High-Level MYCN-Amplified RB1-Proficient Retinoblastoma Tumors Retain Distinct Molecular Signatures.

Purpose: Retinoblastomas are malignant eye tumors diagnosed in young children. Most retinoblastomas are genetically characterized by biallelic inactivation of the RB1 gene. However, 1.5% of tumors demonstrate high-level amplification of the proto-oncogene MYCN. Patients with MYCN-amplified RB1-proficient retinoblastoma receive a diagnosis at an earlier age and show a clinically and histologically more malignant phenotype. This study aimed to identify genome-wide molecular features that distinguish this subtype from other retinoblastomas. Design: Cohort study. Participants: Forty-seven retinoblastoma tumors, comprising 36 RB1 -/-, 4 RB1 +/-, and 7 RB1 +/+ tumors. In total, 5 retinoblastomas displayed high-level MYCN amplification, with 3 being RB1 +/+, 1 being RB1 +/-, and 1 being RB1 -/- . Methods: Integrated analysis, based on gene expression, methylation, and methylation-expression correlations, was performed to identify distinct molecular components of MYCN-amplified RB1-proficient retinoblastomas compared with other retinoblastoma subtypes. The methylation and methylation-expression correlation analysis was initially conducted within a subset of samples (n = 15) for which methylation profiles were available. The significant findings were cross-validated in the entire cohort (n = 47) and in publicly available data. Main Outcome Measures: Differentially expressed genes/pathways, differentially methylated genes, and methylation-driven differential gene expression. Results: A large number of genes (n = 3155) were identified with distinct expression patterns in MYCN-amplified RB1-proficient retinoblastomas. The upregulated and downregulated genes were associated with translation and cell-cycle processes, respectively. Methylation analysis revealed distinct methylated patterns in MYCN-amplified RB1-proficient tumors, many of which showing significant impact on gene expression. Data integration identified a 40-gene expression signature with hypermethylated state resulting in a significant downregulation in MYCN-amplified RB1-proficient retinoblastomas. Cross-validation using the entire cohort and the public domain expression data verified the overall lower expression of these genes not only in retinoblastomas with a MYCN-amplified RB1-proficient background, but also in MYCN-amplified neuroblastomas. These include the metabolism-associated TSTD1 gene and the cyclin-dependent kinase inhibitor gene CDKN2C. Conclusions: MYCN-amplified RB1-proficient retinoblastomas display significantly distinct molecular features compared with other retinoblastomas, including a set of 40 hypermethylation-driven downregulated genes. This gene set can give insight into the biology of MYCN-amplified retinoblastomas and may help us to understand the more aggressive clinical behavior.

Loss of FLCN-FNIP1/2 induces a non-canonical interferon response in human renal tubular epithelial cells.

Germline mutations in the Folliculin (FLCN) tumor suppressor gene cause Birt-Hogg-Dubé (BHD) syndrome, a rare autosomal dominant disorder predisposing carriers to kidney tumors. FLCN is a conserved, essential gene linked to diverse cellular processes but the mechanism by which FLCN prevents kidney cancer remains unknown. Here, we show that disrupting FLCN in human renal tubular epithelial cells (RPTEC/TERT1) activates TFE3, upregulating expression of its E-box targets, including RRAGD and GPNMB, without modifying mTORC1 activity. Surprisingly, the absence of FLCN or its binding partners FNIP1/FNIP2 induces interferon response genes independently of interferon. Mechanistically, FLCN loss promotes STAT2 recruitment to chromatin and slows cellular proliferation. Our integrated analysis identifies STAT1/2 signaling as a novel target of FLCN in renal cells and BHD tumors. STAT1/2 activation appears to counterbalance TFE3-directed hyper-proliferation and may influence immune responses. These findings shed light on unique roles of FLCN in human renal tumorigenesis and pinpoint candidate prognostic biomarkers.

Effective CRISPR/Cas9-mediated correction of a Fanconi anemia defect by error-prone end joining or templated repair.

