Detection of codon 12 mutation in the k-ras oncogene in pancreatic tumors

Mutations at codons 12, 13, or 61 of the H-ras, K-ras, and N-ras have been detected in human neoplasias by a variety of techniques. Some of these techniques are very sensitive and can detect K-ras mutation in 90% of the cases of pancreatic adenocarcinomas. We analyzed 11 samples of pancreatic adenocarcinoma, three samples of pancreatic mucinous cystadenoma, and two samples without tumors in formalin-fixed paraffin embedded tissue sections. K-ras mutations at codon 12 were detected by a two-step PCR-enriched technique in all the samples of pancreatic adenocarcinoma, but not in cystadenoma or control samples. This technique may be useful for early detection of pancreatic cancer.

The type of K-ras mutation determines prognosis in colorectal cancer.

BACKGROUND: Mutations involving the oncogene K-ras in colorectal cancer may be related to tumor aggressiveness. However, the value of K-ras gene determination as a prognostic marker has not been clearly established. PATIENTS AND METHODS: The results from 98 patients recruited in a prospective study analyzing the effect of a K-ras mutation as a prognostic factor in colorectal cancer are reported. RESULTS: Disease-free (P = 0.02) and overall survival (P = 0.03) were significantly reduced for patients harboring a K-ras mutation. Two specific mutations demonstrated a significantly increased risk of disease recurrence, namely, 12-TGT (P = 0.04) and 13-GAC substitutions (P = 0.002). Patients with either of these substitutions had a 2-year disease-free survival rate of 37% compared with that of 67% for the group of patients harboring any other mutation type or a wild-type status (P = 0.01). CONCLUSIONS: The results herein presented suggest that K-ras acts as a prognostic factor in colorectal cancer and that this effect is probably related to a limited number of defined mutations.

Spectrum of K ras mutations in Pakistani colorectal cancer patients

The incidence of colorectal cancer (CRC) is increasing daily worldwide. Although different aspects of CRC have been studied in other parts of the world, relatively little or almost no information is available in Pakistan about different aspects of this disease at the molecular level. The present study was aimed at determining the frequency and prevalence of K ras gene mutations in Pakistani CRC patients. Tissue and blood samples of 150 CRC patients (64% male and 36% female) were used for PCR amplification of K ras and detection of mutations by denaturing gradient gel electrophoresis, restriction fragment length polymorphism analysis, and nucleotide sequencing. The K ras mutation frequency was found to be 13%, and the most prevalent mutations were found at codons 12 and 13. A novel mutation was also found at codon 31. The dominant mutation observed was a G to A transition. Female patients were more susceptible to K ras mutations, and these mutations were predominant in patients with a nonmetastatic stage of CRC. No significant differences in the prevalence of K ras mutations were observed for patient age, gender, or tumor type. It can be inferred from this study that Pakistani CRC patients have a lower frequency of K ras mutations compared to those observed in other parts of the world, and that K ras mutations seemed to be significantly associated with female patients.

Arginine vasopressin controls p27(KiP1) protein expression by PKC activation and irreversibly inhibits the proliferation of K-Ras-dependent mouse Y1 adrenocortical malignant cells

