Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Oncogene”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 343 records · Page 19Linked to original sources
PubMed1995

The effect of oncogenes on the growth and differentiation of oligodendrocyte type 2 astrocyte progenitor cells.

Oncogenes represent altered versions of cellular genes instrumental for control of cell proliferation and differentiation. Several oncogenes have been implicated in glial cell transformation and immortalization in culture (myc, src, mos, ras, and SV40 large T antigen). The purpose of this study is to further our understanding of glial cell neoplasia by investigating the effect of oncogenes on the growth and differentiation of central nervous system glial progenitor cells from the oligodendrocyte type 2 astrocyte (O-2A) lineage. This progenitor cell differentiates into an oligodendrocyte or a type-2 astrocyte according to environmental cues. Drug-selectable retroviral vectors were used to introduce oncogenes either alone or in combination into primary cultures of rat O-2A cells. Established O-2A progenitor cell lines were only obtained after infection with c-myc or SV40 large T antigen, suggesting that among the oncogenes tested only these were capable of immortalizing O-2A progenitor cells. The O-2A/c-myc and O-2A/temperature-sensitive SV40 large T antigen cell lines retained the capacity to differentiate into oligodendrocytes and type-2 astrocytes, thereby providing an opportunity to study the effects of oncogene cooperation on the phenotype of O-2A lineage cells. Superinfection of these cells lines with retroviruses encoding ras or src led to abnormalities of differentiation whose nature and severity depended on the combination of cooperating oncogenes and/or the levels of expression obtained. This study demonstrates that oncogene-modified glial cell lines provide an amenable and unique model system to study differentiation in the central nervous system and the genetic changes involved in the development of glioma.

Animals↗
PubMed1994

Cytoskeletal reorganization in NIH 3T3 fibroblasts expressing the ras oncogene.

Expression of the Ha-ras oncogene in NIH 3T3 fibroblasts leads to a set point shift of cell volume regulation and causes an increase in cell volume by activation of Na+/H+ exchange and Na+, K+, 2Cl- cotransport. Since both ion transport systems are thought to be governed by the cytoskeleton, the aim of this study was to examine the alterations in growth characteristics and cytoskeletal organization due to the expression of the oncogene. The experiments were performed on NIH 3T3 fibroblasts transfected with a transforming Ha-ras MMTV-LTR construct and expressing the oncogene after treatment with low serum medium and 1 mumol/l dexamethasone (+ras cells). Transfected cells not expressing the oncogene (-ras cells) and treated with low serum medium, but without the addition of dexamethasone, served as controls. The growth characteristics were examined and the cytoskeletal architecture was visualized by indirect immunofluorescence microscopy using specific antibodies and fluorescent dyes. Expression of the ras oncogene was accompanied by a significant and serum-independent increase in proliferative activity irrespective from the coating of the dishes with attachment factors (poly-L-lysine, collagen type I). Both, -ras and +ras cells, proliferated slower on substrates coated with poly-L-lysine than on tissue culture plastic or collagen type I. Expression of the ras oncogene also resulted in a significant increase in cell volume which was independent from the substrate. +ras Cells became more elongated, exhibited long cytoplasmic protrusions and tended to detach when compared with -ras cells. Examination of the cytoskeletal architecture in +ras and -ras cells revealed marked differences such as a depolymerization of the stress fiber network to strongly fluorescent "focals" as well as the absence of vinculin-containing attachment plaques (focal contacts), a disorganization of non-muscle myosin and of cell surface fibronectin in +ras cells. In addition, a retraction of microtubules and vimentin filaments to the perinuclear region was also observed in +ras cells. For comparison, NIH 3T3 fibroblasts which were not transfected with the ras oncogene (0ras cells) and which were also subjected to the experimental conditions described above (low serum medium +/- dexamethasone), did not exhibit the cytoskeletal alterations as observed for +ras cells. The results demonstrate that the expression of ras oncogene causes not only profound alterations in the proliferative activity, cell volume and cell morphology, but also a marked reorganization of cytoskeletal architecture, which may participate in the altered regulation of volume-regulatory ion transporters in the cell membrane.

3T3 Cells↗
PubMedDate not supplied

Heterogeneous expression of proto-oncogenes in Hodgkin's disease derived cell lines.

