Mutant c-Ki-ras p21 protein in chemical carcinogenesis in humans exposed to vinyl chloride

Potent Impact of Plastic Nanomaterials and Micromaterials on the Food Chain and Human Health

Plastic products are inexpensive, convenient, and are have many applications in daily life. We overuse plastic-related products and ineffectively recycle plastic that is difficult to degrade. Plastic debris can be fragmented into smaller pieces by many physical and chemical processes. Plastic debris that is fragmented into microplastics or nanoplastics has unclear effects on organismal systems. Recently, this debris was shown to affect biota and to be gradually spreading through the food chain. In addition, studies have indicated that workers in plastic-related industries develop many kinds of cancer because of chronic exposure to high levels of airborne microplastics. Microplastics and nanoplastics are everywhere now, contaminating our water, air, and food chain. In this review, we introduce a classification of plastic polymers, define microplastics and nanoplastics, identify plastics that contaminate food, describe the damage and diseases caused by microplastics and nanoplastics, and the molecular and cellular mechanisms of this damage and disease as well as solutions for their amelioration. Thus, we expect to contribute to the understanding of the effects of microplastics and nanoplastics on cellular and molecular mechanisms and the ways that the uptake of microplastics and nanoplastics are potentially dangerous to our biota. After understanding the issues, we can focus on how to handle the problems caused by plastic overuse.

Induction of Fibrosis and Autophagy in Kidney Cells by Vinyl Chloride

Vinyl chloride (VC) is a noninfective occupational risk factor. It is found in industrial chemicals, volatile organic compounds, cigarette smoke ingredients, etc. It is a kind of toxic gas that causes many diseases. VC exposure causes an increased risk of liver fibrosis and can result in angiosarcoma of the liver. Previous studies have shown that high-doses of VC exposure in mice resulted in acute death with marked tubular necrosis of the renal cortex. In this study, we assessed the nephrotoxicity of VC in vitro and in vivo. As a result, we demonstrated that VC induced fibrosis-associated protein expression, such as connective tissue growth factor (CTGF), plasminogen activator inhibitor-1 (PAI-1) and collagen 1, and autophagy-associated protein expression, such as Beclin 1 and LC3-II, in kidney cells. The beclin1 siRNA experiments found that autophagy inhibited VC-induced fibrosis. Blood urea nitrogen (BUN) and creatinine levels were increased after VC treatment. Furthermore, VC caused glomerulosclerosis and tubular injury in mouse kidney tissues. Kidney tissue sections showed that VC induced fibrosis and autophagy in mouse kidney tissues. In summary, the results of VC-induced fibrosis suggest that autophagy plays an important role in kidney damage. VC may cause nephrotoxicity, and the results illustrate the importance of considering the toxicological hazards of VC in kidney cells.

Elevated serum RAS p21 is an independent prognostic factor in metastatic breast cancer

Background

An important component of the RAS signalling pathway, the RAS p21 oncogene, is frequently hyperactivated in breast cancer. Its expression in tumor tissue has been linked to poor clinical outcome. This study was designed to evaluate the clinical relevance of RAS p21 levels in peripheral blood in a large cohort of metastatic breast cancer patients.

Methods

Two hundred fifty-one patients with metastatic breast cancer were enrolled in this prospective, multicentre, open-label, non-randomized study. Blood samples were collected before start of first-line or later-line treatment. RAS p21 was determined using a sandwich-type ELISA immunoassay. For the determination of the cutoff, blood samples from age-matched healthy controls were analyzed. A value above 452 pg/ml was regarded as elevated (mean + 2 x SD). In the univariate survival analysis, two other cutoffs were considered as well (50th and 75th percentile of patients, i.e. 229 pg/ml and 320 pg/ml). Circulating tumor cells (CTCs) were detected using the CellSearch system.

Results

29 of 251 (12%) patients had RAS p21 levels above the cut-off level of 452 pg/ml. Clinical-pathological parameters, such as hormone receptor and HER2 status, line of therapy and CTC status, did not correlate with RAS p21 levels. Elevated RAS p21 was significantly associated with shorter progression-free and overall survival in the univariate analysis (median PFS: 3.9 months [95%-CI: 1.8–6.0] for patients with elevated RAS p21 levels versus 8.5 months [95%-CI: 7.4–9.5] with non-elevated levels [p = 0.01]; median OS: 7.1 months [95%-CI: 0.3–14.2] versus not reached [p = 0.002], respectively). When RAS p21 cutoffs other than 452 pg/ml were considered, elevated RAS p21 was significantly associated with OS but not with PFS. Classical clinical-pathological factors were included into a multivariate Cox regression analysis. In addition, factors previously shown to influence survival in a univariate analysis, such as serum HER2, CAIX and TIMP1, were included as well. In the multivariate analysis, RAS p21, presence of ≥5 CTCs per 7.5 ml blood, higher grading and higher line of therapy remained independent predictors of shorter OS.

