The Mutational Features of Aristolochic Acid-Induced Mouse and Human Liver Cancers.

BACKGROUND AND AIMS: Aristolochic acid (AA) exposure has been statistically associated with human liver cancers. However, direct evidence of AA exposure-induced liver cancer is absent. This study aims to establish a direct causal relationship between AA exposure and liver cancers based on a mouse model and then explores the AA-mediated genomic alterations that could be implicated in human cancers with AA-associated mutational signature. APPROACH AND RESULTS: We subjected mice, including phosphatase and tensin homolog (Pten)-deficient ones, to aristolochic acid I (AAI) alone or a combination of AAI and CCl4 . Significantly, AAI exposure induced mouse liver cancers, including hepatocellular carcinoma (HCC) and combined HCC and intrahepatic cholangiocarcinoma, in a dose-dependent manner. Moreover, AAI exposure also enhanced tumorigenesis in these CCl4 -treated or Pten-deficient mice. AAI led to DNA damage and AAI-DNA adduct that could initiate liver cancers through characteristic adenine-to-thymine transversions, as indicated by comprehensive genomic analysis, which revealed recurrent mutations in Harvey rat sarcoma virus oncogene. Interestingly, an AA-associated mutational signature was mainly implicated in human liver cancers, especially from China. Moreover, we detected the AAI-DNA adduct in 25.8% (16/62) of paratumor liver tissues from randomly selected Chinese patients with HCC. Furthermore, based on phylogenetic analysis, the characteristic mutations were found in the initiating malignant clones in the AA-implicated mouse and human liver cancers where the mutations of tumor protein p53 and Janus kinase 1 were prone to be significantly enriched in the AA-affected human tumors. CONCLUSIONS: This study provides evidence for AA-induced liver cancer with the featured mutational processes during malignant clonal evolution, laying a solid foundation for the prevention and diagnosis of AA-associated human cancers, especially liver cancers.

Application of qPCR assays based on haloacids transporter gene dehp2 for discrimination of Burkholderia and Paraburkholderia.

BACKGROUND: A major facilitator superfamily transporter Dehp2 was recently shown to be playing an important role in transport and biodegradation of haloacids in Paraburkholderia caribensis MBA4, and Dehp2 is phylogenetically conserved in Burkholderia sensu lato. RESULTS: We designed both Burkholderia sensu stricto-specific and Paraburkholderia-specific qPCR assays based on dehp2 and 16S rRNA, and validated the qPCR assays in 12 bacterial strains. The qPCR assays could detect single species of Burkholderia sensu stricto or Paraburkholderia with high sensitivity and discriminate them in mixtures with high specificity over a wide dynamic range of relative concentrations. At relatively lower cost compared with sequencing-based approach, the qPCR assays will facilitate discrimination of Burkholderia sensu stricto and Paraburkholderia in a large number of samples. CONCLUSIONS: For the first time, we report the utilization of a haloacids transporter gene for discriminative purpose in Burkholderia sensu lato. This enables not only quick decision on proper handling of putative pathogenic samples in Burkholderia sensu stricto group but also future exploitation of relevant species in Paraburkholderia group for haloacids biodegradation purposes.

Single-cell RNA-Seq analysis reveals dynamic trajectories during mouse liver development.

BACKGROUND: The differentiation and maturation trajectories of fetal liver stem/progenitor cells (LSPCs) are not fully understood at single-cell resolution, and a priori knowledge of limited biomarkers could restrict trajectory tracking. RESULTS: We employed marker-free single-cell RNA-Seq to characterize comprehensive transcriptional profiles of 507 cells randomly selected from seven stages between embryonic day 11.5 and postnatal day 2.5 during mouse liver development, and also 52 Epcam-positive cholangiocytes from postnatal day 3.25 mouse livers. LSPCs in developing mouse livers were identified via marker-free transcriptomic profiling. Single-cell resolution dynamic developmental trajectories of LSPCs exhibited contiguous but discrete genetic control through transcription factors and signaling pathways. The gene expression profiles of cholangiocytes were more close to that of embryonic day 11.5 rather than other later staged LSPCs, cuing the fate decision stage of LSPCs. Our marker-free approach also allows systematic assessment and prediction of isolation biomarkers for LSPCs. CONCLUSIONS: Our data provide not only a valuable resource but also novel insights into the fate decision and transcriptional control of self-renewal, differentiation and maturation of LSPCs.

[Establishment and application of quantitative detection for heteroplasmic mtDNA mutation 3243A→G].

OBJECTIVE: To develop a rapid, simple, cost-effective, accurate and sensitive method for quantitative detection of mitochondrial DNA (mtDNA) 3243A→G mutation in order to provide reference for selecting the best detection method under different conditions. METHODS: Genomic DNA was extracted from peripheral leucocytes of 17 individuals from a Wenzhou family featuring maternally inherited diabetes and deafness (MIDD). Heteroplasmic level of mtDNA 3243A→G mutation was determined respectively with polymerase chain reaction-restriction fragment length polymorphism (PCR-RLFP), real time-amplification refractory mutation system-quantitative PCR (RT-ARMS-qPCR) and pyrosquencing. Eleven plasmids with various heteroplasmic levels of the 3243A→G mutation (ranging from 0 to 100%)were constructed as the standards. The reliability of above methods was compared by correlation coefficient based on observed and expected values. RESULTS: For all three methods, measurement of the standards showed a linear correlation between the expected and detected values, i.e., PCR-RFLP (R(2)=0.828), RT-ARMS-qPCR (R(2)=0.998) and pyrosquencing (R(2)=0.997). For the MIDD family, it was consistent that there are 13 members carrying the A3243G mutation with different heteroplasmic levels. And there was no significant difference between the results by RT-ARMS-qPCR and pyrosquencing. CONCLUSION: PCR-RFLP is not appropriate for the quantitative detection but could be used for early clinical screening. Both RT-ARMS-qPCR and pyrosquencing are suitable for the detection of low heteroplasmic level of A3243G mutation. Compared with pyrosquencing, RT-ARMS-qPCR is rapid, reliable and cost-effective, and is the best choice for detecting low mutation loads.