The expression of 20 proto-oncogenes was analysed by Northern blotting in four cell lines derived from patients with Hodgkin's disease (L428, L540, CO and DEV) and compared to lymphoid and myeloid leukemia cell lines and normal hematopoietic cells. Expression of the proto-oncogenes c-myc, p53, c-jun, pim-1, lck, c-syn, c-raf and N-ras were detected in Hodgkin's disease derived cell lines and in normal hematopoietic cells. Transcripts of the proto-oncogene c-met were detected in the Hodgkin's derived cell lines L428 and L540 but not in the lymphoid or myeloid leukemia cell lines or in tonsil cells, peripheral blood mononuclear cells and granulocytes. Expression of the proto-oncogenes N-myc and lck were observed in the Hodgkin's derived cell line CO which express T cell receptor genes and in the T cell lines JM and CEM. L428 cells and CO cells expressed aberrant transcripts of the c-fes proto-oncogene. Thus Hodgkin's disease derived cell lines are heterogeneous in their expression pattern of proto-oncogenes, expressing normal and aberrant transcripts of proto-oncogenes which are not found in untransformed hematopoietic cells.

Blotting, Northern↗
PubMed1989

Transgenic mice as a means to study synergism between oncogenes.

Transgenic mice present a useful model to study the mechanisms underlying malignant transformation. (i) They can provide information on the oncogenic potential of genes as a function of tissue context. (ii) They allow the analysis of the primary effects of an oncogene on proliferation and differentiation before secondary mutations have occurred. (iii) Crossings between transgenic mice carrying different oncogenes can reveal their capacity to cooperate in transformation. (iv) Transgenic mice bearing a particular oncogene can be used to search for (new) (anti)oncogenes that synergize with the transgene. The non-acute transforming murine leukemia viruses (MuLV) appear very useful for this purpose. This has become clear from our studies with pim-I and c-myc transgenic mice. MuLV dramatically accelerates T-cell lymphomagenesis in transgenic mice overexpressing the pim-I oncogene in their lymphoid compartment. In all tumors induced by MuLV in pim-I transgenic mice, either the c-myc or the N-myc gene was activated by proviral insertion. Similarly, MuLV infection of transgenic mice overexpressing the c-myc gene in their B-cell compartment resulted in the acceleration of pre-B-cell lymphomagenesis. A significant fraction of the resulting pre-B-cell tumors showed proviral activation of pim-I. This shows that pim-I and myc synergize efficiently in both B- and T-cell lymphomagenesis. pim-I transgenic mice are also highly sensitive to tumor induction by N-ethyl-N-nitrosourea (ENU) and therefore represent an excellent in vivo model system to test the oncogenic potential of chemical compounds.

Animals↗
PubMed1992

Oncogenes: cause or consequence in the development of glial tumors.

Recent developments in the field of oncogenes and growth stimulatory factors have provided limited but essential models in neuro-oncology. The observation in gliomas of platelet growth factor (PDGF)-like immunoreactivity fits with the autocrine secretion model, rising the possibility for the growth factor independence of the cancer cells. The discovery of the tumor suppressor genes, for which loss of function mutations are oncogenic as in the RB gene of the retinoblastoma and p53 gene, has introduced a new concept of oncogenesis which could be useful even in the cure of the neoplasms. Several oncogenes are amplified and/or expressed in brain tumors, some associated with polymorphism leading to abnormal protein products. Therefore, corresponding functions, such as production of deficient epidermal growth factor receptor (EGFR) encoded by erb-B, are impaired. Abnormal chromosomal patterns have been recognized in brain tumors and found mainly in chromosomes 7 and 22 on which oncogenes erb-B and sis are located, respectively. Location of proto-oncogenes, which are normally expressed in the brain, indicate that they share common distribution patterns mainly involving the cerebellum, hippocampus and olfactory bulbs. These proto-oncogenes may be regulated by physiological and pathological events. The concept of oncogene involvement in brain tumors must be extended to include the other factors such as G-proteins, growth factor receptors, membrane-associated and cytoplasmic protein kinases, which are all responsible for the control of the cell growth and their response to external signals including chemotherapeutic drigs.

