The cell adhesion receptor carcinoembryonic antigen-related cell adhesion molecule 1 regulates nucleocytoplasmic trafficking of DNA polymerase delta-interacting protein 38

New insights in the molecular regulation of the NADPH oxidase 2 activity: Negative modulation by Poldip2

Poldip2 was shown to be involved in oxidative signaling to ensure certain biological functions. It was proposed that, in VSMC, by interaction with the Nox4-associated membrane protein p22^phox, Poldip2 stimulates the level of reactive oxygen species (ROS) production. In vitro, with fractionated membranes from HEK393 cells over-expressing Nox4, we confirmed the up-regulation of NADPH oxidase 4 activity by the recombinant and purified Poldip2. Besides Nox4, the Nox1, Nox2, or Nox3 isoforms are also established partners of the p22^phox protein raising the question of their regulation by Poldip2 and of the effect in cells expressing simultaneously different Nox isoforms. In this study, we have addressed this issue by investigating the potential regulatory role of Poldip2 on NADPH oxidase 2, present in phagocyte cells. Unexpectedly, the effect of Poldip2 on phagocyte NADPH oxidase 2 was opposite to that observed on NADPH oxidase 4. Using membranes from circulating resting neutrophils, the ROS production rate of NADPH oxidase 2 was down-regulated by Poldip2 (2.5-fold). The down-regulation effect could not be correlated to the interaction of Poldip2 with p22^phox but rather, to the interaction of Poldip2 with the p47^phox protein, one of the regulatory proteins of the phagocyte NADPH oxidase. Our results show that the interaction of Poldip2 with p47^phox constitutes a novel regulatory mechanism that can negatively modulate the activity of NADPH oxidase 2 by trapping the so-called "adaptor" subunit of the complex. Poldip2 could act as a tunable switch capable of specifically regulating the activities of NADPH oxidases. This selective regulatory role of Poldip2, positive for Nox4 or negative for Nox2 could orchestrate the level and the type of ROS generated by Nox enzymes in the cells.

The polymerase δ-interacting protein family and their emerging roles in diseases

The polymerase δ-interacting protein (POLDIP) family is a new family that can interact with DNA polymerase δ (delta). The members of the POLDIP family include POLDIP1, POLDIP2, and POLDIP3. Screened by the two-hybrid method, POLDIP1, POLDIP2, and POLDIP3 were initially discovered and named for their ability to bind to the p50 subunit of DNA polymerase δ. Recent studies have confirmed that POLDIPs are involved in the regulation of signal transduction pathways in neurodevelopment, neuropsychiatric diseases, cardiovascular diseases, tumors, and other diseases. However, each protein participates in different signaling pathways. In this review, we elucidate upon the family in terms of their genes and protein structures, their biological functions, in addition to the pathways that they are involved in during the development of diverse diseases. Finally, to provide new insights to the scientific community, we used the TCGA database to analyze and summarize the gene expressions of POLDIP family members in various tumors, as well as the correlations between their expressions and the overall survival times of tumor patients. Our data summary will give researchers working on cancer new concepts.

Characterization of Poldip2 knockout mice: Avoiding incorrect gene targeting

POLDIP2 is a multifunctional protein whose roles are only partially understood. Our laboratory previously reported physiological studies performed using a mouse gene trap model, which suffered from three limitations: perinatal lethality in homozygotes, constitutive Poldip2 inactivation and inadvertent downregulation of the adjacent Tmem199 gene. To overcome these limitations, we developed a new conditional floxed Poldip2 model. The first part of the present study shows that our initial floxed mice were affected by an unexpected mutation, which was not readily detected by Southern blotting and traditional PCR. It consisted of a 305 kb duplication around Poldip2 with retention of the wild type allele and could be traced back to the original targeted ES cell clone. We offer simple suggestions to rapidly detect similar accidents, which may affect genome editing using both traditional and CRISPR-based methods. In the second part of the present study, correctly targeted floxed Poldip2 mice were generated and used to produce a new constitutive knockout line by crossing with a Cre deleter. In contrast to the gene trap model, many homozygous knockout mice were viable, in spite of having no POLDIP2 expression. To further characterize the effects of Poldip2 ablation in the vasculature, RNA-seq and RT-qPCR experiments were performed in constitutive knockout arteries. Results show that POLDIP2 inactivation affects multiple cellular processes and provide new opportunities for future in-depth study of its functions.

