Restoration of proliferating cell nuclear antigen (PCNA) complex formation in xeroderma pigmentosum group a cells following cis-diamminedichloroplatinum (II)-treatment by cell fusion with normal cells

Expression of a novel peptide derived from PCNA damages DNA and reverses cisplatin resistance

BACKGROUND

An 8 amino acid peptide sequence derived from proliferating cell nuclear antigen (PCNA) has been shown to effectively kill several breast cancer and neuroblastoma cell lines when added exogenously to cell cultures.

METHODS

In this study, the expression of the 8 amino acid peptide sequence (caPeptide) was placed under control of a tetracycline responsive promoter in MDA-MB-231 cells.

RESULTS

Endogenous expression of the peptide resulted in an increase in genomic DNA damage. CaPeptide induction combined with treatment of sublethal doses of cisplatin resulted in a marked increase in death of the cisplatin-resistant MDA-MB-231 cell line. CaPeptide was found to interact with POLD3, one of the subunits of DNA polymerase delta necessary for binding to PCNA.

CONCLUSION

These results suggest an important line of inquiry into the possible role that caPeptide might play in the reversal of cisplatin resistance in breast and other cancers. This is of particular interest in those cancers where cisplatin is the first line of chemotherapy and where the acquisition of resistance is a common malady.

Proliferating cell nuclear antigen in normal and regenerating rat livers

Immunohistochemical analysis using proliferating cell nuclear antigen (PCNA) antibody shows a negligible number of cells stained in normal liver, but much higher numbers in regenerating liver 24 and 48 h after surgery. We also verified different results by biochemical analysis. Two forms of PCNA, L type (eluted at low concentrations of KCl from a phosphocellulose column) and H type (eluted at high KCl concentrations), were observed in the nucleoplasm of regenerating livers 24 and 48 h after surgery. Treatment of the H type fraction with nuclease caused the H type to disappear and the amount of L type to increase. PCNAs in the cytoplasm are P type (eluted in the pass through fraction) and L type. Surprisingly, the total amounts of P type and L type in cytoplasmic extracts are comparable to those of L type and H type in the nucleoplasm. These results suggest that newly synthesized PCNA is immediately converted into the P and L complex forms. The P type and some of the L type that lacks a nuclear localization signal remain in the cytoplasm; the rest of the L type with a nuclear localization signal is transferred into the nuclei. Then, some of the L type in the nucleoplasm forms the H type, which binds to DNA. These three types of PCNA are also found in significant amounts in the nucleoplasm and cytoplasm of normal rat liver despite its nonproliferating state.

Detection of chromatin-bound PCNA in mammalian cells and its use to study DNA excision repair

Compelling evidence indicates that proliferating cell nuclear antigen (PCNA) is an indispensable factor not only in DNA replication but in nucleotide excision repair (NER), alternative pathway of base excision repair (BER), and mismatch repair. The common function of PCNA in each of these is to assist in the initiation of DNA synthesis by providing a scaffolding clamp as a trimer catalyzed by RF-C at the 3'-OH terminus of a nascent DNA strand, to which DNA polymerase delta or epsilon can bind. Interestingly, DNA synthesis is reported to be ingeniously inhibited in replication, but not in NER owing to the interaction with CDKN1A (formerly known as p21/WAF1/CIP1). Furthermore, several proteins, XPG, FEN1, and DNA ligase I, recently were shown to competitively bind to the same region of PCNA, the interdomain connector loop, to which DNA polymerase delta or epsilon also binds. PCNA therefore seems to have a regulatory role in these DNA transactions. The in vitro reconstituted experimental system has been a powerful tool to obtain these lines of evidence, but another approach, immunofluorescence studies, also has been a contributor. In fact, the involvement of PCNA in DNA replication, NER, and BER has for the first time been indicated by a unique method that makes visible only in vivo chromatin-bound PCNA. The usefulness of this method and the importance of cooperative studies done with in vitro and in vivo experimental systems is discussed in terms of DNA excision repair.

Multiple roles of the proliferating cell nuclear antigen: DNA replication, repair and cell cycle control

The proliferating cell nuclear antigen (PCNA), the auxiliary protein of DNA polymerase delta and epsilon, is involved in DNA replication and repair. This protein forms a homotrimeric structure which, encircling DNA, loads the polymerase on the DNA template. A role for PCNA in the cell cycle control is recognised on the basis of the interaction with cyclins, cyclin-dependent kinases (cdks) and the cdk-inhibitor p21 waf1/cip1/sdi1 protein. Association with the growth-arrest and DNA-damage inducible proteins gadd45 and MyD118, further demonstrates the role of PCNA as a component of the cell cycle control apparatus.