Animals↗
PubMed1994

Transcriptional activation analysis of oncogene function.

Because no single assay provides a complete analysis of the transformed phenotype, transactivation assays complement the cell growth and tumorigenicity analyses of oncogene function. Transactivation of ORE-containing genes is such a common feature of a diverse variety of viral and cellular oncogenes that it can be considered one aspect of the oncogene-induced phenotype. After the initial identification of oncogenes that activate transcription, studies of the mechanisms of activation and the identification of the downstream target genes should lead to a better understanding of the events leading to cellular transformation. The fact that cell type specificity of transactivation and transformation can be similar means that the transactivation assay may be a useful tool in dissecting cell type-specific transformation. The transactivation assay of oncogene function also has the advantage that it is easy to perform and significantly more rapid than assays based on altered cell growth. This is of particular advantage when one wishes to examine the function of a large number of oncogene mutants generated in vitro. Overall, transactivation assays provide another tool for examining transforming potential and a starting point for the analysis of the downstream targets of oncogenes.

3T3 Cells↗
PubMedDate not supplied

Transient reversion of ras oncogene-induced cell transformation by antibodies specific for amino acid 12 of ras protein.

The proteins encoded by the ras oncogene are thought to trigger expression of the transformed phenotype in some types of cancer cells. In human cells, the ras protein family consists of several members including normal (proto-oncogene) and mutant (oncogene) forms. In general, the proto-oncogene forms are thought to be involved in the normal growth control of cells, while the mutant forms (which apparently result from somatic mutation of the normal ras genes) appear to be responsible, in part, for the loss of normal growth control. On microinjection into living normal cells, the purified ras oncogene protein (p21) induces a characteristic loss of growth control in cells within several hours. The mutant forms of the different ras proteins typically contain a single amino-acid change, usually at position 12 or less frequently at position 61. Here we report that microinjection of antibodies specific for amino acid 12 of the oncogenic v-Ki-ras protein into cells transformed by this protein causes a transient reversion of the cells to a normal phenotype. The fact that this antibody inhibits binding of GTP to the v-Ki-ras protein supports the notion that GTP binding is essential to the transforming function of this oncogene product.

Amino Acid Sequence↗
PubMed1999

Downregulation of the colon tumour-suppressor homeobox gene Cdx-2 by oncogenic ras.

Downregulation of the colon tumour-suppressor homeobox gene Cdx-2 by oncogenic ras Constitutive activation of the ras proto-oncogene is a frequent and early event in colon cancers, but the downstream nuclear targets are not fully understood. The Cdx-1 and Cdx-2 homeobox genes play crucial roles in intestinal cell proliferation and differentiation. In addition, Cdx-2 is a colonic tumour-suppressor gene, whereas Cdx-1 has oncogenic potential. Here, we show that constitutive activation of ras alters Cdx-1 and Cdx-2 expression in human colonic Caco-2 and HT-29 cells that harbour a normal ras proto-oncogene. Oncogenic ras downregulates Cdx-2 through activation of the PKC pathway and a decline in activity of the Cdx-2 promoter AP-1 site. This decline results from a PKC-dependent decrease in the relative expression of c-Jun, an activator of Cdx-2 transcription, compared to c-Fos, an inhibitor of Cdx-2. Unlike Cdx-2, Cdx-1 is upregulated by oncogenic ras and this effect is mediated by activation of the MEK1 pathway. These results indicate that oncogenic ras activation has opposite effects on Cdx-1 and Cdx-2 expression through distinct signalling pathways and they provide the first evidence for a functional link between ras activation and the downregulation of the Cdx-2 tumour-suppressor gene in colon cancer cells.

Avian Proteins↗
PubMed1992

Mitogen-activated protein kinase activation resulting from selective oncogene expression in NIH 3T3 and rat 1a cells.

