ATMIN is required for maintenance of genomic stability and suppression of B cell lymphoma

ATMIN enhances invasion by altering PARP1 in MSS colorectal cancer

Genomic instability is a key cancer indicator. It results from defects in the DNA damage response (DDR) and increased replication stress. Herein, we examined how ataxia-telangiectasia mutated interactor (ATMIN), a DDR pathway involved in mismatch repair-proficient (microsatellite stability [MSS]), acts in colorectal carcinoma (CRC). Firstly, ATMIN mRNA expression was detected in CRC specimens with MSS characteristics, and the effects of ectopic ATMIN expression and ATMIN knockdown on invasion abilities were gauged in MSS cell lines. To understand the molecular mechanism, co-immunoprecipitation analyses in vitro were employed. Interestingly, ATMIN expression was positively correlated with advanced stages (P < .001), lymph node metastases (P = .002), and deeper invasion (P = .037) in MSS tumors; and significantly changed the cell motility in vitro. In the high-throughput analysis, ATMIN was found to act on the Wnt signaling pathway via PARP1. PAPR1 inhibition, in turn, significantly decreased invasion abilities resulting from ATMIN overexpression in cancer cell. Taken together, ATMIN, which alters the Wnt signaling pathway regulating CRC progression, plays as a crucial prognostic factor in MSS tumors.

Comprehensive Analysis of a Zinc Finger Protein Gene–Based Signature with Regard to Prognosis and Tumor Immune Microenvironment in Osteosarcoma

Osteosarcoma is the most common malignant bone tumor that seriously threatens the lives of teenagers and children. Zinc finger (ZNF) protein genes encode the largest transcription factor family in the human genome. Aberrant expressions of ZNF protein genes widely occur in osteosarcoma, and these genes are therefore attractive biomarker candidates for prognosis prediction. In this study, we conducted a comprehensive analysis of ZNF protein genes in osteosarcoma and identified prognosis-related ZNF protein genes. Then, we constructed a prognostic signature based on seven prognosis-related ZNF protein genes and stratified patients into high- and low-risk groups. The seven genes included MKRN3, ZNF71, ZNF438, ZNF597, ATMIN, ZNF692, and ZNF525. After validation of the prognostic signature in internal and external cohorts, we constructed a nomogram including clinical features such as sex and age and the relative risk score based on the risk signature. Functional enrichment analysis of the risk-related differentially expressed genes revealed that the prognostic signature was closely associated with immune-related biological processes and signaling pathways. Moreover, we found significant differences between the high- and low-risk groups for the scores of diverse immune cell subpopulations, including CD8+ T cells, neutrophils, Th1 cells, and TILs. Regarding immune function, APC co-inhibition, HLA, inflammation promotion, para-inflammation, T-cell co-inhibition, and the type I IFN response were significantly different between the high- and low-risk groups. Of the seven ZNF protein genes, lower expressions of ATMIN, MKRN3, ZNF71, ZNF438, and ZNF597 were correlated with a high risk, while higher expressions of ZNF525 and ZNF692 were associated with a high risk. The Kaplan–Meier survival analysis suggested that lower expressions of ATMIN, ZNF438, and ZNF597 and the higher expression of ZNF692 were associated with worse overall survival in osteosarcoma. In conclusion, our ZNF protein gene–based signature was a novel and clinically useful prognostic biomarker for osteosarcoma patients.

ATMIN Suppresses Metastasis by Altering the WNT-Signaling Pathway via PARP1 in MSI-High Colorectal Cancer

BACKGROUND

Constant DNA damage occurs in cells, and the cells are programmed to respond constitutively. This study explored the roles of ataxia-telangiectasia mutated interactor (ATMIN), one of the impaired pathways involving the DNA damage response (DDR) in mismatch repair-deficient [microsatellite instability (MSI)-high] colorectal carcinoma (CRC).

METHODS

Expression of ATMIN messenger RNA (mRNA) was detected in CRC specimens with microsatellite instability (MSI) characteristics. The effects of ectopic ATMIN expression and ATMIN knockdown on invasion abilities were evaluated in MSI-high cell lines, and liver metastasis ability was investigated in vivo. Protein-protein interactions were assessed by coimmunoprecipitation analyses in vitro.

RESULTS

Decreased ATMIN expression was positively correlated with advanced stage of disease (P < 0.05), lymph node metastases (P < 0.05), and deeper invasion (P < 0.05) in MSI-high tumors. Transient or stable ATMIN knockdown significantly increased cell motility. Moreover, in the high-throughput microarray and gene set enrichment analysis, ATMIN was shown to act on the Wnt-signaling pathway via PARP1. This cascade influences β-catenin/transcription factor 4 (TCF4) binding affinity in MSI-high tumors, and PARP1 inhibition significantly decreased the number of metastases from ATMIN knockdown cancer cells.