Crystal structure and molecular dynamics of human POLDIP2, a multifaceted adaptor protein in metabolism and genome stability

Polymerase δ‐interacting protein 2 (POLDIP2, PDIP38) is a multifaceted, “moonlighting” protein, involved in binding protein partners from many different cellular processes, including mitochondrial metabolism and DNA replication and repair. How POLDIP2 interacts with many different proteins is unknown. Towards this goal, we present the crystal structure of POLDIP2 to 2.8 Å, which exhibited a compact two‐domain β‐strand‐rich globular structure, confirmed by circular dichroism and small angle X‐ray scattering approaches. POLDIP2 comprised canonical DUF525 and YccV domains, but with a conserved domain linker packed tightly, resulting in an “extended” YccV module. A central channel was observed, which we hypothesize could influence structural changes potentially mediated by redox conditions, following observation of a modified cysteine residue in the channel. Unstructured regions were rebuilt by ab initio modelling to generate a model of full‐length POLDIP2. Molecular dynamics simulations revealed a highly dynamic N‐terminal region tethered to the YccV‐domain by an extended linker, potentially facilitating interactions with distal binding partners. Models of POLDIP2 complexed with two of its partners, PrimPol and PCNA, indicated that dynamic flexibility of the POLDIP2 N‐terminus and loop regions likely mediate protein interactions.

PDB Code(s): 6Z9C;

Polymerase delta-interacting protein 38 (PDIP38) modulates the stability and activity of the mitochondrial AAA+ protease CLPXP

Over a decade ago Polymerase δ interacting protein of 38 kDa (PDIP38) was proposed to play a role in DNA repair. Since this time, both the physiological function and subcellular location of PDIP38 has remained ambiguous and our present understanding of PDIP38 function has been hampered by a lack of detailed biochemical and structural studies. Here we show, that human PDIP38 is directed to the mitochondrion in a membrane potential dependent manner, where it resides in the matrix compartment, together with its partner protein CLPX. Our structural analysis revealed that PDIP38 is composed of two conserved domains separated by an α/β linker region. The N-terminal (YccV-like) domain of PDIP38 forms an SH3-like β-barrel, which interacts specifically with CLPX, via the adaptor docking loop within the N-terminal Zinc binding domain of CLPX. In contrast, the C-terminal (DUF525) domain forms an immunoglobin-like β-sandwich fold, which contains a highly conserved putative substrate binding pocket. Importantly, PDIP38 modulates the substrate specificity of CLPX and protects CLPX from LONM-mediated degradation, which stabilises the cellular levels of CLPX. Collectively, our findings shed new light on the mechanism and function of mitochondrial PDIP38, demonstrating that PDIP38 is a bona fide adaptor protein for the mitochondrial protease, CLPXP.

Strack et al find that Polymerase δ interacting protein 38 (PDIP38) is targeted to the mitochondrial matrix where it colocalises with the mitochondrial AAA + protein CLPXP. PDIP38 modulates the specificity of CLPXP in vitro and alters the stability of CLPX in vitro and in cells. The PDIP38 structure leads the authors to speculate that PDIP38 is a CLPXP adaptor.

A Multifunctional Protein PolDIP2 in DNA Translesion Synthesis

Polymerase δ-interacting protein 2 (PolDIP2) is involved in the multiple protein-protein interactions and plays roles in many cellular processes including regulation of the nuclear redox environment, organization of the mitotic spindle and chromosome segregation, pre-mRNA processing, mitochondrial morphology and functions, cell migration and cellular adhesion. PolDIP2 is also a binding partner of high-fidelity DNA polymerase delta, PCNA and a number of translesion and repair DNA polymerases. The growing evidence suggests that PolDIP2 is a general regulatory protein in DNA damage response. However PolDIP2 functions in DNA translesion synthesis and repair are not fully understood. In this review, we address the functional interaction of PolDIP2 with human DNA polymerases and discuss the possible functions in DNA damage response.

