A common polymorphism at codon 72 in the p53 tumor suppressor gene encodes either proline (P72) or arginine (R72). Several groups have reported that in cultured cells, this polymorphism influences p53's transcriptional, senescence, and apoptotic functions. However, the impact of this polymorphism within the context of a living organism is poorly understood. We generated knock-in mice with the P72 and R72 variants and analyzed the tissues of these mice for apoptosis and transcription. In the thymus, we find that the P72 variant induces increased apoptosis following ionizing radiation, along with increased transactivation of a subset of p53 target genes, which includes murine Caspase 4 (also called Caspase 11), which we show is a direct p53 target gene. Interestingly, the majority of genes in this subset have roles in inflammation, and their promoters contain NF-B binding sites. We show that caspase 4/11 requires both p53 and NF-B for full induction after DNA damage and that the P72 variant shows increased interaction with p65 RelA, a subunit of NF-B. Consistent with this, we show that P72 mice have a markedly enhanced response to inflammatory challenge compared to that of R72 mice. Our data indicate that the codon 72 polymorphism impacts p53's role in inflammation.

Experimental models that recapitulate mutational landscapes of human cancers are needed to decipher the rapidly expanding data on human somatic mutations. We demonstrate that mutation patterns in immortalised cell lines derived from primary murine embryonic fibroblasts (MEFs) exposed in vitro to carcinogens recapitulate key features of mutational signatures observed in human cancers. In experiments with several cancer-causing agents we obtained high genome-wide concordance between human tumour mutation data and in vitro data with respect to predominant substitution types, strand bias and sequence context. Moreover, we found signature mutations in well-studied human cancer driver genes. To explore endogenous mutagenesis, we used MEFs ectopically expressing activation-induced cytidine deaminase (AID) and observed an excess of AID signature mutations in immortalised cell lines compared to their non-transgenic counterparts. MEF immortalisation is thus a simple and powerful strategy for modelling cancer mutation landscapes that facilitates the interpretation of human tumour genome-wide sequencing data.

The proposal has been put forward that the primary cause of Balkan endemic nephropathy (BEN) is exposure to food crops contaminated with seeds of Aristolochia spp, which contain high levels of aristolochic acids (AA). Recently, tumour DNA samples from patients with BEN were found to harbour principally A to T mutations in the TP53 tumour suppressor gene (Grollman et al., Proc Natl Acad Sci USA 2007;104:12129-34). Using a novel mutation assay in which we can induce and select mutations in human TP53 sequences in vitro by exposure of cultured cells to a mutagen, we found that A to T mutations were elicited by aristolochic acid at sites in TP53 rarely mutated in human cancers in general, but which were observed in the BEN patients. This concordance of specific mutations in patient tumours and aristolochic acid Iexposed cultures supports the argument that AA has a direct role in the aetiology of BEN-associated cancer. ' 2008 Wiley-Liss, Inc.Key words: carcinogenesis; cancer aetiology; mutagenesis Aristolochic acids (AAs) extracted from the plant species Aristolochia are nitrophenanthrene carboxylic acids with potent mutagenic activities and are carcinogenic in rodents. 1,2 Herbal remedies containing Aristolochia have been classified as carcinogenic to humans (Group 1) by the International Agency for Research on Cancer (IARC). 3 AA exposure elicits an unusual type of renal pathology and greatly increases the risk of urothelial carcinoma in afflicted individuals. A recent cluster of AA nephropathy (AAN) cases with associated urothelial malignancy occurred in a Belgian weight-reduction clinic where patients had been exposed inadvertently to AA. 4 AA-DNA adducts, which can persist for years, were detected in the tissues of the AAN patients, unequivocally confirming exposure to the nephrotoxic and carcinogenic substance. This incident provoked renewed attention to the possible role of AA exposure in other patient cohorts displaying the distinctive pathological features of AAN, in particular patients from villages in the Balkans diagnosed with Balkan endemic nephropathy (BEN). The hypothesis that rural populations in the Danube valley at high risk of urothelial cancer have been chronically exposed to AA was greatly strengthened by the recent findings on the unusual spectrum of TP53 mutations displayed by a set of 11 urothelial cancers from BEN patients. 5,6 The predominant DNA sequence change leading to inactivation of the TP53 tumour suppressor gene in these tumours was A:T to T:A. It is plausible that these base changes were caused by exposure to AA because pre-mutagenic AA-specific adducts on adenine, predominantly 7-(deoxyadenosin-N 6 -yl)aristolactam I, were detected in the Balkan patients' tissues, 5 and were reported previously in tissues of AAN patients. 4 Furthermore, it is known that these DNA modifications cause predominantly A to T transversions, 1 which constitute only a minor component of essentially all spontaneous mutation spectra in eukaryotes, regardless of organism or reporter gene.Characteristic base...

arg/arg cells investigated previously. Sequencing of human p53 exons 4-9 in immortalized cultures revealed missense mutations found repeatedly in human tumours. In cell lines ensuing from benzo(a)pyrene-treated cultures the combined p53 mutation pattern from experiments with the 3 codon 72 genotypes showed a predominance of strand-biased G to T transversions (18 of 36 mutations), and mutations recurring at smokers' lung tumour hotspot codons 157 and 273, supporting involvement of tobacco carcinogens in shaping the mutation signature in lung cancers of smokers. Mutations in cell lines from unexposed cultures did not cluster at these codons and G to T transversions were uncommon (2 of 52 mutations) (Fisher's exact test Po0.0001). Most mutations (13/16) in cell lines derived from cells polymorphic at codon 72 were found on the proline allele, with loss of the arginine allele.

