Differential oncogenic potential of geographically distinct Helicobacter pylori CagA isoforms in mice

Infection with cagA‐positive Helicobacter pylori is associated with gastric carcinoma. The cagA‐encoded CagA protein is delivered into gastric epithelial cells and, upon tyrosine phosphorylation at the C‐terminal EPIYA segments, binds and deregulates SHP‐2 oncoprotein. On the basis of the differential alignment of the EPIYA segments, CagA can be subdivided into Western CagA, which is produced by H. pylori isolated in Western countries, and East Asian CagA, which is produced by H. pylori circulating in East Asian countries. Western CagA contains EPIYA‐A, EPIYA‐B and variable numbers of EPIYA‐C segments, whereas East Asian CagA contains EPIYA‐A, EPIYA‐B and variable numbers of EPIYA‐D segments. Upon tyrosine phosphorylation, EPIYA‐C and EPIYA‐D, respectively, serve as low‐affinity and high‐affinity SHP‐2‐binding sites. We previously reported that systemic expression of East Asian CagA (CagA‐ABDD) induces gastrointestinal and hematopoietic malignancies in mice. In this study, we generated transgenic mice that systemically express Western CagA (CagA‐ABCCC), the levels of which are comparable to those in mice expressing East Asian CagA. The mice developed gastric epithelial hypertrophy and gastrointestinal tumors and also showed lymphoid abnormality but not myeloid abnormalities such as granulocytosis and myeloid leukemia found in mice carrying East Asian CagA. The incidence of tumors in mice expressing Western CagA was significantly lower than that in mice expressing East Asian CagA. Our results indicate that Western CagA is qualitatively less oncogenic than East Asian CagA. Differential oncogenic potential of geographically distinct CagA isoforms may contribute to the differential prevalence of gastric carcinoma between East Asian countries and Western countries. © 2009 UICC     

Oncogenic potential of BRAF versus RAS

Mutations in the ERK pathway occur in approximately one-third of all human cancers and most often involve production of mutant RAS or BRAF. Several studies, including our own, have shown that mutations in the BRAF and RAS genes are generally mutually exclusive. This study was performed to determine the relative oncogenic potential of the BRAF and RAS oncogenes. BRAF(V600E)-, H-RAS(G12V)-, and N-RAS(Q61R)-transfected mouse embryonic fibroblasts (MEFs) that lack p53 (p53(-/-)) or contain mutations at codon 172 (p53(R172H) and p53(R172P)) were able to induce morphologically transformed foci in p53(-/-) and p53(R172H) MEFs but not in p53(R172P) MEFs. Interestingly, BRAF(V600E) was less potent than mutant H-RAS(G12V) or N-RAS(Q61R) was in cooperating with mutant p53 as the numbers and sizes of foci induced by BRAF(V600E) were significantly lower and smaller. In vitro growth characteristics and anchorage-independent growth of transfected MEFs corroborated the transformed phenotype, and in vivo tumorigenesis confirmed the results. These results indicate that mutant BRAF(V600E) is weakly oncogenic compared with mutant RAS and that they both cooperate with p53(-/-) and p53(R172H) but not with p53(R172P) in oncogenic transformation.     

Differential oncogenic effects of methylnitrosourea.

We investigated differences in the oncogenic effects of methylnitrosourea (MNU) which were induced by varying dose schedules and changing administration routes. The nervous system represented the target organ when MNU was given intravenously to rats. Carcinogen by other routes resulted in decreased numbers of neurogenic tumors and the appearance of neoplasms at the injection site. Increased oral doses of MNU caused shorter survival times, a decreased incidence of neuroglial tumors, and increased numbers of thymic lymphomas and mesenchymal tumors of the nervous system. The results suggest that many tissues are susceptible to the oncogenic effects of MNU, but the degree of exposure necessary for neoplastic transformation varies.     

Human osteopontin splicing isoforms: Known roles,potential clinical applications and activated signaling pathways

Human osteopontin is subject to alternative splicing, which generates three isoforms, termed OPNa, OPNb and OPNc. These variants show specific expression and roles in different cell contexts. We present an overview of current knowledge of the expression profile of human OPN splicing isoforms (OPN-SIs), their tissue-specific roles, and the pathways mediating their functional properties in different pathophysiological conditions. We also describe their putative application as biomarkers, and their potential use as therapeutic targets by using antibodies, oligonucleotides or siRNA molecules. This synthesis provides new clues for a better understanding of human OPN splice variants, their roles in normal and pathological conditions, and their possible clinical applications.     

A redundant oncogenic potential of the retinoic receptor (RAR) alpha, beta and gamma isoforms in acute promyelocytic leukemia.

Alterations of the retinoic acid receptor (RAR)alpha locus are found in 100% of acute promyelocytic leukemia patients, where chromosomal translocations generate the promyelocytic leukemia (PML)-RARalpha chimeric protein. Here, we have investigated the biological properties of the other RAR isoforms (RARbeta and RARgamma), through the generation and characterization of artificial PML-RAR'x' fusion proteins. Surprisingly, we found that all of the RAR isoforms share an identical oncogenic potential in vitro, thus implying that the selection of the RARalpha locus in leukemia patients must occur--rather than through functional differences among the various RAR isoforms-as the consequence of the nuclear architecture of the different RAR loci.     

