Reactivity of anti-proliferating cell nuclear antigen (PCNA) murine monoclonal antibodies and human autoantibodies to the PCNA multiprotein complexes involved in cell proliferation

The implication of autoantibodies in early diagnosis and monitoring of plasmonic photothermal therapy in the treatment of feline mammary carcinoma

Feline mammary carcinoma (FMC) shows great similarities to human breast cancer in the cellular and molecular levels. So, in cats as in humans, the role of immune responses is indicated to detect and follow up the development of tumors. As a new breast cancer therapeutic approach, Plasmonic Photothermal Therapy (PPTT) is an effective localized treatment for canine and feline mammary-carcinoma. Its systemic effect has not been inquired yet and needs many studies to hypothesis how the PPTT eradicates tumor cells. In this study, it is the first time to detect (P53, PCNA, MUC-1, and C-MYC) feline autoantibodies (AAbs), study the relationship between PCNA AAbs and mammary-tumors, and investigate the effect of PPTT on the humoral immune response of cats with mammary-carcinoma through detection of AAbs level before, during, and after the treatment. The four-AAbs panel was evaluated in serum of normal and clinically diagnosed cats with mammary tumors using Enzyme-Linked Immunosorbent Assay. The panel showed 100% specificity and 93.7% sensitivity to mammary tumors. The panel was evaluated in PPTT monotherapy, mastectomy monotherapy, and combination therapy. PPTT monotherapy decreased AAbs level significantly while mastectomy monotherapy and combination therapy had a nonsignificant effect on AAbs level.

Dissection of affinity captured LINE-1 macromolecular complexes

Long Interspersed Nuclear Element-1 (LINE-1, L1) is a mobile genetic element active in human genomes. L1-encoded ORF1 and ORF2 proteins bind L1 RNAs, forming ribonucleoproteins (RNPs). These RNPs interact with diverse host proteins, some repressive and others required for the L1 lifecycle. Using differential affinity purifications, quantitative mass spectrometry, and next generation RNA sequencing, we have characterized the proteins and nucleic acids associated with distinctive, enzymatically active L1 macromolecular complexes. Among them, we describe a cytoplasmic intermediate that we hypothesize to be the canonical ORF1p/ORF2p/L1-RNA-containing RNP, and we describe a nuclear population containing ORF2p, but lacking ORF1p, which likely contains host factors participating in target-primed reverse transcription.

Antibody against chromatin assembly factor-1 is a novel autoantibody specifically recognized in systemic lupus erythematosus

Autoantibodies to proliferating cell nuclear antigen (PCNA) are specifically, if rarely, present in systemic lupus erythematosus (SLE) patient sera. Even SLE patients lacking PCNA reactivity often show reaction to PCNA-binding protein. Here, immunoreactivity to chromatin assembly factor-1 (CAF-1), an essential molecule for DNA replication and a PCNA-binding protein, was compared for the sera of SLE patients, normal healthy controls (NHCs) and other disease controls, and in autoimmune sera reactive to standard autoantigens, by enzyme-linked immunosorbent assay (ELISA), indirect immunofluorescence, and immunoblotting. CAF1 and IRF1 expression in SLE and NHC peripheral mononuclear cells were compared by quantitative real-time polymerase chain reaction. Serum interferon-γ-inducing protein-10 and anti-double-stranded (ds)DNA antibody levels were measured by ELISA. Increased CAF-1 autoimmune reactivity was recognized in SLE or serum anti-dsDNA antibody-positive patients. Significantly greater central nervous system (CNS) involvement (aseptic meningitis) and serum anti-dsDNA antibody titers were present more often in anti-CAF-1 antibody-positive than antibody-negative SLE patients. IFN-γ positively regulated CAF-1 expression in vitro and was associated with anti-CAF-1 antibody production in SLE. Thus, a novel anti-CAF-1 autoantibody is frequently found in patients with SLE and is a useful biomarker for diagnosis, especially in cases with CNS involvement. Aberrant IFN-γ regulation appears to play an important role in anti-CAF-1 antibody production in SLE.

