Antigenuria positiva a neumococo y vacunación / Positive urine pneumococcal antigen test and vaccination

Introducción y objetivo: La detección del antígeno neumocócico en orina es una prueba útil pero puede presentar falsos positivos, entre ellos, la vacunación neumocócica. Material y métodos: Detección de las antigenurias positivas a neumococo en el Hospital de Denia (enero-febrero/2015). Se determinaron variables epidemiológicas, radiológicas, microbiológicas y antecedente de vacunación neumocócica (neumo-23 y/o neumo-13). Resultados: La antigenuria a neumococo mostró un resultado positivo en el 12,4% de 385 determinaciones. Solo en el 33,3% de los casos con antigenuria positiva se documentó infiltrado radiológico en la radiografía de tórax. En el 35,4% de los pacientes existía antecedente de vacunación neumocócica previa. En la mayor parte de los casos (87,5%) un antígeno neumocócico positivo supuso la prescripción de un tratamiento antibiótico. Conclusiones: La vacunación neumocócica puede generar falsos positivos a la antigenuria por neumococo en la práctica clínica, con la consiguiente prescripción innecesaria de antibióticos en gran número de casos (AU)

Introduction and objective: Although urine pneumococcal antigen is an useful test, it has false positives such as pneumococcal vaccination. Material and methods: Positive urine pneumococcal antigen in Hospital de Denia (January-February/2015). We studied epidemiological, radiological and microbiological variables as well as previous pneumococcal vaccination (neumo-23 and/or neumo-13). Results: Urine pneumococcal antigen test was positive in 12.4% of 385 cases. Only 33.3% of positive cases had pneumonia in chest X-ray, and 35.4% of patients had previous pneumococcal vaccination. In most cases (87.5%), an antibiotic was prescribed. Conclusions: Pneumococcal vaccination can produce a false positive result in the urine pneumococcal antigen test in clinical practice, leading to an unnecessary prescription of antibiotics (AU)

[Positive urine pneumococcal antigen test and vaccination]. / Antigenuria positiva a neumococo y vacunación.

INTRODUCTION AND OBJECTIVE: Although urine pneumococcal antigen is an useful test, it has false positives such as pneumococcal vaccination. MATERIAL AND METHODS: Positive urine pneumococcal antigen in Hospital de Denia (January-February/2015). We studied epidemiological, radiological and microbiological variables as well as previous pneumococcal vaccination (neumo-23 and/or neumo-13). RESULTS: Urine pneumococcal antigen test was positive in 12.4% of 385 cases. Only 33.3% of positive cases had pneumonia in chest X-ray, and 35.4% of patients had previous pneumococcal vaccination. In most cases (87.5%), an antibiotic was prescribed. CONCLUSIONS: Pneumococcal vaccination can produce a false positive result in the urine pneumococcal antigen test in clinical practice, leading to an unnecessary prescription of antibiotics.

The differential palmitoylation states of N-Ras and H-Ras determine their distinct Golgi subcompartment localizations.

Despite a high degree of structural homology and shared exchange factors, effectors and GTPase activating proteins, a large body of evidence suggests functional heterogeneity among Ras isoforms. One aspect of Ras biology that may explain this heterogeneity is the differential subcellular localizations driven by the C-terminal hypervariable regions of Ras proteins. Spatial heterogeneity has been documented at the level of organelles: palmitoylated Ras isoforms (H-Ras and N-Ras) localize on the Golgi apparatus whereas K-Ras4B does not. We tested the hypothesis that spatial heterogeneity also exists at the sub-organelle level by studying the localization of differentially palmitoylated Ras isoforms within the Golgi apparatus. Using confocal, live-cell fluorescent imaging and immunogold electron microscopy we found that, whereas the doubly palmitoylated H-Ras is distributed throughout the Golgi stacks, the singly palmitoylated N-Ras is polarized with a relative paucity of expression on the trans Golgi. Using palmitoylation mutants, we show that the different sub-Golgi distributions of the Ras proteins are a consequence of their differential degree of palmitoylation. Thus, the acylation state of Ras proteins controls not only their distribution between the Golgi apparatus and the plasma membrane, but also their distribution within the Golgi stacks.

In TCR-stimulated T-cells, N-ras regulates specific genes and signal transduction pathways.