Exposure to aristolochic acid I is associated with poor prognosis of liver cancer patients.

The aristolochic acids (AAs), derived from Aristolochia and Asarum species used widely in herbal medicines, are closely associated with liver cancer. The major AA derivatives are aristolochic acid I (AAI) and II (AAII), which can bind DNA covalently to form AA-DNA adducts after metabolic activation in vivo. Among all these AA-DNA adducts, 7-(deoxyadenosine-N6-yl) aristolactam I (dA-AL-I) is the most abundant and persistent DNA lesion in patients. However, the direct evidence indicating AA exposure in human liver cancer is still missing. Here, we analyzed dA-AL-I adduct, the direct biomarker of AAI exposure, by ultra-performance liquid chromatography coupled with triple quadrupole mass spectrometry (UPLC-TQ/MS) in 209 liver cancer patients. Also, DNA samples from mice treated with/without AAI were used as positive and negative controls. dA-AL-I adduct was present in 110 of 209 (52.6%) patients, indicating that these patients were exposed to AAI prior to their clinical investigations and also had a worse prognosis. The relative high AA exposure rate and worse prognosis in our cohort of patients emphasize the significance to increase public awareness to avoid the use of herbal medicine containing AAs or their derivatives.

Error-prone, stress-induced 3' flap-based Okazaki fragment maturation supports cell survival.

How cells with DNA replication defects acquire mutations that allow them to escape apoptosis under environmental stress is a long-standing question. Here, we report that an error-prone Okazaki fragment maturation (OFM) pathway is activated at restrictive temperatures in rad27Δ yeast cells. Restrictive temperature stress activated Dun1, facilitating transformation of unprocessed 5' flaps into 3' flaps, which were removed by 3' nucleases, including DNA polymerase δ (Polδ). However, at certain regions, 3' flaps formed secondary structures that facilitated 3' end extension rather than degradation, producing alternative duplications with short spacer sequences, such as pol3 internal tandem duplications. Consequently, little 5' flap was formed, suppressing rad27Δ-induced lethality at restrictive temperatures. We define a stress-induced, error-prone OFM pathway that generates mutations that counteract replication defects and drive cellular evolution and survival.

SCFFBW7-mediated degradation of Brg1 suppresses gastric cancer metastasis.

Brg1/SMARCA4 serves as the ATPase and the helicase catalytic subunit for the multi-component SWI/SNF chromatin remodeling complex, which plays a pivotal role in governing chromatin structure and gene transcription. However, the upstream signaling pathways regulating Brg1 protein stability and its physiological contribution to carcinogenesis remain largely elusive. Here we report that Brg1 is a bona fide ubiquitin substrate of SCFFBW7. We reveal that CK1δ phosphorylates Brg1 at Ser31/Ser35 residues to facilitate the binding of Brg1 to FBW7, leading to ubiquitination-mediated degradation. In keeping with a tumor suppressive role of FBW7 in human gastric cancer, we find an inverse correlation between FBW7 and Brg1 expression in human gastric cancer clinical samples. Mechanistically, we find that stabilization of Brg1 in gastric cancer cells suppresses E-cadherin expression, subsequently promoting gastric cancer metastasis. Hence, this previously unknown FBW7/Brg1 signaling axis provides the molecular basis and the rationale to target Brg1 in FBW7-compromised human gastric cancers.

PRDM8 internal promoter hyperhydroxymethylation correlates with increased expression of the corresponding transcript in Down syndrome.

Down syndrome (DS) is the most common form of intellectual disability associated with central nervous system abnormalities and results from an extra complete or partial copy of human chromosome 21. However, whether DNA hydroxymethylation is perturbed in a specific gene associated with DS phenotypes, or the alteration of DNA hydroxymethy-lation results in changes of gene expression in DS remains unidentified. The current study mapped 5­methylcytosine and 5­hydroxymethylcytosine at CpG islands of the PR domain containing 8 (PRDM8) in the peripheral blood of 16 DS and 19 normal samples by oxidative bisulfite-pyrosequencing. Furthermore, the association of the expression levels of the two transcripts and epigenetic modification in different genomic contexts of PRDM8 was analyzed. The results demonstrated hypermethylation and hyperhydroxymethylation at the internal promoter of PRDM8 in DS, and significantly increased the expression of PRDM8 transcript variant 2 in the DS patients (median 3.9 vs. 2.04; P=0.016), accompanied by a positive correlation between the expression of two PRDM8 transcripts and hydroxymethylation at the corresponding external and internal promoters in patients, although not in the controls. A similar association was observed between the expression of transcript variant 1 and intragenic methylation of PRDM8. Taken together, the results of the present study suggest a critical role for DNA hydroxymethylation and methylation in regulating abnormal PRDM8 overexpression in DS.