Bone Marrow Failure and Immunodeficiency Associated with Human RAD50 Variants.

PURPOSE: The MRE11-RAD50-NBN (MRN) complex plays a key role in recognizing and signaling DNA double-strand breaks. Pathogenic variants in NBN and MRE11 give rise to the autosomal-recessive diseases, Nijmegen breakage syndrome (NBS) and ataxia telangiectasia-like disorder, respectively. The clinical consequences of pathogenic variants in RAD50 are incompletely understood. We aimed to characterize a newly identified RAD50 deficiency/NBS-like disorder (NBSLD) patient with bone marrow failure and immunodeficiency. METHODS: We report on a girl with microcephaly, mental retardation, bird-like face, short stature, bone marrow failure and B-cell immunodeficiency. We searched for candidate gene by whole-exome sequencing and analyzed the cellular phenotype of patient-derived fibroblasts using immunoblotting, radiation sensitivity assays and lentiviral complementation experiments. RESULTS: Compound heterozygosity for two variants in the RAD50 gene (p.Arg83His and p.Glu485Ter) was identified in this patient. The expression of RAD50 protein and MRN complex formation was maintained in the cells derived from this patient. DNA damage-induced activation of the ATM kinase was markedly decreased, which was restored by the expression of wild-type (WT) RAD50. Radiosensitivity appeared inconspicuous in the patient-derived cell line as assessed by colony formation assay. The RAD50R83H missense substitution did not rescue the mitotic defect in complementation experiments using RAD50-deficient fibroblasts, whereas RAD50WT did. The RAD50E485X nonsense variant was associated with in-frame skipping of exon 10 (p.Glu485_545del). CONCLUSION: These findings indicate important roles of RAD50 in human bone marrow and immune cells. RAD50 deficiency/NBSLD can manifest as a distinct inborn error of immunity characterized by bone marrow failure and B-cell immunodeficiency.

Genome-wide association study and functional follow-up identify 14q12 as a candidate risk locus for cervical cancer.

Cervical cancer is among the leading causes of cancer-related death in females worldwide. Infection by human papillomavirus (HPV) is an established risk factor for cancer development. However, genetic factors contributing to disease risk remain largely unknown. We report on a genome-wide association study (GWAS) on 375 German cervical cancer patients and 866 healthy controls, followed by a replication study comprising 658 patients with invasive cervical cancer, 1361 with cervical dysplasia and 841 healthy controls. Functional validation was performed for the top GWAS variant on chromosome 14q12 (rs225902, close to PRKD1). After bioinformatic annotation and in silico predictions, we performed transcript analysis in a cervical tissue series of 317 samples and demonstrate rs225902 as an expression quantitative trait locus (eQTL) for FOXG1 and two tightly co-regulated long non-coding RNAs at this genomic region, CTD-2251F13 (lnc-PRKD1-1) and CTD-2503I6 (lnc-FOXG1-6). We also show allele-specific effects of the 14q12 variants via luciferase assays. We propose a combined effect of genotype, HPV status and gene expression at this locus on cervical cancer progression. Taken together, this work uncovers a potential candidate locus with regulatory functions and contributes to the understanding of genetic susceptibility to cervical cancer.

3D culture conditions support Kaposi's sarcoma herpesvirus (KSHV) maintenance and viral spread in endothelial cells.

Kaposi's sarcoma-associated herpesvirus (KSHV) is a human tumorigenic virus and the etiological agent of an endothelial tumor (Kaposi's sarcoma) and two B cell proliferative diseases (primary effusion lymphoma and multicentric Castleman's disease). While in patients with late stage of Kaposi's sarcoma the majority of spindle cells are KSHV-infected, viral copies are rapidly lost in vitro, both upon culture of tumor-derived cells or from newly infected endothelial cells. We addressed this discrepancy by investigating a KSHV-infected endothelial cell line in various culture conditions and in tumors of xenografted mice. We show that, in contrast to two-dimensional endothelial cell cultures, KSHV genomes are maintained under 3D cell culture conditions and in vivo. Additionally, an increased rate of newly infected cells was detected in 3D cell culture. Furthermore, we show that the PI3K/Akt/mTOR and ATM/γH2AX pathways are modulated and support an improved KSHV persistence in 3D cell culture. These mechanisms may contribute to the persistence of KSHV in tumor tissue in vivo and provide a novel target for KS specific therapeutic interventions. KEY MESSAGES: In vivo maintenance of episomal KSHV can be mimicked in 3D spheroid cultures 3D maintenance of KSHV is associated with an increased de novo infection frequency PI3K/Akt/mTOR and ATM/ γH2AX pathways contribute to viral maintenance.

Association of genomic variants at the human leukocyte antigen locus with cervical cancer risk, HPV status and gene expression levels.