Poldip2 knockdown inhibits vascular smooth muscle proliferation and neointima formation by regulating the expression of PCNA and p21

Polymerase delta-interacting protein 2 (Poldip2) is a multi-functional protein with numerous roles in the vasculature, including the regulation of cell apoptosis and migration, as well as extracellular matrix deposition; however, its role in VSMC proliferation and neointimal formation is unknown. In this study, we investigated the role of Poldip2 in intraluminal wire-injury induced neointima formation and proliferation of vascular smooth muscle cells in vitro and in vivo. Poldip2 expression was observed in the intima and media of human atherosclerotic arteries, where it colocalized with proliferating cell nuclear antigen (PCNA). Wire injury of femoral arteries of Poldip2^+/+ mice induced robust neointimal formation after 2 weeks, which was impaired in Poldip2^+/‒ mice. PCNA expression was significantly reduced and expression of the cell cycle inhibitor p21 was significantly increased in wire-injured arteries of Poldip2^+/‒ animals compared to wild-type controls. No difference was observed in apoptosis. Downregulation of Poldip2 in rat aortic smooth muscle cells significantly reduced serum-induced proliferation and PCNA expression, but upregulated p21 expression. Downregulation of p21 using siRNA reversed the inhibition of proliferation induced by knockdown of Poldip2. These results indicate that Poldip2 plays a critical role in the proliferation of VSMCs.

Knockdown of POLDIP2 suppresses tumor growth and invasion capacity and is linked to unfavorable transformation ability and metastatic feature in non-small cell lung cancer

The main problem in the treatment of non-small cell lung cancer (NSCLC) is metastasis. Epithelial-mesenchymal transition (EMT) is known as the critical signaling in tumor progression, metastasis, and also the drug resistance. In this study, we reported a novel gene Polymerase delta-interacting protein 2 (POLDIP2) was downregulated in NSCLC tissues and first demonstrated that overexpression of POLDIP2 increased the anchorage-independent growth (AIG) and invasiveness of H1299 cells. In addition, we examined that knockdown of POLDIP2 in H1299 and A549 cells reduced tumorigenicity and metastatic capacity in vitro and also in vivo. Moreover, downregulation of the cell proliferation marker cyclin D1 and EMT markers CDH2, Slug, and Twist was showed in H1299 cells by POLDIP2 knockdown, suggesting that the inhibition of malignancy was affected by modulating key genes for tumor growth and invasiveness. Taken together, our study is the first study that demonstrated that POLDIP2 gene was function as an oncogene in NSCLC and implied the oncogenic ability might be through promoting cell proliferation or EMT.

Polymerase δ-interacting Protein 2: A Multifunctional Protein

Polymerase δ-interacting protein 2 (Poldip2) is a multifunctional protein originally described as a binding partner of the p50 subunit of DNA polymerase δ and proliferating cell nuclear antigen. In addition to its role in DNA replication and damage repair, Poldip2 has been implicated in mitochondrial function, extracellular matrix regulation, cell cycle progression, focal adhesion turnover, and cell migration. However, Poldip2 functions are incompletely understood. In this review, we discuss recent literature on Poldip2 tissue distribution, subcellular localization, and function. We also address the putative function of Poldip2 in cardiovascular disease, neurodegenerative conditions and in renal pathophysiology.

Regulation and Modulation of Human DNA Polymerase δ Activity and Function

This review focuses on the regulation and modulation of human DNA polymerase δ (Pol δ). The emphasis is on the mechanisms that regulate the activity and properties of Pol δ in DNA repair and replication. The areas covered are the degradation of the p12 subunit of Pol δ, which converts it from a heterotetramer (Pol δ4) to a heterotrimer (Pol δ3), in response to DNA damage and also during the cell cycle. The biochemical mechanisms that lead to degradation of p12 are reviewed, as well as the properties of Pol δ4 and Pol δ3 that provide insights into their functions in DNA replication and repair. The second focus of the review involves the functions of two Pol δ binding proteins, polymerase delta interaction protein 46 (PDIP46) and polymerase delta interaction protein 38 (PDIP38), both of which are multi-functional proteins. PDIP46 is a novel activator of Pol δ4, and the impact of this function is discussed in relation to its potential roles in DNA replication. Several new models for the roles of Pol δ3 and Pol δ4 in leading and lagging strand DNA synthesis that integrate a role for PDIP46 are presented. PDIP38 has multiple cellular localizations including the mitochondria, the spliceosomes and the nucleus. It has been implicated in a number of cellular functions, including the regulation of specialized DNA polymerases, mitosis, the DNA damage response, mouse double minute 2 homolog (Mdm2) alternative splicing and the regulation of the NADPH oxidase 4 (Nox4).

