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Biomedical subjects

Carlo Rago

Publications and source records attributed to Carlo Rago.

11 recordsLinked to original sources
PubMed2006

Hypoxia-inducible factor-1alpha promotes nonhypoxia-mediated proliferation in colon cancer cells and xenografts.

Hypoxia-inducible factor-1alpha (HIF-1alpha) is a transcription factor that directly transactivates genes important for the growth and metabolism of solid tumors. HIF-1alpha is overexpressed in cancer, and its level of expression is correlated with patient mortality. Increased synthesis or stability of HIF-1alpha can be induced by hypoxia-dependent or hypoxia-independent factors. Thus, HIF-1alpha is expressed in both nonhypoxic and hypoxic cancer cells. The role of HIF-1alpha in nonhypoxia-mediated cancer cell proliferation remains speculative. We have disrupted HIF-1alpha by targeted homologous recombination in HCT116 and RKO human colon cancer cells. Loss of HIF-1alpha significantly reduced nonhypoxia-mediated cell proliferation in vitro and in vivo. Paradoxically, loss of HIF-1alpha expression did not grossly affect the hypoxic compartments within tumor xenografts in vivo, although HIF-1alpha promoted cell proliferation and survival under hypoxia in vitro. To further test the role of HIF-1alpha within tumor compartments, we generated cells with combined disruptions of both HIF-1alpha and vascular endothelial growth factor (VEGF). In all xenografts, disruption of VEGF led to marked expansion of the hypoxic compartments and growth delay. Nonetheless, the presence or absence of HIF-1alpha did not grossly affect these expanded hypoxic compartments. These data provide compelling evidence that, in a subset of colon cancers, (a) HIF-1alpha is a positive factor for nonhypoxia-mediated cell proliferation in vitro and in vivo and (b) HIF-1alpha is a positive factor for cell proliferation and survival under hypoxic conditions in vitro, but does not grossly contribute to the tumor hypoxic compartments in vivo.

Animals↗
PubMed2006

Targeted disruption of FANCC and FANCG in human cancer provides a preclinical model for specific therapeutic options.

BACKGROUND & AIMS: How specifically to treat pancreatic and other cancers harboring Fanconi anemia gene mutations has raised great interest recently, yet preclinical studies have been hampered by the lack of well-controlled human cancer models. METHODS: We endogenously disrupted FANCC and FANCG in a human adenocarcinoma cell line and determined the impact of these genes on drug sensitivity, irradiation sensitivity, and genome maintenance. RESULTS: FANCC and FANCG disruption abrogated FANCD2 monoubiquitination, confirming an impaired Fanconi anemia pathway function. On treatment with DNA interstrand-cross-linking agents, FANCC and FANCG disruption caused increased clastogenic damage, G2/M arrest, and decreased proliferation. The extent of hypersensitivity varied among agents, with ratios of inhibitory concentration 50% ranging from 2-fold for oxaliplatin to 14-fold for melphalan, a drug infrequently used in solid tumors. No hypersensitivity was observed on gemcitabine, etoposide, 3-aminobenzamide, NU1025, or hydrogen peroxide. FANCC and FANCG disruption also resulted in increased clastogenic damage on irradiation, but only FANCG disruption caused a subsequent decrease in relative survival. Finally, FANCC and FANCG disruption increased spontaneous chromosomal breakage, supporting the role of these genes in genome maintenance and likely explaining why they are mutated in sporadic cancer. CONCLUSIONS: Our human cancer cell model provides optimal controls to elucidate fundamental biologic features of individual Fanconi anemia gene defects and facilitates preclinical studies of therapeutic options. The impact of Fanconi gene defects on drug and irradiation sensitivity renders these genes promising targets for a specific, genotype-based therapy for individual cancer patients, providing a strong rationale for clinical trials.

Adenocarcinoma↗
PubMed2005

Glutathione S-transferase pi1 promotes tumorigenicity in HCT116 human colon cancer cells.