Conclusions

Metastatic breast cancer patients with elevated levels of circulating RAS p21 have significantly worse clinical outcome. Hypothetically, these patients might benefit from therapeutic strategies targeting RAS pathway.

Trial registration

Current Controlled Trials ISRCTN59722891 (DETECT); trial registration date: April, 17th 2010; the trial was registered retrospectively.

Non‑infective occupational risk factors for hepatocellular carcinoma: A review (Review)

Liver cancer is the second leading worldwide cause of cancer‑associated mortalities. Hepatocellular carcinoma, which accounts for the majority of liver tumors, ranks fifth among types of human cancer. Well‑established risk factors for liver cancer include the hepatitis B and C viruses, aflatoxins, alcohol consumption, and oral contraceptives. Tobacco smoking, androgenic steroids, and diabetes mellitus are suspected risk factors. Current knowledge regarding non‑infective occupational risk factors for liver cancer is inconclusive. The relevance of liver disorders to occupational medicine lies in the fact that the majority of chemicals are metabolized in the liver, and toxic metabolites generated via metabolism are the predominant cause of liver damage. However, their non‑specific clinical manifestations that are similar in a number of liver diseases make diagnosis difficult. Furthermore, concomitant conditions, such as viral hepatitis and alcohol or drug abuse, may mask liver disorders that result from occupational hepatotoxic agents and block the demonstration of an occupational cause. The identification of environmental agents that result in human cancer is a long and often difficult process. The purpose of the present review is to summarize current knowledge regarding the association of non‑infective occupational risk exposure and HCC, to encourage further research and draw attention to this global occupational public health problem.

The roles of hyaluronan/RHAMM/CD44 and their respective interactions along the insidious pathways of fibrosarcoma progression

Fibrosarcomas are rare malignant mesenchymal tumors originating from fibroblasts. Importantly, fibrosarcoma cells were shown to have a high content and turnover of extracellular matrix (ECM) components including hyaluronan (HA), proteoglycans, collagens, fibronectin, and laminin. ECMs are complicated structures that surround and support cells within tissues. During cancer progression, significant changes can be observed in the structural and mechanical properties of the ECM components. Importantly, hyaluronan deposition is usually higher in malignant tumors as compared to benign tissues, predicting tumor progression in some tumor types. Furthermore, activated stromal cells are able to produce tissue structure rich in hyaluronan in order to promote tumor growth. Key biological roles of HA result from its interactions with its specific CD44 and RHAMM (receptor for HA-mediated motility) cell-surface receptors. HA-receptor downstream signaling pathways regulate in turn cellular processes implicated in tumorigenesis. Growth factors, including PDGF-BB, TGFβ2, and FGF-2, enhanced hyaluronan deposition to ECM and modulated HA-receptor expression in fibrosarcoma cells. Indeed, FGF-2 through upregulation of specific HAS isoforms and hyaluronan synthesis regulated secretion and net hyaluronan deposition to the fibrosarcoma pericellular matrix modulating these cells' migration capability. In this paper we discuss the involvement of hyaluronan/RHAMM/CD44 mediated signaling in the insidious pathways of fibrosarcoma progression.

Functional genomic studies: insights into the pathogenesis of liver cancer

Liver cancer is the sixth-most-common cancer overall but the third-most-frequent cause of cancer death. Among primary liver cancers, hepatocellular carcinoma (HCC), the major histological subtype, is associated with multiple risk factors, including hepatitis B and C virus infection, alcohol consumption, obesity, and diet contamination. Although previous studies have revealed that certain genetic and epigenetic changes, such as TP53 and β-catenin mutations, occur in HCC cells, the pathogenesis of this cancer remains obscure. Functional genomic approaches-including genome-wide association studies, whole-genome and whole-exome sequencing, array-based comparative genomic hybridization, global DNA methylome mapping, and gene or noncoding RNA expression profiling-have recently been applied to HCC patients with different clinical features to uncover the genetic risk factors and underlying molecular mechanisms involved in this cancer's initiation and progression. The genome-wide analysis of germline and somatic genetic and epigenetic events facilitates understanding of the pathogenesis and molecular classification of liver cancer as well as the identification of novel diagnostic biomarkers and therapeutic targets for cancer.

