Cloning and characterization of a novel p21(Cip1/Waf1)-interacting zinc finger protein, ciz1

CIZ1 in Xist seeded assemblies at the inactive X chromosome

There is growing evidence that X-chromosome inactivation is driven by phase-separated supramolecular assemblies. However, among the many proteins recruited to the inactive X chromosome by Xist long non-coding RNA, so far only a minority (CIZ1, CELF1, SPEN, TDP-43, MATR3, PTBP1, PCGF5) have been shown to form Xist-seeded protein assemblies, and of these most have not been analyzed in detail. With focus on CIZ1, here we describe 1) the contribution of intrinsically disordered regions in RNA-dependent protein assembly formation at the inactive X chromosome, and 2) enrichment, distribution, and function of proteins within Xist-seeded assemblies.

Thirty Years with ERH: An mRNA Splicing and Mitosis Factor Only or Rather a Novel Genome Integrity Protector?

ERH is a 100 to about 110 aa nuclear protein with unique primary and three-dimensional structures that are very conserved from simple eukaryotes to humans, albeit some species have lost its gene, with most higher fungi being a noteworthy example. Initially, studies on Drosophila melanogaster implied its function in pyrimidine metabolism. Subsequently, research on Xenopus laevis suggested that it acts as a transcriptional repressor. Finally, studies in humans pointed to a role in pre-mRNA splicing and in mitosis but further research, also in Caenorhabditis elegans and Schizosaccharomyces pombe, demonstrated its much broader activity, namely involvement in the biogenesis of mRNA, and miRNA, piRNA and some other ncRNAs, and in repressive heterochromatin formation. ERH interacts with numerous, mostly taxon-specific proteins, like Mmi1 and Mei2 in S. pombe, PID-3/PICS-1, TOST-1 and PID-1 in C. elegans, and DGCR8, CIZ1, PDIP46/SKAR and SAFB1/2 in humans. There are, however, some common themes in this wide range of processes and partners, such as: (a) ERH homodimerizes to form a scaffold for several complexes involved in the metabolism of nucleic acids, (b) all these RNAs are RNA polymerase II transcripts, (c) pre-mRNAs, whose splicing depends on ERH, are enriched in transcripts of DNA damage response and DNA metabolism genes, and (d) heterochromatin is formed to silence unwanted transcription, e.g., from repetitive elements. Thus, it seems that ERH has been adopted for various pathways that serve to maintain genome integrity.

Epigenetic instability caused by absence of CIZ1 drives transformation during quiescence cycles

BACKGROUND

Cip1-interacting zinc finger protein 1 (CIZ1) forms RNA-dependent protein assemblies that stabilise epigenetic state, notable at the inactive X chromosome in females. CIZ1 has been linked with a range of human cancers and in mice genetic deletion of CIZ1 manifests as hyperproliferative lymphoid lineages in females. This suggests that its role in maintenance of epigenetic stability is linked with disease.

RESULTS

Here, we show that male and female CIZ1-null primary murine fibroblasts have reduced H4K20me1 and that this compromises nuclear condensation on entry to quiescence. Global transcriptional repression remains intact in condensation-deficient CIZ1-null cells; however, a subset of genes linked with chromatin condensation and homology-directed DNA repair are perturbed. Failure to condense is phenotypically mimicked by manipulation of the H4K20me1 methyltransferase, SET8, in WT cells and partially reverted in CIZ1-null cells upon re-expression of CIZ1. Crucially, during exit from quiescence, nuclear decondensation remains active, so that repeated entry and exit cycles give rise to expanded nuclei susceptible to mechanical stress, DNA damage checkpoint activation, and downstream emergence of transformed proliferative colonies.

CONCLUSIONS

Our results demonstrate a role for CIZ1 in chromatin condensation on entry to quiescence and explore the consequences of this defect in CIZ1-null cells. Together, the data show that CIZ1's protection of the epigenome guards against genome instability during quiescence cycles. This identifies loss of CIZ1 as a potentially devastating vulnerability in cells that undergo cycles of quiescence entry and exit.

Molecular basis for the recognition of CIZ1 by ERH

Enhancer of rudimentary homologue (ERH), a small protein conserved in eukaryotes, is involved in a wide spectrum of cellular events, including cell cycle progression, piRNA biogenesis, miRNA maturation and gene expression. Human ERH is recruited to replication foci by CDKN1A-interacting zinc finger protein 1 (CIZ1), and plays an important role in cell growth control. However, the molecular basis for CIZ1 recognition by ERH remains unknown. By using GST pull-down experiment, we found that a fragment within CIZ1, upstream of its first zinc finger, is sufficient for binding to ERH. We solved the structure of CIZ1-bound ERH, in which the ERH dimer binds to two CIZ1 fragments to form a 2 : 2 heterotetramer. CIZ1 forms intermolecular antiparallel β-strands with ERH, and its binding surface on ERH is distinct from those of other known ERH-binding ligands. The ERH-CIZ1 interface was further validated by mutagenesis and binding experiments. Our structural study complemented by biochemistry experiments not only provides insights into a previously unidentified ligand-binding mode for ERH but also sheds light on the understanding of evolutionarily conserved roles for ERH orthologs.

Zinc in Cognitive Impairment and Aging

Zinc, an essential micronutrient for life, was first discovered in 1869 and later found to be indispensable for the normal development of plants and for the normal growth of rats and birds. Zinc plays an important role in many physiological and pathological processes in normal mammalian brain development, especially in the development of the central nervous system. Zinc deficiency can lead to neurodegenerative diseases, mental abnormalities, sleep disorders, tumors, vascular diseases, and other pathological conditions, which can cause cognitive impairment and premature aging. This study aimed to review the important effects of zinc and zinc-associated proteins in cognitive impairment and aging, to reveal its molecular mechanism, and to highlight potential interventions for zinc-associated aging and cognitive impairments.

Application of Next Generation Sequencing (NGS) in Phage Displayed Peptide Selection to Support the Identification of Arsenic-Binding Motifs

Next generation sequencing (NGS) in combination with phage surface display (PSD) are powerful tools in the newly equipped molecular biology toolbox for the identification of specific target binding biomolecules. Application of PSD led to the discovery of manifold ligands in clinical and material research. However, limitations of traditional phage display hinder the identification process. Growth-based library biases and target-unrelated peptides often result in the dominance of parasitic sequences and the collapse of library diversity. This study describes the effective enrichment of specific peptide motifs potentially binding to arsenic as proof-of-concept using the combination of PSD and NGS. Arsenic is an environmental toxin, which is applied in various semiconductors as gallium arsenide and selective recovery of this element is crucial for recycling and remediation. The development of biomolecules as specific arsenic-binding sorbents is a new approach for its recovery. Usage of NGS for all biopanning fractions allowed for evaluation of motif enrichment, in-depth insight into the selection process and the discrimination of biopanning artefacts, e.g., the amplification-induced library-wide reduction in hydrophobic amino acid proportion. Application of bioinformatics tools led to the identification of an SxHS and a carboxy-terminal QxQ motif, which are potentially involved in the binding of arsenic. To the best of our knowledge, this is the first report of PSD combined with NGS of all relevant biopanning fractions.

