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C Lengauer

Publications and source records attributed to C Lengauer.

At least 37 records · Page 2Linked to original sources
PubMed1999

Netrin-1: interaction with deleted in colorectal cancer (DCC) and alterations in brain tumors and neuroblastomas.

Netrins, a family of laminin-related secreted proteins, have critical roles in axon guidance and cell migration during development. The deleted in colorectal cancer (DCC) protein has been implicated as a netrin-1 receptor component. The expression and function of netrins in adult tissues remain unknown, and direct interaction of netrin-1 with DCC has not been demonstrated. We cloned the human netrin-1 (NTN1L) gene, mapped it to chromosome 17p12-13, and found that it encodes a 604 amino acid protein with 98% identity to mouse netrin-1 and 50% identity with the Caenorhabditis elegans UNC-6 protein. NTN1L transcripts were detected in essentially all normal adult tissues studied, and markedly reduced or absent NTN1L expression was seen in approximately 50% of brain tumors and neuroblastomas. In one neuroblastoma, missense mutations at highly conserved NTN1L codons were found. Netrin-1 protein could be cross-linked to DCC protein on the cell surface, but it did not immunoprecipitate with DCC in the absence of cross-linking and it failed to bind to a soluble fusion protein containing the entire DCC extracellular domain. Our findings demonstrating NTN1L loss of expression and mutations suggest that NTN1L alterations may contribute to the development of some cancers. Furthermore, the binding of netrin-1 to DCC appears to depend on the presence of a coreceptor or accessory proteins.

Amino Acid Sequence↗
PubMed1998

Genetic instabilities in human cancers.

Whether and how human tumours are genetically unstable has been debated for decades. There is now evidence that most cancers may indeed be genetically unstable, but that the instability exists at two distinct levels. In a small subset of tumours, the instability is observed at the nucleotide level and results in base substitutions or deletions or insertions of a few nucleotides. In most other cancers, the instability is observed at the chromosome level, resulting in losses and gains of whole chromosomes or large portions thereof. Recognition and comparison of these instabilities are leading to new insights into tumour pathogenesis.

Chromosome Aberrations↗
PubMed1998

Requirement for p53 and p21 to sustain G2 arrest after DNA damage.

After DNA damage, many cells appear to enter a sustained arrest in the G2 phase of the cell cycle. It is shown here that this arrest could be sustained only when p53 was present in the cell and capable of transcriptionally activating the cyclin-dependent kinase inhibitor p21. After disruption of either the p53 or the p21 gene, gamma radiated cells progressed into mitosis and exhibited a G2 DNA content only because of a failure of cytokinesis. Thus, p53 and p21 appear to be essential for maintaining the G2 checkpoint in human cells.

Apoptosis↗
PubMed1998

Mutations of mitotic checkpoint genes in human cancers.

Genetic instability was one of the first characteristics to be postulated to underlie neoplasia. Such genetic instability occurs in two different forms. In a small fraction of colorectal and some other cancers, defective repair of mismatched bases results in an increased mutation rate at the nucleotide level and consequent widespread microsatellite instability. In most colorectal cancers, and probably in many other cancer types, a chromosomal instability (CIN) leading to an abnormal chromosome number (aneuploidy) is observed. The physiological and molecular bases of this pervasive abnormality are unknown. Here we show that CIN is consistently associated with the loss of function of a mitotic checkpoint. Moreover, in some cancers displaying CIN the loss of this checkpoint was associated with the mutational inactivation of a human homologue of the yeast BUB1 gene; BUB1 controls mitotic checkpoints and chromosome segregation in yeast. The normal mitotic checkpoints of cells displaying microsatellite instability become defective upon transfer of mutant hBUB1 alleles from either of two CIN cancers.

Amino Acid Sequence↗
PubMed1998

Characterization of human FAST-1, a TGF beta and activin signal transducer.

We have identified a human homolog of the Xenopus forkhead activin signal transducer-1 (xFAST-1). Although significantly different in sequence from its Xenopus counterpart, hFAST-1 shared with xFAST-1 the ability to bind to human Smad2 and activate an activin response element (ARE). The hFAST-1-dependent activation of ARE was completely dependent on endogenous Smad4 and stimulation by a TGF beta-like ligand. The hFAST-1 protein was shown to bind to a novel DNA motif, TGT (G/T) (T/G)ATT, an exact copy of which was present within the ARE. A single copy of this motif could activate a reporter in a TGF beta-dependent fashion but only when an adjacent Smad-binding element was present in the construct. These data suggest that responses to TGF beta family members may be mediated by a DNA-binding complex formed by hFAST-1, hSmad2, and hSmad4.