CONCLUSIONS

The results not only indicated the critical role of ATMIN, but also shed new light on PARP1 inhibitors, providing a basis for further clinical trials of MSI-high CRC.

ATM: Main Features, Signaling Pathways, and Its Diverse Roles in DNA Damage Response, Tumor Suppression, and Cancer Development

ATM is among of the most critical initiators and coordinators of the DNA-damage response. ATM canonical and non-canonical signaling pathways involve hundreds of downstream targets that control many important cellular processes such as DNA damage repair, apoptosis, cell cycle arrest, metabolism, proliferation, oxidative sensing, among others. Of note, ATM is often considered a major tumor suppressor because of its ability to induce apoptosis and cell cycle arrest. However, in some advanced stage tumor cells, ATM signaling is increased and confers remarkable advantages for cancer cell survival, resistance to radiation and chemotherapy, biosynthesis, proliferation, and metastasis. This review focuses on addressing major characteristics, signaling pathways and especially the diverse roles of ATM in cellular homeostasis and cancer development.

Deletion of PIN4 Suppresses the Protein Transport Defects Caused by sec12-4 Mutation in Saccharomyces cerevisiae

Newly synthesized secretory proteins are released into the lumen of the endoplasmic reticulum (ER). The secretory proteins are surrounded by coat protein complex II (COPII) vesicles, and transported from the ER and reach their destinations through the Golgi apparatus. Sec12p is a guanine nucleotide exchange factor for Sar1p, which initiates COPII vesicle budding from the ER. The activation of Sar1p by Sec12p and the subsequent COPII coat assembly have been well characterized, but the events that take place upstream of Sec12p remain unclear. In this study, we isolated the novel extragenic suppressor of sec12-4, PIN4/MDT1, a cell cycle checkpoint target. A yeast two-hybrid screening was used to identify Pin4/Mdt1p as a binding partner of the casein kinase I isoform Hrr25p, which we have previously identified as a modulator of Sec12p function. Deletion of PIN4 suppressed both defects of temperature-sensitive growth and the partial protein transport observed in sec12-4 mutants. The results of this study suggest that Pin4p provides novel aspects of Sec12p modulations.

ATMIN Is a Tumor Suppressor Gene in Lung Adenocarcinoma

Tumor cells proliferate rapidly and thus are frequently subjected to replication stress and the risk of incomplete duplication of the genome. Fragile sites are replicated late, making them more vulnerable to damage when DNA replication fails to complete. Therefore, genomic alterations at fragile sites are commonly observed in tumors. FRA16D is one of the most common fragile sites in lung cancer, however, the nature of the tumor suppressor genes affected by FRA16D alterations has been controversial. Here, we show that the ATMIN gene, which encodes a cofactor required for activation of ATM kinase by replication stress, is located close to FRA16D and is commonly lost in lung adenocarcinoma. Low ATMIN expression was frequently observed in human lung adenocarcinoma tumors and was associated with reduced patient survival, suggesting that ATMIN functions as a tumor suppressor in lung adenocarcinoma. Heterozygous Atmin deletion significantly increased tumor cell proliferation, tumor burden, and tumor grade in the LSL-KRasG12D; Trp53 F/F (KP) mouse model of lung adenocarcinoma, identifying ATMIN as a haploinsufficient tumor suppressor. ATMIN-deficient KP lung tumor cells showed increased survival in response to replication stress and consequently accumulated DNA damage. Thus, our data identify ATMIN as a key gene affected by genomic deletions at FRA16D in lung adenocarcinoma. SIGNIFICANCE: These findings identify ATMIN as a tumor suppressor in LUAD; fragility at chr16q23 correlates with loss of ATMIN in human LUAD and deletion of Atmin increases tumor burden in a LUAD mouse model.