Akt1 and dCIZ1 promote cell survival from apoptotic caspase activation during regeneration and oncogenic overgrowth

Apoptosis is an ancient and evolutionarily conserved cell suicide program. During apoptosis, executioner caspase enzyme activation has been considered a point of no return. However, emerging evidence suggests that some cells can survive caspase activation following exposure to apoptosis-inducing stresses, raising questions as to the physiological significance and underlying molecular mechanisms of this unexpected phenomenon. Here, we show that, following severe tissue injury, Drosophila wing disc cells that survive executioner caspase activation contribute to tissue regeneration. Through RNAi screening, we identify akt1 and a previously uncharacterized Drosophila gene CG8108, which is homologous to the human gene CIZ1, as essential for survival from the executioner caspase activation. We also show that cells expressing activated oncogenes experience apoptotic caspase activation, and that Akt1 and dCIZ1 are required for their survival and overgrowth. Thus, survival following executioner caspase activation is a normal tissue repair mechanism usurped to promote oncogene-driven overgrowth.

Identification of DHX9 as a cell cycle regulated nucleolar recruitment factor for CIZ1

CIP1-interacting zinc finger protein 1 (CIZ1) is a nuclear matrix associated protein that facilitates a number of nuclear functions including initiation of DNA replication, epigenetic maintenance and associates with the inactive X-chromosome. Here, to gain more insight into the protein networks that underpin this diverse functionality, molecular panning and mass spectrometry are used to identify protein interaction partners of CIZ1, and CIZ1 replication domain (CIZ1-RD). STRING analysis of CIZ1 interaction partners identified 2 functional clusters: ribosomal subunits and nucleolar proteins including the DEAD box helicases, DHX9, DDX5 and DDX17. DHX9 shares common functions with CIZ1, including interaction with XIST long-non-coding RNA, epigenetic maintenance and regulation of DNA replication. Functional characterisation of the CIZ1-DHX9 complex showed that CIZ1-DHX9 interact in vitro and dynamically colocalise within the nucleolus from early to mid S-phase. CIZ1-DHX9 nucleolar colocalisation is dependent upon RNA polymerase I activity and is abolished by depletion of DHX9. In addition, depletion of DHX9 reduced cell cycle progression from G1 to S-phase in mouse fibroblasts. The data suggest that DHX9-CIZ1 are required for efficient cell cycle progression at the G1/S transition and that nucleolar recruitment is integral to their mechanism of action.

Dihydroartemisinin inhibits the tumorigenesis and metastasis of breast cancer via downregulating CIZ1 expression associated with TGF-β1 signaling

AIMS

Dihydroartemisinin (DHA) is currently considered as the promising cancer therapeutic drug. In this study, we aimed to investigate the anti-proliferative and anti-metastasis effects of DHA.

MAIN METHODS

Utilizing breast cancer cells MCF-7, MDA-MB-231 and BT549, cell proliferation, migration and invasion were detected. RT-qPCR was performed to detect CIZ1, TGF-β1 and Snail expression, and the interactions of these related molecules were analyzed by GeneMANIA database. Western blot detected CIZ1, TGF-β1/Smads signaling and Snail expression in DHA-treated cells, in TGFβ1-induced cells with enhanced metastatic capacity, and in cells treated with DHA plus TGFβ1/TGFβ1 inhibitor SD-208.

KEY FINDINGS

Results indicated DHA inhibited breast cancer cell proliferation and migration, with more potent effects compared with that of artemisinin. RT-qPCR and Western blot showed DHA inhibited CIZ1, TGF-β1 and Snail expression, and these molecules were shown to have protein-protein interactions by bioinformatics. Furthermore, TGFβ1-treatment enhanced MCF-7 migration and invasion, and CIZ1, TGF-β1/Smads signaling and snail activities; DHA, SD-208, combination of DHA and SD-208 reversed these conditions, preliminarily proving the cascade regulation between TGF-β1 signaling and CIZ1. MCF-7 xenografts model demonstrated the inhibition of DHA on tumor burden, and its mechanisms and well-tolerance in vivo; combination of DHA and SD-208 tried by us for the first time showed better treatment effects, but possible liver impairment made its use still keep cautious.

SIGNIFICANCE

DHA treatment inhibits the proliferation and metastasis of breast cancer, through suppressing TGF-β1/Smad signaling and CIZ1, suggesting the promising potential of DHA as a well-tolerated antitumor TGF-β1 pathway inhibitor.

CIZ1-F, an alternatively spliced variant of the DNA replication protein CIZ1 with distinct expression and localisation, is overrepresented in early stage common solid tumours

CIZ1 promotes cyclin-dependent DNA replication and resides in sub-nuclear foci that are part of the protein nuclear matrix (NM), and in RNA assemblies that are enriched at the inactive X chromosome (Xi) in female cells. It is subjected to alternative splicing, with specific variants implicated in adult and pediatric cancers. CIZ1-F is characterized by a frame shift that results from splicing exons 8–12 leading to inclusion of a short alternative reading frame (ARF), excluding the previously characterized C-terminal NM anchor domain. Here, we apply a set of novel variant-selective molecular tools targeted to the ARF to profile the expression of CIZ1-F at both transcript and protein levels, with focus on its relationship with the RNA-dependent and -independent fractions of the NM. Unlike full-length CIZ1, CIZ1-F does not accumulate at Xi, though like full-length CIZ1 it does resist extraction with DNase. Notably, CIZ1-F is sensitive to RNase identifying it as part of the RNA-fraction of the NM. In quiescent cells CIZ1-F transcript expression is suppressed and CIZ1-F protein is excluded from the nucleus, with re-expression not observed until the second cell cycle after exit from quiescence. Importantly, CIZ1-F is over-expressed in common solid tumors including colon and breast, pronounced in early stage but not highly-proliferative late stage tumors. Moreover, expression was significantly higher in hormone receptor negative breast tumors than receptor positive tumors. Together these data show that CIZ1-F is expressed in proliferating cells in an unusual cell cycle-dependent manner, and suggest that it may have potential as a tumor biomarker.

DNA damage and neurodegenerative phenotypes in aged Ciz1 null mice

Cell-cycle dysfunction and faulty DNA repair are closely intertwined pathobiological processes that may contribute to several neurodegenerative disorders. CDKN1A interacting zinc finger protein 1 (CIZ1) plays a critical role in DNA replication and cell-cycle progression at the G1/S checkpoint. Germline or somatic variants in CIZ1 have been linked to several neural and extra-neural diseases. Recently, we showed that germline knockout of Ciz1 is associated with motor and hematological abnormalities in young adult mice. However, the effects of CIZ1 deficiency in much older mice may be more relevant to understanding age-related declines in cognitive and motor functioning and age-related neurologic disorders such as isolated dystonia and Alzheimer disease. Mouse embryonic fibroblasts from Ciz1^-/- mice showed abnormal sensitivity to the effects of γ-irradiation with persistent DNA breaks, aberrant cell-cycle progression, and apoptosis. Aged (18-month-old) Ciz1^-/- mice exhibited marked deficits in motor and cognitive functioning, and, in brain tissues, overt DNA damage, NF-κB upregulation, oxidative stress, vascular dysfunction, inflammation, and cell death. These findings indicate that the deleterious effects of CIZ1 deficiency become more pronounced with aging and suggest that defects of cell-cycle control and associated DNA repair pathways in postmitotic neurons could contribute to global neurologic decline in elderly human populations. Accordingly, the G1/S cell-cycle checkpoint and associated DNA repair pathways may be targets for the prevention and treatment of age-related neurodegenerative processes.