Plastics and carcinogenesis: The example of vinyl chloride

The manufacture, use and disposal of various plastics can pose numerous health risks, including the risk of cancer. A model example of carcinogenic risk from plastics is provided by polyvinyl chloride, since it is composed of the known human carcinogen vinyl chloride (VC). In recent years, much has been learned about the molecular biological pathways of VC carcinogenesis. This has led to molecular epidemiologic studies of VC carcinogenesis in exposed human populations which have identified useful biomarkers of exposure, effect and susceptibility for VC. These studies have in turn provided the basis for new molecular approaches for the prevention and treatment of VC cancers. This model could have much wider applicability for many other carcinogenic exposures and many other human cancers.

Primary vascular tumors of the lungs: a review

Unlike their counterparts in other organ systems, primary vascular neoplasms of the lung are rare. Most of these lesions have only been reported as isolated case studies or small series. When dealing with malignant lesions, metastasis from extrapulmonary sites will have to be excluded before a primary location in the lungs can be confirmed. In this review, the clinicopathologic, immunophenotypical, ultrastructural, and molecular biologic characteristics of primary vascular tumors of the lungs are discussed. The tumoral conditions that will be addressed include hemangioma, lymphangioma, epithelioid hemangioendothelioma, angiosarcoma, and Kaposi's sarcoma. Their respective differential diagnoses will also be discussed.

Vinyl chloride and the liver

Vinyl chloride monomer is a known cause of angiosarcoma of the liver. It also has other toxic effects on the liver, and it has recently been suggested that exposure to vinyl chloride also causes hepatocellular carcinoma. However, the data on which this conclusion is based is incomplete. There is inadequate ascertainment of unequivocal diagnoses. In the largest studies lack of data meant that confounding diseases such as viral hepatitis or alcoholic liver disease could not be assessed. At best, the increase in risk is minimal, based on more than 22,000 exposed workers and more than 640,000 person years of observation. However, based on the available data the hypothesis that vinyl chloride causes or contributes to the development of hepatocellular carcinoma remains unproven.

Gene-environment interactions between DNA repair polymorphisms and exposure to the carcinogen vinyl chloride

We have recently suggested that polymorphisms in metabolism and repair pathways may play a role in modulating the effects of exposure to the carcinogen vinyl chloride in the production of biomarkers of its mutagenic damage. The aim of the present study was to extend these observations by examining gene-environment interactions between several common polymorphisms in the DNA repair genes XRCC1 and ERCC2/XPD and vinyl chloride exposure on the production of vinyl chloride-induced biomarkers of mutation. A cohort of 546 French vinyl chloride workers were genotyped for the XRCC1 codon 194 (Arg>Trp; rs1799782), 280 (Arg>His; rs25489) and 399 (Arg>Gln; rs25487) polymorphisms and the ERCC2/XPD codon 312 (Asp>Asn; rs1799793) and 751 (Lys>Gln; rs13181) polymorphisms. The results demonstrated a statistically significant allele dosage effect of the XRCC1 399 variant on the production of the vinyl chloride-induced mutant p53 biomarker, even after controlling for confounders including cumulative vinyl chloride exposure (p = 0.03), with a potentially supramultiplicative gene-environment interaction. In addition, the results demonstrate statistically significant allele dosage effects of the ERCC2/XPD 312 and 751 variants on the production of the vinyl chloride-induced mutant ras-p21 biomarker, even after controlling for confounders including cumulative vinyl chloride exposure (p < 0.0001 and p = 0.0006, respectively), with a potentially supramultiplicative gene-environment interaction for the codon 751 allele. Finally, the results suggest potential supramultiplicative gene-gene interactions between CYP2E1 (c2 allele; rs3813867) and ERCC2/XPD polymorphisms that are consistent with the proposed carcinogenic pathway for vinyl chloride, which requires metabolic activation by CYP2E1 to reactive intermediates that form DNA adducts that, if not removed by DNA repair mechanisms, result in oncogenic mutations.