The oncogenic potential of Epstein-Barr virus.

Epstein-Barr (EB) virus is a herpesvirus which is the causative agent of infectious mononucleosis. It can also be classified as a human DNA tumor virus as it is also etiologically associated with the development of Burkitt's lymphoma (BL) and nasopharyngeal carcinoma. EB virus involvement in these human tumors is suggested by seroepidemiological studies and the detection of virus DNA and proteins in tumor biopsies. Furthermore, EB virus can be detected in lymphoproliferations and malignant tumors arising from immunosuppressed individuals which further emphasizes its oncogenic potential. EB virus immortalizes B lymphocytes in vitro giving rise to continuously proliferating lymphoblastoid cell lines (LCL). These LCL are not tumorigenic, which suggests that cellular infection by virus alone is not sufficient for full tumorigenicity. This has led to the development of a multistep scenario for the development of BL where EB virus, in conjunction with other suggested cofactors, is necessary to induce the tumorigenic phenotype.     

Uncovering MYC's full oncogenic potential in the hematopoietic system

MYC is an important oncogene in hematopoietic neoplasms in humans, yet the mechanism by which MYC induces the malignant transformation of blood cells has remained elusive. Postulating that mouse models of deregulated MYC expression may be helpful for advancing our understanding of MYC-induced hematopoietic malignancies, Suzanne Cory and her associates took advantage of the Vav promoter to express MYC throughout the hematopoietic system in transgenic mice. They report that the newly developed strain, referred to as VavP-MYC17, is prone to mature T-cell lymphomas (for which few good mouse models exist). They further show that VavP-MYC17 mice that are devoid of mature T cells (and B cells) because of genetic deficiency in Rag1 recombinase develop neoplasms of three distinct blood cell lineages: pre-T cells, pro-B cells, and macrophages. These findings establish that VavP-driven MYC has broad oncogenic potential in the hematopoietic compartment and prompts new views of the cellular assaults of deregulated MYC on hematopoietic stem and early progenitor cells.     

Differential expression and function of AR isoforms in prostate cancer

The androgen receptor (AR) plays a key role in prostate cancer (PCa). Two isoforms of AR, are AR-A and -B, which differ by a lack of the first 187 amino acids in the NH2-terminal transactivation domain of AR-A. Since little is known about the expression and basic function of the AR-A/B isoforms in prostate cancer, the aim of this study was to analyze this possible association. The AR-A, -B and AR-A/B ratio was determined in the tissues of healthy controls, benign prostate hyperplasia (BPH) and PCa by means of Western blot analysis and immunofluorescence. The elevation of AR-A, and -B, as well as the AR-A/B ratio with regard to Gleason scores, were assessed in prostate cancer compared to BPH and normal prostate. In order to further investigate the role of AR A/B isoform function, we transfected PC3 cells with an AR or AR-A expression vector. The overexpression of AR-A and -B significantly decreased the invasion and proliferation of PC3 cells. However, the overexpression of AR-A further decreased proliferation but accelerated the invasion of PC3 cells compared to AR-B. In conclusion, the elevation of AR-A and -B, and the AR-A/B ratio, is associated with prostate cancer occurrence and progression. Furthermore, AR-A could provide a new potential therapy with regard to the decrease in the invasion and proliferation of prostate cancer cells. Our study provides insight into further understanding the biological role of AR-A in its interaction with AR-B and its impact on PCa clinical treatment.     

Overexpression confers an oncogenic potential upon the eph gene

The eph gene encodes a putative receptor tyrosine kinase for an as yet unknown ligand. Some human cancer cells have been found to overexpress eph mRNAs without gene amplification. We show here that NIH3T3 cells acquire tumorigenic ability in nude mice and make colonies in soft agar with a viral LTR (Long Terminal Repeat)-driven artificial expression of the eph gene to a high level. This result supports the alleged contribution of overexpressed receptor tyrosine kinases to cell transformation.     

A novel putative tyrosine kinase receptor with oncogenic potential

We have detected transforming activity by a tumorigenicity assay using NIH3T3 cells transfected with DNA from a chronic myeloproliferative disorder patient. Here, we report the cDNA cloning of the corresponding oncogene, designated UFO, in allusion to the as yet unidentified function of its protein. Nucleotide sequence analysis of a 3116bp cDNA clone revealed a 2682-bp-long open reading frame capable of directing the synthesis of a 894 amino acid polypeptide. The predicted UFO protein exhibits characteristic features of a transmembrane receptor with associated tyrosine kinase activity. The UFO proto-oncogene maps to human chromosome 19q13.1 and is transcribed into two 5.0 kb and 3.2 kb mRNAs in human bone marrow and human tumor cell lines. The UFO locus is evolutionarily conserved between vertebrate species. A 4.0 kb mRNA of the murine UFO homolog is expressed in a variety of different mouse tissues. We thus have identified a novel element of the complex signaling network involved in the control of cell proliferation and differentiation.     