Consequences of Cre-mediated deletion of Ciz1 exon 5 in mice

CIZ1 plays a role in DNA synthesis at the G1/S checkpoint. Ciz1 gene-trap null mice manifest motor dysfunction, cell-cycle abnormalities, and DNA damage. In contrast, it has previously been reported that mouse embryonic fibroblasts derived from presumed Ciz1 knock-out mice (Ciz1^{tm1.1Homy/tm1.1Homy} ) generated by crossing Cre-expressing mice with exon 5-floxed mice (Ciz1^{tm1Homy/tm1Homy} ) do not exhibit evidence of enhanced DNA damage following γ-irradiation or cell-cycle defects. Here, we report that Ciz1^{tm1.1Homy/tm1.1Homy} mice show loss of Ciz1 exon 5 but are neurologically normal and express abnormal transcripts (Ciz1^ΔE5/ΔE5 mice) that are translated into one or more proteins of approximate wild-type size. Therefore, Ciz1^{tm1.1Homy/tm1.1Homy} mice (Ciz1^ΔE5/ΔE5 ) lose residues encoded by exon 5 but may gain function from novel amino acid sequences.

CDKN1A-interacting zinc finger protein 1 is a novel biomarker for lung squamous cell carcinoma

CDKN1A-interacting zinc finger protein 1 (CIZ1), a nuclear protein that participates in DNA replication, is involved in the pathogenesis of several types of cancer. However, the role of CIZ1 in lung squamous cell carcinoma (LSCC) is not fully understood. In the present study, the expression of CIZ1 in tissue microarrays and surgical samples of human LSCCs was examined. CIZ1 expression was found to be significantly increased in LSCC tissues compared with adjacent tissues or normal controls, whereas expression of a CIZ1-interacting protein, p21^Cip1/Waf1, was decreased. CIZ1 staining intensity and CIZ1-positive vascular invasion were positively correlated with at least two categories of the Tumor-Node-Metastasis (TNM) staging system (T stage, N stage or TNM stage). It was also observed that CIZ1 was specifically expressed in the vascular cells of LSCC tissues. These results indicate that overexpression of CIZ1 may contribute to the growth and angiogenesis of LSCC, thus CIZ1 could represent a biomarker for diagnosis and a target for therapeutic intervention.

Repeat E anchors Xist RNA to the inactive X chromosomal compartment through CDKN1A-interacting protein (CIZ1)

X chromosome inactivation is an epigenetic dosage compensation mechanism in female mammals driven by the long noncoding RNA, Xist. Although recent genomic and proteomic approaches have provided a more global view of Xist's function, how Xist RNA localizes to the inactive X chromosome (Xi) and spreads in cis remains unclear. Here, we report that the CDKN1-interacting zinc finger protein CIZ1 is critical for localization of Xist RNA to the Xi chromosome territory. Stochastic optical reconstruction microscopy (STORM) shows a tight association of CIZ1 with Xist RNA at the single-molecule level. CIZ1 interacts with a specific region within Xist exon 7-namely, the highly repetitive Repeat E motif. Using genetic analysis, we show that loss of CIZ1 or deletion of Repeat E in female cells phenocopies one another in causing Xist RNA to delocalize from the Xi and disperse into the nucleoplasm. Interestingly, this interaction is exquisitely sensitive to CIZ1 levels, as overexpression of CIZ1 likewise results in Xist delocalization. As a consequence, this delocalization is accompanied by a decrease in H3K27me3 on the Xi. Our data reveal that CIZ1 plays a major role in ensuring stable association of Xist RNA within the Xi territory.

The nuclear matrix protein CIZ1 facilitates localization of Xist RNA to the inactive X-chromosome territory

Here, Ridings-Figueroa et al. show that the nuclear matrix protein Cip1-interacting zinc finger protein 1 (CIZ1) is highly enriched on the inactive X chromosome (Xi) in mouse and human female cells and is retained by interaction with the RNA-dependent nuclear matrix. Their findings suggest that CIZ1 has an essential role in anchoring Xist to the nuclear matrix in specific somatic lineages.

The nuclear matrix protein Cip1-interacting zinc finger protein 1 (CIZ1) promotes DNA replication in association with cyclins and has been linked to adult and pediatric cancers. Here we show that CIZ1 is highly enriched on the inactive X chromosome (Xi) in mouse and human female cells and is retained by interaction with the RNA-dependent nuclear matrix. CIZ1 is recruited to Xi in response to expression of X inactive-specific transcript (Xist) RNA during the earliest stages of X inactivation in embryonic stem cells and is dependent on the C-terminal nuclear matrix anchor domain of CIZ1 and the E repeats of Xist. CIZ1-null mice, although viable, display fully penetrant female-specific lymphoproliferative disorder. Interestingly, in mouse embryonic fibroblast cells derived from CIZ1-null embryos, Xist RNA localization is disrupted, being highly dispersed through the nucleoplasm rather than focal. Focal localization is reinstated following re-expression of CIZ1. Focal localization of Xist RNA is also disrupted in activated B and T cells isolated from CIZ1-null animals, suggesting a possible explanation for female-specific lymphoproliferative disorder. Together, these findings suggest that CIZ1 has an essential role in anchoring Xist to the nuclear matrix in specific somatic lineages.

Cardiomyocyte--specific expression of the nuclear matrix protein, CIZ1, stimulates production of mono-nucleated cells with an extended window of proliferation in the postnatal mouse heart

Myocardial injury in mammals leads to heart failure through pathological cardiac remodelling that includes hypertrophy, fibrosis and ventricular dilatation. Central to this is inability of the mammalian cardiomyocyte to self-renew due to entering a quiescent state after birth. Modulation of the cardiomyocyte cell-cycle after injury is therefore a target mechanism to limit damage and potentiate repair and regeneration. Here, we show that cardiomyocyte-specific over-expression of the nuclear-matrix­-associated DNA replication protein, CIZ1, extends their window of proliferation during cardiac development, delaying onset of terminal differentiation without compromising function. CIZ1-expressing hearts are enlarged, but the cardiomyocytes are smaller with an overall increase in number, correlating with increased DNA replication after birth and retention of an increased proportion of mono-nucleated cardiomyocytes into adulthood. Furthermore, these CIZ1 induced changes in the heart reduce the impact of myocardial injury, identifying CIZ1 as a putative therapeutic target for cardiac repair.

Summary: An inducible mouse model was developed to show that CIZ1 extends the window of cardiomyocyte proliferation and reduces the impact of injury on cardiac function.