Mitogen-activated protein kinases (MAPKs) are serine/threonine kinases that are rapidly activated in response to a variety of growth factors in many cell types. MAPKs are activated by phosphorylation of both tyrosine and threonine residues. They are proposed to be key integrators of growth factor receptor transduction systems involving conversion of tyrosine kinase signals to serine/threonine kinase activation. We have studied the influence of specific oncogenes on the regulation of MAPK activity in NIH 3T3 and Rat 1a fibroblasts. In NIH 3T3 cells, ras or raf oncogene expression, but not gip2 oncogene expression, induces a significant constitutive MAPK activation. In contrast, in Rat 1a cells, gip2, but not ras or raf oncogene expression, induces a strong constitutive MAPK activation. The findings indicate that, in a cell type-selective manner, different oncoproteins are capable of causing the constitutive activation of MAPK. However, the magnitude of oncogene-induced MAPK activation is not directly correlated with cellular transformation in either cell type. It appears that expression of only a subset of transforming oncogenes in a specific cell type is able to alter the regulation of the MAPK activation pathway. Thus, the network of cytoplasmic serine/threonine kinases will be differentially regulated when the same oncogene is expressed in different cell types.

3T3 Cells↗
PubMed1992

Acquisition of a tumorigenic phenotype by a rat ventral prostate epithelial cell line expressing a transfected activated neu oncogene.

The neu oncogene has been demonstrated to be a potent transforming gene in rodent fibroblasts. The overexpression of the human erbB-2/neu oncogene has been implicated in the development and/or prognosis of several human carcinomas including that of the prostate. To assess the transforming potential of the activated rat neu oncogene in prostatic epithelial carcinogenesis, this laboratory has transfected a cloned non-tumorigenic, rat ventral prostate epithelial cell line, NbE-1.4, with an activated, point-mutated neu oncogene. Transfection of NbE-1.4 cells with the activated neu oncogene expression vector, pSV-neu-T (neu-T), resulted in an altered cell morphology, an increase in soft agar colony-forming efficiency, and conversion to a tumorigenic phenotype. Although the parental NbE-1.4 cells expressed endogenous c-neu mRNA, a reverse transcriptase polymerase chain reaction assay determined that the neu-T-transfected clones expressed only the point-mutated neu-T mRNA. The suppression of the c-neu transcripts occurred regardless of the neu-T mRNA level expressed in these cell clones. These data provide evidence to show that low-level expression of an activated neu oncogene alone was insufficient to transform rat prostate epithelial cells. Rather, overexpression of an activated neu oncogene correlated well with the acquisition of a tumorigenic phenotype by the NbE-1.4 epithelial cell line.

3T3 Cells↗
PubMed1988

Disordered metabolism of microfilament proteins, tropomyosin and actin, in mouse mammary epithelial cells expressing the Ha-ras oncogene.

Synthesis of 37- and 41-kD tropomyosins (TM) is suppressed in fibroblasts expressing transforming oncogenes, which may contribute to the deranged microfilament structure seen in such cells (Cooper et al., Mol. Cell. Biol. 5, 972, 1985). To determine whether TM metabolism was also deranged when epithelial cells expressed a transforming oncogene, we studied cultured mouse mammary epithelial cells which express the activated c-Ha-ras oncogene either constitutively or through glucocorticoid activation of the oncogene linked to a mouse mammary tumor virus (MMTV) promoter. The epithelial cells expressed three major TM species, one at 37 kD and two at 35 kD, but lacked expression of a 41 kD TM typically found in fibroblasts. In oncogene-expressing cells synthesis of the 37 kD TM was not suppressed but synthesis of actin was increased 2-fold. Actin entered the cytoskeleton (CSK) normally, but TM accumulated in the CSK with a 50% reduction from normal in TM:actin ratio. Thus, in both epithelial cells and fibroblasts expressing transforming ras oncogenes, the metabolism of TM and actin is disordered so as to produce TM-deficient cytoskeletal structures which may be functionally or structurally defective. However, the result is achieved by different effects on metabolism of these proteins in the two cell types, suggesting that cellular responses to oncogene actions may be conditioned by the state of cell differentiation.

Actins↗
PubMed1987

Oncogene-mediated multistep transformation of C3H10T1/2 cells.