DNA Damage Tolerance by Eukaryotic DNA Polymerase and Primase PrimPol

PrimPol is a human deoxyribonucleic acid (DNA) polymerase that also possesses primase activity and is involved in DNA damage tolerance, the prevention of genome instability and mitochondrial DNA maintenance. In this review, we focus on recent advances in biochemical and crystallographic studies of PrimPol, as well as in identification of new protein-protein interaction partners. Furthermore, we discuss the possible functions of PrimPol in both the nucleus and the mitochondria.

Spatial Cross-Talk between Oxidative Stress and DNA Replication in Human Fibroblasts

MS-based proteomics has been applied to a differential network analysis of the nuclear-cytoplasmic subcellular distribution of proteins between cell-cycle arrest: (a) at the origin activation checkpoint for DNA replication, or (b) in response to oxidative stress. Significant changes were identified for 401 proteins. Cellular response combines changes in trafficking and in total abundance to vary the local compartmental abundances that are the basis of cellular response. Appreciable changes for both perturbations were observed for 245 proteins, but cross-talk between oxidative stress and DNA replication is dominated by 49 proteins that show strong changes for both. Many nuclear processes are influenced by a spatial switch involving the proteins {KPNA2, KPNB1, PCNA, PTMA, SET} and heme/iron proteins HMOX1 and FTH1. Dynamic spatial distribution data are presented for proteins involved in caveolae, extracellular matrix remodelling, TGFβ signaling, IGF pathways, emerin complexes, mitochondrial protein import complexes, spliceosomes, proteasomes, and so on. The data indicate that for spatially heterogeneous cells cross-compartmental communication is integral to their system biology, that coordinated spatial redistribution for crucial protein networks underlies many functional changes, and that information on dynamic spatial redistribution of proteins is essential to obtain comprehensive pictures of cellular function. We describe how spatial data of the type presented here can provide priorities for further investigation of crucial features of high-level spatial coordination across cells. We suggest that the present data are related to increasing indications that much of subcellular protein transport is constitutive and that perturbation of these constitutive transport processes may be related to cancer and other diseases. A quantitative, spatially resolved nucleus-cytoplasm interaction network is provided for further investigations.

Luminal flow induces NADPH oxidase 4 translocation to the nuclei of thick ascending limbs

Superoxide (O₂⁻) exerts its physiological actions in part by causing changes in gene transcription. In thick ascending limbs flow‐induced O₂⁻ production is mediated by NADPH oxidase 4 (Nox4) and is dependent on protein kinase C (PKC). Polymerase delta interacting protein 2 (Poldip2) increases Nox4 activity, but it is not known whether Nox4 translocates to the nucleus and whether Poldip2 participates in this process. We hypothesized that luminal flow causes Nox4 translocation to the nuclei of thick ascending limbs in a PKC‐dependent process facilitated by Poldip2. To test our hypothesis, we studied the subcellular localization of Nox4 and Poldip2 using confocal microscopy and O₂⁻ production in the absence and presence of luminal flow. Luminal flow increased the ratio of nuclear to cytoplasmic intensity of Nox4 (N/C) from 0.3 ± 0.1 to 0.7 ± 0.1 (P < 0.01) and O₂⁻ production from 89 ± 15 to 231 ± 16 AU/s (P < 0.001). In the presence of flow PKC inhibition reduced N/C from 0.5 ± 0.1 to 0.2 ± 0.1 (P < 0.01). Flow‐induced O₂⁻ production was also blocked (flow: 142 ± 20 AU/s; flow plus PKC inhibition 26 ± 12 AU/s; P < 0.01). The cytoskeleton disruptor cytochalasin D (1 μmol/L) decreased flow‐induced Nox4 translocation by 0.3 ± 0.01 (P < 0.01); however, it did not reduce flow‐induced O₂⁻. Flow did not alter Poldip2 localization. We conclude that: (1) luminal flow elicits Nox4 translocation to the nucleus in a PKC‐ and cytoskeleton‐dependent process; (2) Nox4 activation occurs before translocation; and (3) Poldip2 is not involved in Nox4 nuclear translocation. Flow‐induced Nox4 translocation to the nucleus may play a role in O₂⁻‐dependent changes in thick ascending limbs.