Emerging Roles for Ciz1 in Cell Cycle Regulation and as a Driver of Tumorigenesis

Precise duplication of the genome is a prerequisite for the health and longevity of multicellular organisms. The temporal regulation of origin specification, replication licensing, and firing at replication origins is mediated by the cyclin-dependent kinases. Here the role of Cip1 interacting Zinc finger protein 1 (Ciz1) in regulation of cell cycle progression is discussed. Ciz1 contributes to regulation of the G1/S transition in mammalian cells. Ciz1 contacts the pre-replication complex (pre-RC) through cell division cycle 6 (Cdc6) interactions and aids localization of cyclin A- cyclin-dependent kinase 2 (CDK2) activity to chromatin and the nuclear matrix during initiation of DNA replication. We discuss evidence that Ciz1 serves as a kinase sensor that regulates both initiation of DNA replication and prevention of re-replication. Finally, the emerging role for Ciz1 in cancer biology is discussed. Ciz1 is overexpressed in common tumors and tumor growth is dependent on Ciz1 expression, suggesting that Ciz1 is a driver of tumor growth. We present evidence that Ciz1 may contribute to deregulation of the cell cycle due to its ability to alter the CDK activity thresholds that are permissive for initiation of DNA replication. We propose that Ciz1 may contribute to oncogenesis by induction of DNA replication stress and that Ciz1 may be a multifaceted target in cancer therapy.

A quantitative immunoassay for lung cancer biomarker CIZ1b in patient plasma

OBJECTIVES

Non-invasive tests for early detection of lung cancer are an important unmet clinical need. CIZ1b plasma biomarker can discriminate stage 1 lung cancer from within high-risk groups with clinically useful accuracy, with ROC AUCs in excess of 0.9 for two independent retrospective cohorts, and could therefore meet this need. Our aim was to characterise the native state of the biomarker and develop a quantitative immunoassay.

DESIGN AND METHODS

Selective denaturation, preparative electrophoresis and mass spectrometry of human plasma were used to characterise the biomarker and interaction partners. A sandwich ELISA was generated, and specificity for CIZ1b biomarker tested on lung cancer patient plasma.

RESULTS

CIZ1b biomarker is a denaturation-resistant complex between a C-terminal fragment of CIZ1 bearing the CIZ1b epitope specified by alternative splicing of exon14, and fibrinogen alpha chain. Reconstitution of the biomarker epitope with purified fibrinogen and CIZ1b, but not CIZ1a (non-alternatively spliced exon 14) confirmed the specificity of the results. The endogenous complex is highly stable in lung cancer plasma and can be quantified by pairing of a CIZ1b exon-junction specific antibody with detection of fibrinogen. Application of this sandwich ELISA to a prospectively collected development set of plasmas reveals the same level of accuracy as the western blot used to validate the discriminatory capability of the biomarker.

CONCLUSIONS

Unexpected and unusual molecular structure of CIZ1b in native plasma has complicated immunoassay design, and delayed translation of this promising biomarker. However, CIZ1b can now be measured using a high-throughput, hospital-friendly sandwich ELISA format, overcoming an important barrier to further clinical development and application of this blood test for early stage lung cancer.

Motor phenotypes and molecular networks associated with germline deficiency of Ciz1

A missense mutation in CIZ1 (c.790A>G, p.S264G) was linked to autosomal dominant cervical dystonia in a large multiplex Caucasian pedigree (OMIM614860, DYT23). CIZ1 is a p21((Cip1/Waf1)) -interacting zinc finger protein, widely expressed in neural and extra-neural tissues, and plays a role in DNA synthesis at the G1/S cell-cycle checkpoint. The role of CIZ1 in the nervous system and relative contributions of gain- or loss- of function to the pathogenesis of CIZ1-associated dystonia remain indefinite. Using relative quantitative reverse transcriptase-PCR, cerebellum showed the highest expression levels of Ciz1 in adult mouse brain, over two fold higher than liver, and higher than striatum, midbrain and cerebral cortex. Overall, neural expression of Ciz1 increased with postnatal age. A Ciz1 gene-trap knock-out (KO) mouse model (Ciz1(-/-)) was generated to examine the functional role(s) of CIZ1 in the sensorimotor nervous system and contributions of CIZ1 to cell-cycle control in the mammalian brain. Ciz1 transcripts were absent in Ciz1(-/-) mice and reduced by approximately 50% in Ciz1(+/-) mice. Ciz1(-/-) mice were fertile but smaller than wild-type (WT) littermates. Ciz1(-/-) mice did not manifest dystonia, but exhibited mild motoric abnormalities on balance, open-field activity, and gait. To determine the effects of germline KO of Ciz1 on whole-genome gene expression in adult brain, total RNA from mouse cerebellum was harvested from 6 10-month old Ciz1(-/-) mice and 6 age- and gender- matched WT littermates for whole-genome gene expression analysis. Based on whole-genome gene-expression analyses, genes involved in cellular movement, cell development, cellular growth, cellular morphology and cell-to-cell signaling and interaction were up-regulated in Ciz1(-/-) mice. The top up-regulated pathways were metabolic and cytokine-cytokine receptor interactions. Down-regulated genes were involved in cell cycle, cellular development, cell death and survival, gene expression and cell morphology. Down-regulated networks included those related to metabolism, focal adhesion, neuroactive ligand-receptor interaction, and MAPK signaling. Based on pathway analyses, transcription factor 7-like 2 (TCF7L2), a member of the Wnt/β-catenin signaling pathway, was a major hub for down-regulated genes, whereas NF-κB was a major hub for up-regulated genes. In aggregate, these data suggest that CIZ1 may be involved in the post-mitotic differentiation of neurons in response to external signals and changes in gene expression may compensate, in part, for CIZ1 deficiency in our Ciz1(-/-) mouse model. Although CIZ1 deficiency was associated with mild motor abnormalities, germline loss of Ciz1 was not associated with dystonia on the C57BL/6J background.

The Role of Cdkn1A-Interacting Zinc Finger Protein 1 (CIZ1) in DNA Replication and Pathophysiology

Cdkn1A-interacting zinc finger protein 1 (CIZ1) was first identified in a yeast-2-hybrid system searching for interacting proteins of CDK2 inhibitor p21^Cip1/Waf1. Ciz1 also binds to CDK2, cyclin A, cyclin E, CDC6, PCNA, TCF4 and estrogen receptor-α. Recent studies reveal numerous biological functions of CIZ1 in DNA replication, cell proliferation, and differentiation. In addition, splicing variants of CIZ1 mRNA is associated with a variety of cancers and Alzheimer’s disease, and mutations of the CIZ1 gene lead to cervical dystonia. CIZ1 expression is increased in cancers and rheumatoid arthritis. In this review, we will summarize the biological functions and molecular mechanisms of CIZ1 in these physiological and pathological processes.

CIZ1 promoted the growth and migration of gallbladder cancer cells

Gallbladder cancer (GBC) is one of the most common and aggressive diseases among the gastrointestinal tract malignancies, and the molecular mechanism underlying this disease remains largely unknown. CIZ1 (Cip1 interacting zinc finger protein 1), a binding partner of p21(Cip1/Waf1), has been found to be involved in the tumorigenesis recently. However, the expression pattern and biological functions of CIZ1 in the progression of GBC are not fully understood. In this study, it was found that the expression of CIZ1 was significantly elevated in GBC samples compared to their adjacent normal tissues. Moreover, overexpression of CIZ1 promoted the growth and migration of GBC cells, while knocking down the expression of CIZ1 inhibited the growth, migration, and tumorigenesis of GBC cells in vitro and in vivo. Mechanistically, CIZ1 was found to interact with TCF4 (T-cell factor) and activate beta-catenin/TCF signaling. Our study demonstrated that CIZ1 played an oncogenic role in the progression of GBC and CIZ1 might be a promising target for the treatment of GBC.

