Relationship between insecticide resistance profiles in Anopheles gambiae sensu lato and agricultural practices in Côte d'Ivoire.

BACKGROUND: Insecticide-based malaria vector control is increasingly undermined due to the development of insecticide resistance in mosquitoes. Insecticide resistance may partially be related to the use of pesticides in agriculture, while the level and mechanisms of resistance might differ between agricultural practices. The current study aimed to assess whether phenotypic insecticide resistance and associated molecular resistance mechanisms in Anopheles gambiae sensu lato differ between agricultural practices. METHODS: We collected An. gambiae s.l. larvae in six sites with three different agricultural practices, including rice, vegetable and cocoa cultivation. We then exposed the emerging adult females to discriminating concentrations of bendiocarb (0.1%), deltamethrin (0.05%), DDT (4%) and malathion (5%) using the standard World Health Organization insecticide susceptibility test. To investigate underlying molecular mechanisms of resistance, we used multiplex TaqMan qPCR assays. We determined the frequency of target-site mutations, including Vgsc-L995F/S and Vgsc-N1570Y, and Ace1-G280S. In addition, we measured the expression levels of genes previously associated with insecticide resistance in An. gambiae s.l., including the cytochrome P450-dependent monooxygenases CYP4G16, CYP6M2, CYP6P1, CYP6P3, CYP6P4, CYP6Z1 and CYP9K1, and the glutathione S-transferase GSTe2. RESULTS: The An. gambiae s.l. populations from all six agricultural sites were resistant to bendiocarb, deltamethrin and DDT, while the populations from the two vegetable cultivation sites were additionally resistant to malathion. Most tested mosquitoes carried at least one mutant Vgsc-L995F allele that is associated with pyrethroid and DDT resistance. In the cocoa cultivation sites, we observed the highest 995F frequencies (80-87%), including a majority of homozygous mutants and several in co-occurrence with the Vgsc-N1570Y mutation. We detected the Ace1 mutation most frequently in vegetable-growing sites (51-60%), at a moderate frequency in rice (20-22%) and rarely in cocoa-growing sites (3-4%). In contrast, CYP6M2, CYP6P3, CYP6P4, CYP6Z1 and CYP9K1, previously associated with metabolic insecticide resistance, showed the highest expression levels in the populations from rice-growing sites compared to the susceptible Kisumu reference strain. CONCLUSION: In our study, we observed intriguing associations between the type of agricultural practices and certain insecticide resistance profiles in the malaria vector An. gambiae s.l. which might arise from the use of pesticides deployed for protecting crops.

Socioeconomic Status and Mock Interview Performance among Prospective Medical School Applicants.

We aim to evaluate the association between family income and mock multiple mini interview (MMI) performance for prospective medical school applicants. Each applicant participated in a three-station mock MMI and were scored on four items, each on a sevenpoint scale. Of the 48 prospective applicants participating, 29 (60% survey response rate) completed the survey. Hispanic applicants were significantly more likely to have a family income of less than or equal to $20,000 versus more than $20,000 (p<.05). The adjusted analysis suggested mock MMI total score was significantly lower for prospective medical school applicants with family incomes of less than or equal to $20,000 versus more than $20,000 (ß coefficient 5.37, 95% CI 0.05-10.69, p = .048). The mock MMI performance of prospective applicants with lower family incomes indicates the need for further interview skill preparation or new interview scoring protocols.

Cardiorespiratory morbidity and mortality of opioid overdose during admission to safety-net hospitals.

STUDY OBJECTIVE: Safety-net hospitals disproportionately care for high-risk patients. Prior work has shown safety-net hospitals to have inferior postoperative outcomes with higher cost and worse patient ratings. We aim to examine the association of hospital safety-net burden with morbidity and mortality in patients with opioid overdose hospital admission. DESIGN: Retrospective cross-sectional analysis using the National Inpatient Sample registry from 2010 to 2014. SETTING: Multi-institutional. PATIENTS: We included 547, 399 patients admitted to a United States hospital with an International Classification of Disease, Ninth Revision, code of opioid overdose. To study the association of hospital safety-net burden on mortality and morbidity, we calculated hospital safety-net burden defined as the percent of Medicaid or uninsured among all admitted patients. Hospitals were categorized into one of three categories: low burden hospitals, medium burden hospitals, and high burden hospitals (i.e., safety-net hospitals). We performed a mixed effects multivariable logistic regression analysis to assess the association of hospital safety-net burden with short-term inpatient outcomes. INTERVENTION: None. MEASUREMENTS: The primary outcomes were inpatient mortality and morbidity. MAIN RESULTS: Compared to MBHs and LBHs, HBHs had a greater proportion of minority patients (i.e., Black, Hispanic, and Native American) and patients with median household income in the lowest quartile (p < 0.001). Among prescription opioid overdose admissions, the odds of inpatient mortality and pulmonary and cardiac morbidity were also not significantly higher between HBHs versus LBHs (p > 0.05). CONCLUSIONS: Safety-net hospital disproportionately care for vulnerable populations, however the odds of poor outcomes were no different in opioid overdose. Safety-net hospitals should have equal access to the funding and resources that allows them to deliver the same standard of care as their counterparts.

