Proliferating Cell Nuclear Antigen Function Research Articles

The Functions of PCNA in Tumor Stemness and Invasion.

Invasion is the most prominent lethal feature of malignant cancer. However, how cell proliferation, another important feature of tumor development, is integrated with tumor invasion and the subsequent cell dissemination from primary tumors is not well understood. Proliferating cell nuclear antigen (PCNA) is essential for DNA replication in cancer cells. Loss of phosphorylation at tyrosine 211 (Y211) in PCNA (pY211-PCNA) mitigates PCNA function in proliferation, triggers replication fork arrest/collapse, which in turn sets off an anti-tumor inflammatory response, and suppresses distant metastasis. Here, we show that pY211-PCNA is important in stromal activation in tumor tissues. Loss of the phosphorylation resulted in reduced expression of mesenchymal proteins as well as tumor progenitor markers, and of the ability of invasion. Spontaneous mammary tumors that developed in mice lacking Y211 phosphorylation contained fewer tumor-initiating cells compared to tumors in wild-type mice. Our study demonstrates a novel function of PCNA as an essential factor for maintaining cancer stemness through Y211 phosphorylation.

Identifying Cellular and Viral Factor Recruitment to Herpes Simplex Virus Type 1 Replication Forks

Herpes simplex virus type 1 (HSV‐1) is a ubiquitous pathogen that replicates the 152kbp viral genome within the nucleus of host cells. Replication of the HSV‐1 genome is catalyzed by viral replication machinery consisting of a DNA polymerase (UL30), processivity factor (UL42), helicase‐primase complex, origin binding protein (UL9), and a single stranded DNA binding protein. Despite encoding a viral DNA polymerase processivity factor, we found that host Proliferating Cell Nuclear Antigen (PCNA) interacts with HSV‐1 DNA at replication forks and associates with viral DNA in a replication‐dependent manner. PCNA is a homotrimer that provides processivity to cellular DNA polymerases and selectively recruits DNA damage response and DNA repair factors to cellular replication forks. We therefore hypothesized that PCNA associates at viral replication forks to promote HSV‐1 replication while also tethering cellular DNA repair proteins to replicating viral DNA. To test this, we used two models to identify how associated factors change as a function of PCNA: a known PCNA inhibitor, PCNA‐I1, and a cell line that was engineered to inducibly express a shRNA targeting PCNA. We performed a technique adapted from isolation of proteins on nascent DNA (iPOND) to isolate HSV‐1 DNA from infected cells and identified associated viral and cellular proteins. Cells were infected and replicating viral DNA was selectively labeled with EdC. Labeled DNA was specifically and irreversibly tagged via the covalent attachment of biotin azide via click reaction. Biotin‐tagged DNA was purified on streptavidin‐coated beads and associated proteins were eluted and identified by mass spectrometry. As a complimentary approach, we also performed immunofluorescence (IF) to confirm iPOND data. We found that PCNA is associated with viral DNA despite treatment with PCNA‐I1, an observation that is consistent with IF imaging data. Viral replication proteins UL30, UL42, and UL9 decreased in the presence of PCNA‐I1. DNA damage response proteins such as mismatch repair proteins and RECQL both decreased up to 10‐fold. Of note, however, proteins that make up the MRN complex, a class of proteins that functions in DNA break repair, restart of stalled replication forks, and viral DNA infection, increased in response to PCNA‐I1 treatment. Given this data, PCNA may be involved in tethering viral replication proteins, cellular DNA repair proteins, and/or virion assembly proteins to viral replication forks.

Blocking the PCNA/NKp44 Checkpoint to Stimulate NK Cell Responses to Multiple Myeloma.