Ciz1 is a novel predictor of survival in human colon cancer

Cip1-interacting zinc-finger protein1 (Ciz1) is a nuclear matrix protein associated DNA replication factor which has been implicated in breast and lung cancer progression. However, the clinical significance of Ciz1 expression in colon cancer has not been determined. This study aimed to examine Ciz1 expression pattern and its potential as a biomarker of prognosis in colon cancer. Using quantitative PCR, tissue microarray (TMA), and ELISA, we evaluated Ciz1 mRNA and protein levels in tumor tissues from patients with colon cancer and in paired adjacent normal tissues. Ciz1 mRNA expression was significantly upregulated in 22 of 39 paired samples (P < 0.001). Immunohistochemistry on TMA-containing samples from 203 colon cancer patients indicated that Ciz1 protein expression was significantly higher in tumor tissues than in adjacent normal tissues (Stuart-Maxwell test, P < 0.001). Elevated expression of Ciz1 protein was significantly correlated with T stage (P < 0.001), N stage (P = 0.005), M stage (P = 0.021), and AJCC stage (P = 0.002). Multivariate Cox proportion hazard model analysis revealed that Ciz1 expression is an independent prognostic factor for overall time (OS; hazard ratio (HR): 1.76; 95% confidence interval (CI): 1.04-2.98; P = 0.034) and disease-free survival (DFS; HR: 2.02; 95% CI: 1.14-3.58; P = 0.017) of patients with colon cancer after colectomy. Our data suggested that Ciz1 may be involved in colon cancer progression and could serve as a novel predictor of survival for colon cancer patients.

The enigmatic ERH protein: its role in cell cycle, RNA splicing and cancer

Enhancer of rudimentary homolog (ERH) is a small, highly conserved protein among eukaryotes. Since its discovery nearly 20 years ago, its molecular function has remained enigmatic. It has been implicated to play a role in transcriptional regulation and in cell cycle. We recently showed that ERH binds to the Sm complex and is required for the mRNA splicing of the mitotic motor protein CENP-E. Furthermore, cancer cells driven by mutations in the KRAS oncogene are particularly sensitive to RNAi-mediated suppression of ERH function, and ERH expression is inversely correlated with survival in colorectal cancer patients whose tumors harbor KRAS mutation. These recent findings indicate that ERH plays an important role in cell cycle through its mRNA splicing activity and is critically required for genomic stability and cancer cell survival.

Genetics in dystonia: an update

The past year has been extremely successful with regard to the genetics of dystonia, with the identification of four new dystonia genes (CIZ1, ANO3, GNAL, and TUBB4A). This progress was primarily achieved because of the application of a new technology, next-generation DNA sequencing, which allows rapid and comprehensive assessment of a patient's genome. In addition, a combination of next-generation and traditional Sanger sequencing has expanded the phenotypic spectrum associated with some of the dystonia plus (ATP1A3) and paroxysmal (PRRT2) loci. This article reviews the newly identified genes and phenotypes and discusses the future applications of next-generation sequencing to dystonia research.

Emerging common molecular pathways for primary dystonia

The dystonias are a group of hyperkinetic movement disorders whose principal cause is neuron dysfunction at 1 or more interconnected nodes of the motor system. The study of genes and proteins that cause familial dystonia provides critical information about the cellular pathways involved in this dysfunction, which disrupts the motor pathways at the systems level. In recent years study of the increasing number of DYT genes has implicated a number of cell functions that appear to be involved in the pathogenesis of dystonia. A review of the literature published in English-language publications available on PubMed relating to the genetics and cellular pathology of dystonia was performed. Numerous potential pathogenetic mechanisms have been identified. We describe those that fall into 3 emerging thematic groups: cell-cycle and transcriptional regulation in the nucleus, endoplasmic reticulum and nuclear envelope function, and control of synaptic function. © 2013 Movement Disorder Society.

A genotoxic stress-responsive miRNA, miR-574-3p, delays cell growth by suppressing the enhancer of rudimentary homolog gene in vitro

MicroRNA (miRNA) is a type of non-coding RNA that regulates the expression of its target genes by interacting with the complementary sequence of the target mRNA molecules. Recent evidence has shown that genotoxic stress induces miRNA expression, but the target genes involved and role in cellular responses remain unclear. We examined the role of miRNA in the cellular response to X-ray irradiation by studying the expression profiles of radio-responsive miRNAs and their target genes in cultured human cell lines. We found that expression of miR-574-3p was induced in the lung cancer cell line A549 by X-ray irradiation. Overexpression of miR-574-3p caused delayed growth in A549 cells. A predicted target site was detected in the 3′-untranslated region of the enhancer of the rudimentary homolog (ERH) gene, and transfected cells showed an interaction between the luciferase reporter containing the target sequences and miR-574-3p. Overexpression of miR-574-3p suppressed ERH protein production and delayed cell growth. This delay was confirmed by knockdown of ERH expression. Our study suggests that miR-574-3p may contribute to the regulation of the cell cycle in response to X-ray irradiation via suppression of ERH protein production.

CIZ1 regulates the proliferation, cycle distribution and colony formation of RKO human colorectal cancer cells

Cip1-interacting zinc finger protein 1 (CIZ1) is a nuclear protein that was observed to bind to p21Cip1/Waf1. p21Cip1/Waf1 regulates the cell cycle and is associated with colorectal cancer (CRC) progression. However, the effect of CIZ1 on CRC cells remains unclear. In the present study, CIZ1 was observed to be highly expressed in RKO human CRC cells. Silencing of CIZ1 using small interfering RNA (siRNA) suppressed RKO cell proliferation. Flow cytometric analysis demonstrated that knockdown of CIZ1 decreased the percentage of cells in the S phase and increased the ratio of cells in the G0/G1 phase in parallel with upregulated cell apoptosis. Moreover, the number and size of RKO cell colonies was repressed by knockdown of the CIZ1 gene. These results suggested that CIZ1 may be involved in colon cancer progression by regulating cell proliferation, cell cycle, apoptosis and colony formation. Furthermore, CIZ1‑siRNA may provide a novel tool for CRC investigation and therapy.

Identification of amino acid residues of ERH required for its recruitment to nuclear speckles and replication foci in HeLa cells

ERH is a small, highly evolutionarily conserved nuclear protein of unknown function. Its three-dimensional structure is absolutely unique and it can form a homodimer through a β sheet surface. ERH has been shown to interact, among others, with PDIP46/SKAR and Ciz1. When coexpressed with the latter protein, ERH accumulates in replication foci in the nucleus of HeLa cells. Here, we report that when ERH is coexpressed with PDIP46/SKAR in HeLa cells, it is recruited to nuclear speckles, and identify amino acid residues critical for targeting ERH to both these subnuclear structures. ERH H3A Q9A shows a diminished recruitment to nuclear speckles but it is recruited to replication foci. ERH E37A T51A is very poorly recruited to replication foci while still accumulating in nuclear speckles. Consequently, ERH H3A Q9A E37A T51A is recruited neither to nuclear speckles nor to replication foci. The lack of interactions of these three ERH forms with PDIP46/SKAR and/or Ciz1 was further confirmed in vitro by GST pull-down assay. The residues whose substitutions interfere with the accumulation in nuclear speckles are situated on the β sheet surface of ERH, indicating that only the monomer of ERH can interact with PDIP46/SKAR. Substitutions affecting the recruitment to replication foci map to the other side of ERH, near a long loop between the α1 and α2 helices, thus both the monomer and the dimer of ERH could interact with Ciz1. The construction of the ERH mutants not recruited to nuclear speckles or replication foci will facilitate further studies on ERH actions in these subnuclear structures.