An Update on Racial Disparities With 30-Day Outcomes After Coronary Artery Bypass Graft Under the Affordable Care Act.

OBJECTIVE: The impact of race on outcomes after coronary artery bypass graft (CABG) has been reported before the enactment of the Patient Protection and Affordable Care Act. However, the impact of race on outcomes post-Affordable Care Act enactment remains unclear. The authors evaluated the association of race with outcomes after enactment of the Affordable Care Act in CABG patients. DESIGN: Retrospective analysis of the American College of Surgeons National Surgical Quality Improvement Program database from 2012 to 2016. SETTING: Multi-institutional. PARTICIPANTS: The authors identified 9,698 CABG patients. INTERVENTIONS: CABG. MEASUREMENTS AND MAIN RESULTS: Compared with the white population, the black/African American population had higher rates of congestive heart failure, blood transfusion, bleeding disorder, insulin-dependent diabetes mellitus, active smoking, renal dialysis, and hypertension (all p < 0.05). Compared with whites, Asians tended to have a higher prevalence of blood transfusion, American Society of Anesthesiologists class ≥4, diabetes mellitus, and renal dialysis (all p < 0.05). Postoperative red blood cell transfusion (56.5%) and prolonged hospital length of stay ≥12 days (27.7%) were the most prevalent adverse outcomes. Compared with whites, the adjusted odds of postoperative overall morbidity were higher among blacks/African Americans (odds ratio [OR]: 1.42, 95% confidence interval [CI]: 1.15-1.76, p < 0.001) and Asians (OR: 1.43, 95% CI: 1.06-1.91, p = 0.001). Compared with blacks/African Americans, Asians had higher odds of infection complications (OR: 2.07, 95% CI: 1.10-3.88, p = 0.023). CONCLUSION: Differential outcomes were observed for morbidity and mortality outcome measures. The persistence of racial disparities beyond the Affordable Care Act calls for multidisciplinary action.

The molecular causes of low ATM protein expression in breast carcinoma; promoter methylation and levels of the catalytic subunit of DNA-dependent protein kinase.

AIMS: To investigate whether aberrant methylation of the ATM promoter or loss of the catalytic subunit of DNA-dependent protein kinase (DNA-PKcs) may be the underlying causes of reduced ATM protein levels often seen in breast tumours. METHODS AND RESULTS: Methylation-specific polymerase chain reaction was used to determine the ATM promoter status and DNA-PKcs levels were measured by immunohistochemistry. None of the 74 invasive carcinomas (ICs) studied showed ATM promoter hypermethylation, whereas promoter methylation of CDKN2A/p16 (1.8%) and GSTP1 (15.8%) was detected. Of 92 ICs examined, 68 had reduced DNA-PKcs levels, supporting previous findings that alterations in double-strand break repair are associated with breast cancer pathogenesis. Although no association was found between the DNA-PKcs and ATM scores for the series of 92 tissues and 22/24 tissues with normal DNA-PKcs had reduced ATM, 29 tumours showed low expression of both DNA-PKcs and ATM compared with normal tissues. CONCLUSIONS: No evidence was found that the reduction in ATM protein levels seen in breast carcinoma is the result of epigenetic silencing. However, cross-regulation between DNA-PKcs and ATM may be a possible cause in a subset of tumours and warrants further investigation.

Expression of ATM, p53, and the MRE11-Rad50-NBS1 complex in myoepithelial cells from benign and malignant proliferations of the breast.