It has been recently shown that N-ras plays a preferential role in immune cell development and function; specifically: N-ras, but not H-ras or K-ras, could be activated at and signal from the Golgi membrane of immune cells following a low level T-cell receptor stimulus. The goal of our studies was to test the hypothesis that N-ras and H-ras played distinct roles in immune cells at the level of the transcriptome. First, we showed via mRNA expression profiling that there were over four hundred genes that were uniquely differentially regulated either by N-ras or H-ras, which provided strong evidence in favor of the hypothesis that N-ras and H-ras have distinct functions in immune cells. We next characterized the genes that were differentially regulated by N-ras in T cells following a low-level T-cell receptor stimulus. Of the large pool of candidate genes that were differentially regulated by N-ras downstream of TCR ligation, four genes were verified in qRT-PCR-based validation experiments (Dntt, Slc9a6, Chst1, and Lars2). Finally, although there was little overlap between individual genes that were regulated by N-ras in unstimulated thymocytes and stimulated CD4(+) T-cells, there was a nearly complete correspondence between the signaling pathways that were regulated by N-ras in these two immune cell types.

p15(INK4b) plays a crucial role in murine lymphoid development and tumorigenesis.

To investigate if the cooperation between the Rgr oncogene and the inactivation of INK4b (a CDK inhibitor), as described previously in a sarcoma model, would be operational in a lymphoid system in vivo, we generated a transgenic/knockout murine model. Transgenic mice expressing the Rgr oncogene under a CD4 promoter were crossed into a p15(INK4b)-deficient background. Unexpectedly, mice with a complete ablation of both p15(INK4b) alleles had a lower tumor incidence and higher survival rate when compared with CD4-Rgr progeny with homozygous or heterozygous expression of p15(INK4b). Also, a similar survival pattern was observed in a parallel model in which transgenic mice expressing a constitutively activated N-Ras mutant were crossed into a p15(INK4b)-deficient background. To analyze this paradoxical event, we investigated the hypothesis that the absence of both p15(INK4b) alleles in the presence of the Rgr oncogene could be deleterious for proper thymocyte development. When analyzed, thymocyte development was blocked at the double negative (DN) 3 and DN4 stages in mice missing one or both alleles of p15(INK4b), respectively. We found reduction in overall apoptotic levels in the thymocytes of mice expressing Rgr, compared with their wild-type mice, supporting thymocyte escape from programmed cell death and subsequently facilitating the onset of thymic lymphomas but less for those missing both p15 alleles. These findings provide evidence of the complex interplay between oncogenes and tumor suppressor genes in tumor development and indicate that in the lymphoid tissue the inactivation of both p15 alleles is unlikely to be the first event in tumor development.

Wild type N-ras displays anti-malignant properties, in part by downregulating decorin.

Previously, we have shown that wild type N-ras (wt N-ras) harbors an anti-malignant effect against mutated Ras and in tumors without Ras mutations. To investigate the molecular bases of this anti-malignant activity, we have studied the potency of this anti-malignant effect in a model system against SV40 large T antigen (SV40T). We show that wild-type N-ras (wt N-ras) counteracts the effects of SV40T in NIH3T3 cells as seen by a decrease in proliferation, anchorage independence and changes in migration. We also show that wt N-ras elicits the same anti-malignant effects in some human tumor cell lines (HT1080 and MDA-MB-231). Through mRNA and microRNA (miRNAs) expression profiling we have identified genes (decorin) and miRNAs (mir-29A, let-7b) modulated by wt N-ras potentially responsible for the anti-malignant effect. Wt N-ras appears to mediate its anti-malignant effect by downregulating some of the targets of the TGFß pathway and decorin, which are able to reverse the inhibition of migration induced by wt N-ras. Our experiments show that the molecules that mediate the anti-malignant effect by wt N-ras appear to be different from those modulated by transforming N-ras. The components of the pathways modulated by wt N-ras mediating its anti-malignant effects are potential targets for therapeutic intervention in cancer.

Regulation of HMGA1 expression by microRNA-296 affects prostate cancer growth and invasion.