Simple SummaryMembrane-associated PCNA is expressed on the surface of human MM cell lines and primary MM cells. Mab 14-25-9 interacts with membrane-associated PCNA and blocks its binding to NK-expressed NKp44, thus activating NK function. We showed that mAb 14-25-9 can serve as an immune checkpoint blocker, enhancing the function of NK cells on target human MM cell lines and primary cells.Multiple Myeloma (MM) is a devastating malignancy that evades immune destruction using multiple mechanisms. The NKp44 receptor interacts with PCNA (Proliferating Cell Nuclear Antigen) and may inhibit NK cells’ functions. Here we studied in vitro the expression and function of PCNA on MM cells. First, we show that PCNA is present on the cell membrane of five out of six MM cell lines, using novel anti-PCNA mAb developed to recognize membrane-associated PCNA. Next, we stained primary bone marrow (BM) mononuclear cells from MM patients and showed significant staining of membrane-associated PCNA in the fraction of CD38+CD138+ BM cells that contain the MM cells. Importantly, blocking of the membrane PCNA on MM cells enhanced the activity of NK cells, including IFN-γ-secretion and degranulation. Our results highlight the possible blocking of the NKp44-PCNA immune checkpoint by the mAb 14-25-9 antibody to enhance NK cell responses against MM, providing a novel treatment option.

Something’s gotta give: How PCNA alters its structure in response to mutations and the implications on cellular processes

Proliferating cell nuclear antigen (PCNA) is an essential protein that regulates the systematic recruitment and activity of proteins in a multitude of biochemical processes. Very few proteins, if any, bear similar responsibilities to those of PCNA, and its list of roles only continues to expand. However, even as one of the most well-studied proteins in research, many questions still remain about the complex quaternary structure and function of PCNA. Over the last forty years, we have gained a considerable amount of insight from studying amino acid substitutions within the protein. The combination of phenotypic and structural information about mutant PCNA proteins has shed light on the incredibly dynamic and accommodating nature of this important protein and why it stands at the crossroads of DNA metabolic pathways.

Human PCNA Structure, Function and Interactions.

Proliferating cell nuclear antigen (PCNA) is an essential factor in DNA replication and repair. It forms a homotrimeric ring that embraces the DNA and slides along it, anchoring DNA polymerases and other DNA editing enzymes. It also interacts with regulatory proteins through a sequence motif known as PCNA Interacting Protein box (PIP-box). We here review the latest contributions to knowledge regarding the structure-function relationships in human PCNA, particularly the mechanism of sliding, and of the molecular recognition of canonical and non-canonical PIP motifs. The unique binding mode of the oncogene p15 is described in detail, and the implications of the recently discovered structure of PCNA bound to polymerase δ are discussed. The study of the post-translational modifications of PCNA and its partners may yield therapeutic opportunities in cancer treatment, in addition to illuminating the way PCNA coordinates the dynamic exchange of its many partners in DNA replication and repair.

Dissecting PCNA function with a systematically designed mutant library in yeast

Proliferating cell nuclear antigen (PCNA), encoded by POL30 in Saccharomyces cerevisiae, is a key component of DNA metabolism. Here, a library consisting of 304 PCNA mutants was designed and constructed to probe the contribution of each residue to the biological function of PCNA. Five regions with elevated sensitivity to DNA damaging reagents were identified using high-throughput phenotype screening. Using a series of genetic and biochemical analyses, we demonstrated that one particular mutant, K168A, has defects in the DNA damage tolerance (DDT) pathway by disrupting the interaction between PCNA and Rad5. Subsequent domain analysis showed that the PCNA-Rad5 interaction is a prerequisite for the function of Rad5 in DDT. Our study not only provides a resource in the form of a library of versatile mutants to study the functions of PCNA, but also reveals a key residue on PCNA (K168) which highlights the importance of the PCNA-Rad5 interaction in the template switching (TS) pathway.