The ASCIZ-DYNLL1 axis promotes 53BP1-dependent non-homologous end joining and PARP inhibitor sensitivity

53BP1 controls a specialized non-homologous end joining (NHEJ) pathway that is essential for adaptive immunity, yet oncogenic in BRCA1 mutant cancers. Intra-chromosomal DNA double-strand break (DSB) joining events during immunoglobulin class switch recombination (CSR) require 53BP1. However, in BRCA1 mutant cells, 53BP1 blocks homologous recombination (HR) and promotes toxic NHEJ, resulting in genomic instability. Here, we identify the protein dimerization hub-DYNLL1-as an organizer of multimeric 53BP1 complexes. DYNLL1 binding stimulates 53BP1 oligomerization, and promotes 53BP1's recruitment to, and interaction with, DSB-associated chromatin. Consequently, DYNLL1 regulates 53BP1-dependent NHEJ: CSR is compromised upon deletion of Dynll1 or its transcriptional regulator Asciz, or by mutation of DYNLL1 binding motifs in 53BP1; furthermore, Brca1 mutant cells and tumours are rendered resistant to poly-ADP ribose polymerase (PARP) inhibitor treatments upon deletion of Dynll1 or Asciz. Thus, our results reveal a mechanism that regulates 53BP1-dependent NHEJ and the therapeutic response of BRCA1-deficient cancers.

Combined Genetic and Chromosomal Characterization of Wilms Tumors Identifies Chromosome 12 Gain as a Potential New Marker Predicting a Favorable Outcome

To identify prognostic factors, array CGH (aCGH) patterns and mutations in WT1 and 9 other genes were analyzed in 128 unilateral Wilms tumors (WTs). Twenty patients had no aCGH aberrations, and 31 had WT1 alterations [silent and WT1 types: relapse-free survival (RFS), 95% and 83%, respectively]. Seventy-seven patients had aCGH changes without WT1 alterations (nonsilent/non-WT1 type) and were subtyped into those with or without +12, 11q-, 16q-, or HACE1 loss. RFS was better for those with than those without +12 (P = .010) and worse for those with than those without 11q-, 16q-, or HACE1 loss (P = .001, .025, or 1.2E-04, respectively). Silent and WT1 type and 8 subtype tumors were integrated and classified into 3 risk groups: low risk for the silent type and +12 subgroup; high risk for the no +12 plus 11q-, 16q-, or HACE1 loss subgroup; intermediate risk for the WT1 type and no +12 plus no 11q-, 16q-, or HACE1 loss subgroup. Among the 27 WTs examined, the expression of 146 genes on chromosome 12 was stronger in +12 tumors than in no +12 tumors, while that of 10 genes on 16q was weaker in 16q- tumors than in no 16q- tumors. Overexpression in 75 out of 146 upregulated genes and underexpression in 7 out of 10 downregulated genes correlated with better and worse overall survival, respectively, based on the public database. +12 was identified as a potential new marker predicting a favorable outcome, and chromosome abnormalities may be related to altered gene expression associated with these abnormalities.

Dynein light chain regulates adaptive and innate B cell development by distinctive genetic mechanisms

Mechanistic differences in the development and function of adaptive, high-affinity antibody-producing B-2 cells and innate-like, “natural” antibody-producing B-1a cells remain poorly understood. Here we show that the multi-functional dynein light chain (DYNLL1/LC8) plays important roles in the establishment of B-1a cells in the peritoneal cavity and in the ongoing development of B-2 lymphoid cells in the bone marrow of mice. Epistasis analyses indicate that Dynll1 regulates B-1a and early B-2 cell development in a single, linear pathway with its direct transcriptional activator ASCIZ (ATMIN/ZNF822), and that the two genes also have complementary functions during late B-2 cell development. The B-2 cell defects caused by loss of DYNLL1 were associated with lower levels of the anti-apoptotic protein BCL-2, and could be supressed by deletion of pro-apoptotic BIM which is negatively regulated by both DYNLL1 and BCL-2. Defects in B cell development caused by loss of DYNLL1 could also be partially suppressed by a pre-arranged SW_HELIgm-B cell receptor transgene. In contrast to the rescue of B-2 cell numbers, the B-1a cell deficiency in Dynll1-deleted mice could not be suppressed by the loss of Bim, and was further compounded by the SW_HEL transgene. Conversely, oncogenic MYC expression, which is synthetic lethal with Dynll1 deletion in B-2 cells, did not further reduce B-1a cell numbers in Dynll1-defcient mice. Finally, we found that the ASCIZ-DYNLL1 axis was also required for the early-juvenile development of aggressive MYC-driven and p53-deficient B cell lymphomas. These results identify ASCIZ and DYNLL1 as the core of a transcriptional circuit that differentially regulates the development of the B-1a and B-2 B lymphoid cell lineages and plays a critical role in lymphomagenesis.