The neurohypophyseal hormone arginine vasopressin (AVP) is a classic mitogen in many cells. In K-Ras-dependent mouse Y1 adrenocortical malignant cells, AVP elicits antagonistic responses such as the activation of the PKC and the ERK1/2 mitogenic pathways to down-regulate cyclin D1 gene expression, which induces senescence-associated beta-galactosidase (SA-beta Gal) and leads to cell cycle arrest. Here, we report that in the metabolic background of Y1 cells, PKC activation either by AVP or by PMA inhibits the PI3K/Akt pathway and stabilises the p27(Kip1) protein even in the presence of the mitogen fibroblast growth factor 2 (FGF2). These results suggest that p27(Kip1) is a critical signalling node in the mechanisms underlying the survival of the Y1 cells. In Y1 cells that transiently express wild-type p27(Kip1), AVP caused a severe reduction in cell survival, as shown by clonogenic assays. However, AVP promoted the survival of Y1 cells transiently expressing mutant p27-S10A or mutant p27-T187A, which cannot be phosphorylated at Ser10 and Thr187, respectively. In addition, PKC activation by PMA mimics the toxic effect caused by AVP in Y1 cells, and inhibition of PKC completely abolishes the effects caused by both PMA and AVP in clonogenic assays. The vulnerability of Y1 cells during PKC activation is a phenotype conditioned upon K-ras oncogene amplification because K-Ras down-regulation with an inducible form of the dominant-negative mutant H-RasN17 has resulted in Y1 cells that are resistant to AVP`s deleterious effects. These data show that the survival destabilisation of K-Ras-dependent Y1 malignant cells by AVP requires large quantities of the p27(Kip1) protein as well as phosphorylation of the p27(Kip1) protein at both Ser10 and Thr187. (C) 2011 Elsevier B.V. All rights reserved.

v-K-ras leads to preferential farnesylation of p21ras in FRTL-5 cells: Multiple interference with the isoprenoid pathway

The isoprenoid pathway in FRTL-5 thyroid cells was found to be deeply altered on transformation with v-K-ras. A dramatic overall reduction of protein prenylation was found in v-K-ras-transformed cells in comparison with the parent FRTL-5 cells, as shown by labeling cells with [3H]mevalonic acid. This phenomenon was accompanied by a relative increase of p21ras farnesylation and by a decrease of the ratio between the amounts of geranylgeraniol and farnesol bound to prenylated proteins. Analysis of protein prenylation in FRTL-5 cells transformed by a temperature-sensitive mutant of the v-K-ras oncogene indicated that these variations represent an early and specific marker of active K-ras. Conversely, FRTL-5 cells transformed with Harvey-ras showed a pattern of [3H]-mevalonate (MVA)-labeled proteins similar to that of nontransformed cells. The K-ras oncogene activation also resulted in an overall decrease of [3H]-MVA incorporation into isopentenyl-tRNA together with an increase of unprocessed [3H]-MVA and no alteration in [3H]-MVA uptake. The effects of v-K-ras on protein prenylation could be mimicked in FRTL-5 cells by lowering the concentration of exogenous [3H]-MVA whereas increasing the [3H]-MVA concentration did not revert the alterations observed in transformed cells. Accordingly, v-K-ras expression was found to: (i) down-regulate mevalonate kinase; (ii) induce farnesyl-pyrophosphate synthase expression; and (iii) augment protein farnesyltransferase but not protein geranylgeranyl-transferase-I activity. Among these events, mevalonate kinase down-regulation appeared to be related strictly to differential protein prenylation. This study represents an example of how expression of the v-K-ras oncogene, through multiple interferences with the isoprenoid metabolic pathway, may result in the preferential farnesylation of the ras oncogene product p21ras.

PCR bias toward the wild-type k-ras and p53 sequences: Implications for PCR detection of mutations and cancer diagnosis

PCR-based cancer diagnosis requires detection of rare mutations in k-ras, p53 or other genes. The assumption has been that mutant and wild-type sequences amplify with near equal efficiency, so that they are eventually present in proportions representative of the starting material. Work factor IX suggests that this assumption is invalid for one case of near-sequence identity To test the generality of this phenomenon and its relevance to cancer diagnosis, primers distant from point mutations in p53 and k-ras were used to amplify, wild-type and mutant sequences from these genes. A substantial bias against PCR amplification of mutants was observed for two regions of the p53 gene and one region of k-ras. For kras and p53, bias was observed when the wild-type and mutant sequences were amplified separately or when mixed in equal proportions before PCR. Bias was present with proofreading and non-proofreading polymerases. Mutant and wild-type segments of the factor V cystic fibrosis transmembrane conductance regulator and prothrombin genes were amplified and did not exhibit PCR bias. Therefore, the assumption of equal PCR efficiency for point mutant and wild-type sequences is invalid in several systems. Quantitative or diagnostic PCR will require validation for each locus, and enrichment strategies may be needed to optimize detection of mutants.