AIMS: To analyse the expression of proteins involved in DNA double strand break detection and repair in the luminal and myoepithelial compartments of benign breast lesions and malignant breast tumours with myoepithelial differentiation. METHODS: Expression of the ataxia telangiectasia (ATM) and p53 proteins was immunohistochemically evaluated in 18 benign and malignant myoepithelial tumours of the breast. Fifteen benign breast lesions with prominent myoepithelial compartment were also evaluated for these proteins, in addition to those in the MRE11-Rad50-NBS1 (MRN) complex, and the expression profiles were compared with those seen in eight independent non-cancer (normal breast) samples and in the surrounding normal tissues of the benign and malignant tumours examined. RESULTS: ATM expression was higher in the myoepithelial compartment of three of 15 benign breast lesions and lower in the luminal compartment of eight of these lesions compared with that found in the corresponding normal tissue compartments. Malignant myoepithelial tumours overexpressed ATM in one of 18 cases. p53 was consistently negative in benign lesions and was overexpressed in eight of 18 malignant tumours. In benign breast lesions, expression of the MRN complex was significantly more reduced in myoepithelial cells (up to 73%) than in luminal cells (up to 40%) (p=0.0005). CONCLUSIONS: Malignant myoepithelial tumours rarely overexpress ATM but are frequently positive for p53. In benign breast lesions, expression of the MRN complex was more frequently reduced in the myoepithelial than in the luminal epithelial compartment, suggesting different DNA repair capabilities in these two cell types.

ATM polymorphisms as risk factors for prostate cancer development.

The risk of prostate cancer is known to be elevated in carriers of germline mutations in BRCA2, and possibly also in carriers of BRCA1 and CHEK2 mutations. These genes are components of the ATM-dependent DNA damage signalling pathways. To evaluate the hypothesis that variants in ATM itself might be associated with prostate cancer risk, we genotyped five ATM variants in DNA from 637 prostate cancer patients and 445 controls with no family history of cancer. No significant differences in the frequency of the variant alleles at 5557G>A (D1853N), 5558A>T (D1853V), ivs38-8t>c and ivs38-15g>c were found between the cases and controls. The 3161G (P1054R) variant allele was, however, significantly associated with an increased risk of developing prostate cancer (any G vs CC OR 2.13, 95% CI 1.17-3.87, P=0.016). A lymphoblastoid cell line carrying both the 3161G and the 2572C (858L) variant in the homozygote state shows a cell cycle progression profile after exposure to ionising radiation that is significantly different to that seen in cell lines carrying a wild-type ATM gene. These results provide evidence that the presence of common variants in the ATM gene, may confer an altered cellular phenotype, and that the ATM 3161C>G variant might be associated with prostate cancer risk.

Direct comparison of A- and T-strand minor groove interactions in DNA curvature at A tracts.

To investigate the relative contributions of minor-groove electrostatic interactions in the mechanism of A-tract DNA curvature, we carried out experiments with modified DNA bases in both strands of the tract. We employed 3-deazaadenine nucleoside (D), which lacks the adenine N3 nitrogen in the minor groove and thus cannot act as an electron donor, as well as difluorotoluene (F), a nonpolar thymine mimic. The effects of these analogues in A-tract curvature were quantified using ligation ladder gel mobility methods developed by Crothers and by Maher. Through single substitutions of D in A(5) tracts, we found that this analogue results in decreased curvature only when situated toward the 3' end of the tract. This is distinct from the behavior in the T-rich strand where F substitution causes the greatest reductions in curvature toward the 5' end. To test for cooperative pairwise effects, we also studied 10 different D + F double substitutions and found evidence supporting a number of localized cooperative electrostatic interactions but not between the two most sensitive sites in the opposite strands. These results suggest that there are two discrete locations in the A-tract minor groove where electrostatic interactions are important in causing curvature: one near the 5' end of the T-rich strand, and one near the 3' end of the A-rich strand. The results are consistent with an important role of localized cations in the minor groove. Possible effects of groove solvation and stacking at the A-tract junction are also discussed.

Effects of glutathione depletion on the viability of human NT2-derived neuronal and astroglial cultures.