Nuclear cytoplasmic trafficking of proteins is a major response of human fibroblasts to oxidative stress

We have used a subcellular spatial razor approach based on LC-MS/MS-based proteomics with SILAC isotope labeling to determine changes in protein abundances in the nuclear and cytoplasmic compartments of human IMR90 fibroblasts subjected to mild oxidative stress. We show that response to mild tert-butyl hydrogen peroxide treatment includes redistribution between the nucleus and cytoplasm of numerous proteins not previously associated with oxidative stress. The 121 proteins with the most significant changes encompass proteins with known functions in a wide variety of subcellular locations and of cellular functional processes (transcription, signal transduction, autophagy, iron metabolism, TCA cycle, ATP synthesis) and are consistent with functional networks that are spatially dispersed across the cell. Both nuclear respiratory factor 2 and the proline regulatory axis appear to contribute to the cellular metabolic response. Proteins involved in iron metabolism or with iron/heme as a cofactor as well as mitochondrial proteins are prominent in the response. Evidence suggesting that nuclear import/export and vesicle-mediated protein transport contribute to the cellular response was obtained. We suggest that measurements of global changes in total cellular protein abundances need to be complemented with measurements of the dynamic subcellular spatial redistribution of proteins to obtain comprehensive pictures of cellular function.

Polymerase δ-interacting protein 2 promotes postischemic neovascularization of the mouse hindlimb

OBJECTIVE

Collateral vessel formation can functionally compensate for obstructive vascular lesions in patients with atherosclerosis. Neovascularization processes are triggered by fluid shear stress, hypoxia, growth factors, chemokines, proteases, and inflammation, as well as reactive oxygen species, in response to ischemia. Polymerase δ-interacting protein 2 (Poldip2) is a multifunctional protein that regulates focal adhesion turnover and vascular smooth muscle cell migration and modifies extracellular matrix composition. We, therefore, tested the hypothesis that loss of Poldip2 impairs collateral formation.

APPROACH AND RESULTS

The mouse hindlimb ischemia model has been used to understand mechanisms involved in postnatal blood vessel formation. Poldip2(+/-) mice were subjected to femoral artery excision, and functional and morphological analysis of blood vessel formation was performed after injury. Heterozygous deletion of Poldip2 decreased the blood flow recovery and spontaneous running activity at 21 days after injury. H2O2 production, as well as the activity of matrix metalloproteinases-2 and -9, was reduced in these animals compared with Poldip2(+/+) mice. Infiltration of macrophages in the peri-injury muscle was also decreased; however, macrophage phenotype was similar between genotypes. In addition, the formation of capillaries and arterioles was impaired, as was angiogenesis, in agreement with a decrease in proliferation observed in endothelial cells treated with small interfering RNA against Poldip2. Finally, regression of newly formed vessels and apoptosis was more pronounced in Poldip2(+/-) mice.

CONCLUSIONS

Together, these results suggest that Poldip2 promotes ischemia-induced collateral vessel formation via multiple mechanisms that likely involve reactive oxygen species-dependent activation of matrix metalloproteinase activity, as well as enhanced vascular cell growth and survival.

Poldip2 knockout results in perinatal lethality, reduced cellular growth and increased autophagy of mouse embryonic fibroblasts

Polymerase-δ interacting protein 2 (Poldip2) is an understudied protein, originally described as a binding partner of polymerase delta and proliferating cell nuclear antigen (PCNA). Numerous roles for Poldip2 have been proposed, including mitochondrial elongation, DNA replication/repair and ROS production via Nox4. In this study, we have identified a novel role for Poldip2 in regulating the cell cycle. We used a Poldip2 gene-trap mouse and found that homozygous animals die around the time of birth. Poldip2-/- embryos are significantly smaller than wild type or heterozygous embryos. We found that Poldip2-/- mouse embryonic fibroblasts (MEFs) exhibit reduced growth as measured by population doubling and growth curves. This effect is not due to apoptosis or senescence; however, Poldip2-/- MEFs have higher levels of the autophagy marker LC3b. Measurement of DNA content by flow cytometry revealed an increase in the percentage of Poldip2-/- cells in the G1 and G2/M phases of the cell cycle, accompanied by a decrease in the percentage of S-phase cells. Increases in p53 S20 and Sirt1 were observed in passage 2 Poldip2-/- MEFs. In passage 4/5 MEFs, Cdk1 and CyclinA2 are downregulated in Poldip2-/- cells, and these changes are reversed by transfection with SV40 large T-antigen, suggesting that Poldip2 may target the E2F pathway. In contrast, p21CIP1 is increased in passage 4/5 Poldip2-/- MEFs and its expression is unaffected by SV40 transfection. Overall, these results reveal that Poldip2 is an essential protein in development, and underline its importance in cell viability and proliferation. Because it affects the cell cycle, Poldip2 is a potential novel target for treating proliferative conditions such as cancer, atherosclerosis and restenosis.

