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E R Fearon

Publications and source records attributed to E R Fearon.

At least 19 recordsLinked to original sources
PubMed1992

Karyoplasmic interaction selection strategy: a general strategy to detect protein-protein interactions in mammalian cells.

We describe a strategy and reagents for study of protein-protein interactions in mammalian cells, termed the karyoplasmic interaction selection strategy (KISS). With this strategy, specific protein-protein interactions are identified by reconstitution of the functional activity of the yeast transcriptional activator GAL4 and the resultant transcription of a GAL4-regulated reporter gene. Reconstitution of GAL4 function results from specific interaction between two chimeric proteins: one contains the DNA-binding domain of GAL4; the other contains a transcriptional activation domain. Transcription of the reporter gene occurs if the two chimeric proteins can form a complex that reconstitutes the DNA-binding and transcriptional activation functions of GAL4. Using the KISS system, we demonstrate specific interactions for sequences from three different pairs of proteins that complex in the cytoplasm. In addition, we demonstrate that reporter genes encoding cell surface or drug-resistance markers can be specifically activated as a result of protein-protein interactions. With these selectable markers, the KISS system can be used to screen specialized cDNA libraries to identify novel protein interactions.

Amino Acid Sequence↗
PubMed1992

Progressing toward a molecular description of colorectal cancer development.

During the past decade, the powerful techniques of molecular biology and genetics have been applied to the study of human cancer. Colorectal tumors have proved to be an excellent system in which to search for and study the mutations involved in the development and progression of a common human cancer because of their natural history and several inherited syndromes that strongly predispose to colorectal cancer. A current view is that colorectal cancer results, at least in part, from the accumulation of multiple mutations in oncogenes and tumor suppressor genes in an affected cell. Although the genetic alterations often occur in a preferred sequence, the total accumulation of changes, rather than their order with respect to one another, appears to be a critical determinant of the biological properties of the tumor cell. Study of the inherited and somatic mutations in colorectal tumor cells may provide insights not only into the pathogenesis of cancer, but may also lead to future understanding of the mechanisms of the origin of mutations and the role of environmental and dietary factors in colorectal tumor development.

Adenoma↗
PubMed1992

Genetic alterations underlying colorectal tumorigenesis.

Colorectal tumours have proven to be an excellent system in which to identify and study the genetic alterations involved in the development of a common human neoplasm. A prevalent view is that colorectal tumours appear to arise as the result of multiple genetic alterations in the alleles of both oncogenes and tumour suppressor genes. The accumulation of genetic alterations appears to accompany the clinical and biological progression of the tumours and may determine the phenotype of the tumour cells. In addition to the many somatic alterations identified at various stages of colorectal tumour development, recent studies have led to the identification of the adenomatous polyposis coli (APC) gene, which, when mutated in the germline, predisposes to the development of colorectal tumours. On the basis of studies of inherited and somatic mutations in colorectal tumours, a genetic model for colorectal cancer development has been proposed. Although the model is undoubtedly incomplete, it nevertheless provides a useful framework for further studies of the multiple events that underlie human tumour initiation and progression. Numerous questions remain to be answered, including identification of the normal function of the genes implicated in tumorigenesis, how mutations in these genes arise and are selected for and what the relative contribution of the altered genes is to various stages of the neoplastic process. Nevertheless, an optimistic outlook is that fundamental insights into the pathogenesis of human cancer are within our reach.

Chromosome Deletion↗
PubMed1991

Scrambled exons.

Using a sensitive assay for RNA expression, we identified several abnormally spliced transcripts in which exons from a candidate tumor suppressor gene (DCC) were scrambled during the splicing process in vivo. Cloning and sequencing of PCR-amplified segments of the abnormally spliced transcripts showed that exons were joined accurately at consensus splice sites, but in an order different from that present in the primary transcript. Four scrambled transcripts were identified, each involving a different pair of exons. The scrambled transcripts were found at relatively low levels in a variety of normal and neoplastic cells of rodent and human origin, primarily in the nonpolyadenylated component of cytoplasmic RNA. These results demonstrate that the splicing process does not always pair sequential exons in the order predicted from their positions in genomic DNA, thus creating a novel type of RNA product.

Amino Acid Sequence↗
PubMed1991

Intracellular leucine zipper interactions suggest c-Myc hetero-oligomerization.