Cancer epidemiology: study designs and data analysis

Among the scientific interests of cancer epidemiology is the identification of both environmental and genetic factors associated with cancer development. Observational designs requiring sophisticated methodology are applied to control for potential confounding factors. The enormous biotechnological potential developed in the last two decades has allowed the integration of a plethora of new biomarkers in epidemiological studies to better define the exposure and "neoclassic" outcomes, as well as incorporating genetic susceptibility factors in both classical and new epidemiological designs. The integration of scopes, objectives, data and tools coming from different disciplines also benefits epidemiology, thus evolving into "systems epidemiology". In this manuscript, we review the basic concepts of study designs and data analysis and introduce readers to the more innovative aspects that are now being applied in epidemiological studies.

Parental Exposure to Medications and Hydrocarbons and ras Mutations in Children with Acute Lymphoblastic Leukemia: A Report from the Children's Oncology Group

Ras proto-oncogene mutations have been implicated in the pathogenesis of many malignancies, including leukemia. While both human and animal studies have linked several chemical carcinogens to specific ras mutations, little data exist regarding the association of ras mutations with parental exposures and risk of childhood leukemia. Using data from a large case-control study of childhood acute lymphoblastic leukemia (ALL; age &lt;15 years) conducted by the Children's Cancer Group, we used a case-case comparison approach to examine whether reported parental exposure to hydrocarbons at work or use of specific medications are related to ras gene mutations in the leukemia cells of children with ALL. DNA was extracted from archived bone marrow slides or cryopreserved marrow samples for 837 ALL cases. We examined mutations in K-ras and N-ras genes at codons 12, 13, and 61 by PCR and allele-specific oligonucleotide hybridization and confirmed them by DNA sequencing. We interviewed mothers and, if available, fathers by telephone to collect exposure information. Odds ratios (ORs) and 95% confidence intervals (CIs) were derived from logistic regression to examine the association of parental exposures with ras mutations. A total of 127 (15.2%) cases had ras mutations (K-ras 4.7% and N-ras 10.68%). Both maternal (OR 3.2, 95% CI 1.7-6.1) and paternal (OR 2.0, 95% CI 1.1-3.7) reported use of mind-altering drugs were associated with N-ras mutations. Paternal use of amphetamines or diet pills was associated with N-ras mutations (OR 4.1, 95% CI 1.1-15.0); no association was observed with maternal use. Maternal exposure to solvents (OR 3.1, 95% CI 1.0-9.7) and plastic materials (OR 6.9, 95% CI 1.2-39.7) during pregnancy and plastic materials after pregnancy (OR 8.3, 95% CI 1.4-48.8) were related to K-ras mutation. Maternal ever exposure to oil and coal products before case diagnosis (OR 2.3, 95% CI 1.1-4.8) and during the postnatal period (OR 2.2, 95% CI 1.0-5.5) and paternal exposure to plastic materials before index pregnancy (OR 2.4, 95% CI 1.1-5.1) and other hydrocarbons during the postnatal period (OR 1.8, 95% CI 1.0-1.3) were associated with N-ras mutations. This study suggests that parental exposure to specific chemicals may be associated with distinct ras mutations in children who develop ALL.

Molecular epidemiology of plasma oncoproteins in vinyl chloride monomer workers in Taiwan

AIMS

To determine the presence of Asp13-p21-ki-ras oncoprotein and p53 oncoprotein in the plasma of vinyl chloride monomer (VCM)-workers in Taiwan.

METHODS

We used enhanced chemiluminescence (ECL) western blotting to detect Asp13-p21-ki-ras and ELISA to detect mutant p53 protein (p53-Ag) and anti-p53 antibodies (p53-Ab) in the plasma of VCM-exposed workers.

RESULTS

Twenty-five out of 251 (10%) VCM-workers were positive for Asp13-p21-ki-ras in plasma, but 0 out of 36 controls were positive. There were 15 out of 95 (15.8%) plasma-positives among the more highly exposed (> 480 ppm-month) workers and 10 out of 156 (6.4%) plasma-positives among the lesser exposed (< or = 480 ppm-month). Compared to the unexposed controls, age and drinking adjusted odds ratios (95% CI) were 1.2 (0.1, 9.8) in the lower exposed workers, and 4.8 (0.8, 28) in the higher exposed workers, and there was a significant linear trend between exposure and plasma positivity (P=0.001). Thirty-three out of 251 (13.2%) VCM-workers were positive for the p53 over-expression (10% with positive p53-Ag and 2.8% with positive p53-Ab). There was a significant association between cumulative VCM exposure concentration and positive p53 expression (P=0.032) among VCM-workers after adjusting for age, hepatitis, drinking and smoking status.