Novel diagnostic and clinical aspects of anti-PCNA antibodies detected by novel detection methods

Autoantibodies targeting the proliferating cell nuclear antigen have been considered as a specific biomarker for systemic lupus erythematosus, and were historically identified by indirect immunofluorescence and then confirmed by other more specific immunoassays. Our objective was to investigate the anti-PCNA immune response in various disease conditions. Unselected sera referred to a clinical diagnostic laboratory and other sera from various diseases cohorts and controls were tested for anti-PCNA antibodies by enzyme-linked immunosorbent assay (ELISA), line immunoassay (LIA) and an addressable laser bead assay (ALBIA) using full-length human proliferating cell nuclear antigen. Two out of 2500 sequential, unselected sera (0.07%) referred to a diagnostic laboratory for autoantibody analysis showed a proliferating cell nuclear antigen-like staining pattern. Good agreement was found between ELISA, ALBIA and LIA. At cut-off values resulting in 100% specificity, 52.5% (ELISA), 42.5% (ALBIA) and 35% (LIA) of samples with a proliferating cell nuclear antigen-like indirect immunofluorescence staining pattern were positive. In the indirect immunofluorescence proliferating cell nuclear antigen immunoblot (IB)-positive group, anti-PCNA antibodies were frequently accompanied by anti-Ro52, and in the indirect immunofluorescence PCNA-negative but LIA PCNA-positive group by various other autoantibodies. The prevalence of anti-PCNA antibodies was highest in Sjögren’s syndrome (5.0%). In conclusion, the proliferating cell nuclear antigen-like staining pattern was rarely found (0.07%) in sequential, unselected sera. Further, indirect immunofluorescence is not an accurate screening method to identify anti-PCNA antibodies as their presence may be masked by other autoantibodies. The specific association of anti-PCNA antibodies with systemic lupus erythematosus was not confirmed in our study. Lupus (2010) 19, 1527—1533.

Interpretative comments on autoantibody tests

Immunology laboratories perform diagnostic tests to identify the autoantibody markers needed to classify disorders which are complex, often rare, and hard to define. The recent introduction of new markers and the use of increasingly complicated assay procedures can cause difficulty in interpreting test results. Moreover, during the performance of some tests, some autoantibodies which were not requested, and consequently not expected, may be identified by chance. It is advisable for these positive results to be reported only when they have a high predictive value and suggest the possible presence of an autoimmune disease. An interpretative comment on autoantibody test results is crucial in a number of cases: when autoantibodies with a significant clinical correlation (high specificity) are found; when two or more methods are used to determine the same autoantibody and the results disagree; when unexpected autoantibody positivity is found and in case of results generated by further diagnostic tests conducted by the laboratory on its own initiative. The interpretative comment should be based on the patient's personal characteristics (sex, age) and the other laboratory parameters available; it should specify the diagnostic accuracy of the assay methods used, the clinical and diagnostic correlations of the antibodies which tested positive, and any further tests needed to complete the diagnostic process.

Co-immunoprecipitation of putative proteins that interact with mosquito proliferating cell nuclear antigen

We have sequenced cDNAs encoding proliferating cell nuclear antigen (PCNA) from Aedes albopictus cells and from Aedes aegypti mosquitoes. The mosquito cDNAs contained an open reading frame encoding a 260 amino acid protein with a calculated mass of 29.0 kDa and a pI of 4.46. There was a single amino acid difference between PCNA proteins from Ae. albopictus and Ae. aegypti. In An. gambiae, the PCNA homolog contained 260 residues, and the pcna gene was interrupted by a single 67 nucleotide intron in the betaC2 region of the protein. A phylogenetic comparison grouped known Dipteran PCNA sequences into two clusters, representing the Nematocera and the Cyclorrhapha. PCNA transcripts measured 1.1 kb, and were stable, as was PCNA protein. Mosquito PCNA was efficiently recognized by a commercially available mouse anti-PCNA monoclonal antibody, which coprecipitated 29 kDa and 35 kDa proteins from mosquito cells representing different growth states. These results support the feasibility of recovering mosquito cell cycle inhibitory proteins by virtue of their interaction with PCNA.