PURPOSE: High-motility group AT-hook gene 1 (HMGA1) is a non-histone nuclear binding protein that is developmentally regulated. HMGA1 is significantly overexpressed in and associated with high grade and advance stage of prostate cancer (PC). The oncogenic role of HMGA1 is at least mediated through chromosomal instability and structural aberrations. However, regulation of HMGA1 expression is not well understood. Identification of microRNA-mediated HMGA1 regulation will provide a promising therapeutic target in treating PC. EXPERIMENTAL DESIGN: In this study, we examined the functional relation between miR-296 and HMGA1 expression in several PC cell lines and a large PC cohort. We further examined the oncogenic property of HMGA1 regulated by miR-296. RESULTS: Here we report that miR-296, a microRNA predicted to target HMGA1, specifically represses HMGA1 expression by promoting degradation and inhibiting HMGA1translation. Repression of HMGA1 by miR-296 is direct and sequence specific. Importantly, ectopic miR-296 expression significantly reduced PC cell proliferation and invasion, in part through the downregulation of HMGA1. Examining PC patient samples, we found an inverse correlation between HMGA1 and miR-296 expression: high levels of HMGA1 were associated with low miR-296 expression and strongly linked to more advanced tumor grade and stage. CONCLUSIONS: Our results indicate that miR-296 regulates HMGA1 expression and is associated with PC growth and invasion.

Uroplakins in urothelial biology, function, and disease.

Urothelium covers the inner surfaces of the renal pelvis, ureter, bladder, and prostatic urethra. Although morphologically similar, the urothelia in these anatomic locations differ in their embryonic origin and lineages of cellular differentiation, as reflected in their different uroplakin content, expandability during micturition, and susceptibility to chemical carcinogens. Previously thought to be an inert tissue forming a passive barrier between the urine and blood, urothelia have recently been shown to have a secretory activity that actively modifies urine composition. Urothelial cells express a number of ion channels, receptors, and ligands, enabling them to receive and send signals and communicate with adjoining cells and their broader environment. The urothelial surface bears specific receptors that not only allow uropathogenic E. coli to attach to and invade the bladder mucosa, but also provide a route by which the bacteria ascend through the ureters to the kidney to cause pyelonephritis. Genetic ablation of one or more uroplakin genes in mice causes severe retrograde vesicoureteral reflux, hydronephrosis, and renal failure, conditions that mirror certain human congenital diseases. Clearly, abnormalities of the lower urinary tract can impact the upper tract, and vice versa, through the urothelial connection. In this review, we highlight recent advances in the field of urothelial biology by focusing on the uroplakins, a group of urothelium-specific and differentiation-dependent integral membrane proteins. We discuss these proteins' biochemistry, structure, assembly, intracellular trafficking, and their emerging roles in urothelial biology, function, and pathological processes. We also call attention to important areas where greater investigative efforts are warranted.

LEF1 in androgen-independent prostate cancer: regulation of androgen receptor expression, prostate cancer growth, and invasion.

A major obstacle in treating prostate cancer is the development of androgen-independent disease. In this study, we examined LEF1 expression in androgen-independent cancer as well as its regulation of androgen receptor (AR) expression, prostate cancer growth, and invasion in androgen-independent prostate cancer cells. Affymetrix microarray analysis of LNCaP and LNCaP-AI (androgen-independent variant LNCaP) cells revealed 100-fold increases in LEF1 expression in LNCaP-AI cells. We showed that LEF1 overexpression in LNCaP cells resulted in increased AR expression and consequently enhanced growth and invasion ability, whereas LEF1 knockdown in LNCaP-AI cells decreased AR expression and, subsequently, growth and invasion capacity. Chromatin immunoprecipitation, gel shift, and luciferase assays confirmed LEF1 occupancy and regulation of the AR promoter. Thus, we identified LEF1 as a potential marker for androgen-independent disease and as a key regulator of AR expression and prostate cancer growth and invasion. LEF1 is highly expressed in androgen-independent prostate cancer, potentially serving as a marker for androgen-independent disease.

Origin of the tetraspanin uroplakins and their co-evolution with associated proteins: implications for uroplakin structure and function.

Genome level information coupled with phylogenetic analysis of specific genes and gene families allow for a better understanding of the structure and function of their protein products. In this study, we examine the mammalian uroplakins (UPs) Ia and Ib, members of the tetraspanin superfamily, that interact with uroplakins UPII and UPIIIa/IIIb, respectively, using a phylogenetic approach of these genes from whole genome sequences. These proteins interact to form urothelial plaques that play a central role in the permeability barrier function of the apical urothelial surface of the urinary bladder. Since these plaques are found exclusively in mammalian urothelium, it is enigmatic that UP-like genomic sequences were recently found in lower vertebrates without a typical urothelium. We have cloned full-length UP-related cDNAs from frog (Xenopus laevis), chicken (Gallus gallus), and zebrafish (Danio rerio), and combined these data with sequence information from their orthologs in all the available fully sequenced and annotated animal genomes. Phylogenetic analyses of all the available uroplakin sequences, and an understanding of their distribution in several animal taxa, suggest that: (i) the UPIa/UPIb and UPII/UPIII genes evolved by gene duplication in the common ancestor of vertebrates; (ii) uroplakins can be lost in different combinations in vertebrate lineages; and (iii) there is a strong co-evolutionary relationship between UPIa and UPIb and their partners UPII and UPIIIa/IIIb, respectively. The co-evolution of the tetraspanin UPs and their associated proteins may fine-tune the structure and function of uroplakin complexes enabling them to perform diverse species- and tissue-specific functions. The structure and function of uroplakins, which are also expressed in Xenopus kidney, oocytes and fat body, are much more versatile than hitherto appreciated.

