in paraffin sections of normal ovaries, benign cystadenomas and ovarian carcinomas, and in immortalized normal ovarian surface epithelial cells and ovarian carcinoma cells in culture. METHODS AND RESULTS: Immunocytochemistry was used to study expression of the proteins in paraffin sections and western blotting was used to determine levels of expression of the proteins in cell extracts. E-cadherin expression was found to be absent in ovarian surface epithelial cells in culture and infrequently expressed in normal ovarian surface epithelial cells in vivo, although apical punctate staining was occasionally seen. Seven of nine benign cystadenomas and 29/34 epithelial ovarian carcinomas showed some expression of E-cadherin, but expression was absent in poorly differentiated tumours. Expression of alpha and beta catenin was consistently detected on the lateral membranes of normal ovarian epithelium and benign cystadenomas. alpha and beta catenin expression was lost in 18% and 21% of ovarian carcinomas, respectively: other ovarian carcinomas expressed these proteins at a reduced level. A small number of these tumours showed a diffuse cytoplasmic rather than membranous staining. Reduced staining for alpha and beta catenin appeared to correlate with a more spindly, less adhesive morphology and increased invasive potential in matrigel. CONCLUSIONS: The results suggest that E-cadherin expression is generally induced in well differentiated ovarian cancers. In contrast, alpha and beta catenins are consistently expressed in the normal ovarian surface epithelium and benign tumours, but are sometimes reduced or absent in ovarian carcinomas. It is likely that the catenins associate with membrane proteins other than E-cadherin in ovarian epithelium, and they may possibly function as tumour suppressors in this epithelium.

Animals↗
PubMed1998

Genetic heterogeneity and penetrance analysis of the BRCA1 and BRCA2 genes in breast cancer families. The Breast Cancer Linkage Consortium.

The contribution of BRCA1 and BRCA2 to inherited breast cancer was assessed by linkage and mutation analysis in 237 families, each with at least four cases of breast cancer, collected by the Breast Cancer Linkage Consortium. Families were included without regard to the occurrence of ovarian or other cancers. Overall, disease was linked to BRCA1 in an estimated 52% of families, to BRCA2 in 32% of families, and to neither gene in 16% (95% confidence interval [CI] 6%-28%), suggesting other predisposition genes. The majority (81%) of the breast-ovarian cancer families were due to BRCA1, with most others (14%) due to BRCA2. Conversely, the majority of families with male and female breast cancer were due to BRCA2 (76%). The largest proportion (67%) of families due to other genes was found in families with four or five cases of female breast cancer only. These estimates were not substantially affected either by changing the assumed penetrance model for BRCA1 or by including or excluding BRCA1 mutation data. Among those families with disease due to BRCA1 that were tested by one of the standard screening methods, mutations were detected in the coding sequence or splice sites in an estimated 63% (95% CI 51%-77%). The estimated sensitivity was identical for direct sequencing and other techniques. The penetrance of BRCA2 was estimated by maximizing the LOD score in BRCA2-mutation families, over all possible penetrance functions. The estimated cumulative risk of breast cancer reached 28% (95% CI 9%-44%) by age 50 years and 84% (95% CI 43%-95%) by age 70 years. The corresponding ovarian cancer risks were 0.4% (95% CI 0%-1%) by age 50 years and 27% (95% CI 0%-47%) by age 70 years. The lifetime risk of breast cancer appears similar to the risk in BRCA1 carriers, but there was some suggestion of a lower risk in BRCA2 carriers <50 years of age.

Adult↗
PubMed1998

Haplotype and phenotype analysis of nine recurrent BRCA2 mutations in 111 families: results of an international study.

Several BRCA2 mutations are found to occur in geographically diverse breast and ovarian cancer families. To investigate both mutation origin and mutation-specific phenotypes due to BRCA2, we constructed a haplotype of 10 polymorphic short tandem-repeat (STR) markers flanking the BRCA2 locus, in a set of 111 breast or breast/ovarian cancer families selected for having one of nine recurrent BRCA2 mutations. Six of the individual mutations are estimated to have arisen 400-2,000 years ago. In particular, the 6174delT mutation, found in approximately 1% of individuals of Ashkenazi Jewish ancestry, was estimated to have arisen 29 generations ago (1-LOD support interval 22-38). This is substantially more recent than the estimated age of the BRCA1 185delAG mutation (46 generations), derived from our analogous study of BRCA1 mutations. In general, there was no evidence of multiple origins of identical BRCA2 mutations. Our study data were consistent with the previous report of a higher incidence of ovarian cancer in families with mutations in a 3.3-kb region of exon 11 (the ovarian cancer cluster region [OCCR]) (P=.10); but that higher incidence was not statistically significant. There was significant evidence that age at diagnosis of breast cancer varied by mutation (P<.001), although only 8% of the variance in age at diagnosis could be explained by the specific mutation, and there was no evidence of family-specific effects. When the age at diagnosis of the breast cancer cases was examined by OCCR, cases associated with mutations in the OCCR had a significantly older mean age at diagnosis than was seen in those outside this region (48 years vs. 42 years; P=.0005).