Activins↗
PubMed1998

Somatic mutations of the mitochondrial genome in human colorectal tumours.

Alterations of oxidative phosphorylation in tumour cells were originally believed to have a causative role in cancerous growth. More recently, mitochondria have again received attention with regards to neoplasia, largely because of their role in apoptosis and other aspects of tumour biology. The mitochondrial genome is particularly susceptible to mutations because of the high level of reactive oxygen species (ROS) generation in this organelle, coupled with a low level of DNA repair. However, no detailed analysis of mitochondrial DNA in human tumours has yet been reported. In this study, we analysed the complete mtDNA genome of ten human colorectal cancer cell lines by sequencing and found mutations in seven (70%). The majority of mutations were transitions at purines, consistent with an ROS-related derivation. The mutations were somatic, and those evaluated occurred in the primary tumour from which the cell line was derived. Most of the mutations were homoplasmic, indicating that the mutant genome was dominant at the intracellular and intercellular levels. We showed that mitochondria can rapidly become homogeneous in colorectal cancer cells using cell fusions. These findings provide the first examples of homoplasmic mutations in the mtDNA of tumour cells and have potential implications for the abnormal metabolic and apoptotic processes in cancer.

Base Sequence↗
PubMed1998

Comparative genomic hybridization as part of a new diagnostic strategy in childhood hyperdiploid acute lymphoblastic leukemia.

The detailed definition of karyotype changes associated with hyperdiploid acute lymphoblastic leukemia (ALL) is a precondition for their exploitation in minimal residual disease studies with fluorescence in situ hybridization analysis (FISH). In addition, certain karyotype patterns may have different prognostic implications. We have therefore used comparative genomic hybridization (CGH) to analyze the quantitative karyotype abnormalities in 14 cases of hyperdiploid ALL and correlated the results with those obtained by flow cytometry and conventional cytogenetic analyses. Despite an overall good agreement between the karyotypes obtained by classical banding techniques and CGH, we came across at least one karyotype discrepancy per case. Clarification of the discordant findings with fluorescence in situ hybridization (FISH) showed that all stem lines had been correctly defined by CGH. In eight cases, however, cytogenetic analyses revealed structural abnormalities that were undetectable by CGH. The other discrepancies were mainly due to a cytogenetic misinterpretation of similar sized and shaped chromosomes. Based on these findings we present a new diagnostic strategy for childhood ALL that includes flow cytometry and classical cytogenetics as well as CGH for the analysis of aneuploid cases and FISH to resolve the unavoidable discrepancies.

Adolescent↗
PubMed1997

Genetic instability in colorectal cancers.

It has long been considered that genetic instability is an integral component of human neoplasia. In a small fraction of tumours, mismatch repair deficiency leads to a microsatellite instability at the nucleotide sequence level. In other tumours, an abnormal chromosome number (aneuploidy) has suggested an instability, but the nature and magnitude of the postulated instability is a matter of conjecture. We show here that colorectal tumours without microsatellite instability exhibit a striking defect in chromosome segregation, resulting in gains or losses in excess of 10(-2) per chromosome per generation. This form of chromosomal instability reflected a continuing cellular defect that persisted throughout the lifetime of the tumour cell and was not simply related to chromosome number. While microsatellite instability is a recessive trait, chromosomal instability appeared to be dominant. These data indicate that persistent genetic instability may be critical for the development of all colorectal cancers, and that such instability can arise through two distinct pathways.

Aneuploidy↗
PubMed1997

DNA methylation and genetic instability in colorectal cancer cells.

Apparent alterations in DNA methylation have been observed in many cancers, but whether such alterations represent a persistent alteration in the normal methylation process is not known. In this study, we report a striking difference in the expression of exogenously introduced retroviral genes in various colorectal cancer cell lines. Extinguished expression was associated with DNA methylation and could be reversed by treatment with the demethylating agent 5-azacytidine. A striking correlation between genetic instability and methylation capacity suggested that methylation abnormalities may play a role in chromosome segregation processes in cancer cells.