Biochemical and biological analyses of Rgr RalGEF oncogene.

The Ras superfamily of GTP-binding proteins is involved in many cellular processes, including cell proliferation, movement, and morphology. One such member, Ral GTPase, activates downstream signaling molecules after a conversion to the active state on GTP binding. The RalGDS-related (Rgr) oncogene belongs to the RalGDS family of guanine nucleotide exchange factors (GEFs). RalGEFs activate Ral by stimulating the dissociation of GDP, allowing the binding of GTP and the initiation of downstream signaling events by Ral effectors. Rgr was first identified as a fusion between the rabbit homolog of the Rad 23 gene and the Rgr gene in a rabbit squamous cell carcinoma. The Rgr portion of the fusion was demonstrated to contain the oncogenic activity. The human form of the Rgr oncogene was identified recently, and expression was detected in human T-cell malignancies. This chapter describes the analysis of rabbit and human Rgr function using various methods. These assays may be used for the study of oncogene function in other systems.

Mouse p10, an alternative spliced form of p15INK4b, inhibits cell cycle progression and malignant transformation.

The INK4 family of proteins negatively regulates cell cycle progression at the G(1)-S transition by inhibiting cyclin-dependent kinases. Two of these cell cycle inhibitors, p16(INK4A) and p15(INK4B), have tumor suppressor activities and are inactivated in human cancer. Interestingly, both INK4 genes express alternative splicing variants. In addition to p16(INK4A), the INK4A locus encodes a splice variant, termed p12--specifically expressed in human pancreas--and ARF, a protein encoded by an alternative reading frame that acts as a tumor suppressor through the p53 pathway. Similarly, the human INK4B locus encodes the p15(INK4B) tumor suppressor and one alternatively spliced form, termed as p10. We show here that p10, which arises from the use of an alternative splice donor site within intron 1, is conserved in the mouse genome and is widely expressed in mouse tissues. Similarly to mouse p15(INK4B), p10 expression is also induced by oncogenic insults and transforming growth factor-beta treatment and acts as a cell cycle inhibitor. Importantly, we show that mouse p10 is able to induce cell cycle arrest in a p53-dependent manner. We also show that mouse p10 is able to inhibit foci formation and anchorage-independent growth in wild-type mouse embryonic fibroblasts, and that these antitransforming properties of mouse p10 are also p53-dependent. These results indicate that the INK4B locus, similarly to INK4A-ARF, harbors two different splicing variants that can be involved in the regulation of both the p53 and retinoblastoma pathways, the two major molecular pathways in tumor suppression.

Differential expression of cell cycle regulators in phenotypic variants of transgenically induced bladder tumors: implications for tumor behavior.

Proteins controlling cell growth, differentiation, apoptosis, and oncogenic stress are often deregulated in tumor cells. However, whether such deregulations affect tumor behavior remains poorly understood in many tumor types. We recently showed that the urothelium-specific expression of activated H-ras and SV40 T antigen in transgenic mice produced two distinctive types of tumors strongly resembling the human superficial papillary tumors and carcinoma in situ of the bladder, respectively. Here we assessed the expression of a key set of cell cycle regulators in these mouse tumors and in a new transgenic line expressing a cyclin D1 oncogene in the urothelium. We found that urothelia of the wild-type and cyclin D1 transgenic mice exhibited a profile of cell cycle regulators found in quiescent (G(0)) cells, indicating that urothelium overexpressing the cyclin D1 (an 8-fold increase) is reminiscent of normal urothelium and remains slow-cycling. Low-grade superficial papillary tumors induced by activated H-ras had no detectable Rb family proteins (Rb, p107, and p130) and late cell cycle cyclins and kinases (cyclin A, E, and CDK1), but had increased level of p16, p53, and MDM2. These data suggest that the inactivation of the Rb pathway plays an important role in H-ras-induced superficial papillary tumors and that oncogenic H-ras can induce a compensatory activation of alternative tumor suppressor pathways. In contrast, carcinoma in situ of the bladder induced by SV40 T antigen had increased expression of cell cycle regulators mainly active in post-G(1) phases. The fact that phenotypically different bladder tumors exhibit different patterns of cell cycle regulators may explain why these tumors have different propensity to progress to invasive tumors. Our results indicate that the transgenic mouse models can be used not only for studying tumorigenesis but also for evaluating therapeutic strategies that target specific cell cycle regulators.