DNA polymerase δ-interacting protein 2 is a processivity factor for DNA polymerase λ during 8-oxo-7,8-dihydroguanine bypass

The bypass of DNA lesions by the replication fork requires a switch between the replicative DNA polymerase (Pol) and a more specialized translesion synthesis (TLS) Pol to overcome the obstacle. DNA Pol δ-interacting protein 2 (PolDIP2) has been found to physically interact with Pol η, Pol ζ, and Rev1, suggesting a possible role of PolDIP2 in the TLS reaction. However, the consequences of PolDIP2 interaction on the properties of TLS Pols remain unknown. Here, we analyzed the effects of PolDIP2 on normal and TLS by five different human specialized Pols from three families: Pol δ (family B), Pol η and Pol ι (family Y), and Pol λ and Pol β (family X). Our results show that PolDIP2 also physically interacts with Pol λ, which is involved in the correct bypass of 8-oxo-7,8-dihydroguanine (8-oxo-G) lesions. This interaction increases both the processivity and catalytic efficiency of the error-free bypass of a 8-oxo-G lesion by both Pols η and λ, but not by Pols β or ι. Additionally, we provide evidence that PolDIP2 stimulates Pol δ without affecting its fidelity, facilitating the switch from Pol δ to Pol λ during 8-oxo-G TLS. PolDIP2 stimulates Pols λ and η mediated bypass of other common DNA lesions, such as abasic sites and cyclobutane thymine dimers. Finally, PolDIP2 silencing increases cell sensitivity to oxidative stress and its effect is further potentiated in a Pol λ deficient background, suggesting that PolDIP2 is an important mediator for TLS.

PDIP38 is translocated to the spliceosomes/nuclear speckles in response to UV-induced DNA damage and is required for UV-induced alternative splicing of MDM2

PDIP38 (polymerase delta interacting protein 38) was originally discovered as a protein that interacts with DNA polymerase δ and PCNA. PDIP38 is present in multiple intracellular locations and is a multifunctional protein that has been implicated in several diverse cellular functions. We investigated the nuclear localization of PDIP38 in order to gain insights to its response to UV damage. PDIP38 was found to form distinct nuclear foci in response to UV irradiation in several cell lines, including HeLa S3 and A549 cells. However, these foci were not those associated with UV repair foci. Using various markers for different nuclear subcompartments, the UV-induced PDIP38 foci were identified as spliceosomes/nuclear speckles, the storage and assembly sites for mRNA splicing factors. To assess the role of PDIP38 in the regulation of splicing events, the effects of PDIP38 depletion on the UV-induced alternate splicing of MDM2 transcripts were examined by nested RT-PCR. Alternatively spliced MDM2 products were induced by UV treatment but were greatly reduced in cells expressing shRNA targeting PDIP38. These findings indicate that upon UV-induced DNA damage, PDIP38 is translocated to spliceosomes and contributes to the UV-induced alternative splicing of MDM2 transcripts. Similar results were obtained when cells were subjected to transcriptional stresses with actinomycin D or α-amanitin. Taken together, these studies show that PDIP38 is a protein regulated in a dynamic manner in response to genotoxic stress, as evidenced by its translocation to the spliceosomes. Moreover, PDIP38 is required for the induction of the alternative splicing of MDM2 in response to UV irradiation.

Polymerase delta interacting protein 2 sustains vascular structure and function

OBJECTIVE

On the basis of previous evidence that polymerase delta interacting protein 2 (Poldip2) increases reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 4 (Nox4) activity in vascular smooth muscle cells, we hypothesized that in vivo knockdown of Poldip2 would inhibit reactive oxygen species production and alter vascular function.