Azacitidine↗
PubMed1997

14-3-3sigma is a p53-regulated inhibitor of G2/M progression.

Exposure of colorectal cancer (CRC) cells to ionizing radiation results in a cell-cycle arrest in G1 and G2. The G1 arrest is due to p53-mediated induction of the cyclin-dependent kinase inhibitor p21WAF1/CIP1/SDI1, but the basis for the G2 arrest is unknown. Through a quantitative analysis of gene expression patterns in CRC cell lines, we have discovered that 14-3-3sigma is strongly induced by gamma irradiation and other DNA-damaging agents. The induction of 14-3-3sigma is mediated by a p53-responsive element located 1.8 kb upstream of its transcription start site. Exogenous introduction of 14-3-3sigma into cycling cells results in a G2 arrest. As the fission yeast 14-3-3 homologs rad24 and rad25 mediate similar checkpoint effects, these results document a molecular mechanism for G2/M control that is conserved throughout eukaryotic evolution and regulated in human cells by p53.

14-3-3 Proteins↗
PubMed1996

Mammalian cells resistant to tumor suppressor genes.

Expression of p53 causes growth arrest or apoptosis in many normal and neoplastic cell types, but the relationship between these two effects has remained obscure. To begin to dissect the underlying mechanisms at a genetic level, we have generated mutant cells resistant to the action of wild-type p53. Rat embryo fibroblasts transformed with ras and a temperature-sensitive p53 (tsp53(135val)) gene were chemically mutagenized and selected for growth at a temperature at which p53 adopts a wild-type conformation (31.5 degrees C). Clones that grew exponentially at 31.5 degrees C were selected. Cell fusion experiments demonstrated that the mutations conferring resistance to p53-mediated growth arrest were dominant. The mutagenized clones were resistant not only to p53-mediated growth arrest, but also to the apoptosis induced by E1A in conjunction with p53, and partially resistant to the retinoblastoma tumor suppressor, pRB. The results suggest that a single downstream pathway can control the induction of growth arrest and apoptosis, and that both p53 and RB function through this pathway.

Adenovirus E1A Proteins↗
PubMed1996

Uncoupling of S phase and mitosis induced by anticancer agents in cells lacking p21.

Precise coordination of the S and M phases of the eukaryotic cell cycle is critical not only for normal cell division, but also for effective growth arrest under conditions of stress. When damaged, a cell must communicate signals to both the mitotic and DNA synthesis machineries so that a mitotic block is not followed by an extra S phase, or vice versa. The biochemical mechanisms regulating this coordination, termed checkpoints, have been identified in lower eukaryotes, but are largely unknown in mammalian cells. Here we show that p21 WAF1/CIP1, the prototype inhibitor of cyclin-dependent kinases (CDKs), is required for this coordination in human cells. In the absence of p21, DNA-damaged cells arrest in a G2-like state, but then undergo additional S phases without intervening normal mitoses. They thereby acquire grossly deformed, polyploid nuclei and subsequently die through apoptosis. Perhaps not by coincidence, the DNA-damaging agents that can cause S/M uncoupling are used in the clinic to kill cancer cells preferentially.

Antineoplastic Agents↗
PubMed1996

Evaluation of candidate tumour suppressor genes on chromosome 18 in colorectal cancers.

Chromosome deletions are the most common genetic events observed in cancer. These deletions are generally thought to reflect the existence of a tumour suppressor gene within the lost region. However, when the lost region does not precisely coincide with a hereditary cancer locus, identification of the putative tumour suppressor gene (target of the deletion) can be problematic. For example, previous studies have demonstrated that chromosome 18q is lost in over 60% of colorectal as well as in other cancers, but the lost region could not be precisely determined. Here we present a rigorous strategy for mapping and evaluating allelic deletions in sporadic tumours, and apply it to the evaluation of chromosome 18 in colorectal cancers. Using this approach, we define a minimally lost region (MLR) on chromosome 18q21, which contains at least two candidate tumour suppressor genes, DPC4 and DCC. The analysis further suggested genetic heterogeneity, with DPC4 the deletion target in up to a third of the cases and DCC or a neighbouring gene the target in the remaining tumours.