H-Ras signaling and K-Ras signaling are differentially dependent on endocytosis

dEndocytosis is required for efficient mitogen-activated protein kinase (MAPK) activation by activated growth factor receptors. We examined if H-Ras and K-Ras proteins, which are distributed across different plasma membrane microdomains, have equal access to the endocytic compartment and whether this access is necessary for downstream signaling. Inhibition of endocytosis by dominant interfering dynamin-K44A blocked H-Ras but not K-Ras-mediated PC12 cell differentiation and selectively inhibited H-Ras- but not K-Ras-mediated Raf-1 activation in BHK cells. H-Ras- but not K-Ras-mediated Raf-1 activation was also selectively dependent on phosphoinositide 3-kinase activity. Stimulation of endocytosis and endocytic recycling by wildtype Rab5 potentiated H-Ras-mediated Raf-1 activation. In contrast, Rab5-Q79L, which stimulates endocytosis but not endocytic recycling, redistributed activated H-Ras from the plasma membrane into enlarged endosomes and inhibited H-Ras-mediated Raf-1 activation. Rab5-Q79L expression did not cause the accumulation of wild-type H-Ras in enlarged endosomes. Expression of wild-type Rab5 or Rab5-Q79L increased the specific activity of K-Ras-activated Raf-1 but did not result in any redistribution of K-Ras from the plasma membrane to endosomes. These results show that H-Ras but not K-Ras signaling though the Raf/MEK/MAPK cascade requires endocytosis and enclocytic recycling. The data also suggest a mechanism for returning Raf-1 to the cytosol after plasma membrane recruitment.

Síntesi de siRNAs (short interfering RNAs) modificats amb nucleobases 5-metil i 5-propinil pirimidíniques i avaluació de la seva activitat in vitro en cultius cel•lulars i de la seva estabilitat en sèrum humà. Disseny de siRNAs dirigits a la inhibició de l'expressió de mutacions de l'oncogen K-ras.

Projecte de recerca elaborat a partir d’una estada a la Stanford University, EEUU, entre 2007 i 2009. El present projecte es basa 1) en la síntesi de cadenes d'ARN dirigides a la inhibició de l'expressió gènica per un mecanisme d'ARN d'interferència (siRNAs o short interefering RNAs) i 2) en l'avaluació de l'activitat in vitro d'aquests oligonucleòtids en cultius cel•lulars. Concretament, la meva recerca ha estat enfocada principalment a l'estudi de cadenes de siRNA modificades amb nucleobases 5-metil i 5-propinil pirimidíniques. Es tractava d'avaluar l'efecte que exerceixen els factors estèrics en el major groove (solc major) dels siRNAs sobre la seva activitat biològica. En aquest sentit, he dut aterme síntesi de fosforamidits de nucleòsis pirimidínics modificats a la posició C-5 de la nucleobase. A continuació he incorporat aquestes unitats nucleosídiques en cadenes d'ARN emprant un sintetitzador d’ADN/ARN i he estudiat l'estabilitat dels corresponents dúplexs d'ARN mitjançant experiments de desnaturalització tèrmica. Finalment he dut a terme experiments d'inhibició de l'expressió gènica en cèl.lules HeLa per tal d'avaluar l'activitat biològia d'aquests siRNAs modificats. Els resultats d'aquests estudis han posat de manifest que la presència de grups voluminosos com el propinil a l'extrem 5' del dúplex de siRNA (definit per la cadena guia o antisense) influeix de forma molt negativa en la seva activitat biològica. En canvi, grups menys voluminosos com el metil hi influeixen positivament, de manera que algunes de les cadenes sintetitzades han resultat ser més actives que els corresponents siRNAs naturals (wild type siRNAs). A més, aquest tipus de modificació contribueix positivament en l'estabilitat de cadenes de siRNA en sèrum humà. Aquest treball ha estat publicat (Terrazas, M.; Kool, E.T. "Major Groove Modifications Improve siRNA Stability and Biological Activity" Nucleic Acids Res. 2009, in press).