The level of glutathione (GSH) is often reduced in brains that are affected by neurodegeneration. It is not known, however,whether this is a cause or a consequence of the disease. Here we have examined the effects of GSH depletion on the viability of human neurons cultured in either the presence or the absence of astrocytes, both derived from NT2/D1 cells. We established that the endogenous concentration of GSH is 10 times lower in neurons than in astrocytes (1.42 versus 18.9 pmol microg protein(-1)) and that pure neuronal cultures begin to die by apoptosis within 24 h of GSH depletion. By contrast, neurons that are co-cultured with astrocytes remain viable for several days, even with a profoundly decreased GSH content. However, they die rapidly when challenged additionally with nitrative stress. In addition, astrocytes survive for prolonged periods of time (>12 days) under severely reduced GSH concentrations. Our study shows clear differences in the content and sensitivity to depletion of GSH in neurons and astrocytes and establishes the significance of neuronal-glial interactions for the maintenance of neuronal viability under reduced GSH content. However, with chronic GSH depletion, these interactions might not be sufficient to protect neurons from other injurious factors (i.e. reactive oxygen and nitrogen species), which indicates that defective GSH metabolism might facilitate the progression of neurodegeneration.

Altered expression of DNA double-strand break detection and repair proteins in breast carcinomas.

AIMS: To determine whether the expression of DNA damage detection and repair proteins is frequently altered in breast carcinomas. METHODS AND RESULTS: The expression profiles of five such proteins: ATM, p53, NBS1, MRE11 and Rad50 were analysed in 99 in-situ and invasive ductal breast carcinomas of different grades using an immunohistochemical approach, and compared with those seen in eight independent non-cancer (normal) breast samples and in the surrounding normal tissues of the breast carcinomas examined. ATM protein expression was reduced in 75% of the tumours compared with the levels found in normal tissues. Fewer tumours had reduced protein levels of the members of the MRE11, NBS1 and Rad50 (MNR) complex (31%, 46% and 28%, respectively) with p53 being over-expressed in 30%. In the majority of tumours (92%) we observed a good correlation between the expression of the three proteins of the MNR complex with low NBS1, MRE11 or Rad50 expression rarely found alone, suggesting that this event occurs subsequently to the deregulation in expression of other DNA repair proteins. CONCLUSION: The pattern of protein changes observed supports our hypothesis that alterations in DNA double-strand break repair capacity are involved in mammary carcinogenesis.

Variation in radiation-induced apoptosis in ataxia telangiectasia lymphoblastoid cell lines.

PURPOSE: To investigate and compare the ability of Epstein-Barr virus-transformed lymphoblastoid cell lines (LCL) from healthy individuals (normals) and ataxia telangiectasia (A-T) patients to undergo apoptosis after exposure to ionizing radiation. MATERIALS AND METHODS: Four normal and eight A-T LCL were exposed to doses of up to 20 Gy ionizing radiation. Apoptosis induction was studied 24 h after irradiation using three different methods: measurement of caspase-3 activity, PARP-1 cleavage and estimation of the sub-G(1) cell fraction. RESULTS: Of the eight A-T LCL tested, all harbouring truncating ATM mutations, five had a higher level of spontaneous apoptosis than the normal LCL as assessed by the sub-G(1) cell fraction. Four of the eight A-T LCLs showed a similar level of radiation-induced apoptosis after exposure to 5 Gy as the normal LCL. The other four A-T LCL showed a greater radiation-induced apoptotic response, as assessed by at least one of the three techniques. CONCLUSIONS: LCL from A-T patients can undergo ionizing radiation-induced apoptosis in spite of a defect in ATM-p53-dependent signalling pathways. However, the apoptotic response is characterized by a large degree of variability between the A-T cell lines, the causes of which remain to be established.

[What do we know about ATM protein expression in breast tissue?]. / Que savons-mous de l'expression de la protéine ATM dans le tissu mammaire?

The great majority of breast cancer cases are not associated with a mutated gene of high penetrance such as BRCA1, BRCA2 and TP53. Genes of low penetrance, frequently mutated in the general population, might play an important role in breast cancer development. The ATM gene, which encodes the ATM protein, mutated in the disorder ataxia telangiectasia (AT) could be such a susceptibility gene. Indeed, 1% of the general population is estimated to be AT heterozygote and females have an increased risk of developing breast cancer. The ATM protein is involved in the signalling pathway of DNA double-strand breaks. Studies on its expression in normal breast tissues have shown that ATM is expressed in the epithelial cells of breast ducts, but not in the myoepithelial cells. In sclerosing adenosis, a benign lesion of the breast, the ATM protein is expressed in both cell types whereas its expression is absent or reduced in tumour epithelial cells in about 30-50% of invasive carcinomas. Moreover, the study of the p53 status in some of these tumours has revealed that the ATM/p53 signalling pathway is frequently altered either by a very low ATM expression or by the presence of a mutated p53. It remains to be determined whether alterations in the expression of other proteins also involved in this DNA damage signalling cascade are specifically associated with breast cancer development and/or a radiosensitive phenotype seen in some breast cancer patients after radiotherapy.