Fanconi anemia (FA) is a cancer predisposition syndrome characterized by congenital abnormalities, bone marrow failure, and hypersensitivity to aldehydes and crosslinking agents. For FA patients, gene editing holds promise for therapeutic applications aimed at functionally restoring mutated genes in hematopoietic stem cells. However, intrinsic FA DNA repair defects may obstruct gene editing feasibility. Here, we report on the CRISPR/Cas9-mediated correction of a disruptive mutation in Fancf. Our experiments revealed that gene editing could effectively restore Fancf function via error-prone end joining resulting in a 27% increased survival in the presence of mitomycin C. In addition, templated gene correction could be achieved after double strand or single strand break formation. Although templated gene editing efficiencies were low (≤6%), FA corrected embryonic stem cells acquired a strong proliferative advantage over non-corrected cells, even without imposing genotoxic stress. Notably, Cas9 nickase activity resulted in mono-allelic gene editing and avoidance of undesired mutagenesis. In conclusion: DNA repair defects associated with FANCF deficiency do not prohibit CRISPR/Cas9 gene correction. Our data provide a solid basis for the application of pre-clinical models to further explore the potential of gene editing against FA, with the eventual aim to obtain therapeutic strategies against bone marrow failure.

Genomic landscape of retinoblastoma in Rb-/- p130-/- mice resembles human retinoblastoma.

Several murine retinoblastoma models have been generated by deleting the genes encoding for retinoblastoma susceptibility protein pRb and one of its family members p107 or p130. In Rb-/- p107-/- retinoblastomas, somatic copy number alterations (SCNAs) like Mdm2 amplification or Cdkn2a deletion targeting the p53-pathway occur, which is uncommon for human retinoblastoma. In our study, we determined SCNAs in retinoblastomas developing in Rb-/- p130-/- mice and compared this to murine Rb-/- p107-/- tumors and human tumors. Chimeric mice were made by injection of 129/Ola-derived Rb-/- p130-/- embryonic stem cells into wild type C57BL/6 blastocysts. SCNAs of retinoblastoma samples were determined by low-coverage (∼0.5×) whole genome sequencing. In Rb-/- p130-/- tumors, SCNAs included gain of chromosomes 1 (3/23 tumors), 8 (1/23 tumors), 10 (1/23 tumors), 11 (2/23 tumors), and 12 (4/23 tumors), which could be mapped to frequently altered chromosomes in human retinoblastomas. While the altered chromosomes in Rb-/- p130-/- tumors were similar to those in Rb-/- p107-/- tumors, the alteration frequencies were much lower in Rb-/- p130-/- tumors. Most of the Rb-/- p130-/- tumors (16/23 tumors, 70%) were devoid of SCNAs, in strong contrast to Rb-/- p107-/- tumors, which were never (0/15 tumors) SCNA-devoid. Similarly, to human retinoblastoma, increased age at diagnosis significantly correlated with increased SCNA frequencies. Additionally, focal loss of Cdh11 was observed in one Rb-/- p130-/- tumor, which enforces studies in human retinoblastoma that identified CDH11 as a retinoblastoma suppressor. Moreover, based on a comparison of genes altered in human and murine retinoblastoma, we suggest exploring the role of HMGA1 and SRSF3 in retinoblastoma development. © 2016 Wiley Periodicals, Inc.

Somatic genomic alterations in retinoblastoma beyond RB1 are rare and limited to copy number changes.

Retinoblastoma is a rare childhood cancer initiated by RB1 mutation or MYCN amplification, while additional alterations may be required for tumor development. However, the view on single nucleotide variants is very limited. To better understand oncogenesis, we determined the genomic landscape of retinoblastoma. We performed exome sequencing of 71 retinoblastomas and matched blood DNA. Next, we determined the presence of single nucleotide variants, copy number alterations and viruses. Aside from RB1, recurrent gene mutations were very rare. Only a limited fraction of tumors showed BCOR (7/71, 10%) or CREBBP alterations (3/71, 4%). No evidence was found for the presence of viruses. Instead, specific somatic copy number alterations were more common, particularly in patients diagnosed at later age. Recurrent alterations of chromosomal arms often involved less than one copy, also in highly pure tumor samples, suggesting within-tumor heterogeneity. Our results show that retinoblastoma is among the least mutated cancers and signify the extreme sensitivity of the childhood retina for RB1 loss. We hypothesize that retinoblastomas arising later in retinal development benefit more from subclonal secondary alterations and therefore, these alterations are more selected for in these tumors. Targeted therapy based on these subclonal events might be insufficient for complete tumor control.