Adult↗
PubMed1998

Transfection of rat ovarian surface epithelium with erb-B2/neu induces transformed phenotypes in vitro and the tumorigenic phenotype in vivo.

The neu/cerb-B2 gene is frequently amplified and/or overexpressed in human epithelial ovarian cancers. We have established an inbred animal model for ovarian cancer that mimics aspects of human ovarian cancer by transducing a spontaneously immortalized rat ovarian surface epithelial cell line in culture with ecotropic retroviruses expressing a mutated rat neu/c-erb-B2 oncogene. Transfectants expressing neu at a high level exhibited altered morphology and behavior in two-dimensional and three-dimensional culture in Matrigel, could be cloned in soft agar, and were more invasive through a Matrigel membrane than control transfectants transduced with a similar retrovirus expressing the beta-galactosidase gene. When injected intraperitoneally, neu-expressing transfectants produced highly invasive, rapidly growing tumors that coated the peritoneal cavity and induced ascites formation. Furthermore, neu transfectants could be grown as solid tumors when injected subepithelially into the ovary. The neu-transfected cells also formed tumors when injected subcutaneously into the mammary fat pad, although they grew relatively poorly and often regressed. Transfectants expressing beta-galactosidase failed to produce tumors at any of the sites injected. A second rat ovarian surface epithelial cell line was similarly transduced with the neu/c-erb-B2-expressing retrovirus. However, transformed phenotypes and tumorigenicity were not induced in this cell line. These experiments show directly that overexpression of neu in an established line of rat ovarian epithelium is extremely oncogenic. This animal model system may prove useful for the study of ovarian cancer biology in immunocompetent animals.

Animals↗
PubMed1998

Inherited predisposition to breast cancer.

Breast and ovarian cancers sometimes occur in families. Linkage studies in these families have led to the mapping and then cloning of two predisposing genes, BRCA1 and BRCA2. Together these genes probably account for rather less than 5% of all breast and ovarian cancers. In the medium term, understanding the function of the proteins encoded by these genes should lead to a better understanding of how the cancers develop, and the design of new approaches to treatment and prevention. Of more immediate concern is the possibility of genetic testing for cancer susceptibility in families. In multiple-case families, where the BRCA1 or BRCA2 mutation is likely to be present and there are clear clinical decisions to be taken, genetic testing is not controversial. The costs and benefits of wider testing are much less clear.

BRCA1 Protein↗
PubMed1997

Expression of multiple endocrine neoplasia 2B RET in neuroblastoma cells alters cell adhesion in vitro, enhances metastatic behavior in vivo, and activates Jun kinase.

Point mutations, deletions, and recombinations of the RET proto-oncogene are associated with several inherited human diseases of neural crest-derived cells: Hirschsprung's disease, familial medullary thyroid carcinoma, and the multiple endocrine neoplasia (MEN) syndromes, types 2A and 2B. RET expression is restricted to normal and malignant cells of neural crest origin, such as human neuroblastoma cells. To better understand the role of the activated RET oncogene in neural crest cells, we transfected two adherent human neuroblastoma tumor cell lines with oncogenic MEN2 mutant RET cDNAs. Transfectant clones from both cell lines overexpressing MEN2B RET demonstrated a marked increase in the cell fraction growing in suspension. Both control and MEN2B cells formed tumors at the site of injection in all cases. However, mice injected with MEN2B cells developed lung metastases at a much higher frequency than control mice. Only RET protein derived from MEN2A transfectant cells had increased autokinase activity, whereas MEN2B transfectant cells demonstrated selective activation of the mitogen-activated protein kinase, Jun kinase-1 (Jnk1). These results indicate a biochemical signaling pathway that may link oncogenic RET with the metastatic process.