Proliferating cell nuclear antigen promotes DNA synthesis past template lesions by mammalian DNA polymerase delta

Consistent with previous observations, proliferating cell nuclear antigen (PCNA) promotes DNA synthesis by calf thymus DNA polymerase delta (pol delta) past several chemically defined template lesions including model abasic sites, 8-oxo-deoxyguanosine (dG) and aminofluorene-dG (but not acetylaminofluorene-dG). This synthesis is potentially mutagenic. The model abasic site was studied most extensively. When all deoxyribonucleoside triphosphates and a template bearing a model abasic site were present, DNA synthesis by pol delta beyond this site was stimulated 53-fold by addition of homologous PCNA. On an unmodified template (lacking any lesions), PCNA stimulated pol delta by 1.3-fold. Product analysis demonstrated that as expected from the "A-rule," fully and near-fully extended primers incorporated predominantly dAMP opposite the template lesion. Moreover, corollary primer extension studies demonstrated that in the presence (but not the absence) of PCNA, pol delta preferentially elongated primers containing dAMP opposite the model abasic template site. p21, a specific inhibitor of PCNA-dependent DNA replication, inhibits PCNA-stimulated synthesis past model abasic template sites. We propose that DNA synthesis past template lesions by pol delta promoted by PCNA results from the fundamental mechanism by which PCNA stimulates pol delta, i.e., stabilization of the pol delta. template-primer complex.

Age-related changes in proliferating cell nuclear antigen levels

To clarify the effect of aging on rat liver regeneration, we compared proliferating cell nuclear antigen (PCNA) levels in control and regenerating livers from young and aged rats 48 h after partial hepatectomy. The nucleoplasm and cytoplasm from regenerating livers of 2-month and 24 month-old rats were fractionated by phosphocellulose column chromatography, aliquots of fractions were transferred to nitrocellulose filters and the amounts of PCNA in each fraction were measured by an immunostaining method. Two forms of PCNA, L type (eluted at low concentrations of KC1) and H type (eluted at high KC1 concentrations) were observed in the nucleoplasm from both control and regenerating young rat liver. On the other hand, the cytoplasm contained P type (eluted in the pass-through fraction), L type and H type PCNA. In control liver from aged rats, three types of PCNA in the cytoplasm and two types in the nucleoplasm were present at decreased levels. In regenerating liver from young rats, the increases in L type in the cytoplasm and H type in the nucleoplasm were remarkable. However, none of the three PCNA types increased significantly during liver regeneration in aged rats. Treatment with DNase resulted in the disappearance of the H type with a concomitant increase in the P and L types. These results suggest that the H type is a complex form consisting of the P and L types of PCNA and DNA. These results suggest that the increase in the L type in the cytoplasm reflects newly synthesized PCNA production for cellular proliferation and that the increase in the H type in the nucleoplasm is a reflection of binding to DNA and the fundamental role of PCNA itself in liver regeneration in young rats. On the other hand, there was little increase in any of the three types in regenerating liver from 24-month-old rats. Thus, PCNA content may be closely related to the decrease in the rate of cellular proliferation in aged animals.

Repair of UV-damaged DNA by mammalian cells and Saccharomyces cerevisiae

Cells use many strategies to repair genomic damage caused by environmental agents and arising from the natural instability of the polynucleotide structure. Nucleotide excision repair is the most versatile DNA repair pathway and is the main defense of mammalian cells against UV-induced DNA damage. Defects in proteins involved in this pathway can lead to inherited disorders (such as xeroderma pigmentosum, Cockayne's syndrome and trichothiodystrophy) that are associated with hypersensitivity to sunlight. Most of the proteins and genes involved in these syndromes have now been identified. Study of UV-sensitive yeast RAD mutants has greatly aided this process and has revealed strong conservation of the components of nucleotide excision repair in eukaryotes. It has recently become clear that some of the proteins involved in the DNA repair process have dual functions and also participate in basal transcription and DNA replication.

Proliferating cell nuclear antigen in gallbladder carcinoma

Proliferating cell nuclear antigen (PCNA) expression was studied in 103 gallbladder carcinomas and 23 metastatic lesions as well as in 25 control non-neoplastic gallbladder specimens. Positive nuclear staining was observed in 88% of controls, in 92% of carcinomas and in 70% of metastases. The mean number of positive cells was 21.2% in controls, 44.1% in primary carcinomas and 32% in metastatic cancer cells. Differences which were significant were control v. primary tumour, P < 0.000001; control v. metastasis, P < 0.01 and primary tumour v. metastasis, P < 0.006. In 57 (60%) of the primary tumours there was positive staining in over 40% of tumour cells. We were not able to demonstrate any relationship between macroscopic or microscopic features and PCNA expression. However, tumours confined to the mucosa expressed PCNA more frequently than did more advanced tumours.