Abnormal expression of the ATM and TP53 genes in sporadic breast carcinomas.

The ataxia telangiectasia gene (ATM) has been implicated as a risk factor in the development of sporadic breast carcinomas. ATM protein expression was analyzed by immunohistochemistry in 17 breast carcinomas with two monoclonal antibodies whose immunohistochemical use was first validated by comparing the immunoreactivity observed in spleen samples from ataxia telangiectasia and trauma patients. In normal breast ducts, ATM showed nuclear expression in the epithelial but not in the myoepithelial cells. In contrast, this nuclear expression was absent or low in the epithelial cancer cells in 10 of 17 (59%) of the tumors studied. Allelic imbalance in the ATM gene was found in three of seven tumors examined. Two of these showed reduced ATM protein expression, but this did not correlate with the presence of ATM mutations in the tumor DNA detected by restriction endonuclease fingerprinting screening. These results suggest that the reduced ATM protein expression could be attributable, in certain tumors, to deletions or rearrangements within or close to the ATM gene. Positive p53 immunostaining was found in 10 tumors, with TP53 mutations detected in 8. Three tumors had both low ATM expression and mutated TP53. Our results indicate that in the majority (15 of 17) of the sporadic breast carcinomas examined, not only is the functionality of the ATM-p53-mediated DNA damage response compromised, but also other signaling pathways activated by these two multifunctional proteins are likely to be impaired, which could be a contributing factor to tumor development and progression.

Establishment and characterization of a spontaneously immortalized myofibroblast cell line derived from a human liver angiosarcoma.

BACKGROUND/AIM: Fibrosis and/or cirrhosis are present in the precursor stages of most liver cancers. However, little is known about the reciprocal interactions of fibroblasts, mainly responsible for fibrosis, and the other liver cells. We report here the isolation of a new liver myofibroblast cell line from a human liver angiosarcoma and its characterization. METHODS: The cells were isolated by the explant technique and characterization was performed, on one hand, using immunohistochemical and ultrastructural analysis and, in the other hand, by determining their karyotype, ras and p53 status and their tumorigenic properties. RESULTS: To date, the cells have undergone approximately 170 population doublings and are still proliferating. Immunohistochemically, they were negative for desmin, smooth muscle myosin, cytokeratin 19 and von Willebrand factor, positive for vimentin and alpha-smooth muscle actin, with an important deposition of fibronectin around the cells. Ultrastructure showed particularly cytoplasmic microfilament bundles. Their chromosome number ranged from 38 to 168 with a bimodal population, near diploid and hypotetraploid. No mutations were found in codons 12, 13 or 61 of Ha-, Ki- and N-ras genes but a homozygous missense mutation in codon 179 (CAT-->CTT) was detected in the p53 gene. They were unable to form foci in soft agar or tumors in nude mice. CONCLUSIONS: Taken together, these results show that these cells, called BM 2.2.1, exhibited typical myofibroblast-like features. Although they contained a karyotype suggestive of tumoral cells and a homozygous mutated p53 gene, they were not tumorigenic. The nature of these cells and the abnormalities of the p53 gene and the karyotype, suggest that: i) they were a component of the tumor stroma, and ii) they could have been involved in angiosarcoma development. Thus, this cell line may be valuable for the study of cellular interactions in liver carcinogenesis.

The ATM gene and breast cancer: is it really a risk factor?