Clinical and serological features of 35 patients with anti-Ki autoantibodies

The objective of this study was to analyse clinical and serological associations of anti-Ki antibodies. Thirty-five patients with anti-Ki antibodies, detected by CIE, selected from laboratory routine, were studied. All patients were affected by autoimmune diseases: SLE and pSS were the most frequent diagnoses. The cohort was constituted by 27 female and eight males. Main clinical features were skin involvement (60%), xerophtalmia (48.6%), Raynaud's phenomenon (43%), photosensitivity (34%), xerostomia (31.4%). CNS involvement was present in four (11.4%) and renal disease in seven cases (20%). ANA, anti-dsDNA and RF were detected in 100%, 60% and 34.5%. In SLE, anti-Ki was detected in 6% of cases, more frequently in males compared to other SLE patients without anti-Ki (P < 0.004). Nineteen anti-Ki positive patients affected by SLE showed more frequently malar rash and multiple autoantibody specificities compared to 16 anti-Ki positive patients with other diseases (P = 0.044 and P = 0.0003, respectively). Our study confirms a preferential occurrence of anti-Ki antibodies in patients with sicca and skin involvement. Malar rash and multiple ANA specificities were significantly associated with SLE compared to other diseases in our study. Anti-Ki were detected in 6% of patients with SLE with a significant prevalence in males.

Proteomic analysis of complexes formed by human topoisomerase I

Human topoisomerase I is a nuclear enzyme that catalyses DNA relaxation and phosphorylation of SR proteins. Topoisomerase I participates in several protein-protein interactions. We performed a proteomic analysis of protein partners of topoisomerase I. Two methods were applied to proteins of the nuclear extract of HeLa cells: a co-immunoprecipitation and an affinity chromatography combined with mass spectrometry. Complexes formed by topoisomerase I with its protein partners were immunoprecipitated by scleroderma anti-topoisomerase I antibodies. To identify binding sites for the protein partners, baits corresponding to fragments of topoisomerase I were constructed and used in the affinity chromatography. The N-terminal domain and the cap region of the core domain appeared to be the main regions that bound proteins. We identified 36 nuclear proteins that were associated with topoisomerase I. The proteins were mainly involved in RNA metabolism. We found 29 new and confirmed 7 previously identified protein partners of topoisomerase I. More than 40% proteins that associate with the cap region contain two closely spaced RRM domains. Docking calculations identified the RRM domains as a possible site for the interaction of these proteins with the cap region.

Effect of norcantharidin on proliferation and invasion of human gallbladder carcinoma GBC-SD cells

AIM: To investigate the effect of norcantharidin on proliferation and invasion of human gallbladder carcinoma GBC-SD cells in vitro and its anticancer mechanism.

METHODS: Human gallbladder carcinoma GBC-SD cells were cultured by cell culture technique. The growth and the invasiveness of GBC-SD cells in vitro were evaluated by the tetrazolium-based colorimetric assay and by the Matrigel experiment and the crossing-river test. Expression of PCNA, Ki-67, MMP₂ and TIMP₂ proteins of GBC-SD cells was determined by streptavidin–biotin complex method.

RESULTS: In vitro norcantharidin inhibited the growth and proliferation of GBC-SD cells in a dose- and time-dependent manner, with the IC₅₀ value of 56.18 μg/mL at 48 h. Norcantharidin began to inhibit the invasion of GBC-SD cells at the concentration of 5 μg/mL, and the invasive action of GBC-SD cells was inhibited completely and their crossing-river time was prolonged significantly at 40 μg/mL. After treatment with norcantharidin, the expression of PCNA, Ki-67, and MMP₂ was significantly decreased. With the increase in TIMP₂ expression, the MMP₂ to TIMP₂ ratio was decreased significantly (P<0.05).

CONCLUSION: Norcantharidin inhibits the proliferation and growth of human gallbladder carcinoma cells in vitro at relatively low concentrations by inhibiting PCNA and Ki-67 expression. Its anti-invasive activity may be the result of decrease in MMP₂ to TIMP₂ ratio and reduced cell motility.