Mechanistic study of the superior anti-cancer properties of a first-in-class small molecule targeting PCNA.

e14636 Background: Proliferating cell nuclear antigen (PCNA), through its interaction with various proteins involved in DNA synthesis, cell cycle regulation, and DNA repair, plays a central role in maintaining genome stability. We previously reported a novel cancer associated PCNA isoform (dubbed caPCNA), which was predominantly expressed in a broad range of cancer cells and tumor tissues, but not significantly in non-malignant cells. We found that the caPCNA-specific antigenic site lies between L126 and Y133, a region within the interdomain connector loop of PCNA that is known to be a major binding site for many of PCNA’s interacting proteins. A cell permeable peptide harboring the L126-Y133 sequence inhibited PCNA function in cancer cells and selectively kills cancer cells and xenograft tumors. Methods: Based on these observations, we sought small molecules targeting this peptide region of PCNA as potential broad-spectrum anti-cancer agents. Results: Our effort led to a drug candidate, AOH1996, which selectively kills a broad range of cancer cells at high nanomolar concentrations, but is not associated with significant toxicity to non-malignant cells. It also works synergistically with DNA damaging chemotherapeutic drugs, such as cisplatin and irinotecan, to selectively kill cancer cells. This compound is orally available to animals and suppresses tumor growth in a dosage form compatible to clinical applications. Importantly, it doesn’t cause significant toxicity at 2.5 times its effective dose. Mechanistically, AOH1996 competes with T3, a known PCNA ligand, for binding to PCNA. However, the mechanism by which AOH1996 exerts its effect on cancer cells may not be identical to what have been reported for the T3 analogs. In particular, we found that AOH1996 interferes with the association of PCNA and MCM7 to euchromatin, leading to DNA replication stress, blockade of homologous recombination-mediated DNA repair, and induction of apoptosis in cancer cells. Conclusions: These findings demonstrated the potential of this compound as a novel therapeutic agent warranting clinical investigation for cancer treatment. We have started planning a phase 1 clinical study for this compound.

Cloning and comparative studies of proliferating cell nuclear antigen (PCNA) genes for nine dinoflagellates

Proliferating cell nuclear antigen (PCNA), a co-factor of DNA polymerases δ and e, is associated with active cell proliferation, particularly with the S phase of the eukaryotic cell cycle, and the expression of this gene has been therefore proposed as a molecular marker for estimating phytoplankton growth rate and even population dynamics. In this study, the full-length cDNA sequences of PCNA for nine dinoflagellate species (ten strains) were obtained, analyzed, and further characterized with the expression in response to alterations of growth stage and life cycle. All the ten genes have a 777 or 780 bp ORF and encode a protein of 258 or 259 amino acids, similar to PCNAs from vertebrates and plants. The deduced amino acid sequences include conservative motif characteristic to the PCNA gene family, implying conserved functions of PCNA among organisms of different taxa. Alignment analysis in combination with other sequences available in NCBI database exhibited high amino acid similarities (79.2–96.9%) among PCNAs from 17 dinoflagellate species. Phylogenetic tree derived from 37 PCNA sequences of dinoflagellates was consistent with the taxonomic affiliation of these taxa. Then, we used the cosmopolitan, toxic, and resting cyst-producing dinoflagellate Scrippsiella trochoidea as a representative of HAB-forming dinoflagellates to investigate PCNA (StPCNA) expression at different stages of growth and life cycle and the results of real-time quantitative PCR revealed clearly a stage-dependent pattern in the transcription of StPCNA. The transcripts dramatically reduced from an exponential to a stationary growth stage and then further significantly decreased from a stationary stage to dormant stage (resting cysts), a pattern in accordance with that previously reported from the dinoflagellates Alexandrium catenella and Prorocentrum donghaiense. In terms of its minimal implication, this work enhances the previous perception about the function and possible application of PCNA gene, and more importantly, our results indicated that PCNA is not silent during the dormant stage of dinoflagellates.

Phosphorylation of proliferating cell nuclear antigen promotes cancer progression by activating the ATM/Akt/GSK3β/Snail signaling pathway