Evidence for different expression profiles for c-Met, EGFR, PTEN and the mTOR pathway in low and high grade endometrial carcinomas in a cohort of consecutive women. Occurrence of PIK3CA and K-Ras mutations and microsatellite instability.

Molecular and genetic investigations in endometrial carcinogenesis may have prognostic and therapeutic implications. We studied the expression of EGFR, c-Met, PTEN and the mTOR signalling pathway (phospho-AKT/phospho-mTOR/phospho-RPS6) in 69 consecutive tumours and 16 tissue microarrays. We also analysed PIK3CA, K-Ras mutations and microsatellite instability (MSI). We distinguished two groups: group 1 (grade 1 and 2 endometrioid cancers) and group 2 (grade 3 endometrioid and type II clear and serous cell cancers). We hypothesised that these histological groups might have different features. We found that a) survival was higher in group 1 with less aggressive tumours (P⟨0.03); b) EGFR (P=0.01), PTEN and the AKT/mTOR/RPS6 signalling pathway were increased in group 1 versus group 2 (P=0.05 for phospho-mTOR); c) conversely, c-Met was higher (P⟨0.03) in group 2 than in group 1; d) In group 1, EGFR was correlated with c-Met, phospho-mTOR, phospho-RPS6 and the global activity of the phospho-AKT/phospho-mTOR/phospho-RPS6 pathway. In group 2, EGFR was correlated only with the phospho-AKT/phospho-mTOR/phospho-RPS6 pathway, whereas c-Met was correlated with PTEN; e) survival was higher for tumours with more than 50% PTEN-positive cells; f) K-RAS and PIK3CA mutations occurred in 10-12% of the available tumours and MSI in 40.4%, with a loss of MLH1 and PMS2 expression. Our results for endometrial cancers provide the first evidence for a difference in status between groups 1 and 2. The patients may benefit from different targeted treatments, anti-EGFR agents and rapamycin derivatives (anti-mTOR) for group 1 and an anti c-MET/ligand complex for group 2.

Oncogenic K-Ras segregates at spatially distinct plasma membrane signaling platforms according to its phosphorylation status

Activating mutations in the K-Ras small GTPase are extensively found in human tumors. Although these mutations induce the generation of a constitutively GTP-loaded, active form of K-Ras, phosphorylation at Ser181 within the C-terminal hypervariable region can modulate oncogenic K-Ras function without affecting the in vitro affinity for its effector Raf-1. In striking contrast, K-Ras phosphorylated at Ser181 shows increased interaction in cells with the active form of Raf-1 and with p110α, the catalytic subunit of PI 3-kinase. Because the majority of phosphorylated K-Ras is located at the plasma membrane, different localization within this membrane according to the phosphorylation status was explored. Density-gradient fractionation of the plasma membrane in the absence of detergents showed segregation of K-Ras mutants that carry a phosphomimetic or unphosphorylatable serine residue (S181D or S181A, respectively). Moreover, statistical analysis of immunoelectron microscopy showed that both phosphorylation mutants form distinct nanoclusters that do not overlap. Finally, induction of oncogenic K-Ras phosphorylation - by activation of protein kinase C (PKC) - increased its co-clustering with the phosphomimetic K-Ras mutant, whereas (when PKC is inhibited) non-phosphorylated oncogenic K-Ras clusters with the non-phosphorylatable K-Ras mutant. Most interestingly, PI 3-kinase (p110α) was found in phosphorylated K-Ras nanoclusters but not in non-phosphorylated K-Ras nanoclusters. In conclusion, our data provide - for the first time - evidence that PKC-dependent phosphorylation of oncogenic K-Ras induced its segregation in spatially distinct nanoclusters at the plasma membrane that, in turn, favor activation of Raf-1 and PI 3-kinase.