CONCLUSIONS

Asp13-p21-ki-ras oncoprotein and p53 over-expression (p53-Ag or p53-Ab) can be found in the plasma of VCM-workers in Taiwan, and a significant dose-response relationship exists between plasma oncoproteins expression and VCM exposure.

Occupational exposure to dyes, metals, polycyclic aromatic hydrocarbons and other agents and K-ras activation in human exocrine pancreatic cancer

ras genes are known critical DNA targets for chemical carcinogens. Exocrine pancreatic cancer (EPC) is the human tumor with the highest prevalence of K-ras mutations at diagnosis. We analyzed the relationship between past occupational exposure to dyes, metals, polycyclic aromatic hydrocarbons (PAHs) and other agents and mutations in codon 12 of the K-ras gene in 107 incident cases of EPC. Information on occupational and life-style factors was obtained from personal interviews conducted during hospital stay. Occupational exposures were examined using industrial hygienists (IH) assessment and the Finnish job-exposure matrix (Finjem). Specific occupational exposures among K-ras mutated EPC cases (n = 83) were compared to those of K-ras wild-type EPC cases (n = 24) (case-case analysis). Multivariate-adjusted odds ratios (OR) and their corresponding 95% confidence limits were estimated by unconditional logistic regression. Cases with K-ras mutations were significantly more likely than wild-type cases to have been exposed to dyes and organic pigments (OR 4.8; p<0.05). There was some indication of weaker associations between K-ras mutations and occupational exposure to lead, PAHs, benzo[a]pyrene, gasoline, nickel, inhalatory exposure to chromium and sedentary work. The association with chromium compounds was stronger for G to T transversions, a finding compatible with experimental studies on mutation spectra for chromium. Results lend moderate support to the hypothesis of indirect relationships between occupational exposure to dyes and organic pigments and the activation of the K-ras gene in the etiopathogenesis of human exocrine pancreatic cancer.

Exploring environmental causes of altered ras effects: fragmentation plus integration?

Mutations in ras genes are the most common abnormality of oncogenes in human cancer and a major example of activation by point mutation. Experimental and epidemiological studies support the notion that Ki-ras activation and expression may be chemically related. We discuss the potential role of several environmental compounds in the induction or promotion of ras mutations in humans, with a focus on exocrine pancreatic cancer, the human tumor with the highest prevalence at diagnosis of Ki-ras mutations. Organochlorine compounds, organic solvents, and coffee compounds may play an indirect role in causing Ki-ras mutations, rather than as direct inducers of the mutations. Although for some organochlorine compounds the induction of point mutations in ras oncogenes cannot be excluded, it seems more likely that the effects of these compounds are mediated through nongenomic or indirectly genotoxic mechanisms of action. Organic solvents also may act via enzymatic induction of ras mutagens or by providing a proliferation advantage to ras-mutated cell clones. In exocrine pancreatic cancer, caffeine, other coffee compounds, or other factors with which coffee drinking is associated could modulate Ki-ras activation by interfering with DNA repair, cell-cycle checkpoints, and apoptosis. Asbestos, cigarette smoking, and some dietary factors also may be involved in the initiation or the promotion of Ki-ras mutations in lung and colon cancers. Further development of the mechanistic scenarios proposed here could contribute to a meaningful integration of biological, clinical, and environmental knowledge on the causes of altered ras effects.

Association between the ras p21 oncoprotein in blood samples and breast cancer

To assess the potential of using oncoprotein levels in blood as a marker of breast cancer status, we measured ras p21 in blood samples taken from 34 breast cancer cases and 60 non-cancer controls including 26 women with benign breast disease (BBD) and 34 healthy women. Plasma samples drawn before surgery or at routine office visit were analyzed for ras p21 by Western blot with computer aided image analysis to measure staining intensity in integrated pixel units (IPU). We found detectable levels of ras p21 in 53% of the blood samples of cases, in 27% of the BBD controls and 26% of the healthy controls. Comparing cases to the combined control group (n=60) and controlling for known breast cancer risk factors, ras p21 was associated with breast cancer status (odds ratio=5.22, 95% CI=1.58-17.23). The median levels of ras p21 staining were higher in cases (7.04 IPU, P=0.03) compared to BBD controls (0.00 IPU) or healthy controls (0.00 IPU). The sensitivity of the assay for detecting breast cancer was 50% which compares favorably with that seen for erbB-2 ( approximately 10%), a more extensively studied blood-borne tumor marker. Ras p21 may be useful in the early detection of breast tumors and in post-surgical follow-up of patients, giving patients and physicians new tools for managing breast cancer.