Amino Acid Substitution↗
PubMed1997

Aberrant splicing of the TSG101 and FHIT genes occurs frequently in multiple malignancies and in normal tissues and mimics alterations previously described in tumours.

Intragenic deletions of TSG101, the human homolog of a mouse gene (tsg101) that acts to suppress malignant cell growth, were reported in human breast tumours. We screened TSG101 for somatic mutations in DNA and RNA samples isolated from a variety of common human malignancies, EBV-immortalised B-cells, and normal lung parenchyma. Intragenic TSG101 deletions in RNA transcripts were frequently found in all types of samples. Analysis of DNA failed to show genomic rearrangements corresponding to transcripts containing deletions in the same samples. The breakpoints of most transcript deletions coincide with genuine or cryptic splice site sequences, suggesting that they result from alternative or aberrant splicing. A similar spectrum of transcript deletions has previously been described in the putative tumour suppressor gene FHIT. We analysed FHIT in the same series of RNA samples and detected truncated FHIT transcripts frequently in both tumour and normal tissues. In addition, transcripts from TSG101, FHIT and seven other genes were analysed in RNA isolated from normal peripheral blood lymphocytes. Large TSG101 and FHIT intragenic transcript deletions were detected and these appeared to be the predominant transcript in 'aged' lymphocytes. Similar alterations were not detected in transcripts of the other genes which were analysed. Our findings demonstrate that truncated TSG101 and FHIT transcripts are commonly detected in both normal and malignant tissues and that a significant fraction of these are likely to be the result of aberrant splicing. While we cannot exclude that alterations in TSG101 and FHIT occur during cancer development, our data indicate that in this context the commonly observed transcript abnormalities are misleading.

Acid Anhydride Hydrolases↗
PubMed1997

Germline mutation of RET codon 883 in two cases of de novo MEN 2B.

Germline mutations in the RET proto-oncogene are seen in the majority of patients with the dominantly inherited cancer syndromes multiple endocrine neoplasia type 2 (MEN 2). The clinical subtypes of MEN 2 (MEN 2A, MEN 2B and familial MTC) all have medullary thyroid carcinoma, but vary in the involvement of pheochromocytoma, parathyroid adenoma/hyperplasia and developmental abnormalities. A single RET mutation, resulting in the substitution M918T, has been identified in 94% of cases of MEN 2B (which consists of MTC, pheochromocytoma and developmental abnormalities). Here we report the identification of a new germline RET mutation (A883F) in two de novo cases of MEN 2B. Identification of this new mutation will contribute to understanding the molecular basis of MEN 2B, and will assist in the clinical management of families harbouring this mutation.

Amino Acid Sequence↗
PubMed1997

Family history and the risk of breast cancer: a systematic review and meta-analysis.

An increased risk of breast cancer in women with a family history of breast cancer has been demonstrated by many studies using a variety of study designs. However, the extent of this risk varies according to the nature of the family history (type of relative affected, age at which relative developed breast cancer and number of relatives affected) and may also vary according to age of the individual. The aim of our study was to identify all the published studies which have quantified the risk of breast cancer associated with a family history of the disease, and to summarise the evidence from these studies, with particular emphasis on age-specific risks according to subject and relative age. Seventy-four published studies were identified. The pooled estimate of relative risk (RR) associated with various family histories was as follows: any relative, RR = 1.9 (95% CI, 1.7-2.0); a first-degree relative, RR = 2.1 (CI = 2.0, 2.2); mother, RR = 2.0 (CI = 1.8, 2.1); sister, RR = 2.3 (CI = 2.1, 2.4); daughter, RR = 1.8 (CI = 1.6, 2.0); mother and sister, RR = 3.6 (CI = 2.5, 5.0); and a second-degree relative, RR = 1.5 (CI = 1.4, 1.6). Risks were increased in subjects under age 50 and when the relative had been diagnosed before age 50.

Adult↗
PubMed1997

Contribution of BRCA1 mutations to ovarian cancer.