Antibody-producing B cells can be segregated into two major populations: The better known conventional B-2 cells typically produce high-affinity and mono-specific antibodies, but only after they encounter a particular pathogen or in response to vaccines. In contrast, the B-1a cells constitutively produce lower-affinity broad-specificity “natural” antibodies that serve as a preemptive defense against a wide range of microbes. Here we reveal that the transcription factor ASCIZ and its target DYNLL1 are essential for mice to have a normally sized pool of B-1a cells in place shortly after birth. We show that these two factors function in a single linear pathway during the development of B-1a cells. This interaction represents a rare example where the activity of a transcription factor, in this case ASCIZ, can be explained by the effects of a single target gene, in this case Dynll1. While ASCIZ and DYNLL1 are also required for producing normal numbers of B-2 cells, we discovered that they regulate B-1a cells and B-2 cells by distinct genetic mechanisms. Finally, we found that ASCIZ also contributes to the early onset of B-1a B cell-derived lymphoid cancers in juvenile mice. The results provide insight into the development of an important cell population of the immune system.

ASCIZ/ATMIN is dispensable for ATM signaling in response to replication stress

•

ASCIZ/ATMIN is not required for ATM activation by replication stress in MEFs.

•

ATM activation is normal in human ASCIZ/ATMIN KO cells.

•

ASCIZ/ATMIN is dispensable for aphidicolin-induced 53BP1 focus formation.

The ATM kinase plays critical roles in the response to DNA double-strand breaks, and can also be activated by prolonged DNA replication blocks. It has recently been proposed that replication stress-dependent ATM activation is mediated by ASCIZ (also known as ATMIN, ZNF822), an essential developmental transcription factor. In contrast, we show here that ATM activation, and phosphorylation of its substrates KAP1, p53 and H2AX in response to the replication blocking agent aphidicolin was unaffected in both immortalized and primary ASCIZ/ATMIN-deficient murine embryonic fibroblasts compared to control cells. Similar results were also obtained in human ASCIZ/ATMIN-deleted lymphoma cells. The results demonstrate that ASCIZ/ATMIN is dispensable for ATM activation, and contradict the previously reported dependence of ATM on ASCIZ/ATMIN.

Ataxia-telangiectasia mutated interactor regulates head and neck cancer metastasis via KRas expression

OBJECTIVES

Relapse is the most serious problem affecting the morbidity and mortality rates of patients with head and neck squamous cell carcinoma (HNSCC). Although HNSCC has been studied for several decades, the exact mechanism of cancer recurrence remains unclear.

MATERIALS AND METHODS

ataxia-telangiectasia mutated interactor (ATMIN) messenger RNA(mRNA) expression was detected in HNSCC samples by quantitative RT-PCR, and was analyzed with patients' clinical outcomes by Kaplan-Meier analyses. The ectopic ATMIN expression or ATMIN silencing on invasion ability was evaluated in HNSCC cell lines. Lymph node metastasis ability was investigated by buccal orthotopic implantation in vivo. All statistical tests were two-sided.

RESULTS

ATMIN mRNA expression was positively correlated with patients' clinical outcomes. ATMIN blockage reduced invasion, migration, and metastasis abilities both in vitro and in vivo. Evidence from a buccal orthotopic implantation mice model showed that silenced ATMIN expression prolongs mice survival and reduced lymph node metastasis. In high-throughput microarray and bioinformative analyses, KRas was identified as a crucial downstream effector in ATMIN-mediated HNSCC metastasis and was positively associated with patients' clinical stages and ATMIN mRNA expression.

CONCLUSIONS

The role of ATMIN and its regulatory mechanisms in HNSCC progression are reported for the first time. The study results improve our understanding of the ATMIN-KRas axis leading to HNSCC migration or invasion and metastasis and facilitates the identification of possible therapy targets of downstream genes for designing effective therapeutic strategies in personalized medicine.

Perturbed hematopoiesis in mice lacking ATMIN

The ataxia telangiectasia mutated (ATM)-interacting protein ATMIN mediates noncanonical ATM signaling in response to oxidative and replicative stress conditions. Like ATM, ATMIN can function as a tumor suppressor in the hematopoietic system: deletion of Atmin under the control of CD19-Cre results in B-cell lymphomas in aging mice. ATM signaling is essential for lymphopoiesis and hematopoietic stem cell (HSC) function; however, little is known about the role of ATMIN in hematopoiesis. We thus sought to investigate whether the absence of ATMIN would affect primitive hematopoietic cells in an ATM-dependent or -independent manner. Apart from its role in B-cell development, we show that ATMIN has an ATM-independent function in the common myeloid progenitors (CMPs) by deletion of Atmin in the entire hematopoietic system using Vav-Cre. Despite the lack of lymphoma formation, ATMIN-deficient mice developed chronic leukopenia as a result of high levels of apoptosis in B cells and CMPs and induced a compensatory mechanism in which HSCs displayed enhanced cycling. Consequently, ATMIN-deficient HSCs showed impaired regeneration ability with the induction of the DNA oxidative stress response, especially when aged. ATMIN, therefore, has multiple roles in different cell types, and its absence results in perturbed hematopoiesis, especially during stress conditions and aging.

