Genome wide identification of recessive cancer genes by combinatorial mutation analysis

ANP32B suppresses B-cell acute lymphoblastic leukemia through activation of PU.1 in mice

ANP32B, a member of the acidic leucine-rich nuclear phosphoprotein 32 kDa (ANP32) family of proteins, is critical for normal development because its constitutive knockout mice are perinatal lethal. It is also shown that ANP32B acts as a tumor-promoting gene in some kinds of cancer such as breast cancer and chronic myelogenous leukemia. Herein, we observe that ANP32B is lowly expressed in B-cell acute lymphoblastic leukemia (B-ALL) patients, which correlates with poor prognosis. Furthermore, we utilized the N-myc or BCR-ABL^p190 -induced B-ALL mouse model to investigate the role of ANP32B in B-ALL development. Intriguingly, conditional deletion of Anp32b in hematopoietic cells significantly promotes leukemogenesis in two B-ALL mouse models. Mechanistically, ANP32B interacts with purine rich box-1 (PU.1) and enhances the transcriptional activity of PU.1 in B-ALL cells. Overexpression of PU.1 dramatically suppresses B-ALL progression, and highly expressed PU.1 significantly reverses the accelerated leukemogenesis in Anp32b-deficient mice. Collectively, our findings identify ANP32B as a suppressor gene and provide novel insight into B-ALL pathogenesis.

Prognostic value of the DNA integrity index in patients with malignant lung tumors

Introduction

Lung cancer survival remains poor in the western world due to late presentation in most cases, leading to difficulty of treatment in these advanced and metastatic patients. Therefore, the development of a robust biomarker for prognosis and to monitor treatment response and relapse would be of great benefit. The use of Alu repeats and DNA Integrity Index has been shown to hold both diagnostic and prognostic value, and as it is obtained from the plasma of patients, it can serve as a non-invasive tool for routine monitoring. This study evaluates the efficiency of this technique in malignant lung cancer patients.

Methods

Plasma samples were collected from 48 patients, consisting of 29 lung cancer patients and 19 non-cancer controls. Alu repeat ratio and confounders were measured.

Results

Observations showed a higher Alu repeat ratio amongst the cancer group compared to controls (p=0.035), mean Alu ratio 0.38 (range 0.01-0.93) and 0.22 (0.007-0.44) respectively, ROC curve analysis AUC 0.61 (p=0.22). Analysis by staging was more promising, whereby a higher DNA Integrity Index was seen in advanced cases compared to both early stage and controls, p<0.0001; AUC: 0.92 (P=0.0002) and p=0.0006, AUC – 0.88 (p=0.0007) respectively, however no significant difference was observed in the early stage compared to controls. Short term survival data also showed a DNA Integrity Index of >0.5 to be associated with poorer overall survival p=0.03.

Conclusion

The results of this study show a potential use of Alu repeats ratios for prognostic purposes in the advanced setting for lung cancer patients.

BALB/c-congenic ANP32B-deficient mice reveal a modifying locus that determines viability

We previously found that deletion of the multifunctional factor ANP32B (a.k.a. SSP29, APRIL, PAL31, PHAPI2) resulted in a severe but strain-specific defect resulting in perinatal lethality. The difficulty in generating an adult cohort of ANP32B-deficient animals limited our ability to examine adult phenotypes, particularly cancer-related phenotypes. We bred the Anp32b-null allele into the BALB/c and FVB/N genetic background. The BALB/c, but not the FVB/N, background provided sufficient frequency of adult Anp32b-null (Anp32b^−/−) animals. From these, we found no apparent oncogenic role for this protein in mammary tumorigenesis contrary to what was predicted based on human data. We also found runtism, pathologies in various organ systems, and an unusual clinical chemistry signature in the adult Anp32b^−/− mice. Intriguingly, genome-wide single-nucleotide polymorphism analysis suggested that our colony retained an unlinked C57BL/6J locus at high frequency. Breeding this locus to homozygosity demonstrated that it had a strong effect on Anp32b^−/− viability indicating that this locus contains a modifier gene of Anp32b with respect to development. This suggests a functionally important genetic interaction with one of a limited number of candidate genes, foremost among them being the variant histone gene H2afv. Using congenic breeding strategies, we have generated a viable ANP32B-deficient animal in a mostly pure background. We have used this animal to reliably exclude mouse ANP32B as an important oncogene in mammary tumorigenesis. Our further phenotyping strengthens the evidence that ANP32B is a widespread regulator of gene expression. These studies may also impact the choice of subsequent groups with respect to congenic breeding versus de novo zygote targeting strategies for background analyses in mouse genetics.