Inhibition of Ras oncogenic activity by Ras protooncogenes.

Point mutations in ras genes have been found in a large number and wide variety of human tumors. These oncogenic Ras mutants are locked in an active GTP-bound state that leads to a constitutive and deregulated activation of Ras function. The dogma that ras oncogenes are dominant, whereby the mutation of a single allele in a cell will predispose the host cell to transformation regardless of the presence of the normal allele, is being challenged. We have seen that increasing amounts of Ras protooncogenes are able to inhibit the activity of the N-Ras oncogene in the activation of Elk in NIH 3T3 cells and in the formation of foci. We have been able to determine that the inhibitory effect is by competition between Ras protooncogenes and the N-Ras oncogene that occurs first at the effector level at the membranes, then at the processing level and lastly at the effector level in the cytosol. In addition, coexpression of the N-Ras protooncogene in thymic lymphomas induced by the N-Ras oncogene is associated with increased levels of p107, p130 and cyclin A and decreased levels of Rb. In the present report, we have shown that the N-Ras oncogene is not truly dominant over Ras protooncogenes and their competing activities might be depending on cellular context.

Using sindbis viral vectors for specific detection and suppression of advanced ovarian cancer in animal models.

We studied the therapeutic value of Sindbis vectors for advanced metastatic ovarian cancer by using two highly reproducible and clinically accurate mouse models: a SCID xenograft model, established by i.p. inoculation of human ES-2 ovarian cancer cells, and a syngenic C57BL/6 model, established by i.p. inoculation of mouse MOSEC ovarian cancer cells. We demonstrate through imaging, histologic, and molecular data that Sindbis vectors systemically and specifically infect/detect and kill metastasized tumors in the peritoneal cavity, leading to significant suppression of the carcinomatosis in both animal models. Use of two different bioluminescent genetic markers for the IVIS Imaging System permitted demonstration, for the first time, of an excellent correlation between vector delivery and metastatic locations in vivo. Sindbis vector infection and growth suppression of murine MOSEC tumor cells indicate that Sindbis tumor specificity is not attributable to a species difference between human tumor and mouse normal cells. Sindbis virus is known to infect mammalian cells using the Mr 67,000 laminin receptor. Immunohistochemical staining of tumor cells indicates that laminin receptor is elevated in tumor versus normal cells. Down-regulated expression of laminin receptor with small interfering RNA significantly reduces the infectivity of Sindbis vectors. Tumor overexpression of the laminin receptor may explain the specificity and efficacy that Sindbis vectors demonstrate for tumor cells in vivo. We show that incorporation of antitumor cytokine genes such as interleukin-12 and interleukin-15 genes enhances the efficacy of the vector. These results suggest that Sindbis viral vectors may be promising agents for both specific detection and growth suppression of metastatic ovarian cancer.

The Rgr oncogene induces tumorigenesis in transgenic mice.

To study the oncogenic potential of Rgr in vivo, we have generated several transgenic Rgr mouse lines, which express the oncogene under the control of different promoters. These studies revealed that Rgr expression leads to the generation of various pathological alterations, including fibrosarcomas, when its transgenic expression is restricted to nonlymphoid tissues. Moreover, the overall incidence and latency of fibrosarcomas were substantially increased and shortened, respectively, in a p15INK4b-defective background. More importantly, we also have demonstrated that Rgr expression in thymocytes of transgenic mice induces severe alterations in the development of the thymocytes, which eventually lead to a high incidence of thymic lymphomas. This study demonstrates that oncogenic Rgr can induce expression of p15INK4b and, more importantly, that both Rgr and p15INK4b cooperate in the malignant phenotype in vivo. These findings provide new insights into the tumorigenic role of Rgr as a potent oncogene and show that p15INK4b can act as a tumor suppressor gene.