RAD18, WRNIP1 and ATMIN promote ATM signalling in response to replication stress

The DNA replication machinery invariably encounters obstacles that slow replication fork progression, and threaten to prevent complete replication and faithful segregation of sister chromatids. The resulting replication stress activates ATR, the major kinase involved in resolving impaired DNA replication. In addition, replication stress also activates the related kinase ATM, which is required to prevent mitotic segregation errors. However, the molecular mechanism of ATM activation by replication stress is not defined. Here, we show that monoubiquitinated Proliferating Cell Nuclear Antigen (PCNA), a marker of stalled replication forks, interacts with the ATM cofactor ATMIN via WRN-interacting protein 1 (WRNIP1). ATMIN, WRNIP1 and RAD18, the E3 ligase responsible for PCNA monoubiquitination, are specifically required for ATM signalling and 53BP1 focus formation induced by replication stress, not ionising radiation. Thus, WRNIP1 connects PCNA monoubiquitination with ATMIN/ATM to activate ATM signalling in response to replication stress and contribute to the maintenance of genomic stability.

A Comprehensive Analysis of the Dynamic Response to Aphidicolin-Mediated Replication Stress Uncovers Targets for ATM and ATMIN

The cellular response to replication stress requires the DNA-damage-responsive kinase ATM and its cofactor ATMIN; however, the roles of this signaling pathway following replication stress are unclear. To identify the functions of ATM and ATMIN in response to replication stress, we utilized both transcriptomics and quantitative mass-spectrometry-based phosphoproteomics. We found that replication stress induced by aphidicolin triggered widespread changes in both gene expression and protein phosphorylation patterns. These changes gave rise to distinct early and late replication stress responses. Furthermore, our analysis revealed previously unknown targets of ATM and ATMIN downstream of replication stress. We demonstrate ATMIN-dependent phosphorylation of H2AX and of CRMP2, a protein previously implicated in Alzheimer's disease but not in the DNA damage response. Overall, our dataset provides a comprehensive resource for discovering the cellular responses to replication stress and, potentially, associated pathologies.

Inactivation of the ATMIN/ATM pathway protects against glioblastoma formation

Glioblastoma multiforme (GBM) is the most aggressive human primary brain cancer. Using a Trp53-deficient mouse model of GBM, we show that genetic inactivation of the Atm cofactor Atmin, which is dispensable for embryonic and adult neural development, strongly suppresses GBM formation. Mechanistically, expression of several GBM-associated genes, including Pdgfra, was normalized by Atmin deletion in the Trp53-null background. Pharmacological ATM inhibition also reduced Pdgfra expression, and reduced the proliferation of Trp53-deficient primary glioma cells from murine and human tumors, while normal neural stem cells were unaffected. Analysis of GBM datasets showed that PDGFRA expression is also significantly increased in human TP53-mutant compared with TP53-wild-type tumors. Moreover, combined treatment with ATM and PDGFRA inhibitors efficiently killed TP53-mutant primary human GBM cells, but not untransformed neural stem cells. These results reveal a new requirement for ATMIN-dependent ATM signaling in TP53-deficient GBM, indicating a pro-tumorigenic role for ATM in the context of these tumors.

Mechanisms and consequences of ATMIN repression in hypoxic conditions: roles for p53 and HIF-1

Hypoxia-induced replication stress is one of the most physiologically relevant signals known to activate ATM in tumors. Recently, the ATM interactor (ATMIN) was identified as critical for replication stress-induced activation of ATM in response to aphidicolin and hydroxyurea. This suggests an essential role for ATMIN in ATM regulation during hypoxia, which induces replication stress. However, ATMIN also has a role in base excision repair, a process that has been demonstrated to be repressed and less efficient in hypoxic conditions. Here, we demonstrate that ATMIN is dispensable for ATM activation in hypoxia and in contrast to ATM, does not affect cell survival and radiosensitivity in hypoxia. Instead, we show that in hypoxic conditions ATMIN expression is repressed. Repression of ATMIN in hypoxia is mediated by both p53 and HIF-1α in an oxygen dependent manner. The biological consequence of ATMIN repression in hypoxia is decreased expression of the target gene, DYNLL1. An expression signature associated with p53 activity was negatively correlated with DYNLL1 expression in patient samples further supporting the p53 dependent repression of DYNLL1. Together, these data demonstrate multiple mechanisms of ATMIN repression in hypoxia with consequences including impaired BER and down regulation of the ATMIN transcriptional target, DYNLL1.