CIZ1, a p21Cip1/Waf1-interacting protein, functions as a tumor suppressor in vivo

CIZ1 is a nuclear protein involved in DNA replication and is also implicated in human diseases including cancers. To gain an insight into its function in vivo, we generated mice lacking Ciz1. Ciz1-deficient (Ciz1(-/-)) mice grew without any obvious abnormalities, and Ciz1(-/-) mouse embryonic fibroblasts (MEFs) did not show any defects in cell cycle status, cell growth, and DNA damage response. However, Ciz1(-/-) MEFs were sensitive to hydroxyurea-mediated replication stress and susceptible to oncogene-induced cellular transformation. In addition, Ciz1(-/-) mice developed various types of leukemias by retroviral insertional mutagenesis. These results indicate that CIZ1 functions as a tumor suppressor in vivo.

Variant Ciz1 is a circulating biomarker for early-stage lung cancer

There is an unmet need for circulating biomarkers that can detect early-stage lung cancer. Here we show that a variant form of the nuclear matrix-associated DNA replication factor Ciz1 is present in 34/35 lung tumors but not in adjacent tissue, giving rise to stable protein quantifiable by Western blot in less than a microliter of plasma from lung cancer patients. In two independent sets, with 170 and 160 samples, respectively, variant Ciz1 correctly identified patients who had stage 1 lung cancer with clinically useful accuracy. For set 1, mean variant Ciz1 level in individuals without diagnosed tumors established a threshold that correctly classified 98% of small cell lung cancers (SCLC) and non-SCLC patients [receiver operator characteristic area under the curve (AUC) 0.958]. Within set 2, comparison of patients with stage 1 non-SCLC with asymptomatic age-matched smokers or individuals with benign lung nodules correctly classified 95% of patients (AUCs 0.913 and 0.905), with overall specificity of 76% and 71%, respectively. Moreover, using the mean of controls in set 1, we achieved 95% sensitivity among patients with stage 1 non-SCLC patients in set 2 with 74% specificity, demonstrating the robustness of the classification. RNAi-mediated selective depletion of variant Ciz1 is sufficient to restrain the growth of tumor cells that express it, identifying variant Ciz1 as a functionally relevant driver of cell proliferation in vitro and in vivo. The data show that variant Ciz1 is a strong candidate for a cancer-specific single marker capable of identifying early-stage lung cancer within at-risk groups without resort to invasive procedures.

Mutations in CIZ1 cause adult onset primary cervical dystonia

OBJECTIVE

Primary dystonia is usually of adult onset, can be familial, and frequently involves the cervical musculature. Our goal was to identify the causal mutation in a family with adult onset, primary cervical dystonia.

METHODS

Linkage and haplotype analyses were combined with solution-based whole-exome capture and massively parallel sequencing in a large Caucasian pedigree with adult onset, primary cervical dystonia to identify a cosegregating mutation. High-throughput screening and Sanger sequencing were completed in 308 Caucasians with familial or sporadic adult onset cervical dystonia and matching controls for sequence variants in this mutant gene.

RESULTS

Exome sequencing led to the identification of an exonic splicing enhancer mutation in exon 7 of CIZ1 (c.790A>G, p.S264G), which encodes CIZ1, Cip1-interacting zinc finger protein 1. CIZ1 is a p21(Cip1/Waf1) -interacting zinc finger protein expressed in brain and involved in DNA synthesis and cell-cycle control. Using a minigene assay, we showed that c.790A>G altered CIZ1 splicing patterns. The p.S264G mutation also altered the nuclear localization of CIZ1. Screening in subjects with adult-onset cervical dystonia identified 2 additional CIZ1 missense mutations (p.P47S and p.R672M).

INTERPRETATION

Mutations in CIZ1 may cause adult onset, primary cervical dystonia, possibly by precipitating neurodevelopmental abnormalities that manifest in adults and/or G1/S cell-cycle dysregulation in the mature central nervous system.

Cancer associated variant expression and interaction of CIZ1 with cyclin A1 in differentiating male germ cells

CIZ1 is a nuclear matrix associated DNA replication factor unique to higher eukaryotes, for which alternatively spliced isoforms have been associated with a range of disorders. In vitro the CIZ1 N-terminus interacts with cyclins E and A via distinct sites, enabling functional cooperation with cyclin A-Cdk2 to promote replication initiation. C-terminal sequences anchor CIZ1 to fixed sites on the nuclear matrix imposing spatial constraint on cyclin dependent kinase activity. Here we demonstrate that CIZ1 is predominantly expressed as predicted full-length product throughout mouse development, consistent with a ubiquitous role in cell and tissue renewal. CIZ1 is expressed in proliferating stem cells of the testis, but is notably down-regulated following commitment to differentiation. Significantly, CIZ1 is re-expressed at high levels in non-proliferative spermatocytes prior to meiotic division. Sequence analysis identifies at least seven alternatively spliced variants at this time, including a dominant cancer-associated form and a set of novel isoforms. Furthermore, we show that in these post-replicative cells CIZ1 interacts with the germ cell specific cyclin, A1, that has been implicated in DNA double-strand break repair. Consistent with this role, antibody depletion of CIZ1 reduces the capacity for testis extract to repair digested plasmid DNA in vitro. Together, the data imply novel post-replicative roles for CIZ1 in germ cell differentiation that may include meiotic recombination, a process intrinsic to genome stability and diversification.

Expression profiling reveals MSX1 and EphB2 expression correlates with the invasion capacity of Wilms tumors

BACKGROUND

Wilms tumor is the most common pediatric renal malignancy, but the parameters that are important to its invasion capacity are poorly understood. The aim of this study was to identify new proteins associated with the invasion capacity of Wilms tumor.

PROCEDURE

Gene expression profiles for 15 primary Wilms tumor samples were determined by Affymetrix Genechip® Human Genome Ul33A microarray analysis. The gene expression profiles for selected genes was further confirmed by quantitative RT-PCR analysis. Immunohistochemical analysis was performed on 25 Wilms tumor cases to confirm expression for Bcl2A1, EphB2, MSX1, and RIN1.

RESULTS

Using microarray analysis 14 genes showed differential expression (P < 0.05) comparing stage 1 non-invasive Wilms tumor to stages 2-4 invasive Wilms tumor. The differential expression for Bcl2A1, EphB2, MSX1, and RIN1 was confirmed by quantitative RT-PCR. MSX1 protein was statistically significantly lower in stages 2-4 invasive Wilms tumor cases compared to stage 1 non-invasive cases (P = 0.013). EphB2 protein was higher in stages 2-4 Wilms tumor cases compared to stage 1 cases (P = 0.006). There was no statistically significant difference between stages 1 and 2-4 Wilms tumor for Bcl2A1 (P = 0.230) or RIN1 (P = 0.969) at the protein level.