GSTP1 is a member of the glutathione S-transferase enzyme superfamily, which catalyzes the conjugation of electrophiles with glutathione in the process of detoxification. GSTP1 is widely overexpressed in colorectal cancer, from aberrant crypt foci to advanced carcinomas. Increased expression of GSTP1 is associated with multidrug resistance and a worse clinical prognosis. However, GSTP1-null mice have an increased risk of tumor formation. Thus, the biological function of GSTP1 in colorectal cancer biology remains speculative. In an effort to gain further insights into the role of GSTP1 in tumorigenesis, we disrupted the GSTP1 gene in HCT116 human colorectal cancer cells using targeted homologous recombination. We find that loss of GSTP1 resulted in impaired clonogenic survival and proliferation. Specifically, under growth-limiting conditions, (a) GSTP1 protected HCT116 cells from oxidative stress and associated apoptosis and (b) promoted mitogen-activated protein kinase-extracellular signal-regulated kinase kinase/extracellular signal-regulated kinase-mediated G1-S cell cycle progression. In vivo, GSTP1 was critical for engraftment and growth of HCT116 tumor xenografts. These studies directly show that GSTP1 promotes clonogenic survival and proliferation in HCT116 human colon cancer cells.

Animals↗
PubMed2005

Mutant PIK3CA promotes cell growth and invasion of human cancer cells.

PIK3CA is mutated in diverse human cancers, but the functional effects of these mutations have not been defined. To evaluate the consequences of PIK3CA alterations, the two most common mutations were inactivated by gene targeting in colorectal cancer (CRC) cells. Biochemical analyses of these cells showed that mutant PIK3CA selectively regulated the phosphorylation of AKT and the forkhead transcription factors FKHR and FKHRL1. PIK3CA mutations had little effect on growth under standard conditions, but reduced cellular dependence on growth factors. PIK3CA mutations resulted in attenuation of apoptosis and facilitated tumor invasion. Treatment with the PI3K inhibitor LY294002 abrogated PIK3CA signaling and preferentially inhibited growth of PIK3CA mutant cells. These data have important implications for therapy of cancers harboring PIK3CA alterations.

Amino Acid Substitution↗
PubMed2005

Combined laser capture microdissection and serial analysis of gene expression from human tissue samples.

Cell-specific gene expression profiling from heterogeneous human tissues is confounded by cell purification limitations. Here, we describe a technique to generate gene expression profiles of pure populations of prostate cancer cells obtained from fresh-frozen prostatectomy specimens and small initial quantities of RNA by combining laser capture microdissection and microserial analysis of gene expression (LCM-microSAGE). Two microSAGE libraries were obtained from approximately 100,000 laser pulses, estimated to contain fewer than 3 x 10(5) cells and 20-30 ng mRNA. Two libraries were sequenced to a depth of 10,111 and 10,463 unique tags from normal and cancer cells, representing 6453 and 6923 genes, respectively. Most transcripts were expressed at similar levels, but cancer cells compared with normal cells had increased expression of 385 tags and decreased expression of 389 tags. A total of 20 genes were differentially expressed (P<0.05); five of these genes were upregulated and 15 were downregulated in cancer cells. Quantitative reverse transcriptase-polymerase chain reaction results from three selected genes corroborated the existence of cell-specific gene expression in LCM-microSAGE-derived libraries. In conclusion, the LCM-microSAGE approach demonstrates that large-scale expression profiles of known and unknown transcripts can be generated from pure populations of target cells obtained from human tissue samples comprised of heterogeneous mixtures of cell types.

Gene Expression Profiling↗
PubMed2004

X-linked inhibitor of apoptosis protein (XIAP) is a nonredundant modulator of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-mediated apoptosis in human cancer cells.