DNA Repair Cofactors ATMIN and NBS1 Are Required to Suppress T Cell Activation

Proper development of the immune system is an intricate process dependent on many factors, including an intact DNA damage response. The DNA double-strand break signaling kinase ATM and its cofactor NBS1 are required during T cell development and for the maintenance of genomic stability. The role of a second ATM cofactor, ATMIN (also known as ASCIZ) in T cells is much less clear, and whether ATMIN and NBS1 function in synergy in T cells is unknown. Here, we investigate the roles of ATMIN and NBS1, either alone or in combination, using murine models. We show loss of NBS1 led to a developmental block at the double-positive stage of T cell development, as well as reduced TCRα recombination, that was unexpectedly neither exacerbated nor alleviated by concomitant loss of ATMIN. In contrast, loss of both ATMIN and NBS1 enhanced DNA damage that drove spontaneous peripheral T cell hyperactivation, proliferation as well as excessive production of proinflammatory cytokines and chemokines, leading to a highly inflammatory environment. Intriguingly, the disease causing T cells were largely proficient for both ATMIN and NBS1. In vivo this resulted in severe intestinal inflammation, colitis and premature death. Our findings reveal a novel model for an intestinal bowel disease phenotype that occurs upon combined loss of the DNA repair cofactors ATMIN and NBS1.

The Effect of MicroRNA-124 Overexpression on Anti-Tumor Drug Sensitivity

MicroRNAs play critical roles in regulating various physiological processes, including growth and development. Previous studies have shown that microRNA-124 (miR-124) participates not only in regulation of early neurogenesis but also in suppression of tumorigenesis. In the present study, we found that overexpression of miR-124 was associated with reduced DNA repair capacity in cultured cancer cells and increased sensitivity of cells to DNA-damaging anti-tumor drugs, specifically those that cause the formation of DNA strand-breaks (SBs). We then examined which DNA repair–related genes, particularly the genes of SB repair, were regulated by miR-124. Two SB repair–related genes, encoding ATM interactor (ATMIN) and poly (ADP-ribose) polymerase 1 (PARP1), were strongly affected by miR-124 overexpression, by binding of miR-124 to the 3¢-untranslated region of their mRNAs. As a result, the capacity of cells to repair DNA SBs, such as those resulting from homologous recombination, was significantly reduced upon miR-124 overexpression. A particularly important therapeutic implication of this finding is that overexpression of miR-124 enhanced cell sensitivity to multiple DNA-damaging agents via ATMIN- and PARP1-mediated mechanisms. The translational relevance of this role of miR-124 in anti-tumor drug sensitivity is suggested by the finding that increased miR-124 expression correlates with better breast cancer prognosis, specifically in patients receiving chemotherapy. These findings suggest that miR-124 could potentially be used as a therapeutic agent to improve the efficacy of chemotherapy with DNA-damaging agents.

ATMIN is a transcriptional regulator of both lung morphogenesis and ciliogenesis

Initially identified in DNA damage repair, ATM-interactor (ATMIN) further functions as a transcriptional regulator of lung morphogenesis. Here we analyse three mouse mutants, Atmin^gpg6/gpg6, Atmin^H210Q/H210Q and Dynll1^GT/GT, revealing how ATMIN and its transcriptional target dynein light chain LC8-type 1 (DYNLL1) are required for normal lung morphogenesis and ciliogenesis. Expression screening of ciliogenic genes confirmed Dynll1 to be controlled by ATMIN and further revealed moderately altered expression of known intraflagellar transport (IFT) protein-encoding loci in Atmin mutant embryos. Significantly, Dynll1^GT/GT embryonic cilia exhibited shortening and bulging, highly similar to the characterised retrograde IFT phenotype of Dync2h1. Depletion of ATMIN or DYNLL1 in cultured cells recapitulated the in vivo ciliogenesis phenotypes and expression of DYNLL1 or the related DYNLL2 rescued the effects of loss of ATMIN, demonstrating that ATMIN primarily promotes ciliogenesis by regulating Dynll1 expression. Furthermore, DYNLL1 as well as DYNLL2 localised to cilia in puncta, consistent with IFT particles, and physically interacted with WDR34, a mammalian homologue of the Chlamydomonas cytoplasmic dynein 2 intermediate chain that also localised to the cilium. This study extends the established Atmin-Dynll1 relationship into a developmental and a ciliary context, uncovering a novel series of interactions between DYNLL1, WDR34 and ATMIN. This identifies potential novel components of cytoplasmic dynein 2 and furthermore provides fresh insights into the molecular pathogenesis of human skeletal ciliopathies.