CONCLUSION

Our results indicate that MSX1 may be associated with the invasion capacity of Wilms tumors. RIN1 is a downstream effector of RAS and Bcl2A1 functions as an anti-apoptotic protein. EphB2 is an ephrin receptor and is up-regulated in invasive tumors but its role needs to be confirmed in further cases of Wilms tumors.

PDRG1, a novel tumor marker for multiple malignancies that is selectively regulated by genotoxic stress

We have previously cloned and characterized a novel p53 and DNA damage-regulated gene named PDRG1. PDRG1 was found to be differentially regulated by ultraviolet (UV) radiation and p53. In this study, we further investigated stress regulation of PDRG1 and found it to be selectively regulated by agents that induce genotoxic stress (DNA damage). Using cancer profiling arrays, we also investigated PDRG1 expression in matching normal and tumor samples representing various malignancies and found its expression to be upregulated in multiple malignancies including cancers of the colon, rectum, ovary, lung, stomach, breast and uterus when compared to their respective matched normal tissues. Western blot and immunohistochemical analyses were also performed on select specimen sets of colon cancers and matching normal tissues and the results also indicated PDRG1 overexpression in tumors relative to normal tissues. To gain insight into the function of PDRG1, we performed PDRG1 knockdown in human colon cancer cells and found its depletion to result in marked slowdown of tumor cell growth. These results suggest that PDGR1 may be linked to cell growth regulation. Yeast two-hybrid screen also led to the identification of PDCD7, CIZ1 and MAP1S as PDRG1-interacting proteins that are involved in apoptosis and cell cycle regulation which further implicate PDRG1 in controlling cell growth regulation. Taken together, our results indicate that PDRG1 expression is increased in multiple human malignancies suggesting it to be a high-value novel tumor marker that could play a role in cancer development and/or progression.

Differential detection of alternatively spliced variants of Ciz1 in normal and cancer cells using a custom exon-junction microarray

Background

Ciz1 promotes initiation of mammalian DNA replication and is present within nuclear matrix associated DNA replication factories. Depletion of Ciz1 from normal and cancer cells restrains entry to S phase and inhibits cell proliferation. Several alternative splicing events with putative functional consequences have been identified and reported, but many more variants are predicted to exist based on publicly available mRNAs and expressed sequence tags.

Methods

Here we report the development and validation of a custom exon and exon-junction microarray focused on the human CIZ1 gene, capable of reproducible detection of differential splice-variant expression.

Results

Using a pair of paediatric cancer cell lines and a pool of eight normal lines as reference, the array identified expected and novel CIZ1 splicing events. One novel variant (delta 8-12) that encodes a predicted protein lacking key functional sites, was validated by quantitative RT-PCR and found to be over-represented in a range of other cancer cell lines, and over half of a panel of primary lung tumours.

Conclusions

Expression of CIZ1 delta 8-12 appears to be restricted to cancer cells, and may therefore be a useful novel biomarker

Ciz1 cooperates with cyclin-A-CDK2 to activate mammalian DNA replication in vitro

Initiation of mammalian DNA replication can be reconstituted from isolated G1-phase nuclei and cell extracts, supplemented with cyclin-dependent protein kinases (CDKs). Under these conditions, cyclin E supports pre-replication complex assembly, whereas cyclin-A-associated kinase acts later to terminate assembly and activate DNA replication. The mechanism by which these events are coordinated is unknown. Here, we show that the replication factor Ciz1 interacts with cyclins E and A sequentially through distinct cyclin-binding motifs. Cyclin A displaces cyclin E from Ciz1 in a manner that is dependent on functional domains that are essential for its role in DNA replication. Furthermore, in cell-free assays, recombinant cyclin-A-CDK2 complexes and recombinant Ciz1 cooperate to promote initiation of DNA replication in late G1-phase nuclei. In addition, Ciz1 supports immobilization of cyclin A in isolated nuclei and depletion of Ciz1 by RNAi impairs immobilization, suggesting that Ciz1 promotes initiation by helping to target the kinase to a specific subnuclear compartment. We propose that Ciz1 acts to coordinate the functions of cyclins E and A in the nucleus, by delivering cyclin-A-associated kinase to sites that are specified by cyclin E, helping to ensure that they execute their functions in the same place and in the correct order.

Altered splicing in exon 8 of the DNA replication factor CIZ1 affects subnuclear distribution and is associated with Alzheimer's disease

In order to understand the gene-mediated processes underlying sporadic Alzheimer's disease (AD), we carried out a subtractive cloning screen for novel AD candidate genes. We identified the gene encoding the DNA replication factor CIZ1 (CDKN1A interacting zinc finger protein 1) as being more highly expressed in Alzheimer tissue than in healthy brains. We show here that an isoform of CIZ1 which lacks a glutamine-rich region, due to alternative splicing in exon 8, is upregulated in AD brains relative to the full-length CIZ1 protein. We demonstrate for the first time that a minimal 28 amino acid sequence within this region is required for CIZ1 to associate with the nuclear matrix and to form nuclear foci.

Ciz1, a p21 cip1/Waf1-interacting zinc finger protein and DNA replication factor, is a novel molecular partner for human enhancer of rudimentary homolog

Enhancer of rudimentary homolog (Drosophila) (ERH) is a small, highly conserved, nuclear protein with a unique three-dimensional structure, whose gene has been identified in animals, plants and protists, but not in fungi. Involvement of ERH in fundamental processes such as regulation of pyrimidine metabolism, cell cycle progression, transcription and cell growth control has been suggested. Here, employing a yeast two-hybrid system, a glutathione S-transferase pull-down assay and tandem MS, we demonstrate that Ciz1 is a bona fide interactor of human ERH. Ciz1 is a nuclear zinc finger protein interacting with p21(Cip1/Waf1), a universal inhibitor of cyclin-dependent kinases, and is a DNA replication factor. The region of Ciz1 necessary for the interaction with ERH spans residues 531-644, encompassing its first zinc finger motif. This region overlaps the p21(Cip1/Waf1)-binding site, suggesting that the interaction with ERH could block the binding of p21(Cip1/Waf1) by Ciz1 in the cell. When ERH and Ciz1 are coexpressed in HeLa cells, Ciz1 recruits ERH to DNA replication foci.

Cancer-associated missplicing of exon 4 influences the subnuclear distribution of the DNA replication factor CIZ1

Cip1-interacting zinc finger protein 1 (CIZ1, also known as CDKN1A-interacting zinc finger protein 1) stimulates initiation of mammalian DNA replication and is normally tethered to the nuclear matrix within DNA replication foci. Here, we show that an alternatively spliced human CIZ1 variant, lacking exon 4 (Delta E4), is misexpressed as a consequence of intronic mutation in Ewing tumor (ET) cell lines. In all ET lines tested, exon 4 is skipped and an upstream mononucleotide repeat element is expanded to contain up to 28 thymidines, compared to 16 in controls. In exon-trap experiments, a 24T variant produced three-fold more exon skipping than a 16T variant, demonstrating a direct effect on splicing. In functional assays, Delta E4 protein retains replication activity, but fails to form subnuclear foci. Furthermore, coexpression of mouse Delta E4 with Ciz1 prevents Ciz1 from localizing appropriately, having a dominant negative effect on foci formation. The data show that conditional exclusion of exon 4 influences the spatial distribution of the Ciz1 protein within the nucleus, and raise the possibility that CIZ1 alternative splicing could influence organized patterns of DNA replication.