Ras activation in Jurkat T cells following low-grade stimulation of the T-cell receptor is specific to N-Ras and occurs only on the Golgi apparatus.

Ras activation is critical for T-cell development and function, but the specific roles of the different Ras isoforms in T-lymphocyte function are poorly understood. We recently reported T-cell receptor (TCR) activation of ectopically expressed H-Ras on the the Golgi apparatus of T cells. Here we studied the isoform and subcellular compartment specificity of Ras signaling in Jurkat T cells. H-Ras was expressed at much lower levels than the other Ras isoforms in Jurkat and several other T-cell lines. Glutathione S-transferase-Ras-binding domain (RBD) pulldown assays revealed that, although high-grade TCR stimulation and phorbol ester activated both N-Ras and K-Ras, low-grade stimulation of the TCR resulted in specific activation of N-Ras. Surprisingly, whereas ectopically expressed H-Ras cocapped with the TCRs in lipid microdomains of the Jurkat plasma membrane, N-Ras did not. Live-cell imaging of Jurkat cells expressing green fluorescent protein-RBD, a fluorescent reporter of GTP-bound Ras, revealed that N-Ras activation occurs exclusively on the Golgi apparatus in a phospholipase Cgamma- and RasGRP1-dependent fashion. The specificity of N-Ras signaling downstream of low-grade TCR stimulation was dependent on the monoacylation of the hypervariable membrane targeting sequence. Our data show that, in contrast to fibroblasts stimulated with growth factors in which all three Ras isoforms become activated and signaling occurs at both the plasma membrane and Golgi apparatus, Golgi-associated N-Ras is the critical Ras isoform and intracellular pool for low-grade TCR signaling in Jurkat T cells.

p53 deficiency provokes urothelial proliferation and synergizes with activated Ha-ras in promoting urothelial tumorigenesis.

Mutation and deletion of the p53 tumor suppressor gene are arguably the most prevalent among the multiple genetic alterations found in human bladder cancer, but these p53 defects are primarily associated with the advanced diseases, and their roles in bladder tumor initiation and in synergizing with oncogenes in tumor progression have yet to be defined. Using the mouse uroplakin II gene promoter, we have targeted into urothelium of transgenic mice a dominant-negative mutant of p53 that lacks the DNA-binding domain but retains the tetramerization domain. Urothelium-expressed p53 mutant binds to and stabilizes the endogenous wild-type p53, induces nuclear abnormality, hyperplasia and occasionally dysplasia, without eliciting frank carcinomas. Concurrent expression of the p53 mutant with an activated Ha-ras, the latter of which alone induces urothelial hyperplasia, fails to accelerate tumor formation. In contrast, the expression of the activated Ha-ras in the absence of p53, as accomplished by crossing the activated Ha-ras transgenic mice with the p53 knockout mice, results in early-onset bladder tumors that are either low-grade superficial papillary or high grade in nature. These results provide the first in vivo experimental evidence that p53 deficiency predisposes the urothelium to hyperproliferation, but is insufficient for bladder tumorigenesis; that the mere reduction of p53 dosage, as produced in transgenic mice expressing the dominant-negative p53 or in heterozygous p53 knockouts, is incapable of synergizing with Ha-ras to induce bladder tumors; and that the complete loss of p53 is a prerequisite for collaborating with activated Ha-ras to promote bladder tumorigenesis.

Complex effects of Ras proto-oncogenes in tumorigenesis.

Ras proteins have been found mutated in about one-third of human tumors. In vitro, Ras has been shown to regulate distinct and contradictory effects, such as cellular proliferation and apoptosis. Nonetheless, the effects that the wild-type protein elicits in tumorigenesis are poorly understood. Depending on the type of tissue, Ras proto-oncogenes appear to either promote or inhibit the tumor phenotype. In this report, we treated wild-type and N-ras knockout mice with 3-methylcholanthrene (MCA) to induce fibrosarcomas and found that MCA is more carcinogenic in wild-type mice than in knockout mice. After injecting different doses of a tumorigenic cell line, the wild-type mice exhibited a shorter latency of tumor development than the knockouts, indicating that there are N-ras-dependent differences in the stromal cells. Likewise, we have analyzed B-cell lymphomas induced by either N-methylnitrosourea or by the N-ras oncogene in mice that over-express the N-ras proto-oncogene and found that the over-expression of wild-type N-ras is able to increase the incidence of these lymphomas. Considered together, our results indicate that Ras proto-oncogenes can enhance or inhibit the malignant phenotype in vivo in different systems.