ATMIN is required for the ATM-mediated signaling and recruitment of 53BP1 to DNA damage sites upon replication stress

Unresolved replication intermediates can block the progression of replication forks and become converted into DNA lesions, hence exacerbating genomic instability. The p53-binding protein 1 (53BP1) forms nuclear bodies at sites of unrepaired DNA lesions to shield these regions against erosion, in a manner dependent on the DNA damage kinase ATM. The molecular mechanism by which ATM is activated upon replicative stress to localize the 53BP1 protection complex is unknown. Here we show that the ATM-INteracting protein ATMIN (also known as ASCIZ) is partially required for 53BP1 localization upon replicative stress. Additionally, we demonstrate that ATM activation is impaired in cells lacking ATMIN and we define that ATMIN is required for initiating ATM signaling following replicative stress. Furthermore, loss of ATMIN leads to chromosomal segregation defects. Together these data reveal that chromatin integrity depends on ATMIN upon exposure to replication-induced stress.

ATM activation in hypoxia - causes and consequences

The DNA damage response is a complex signaling cascade that is triggered by cellular stress. This response is essential for the maintenance of genomic integrity and is considered to act as a barrier to the early stages of tumorigenesis. The integral role of ataxia telangiectasia mutated (ATM) kinase in the response to DNA damaging agents is well characterized; however, ATM can also be activated by non-DNA damaging agents. In fact, much has been learnt recently about the mechanism of ATM activation in response to physiologic stresses such as hypoxia that do not induce DNA damage. Regions of low oxygen concentrations that occur in solid tumors are associated with a poor prognostic outcome irrespective of treatment modality. Severe levels of hypoxia induce replication stress and trigger the activation of DNA damage response pathways including ataxia telangiectasia and Rad3-related (ATR)- and ATM-mediated signaling. In this review, we discuss hypoxia-driven ATM signaling and the possible contribution of ATM activation in this context to tumorigenesis.

ATM signalling and cancer

ATM, the protein kinase mutated in the rare human disease ataxia telangiectasia (A-T), has been the focus of intense scrutiny over the past two decades. Initially this was because of the unusual radiosensitive phenotype of cells from A-T patients, and latterly because investigating ATM signalling has yielded valuable insights into the DNA damage response, redox signalling and cancer. With the recent explosion in genomic data, ATM alterations have been revealed both in the germline as a predisposing factor for cancer and as somatic changes in tumours themselves. Here we review these findings, as well as advances in the understanding of ATM signalling mechanisms in cancer and ATM inhibition as a strategy for cancer treatment.

Competition between NBS1 and ATMIN controls ATM signaling pathway choice

Ataxia telangiectasia mutated (ATM) protein kinase activation by DNA double-strand breaks (DSBs) requires the Mre11-Rad50-NBS1 (MRN) complex, whereas ATM interactor (ATMIN) protein is required for ATM signaling induced by changes in chromatin structure. We show here that NBS1 and ATMIN proteins compete for ATM binding and that this mechanism controls ATM function. DSB-induced ATM substrate phosphorylation was increased in atmin mutant cells. Conversely, NBS1 deficiency resulted in increased ATMIN-dependent ATM signaling. Thus, the absence of one cofactor increased flux through the alternative pathway. Notably, ATMIN deficiency rescued the cellular lethality of NBS1-deficient cells, and NBS1/ATMIN double deficiency resulted in complete abrogation of ATM signaling and profound radiosensitivity. Hence, ATMIN and NBS1 mediate all ATM signaling by DSBs, and increased ATMIN-dependent ATM signaling explains the different phenotypes of nbs1- and atm-mutant cells. Thus, the antagonism and redundancy of ATMIN and NBS1 constitute a crucial regulatory mechanism for ATM signaling and function.