Codon 12 and codon 13 mutations at the K-ras gene induce different soft tissue sarcoma types in nude mice

K-ras codon 12 mutation is more oncogenic in in vitro and in vivo experimental systems than K-ras codon 13 mutation. Moreover, human colorectal tumors bearing a codon 12 mutation are more aggressive, invasive, and metastatic than the same tumor types carrying a codon 13 mutation. However, despite the association between specific sarcoma types and codon 12 or codon 13 mutations, the relationship between the position of the mutated codon at ras genes and tumor aggressiveness has not been studied in this tumor type. Here, we used a nude mice model to evaluate the tumorogenic capacity of stable transfectants of NIH3T3 fibroblasts, expressing K-ras mutated at codon 12 (K12) or 13 (K13), and morphologically, functionally, and molecularly compared these tumors. We found histopathological differences between them, K12-derived tumors showing fibrosarcoma-like features, whereas K13-derived tumors resembled malignant fibrous histiocytomas. Moreover, K12 tumors showed shorter latency of appearance, lower apoptotic and mitotic rates, and higher expression of markers for sarcoma aggressiveness (Ki67, p53 and c-myc) than K13 tumors. They also showed differences in the expression or activation of Ras, Ras downstream pathways [c-Jun N-terminal kinase (JNK), MAPK and AKT], and apoptotic [AKT, Bcl-2, Focal adhesion kinase (FAK)] and mitotic (cyclin B1) regulators, which could explain their functional differences. Most remarkably, the significantly diminished apoptotic rate observed in K12-derived tumors was associated with enhanced antiapoptotic signaling through the AKT pathway. These morphological, functional, and molecular differences demonstrate that codon 12 and codon 13 mutations in the K-ras oncogene can induce two different soft tissue sarcoma types in our in vivo model.

Frequent k- ras -2 mutations and p16(INK4A)methylation in hepatocellular carcinomas in workers exposed to vinyl chloride

Vinyl chloride (VC) is a know animal and human carcinogen associated with liver angiosarcomas (LAS) and hepatocellular carcinomas (HCC). In VC-associated LAS mutations of the K- ras -2 gene have been reported; however, no data about the prevalence of such mutations in VC associated HCCs are available. Recent data indicate K- ras -2 mutations induce P16 methylation accompanied by inactivation of the p16 gene. The presence of K- ras -2 mutations was analysed in tissue from 18 patients with VC associated HCCs. As a control group, 20 patients with hepatocellular carcinoma due to hepatitis B (n = 7), hepatitis C (n = 5) and alcoholic liver cirrhosis (n = 8) was used. The specific mutations were determined by direct sequencing of codon 12 and 13 of the K- ras -2 gene in carcinomatous and adjacent non-neoplastic liver tissue after microdissection. The status of p16 was evaluated by methylation-specific PCR (MSP), microsatellite analysis, DNA sequencing and immunohistochemical staining. All patients had a documented chronic quantitated exposure to VC (average 8883 ppmy, average duration: 245 months). K- ras -2 mutations were found in 6 of 18 (33%) examined VC-associated HCCs and in 3 cases of adjacent non-neoplastic liver tissue. There were 3 G --> A point mutations in the tumour tissue. All 3 mutations found in non-neoplastic liver from VC-exposed patients were also G --> A point mutations (codon 12- and codon 13-aspartate mutations). Hypermethylation of the 5' CpG island of the p16 gene was found in 13 of 18 examined carcinomas (72%). Of 6 cancers with K- ras -2 mutations, 5 specimens also showed methylated p16. Within the control group, K- ras -2 mutation were found in 3 of 20 (15%) examined HCC. p16 methylation occurred in 11 out of 20 (55%) patients. K- ras -2 mutations and p16 methylation are frequent events in VC associated HCCs. We observed a K- ras -2 mutation pattern characteristic of chloroethylene oxide, a carcinogenic metabolite of VC. Our results strongly suggest that K- ras -2 mutations play an important role in the pathogenesis of VC-associated HCC.

ras gene activation and infrequent mutation in papillary serous carcinoma of the peritoneum

OBJECTIVE

The ras genes are a well-studied family of proto-oncogenes whose involvement in many cancers has been delineated. However, K-ras mutations have not previously been examined in papillary serous carcinoma of the peritoneum (PSCP), a tumor which resembles serous epithelial ovarian carcinoma (SEOC) both in histology and epidemiology. In this study we examine the role of the K-ras oncogene in PSCP compared to SEOC.