We have examined the response of the mouse embryonic cell line C3H10T1/2 to transfection with the activated human c-H-ras oncogene and the gag-myc oncogene from avian myelocytomatosis virus 29. C3H10T1/2 cells are not morphologically transformed following transfection with the gag-myc oncogene. A low level of focus formation is observed following transfection of the c-H-ras oncogene. When C3H10T1/2 cells are cotransfected with the ras and myc oncogenes, focus formation is increased by an average of 13 fold. In addition, C3H10T1/2 ras/myc foci have a distinct, transformed morphology which correlates with an increased potential for anchorage-independent growth. Although morphological transformation in this system is largely a function of ras oncogene expression, our studies demonstrate that it is potentiated by the presence of a functional gag-myc protein. Oncogene-mediated multistep transformation, which was first described in primary embryo cultures, is not a general property of established cell lines. The C3H10T1/2 cell line is an exception and provides a model system in which partially transformed phenotypes, in a progression toward malignant transformation, can be isolated and studied.

Animals↗
PubMed1987

Independently activated dbl oncogenes exhibit similar yet distinct structural alterations.

The dbl oncogene was initially isolated following transfection of NIH3T3 cells with DNA of a human diffuse B cell lymphoma. Its transcribed sequences were shown to be distributed over a 30-kb span within a molecularly cloned 45-kb segment of human DNA which contained the transforming gene. By restriction mapping, its transcribed region corresponded to that of its normal allele, except at the 5' end where a rearrangement involved transcribed dbl oncogene sequences from another locus. An independent isolate of a dbl-related transforming gene was obtained following transfection of NIH3T3 cells with DNA of a human nodular poorly differentiated lymphoma (NPDL). Physical mapping indicated that this transforming gene, designated NPDL-dbl, shared considerable homology with the dbl oncogene, but differed at both 5' and 3' termini. Its point of divergence from the normal allele at the 5' end was at least 10 kb upstream from that of the dbl oncogene. The oncogenes each expressed truncated transcripts compared to the 5.3-kb normal transcript. The dbl and NPDL-dbl oncogene translational products of 66 and 76 kDa, respectively, were consistent with their corresponding major 2.8- and 3.5-kb transcripts. It was not possible to detect evidence of the 5' structural rearrangements associated with these oncogenes in either of the original tumors. Thus, if these rearrangements were critical to their activation, they occurred in the process of gene transfer or in vivo in only a minority of tumor cells.

Animals↗
PubMed2001

Relationship between the presence of oncogenic HPV DNA assessed by polymerase chain reaction and Ki-67 immunoquantitative features in cervical intraepithelial neoplasia.

The aims of this study were firstly to determine which Ki-67 immunoquantitative parameters correlate with the presence of oncogenic human papillomavirus (HPV) in cervical intraepithelial neoplasia (CIN) lesions; and secondly to compare prospectively the routinely assessed CIN grades with the Ki-67 quantitative pathological CIN grade, the expert revised grade, and the presence of oncogenic HPV DNA. HPV polymerase chain reaction (PCR) and Ki-67 immunoquantitation were performed on 90 consecutive biopsies (16 CIN 1, 35 CIN 2, and 39 CIN 3). CIN grade was assessed routinely by six different pathologists. The presence of the lesion was confirmed in a histological section following the material used for PCR and Ki-67 analysis. In a second prospective routine test set analysis, 66 more CIN lesions (14 CIN 1, 15 CIN 2, and 37 CIN 3) were routinely graded (also by six different pathologists, routine CIN grade=CIN(ROUT)), studied for oncogenic HPV DNA, and graded by quantitative Ki-67 features (quantitative pathological CIN grade=CIN(QP)). These latter cases were blindly revised by one of the authors (reference CIN grade=CIN(REF)). Eight of the nine Ki-67 immunoquantitative features showed a significant difference between the oncogenic HPV-positive and -negative cases. The best single discriminator was the 90th percentile of the stratification index (SI90). All 61 cases with Ki-67 SI90>0.60 were HPV-positive (68% of the total group studied). Of the 29 cases with SI90< or =0.60, 16 were negative and 13 positive for oncogenic HPV and none of the Ki-67 features (either single or combined) could distinguish them. Using stepwise multivariate analysis, the best discriminating combination of features was SI90 and the percentage of Ki-67-positive nuclei in the deep third layer of the epithelium (PERC DL). The combination of SI90 and the percentage of Ki-67-positive nuclei per 100 microm basal membrane was nearly as strong as that of SI90 and PERC DL. With these two features, 86% of the cases were correctly classified. The subjective estimate of SI90 (>0.60 or < or =0.60) by two independent observers was not accurate and not reproducible. In the prospective routine test set analysis of 66 cases, the 37 CIN(ROUT)=3 all had CIN(QP) and CIN(REF)=3 and all these cases were oncogenic HPV-positive. Eight of the 14 original CIN(ROUT)=1 grades were oncogenic HPV (=HPV)-positive and five of these eight were upgraded by CIN(QP) to CIN 2 and CIN 3. These upgrades were in agreement with the blind reference revisions. The six HPV-negative CIN(ROUT)=1 cases were CIN 1 both by CIN(QP) and by CIN(REF). Thirteen of the 15 original CIN(ROUT)=2 grades were HPV-positive and seven of these were CIN(QP)=3. All six HPV-positive CIN(ROUT)=2 cases that were CIN(QP)=2 were also CIN(REF)=2 at blind revision. In conclusion, this study has shown firstly, that in CIN lesions, Ki-67 immunoquantitative features and the presence of oncogenic HPV are highly correlated, and also within one subjective CIN grade; secondly, that subjective impressions of SI90 are not as accurate or reproducible as quantitative image analysis results; and thirdly, that the routine application of QP CIN-grading gives results that are in very good agreement with CIN grades assessed by an expert. Thus, routine QP-grading may be used to correct the subjective grade assessed by non-expert pathologists.