APPROACH AND RESULTS

Because homozygous Poldip2 deletion is lethal, Poldip2(+/-) mice were used. Poldip2 mRNA and protein levels were reduced by ≈50% in Poldip2(+/-) aorta, with no change in p22phox, Nox1, Nox2, and Nox4 mRNAs. NADPH oxidase activity was also inhibited in Poldip2(+/-) tissue. Isolated aortas from Poldip2(+/-) mice demonstrated impaired phenylephrine and potassium chloride-induced contractions, increased stiffness, and reduced compliance associated with disruption of elastic lamellae and excessive extracellular matrix deposition. Collagen I secretion was elevated in cultured vascular smooth muscle cells from Poldip2(+/-) mice and restored by H2O2 supplementation, suggesting that this novel function of Poldip2 is mediated by reactive oxygen species. Furthermore, Poldip2(+/-) mice were protected against aortic dilatation in a model of experimental aneurysm, an effect consistent with increased collagen secretion.

CONCLUSIONS

Poldip2 knockdown reduces H2O2 production in vivo, leading to increases in extracellular matrix, greater vascular stiffness, and impaired agonist-mediated contraction. Thus, unaltered expression of Poldip2 is necessary for vascular integrity and function.

Novel Nox homologues in the vasculature: focusing on Nox4 and Nox5

The Noxes (NADPH oxidases) are a family of ROS (reactive oxygen species)-generating enzymes. Of the seven family members, four have been identified as important sources of ROS in the vasculature: Nox1, Nox2, Nox4 and Nox5. Although Nox isoforms can be influenced by the same stimulus and co-localize in cellular compartments, their tissue distribution, subcellular regulation, requirement for cofactors and NADPH oxidase subunits and ability to generate specific ROS differ, which may help to understand the multiplicity of biological functions of these oxidases. Nox4 and Nox5 are the newest isoforms identified in the vasculature. Nox4 is the major isoform expressed in renal cells and appear to produce primarily H2O2. The Nox5 isoform produces ROS in response to increased levels of intracellular Ca2+ and does not require the other NADPH oxidase subunits for its activation. The present review focuses on these unique Noxes, Nox4 and Nox5, and provides novel concepts related to the regulation and interaction in the vasculature, and discusses new potential roles for these isoforms in vascular biology.

Crosstalk between replicative and translesional DNA polymerases: PDIP38 interacts directly with Poleta

Replicative DNA polymerases duplicate genomes in a very efficient and accurate mode. However their progression can be blocked by DNA lesions since they are unable to accommodate bulky damaged bases in their active site. In response to replication blockage, monoubiquitination of PCNA promotes the switch between replicative and specialized polymerases proficient to overcome the obstacle. In this study, we characterize novel connections between proteins involved in replication and TransLesion Synthesis (TLS). We demonstrate that PDIP38 (Poldelta interacting protein of 38kDa) directly interacts with the TLS polymerase Poleta. Interestingly, the region of Poleta interacting with PDIP38 is found to be located within the ubiquitin-binding zinc finger domain (UBZ) of Poleta. We show that the depletion of PDIP38 increases the number of cells with Poleta foci in the absence of DNA damage and diminishes cell survival after UV irradiation. In addition, PDIP38 is able to interact directly not only with Poleta but also with the specialized polymerases Rev1 and Polzeta (via Rev7). We thus suggest that PDIP38 serves as a mediator protein helping TLS Pols to transiently replace replicative polymerases at damaged sites.

Complex sense-antisense architecture of TNFAIP1/POLDIP2 on 17q11.2 represents a novel transcriptional structural-functional gene module involved in breast cancer progression

Background

A sense-antisense gene pair (SAGP) is a gene pair where two oppositely transcribed genes share a common nucleotide sequence region. In eukaryotic genomes, SAGPs can be organized in complex sense-antisense architectures (CSAGAs) in which at least one sense gene shares loci with two or more antisense partners. As shown in several case studies, SAGPs may be involved in cancers, neurological diseases and complex syndromes. However, CSAGAs have not yet been characterized in the context of human disease or cancer.