Genetic variation in C12orf51 is associated with prognosis of intestinal-type gastric cancer in a Chinese population

Recent genome-wide association study (GWAS) on esophageal squamous-cell carcinoma (ESCC) among Chinese population has identified two novel single nucleotide polymorphisms (SNPs) rs11066280 and rs2074356 on C12orf51 gene. We hypothesized that SNPs rs11066280 and rs2074356 could influence gastric cancer survival outcomes. We genotyped the SNPs rs11066280 and rs2074356 in 940 patients with surgically resected gastric cancer. Analyses of genotype association with survival outcomes were assessed by the Kaplan-Meier method, Cox proportional hazards models and the log-rank test. There was no significant association between rs11066280 and survival of gastric cancer. However, in the stratification analysis of histology, we found that the rs11066280 TA/AA genotypes were associated with a poor survival of intestinal-type gastric cancer (log-rank P=0.041, hazard ratio [HR]=1.40, 95% confidence interval [CI]=1.02-1.93), Moreover, this hazardous effect was more prominent among patients with tumor size>5cm, no distant metastasis, chemotherapy and drinking. No significant association was observed between rs2074356 and the survival of gastric cancer. C12orf5 rs11066280 could be useful marker of survival assessment and individualized clinical therapy for gastric cancer, particularly among the intestinal-type gastric cancer.

Cracking the ANP32 whips: important functions, unequal requirement, and hints at disease implications

The acidic (leucine-rich) nuclear phosphoprotein 32 kDa (ANP32) family is composed of small, evolutionarily conserved proteins characterized by an N-terminal leucine-rich repeat domain and a C-terminal low-complexity acidic region. The mammalian family members (ANP32A, ANP32B, and ANP32E) are ascribed physiologically diverse functions including chromatin modification and remodelling, apoptotic caspase modulation, protein phosphatase inhibition, as well as regulation of intracellular transport. In addition to reviewing the widespread literature on the topic, we present a concept of the ANP32s as having a whip-like structure. We also present hypotheses that ANP32C and other intronless sequences should not currently be considered bona fide family members, that their disparate necessity in development may be due to compensatory mechanisms, that their contrasting roles in cancer are likely context-dependent, along with an underlying hypothesis that ANP32s represent an important node of physiological regulation by virtue of their diverse biochemical activities.

Functional complementation between transcriptional methylation regulation and post-transcriptional microRNA regulation in the human genome

BACKGROUND

DNA methylation in the 5' promoter regions of genes and microRNA (miRNA) regulation at the 3' untranslated regions (UTRs) are two major epigenetic regulation mechanisms in most eukaryotes. Both DNA methylation and miRNA regulation can suppress gene expression and their corresponding protein product; thus, they play critical roles in cellular processes. Although there have been numerous investigations of gene regulation by methylation changes and miRNAs, there is no systematic genome-wide examination of their coordinated effects in any organism.

RESULTS

In this study, we investigated the relationship between promoter methylation at the transcription level and miRNA regulation at the post-transcription level by taking advantage of recently released human methylome data and high quality miRNA and other gene annotation data. We found methylation level in the promoter regions and expression level was negatively correlated. Then, we showed that miRNAs tended to target the genes with a low DNA methylation level in their promoter regions. We further demonstrated that this observed pattern was not attributed to the gene expression level, expression broadness, or the number of transcription factor binding sites. Interestingly, we found miRNA target sites were significantly enriched in the genes located in differentially methylated regions or partially methylated domains. Finally, we explored the features of DNA methylation and miRNA regulation in cancer genes and found cancer genes tended to have low methylation level and more miRNA target sites.

CONCLUSION

This is the first genome-wide investigation of the combined regulation of gene expression. Our results supported a complementary regulation between DNA methylation (transcriptional level) and miRNA function (post-transcriptional level) in the human genome. The results were helpful for our understanding of the evolutionary forces towards organisms' complexity beyond traditional sequence level investigation.

A continuum model for tumour suppression

This year, 2011, marks the forty-year anniversary of the statistical analysis of retinoblastoma that provided the first evidence that tumorigenesis can be initiated by as few as two mutations. This work provided the foundation for the two-hit hypothesis that explained the role of recessive tumour suppressor genes (TSGs) in dominantly inherited cancer susceptibility syndromes. However, four decades later, it is now known that even partial inactivation of tumour suppressors can critically contribute to tumorigenesis. Here we analyse this evidence and propose a continuum model of TSG function to explain the full range of TSG mutations found in cancer.