Alleles↗
PubMed1995

Multiple genetic loci within 11p15 defined by Beckwith-Wiedemann syndrome rearrangement breakpoints and subchromosomal transferable fragments.

Beckwith-Wiedemann syndrome (BWS) involves fetal overgrowth and predisposition to a wide variety of embryonal tumors of childhood. We have previously found that BWS is genetically linked to 11p15 and that this same band shows loss of heterozygosity in the types of tumors to which children with BWS are susceptible. However, 11p15 contains > 20 megabases, and therefore, the BWS and tumor suppressor genes could be distinct. To determine the precise physical relationship between these loci, we isolated yeast artificial chromosomes, and cosmid libraries from them, within the region of loss of heterozygosity in embryonal tumors. Five germ-line balanced chromosomal rearrangement breakpoint sites from BWS patients, as well as a balanced chromosomal translocation breakpoint from a rhabdoid tumor, were isolated within a 295- to 320-kb cluster defined by a complete cosmid contig crossing these breakpoints. This breakpoint cluster terminated approximately 100 kb centromeric to the imprinted gene IGF2 and 100 kb telomeric to p57KIP2, an inhibitor of cyclin-dependent kinases, and was located within subchromosomal transferable fragments that suppressed the growth of embryonal tumor cells in genetic complementation experiments. We have identified 11 transcribed sequences in this BWS/tumor suppressor coincident region, one of which corresponded to p57KIP2. However, three additional BWS breakpoints were > 4 megabases centromeric to the other five breakpoints and were excluded from the tumor suppressor region defined by subchromosomal transferable fragments. Thus, multiple genetic loci define BWS and tumor suppression on 11p15.

Base Sequence↗
PubMed1995

Determination and regional assignment of grouped sets of microclones in chromosome 1pter-p35.

In an approach to mapping physically the most distal 30 Mb of human chromosome 1p, region-specific clone libraries were generated by microdissection and microcloning. PFGE blot hybridization of single or low-copy microclones against rare-cutter digests of genomic DNA revealed physical linkage for groups of markers. Supplementary PFGE analysis of 31 1p36-p35-specific probes for genetically mapped loci established a total of 15 grouped sets, consisting of altogether 69 markers. Twelve of the grouped sets were located in 1pter-p36.12, as revealed by microcell hybrid mapping; the remaining three were localized proximal to 1p36.12. Regional assignment and ordering of most grouped sets was achieved either by evaluating the included genetic markers or by fluorescence in situ hybridization of representative probes. The genomic extent of individual grouped sets encompassed between 1100 and 2100 kb, covering a total of approximately 22 Mb of the distal chromosome 1p region. One particular grouped set was shown to contain seven polymorphic marker loci that were previously suggested to be distributed across the entire 1pter-p35 region. The increase in the number of hybridization marker probes in 1p36 and their physical mapping is expected to facilitate positional cloning experiments in this region; in particular, the construction of clone contigs may be greatly facilitated.

Blotting, Southern↗
PubMed1995

Cdc6 is an unstable protein whose de novo synthesis in G1 is important for the onset of S phase and for preventing a 'reductional' anaphase in the budding yeast Saccharomyces cerevisiae.

S phase entry depends on cyclin-dependent kinases whose activation during late G1 due partly to the synthesis of unstable cyclin subunits. We identify here a second type of unstable protein, Cdc6, whose synthesis during G1 is important for initiation of DNA replication. The CDC6 gene is normally transcribed at the end of mitosis, but in cells with a prolonged G1 phase there is a second burst of transcription in late G1. The former is due to Swi5, while the latter is due to MBF or SBF transcription factors. Small G1 cells that cannot synthesize Cdc6 in late G1 progress through S phase very slowly. Cells that transcribe CDC6 neither at the end of mitosis nor in late G1 fail to replicate DNA but, despite this, undergo mitosis and produce daughter cells with fractional DNA contents. This 'reductional' anaphase occurs with almost wild-type kinetics and depends on the activity of G2 cyclins. Thus, cells that fail to duplicate chromosomes due to a cdc6 defect cannot prevent the onset of mitosis, unlike other mutants with replication defects. We show, by fluorescence in situ hybridization, that chromosomes which remain unduplicated due to a lack of Cdc6 synthesis are segregated intact to spindle poles during the 'reductional' anaphase.

Anaphase↗