三苯氧胺对子宫内膜癌的潜在致癌作用机制

三苯氧胺是一种具有抗雌激素作用的非甾体类化合物,已成为各期乳腺癌患者的一线内分泌治疗药物。但最新的临床研究表明,使用三苯氧胺作为辅助治疗的乳腺癌患者并发子宫内膜癌的危险性增加。通常认为,三苯氧胺在乳腺组织中具有抗雌激素作用,但是在子宫内膜细胞中却表现出类雌激素作用。越来越多的临床试验正聚焦于三苯氧胺与子宫内膜癌的关系,三苯氧胺对子宫内膜的潜在致癌作用机制也成为当前研究的一项热点。     

In vitro assessment of the oncogenic potential of nitroimidazole radiosensitizers

Two hypoxic cell radiosensitizers, RSU-1069 and Ro-03-8799 were investigated for their in vitro cytotoxicity and ability to induce oncogenic transformation and sister chromatid exchanges in the C3H 10T1/2 cell system. Their effects were then compared to those of the clinically used sensitizer misonidazole. Equitoxic doses of Ro-03-8799 and RSU-1069 were approximately 3-fold and 150-fold less than misonidazole, respectively, with both agents exhibiting dose and contact time dependence for cell killing. Both sensitizers appeared no more oncogenic than misonidazole when administered at equitoxic dosages. At doses of equivalent sensitizing efficiencies relative to misonidazole, RSU-1069, but not Ro-03-8799, induced significantly higher transformation incidence. In conjunction with gamma-irradiation, both Ro-03-8799 and misonidazole induced an additive transformation response. Preliminary studies also indicate that RSU-1069, at a concentration of 0.03 mM, induced significantly higher sister chromatid exchanges (SCE) per chromosome than either Ro-03-8799 or misonidazole at concentrations 30-fold higher. Although several earlier studies have indicated that RSU-1069 may be more efficient than misonidazole as an hypoxic cell sensitizer, the present findings suggest that it may also carry a higher risk of inducing tumors by itself at clinically relevant concentrations.     

Expression of oncogenic BARD1 isoforms affects colon cancer progression and correlates with clinical outcome

Background:

Colon cancer predisposition is associated with mutations in BRCA1. BRCA1 protein stability depends on binding to BARD1. In different cancers, expression of differentially spliced BARD1 isoforms is correlated with poor prognosis and decreased patient survival. We therefore suspected a role of BARD1 isoforms in colon cancer.

Methods:

We performed immunohistochemistry in 168 colorectal cancers, using four antibodies directed against differentially expressed regions of BARD1. We determined structure and relative expression of BARD1 mRNA isoforms in 40 tumour and paired normal peri-tumour tissues. BARD1 expression was correlated with clinical outcome.

Results:

BARD1 isoforms were expressed in 98% of cases and not correlated with BRCA1. BARD1 mRNA isoforms were upregulated in all tumours as compared with paired normal peri-tumour tissues. Non-correlated expression and localisation of different epitopes suggested insignificant expression of full-length (FL) BARD1. Expression of N- and C-terminal epitopes correlated with increased survival, but expression of epitopes mapping to the middle of BARD1 correlated with decreased survival. Middle epitopes are present in oncogenic BARD1 isoforms, which have pro-proliferative functions. Correlated upregulation of only N- and C-terminal epitopes reflects the expression of isoforms BARD1δ and BARD1ϕ.

Conclusion:

Our results suggest that BARD1 isoforms, but not FL BARD1, are expressed in colon cancer and affect its progression and clinical outcome.     

The oncogenic epidermal growth factor receptor variant Xiphophorus melanoma receptor kinase induces motility in melanocytes by modulation of focal adhesions

One of the most prominent features of malignant melanoma is the fast generation of metastasizing cells, resulting in the poor prognosis of patients with this tumor type. For this process, cells must gain the ability to migrate. The oncogenic receptor Xmrk (Xiphophorus melanoma receptor kinase) from the Xiphophorus melanoma system is a mutationally activated version of the epidermal growth factor receptor that induces the malignant transformation of pigment cells. Here, we show that the activation of Xmrk leads to a clear increase of pigment cell motility in a fyn-dependent manner. Stimulation of Xmrk induces its interaction with the focal adhesion kinase (FAK) and the interaction of active, receptor-bound fyn with FAK. This results in changes in FAK activity and induces the modulation of stress fibers and focal adhesions. Overexpression of dominant-negative FAK shows that the activity of innate FAK and a receptor-induced focal adhesion turnover are a prerequisite for pigment cell migration. Our findings show that in our system, Xmrk is sufficient for the induction of pigment cell motility and underlines a role of the src family protein tyrosine kinase fyn in melanoma development and progression.