Genome-wide association study identifies three new susceptibility loci for esophageal squamous-cell carcinoma in Chinese populations

Esophageal squamous-cell carcinoma (ESCC) is one of the most prevalent cancers worldwide and occurs at a relatively high frequency in China. To identify genetic susceptibility loci for ESCC, we conducted a genome-wide association study on 2,031 individuals with ESCC (cases) and 2,044 controls of Chinese descent using 666,141 autosomal SNPs. We evaluated promising associations in an additional 6,276 cases and 6,165 controls of Chinese descent from different areas of China. We identified seven susceptibility loci on chromosomes 5q11, 6p21, 10q23, 12q24 and 21q22 (ranging from P = 7.48 × 10(-12) to P = 2.44 × 10(-31)); among these loci, 5q11, 6p21 and 21q22 were newly identified. Three variants in high linkage disequilibrium on 12q24 confer their risks to ESCC in a gene-lifestyle interaction manner, with more pronounced risk enhancement seen in tobacco and alcohol users. Furthermore, the identified variants had a cumulative association with ESCC risk (P(trend) = 7.92 × 10(-56)). These findings highlight the involvement of multiple genetic loci and gene-environment interaction in the development of esophageal cancer.

Alu distribution and mutation types of cancer genes

Background

Alu elements are the most abundant retrotransposable elements comprising ~11% of the human genome. Many studies have highlighted the role that Alu elements have in genetic instability and how their contribution to the assortment of mutagenic events can lead to cancer. As of yet, little has been done to quantitatively assess the association between Alu distribution and genes that are causally implicated in oncogenesis.

Results

We have investigated the effect of various Alu densities on the mutation type based classifications of cancer genes. In order to establish the direct relationship between Alus and the cancer genes of interest, genome wide Alu-related densities were measured using genes rather than the sliding windows of fixed length as the units. Several novel genomic features, such as the density of the adjacent Alu pairs and the number of Alu-Exon-Alu triplets, were developed in order to extend the investigation via the multivariate statistical analysis toward more advanced biological insight. In addition, we characterized the genome-wide intron Alu distribution with a mixture model that distinguished genes containing Alu elements from those with no Alus, and evaluated the gene-level effect of the 5'-TTAAAA motif associated with Alu insertion sites using a two-step regression analysis method.

Conclusions

The study resulted in several novel findings worthy of further investigation. They include: (1) Recessive cancer genes (tumor suppressor genes) are enriched with Alu elements (p < 0.01) compared to dominant cancer genes (oncogenes) and the entire set of genes in the human genome; (2) Alu-related genomic features can be used to cluster cancer genes into biological meaningful groups; (3) The retention of exon Alus has been restricted in the human genome development, and an upper limit to the chromosome-level exon Alu densities is suggested by the distribution profile; (4) For the genes with at least one intron Alu repeat in individual chromosomes, the intron Alu densities can be well fitted by a Gamma distribution; (5) The effect of the 5'-TTAAAA motif on Alu densities varies across different chromosomes.

A comparative study of cancer proteins in the human protein-protein interaction network

Background

Cancer is a complex disease. So far, many genes have been reported to involve in the development of cancer. Rather than the traditional approach to studying individual genes or loci, a systematic investigation of cancer proteins in the human protein-protein interaction network may provide important biological information for uncovering the molecular mechanisms of cancer and, potentially, other complex diseases.

Results

We explored global and local network characteristics of the proteins encoded by cancer genes (cancer proteins) in the human interactome. We found that the network topology of the cancer proteins was much different from that of the proteins encoded by essential genes (essential proteins) or control genes (control proteins). Relative to the essential proteins or control proteins, cancer proteins tended to have higher degree, higher betweenness, shorter shortest-path distance, and weaker clustering coefficient in the human interactome. We further separated the cancer proteins into two groups (recessive and dominant cancer proteins) and compared their topological features. Recessive cancer proteins had higher betweenness than dominant cancer proteins, while their degree distribution and characteristic shortest path distance were also significantly different. Finally, we found that cancer proteins were not randomly distributed in the human interactome and they connected strongly with each other.

Conclusion

Our study revealed much stronger protein-protein interaction characteristics of cancer proteins relative to the essential proteins or control proteins in the whole human interactome. We also found stronger network characteristics of recessive than dominant cancer proteins. The results are helpful for cancer candidate gene prioritization and verification, biomarker discovery, and, ultimately, understanding the etiology of cancer at the systems biological level.