Freqüência de mutação no códon 12 do gene K-ras no carcinoma ductal invasivo de mama

Objetivo: pesquisar a freqüência de mutação pontual no códon 12 do gene K-ras, em espécimes cirúrgicos de pacientes portadoras de carcinoma ductal invasivo de mama. Material e Métodos: foram utilizados cortes de 50 espécimes cirúrgicos incluídos em blocos de parafina, de pacientes portadoras de carcinoma ductal invasivo de mama, com graus histológicos II e III. Os cortes destinados ao estudo foram desparafinizados e submetidos a extração do DNA, por meio do emprego da proteinase K. Para a amplificação do fragmento a ser analisado, utilizou-se a reação em cadeia da polimerase, seguida por clivagem com o emprego de enzima de restrição de comprimento variável (RFLP). A verificação da presença de mutação nas amostras foi feita com o emprego de eletroforese em gel de agarose, com marcador de peso molecular "Ladder 123" (GIBCO-BRL), e a documentação dos resultados, mediante fotografia, utilizando-se luz ultravioleta transmitida. Resultados: em cinco dos 50 carcinomas ductais invasivos de mama estudados (10%) constatou-se a presença de mutação no códon 12 do gene K-ras, sendo todas elas polimórficas para esse caráter. As afetadas pelos tumores, que apresentavam a referida mutação, encontravam-se na pós-menopausa. Em quatro dos cinco casos em que se constatou a mutação, o grau histológico dos tumores era II e no caso restante III.

Detección de mutaciones en el oncogen k - ras en neoplasias epiteliales colorrectales

Tesis (Maestría en Ciencias con Especialidad en Biología Molecular e Ingenieria Genética) UANL

Rôles de K-RAS et de ERCC1 dans le traitement des carcinomes épidermoïdes avancés de la tête et du cou traités par chimioradiothérapie concomitante

Introduction: Les mutations du gène RAS sont présentes dans plusieurs types de cancers et ont une influence sur la réponse à la chimiothérapie. Excision repair cross- complementation group 1 (ERCC1) est un gène impliqué dans la réparation de l’acide désoxyribonucléique (ADN), et son polymorphisme au codon 118 est également associé à la réponse au traitement. Le peu d’études pronostiques portant sur ces deux gènes dans les cancers oto-rhino-laryngologiques (ORL) ne permet de tirer des conclusions claires. Objectifs: Déterminer l’influence des mutations de K-RAS codons 12 et 13 et du polymorphisme de ERCC1 codon 118 dans le traitement des cancers épidermoïdes avancés tête et cou traités par chimioradiothérapie concomitante à base de sels de platine. Méthode: Extraction de l’ADN provenant de spécimens de biopsie de patients traités par chimioradiothérapie concomitante pour des cancers avancés tête et cou, et ayant un suivi prospectif d’au moins deux ans. Identification des mutations de K-RAS codons 12 et 13 et du polymorphisme de ERCC1 au codon 118 dans les spécimens et corrélation de ces marqueurs avec la réponse au traitement. Résultats: Les mutations de K-RAS codon 12 sont associées à un moins bon contrôle loco-régional par rapport aux tumeurs ne démontrant pas la mutation (32% vs 83% p=0.03), sans affecter pour autant la survie globale. Aucune mutation de K-RAS codon 13 n’a été identifiée. Les différents polymorphismes de ERCC1 n’ont pas eu d’impact sur la réponse au traitement. Conclusion: Les mutations de K-RAS codons 12 et 13 et le polymorphisme de ERCC1 au codon 118 ne semblent pas mettre en évidence les patients qui bénéficieraient d’une autre modalité thérapeutique.

No mutations found in exons of TP53, H-RAS and K-RAS genes in liver of male Wistar rats submitted to a medium-term chemical carcinogenesis assay

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)