METHODS

Using single-strand conformational polymorphism analysis and cycle sequencing protocols, we evaluated our collection of 51 cases of PSCP for K-ras mutations and compared these findings with the experience in SEOC. We then examined 5 cases of PSCP for activation of ras proteins and MAP kinase to evaluate the potential involvement of the ras pathway in PSCP tumorigenesis.

RESULTS

We found only one K-ras mutation in our 51 cases (2%) of PSCP compared to three mutations in 46 cases (6.5%) of high-grade, late-stage SEOC. This was not significantly different (P > 0.10). In the single PSCP case with a K-ras mutation, the mutation was found in only one of five tumor sites tested. All four mutations involved a single nucleotide alteration in codon 12 (GGT to GTT, Gly to Val). To evaluate the ras pathway in PSCP, we used the known activated ras binding domain on Raf-1 to perform an assay to test for activated ras. We identified ras activation in 4 of 5 PSCP cases tested and, to confirm that the activation was functional, we tested and found similar activation of MAP kinase, a downstream mediator for K-ras expression.

CONCLUSIONS

K-ras mutations occur at low rates in both PSCP and high-grade, late-stage SEOC, and therefore K-ras mutations are not involved in the development of these two diseases. Finding the mutation in only one of multiple tumor sites in the PSCP case supports growing evidence for a multifocal origin of PSCP. Our findings of ras activation in four of five cases of PSCP suggest that ras activation by mechanisms other than genetic mutation is important for PSCP tumorigenesis.

Human hemangiosarcomas have a common polymorphism but no mutations in the connexin37 gene

Gap junctional intercellular communication is often impaired in cancers, and the genes which encode the connexin gap junction proteins are considered to be tumor-suppressor genes. In this study, we analyzed the presence of mutations in the connexin 37 (Cx37) gene in 22 human hepatic angiosarcomas, 6 and 4 of which were associated with exposure to vinyl chloride and Thorotrast, respectively. The other 12 samples were from patients with no history of exposure to these 2 agents. In 9 samples, a proline (ACC) to serine (ACT) amino acid change in codon 319 was detected. However, DNA from non-tumorigenic tissue of the same patients also showed this amino acid change, suggesting that this is a polymorphism rather than a mutation. Subsequent analysis of 84 DNA samples from normal donors revealed the frequencies of Pro/Pro, Pro/Ser and Ser/Ser alleles to be 65.5%, 23.8% and 10.7%, respectively, while among the group of angiosarcoma patients the corresponding figures were 59.1%, 31.8% and 9. 1%, respectively. Thus, there was no correlation between the polymorphism at codon 319 and hepatic angiosarcoma occurrence. However, among the 6 cases of vinyl chloride-associated angiosarcoma, the percentages of the polymorphic alleles were 33.3%, 66.7% and 0%, respectively. While the number of samples was too small to allow us to conclude that the Ser319 allele in Cx37 predisposes to this rare type of human cancer, it may be noted that codon 319 is located at the cytoplasmic tail of Cx37, where most regulatory sequences reside, and that it could be a site of phosphorylation for some protein kinases, which may in turn affect the function of Cx37, including intercellular communication.

Spontaneous and thiazolidinedione-induced B6C3F1 mouse hemangiosarcomas exhibit low ras oncogene mutation frequencies

Hemangiosarcomasare uncommon malignant endothelial cell tumors in humans and experimental animal species. The mechanisms giving rise to these tumors are poorly understood even though the histotypes are comparable between humans and rodents. Activating mutations in cellular ras protooncogenes have been detected in sporadic and chemically induced human and rodent hemangiosarcomas. Ras activation significantly modulates tumor angiogenesis, suggesting that mutations in ras genes might be causally related to vascular tumorigenesis. To more clearly define the role of ras in experimental vascular tumorigenesis, mutations in the Ki- and Ha-ras genes were characterized in 63 hemangiosarcomas that arose unexpectedly in control and treated B6C3F1 mice during a two-year carcinogenicity study of the thiazolidinedione troglitazone. DNA was extracted from paraffin sections of mouse hemangiosarcomas, control liver, or positive control hepatocellular carcinomas with defined mutations in the Ki- or Ha-ras genes. Exons 1 and 2 of the Ki- and Ha-ras genes were independently amplified using primer extension preamplification/locus-specific heminested PCR, and PCR amplicons were directly sequenced to identify mutations in codons 12, 13, or 61. Activating mutations were detected in 3 of 63 hemangiosarcomas: a single G-->A transition in the second position of Ki-ras codon 13 in a tumor from a treated animal and two G-->T transversions in the second position of Ha-ras codon 13, one in a single tumor from a control animal and one in a tumor from a treated animal. These mutations are consistent with endogenous mutagenesis arising from oxidative DNA damage. The low frequency of mutation (<5%) indicates that ras mutations did not contribute significantly to hemangiosarcoma development and suggests that mutational ras activation may not be a necessary step in vascular tumorigenesis in mice.

