摘要:
Improvements on the basic method used for BEAMing increase sensitivity and increase the signal-to-noise ratio. The improvements have permitted the determination of intrinsic error rates of various DNA polymerases and have permitted the detection of rare and subtle mutations in DNA isolated from plasma of cancer patients.
摘要:
Serial analysis of gene expression (SAGE) was used to identify transcripts encoding secreted or cell-surface proteins that were expressed in benign and malignant tumors of the colorectum. A total of 290,394 tags were analyzed from normal, adenomatous and cancerous colonic epithelium. Of the 21,343 different transcripts observed, 957 were found to be differentially expressed between normal and adenoma or between normal and cancer. Forty-nine transcripts were elevated ≥ 20-fold in adenomas, 40 transcripts were elevated ≥ 20-fold in cancers, and nine transcripts were elevated ≥ 20-fold in both. Product of six these nine transcripts (TGFBI, LYS, RDP, MIC-1, REGA, and DEHL) were predicted to be secreted or to reside on the cell surface and these were analyzed in more detail. The abnormal expression levels predicted by SAGE were confirmed by quantitative PCR analyses of each of these six genes. Moreover, the cell types responsible for the elevated expression were identified by in situ hybridization and by PCR analyses of epithelial cells immunoaffinity purified from primary tumors.
摘要:
The APC tumor suppressor protein binds to beta -catenin, a protein recently shown to interact with Tcf/Lef transcription factors. Here, the gene encoding a Tcf family member that is expressed in colonic epithelium (hTcf-4) was cloned and characterized. hTcf-4 transactivates transcription only when associated with beta -catenin. Nuclei of APC colon carcinoma cells were found to contain a stable beta -catenin-hTCF-4 complex that was constitutively active, as measured by transcription of a Tcf reporter gene. Reintroduction of APC removed beta -catenin from hTcf4 and abrogated the transcriptional transactivation. Constitutive transcription of TCF target genes, caused by loss of APC function, may be a crucial event in the early transformation of colonic epithelium. It is also shown here that the products of mutant APC genes found in colorectal tumors are defective in regulating beta -catenin/Tcf-4 transcriptional activation. Furthermore, colorectal tumors with intact APC genes were shown to contain subtle activating mutations of beta -catenin that altered functionally significant phosphorylation sites. These results indicate that regulation of beta -catenin is critical to APC's tumor suppressive effect and that this regulation can be circumvented by mutations in either APC or beta -catenin.
摘要:
The identification of pre-defined mutations expected to be present in a minor fraction of a cell population is important for a variety of basic research and clinical applications. The exponential, analog nature of the polymerase chain reaction is transformed into a linear, digital signal suitable for this purpose. Single molecules can be isolated by dilution and individually amplified; each product is then separately analyzed for the presence of mutations. The process provides a reliable and quantitative measure of the proportion of variant sequences within a DNA sample.
摘要:
The APC tumor suppressor protein binds to β-catenin, a protein recently shown to interact with Tcf/Lef transcription factors. Here, the gene encoding a Tcf family member that is expressed in colonic epithelium (hTcf-4) was cloned and characterized. hTcf-4 transactivates transcription only when associated with β-catenin. Nuclei of APC-/- colon carcinoma cells were found to contain a stable β-catenin-hTCF-4 complex that was constitutively active, as measured by transcription of a Tcf reporter gene. Reintroduction of APC removed β-catenin from hTcf4 and abrogated the transcriptional transactivation. Constitutive transcription of TCF target genes, caused by loss of APC function, may be a crucial event in the early transformation of colonic epithelium. It is also shown here that the products of mutant APC genes found in colorectal tumors are defective in regulating β-catenin/Tcf-4 transcriptional activation. Furthermore, colorectal tumors with intact APC genes were shown to contain subtle activating mutations of β-catenin that altered functionally significant phosphorylation sites. These results indicate that regulation of β-catenin is critical to APC"s tumor suppressive effect and that this regulation can be circumvented by mutations in either APC or β-catenin.
摘要:
The accumulation of homoplasmic somatic mutations has been observed in the mitochondrial DNA of certain tumor cells. The presence or a recurrence of a tumor can be detected by determining the presence of single basepair mutations in the mitochondrial genome from a cell sample of a patient.
摘要:
A diagnostic strategy for detection of inherited diseases caused by germline mutations is based on somatic cell hybridization. Each allele of a human gene involved in the inherited disease is isolated in a somatic cell hybrid. The products of the isolated human allele are then observed in the absence of the other allele of the human.
摘要:
The hPMS2 gene encodes a protein which is involved in DNA mismatch repair and is mutated in a subset of patients with hereditary nonpolyposis colon cancer (HNPCC). The previously published hPMS2 cDNA sequence lacks an upstream in-frame stop codon preceding the presumptive initiating methionine. To further evaluate the 5' terminus of the hPMS2 coding region, we isolated additional cDNA clones, RT-PCR products, and the corresponding 5' genomic segment of the hPMS2 locus. The hPMS2 gene transcripts were found to have heterogeneous but collinear 5' termini, one of which contained an in-frame termination codon preceding the initiating methionine. In addition, a gene encoding a 34.5 kDa polypeptide was found to transcriptionally initiate within hPMS2 from the opposite strand.
摘要:
Mitochondrial mutations occur as a product of contact of a person with an environmental pollutant. Mitochondrial mutations are readily detectable in body fluids. Measurement of mitochondrial mutations in body fluids can be used as a dosimeter to monitor exposure to the environmental pollutant. Mitochondrial mutations can also be detected in cancer patients. Probes and primers containing mutant mitochondrial sequences can be used to monitor patient condition.
摘要:
To gain a better understanding of tumor angiogenesis, new techniques for isolating endothelial cells (ECs) and evaluating gene expression patterns were developed. When transcripts from ECs derived from normal and malignant colorectal tissues were compared with transcripts from non-endothelial cells, over 170 genes predominantly expressed in the endothelium were identified. Comparison between normal- and tumor-derived endothelium revealed 79 differentially expressed genes, including 46 that were specifically elevated in tumor-associated endothelium. Experiments with representative genes from this group demonstrated that most were similarly expressed in the endothelium of primary lung, breast, brain, and pancreatic cancers as well as in metastatic lesions of the liver. These results demonstrate that neoplastic and normal endothelium in humans are distinct at the molecular level, and have significant implications for the development of anti-angiogenic therapies in the future.