Adult↗
PubMed1992

Angiotensin-II-induced expression of proto-oncogene (c-fos, jun-B and c-jun) mRNA in bovine adrenocortical fasciculata cells (BAC) is mediated by AT-1 receptors.

We have shown previously that angiotensin-II (A-II) controls proto-oncogene (c-fos, jun-B and c-jun) mRNA accumulation in bovine adrenal fasciculata cells (BAC). Since BAC contain both subtypes (AT-1 and AT-2) of the A-II receptor, we have investigated which subtype was involved in the effect of A-II on proto-oncogene mRNA by using a selective antagonist for AT-1 (DUP 753) and for AT-2 (CGP 42112A). DUP 753, but not CGP 42112A, inhibited the stimulatory effect of A-II on proto-oncogene mRNA, with ID50s of 4 x 10(-7) M, 7 x 10(-7) M and 2 x 10(-6) M for c-fos, jun-B and c-jun, respectively. Neither of the two antagonists by themselves had a direct effect on proto-oncogene mRNA. As the A-II AT-1 receptors are coupled to the phospholipase C system in BAC, we have investigated whether the A-II effects on the proto-oncogenes were mediated by protein kinase C (PKC) or by Ca2+ calmodulin. First, activation of PKC by the phorbol ester, PMA, increased the level of three proto-oncogene mRNAs, whereas calcium ionophore had no effect. Second, staurosporine, a specific inhibitor of PKC, reduced the stimulatory action of A-II on proto-oncogene mRNA by 80-90%, whereas trifluoroperazine, an inhibitor of calmodulin, had no significant effect. These results demonstrate that the effects of A-II on proto-oncogene mRNA are mediated by AT1 receptor subtypes, mainly through activation of the PKC pathway.

Angiotensin II↗
PubMed2006

Oncogene-induced senescence is a DNA damage response triggered by DNA hyper-replication.

Early tumorigenesis is associated with the engagement of the DNA-damage checkpoint response (DDR). Cell proliferation and transformation induced by oncogene activation are restrained by cellular senescence. It is unclear whether DDR activation and oncogene-induced senescence (OIS) are causally linked. Here we show that senescence, triggered by the expression of an activated oncogene (H-RasV12) in normal human cells, is a consequence of the activation of a robust DDR. Experimental inactivation of DDR abrogates OIS and promotes cell transformation. DDR and OIS are established after a hyper-replicative phase occurring immediately after oncogene expression. Senescent cells arrest with partly replicated DNA and with DNA replication origins having fired multiple times. In vivo DNA labelling and molecular DNA combing reveal that oncogene activation leads to augmented numbers of active replicons and to alterations in DNA replication fork progression. We also show that oncogene expression does not trigger a DDR in the absence of DNA replication. Last, we show that oncogene activation is associated with DDR activation in a mouse model in vivo. We propose that OIS results from the enforcement of a DDR triggered by oncogene-induced DNA hyper-replication.