The human leukocyte antigen (HLA) locus on chromosome 6 has been reported to be associated with cervical cancer. We investigated two independent single-nucleotide polymorphisms in a large case-control series of cervical dysplasia and carcinoma that has been newly established by the German Cervigen Consortium, comprising a total of 2481 cases and 1556 healthy females. We find significant associations for both variants, rs9272117 at HLA-DQA1 and rs2844511 at MICA and HCP5, with cervical disease. Both variants showed evidence of association with invasive cervical cancer (rs9272117: OR 0.89, 95% CI 0.79-0.99, P = .036; rs2844511: OR 1.17, 95% CI 1.04-1.31, P = .008) and with high-grade dysplasia (rs9272117: OR 0.78, 95% CI 0.70-0.87, P = 7.1 × 10-6 ; rs2844511: OR 1.13, 95% CI 1.01-1.26, P = .035), as well as in a combined analysis of both groups (rs9272117: OR 0.83, 95% CI 0.75-0.91, P = 6.9 × 10-5 ; rs2844511: OR 1.14, 95% CI 1.04-1.26, P = .005). Variant rs2844511, but not rs9272117, also showed modest evidence of association with low-grade dysplasia (OR 1.26, 95% CI 1.04-1.54, P = .019). In case-only analyses, rs2844511 tended to predict HPV status (P = .044) and rs9272117 tended to associate with HPV16 (P = .022). RNA studies in cervical samples showed a significant correlation in the transcript levels of MICA, HCP5 and HLA-DQA1, suggesting extensive co-regulation. All three genes were upregulated in HPV16-positive samples. In stratified analyses, rs9272117 was associated with HLA-DQA1 levels, specifically in HPV-positive samples, while rs2844511 was associated with MICA and HCP5 levels. The risk allele of rs2844511 was required for correlations between MICA or HCP5 with HLA-DQA1. Altogether, our results support 6p21.32-33 as the first consistent cervical cancer susceptibility locus and provide evidence for a link between genetic risk variants, HPV16 status and transcript levels of HLA-DQA1, HCP5 and MICA, which may contribute to tumor immune evasion.

Human RAD50 deficiency: Confirmation of a distinctive phenotype.

DNA double-strand breaks (DSBs) are highly toxic DNA lesions that can lead to chromosomal instability, loss of genes and cancer. The MRE11/RAD50/NBN (MRN) complex is keystone involved in signaling processes inducing the repair of DSB by, for example, in activating pathways leading to homologous recombination repair and nonhomologous end joining. Additionally, the MRN complex also plays an important role in the maintenance of telomeres and can act as a stabilizer at replication forks. Mutations in NBN and MRE11 are associated with Nijmegen breakage syndrome (NBS) and ataxia telangiectasia (AT)-like disorder, respectively. So far, only one single patient with biallelic loss of function variants in RAD50 has been reported presenting with features classified as NBS-like disorder. Here, we report a long-term follow-up of an unrelated patient with facial dysmorphisms, microcephaly, skeletal features, and short stature who is homozygous for a novel variant in RAD50. We could show that this variant, c.2524G > A in exon 15 of the RAD50 gene, induces aberrant splicing of RAD50 mRNA mainly leading to premature protein truncation and thereby, most likely, to loss of RAD50 function. Using patient-derived primary fibroblasts, we could show abnormal radioresistant DNA synthesis confirming pathogenicity of the identified variant. Immunoblotting experiments showed strongly reduced protein levels of RAD50 in the patient-derived fibroblasts and provided evidence for a markedly reduced radiation-induced AT-mutated signaling. Comparison with the previously reported case and with patients presenting with NBS confirms that RAD50 mutations lead to a similar, but distinctive phenotype.

RAD50 regulates mitotic progression independent of DNA repair functions.

The Mre11A/RAD50/NBN complex (MRN) is an essential regulator of the cellular damage response after DNA double-strand breaks (DSBs). More recent work has indicated that MRN may also impact on the duration of mitosis. We show here that RAD50-deficient fibroblasts exhibit a marked delay in mitotic progression that can be rescued by lentiviral transduction of RAD50. The delay was observed throughout all mitotic phases in live cell imaging using GFP-labeled H2B as a fluorescent marker. In complementation assays with RAD50 phosphorylation mutants, modifications at Ser635 had little effect on mitotic progression. By contrast with RAD50, fibroblast strains deficient in ATM or NBN did not show a significant slowing of mitotic progression. Ataxia-telangiectasia-like disorder (ATLD) fibroblasts with nuclease-deficient MRE11A (p.W210C) tended to show slower mitosis, though by far not as significant as RAD50-deficient cells. Inhibitor studies indicated that ATM kinase activity might not grossly impact on mitotic progression, while treatment with MRE11A inhibitor PFM39 modestly prolonged mitosis. Inhibition of ATR kinase significantly prolonged mitosis but this effect was mostly independent of RAD50 status. Taken together, our data unravel a mitotic role of RAD50 that can be separated from its known functions in DNA repair.

The EBV nuclear antigen 1 (EBNA1) enhances B cell immortalization several thousandfold.

The Epstein-Barr virus (EBV) nuclear antigen 1 (EBNA1) is one of the earliest viral proteins expressed after infection and is the only latent protein consistently expressed in viral-associated tumors. EBNA1's crucial role in viral DNA replication, episomal maintenance, and partitioning is well examined whereas its importance for the immortalization process and the tumorgenicity of EBV is unclear. To address these open questions, we generated, based on the maxi-EBV system, an EBNA1-deficient EBV mutant and used this strain to infect primary human B cells. Surprisingly, lymphoblastoid cell lines (LCL) emerged from these experiments, although with very low frequency. These cell lines were indistinguishable from normal LCLs with respect to proliferation and growth conditions. A detailed analysis indicated that the entire viral DNA was integrated into the cellular genome. At least 5 of the 11 latent EBV proteins were expressed, indicating the integrity of the EBV genome. EBNA1-positive and DeltaEBNA1-EBV-LCLs were injected into severe combined immunodeficient (SCID) mice to examine their tumorgenicity in comparison. Both groups supported tumor growth, indicating that EBNA1 is not mandatory for EBV's oncogenic potential. The results shown provide genetic evidence that EBNA1 is not essential to establish LCLs but promotes the efficiency of this process significantly.