DNA replication regulation protein Mcm7 as a marker of proliferation in prostate cancer

BACKGROUND

Recent studies have shown that minichromosome maintenance (MCM) proteins (Mcm2-7) may be useful proliferation markers in dysplasia and cancer in various tissues.

AIMS

To investigate the use of Mcm7 as a proliferation marker in 79 lymph node negative prostate cancers and compare it with Ki-67, a commonly used cell proliferation marker.

METHODS

The percentage of proliferating cells (proliferation index; PI) was calculated for basal and luminal epithelial cells in benign prostate tissue, prostatic intraepithelial neoplasia (PIN), and epithelial cells in adenocarcinoma. The PI for each biomarker was correlated with the preoperative prostate specific antigen concentration, the Gleason score, surgical resection margin status, and the AJCC pT stage for each patient.

RESULTS

The mean PIs for Ki-67 and Mcm7 were: benign luminal epithelium 0.7 and 1.2 and benign basal epithelium 0.8 and 8.2; PIN non-basal epithelium 4.9 and 10.6 and PIN basal epithelium 0.7 and 3.1; adenocarcinoma 9.8 and 22.7, respectively. Mcm7 had a significantly higher mean PI (p<0.0001) than Ki-67 for all cell categories except benign luminal epithelial cells. Mcm7 was a better discriminatory marker of proliferation between benign epithelium, PIN, and invasive adenocarcinoma (p<0.0001) than Ki-67. The drop in Mcm7 mean basal cell PI from benign epithelium to PIN epithelium was significantly larger than for Ki-67 (p<0.0001). Mcm7 had a significantly higher PI than Ki-67 at each risk level.

CONCLUSION

Mcm7 may be a useful proliferation marker in prostatic neoplasia and warrants further evaluation as a complementary tool in the diagnosis of PIN and prostate carcinoma.

Distinct pools of proliferating cell nuclear antigen associated to DNA replication sites interact with the p125 subunit of DNA polymerase δ or DNA ligase I

Proliferating cell nuclear antigen (PCNA) plays an essential role in DNA replication, repair, and cell cycle control. PCNA is a homotrimeric ring that, when encircling DNA, is not easily extractable. Consequently, the dynamics of protein-protein interactions established by PCNA at DNA replication sites is not well understood. We have used DNase I to release DNA-bound PCNA together with replication proteins including the p125-catalytic subunit of DNA polymerase delta (p125-pol delta), DNA ligase I, cyclin A, and cyclin-dependent kinase 2 (CDK2). Interaction with these proteins was investigated by immunoprecipitation with antibodies binding near the interdomain connector loop or to the C-terminal domain of PCNA, respectively, or with antibodies to p125-pol delta or DNA ligase I. PCNA interaction with p125-pol delta or DNA ligase I was detected only by the latter antibodies, and found to be mutually exclusive. In contrast, antibodies to PCNA co-immunoprecipitated only CDK2. A GST-p21(waf1/cip1) C-terminal peptide displaced p125-pol delta and DNA ligase I, but not CDK2, from PCNA. These results suggest that PCNA trimers bound to DNA during the S phase are organized as distinct pools able to bind selectively different partners. Among them, p125-pol delta and DNA ligase I interact with PCNA in a mutually exclusive manner.

Changes of TGF-a, HGF, PCNA and IGFBP-1s mRNA after partial hepatectomy in rat liver

AIM

To explore expression of TGF-α, HGF, PCNA and IGFBP-1s mRNA in hepatocyte and Kuffer cell (KC) and to study the effects of KC on liver regeneration after partial hepatectomy in cirrhotic rats.

METHODS

Using the model of partial hepatectomy in cirrhotic rats, we separated hepatocytes and KCs and employed Northern hybridization.

RESULTS

The expression of HGF mRNA in KC was earlier than that of hepatocyte, and peaked at 6 hr after operation. But the expression contents of TGF-α mRNA in hepatocyte was more than that of KC. The expression contents of IGFBP-1s mRNA in hepatocyte was lower and KC had no expressions. The expression of PCNA mRNA in hepatocyte was markedly depressed at 6h postoperation.