Animals↗
PubMed2000

NF-kappa B is required for H-ras oncogene induced abnormal cell proliferation and tumorigenesis.

Oncogenic mutations in ras lead to constitutive activation of downstream signaling pathways that modulate the activities of transcription factors. In turn, these factors control the expression of a subset of genes responsible for neoplastic cell transformation. Recent studies suggest that transcription factor NF-kappa B contributes to cell transformation by inhibiting the cell death signal activated by oncogenic Ras. In this study, inhibition of NF-kappa B activity by forced expression of a super-repressor form of I kappa B alpha, the major inhibitor of NF-kappa B, markedly decreased the growth rate, saturation density and tumorigenicity of oncogenic H-Ras transformed rat embryo fibroblasts. Such clonally isolated cells overexpressing I kappa B alpha super-repressor not only were viable but also exhibited no sign of spontaneous apoptosis. Inhibition of NF-kappa B in these cells was functionally demonstrated by both the loss of cytokine induced DNA binding activity and a profoundly increased sensitivity to cell death in response to TNF-alpha treatment. In contrast, inhibition of NF-kappa B activity in non-transformed fibroblasts had minimal effect on growth, but rendered the cells resistant to a subsequent transformation by H-ras oncogene. Similar results were also obtained with rat intestinal epithelial cells harboring an inducible ras oncogene. Taken together, these findings suggest that NF-kappa B activity is essential for abnormal cell proliferation and tumorigenicity activated by the ras oncogene and highlight an alternative functional role for NF-kappa B in oncogenic Ras-mediated cell transformation that is distinct from its anti-apoptotic activity. Oncogene (2000) 19, 841 - 849.

Animals↗
PubMed1999

The ras oncogene-mediated sensitization of human cells to topoisomerase II inhibitor-induced apoptosis.

BACKGROUND: Among the inhibitors of the enzyme topoisomerase II (an important target for chemotherapeutic drugs) tested in the National Cancer Institute's In Vitro Antineoplastic Drug Screen, NSC 284682 (3'-hydroxydaunorubicin) and NSC 659687 [9-hydroxy-5,6-dimethyl-1-(N-[2(dimethylamino)ethyl]carbamoyl)-6H-pyrido -(4,3-b)carbazole] were the only compounds that were more cytotoxic to tumor cells harboring an activated ras oncogene than to tumor cells bearing wild-type ras alleles. Expression of the multidrug resistance proteins P-glycoprotein and MRP (multidrug resistance-associated protein) facilitates tumor cell resistance to topoisomerase II inhibitors. We investigated whether tumor cells with activated ras oncogenes showed enhanced sensitivity to other topoisomerase II inhibitors in the absence of the multidrug-resistant phenotype. METHODS: We studied 20 topoisomerase II inhibitors and individual cell lines with or without activated ras oncogenes and with varying degrees of multidrug resistance. RESULTS: In the absence of multidrug resistance, human tumor cell lines with activated ras oncogenes were uniformly more sensitive to most topoisomerase II inhibitors than were cell lines containing wild-type ras alleles. The compounds NSC 284682 and NSC 659687 were especially effective irrespective of the multidrug resistant phenotype. The ras oncogene-mediated sensitization to topoisomerase II inhibitors was far more prominent with the non-DNA-intercalating epipodophyllotoxins than with the DNA-intercalating inhibitors. This difference in sensitization appears to be related to a difference in apoptotic sensitivity, since the level of DNA damage generated by etoposide (an epipodophyllotoxin derivative) in immortalized human kidney epithelial cells expressing an activated ras oncogene was similar to that in the parental cells, but apoptosis was enhanced only in the former cells. CONCLUSIONS: Activated ras oncogenes appear to enhance the sensitivity of human tumor cells to topoisomerase II inhibitors by potentiating an apoptotic response. Epipodophyllotoxin-derived topoisomerase II inhibitors should be more effective than the DNA-intercalating inhibitors against tumor cells with activated ras oncogenes.

Antineoplastic Agents↗