Results

We characterize five genes (TMEM97, IFT20, TNFAIP1, POLDIP2 and TMEM199) organized in a CSAGA on 17q11.2 (we term this the TNFAIP1/POLDIP2 CSAGA) and demonstrate their strong and reproducible co-regulatory transcription pattern in breast cancer tumours. Genes of the TNFAIP1/POLDIP2 CSAGA are located inside the smallest region of recurrent amplification on 17q11.2 and their expression profile correlates with the DNA copy number of the region. Survival analysis of a group of 410 breast cancer patients revealed significant survival-associated individual genes and gene pairs in the TNFAIP1/POLDIP2 CSAGA. Moreover, several of the gene pairs associated with survival, demonstrated synergistic effects. Expression of genes-members of the TNFAIP1/POLDIP2 CSAGA also strongly correlated with expression of genes of ERBB2 core region of recurrent amplification on 17q12. We clearly demonstrate that the observed co-regulatory transcription profile of the TNFAIP1/POLDIP2 CSAGA is maintained not only by a DNA amplification mechanism, but also by chromatin remodelling and local transcription activation.

Conclusion

We have identified a novel TNFAIP1/POLDIP2 CSAGA and characterized its co-regulatory transcription profile in cancerous breast tissues. We suggest that the TNFAIP1/POLDIP2 CSAGA represents a clinically significant transcriptional structural-functional gene module associated with amplification of the genomic region on 17q11.2 and correlated with expression ERBB2 amplicon core genes in breast cancer. Co-expression pattern of this module correlates with histological grades and a poor prognosis in breast cancer when over-expressed. TNFAIP1/POLDIP2 CSAGA maps the risks of breast cancer relapse onto the complex genomic locus on 17q11.2.

Poldip2, a novel regulator of Nox4 and cytoskeletal integrity in vascular smooth muscle cells

RATIONALE

NADPH oxidases (Noxes) regulate vascular physiology and contribute to the pathogenesis of vascular disease. In vascular smooth muscle cells (VSMCs), the interactions of individual Nox homologs with regulatory proteins are poorly defined.

OBJECTIVE

The objective of this study was to identify novel NADPH oxidase regulatory proteins.

METHODS AND RESULTS

Using a yeast 2-hybrid screen, we identified a novel p22phox binding partner, Poldip2, and demonstrated that it associates with p22phox, NADPH oxidase (Nox)1, and Nox4 and colocalizes with p22phox at sites of Nox4 localization. Poldip2 increases Nox4 enzymatic activity by 3-fold and positively regulates basal reactive oxygen species production in VSMCs (O2(.-): 86.3+/-15.6% increase; H2O2: 40.7+/-4.5% increase). Overexpression of Poldip2 activates Rho (180.2+/-24.8% increase), strengthens focal adhesions, and increases stress fiber formation. These phenotypic changes are blocked by dominant negative Rho. In contrast, depletion of either Poldip2 or Nox4 results in a loss of these structures, which is rescued by adding back active Rho. Cell migration, which requires dynamic cytoskeletal remodeling, is impaired by either excess (70.1+/-14.7% decrease) or insufficient Poldip2 (63.5+/-5.9% decrease).

CONCLUSIONS

These results suggest that Poldip2 associates with p22phox to activate Nox4, leading to regulation of focal adhesion turnover and VSMC migration, thus linking reactive oxygen species production and cytoskeletal remodeling. Poldip2 may be a novel therapeutic target for vascular pathologies with a significant VSMC migratory component, such as restenosis and atherosclerosis.

Direct interaction of tumor suppressor CEACAM1 with beta catenin: identification of key residues in the long cytoplasmic domain

CEACAM1-4L (carcinoembryonic antigen cell adhesion molecule 1, with 4 extracellular Ig-like domains and a long, 71 amino acid cytoplasmic domain) is expressed in epithelial cells and activated T-cells, but is down-regulated in most epithelial cell cancers and T-cell leukemias. A highly conserved sequence within the cytoplasmic domain has ca 50% sequence homology with Tcf-3 and -4, transcription factors that bind beta-catenin, and to a lesser extent (32% homology), with E-cadherin that also binds beta-catenin. We show by quantitative yeast two-hybrid, BIAcore, GST-pull down, and confocal analyses that this domain directly interacts with beta-catenin, and that H-469 and K-470 are key residues that interact with the armadillo repeats of beta-catenin. Jurkat cells transfected with CEACAM1-4L have 2-fold less activity in the TOPFLASH reporter assay, and in MCF7 breast cancer cells that fail to express CEACAM1, transfection with CEACAM1 and growth in Ca2+ media causes redistribution of beta-catenin from the cytoplasm to the cell membrane, demonstrating a functional role for the long cytoplasmic domain of CEACAM1 in regulation of beta-catenin activity.