The physiological significance of in vitro leucine zipper interactions was studied by the use of two strategies which detect specific protein-protein interactions in mammalian cells. Fusion genes were constructed which produce chimeric proteins containing leucine zipper domains from several proteins fused either to the DNA-binding domain of the Saccharomyces cerevisiae GAL4 protein or to the transcriptional activation domain of the herpes simplex virus VP16 protein. Previous studies in mammalian cells have demonstrated that a single chimeric polypeptide containing these two domains will activate transcription of a reporter gene present downstream of the GAL4 DNA-binding site. Similarly, if the GAL4 DNA-binding domain of a chimeric protein could be complexed through leucine zipper interactions with the VP16 activation domain of another chimeric protein, then transcriptional activation of the reporter gene would be detected. Using this strategy for detecting leucine zipper interactions, we observed homo-oligomerization between leucine zipper domains of the yeast protein GCN4 and hetero-oligomerization between leucine zipper regions from the mammalian transcriptional regulating proteins c-Jun and c-Fos. In contrast, homo-oligomerization of the leucine zipper domain from c-Myc was not detectable in cells. The inability of the c-Myc leucine zipper to homo-oligomerize strongly in cells was confirmed independently. The second strategy to detect leucine zipper interactions takes advantage of the observation that the addition of nuclear localization sequences to a cytoplasmic protein will allow the cytoplasmic protein to be transported to and retained in the nucleus. Chimeric genes encoding proteins with sequences from a cytoplasmic protein fused either to the GCN4 or c-Myc leucine zipper domains were constructed. Experiments with the c-Myc chimeric protein failed to demonstrate transport of the cytoplasmic marker protein to the nucleus in cells expressing the wild-type c-Myc protein. In contrast, the cytoplasmic marker was translocated into the nucleus when the GCN4 leucine zippers were present on both the cytoplasmic marker and a nuclear protein, presumably as a result of leucine zipper interaction. These results suggest that c-Myc function requires hetero-oligomerization to an as yet undefined factor.

Amino Acid Sequence↗
PubMed1991

A genetic basis for the multi-step pathway of colorectal tumorigenesis.

Colorectal tumors provide an excellent system in which to search for and study the genetic alterations involved in the development of a common human cancer. Data from many clinical and histopathological studies suggest that most carcinomas arise from preexisting adenomas. In addition, colorectal tumors of various stages of development can be obtained for studies of genetic alterations, unlike the situation in many other common human cancers in which only the most advanced lesions can be studied. A current view is that colorectal tumor development and progression results from the accumulation of somatic genetic alterations (mutations) in both oncogenes and tumor suppressor genes. Mutations in four to five genes may be necessary for the development of a malignant tumor; fewer changes may suffice for benign tumor formation. Although the genetic alterations often occur in a preferred sequence, the total accumulation of changes, rather than their order with respect to one another, appears to be a critical determinant of the biological properties of the tumor. Study of the genes targeted by somatic mutation in these tumors may provide insights, not only into the pathogenesis of the disease, but also into the mechanisms of origin of mutations and the potential environmental and dietary factors underlying colorectal tumor development.

Adenomatous Polyposis Coli↗
PubMed1990

Suppression of human colorectal carcinoma cell growth by wild-type p53.

Mutations of the p53 gene occur commonly in colorectal carcinomas and the wild-type p53 allele is often concomitantly deleted. These findings suggest that the wild-type gene may act as a suppressor of colorectal carcinoma cell growth. To test this hypothesis, wild-type or mutant human p53 genes were transfected into human colorectal carcinoma cell lines. Cells transfected with the wild-type gene formed colonies five- to tenfold less efficiently than those transfected with a mutant p53 gene. In those colonies that did form after wild-type gene transfection, the p53 sequences were found to be deleted or rearranged, or both, and no exogenous p53 messenger RNA expression was observed. In contrast, transfection with the wild-type gene had no apparent effect on the growth of epithelial cells derived from a benign colorectal tumor that had only wild-type p53 alleles. Immunocytochemical techniques demonstrated that carcinoma cells expressing the wild-type gene did not progress through the cell cycle, as evidenced by their failure to incorporate thymidine into DNA. These studies show that the wild-type gene can specifically suppress the growth of human colorectal carcinoma cells in vitro and that an in vivo-derived mutation resulting in a single conservative amino acid substitution in the p53 gene product abrogates this suppressive ability.

Cell Division↗
PubMed1990

Interleukin-2 production by tumor cells bypasses T helper function in the generation of an antitumor response.

A poorly immunogenic murine colon cancer was used to investigate mechanisms of antitumor immunity. Injection of tumor cells engineered by gene transfection to secrete IL-2 stimulated an MHC class I-restricted cytolytic T lymphocyte (CTL) response against the parental tumor. The tumor cells secreting IL-2 produced an antitumor response in vivo, even in the absence of CD4+ T cells. Animals immunized with the engineered cells were protected against subsequent challenge with the parental tumor cell line. Similar findings were demonstrated for other tumor types. Thus, provision of a helper lymphokine in a paracrine fashion induced a tumor-specific immune response involving activation of endogenous CTLs and other immune effector cells. These findings demonstrate that the failure of an effective antitumor immune response may be primarily due to a helper arm deficiency of the immune system rather than a paucity of tumor-specific cytotoxic effector cells. Furthermore, they outline a novel strategy for augmenting tumor immunity.