BACKGROUND: Inherited mutations in the BRCA1 gene confer a high risk of breast and ovarian cancer in some families. To determine the contribution of BRCA1 mutations to ovarian cancer in the general population, we analyzed DNA samples from a consecutive series of women with ovarian cancer seen at one center. METHODS: We studied 374 women who received a diagnosis of epithelial ovarian cancer before the age of 70 years and were treated at the Royal Marsden Hospital between July 1993 and September 1995. Genomic DNA was analyzed by multiplex heteroduplex analysis. Variants were further identified by sequencing. RESULTS: Probable germ-line BRCA1 mutations were identified in 13 of the 374 women (3 percent; 95 percent confidence interval, 2 to 6 percent). Six of the variants have not been described previously. Of the 13 mutations, 12 are predicted to result in a truncated protein product. An additional variant results in an in-frame deletion just outside the putative zinc-finger domain. Nine of the 12 women with truncating mutations had family histories of breast or ovarian cancer or both. CONCLUSIONS: Assuming that our method has a sensitivity of 70 percent, mutations in BRCA1 occur in approximately 5 percent (95 percent confidence interval, 3 to 8 percent) of women in whom ovarian cancer is diagnosed before the age of 70 years.

Adenocarcinoma, Clear Cell↗
PubMed1997

RET alternate splicing influences the interaction of activated RET with the SH2 and PTB domains of Shc, and the SH2 domain of Grb2.

Activating germline mutations of the RET receptor tyrosine kinase are found in the majority of cases of inherited cancer syndrome MEN 2, and inactivating mutations in some cases of dominantly inherited Hirschsprung disease. Using RET activated by a MEN 2 mutation, we show that both the SH2 and PTB domains of the adaptor protein Shc interact with RET, and we identify the PTB domain interaction site. Interaction with both the SH2 and PTB domains of Shc contributes to the transcriptional activation of a serum response element. RET alternate splicing affects the strength of interaction with both the Shc SH2 and PTB domains. In addition, a splice isoform-specific HSCR missense mutation, which does not inactivate the RET kinase activity, decreases the strength of the PTB domain interaction and the level of RET-dependent Shc phosphorylation.

Adaptor Proteins, Signal Transducing↗
PubMed1997

Overexpression of cyclin D1 in epithelial ovarian cancers.

Amplification and overexpression of the cell cycle-related gene cyclin D1 have been demonstrated in several human malignancies and have been shown to be directly oncogenic in breast epithelium and lymphocytes. Overexpression of the gene can occur in the absence of gene amplification. We have investigated whether cyclin D1 is overexpressed in a panel of 43 sporadic epithelial ovarian cancers using immunohistochemistry. Cyclin D1 was overexpressed in 26% of these tumors. Overexpression of cyclin D1 is associated with borderline or well-differentiated, grade 1 tumors but does not correlate with a particular histological type, overexpression of the c-erb-B2 oncogene, or presence of estrogen receptors. It is suggested that overexpression of cyclin D1 may contribute to the pathogenesis of epithelial ovarian cancers, including a subset of tumors different from those overexpressing the c-erb-B2 oncogene.

Cyclin D1↗
PubMed1997

Cancer and genes: how will molecular biology reshape our clinical practice?

Cancers develop through a succession of stages marked by the accumulation of genetic events within the cell. The rate of occurrence of these events is influenced by the genetic make-up of the individual (e.g., differences in the metabolism of carcinogens, and in the capacity for DNA repair). Knowledge of these events will help define precise targets for early diagnosis. Molecular profiles of cancers will predict prognosis and guide the selection of appropriate therapy. Genetic differences between cancers and normal cells may at last be exploited to make cancer treatment truly selective. An example in clinical trials is the 'smart virus' that replicates in and destroys only cancer cells because of their defective p53 function. An understanding of the genetic background of individuals should allow those at particular risk to be recognised and to develop prevention programmes involving targeted screening or the avoidance of predisposing environmental factors. Here, however, human behaviour and the efficacy of early detection methods are likely to be limiting factors, as is already clear from experience with tobacco smoking and with genes for breast cancer and ovarian cancer.

Humans↗
PubMed1997

Mutations of the BRCA1 and BRCA2 genes and the possibilities for predictive testing.

Two cancer susceptibility genes, BRCA1 on chromosome 17q12-21 and BRCA2 on chromosome 13q12-13, are thought to be responsible for approximately 80% of families containing multiple cases of early-onset female breast cancer. Germline mutations of BRCA1 are also associated with ovarian cancer and mutations of BRCA2 are associated with an increased risk of male breast cancer, ovarian cancer, prostate cancer and pancreatic cancer. The recent isolation of both genes should make possible the identification of the genetic defect that predisposes affected individuals to breast and ovarian cancer and might lead to the use of genetic information for predictive testing.

BRCA2 Protein↗