C-terminal domains deliver the DNA replication factor Ciz1 to the nuclear matrix

Cip1-interacting zinc finger protein 1 (Ciz1) stimulates DNA replication in vitro and is required for mammalian cells to enter S phase. Here, we show that a significant proportion of Ciz1 is retained in nuclear foci following extraction with nuclease and high salt. This suggests that Ciz1 is normally immobilized by interaction with non-chromatin nuclear structures, consistent with the nuclear matrix. Furthermore, matrix-associated Ciz1 foci strikingly colocalize with sites of newly synthesized DNA in S phase nuclei, suggesting that Ciz1 is present in DNA replication factories. Analysis of green fluorescent protein-tagged fragments indicates that nuclear immobilization of Ciz1 is mediated by sequences in its C-terminal third, encoded within amino acids 708-830. Immobilization occurs in a cell-cycle-dependent manner, most probably during late G1 or early S phase, to coincide with its reported point of action. Although C-terminal domains are sufficient for immobilization, N-terminal domains are also required to specify focal organization. Combined with previous work, which showed that the DNA replication activity of Ciz1 is encoded by N-terminal sequences, we suggest that Ciz1 is composed of two functionally distinct domains: an N-terminal replication domain and a C-terminal nuclear matrix anchor. This could contribute to the formation or function of DNA replication factories in mammalian cells.

Ciz1, a Novel DNA-Binding Coactivator of the Estrogen Receptor α, Confers Hypersensitivity to Estrogen Action

The transcriptional activity of the estrogen receptor (ER) is affected by regulatory cofactors, including chromatin-remodeling complexes, coactivators, and corepressors. Coregulators are recruited to target gene promoters through protein-protein interactions with ER and function as linker molecules between the DNA, DNA-binding proteins, and DNA-modifying enzymes. We recently showed that Cip-interacting zinc finger protein 1 (Ciz1) participates in the regulation of the cell cycle in estrogen-stimulated breast cancer cells. Despite the emerging significance of Ciz1 in the biology of breast cancer cells, regulation of endogenous Ciz1 in hormone-responsive cancer cells remains unknown. To shed light on the role of Ciz1 in breast tumorigenesis, we defined the regulation of Ciz1 by the ER pathway and found that Ciz1 is an estrogen-responsive gene. We also discovered that Ciz1 protein, a DNA-binding factor, coregulates ER by enhancing ER transactivation activity by promoting the recruitment of the ER complex to the target gene chromatin. In addition, we found that Ciz1 overexpression confers estrogen hypersensitivity to breast cancer cells and promotes the growth rate, anchorage independency, and tumorigenic properties of breast cancer cells. These findings revealed the inherent role of Ciz1, a novel DNA binding and ER coactivator, in amplifying estrogenic responses and promoting breast cancer tumorigenesis.

Dynein light chain 1 contributes to cell cycle progression by increasing cyclin-dependent kinase 2 activity in estrogen-stimulated cells

Progression of hormone-responsive cancers is characterized by deregulation of the cell cycle and cytoskeleton signaling. In addition, development of breast and endometrial cancer is influenced by the stimulatory action of estrogen. Up-regulation of dynein light chain 1 (DLC1), a component of cytoskeleton signaling, was recently found to promote tumorigenesis. The purpose of our study was to determine the role that DLC1 up-regulation plays in cell cycle progression. To achieve this goal, we used human breast ductal carcinoma ZR-75 cells overexpressing DLC1 as a model system. We found that ZR-75 cells with up-regulated DLC1 were hypersensitive to estrogen-dependent growth stimulation and that DLC1 had an accelerating effect on the G(1)-S transition and stimulated cyclin-dependent kinase 2 (Cdk2) activity. To better understand the promotion of the G(1)-S transition by DLC1, we sought to identify new DLC1-interacting proteins with roles in cell cycle regulation. Using a modified proteomic strategy, we identified two such DLC1-interacting proteins: Cdk2 and Cip-interacting zinc finger protein 1 (Ciz1). DLC1 was verified to interact with Cdk2 and Ciz1 in vivo. We also showed that down-regulation of DLC1 and Ciz1 reduced both Cdk2 activity and cell cycle progression of breast cancer ZR-75 and MCF-7 and endometrial Ishikawa cancer cells. Further, we showed that overexpression of DLC1 is accompanied by a reduction of nuclear p21(WAF1). These findings suggest that interactions among DLC1, Cdk2, and Ciz1 play a regulatory role in cell cycle progression of cancer cells presumably by influencing the levels of nuclear p21(WAF1).

Ciz1 promotes mammalian DNA replication

Using a cell-free system that reconstitutes initiation of mammalian DNA replication, we identified a cyclin A-responsive protein, p21(Cip1)-interacting zinc finger protein 1 (Ciz1). In cell-free experiments, Ciz1 protein increases the number of nuclei that initiate DNA replication, and in intact cells GFP-tagged Ciz1 stimulates DNA synthesis, in both a wild-type and a p21(Cip1) null background. Furthermore, mutation of a putative cyclin-dependent kinase phosphorylation site at threonines 191/2 alters Ciz1 activity in vitro, indicating that this site plays a role in regulating Ciz1. Consistent with a role in DNA replication, endogenous Ciz1 is present in nuclear foci that co-localize with PCNA during S phase, and targeted depletion of Ciz1 transcripts restrains cell proliferation by inhibiting entry to S phase. Ciz1-depleted cells accumulate with chromatin bound Mcm3 and PCNA but fail to synthesize DNA efficiently. These cell-based and cell-free experiments suggest that Ciz1 functions to promote DNA replication after replication complex formation. Finally, alternatively spliced forms of Ciz1 occur in embryonic cells from mouse and man, raising the possibility that Ciz1 splicing contributes to the regulation of DNA replication during development.

Ciz1, Cip1 interacting zinc finger protein 1 binds the consensus DNA sequence ARYSR(0-2)YYAC

The matrin 3 family of nuclear proteins consists of members with potentially diverse activities. Matrin 3 and NP220 share RNA-binding domains, and NP220 has been shown to recognize and bind to the DNA sequence, CCCCC (G/C). We have isolated and characterized another member of the matrin 3 family, designated NP94, from a medulloblastoma. This protein, also named Ciz1, has previously been characterized for its ability to interact with p21(Cip1/Waf1) and contains 3 zinc finger domains and a matrin 3-homologous domain 3. Our immunofluorescence and Northern blot analysis data indicate that Ciz1 is localized in the nucleus and is expressed in a wide range of tissues, especially the pancreas and the brain; within the brain, the highest message levels are found in the cerebellum. A modified selected and amplified binding (SAAB) sequence method was used to identify DNA sequences recognized by Ciz1. From the analysis of the retrieved SAAB sequences and verification using electrophoretic mobility shift assays, we formulated a consensus DNA sequence, ARYSR(0-2)YYAC, recognized by Ciz1. The potential activities of Ciz1, including those involved in brain tumorigenesis, are discussed.