Proliferating cell nuclear antigen (PCNA) and its posttranslational modifications regulate DNA metabolic reactions, including DNA replication and repair, at replication forks. PCNA phosphorylation at Tyr-211 (PCNA-Y211p) inhibits DNA mismatch repair and induces misincorporation during DNA synthesis. Here, we describe an unexpected role of PCNA-Y211p in cancer promotion and development. Cells expressing phosphorylation-mimicking PCNA, PCNA-Y211D, show elevated hallmarks specific to the epithelial-mesenchymal transition (EMT), including the up-regulation of the EMT-promoting factor Snail and the down-regulation of EMT-inhibitory factors E-cadherin and GSK3β. The PCNA-Y211D-expressing cells also exhibited active cell migration and underwent G2/M arrest. Interestingly, all of these EMT-associated activities required the activation of ATM and Akt kinases, as inactivating these protein kinases by gene knockdown or inhibitors blocked EMT-associated signaling and cell migration. We concluded that PCNA phosphorylation promotes cancer progression via the ATM/Akt/GSK3β/Snail signaling pathway. In conclusion, this study identifies a novel PCNA function and reveals the molecular basis of phosphorylated PCNA-mediated cancer development and progression.

Proliferating cell nuclear antigen promotes cell proliferation and tumorigenesis by up-regulating STAT3 in non-small cell lung cancer

Proliferating cell nuclear antigen (PCNA) functions as a bridging molecule, which targets proteins that have distinct roles in cell growth. The expression of PCNA is dysregulated in some tumors and takes part in the progression of oncogenesis. However, the roles of PCNA in the progression of non-small cell lung cancer (NSCLC) remain unknown. The present study aimed to investigate the function of PCNA in the occurrence and development of NSCLC and its underlying molecular mechanisms. Western blotting, RT-PCR, and immunohistochemistry assays were used to detect the expression pattern of PCNA in NSCLC tissues and cells. A log rank test was performed to compare the overall survival (OS) of patients with high/low expression of PCNA. Besides, the relationship between PCNA and signal transducer and activator of transcription-3 (STAT3) proteins were evaluated. Then, MTT, flow cytometry, clonal formation, and in vivo xenograft assays were conducted to investigate the effects of PCNA/STAT3 on cell growth, clonal formation, apoptosis, and tumorigenesis. Results showed that PCNA expression was elevated in NSCLC tissues and cells and it could combine with STAT3 and increased its expression and phosphorylation. Moreover, the expression of PCNA showed a positive correlation with the TNM grade and occurrence rate of the lymphatic metastasis and poor prognosis of NSCLC patients. Overexpression of PCNA promoted cell proliferation, clonal formation, and tumorigenesis in lung cancer cells and inhibited cell apoptosis. In contrast, these effects were inhibited when knockdown of STAT3. In conclusion, this study demonstrates that PCNA functions as an oncogene in the progression of NSCLC through up-regulation of STAT3. These findings point to a potentially new therapeutic strategy for NSCLC.

NKp44-Derived Peptide Binds Proliferating Cell Nuclear Antigen and Mediates Tumor Cell Death.

Proliferating cell nuclear antigen (PCNA) is considered as a hub protein and is a key regulator of DNA replication, repair, cell cycle control, and apoptosis. PCNA is overexpressed in many cancer types, and PCNA overexpression is correlated with cancer virulence. Membrane-associated PCNA is a ligand for the NKp44 (NCR2) innate immune receptor. The purpose of this study was to characterize the PCNA-binding site within NKp44. We have identified NKp44-derived linear peptide (pep8), which can specifically interact with PCNA and partly block the NKp44–PCNA interaction. We then tested whether NKp44-derived pep8 (NKp44-pep8) fused to cell-penetrating peptides (CPPs) can be employed for targeting the intracellular PCNA for the purpose of anticancer therapy. Treatment of tumor cells with NKp44-pep8, fused to R11-NLS cell-penetrating peptide (R11-NLS-pep8), reduced cell viability and promoted cell death, in various murine and human cancer cell lines. Administration of R11-NLS-pep8 to tumor-bearing mice suppressed tumor growth in the 4T1 breast cancer and the B16 melanoma in vivo models. We therefore identified the NKp44 binding site to PCNA and further developed an NKp44-peptide-based agent that can inhibit tumor growth through interfering with the function of intracellular PCNA in the tumor cell.

Physical and functional interplay between PCNA DNA clamp and Mre11-Rad50 complex from the archaeon Pyrococcus furiosus.