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BackgroundThere is strong but mostly circumstantial evidence that genetic factors modulate the severity of influenza infection in humans. Using genetically diverse but fully inbred strains of mice it has been shown that host sequence variants have a strong influence on the severity of influenza A disease progression. In particular, C57BL/6J, the most widely used mouse strain in biomedical research, is comparatively resistant. In contrast, DBA/2J is highly susceptible.ResultsTo map regions of the genome responsible for differences in influenza susceptibility, we infected a family of 53 BXD-type lines derived from a cross between C57BL/6J and DBA/2J strains with influenza A virus (PR8, H1N1). We monitored body weight, survival, and mean time to death for 13 days after infection. Qivr5 (quantitative trait for influenza virus resistance on chromosome 5) was the largest and most significant QTL for weight loss. The effect of Qivr5 was detectable on day 2 post infection, but was most pronounced on days 5 and 6. Survival rate mapped to Qivr5, but additionally revealed a second significant locus on chromosome 19 (Qivr19). Analysis of mean time to death affirmed both Qivr5 and Qivr19. In addition, we observed several regions of the genome with suggestive linkage. There are potentially complex combinatorial interactions of the parental alleles among loci. Analysis of multiple gene expression data sets and sequence variants in these strains highlights about 30 strong candidate genes across all loci that may control influenza A susceptibility and resistance.ConclusionsWe have mapped influenza susceptibility loci to chromosomes 2, 5, 16, 17, and 19. Body weight and survival loci have a time-dependent profile that presumably reflects the temporal dynamic of the response to infection. We highlight candidate genes in the respective intervals and review their possible biological function during infection.

Achieving durable clinical responses to immune checkpoint inhibitors remains a challenge. Here, we demonstrate that immunotherapy with anti–CTLA-4 and its combination with anti–PD-1 rely on tumor cell–intrinsic activation of the cytosolic RNA receptor RIG-I. Mechanistically, tumor cell–intrinsic RIG-I signaling induced caspase-3–mediated tumor cell death, cross-presentation of tumor-associated antigen by CD103+ dendritic cells, subsequent expansion of tumor antigen–specific CD8+ T cells, and their accumulation within the tumor tissue. Consistently, therapeutic targeting of RIG-I with 5′– triphosphorylated RNA in both tumor and nonmalignant host cells potently augmented the efficacy of CTLA-4 checkpoint blockade in several preclinical cancer models. In humans, transcriptome analysis of primary melanoma samples revealed a strong association between high expression of DDX58 (the gene encoding RIG-I), T cell receptor and antigen presentation pathway activity, and prolonged overall survival. Moreover, in patients with melanoma treated with anti–CTLA-4 checkpoint blockade, high DDX58 RIG-I transcriptional activity significantly associated with durable clinical responses. Our data thus identify activation of RIG-I signaling in tumors and their microenvironment as a crucial component for checkpoint inhibitor–mediated immunotherapy of cancer.

Background Antibody-mediated targeting of regulatory T cell receptors such as CTLA-4 enhances antitumor immune responses against several cancer entities including malignant melanoma. Yet, therapeutic success in patients remains variable underscoring the need for novel combinatorial approaches. Methods Here we established a vaccination strategy that combines engagement of the nucleic acid-sensing pattern recognition receptor RIG-I, antigen and CTLA-4 blockade. We used in vitro transcribed 5′-triphosphorylated RNA (3pRNA) to therapeutically target the RIG-I pathway. We performed in vitro functional analysis in bone-marrow derived dendritic cells and investigated RIG-I-enhanced vaccines in different murine melanoma models. Findings We found that protein vaccination together with RIG-I ligation via 3pRNA strongly synergizes with CTLA-4 blockade to induce expansion and activation of antigen-specific CD8 + T cells that translates into potent antitumor immunity. RIG-I-induced cross-priming of cytotoxic T cells as well as antitumor immunity were dependent on the host adapter protein MAVS and type I interferon (IFN-I) signaling and were mediated by dendritic cells. Interpretation Overall, our data demonstrate the potency of a novel combinatorial vaccination strategy combining RIG-I-driven immunization with CTLA-4 blockade to prevent and treat experimental melanoma. Fund German Research Foundation (SFB 1335, SFB 1371), EMBO, Else Kröner-Fresenius-Foundation, German Cancer Aid, European Hematology Association, DKMS Foundation for Giving Life, Dres. Carl Maximilian and Carl Manfred Bayer-Foundation.