The genetic determinants for most breast cancer cases remain elusive. Whilst mutations in BRCA1 and BRCA2 significantly contribute to familial breast cancer risk, their contribution to sporadic breast cancer is low. In such cases genes frequently altered in the general population, such as the gene mutated in Ataxia telangiectasia (AT), ATM may be important risk factors. The initial interest in studying ATM heterozygosity in breast cancer arose from the findings of epidemiological studies of AT families in which AT heterozygote women had an increased risk of breast cancer and estimations that 1% of the population are AT heterozygotes. One of the clinical features of AT patients is extreme cellular sensitivity to ionising radiation. This observation, together with the finding that a significant proportion of breast cancer patients show an exaggerated acute or late normal tissue reactions after radiotherapy, has lead to the suggestion that AT heterozygosity plays a role in radiosensitivity and breast cancer development. Loss of heterozygosity in the region of the ATM gene on chromosome 11, has been found in about 40% of sporadic breast tumours. However, screening for ATM mutations in sporadic breast cancer cases, showing or not adverse effects to radiotherapy, has not revealed the magnitude of involvement of the ATM gene expected. Their size and the use of the protein truncation test to identify mutations limit many of these studies. This latter parameter is critical as the profile of mutations in AT patients may not be representative of the ATM mutations in other diseases. The potential role of rare sequence variants within the ATM gene, sometimes reported as polymorphisms, also needs to be fully assessed in larger cohorts of breast cancer patients and controls in order to determine whether they represent cancer and/or radiation sensitivity predisposing mutations.

Ras gene mutations in vinyl chloride-induced liver tumours are carcinogen-specific but vary with cell type and species.

Previous studies have shown that a high proportion (5/6) of human liver angiosarcomas (ASL) associated with exposure to vinyl chloride (VC) contains a GC-->AT mutation at the Ki-ras codon 13. This mutation, however, has not been found in 5 ASL or 2 hepatocellular carcinomas (HCC) induced in rats by VC. These 2 HCC did contain a mutation at codon 61 of the Ha-ras gene. In order to extend this study and further explore the mechanisms of tumour induction, an additional 6 ASL and 6 HCC induced in rats by VC were analysed for ras gene point mutations, as well as 10 rat and 10 murine ASL induced by vinyl fluoride (VF), and 5 ASL, 6 Kupffer cell sarcomas, 4 HCC and 2 cholangiocellular carcinomas induced by Thorotrast in rats. Tumour DNA was analysed by PCR-SSCP and direct sequencing. None of the rodent ASL contained a mutation at codon 13 of the Ki-ras gene showing that the ras gene mutational pattern is species-specific. The CAA-->CTA mutation, previously found at codon 61 of the Ha-ras gene in rat HCC, was observed in 5 further VC-induced HCC but was not detected in the Thorotrast-induced HCC, suggesting carcinogen-specificity. This mutation was also absent in VC-induced ASL, which supports the cell-specificity of the ras mutational pattern in chemically induced tumours. No predominant mutation was detected in VF- and Thorotrast-induced tumours. Thus, a given mutation in a tumour may be carcinogen-specific but also depend on the species and the cell type.

Radiation, DNA damage and cancer.

The characterization of the rare, radiation-sensitive and cancer-prone syndromes, ataxia telangiectasia and Nijmegen breakage syndrome, has demonstrated that genetic predisposition increases the risk of developing cancer after exposure to ionizing radiation (IR). Molecular analyses of these disorders provide valuable insights into the normal function of these two gene products in the cellular response to IR-induced DNA damage. Their contribution to a cellular radiosensitive phenotype and their role in sporadic cancers can now be fully assessed. For example, the gene ataxia telangiectasia mutated (ATM) has recently been shown to be a tumour suppressor gene in T-cell prolymphocytic leukaemia, and there is increasing evidence that individuals with one mutated ATM or Nijmegen breakage syndrome (NBS1) allele have an increased predisposition to cancer.

Vinyl chloride-specific mutations in humans and animals.

Vinyl chloride is a potent hepatocarcinogen which reacts with DNA to generate etheno bases. In order to determine whether mutational patterns in target genes in vivo are characteristic of vinyl chloride and could be explained by the mutagenic properties of the etheno bases, human and rat liver tumours associated with exposure to vinyl chloride were analysed for point mutations in the ras and p53 genes. In this paper, we review these data and report our latest results on animal tumours. Two alterations were found which could be attributed to a direct effect of vinyl chloride: a GC-->AT transition which leads to a GGC-->GAC mutation at codon 13 of the Ki-ras gene in human liver angiosarcomas, and lesions at AT base pairs, mostly AT-->TA transversions, which lead to mutations in the p53 gene in human and rat angiosarcomas and to a CAA-->CTA mutation at codon 61 of the Ha-ras gene in rat hepatocellular carcinomas.