Loss of photoreceptorness and gain of genomic alterations in retinoblastoma reveal tumor progression.

BACKGROUND: Retinoblastoma is a pediatric eye cancer associated with RB1 loss or MYCN amplification (RB1 (+/+) MYCN(A) ). There are controversies concerning the existence of molecular subtypes within RB1(-/-) retinoblastoma. To test whether these molecular subtypes exist, we performed molecular profiling. METHODS: Genome-wide mRNA expression profiling was performed on 76 primary human retinoblastomas. Expression profiling was complemented by genome-wide DNA profiling and clinical, histopathological, and ex vivo drug sensitivity data. FINDINGS: RNA and DNA profiling identified major variability between retinoblastomas. While gene expression differences between RB1 (+/+) MYCN(A) and RB1(-/-) tumors seemed more dichotomous, differences within the RB1(-/-) tumors were gradual. Tumors with high expression of a photoreceptor gene signature were highly differentiated, smaller in volume and diagnosed at younger age compared with tumors with low photoreceptor signature expression. Tumors with lower photoreceptor expression showed increased expression of genes involved in M-phase and mRNA and ribosome synthesis and increased frequencies of somatic copy number alterations. INTERPRETATION: Molecular, clinical and histopathological differences between RB1(-/-) tumors are best explained by tumor progression, reflected by a gradual loss of differentiation and photoreceptor expression signature. Since copy number alterations were more frequent in tumors with less photoreceptorness, genomic alterations might be drivers of tumor progression. RESEARCH IN CONTEXT: Retinoblastoma is an ocular childhood cancer commonly caused by mutations in the RB1 gene. In order to determine optimal treatment, tumor subtyping is considered critically important. However, except for very rare retinoblastomas without an RB1 mutation, there are controversies as to whether subtypes of retinoblastoma do exist. Our study shows that retinoblastomas are highly diverse but rather than reflecting distinct tumor types with a different etiology, our data suggests that this diversity is a result of tumor progression driven by cumulative genetic alterations. Therefore, retinoblastomas should not be categorized in distinct subtypes, but be described according to their stage of progression.

Defects in the Fanconi Anemia Pathway and Chromatid Cohesion in Head and Neck Cancer.

Failure to repair DNA damage or defective sister chromatid cohesion, a process essential for correct chromosome segregation, can be causative of chromosomal instability (CIN), which is a hallmark of many types of cancers. We investigated how frequent this occurs in head and neck squamous cell carcinoma (HNSCC) and whether specific mechanisms or genes could be linked to these phenotypes. The genomic instability syndrome Fanconi anemia is caused by mutations in any of at least 16 genes regulating DNA interstrand crosslink (ICL) repair. Since patients with Fanconi anemia have a high risk to develop HNSCC, we investigated whether and to which extent Fanconi anemia pathway inactivation underlies CIN in HNSCC of non-Fanconi anemia individuals. We observed ICL-induced chromosomal breakage in 9 of 17 (53%) HNSCC cell lines derived from patients without Fanconi anemia. In addition, defective sister chromatid cohesion was observed in five HNSCC cell lines. Inactivation of FANCM was responsible for chromosomal breakage in one cell line, whereas in two other cell lines, somatic mutations in PDS5A or STAG2 resulted in inadequate sister chromatid cohesion. In addition, FANCF methylation was found in one cell line by screening an additional panel of 39 HNSCC cell lines. Our data demonstrate that CIN in terms of ICL-induced chromosomal breakage and defective chromatid cohesion is frequently observed in HNSCC. Inactivation of known Fanconi anemia and chromatid cohesion genes does explain CIN in the minority of cases. These findings point to phenotypes that may be highly relevant in treatment response of HNSCC.

Proper genomic profiling of (BRCA1-mutated) basal-like breast carcinomas requires prior removal of tumor infiltrating lymphocytes.