Several archaeal species prevalent in extreme environments are particularly exposed to factors likely to cause DNA damages. These include hyperthermophilic archaea (HA), living at temperatures >70°C, which arguably have efficient strategies and robust genome guardians to repair DNA damage threatening their genome integrity. In contrast to Eukarya and other archaea, homologous recombination appears to be a vital pathway in HA, and the Mre11–Rad50 complex exerts a broad influence on the initiation of this DNA damage response process. In a previous study, we identified a physical association between the Proliferating Cell Nuclear Antigen (PCNA) and the Mre11–Rad50 (MR) complex. Here, by performing co-immunoprecipitation and SPR analyses, we identified a short motif in the C- terminal portion of Pyrococcus furiosus Mre11 involved in the interaction with PCNA. Through this work, we revealed a PCNA-interaction motif corresponding to a variation on the PIP motif theme which is conserved among Mre11 sequences of Thermococcale species. Additionally, we demonstrated functional interplay in vitro between P. furiosus PCNA and MR enzymatic functions in the DNA end resection process. At physiological ionic strength, PCNA stimulates MR nuclease activities for DNA end resection and promotes an endonucleolytic incision proximal to the 5′ strand of double strand DNA break.

The herpes simplex virus 1 UL36USP deubiquitinase suppresses DNA repair in host cells via deubiquitination of proliferating cell nuclear antigen

Herpes simplex virus 1 (HSV-1) infection manipulates distinct host DNA-damage responses to facilitate virus proliferation, but the molecular mechanisms remain to be elucidated. One possible HSV-1 target might be DNA damage-tolerance mechanisms, such as the translesion synthesis (TLS) pathway. In TLS, proliferating cell nuclear antigen (PCNA) is monoubiquitinated in response to DNA damage-caused replication fork stalling. Ubiquitinated PCNA then facilitates the error-prone DNA polymerase η (polη)-mediated TLS, allowing the fork to bypass damaged sites. Because of the involvement of PCNA ubiquitination in DNA-damage repair, we hypothesized that the function of PCNA might be altered by HSV-1. Here we show that PCNA is a substrate of the HSV-1 deubiquitinase UL36USP, which has previously been shown to be involved mainly in virus uptake and maturation. In HSV-1-infected cells, viral infection-associated UL36USP consistently reduced PCNA ubiquitination. The deubiquitination of PCNA inhibited the formation of polη foci and also increased cell sensitivity to DNA-damage agents. Moreover, the catalytically inactive mutant UL36C40A failed to deubiquitinate PCNA. Of note, the levels of virus marker genes increased strikingly in cells infected with wild-type HSV-1, but only moderately in UL36C40A mutant virus-infected cells, indicating that the UL36USP deubiquitinating activity supports HSV-1 virus replication during infection. These findings suggest a role of UL36USP in the DNA damage-response pathway.

Functional Analysis of the Role of Phosphorylated PCNA in Cancer Development and its Potential in Cancer Therapy

Proliferating cell nuclear antigen (PCNA), a ring‐shaped homotrimer, is an essential factor in DNA metabolism including DNA replication and repair. PCNA functions in these reactions appear to be regulated by posttranslational modifications, such as ubiquitylation, sumoylation and phosphorylation. Recently, we have shown that PCNA phosphorylation by EGFR at tyrosine 211 (Y211) disrupts PCNA interactions with mismatch recognition proteins, thereby inhibiting DNA mismatch repair (MMR). In addition, phosphorylated PCNA promotes misincorporation during DNA replication. However, it is unknown whether one, two or all three phosphorylated subunits are responsible for MMR inhibition and error‐prone DNA synthesis. To answer this question, we created a series of phosphorylation‐mimicking and non‐phosphorylation‐mimicking PCNA molecules with variously phosphorylated subunits, and examined their roles in MMR and DNA synthesis in vitro and in vivo. Our biochemical experiments reveal that all forms of phosphorylated PCNA inhibit MMR, with the inhibition activity proportional to the increased levels of phosphorylation; all forms of phosphorylated PCNA slow down the speed of DNA synthesis while conducting error‐prone DNA synthesis. Our in vivo data show that high‐levels of PCNA phosphorylation induce cell death. This study therefore provides novel mechanisms for phosphorylated PCNA in cancer development and its potential role in cancer therapy.Support or Funding InformationThis work is supported in part by grants from National Natural Science Foundation of China (31370766), by Tsinghua‐Peking Joint Center for Life Sciences, and by National Institutes of Health of the United States (GM089684).