Although the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has been shown to play an important role in the immunosurveillance of neoplasia, apoptotic factors that modulate the sensitivity of cancer cells to TRAIL are poorly understood. The inhibitor of apoptosis proteins (IAPs) have generated considerable interest as potential targets for cancer therapy, but the lack of a phenotype in X-linked IAP (XIAP) knockout mice has generated speculation that IAP function may be redundant. Using gene targeting technology, we show that disruption of the gene encoding XIAP in human cancer cells did not interfere with basal proliferation, but caused a remarkable sensitivity to TRAIL. These results demonstrate that XIAP is a nonredundant modulator of TRAIL-mediated apoptosis and provide a rationale for XIAP as a therapeutic target.

Apoptosis↗
PubMed2004

Inactivation of hCDC4 can cause chromosomal instability.

Aneuploidy, an abnormal chromosome number, has been recognized as a hallmark of human cancer for nearly a century; however, the mechanisms responsible for this abnormality have remained elusive. Here we report the identification of mutations in hCDC4 (also known as Fbw7 or Archipelago) in both human colorectal cancers and their precursor lesions. We show that genetic inactivation of hCDC4, by means of targeted disruption of the gene in karyotypically stable colorectal cancer cells, results in a striking phenotype associated with micronuclei and chromosomal instability. This phenotype can be traced to a defect in the execution of metaphase and subsequent transmission of chromosomes, and is dependent on cyclin E--a protein that is regulated by hCDC4 (refs 2-4). Our data suggest that chromosomal instability is caused by specific genetic alterations in a large fraction of human cancers and can occur before malignant conversion.

Aneuploidy↗
PubMed2004

Facile methods for generating human somatic cell gene knockouts using recombinant adeno-associated viruses.

Emerging evidence suggests that recombinant adeno-associated viral (rAAV) vectors can be used for specific gene targeting in human somatic cells. We have developed an rAAV vector construction procedure employing fusion PCR and a single cloning step that considerably simplifies the knockout process. We demonstrate its utility by disrupting genes at specific positions within human colon cancer cells as well as within immortalized normal epithelial cells. This technology should be broadly applicable to in vitro studies that require the manipulation of the human genome.

Cell Line↗
PubMed2002

Prevalence of somatic alterations in the colorectal cancer cell genome.

Although a small fraction of human cancers have increased rates of somatic mutation because of known deficiencies in DNA repair, little is known about the prevalence of somatic alterations in the vast majority of human cancers. To systematically assess nonsynonymous somatic alterations in colorectal neoplasia, we used DNA sequencing to analyze approximately 3.2 Mb of coding tumor DNA comprising 1,811 exons from 470 genes. In total, we identified only three distinct somatic mutations, comprising two missense changes and one 14-bp deletion, each in a different gene. The accumulation of approximately one nonsynonymous somatic change per Mb of tumor DNA is consistent with a rate of mutation in tumor cells that is similar to that of normal cells. These data suggest that most sporadic colorectal cancers do not display a mutator phenotype at the nucleotide level. They also have significant implications for the interpretation of somatic mutations in candidate tumor-suppressor genes.

Colorectal Neoplasms↗
PubMed2002

Using the transcriptome to annotate the genome.

A remaining challenge for the human genome project involves the identification and annotation of expressed genes. The public and private sequencing efforts have identified approximately 15,000 sequences that meet stringent criteria for genes, such as correspondence with known genes from humans or other species, and have made another approximately 10,000-20,000 gene predictions of lower confidence, supported by various types of in silico evidence, including homology studies, domain searches, and ab initio gene predictions. These computational methods have limitations, both because they are unable to identify a significant fraction of genes and exons and because they are unable to provide definitive evidence about whether a hypothetical gene is actually expressed. As the in silico approaches identified a smaller number of genes than anticipated, we wondered whether high-throughput experimental analyses could be used to provide evidence for the expression of hypothetical genes and to reveal previously undiscovered genes. We describe here the development of such a method--called long serial analysis of gene expression (LongSAGE), an adaption of the original SAGE approach--that can be used to rapidly identify novel genes and exons.

DNA, Complementary↗