Disruption of mouse Cenpj, a regulator of centriole biogenesis, phenocopies Seckel syndrome

Disruption of the centromere protein J gene, CENPJ (CPAP, MCPH6, SCKL4), which is a highly conserved and ubiquitiously expressed centrosomal protein, has been associated with primary microcephaly and the microcephalic primordial dwarfism disorder Seckel syndrome. The mechanism by which disruption of CENPJ causes the proportionate, primordial growth failure that is characteristic of Seckel syndrome is unknown. By generating a hypomorphic allele of Cenpj, we have developed a mouse (Cenpj(tm/tm)) that recapitulates many of the clinical features of Seckel syndrome, including intrauterine dwarfism, microcephaly with memory impairment, ossification defects, and ocular and skeletal abnormalities, thus providing clear confirmation that specific mutations of CENPJ can cause Seckel syndrome. Immunohistochemistry revealed increased levels of DNA damage and apoptosis throughout Cenpj(tm/tm) embryos and adult mice showed an elevated frequency of micronucleus induction, suggesting that Cenpj-deficiency results in genomic instability. Notably, however, genomic instability was not the result of defective ATR-dependent DNA damage signaling, as is the case for the majority of genes associated with Seckel syndrome. Instead, Cenpj(tm/tm) embryonic fibroblasts exhibited irregular centriole and centrosome numbers and mono- and multipolar spindles, and many were near-tetraploid with numerical and structural chromosomal abnormalities when compared to passage-matched wild-type cells. Increased cell death due to mitotic failure during embryonic development is likely to contribute to the proportionate dwarfism that is associated with CENPJ-Seckel syndrome.

The Zinc-finger protein ASCIZ regulates B cell development via DYNLL1 and Bim

Developing B lymphocytes expressing defective or autoreactive pre-B or B cell receptors (BCRs) are eliminated by programmed cell death, but how the balance between death and survival signals is regulated to prevent immunodeficiency and autoimmunity remains incompletely understood. In this study, we show that absence of the essential ATM (ataxia telangiectasia mutated) substrate Chk2-interacting Zn(2+)-finger protein (ASCIZ; also known as ATMIN/ZNF822), a protein with dual functions in the DNA damage response and as a transcription factor, leads to progressive cell loss from the pre-B stage onwards and severely diminished splenic B cell numbers in mice. This lymphopenia cannot be suppressed by deletion of p53 or complementation with a prearranged BCR, indicating that it is not caused by impaired DNA damage responses or defective V(D)J recombination. Instead, ASCIZ-deficient B cell precursors contain highly reduced levels of DYNLL1 (dynein light chain 1; LC8), a recently identified transcriptional target of ASCIZ, and normal B cell development can be restored by ectopic Dynll1 expression. Remarkably, the B cell lymphopenia in the absence of ASCIZ can also be fully suppressed by deletion of the proapoptotic DYNLL1 target Bim. Our findings demonstrate a key role for ASCIZ in regulating the survival of developing B cells by activating DYNLL1 expression, which may then modulate Bim-dependent apoptosis.

ATM substrate Chk2-interacting Zn2+ finger (ASCIZ) Is a bi-functional transcriptional activator and feedback sensor in the regulation of dynein light chain (DYNLL1) expression

The highly conserved DYNLL1 (LC8) protein was originally discovered as a light chain of the dynein motor complex, but is increasingly emerging as a sequence-specific regulator of protein dimerization with hundreds of targets and wide-ranging cellular functions. Despite its important roles, DYNLL1's own regulation remains poorly understood. Here we identify ASCIZ (ATMIN/ZNF822), an essential Zn(2+) finger protein with dual roles in the DNA base damage response and as a developmental transcription factor, as a conserved regulator of Dynll1 gene expression. DYNLL1 levels are reduced by ∼10-fold in the absence of ASCIZ in human, mouse and chicken cells. ASCIZ binds directly to the Dynll1 promoter and regulates its activity in a Zn(2+) finger-dependent manner. DYNLL1 protein in turn interacts with ten binding sites in the ASCIZ transcription activation domain, and high DYNLL1 levels inhibit the transcriptional activity of ASCIZ. In addition, DYNLL1 was also required for DNA damage-induced ASCIZ focus formation. The dual ability of ASCIZ to activate Dynll1 gene expression and to sense free DYNLL1 protein levels enables a simple dynamic feedback loop to adjust DYNLL1 levels to cellular needs. The ASCIZ-DYNLL1 feedback loop represents a novel mechanism for auto-regulation of gene expression, where the gene product directly inhibits the transcriptional activator while bound at its own promoter.

Perspectives on common variable immune deficiency

Common variable immunodeficiency (CVID) is considered to be a collection of genetic immune defects with complex inheritance patterns. While the main phenotype is loss of B cell function, the majority of the genetic mechanisms leading to CVID remain elusive. In the past two decades there have been increasing efforts to unravel the genetic defects in CVID. Here, we provide an overview of our current understanding of the genetic basis of these defects, as revealed over time by earlier linkage studies in large cohorts, analysis of families with recessive inheritance, targeted gene approaches, and genome-wide association studies using single nucleotide polymorphism arrays and copy number variation, and whole genome studies.