PCNA is recruited to irradiated chromatin in late S-phase and is most pronounced in G2 phase of the cell cycle.

DNA repair is a complex process that prevents genomic instability. Many proteins play fundamental roles in regulating the optimal repair of DNA lesions. Proliferating cell nuclear antigen (PCNA) is a key factor that initiates recombination-associated DNA synthesis after injury. Here, in very early S-phase, we show that the fluorescence intensity of mCherry-tagged PCNA after local micro-irradiation was less than the fluorescence intensity of non-irradiated mCherry-PCNA-positive replication foci. However, PCNA protein accumulated at locally irradiated chromatin in very late S-phase of the cell cycle, and this effect was more pronounced in the following G2 phase. In comparison to the dispersed form of PCNA, a reduced mobile fraction appeared in PCNA-positive replication foci during S-phase, and we observed similar recovery time after photobleaching at locally induced DNA lesions. This diffusion of mCherry-PCNA in micro-irradiated regions was not affected by cell cycle phases. We also studied the link between function of PCNA and A-type lamins in late S-phase. We found that the accumulation of PCNA at micro-irradiated chromatin is identical in wild-type and A-type lamin-deficient cells. Only micro-irradiation of the nuclear interior, and thus the irradiation of internal A-type lamins, caused the fluorescence intensity of mCherry-tagged PCNA to increase. In summary, we showed that PCNA begins to play a role in DNA repair in late S-phase and that PCNA function in repair is maintained during the G2 phase of the cell cycle. However, PCNA mobility is reduced after local micro-irradiation regardless of the cell cycle phase.

Quaternary structures of human cytoplasmic and nuclear PCNA are the same

Properties and mechanisms of PCNA (proliferating cell nuclear antigen) functions have been investigated for a long time and are studied in great detail. As follows from its name, most known PCNA functions (DNA replication, DNA repair, DNA recombination and others) are connected with cell proliferation and localization of this protein in nuclei. In addition, there is good reason to believe that PCNA also performs some functions in the cytoplasm. However, the possible role and mechanisms of PCNA action in the cytoplasm require careful study and clarification. Interestingly, such cells as neutrophils differ in that they are non-dividing on one hand and on the other hand contain a rather large amount of PCNA, which is localized only in the cytoplasm, that is, they are an ideal model for the study of cytoplasmic PCNA. Using cross-linkages with formaldehyde, we showed that this cytoplasmic PCNA is cross-linked in a similar way, that is, organized in the same way as the nuclear PCNA that is present in the proliferating cells. Previously, we showed that PCNA in such cells is organized into a dynamic complex of double trimer on the basis of the back-to-back principle (Naryzhny S.N. et al. (2005) J. Biol. Chem., 280, 13888). Apparently, such organization of this hub-protein allows it to better coordinate the processes taking place in the cytoplasm as well.

Proliferating cell nuclear antigen in neutrophil fate.

The life span of a neutrophil is a tightly regulated process as extended survival is beneficial for pathogen elimination and cell death necessary to prevent cytotoxic content release from activated neutrophils at the inflammatory site. Therefore, the control between survival and death must be a dynamic process. We have previously described that proliferating cell nuclear antigen (PCNA) which is known as a nuclear protein pivotal in DNA synthesis, is a key element in controlling neutrophil survival through its association with procaspases. Contrary to the dogma which asserted that PCNA has a strictly nuclear function, in mature neutrophils, PCNA is present exclusively within the cytosol due to its nuclear export at the end of the granulocytic differentiation. More recent studies are consistent with the notion that the cytosolic scaffold of PCNA is aimed at modulating neutrophil fate rather than simply preventing death. Ultimately, targeting neutrophil survival might have important applications not just in the field of immunology and inflammation, but also in hematology and transfusion. The neutrophil emerges as a unique and powerful cellular model to unravel the basic mechanisms governing the cell cycle-independent functions of PCNA and should be considered as a leader of the pack.