Animals↗
PubMed1990

Identification of a chromosome 18q gene that is altered in colorectal cancers.

Allelic deletions involving chromosome 18q occur in more than 70 percent of colorectal cancers. Such deletions are thought to signal the existence of a tumor suppressor gene in the affected region, but until now a candidate suppressor gene on this chromosomal arm had not been identified. A contiguous stretch of DNA comprising 370 kilobase pairs (kb) has now been cloned from a region of chromosome 18q suspected to reside near this gene. Potential exons in the 370-kb region were defined by human-rodent sequence identities, and the expression of potential exons was assessed by an "exon-connection" strategy based on the polymerase chain reaction. Expressed exons were used as probes for cDNA screening to obtain clones that encoded a portion of a gene termed DCC; this cDNA was encoded by at least eight exons within the 370-kb genomic region. The predicted amino acid sequence of the cDNA specified a protein with sequence similarity to neural cell adhesion molecules and other related cell surface glycoproteins. While the DCC gene was expressed in most normal tissues, including colonic mucosa, its expression was greatly reduced or absent in most colorectal carcinomas tested. Somatic mutations within the DCC gene observed in colorectal cancers included a homozygous deletion of the 5' end of the gene, a point mutation within one of the introns, and ten examples of DNA insertions within a 0.17-kb fragment immediately downstream of one of the exons. The DCC gene may play a role in the pathogenesis of human colorectal neoplasia, perhaps through alteration of the normal cell-cell interactions controlling growth.

Alleles↗
PubMed1990

Mutant p53 DNA clones from human colon carcinomas cooperate with ras in transforming primary rat cells: a comparison of the "hot spot" mutant phenotypes.

The majority of the p53 genes derived from human colorectal carcinomas contain point mutations. A significant number of these mutations occur in or around amino acids 143, 175, 273, or 281. Experiments presented here demonstrate for the first time that p53 DNA clones containing any one of these mutations cooperate with the activated ras oncogene to transform primary rat embryo cells in culture. These transformed cells produce elevated levels of the human p53 protein, which has extended half-lives (1.5-7 h), as compared to the wild-type human p53 protein (20-30 min). The p53 mutant with an alteration at residue 175 (p53-175H) binds tightly to the cellular heat shock protein, hsc70. In contrast, the p53 mutants possessing mutations at either residue 273 or 281 (p53-273H/281G) do not bind detectably to this heat shock protein and generally are less efficient at forming transformed foci in culture. The transformed cell lines are tumorigenic in nude mice. Thus, two classes of p53 mutant proteins can be distinguished: p53-175H, which cooperates with ras efficiently and binds to hsc70, and p53-273H/281G, which has a reduced efficiency of transformed foci formation and does not bind hsc70. This demonstrates that complex formation between mutant p53 and hsc70 is not required for p53-mediated transformation, but rather it facilitates this function, perhaps by ensuring sequestration of the endogenous wild-type p53 protein. The positive effect on cell proliferation by these mutant p53 proteins is consistent with a role for activated p53 mutants in the genesis of colorectal carcinomas.

Animals↗
PubMed1989

Clinical and pathological associations with allelic loss in colorectal carcinoma [corrected].

Clinical and pathological associations with molecular genetic alterations were studied in colorectal carcinomas from 83 patients. Fractional allelic loss, a measure of allelic deletions throughout the genome, and allelic deletions of specific chromosomal arms (the short arm of 17 and long arm of 18) each provided independent prognostic information by multivariate analysis when considered individually with Dukes' classification. Distant metastasis was significantly associated with high fractional allelic loss and with deletions of 17p and 18q. Mutations of ras proto-oncogenes and deletions of 5q had no prognostic importance. Statistically significant associations were also found between allelic losses and a family history of cancer, left-sided tumor location, and absence of extracellular tumor mucin. Allelic deletion analysis thus identified subsets of colorectal carcinoma with increased predilection for distant metastasis and cancer-related death. Further studies may define a subset of genetic alterations that can be used clinically to help assess prognosis.

Adult↗
PubMed1989

Allelotype of colorectal carcinomas.

To examine the extent and variation of allelic loss in a common adult tumor, polymorphic DNA markers were studied from every nonacrocentric autosomal arm in 56 paired colorectal carcinoma and adjacent normal colonic mucosa specimens. This analysis was termed an allelotype, in analogy with a karyotype. Three major conclusions were drawn from this analysis: (i) Allelic deletions were remarkably common; one of the alleles of each polymorphic marker tested was lost in at least some tumors, and some tumors lost more than half of their parental alleles. (ii) In addition to allelic deletions, new DNA fragments not present in normal tissue were identified in five carcinomas; these new fragments contained repeated sequences of the variable number of tandem repeat type. (iii) Patients with more than the median percentage of allelic deletions had a considerably worse prognosis than did the other patients, although the size and stage of the primary tumors were very similar in the two groups. In addition to its implications concerning the genetic events underlying tumorigenesis, tumor allelotype may provide a molecular tool for improved estimation of prognosis in patients with colorectal cancer.