CONCLUSION

The expression of HGF and TGF-α mRNA is correlated with liver regeneration after operation in cirrhotic rats. TGF-α is very important for liver regeneration. The lower expression of IGFBP-1s mRNA shows the metabolic damage in cirrhotic rats postoperatively, but the expression of PCNA mRNA indicates the ability of liver regeneration.

Autoimmune responses to proliferating cell nuclear antigen multiprotein complexes involved in cell proliferation are strongly associated with their structure and biologic function in patients with systemic lupus erythematosus

OBJECTIVE

To analyze the reaction of lupus sera with proliferating cell nuclear antigen (PCNA) multiprotein complexes (PCNA complexes), which are part of the protein machinery involved in cell proliferation.

METHODS

PCNA complexes were purified from rabbit thymus extract by affinity chromatography using anti-PCNA monoclonal antibodies (TOB7, TO17, and TO30); monomeric and trimeric PCNA forms (AK-PCNA) were purified using anti-PCNA serum AK. The reactions to these antigens of 10 anti-PCNA-positive and 40 anti-PCNA-negative sera selected from 560 lupus patients were tested by immunoblotting, immunoprecipitation, and enzyme-linked immunosorbent assays (ELISAs).

RESULTS

With one exception (serum OK), anti-PCNA-positive sera reacted exclusively with only the 34-kd polypeptide. In contrast, 14 of 40 anti-PCNA-negative sera reacted with multiple proteins within PCNA complexes. Most anti-PCNA-positive sera probably recognize as epitopes the binding sites for other proteins on PCNA, which are likely hidden when PCNA is complexed with other proteins. As a consequence, only serum OK reacted with the PCNA complex in a series of ELISAs. Using AK-PCNA as a competitive inhibitor, it was determined that serum OK reacts with both the 58-kd polypeptide and the 34-kd PCNA within complexes. Together with the results of a longitudinal analysis, these results suggest that the immune system of patient OK likely recognized the complexed PCNA protein, after which the autoimmune response spread to other elements of the complexes.

CONCLUSION

Intermolecular-intrastructural help, leading to the spread of autoimmune response from PCNA to other proteins associated with its biologic function, plays a crucial role in the induction of the autoimmune response seen in lupus patients.

Direct interaction between mammalian DNA polymerase beta and proliferating cell nuclear antigen

Proliferating cell nuclear antigen (PCNA) plays an essential role in nucleic acid metabolism as a component of the DNA replication and DNA repair machinery. As such, PCNA interacts with many proteins that have a sequence motif termed the PCNA interacting motif (PIM) and also with proteins lacking a PIM. Three regions in human and rat DNA polymerases beta (beta-pol) that resemble the consensus PIM were identified, and we show here that beta-polymerase and PCNA can form a complex both in vitro and in vivo. Immunoprecipitation experiments, yeast two-hybrid analysis, and overlay binding assays were used to examine the interaction between the two proteins. Competition experiments with synthetic PIM-containing peptides suggested the importance of a PIM in the interaction, and studies of a beta-polymerase PIM mutant, H222A/F223A, demonstrated that this alteration blocked the interaction with PCNA. The results indicate that at least one of the PIM-like sequences in beta-polymerase appears to be a functional PIM and was required in the interaction between beta-polymerase and PCNA.

Symbolic discriminant analysis of microarray data in autoimmune disease

New laboratory technologies such as DNA microarrays have made it possible to measure the expression levels of thousands of genes simultaneously in a particular cell or tissue. The challenge for genetic epidemiologists will be to develop statistical and computational methods that are able to identify subsets of gene expression variables that classify and predict clinical endpoints. Linear discriminant analysis is a popular multivariate statistical approach for classification of observations into groups. This is because the theory is well described and the method is easy to implement and interpret. However, an important limitation is that linear discriminant functions need to be prespecified. To address this limitation and the limitation of linearity, we have developed symbolic discriminant analysis (SDA) for the automatic selection of gene expression variables and discriminant functions that can take any form. In the present study, we demonstrate that SDA is capable of identifying combinations of gene expression variables that are able to classify and predict autoimmune diseases.