INTRODUCTION: BRCA1-mutated breast carcinomas may have distinct biological features, suggesting the involvement of specific oncogenic pathways in tumor development. The identification of genomic aberrations characteristic for BRCA1-mutated breast carcinomas could lead to a better understanding of BRCA1-associated oncogenic events and could prove valuable in clinical testing for BRCA1-involvement in patients. METHODS: For this purpose, genomic and gene expression profiles of basal-like BRCA1-mutated breast tumors (n = 27) were compared with basal-like familial BRCAX (non-BRCA1/2/CHEK2*1100delC) tumors (n = 14) in a familial cohort of 120 breast carcinomas. RESULTS: Genome wide copy number profiles of the BRCA1-mutated breast carcinomas in our data appeared heterogeneous. Gene expression analyses identified varying amounts of tumor infiltrating lymphocytes (TILs) as a major cause for this heterogeneity. Indeed, selecting tumors with relative low amounts of TILs, resulted in the identification of three known but also five previously unrecognized BRCA1-associated copy number aberrations. Moreover, these aberrations occurred with high frequencies in the BRCA1-mutated tumor samples. Using these regions it was possible to discriminate BRCA1-mutated from BRCAX breast carcinomas, and they were validated in two independent cohorts. To further substantiate our findings, we used flow cytometry to isolate cancer cells from formalin-fixed, paraffin-embedded, BRCA1-mutated triple negative breast carcinomas with estimated TIL percentages of 40% and higher. Genomic profiles of sorted and unsorted fractions were compared by shallow whole genome sequencing and confirm our findings. CONCLUSION: This study shows that genomic profiling of in particular basal-like, and thus BRCA1-mutated, breast carcinomas is severely affected by the presence of high numbers of TILs. Previous reports on genomic profiling of BRCA1-mutated breast carcinomas have largely neglected this. Therefore, our findings have direct consequences on the interpretation of published genomic data. Also, these findings could prove valuable in light of currently used genomic tools for assessing BRCA1-involvement in breast cancer patients and pathogenicity assessment of BRCA1 variants of unknown significance. The BRCA1-associated genomic aberrations identified in this study provide possible leads to a better understanding of BRCA1-associated oncogenesis.

DNA helicases FANCM and DDX11 are determinants of PARP inhibitor sensitivity.

The encouraging response rates of BRCA1- and BRCA2-mutated cancers toward PARP inhibitors make it worthwhile to identify other potential determinants of PARP inhibitor responsiveness. Since the Fanconi anemia (FA) pathway coordinates several DNA repair pathways, including homologous recombination in which BRCA1 and BRCA2 play important roles, we investigated whether this pathway harbors other predictors of PARP inhibitor sensitivity. Lymphoblastoid cell lines derived from individuals with FA or clinically related syndromes, such as Warsaw breakage syndrome, were tested for PARP inhibitor sensitivity. Remarkably, we found a strong variability in PARP inhibitor sensitivity among different FANCD1/BRCA2-deficient lymphoblasts, suggesting that PARP inhibitor response depends on the type of FANCD1/BRCA2 mutation. We identified the DNA helicases FANCM and DDX11 as determinants of PARP inhibitor response. These results may extend the utility of PARP inhibition as effective anticancer treatment.

A novel splice site mutation in the noncoding region of BRCA2: implications for Fanconi anemia and familial breast cancer diagnostics.

Fanconi anemia (FA) is a rare recessive disorder with chromosomal instability, congenital abnormalities, and a high cancer risk. The breast cancer susceptibility gene BRCA2 (FANCD1) is one of the 16 genes involved in this recessive disease. We have identified a novel mutation of the splice donor site of intron 1 in the noncoding region of BRCA2 in a Japanese FA family. This mutation may account for the FA phenotype in a patient originally reported to have biallelic mutations in BRCA2. Subsequent functional studies revealed that one of the mutations, K2729N, was a neutral change. As reported here, a more careful analysis resulted in the identification of a novel splice site mutation. Functional analysis using a mouse embryonic stem cell-based assay revealed that it causes aberrant splicing, reduced transcript levels and hypersensitivity to DNA damaging agents, suggesting that it is likely to be pathogenic. Although similar pathogenic variants in the noncoding region of BRCA1 and 2 were not identified in a cohort of 752 familial breast cancer cases, we still think this finding is relevant for mutation analysis in Hereditary Breast and Ovarian Cancer Syndrome families in a diagnostic setting.

Analysis of the novel fanconi anemia gene SLX4/FANCP in familial breast cancer cases.