Alleles↗
PubMed1989

Chromosome 17 deletions and p53 gene mutations in colorectal carcinomas.

Previous studies have demonstrated that allelic deletions of the short arm of chromosome 17 occur in over 75% of colorectal carcinomas. Twenty chromosome 17p markers were used to localize the common region of deletion in these tumors to a region contained within bands 17p12 to 17p13.3. This region contains the gene for the transformation-associated protein p53. Southern and Northern blot hybridization experiments provided no evidence for gross alterations of the p53 gene or surrounding sequences. As a more rigorous test of the possibility that p53 was a target of the deletions, the p53 coding regions from two tumors were analyzed; these two tumors, like most colorectal carcinomas, had allelic deletions of chromosome 17p and expressed considerable amounts of p53 messenger RNA from the remaining allele. The remaining p53 allele was mutated in both tumors, with an alanine substituted for valine at codon 143 of one tumor and a histidine substituted for arginine at codon 175 of the second tumor. Both mutations occurred in a highly conserved region of the p53 gene that was previously found to be mutated in murine p53 oncogenes. The data suggest that p53 gene mutations may be involved in colorectal neoplasia, perhaps through inactivation of a tumor suppressor function of the wild-type p53 gene.

Alleles↗
PubMed1988

Genetic alterations during colorectal-tumor development.

Because most colorectal carcinomas appear to arise from adenomas, studies of different stages of colorectal neoplasia may shed light on the genetic alterations involved in tumor progression. We looked for four genetic alterations (ras-gene mutations and allelic deletions of chromosomes 5, 17, and 18) in 172 colorectal-tumor specimens representing various stages of neoplastic development. The specimens consisted of 40 predominantly early-stage adenomas from 7 patients with familial adenomatous polyposis, 40 adenomas (19 without associated foci of carcinoma and 21 with such foci) from 33 patients without familial polyposis, and 92 carcinomas resected from 89 patients. We found that ras-gene mutations occurred in 58 percent of adenomas larger than 1 cm and in 47 percent of carcinomas. However, ras mutations were found in only 9 percent of adenomas under 1 cm in size. Sequences on chromosome 5 that are linked to the gene for familial adenomatous polyposis were not lost in adenomas from the patients with polyposis but were lost in 29 to 35 percent of adenomas and carcinomas, respectively, from other patients. A specific region of chromosome 18 was deleted frequently in carcinomas (73 percent) and in advanced adenomas (47 percent) but only occasionally in earlier-stage adenomas (11 to 13 percent). Chromosome 17p sequences were usually lost only in carcinomas (75 percent). The four molecular alterations accumulated in a fashion that paralleled the clinical progression of tumors. These results are consistent with a model of colorectal tumorigenesis in which the steps required for the development of cancer often involve the mutational activation of an oncogene coupled with the loss of several genes that normally suppress tumorigenesis.

Adenoma↗
PubMed1988

Induction in a murine tumor of immunogenic tumor variants by transfection with a foreign gene.

Transfection of the undifferentiated murine colon carcinoma line CT-26 with the gene coding for the hemagglutination antigen (HA) of influenza virus resulted in the generation of highly immunogenic tumor cells. CT-26 cells transfected with HA not only failed to grow in syngeneic mice but also protected normal animals against a challenge with otherwise lethal doses of parental nontransfected cells. The immunogenicity of HA-transfected cells appeared to correlate with surface HA expression in that tumorigenic clones of HA-transfected CT-26 cells expressed little HA, while immunogenic clones were high expressers of HA. Irradiation of immunogenic HA clones did not abrogate their immunogenicity. These observations demonstrate that immune recognition of a poorly immunogenic tumor can be produced by immunization with tumor cells expressing a defined, foreign cell surface antigen.

Animals↗
PubMed1988

Carrier detection in the Wiskott Aldrich syndrome.

The Wiskott-Aldrich syndrome (WAS) is an X-linked recessive disease characterized by immunodeficiency and severe thrombocytopenia in affected males, but no demonstrable clinical abnormalities in carrier females. Through analysis of the methylation patterns of X-linked genes that display restriction fragment length polymorphisms (RFLPs), we studied the pattern of X-chromosome inactivation in various cell populations from female relatives of patients with WAS. The peripheral blood T cells, granulocytes, and B cells of eight obligate WAS carriers were found to display specific patterns of X-chromosome inactivation clearly different from these of normal controls. Thus, carriers of WAS could be accurately identified using this analysis.

B-Lymphocytes↗