Environmental factors as regulators and effectors of multistep carcinogenesis

This review highlights current knowledge of environmental factors in carcinogenesis and their cellular targets. The hypothesis that environmental factors influence carcinogenesis is widely supported by both epidemiological and experimental studies. The fact that only a small fraction of cancers can be attributed to germline mutations in cancer-related genes further buttresses the importance of environmental factors in carcinogenesis. Furthermore, penetrance of germline mutations may be modified by either environmental or other genetic factors. Examples of environmental factors that have been associated with increased cancer risk in the human population include chemical and physical mutagens (e.g. cigarette smoke, heterocyclic amines, asbestos and UV irradiation), infection by certain viral or bacterial pathogens, and dietary non-genotoxic constituents (e.g. macro- and micronutrients). Among molecular targets of environmental influences on carcinogenesis are somatic mutation (genetic change) and aberrant DNA methylation (epigenetic change) at the genomic level and post-translational modifications at the protein level. At both levels, changes elicited affect either the stability or the activity of key regulatory proteins, including oncoproteins and tumor suppressor proteins. Together, via multiple genetic and epigenetic lesions, environmental factors modulate important changes in the pathway of cellular carcinogenesis.

Critical genes as early warning signs: example of vinyl chloride

We have analysed liver angiosarcomas from individuals having been occupationally exposed to vinyl chloride (VC) to identify, in cancer-related genes, lesions which could be VC-specific. Two genetic alterations have been identified: the first one is a GGC --> GAT (Gly --> Asp, Asp13p21) mutation at codon 13 in the Ki-ras gene, found in five out of six tumors. The second one is an AT --> TA transversion in the p53 gene resulting in missense mutations at different codons and was found in three out of six tumors. By analysing both the tumors and sera from the same patients, we have shown that the Asp13p21 and mutant p53 proteins could be detected reliably in the serum. We thereafter analysed 225 serum samples, selected from a cohort of about 900 VC-exposed workers, for the presence of the two mutant proteins and p53 antibodies. A statistical analysis supports a strong dose-response relationship between the serum markers positivity and the VC-exposure. A follow-up of this cohort should now allow us to assert the predictive value of these markers.

Molecular markers of carcinogenesis

The protein products of oncogenes and tumor suppressor genes play critical roles in the development of many cancers. The expression of a number of these proteins can be detected in extracellular fluids such as blood. This article reviews the literature on the application of methods for the detection of the proteins of oncogenes and tumor suppressor genes in the blood of humans with cancer or at risk for the development of cancer. The detection of these proteins in blood may be useful molecular markers of carcinogenesis that could play an important part in cancer diagnosis, prognosis, and prevention.

The altered activity of membrane-bound protein kinase C in human liver cancer

The activity of protein kinase C (PKC) in human liver cancer and adjacent normal liver tissue was determined. It was found that the activity of the membrane-bound PKC was significantly decreased in cancer tissue compared with that of the adjacent normal tissues (245.3 +/- 49.3 versus 396.9 +/- 82.4 pmol 32P/min per mg, P < 0.05); while the PKC activity in the cytosolic fraction was not significantly different (50.6 +/- 11.3 versus 40.0 +/- 6.6 pmol 32P/min per mg) concerning protein concentration. The reduced expression of membrane-bound PKC activity was observed at least in 8 of 9 patients. Moreover, the cancer tissue showed a significant decrease in total membranous PKC activity compared with the adjacent normal tissue of each patient (163.1 +/- 38.8 versus 433.8 +/- 92.4 pmol 32P/min per g tissue; P < 0.005) and no difference in total cytosolic PKC activity (285.9 +/- 58.8 versus 311.6 +/- 44.0 pmol 32P/min per g tissue). These results indicate that the progression of the human liver cancer might be associated with the decrease of membrane-bound PKC activity.