SLX4/FANCP is a recently discovered novel disease gene for Fanconi anemia (FA), a rare recessive disorder characterized by chromosomal instability and increased cancer susceptibility. Three of the 15 FA genes are breast cancer susceptibility genes in heterozygous mutation carriers--BRCA2, PALB2, and BRIP1. To investigate if defects in SLX4 also predispose to breast cancer, the gene was sequenced in a cohort of 729 BRCA1/BRCA2-negative familial breast cancer cases. We identified a single splice site mutation (c.2013+2T>A), which causes a frameshift by skipping of exon 8. We also identified 39 missense variants, four of which were selected for functional testing in a Mitomycin C-induced growth inhibition assay, and appeared indistinguishable from wild type. Although this is the first study that describes a truncating SLX4 mutation in breast cancer patients, our data indicate that germline mutations in SLX4 are very rare and are unlikely to make a significant contribution to familial breast cancer.

Routine testing for PALB2 mutations in familial pancreatic cancer families and breast cancer families with pancreatic cancer is not indicated.

PALB2-mutation carriers not only have an increased risk for breast cancer (BC) but also for pancreatic cancer (PC). Thus far, PALB2 mutations have been mainly found in PC patients from families affected by both PC and BC. As it is well known that the prevalence of gene mutations varies between different populations, we studied the prevalence of PALB2 mutations in a Dutch cohort of non-BRCA1/2 familial PC (FPC) families and in non-BRCA1/2 familial BC (FBC) families with at least one PC case. Mutation analysis included direct sequencing and multiplex ligation-dependent probe amplification (MLPA) and was performed in a total of 64 patients from 56 distinct families (28 FPC families, 28 FBC families). In total, 31 patients (48%) originated from FPC families; 24 were FPC patients (77%), 6 had a personal history of BC (19%) and 1 was a suspected carrier (3.2%). The remaining 33 patients (52%) were all female BC patients of whom 31 (94%) had a family history of PC and 2 (6.1%) had a personal history of PC. In none of these 64 patients a PALB2 mutation was found. Therefore, PALB2 does not have a major causal role in familial clustering of PC and BC in non-BRCA1/2 families in the Dutch population.

CHEK2*1100delC homozygosity is associated with a high breast cancer risk in women.

BACKGROUND: Mutations in the CHEK2 gene confer a moderately increased breast cancer risk. The risk for female carriers of the CHEK2*1100delC mutation is twofold increased. Breast cancer risk for carrier women is higher in a familial breast cancer setting which is due to coinheritance of additional genetic risk factors. This study investigated the occurrence of homozygosity for the CHEK2*1100delC allele among familial breast cancer cases and the associated breast cancer risk. METHODS AND RESULTS: Homozygosity for the CHEK2*1100delC allele was identified in 8/2554 Dutch independent familial non-BRCA1/2 breast cancer cases. The genotype relative risk for breast cancer of homozygous and heterozygous familial breast cancer cases was 101.34 (95% CI 4.47 to 121 000) and 4.04 (95% CI 0.88 to 21.0), respectively. Female homozygotes appeared to have a greater than twofold increased breast cancer risk compared to familial CHEK2*1100delC heterozygotes (p=0.044). These results and the occurrence of multiple primary tumours in 7/10 homozygotes indicate a high cancer risk in homozygous women from non-BRCA1/2 families. CONCLUSIONS: Intensive breast surveillance is therefore justified in these homozygous women. It is concluded that diagnostic testing for biallelic mutations in CHEK2 is indicated in non-BRCA1/2 breast cancer families, especially in populations with a relatively high prevalence of deleterious mutations in CHEK2.

Fanconi anemia gene mutations are not involved in sporadic Wilms tumor.

Bi-allelic germline mutations of the Fanconi anemia (FA) genes, PALB2/FANCN and BRCA2/FANCD1, have been reported in a few Wilms tumor (WT) patients with an atypical FA phenotype. Therefore, we screened a random cohort of 47 Dutch WT cases for germline mutations in these two FA-genes by DNA sequencing and Multiplex Ligation-dependent Probe Amplification (MLPA). Although several cases appeared to carry missense variants, no bi-allelic pathogenic mutations were identified, indicating that bi-allelic mutations in these FA-genes do not contribute significantly to the occurrence of WT.