The Many Roles of PCNA in Eukaryotic DNA Replication.

Proliferating cell nuclear antigen (PCNA) plays critical roles in many aspects of DNA replication and replication-associated processes, including translesion synthesis, error-free damage bypass, break-induced replication, mismatch repair, and chromatin assembly. Since its discovery, our view of PCNA has evolved from a replication accessory factor to the hub protein in a large protein-protein interaction network that organizes and orchestrates many of the key events at the replication fork. We begin this review article with an overview of the structure and function of PCNA. We discuss the ways its many interacting partners bind and how these interactions are regulated by posttranslational modifications such as ubiquitylation and sumoylation. We then explore the many roles of PCNA in normal DNA replication and in replication-coupled DNA damage tolerance and repair processes. We conclude by considering how PCNA can interact physically with so many binding partners to carry out its numerous roles. We propose that there is a large, dynamic network of linked PCNA molecules at and around the replication fork. This network would serve to increase the local concentration of all the proteins necessary for DNA replication and replication-associated processes and to regulate their various activities.

Structural and Functional Insight into Proliferating Cell Nuclear Antigen.

Proliferating cell nuclear antigen (PCNA) is a critical eukaryotic replication accessory factor that supports DNA binding in DNA processing, such as DNA replication, repair, and recombination. PCNA consists of three toroidal-shaped monomers that encircle doublestranded DNA. The diverse functions of PCNA may be regulated by its interactions with partner proteins. Many of the PCNA partner proteins generally have a conserved PCNAinteracting peptide (PIP) motif, located at the N- or C- terminal region. The PIP motif forms a 310 helix that enters into the hydrophobic groove produced by an interdomain-connecting loop, a central loop, and a C-terminal tail in the PCNA. Post-translational modification of PCNA also plays a critical role in regulation of its function and binding partner proteins. Structural and biochemical studies of PCNA-protein will be useful in designing therapeutic agents, as well as estimating the outcome of anticancer drug development. This review summarizes the characterization of eukaryotic PCNA in relation to the protein structures, functions, and modifications, and interaction with proteins.

Proliferating Cell Nuclear Antigen Has an Association with Prognosis and Risks Factors of Cancer Patients: a Systematic Review.

Proliferating cell nuclear antigen (PCNA) is reported as a famous marker in various tumors. A couple of articles have been published about the clinical function of PCNA on cancer progression; however, these results are conflicting in some degree. Thus, it is crucial to perform a systematic review and meta-analysis to identify their real actions. Here, we took cervical cancer and glioma as example and then pooled hazard ratios (HRs) or odds ratios (ORs) with 95% confidence intervals (95% CIs). In the present study, the PCNA expression in cervical cancer and gliomas patients was both correlated with 5-year-overall survival (OS) (HR = 4.41, 95% CI 2.71-7.17, p = 0.000; HR = 4.40, 95% CI 3.00-6.47, p = 0.000; respectively). In addition, a fixed effect model revealed a significant association between PCNA and FIGO stage (OR = 4.48, 95% CI 3.48-5.77, p = 0.000) or WHO grade (OR = 5.64, 95% CI 4.15-7.68, p = 0.000), rather than age (OR = 1.01, 95% CI 0.71-1.43, p = 0.957; OR = 1.00, 95% CI 0.80-1.24, p = 0.989; respectively). No heterogeneity was observed across all studies. According to funnel plot, no publication bias was reported. In conclusion, our systematic review suggests that PCNA expression is significantly associated with poor 5-year survival, advanced stage or higher WHO grade, which might be suggested as a useful prognostic and diagnostic biomarker, or an effective therapy target in cervical cancer, gliomas, or even more cancers.