Human neutrophils isolated from peripheral blood contain Ku protein but not DNA-dependent protein kinase

iTRAQ-based quantitative proteomics reveals biomarkers/pathways in psoriasis that can predict the efficacy of methotrexate

BACKGROUND

Methotrexate (MTX) is the first-line medicine to treat psoriasis. So far, there has been less research on protein biomarkers to predict its efficacy by the proteomic technique.

OBJECTIVES

To evaluate differentially expressed proteins in peripheral mononuclear cells (PBMCs) between good responders (GRs) and non-responders (NRs) after MTX treatment, compared with normal controls (NCs).

METHODS

We quantified protein expression of PBMCs with 4 GRs and 4 NRs to MTX and 4 NCs by isobaric tags for relative and absolute quantification (iTRAQ), analyzing and identifying proteins related to efficacy of MTX in 18 psoriatic patients.

RESULTS

A total of 3,177 proteins had quantitative information, and 403 differentially expressed proteins (fold change ≥ 1.2, p < .05) were identified. Compared to NCs, upregulated proteins (ANXA6, RPS27A, EZR, XRCC6), participating in the activation of NF-κB, the JAK-STAT pathway, and neutrophil degranulation were detected in GRs. The proteins (GPV, FN1, STOM), involving platelet activation, signaling and aggregation as well as neutrophil degranulation were significantly downregulated in GRs. These proteins returned to normal levels after MTX treatment. Furthermore, Western blotting identified the expression of ANXA6 and STAT1 in PBMCs, which were significantly downregulated in GRs, but not in NRs.

CONCLUSIONS

We identified seven differentially expressed and regulated proteins (ANXA6, GPV, FN1, XRCC6, STOM, RPS27A, and EZR) as biomarkers to predict MTX efficacy in NF-κB signaling, JAK-STAT pathways, neutrophil degranulation, platelet activation, signaling and aggregation.

Compromised DNA Repair and Signalling in Human Granulocytes

In previous studies, we showed impaired DNA repair in human monocytes. Here, we addressed the question of whether human neutrophilic granulocytes that arise from the same precursor as monocytes exhibit a similar phenotype and are impaired in repairing their DNA. We show that neutrophilic granulocytes isolated from peripheral blood display a lack of the same repair proteins that are missing in monocytes and do not show repair of their DNA when damaged by ionising radiation (IR) or chemical ROS. Contrary to T cells, we observed no decline in the number of single-strand breaks following γ-radiation. Also, granulocytes did not show γH2AX foci formation while T cells and peripheral blood lymphocytes (PBL) responded. In comparison to PBL, XRCC1, PARP-1 and ligase III were not expressed and there was also no discernible signal for key damage response proteins ATM, ATR and DNA-PKCS as well as γH2AX in neutrophils. Time course and dose-response experiments confirmed the absence of H2AX phosphorylation after radiation treatment although an accumulation of double-strand breaks was detected in the neutral Comet assay. Overall, the data indicate that terminally differentiated neutrophilic granulocytes in the peripheral blood display strong downregulation of DNA repair and DNA damage response factors, which should be taken into account if studies with whole peripheral blood containing granulocytes are performed, causing a significant intra-experimental variation in the cellular repair capacity.

The profiles of gamma-H2AX along with ATM/DNA-PKcs activation in the lymphocytes and granulocytes of rat and human blood exposed to gamma rays

Establishing a rat model suitable for γ-H2AX biodosimeter studies has important implications for dose assessment of internal radionuclide contamination in humans. In this study, γ-H2AX, p-ATM and p-DNA-PKcs foci were enumerated using immunocytofluorescence method, and their protein levels were measured by Western blot in rat blood lymphocytes and granulocytes exposed to γ-rays compared with human blood lymphocytes and granulocytes. It was found that DNA double-strand break repair kinetics and linear dose responses in rat lymphocytes were similar to those observed in the human counterparts. Moreover, radiation induced clear p-ATM and p-DNA-PKcs foci formation and an increase in ratio of co-localization of p-ATM or p-DNA-PKcs with γ-H2AX foci in rat lymphocytes similar to those of human lymphocytes. The level of γ-H2AX protein in irradiated rat and human lymphocytes was significantly reduced by inhibitors of ATM and DNA-PKcs. Surprisingly, unlike human granulocytes, rat granulocytes with DNA-PKcs deficiency displayed a rapid accumulation, but delayed disappearance of γ-H2AX foci with essentially no change from 10 h to 48 h post-irradiation. Furthermore, inhibition of ATM activity in rat granulocytes also decreased radiation-induced γ-H2AX foci formation. In comparison, human granulocytes showed no response to irradiation regarding γ-H2AX, p-ATM or p-DNA-PKcs foci. Importantly, incidence of γ-H2AX foci in lymphocytes after total-body radiation of rats was consistent with that of in vitro irradiation of rat lymphocytes. These findings show that rats are a useful in vivo model for validation of γ-H2AX biodosimetry for dose assessment in humans. ATM and DNA-PKcs participate together in DSB repair in rat lymphocytes similar to that of human lymphocytes. Further, rat granulocytes, which have the characteristic of delayed disappearance of γ-H2AX foci in response to radiation, may be a useful experimental system for biodosimetry studies.

Expression of DNA-dependent protein kinase in human granulocytes

Human polymorphonuclear leukocytes (PMN) have been reported to completely lack of DNA-dependent protein kinase (DNA-PK) which is composed of Ku protein and the catalytic subunit DNA-PKcs, needed for nonhomologous end-joining (NHEJ) of DNA double-strand breaks. Promyelocytic HL-60 cells express a variant form of Ku resulting in enhanced radiation sensitivity. This raises the question if low efficiency of NHEJ, instrumental for the cellular repair of oxidative damage, is a normal characteristic of myeloid differentiation. Here we confirmed the complete lack of DNA-PK in PMN protein extracts, and the expression of the truncated Ku86 variant form in HL-60. However, this degradation of DNA-PK was shown to be due to a DNA-PK-degrading protease in PMN and HL-60. In addition, by using a protease-resistant whole cell assay, both Ku86 and DNA-PKcs could be demonstrated in PMN, suggesting the previously reported absence in PMN of DNA-PK to be an artefact. The levels of Ku86 and DNA-PKcs were much reduced in PMN, as compared with that of the lymphocytes, whereas HL-60 displayed a markedly elevated DNA-PK concentration. In conclusion, our findings provide evidence of reduced, not depleted expression of DNA-PK during the mature stages of myeloid differentiation.

Involvement of DNA-dependent protein kinase in down-regulation of cell cycle progression

The catalytic polypeptide of DNA-dependent protein kinase (p470) is encoded by the gene responsible for murine severe combined immunodeficiency (SCID) devoid of DNA double-strand break repair and V(D)J recombination. Here, we have characterized the role of p470 in cell proliferation using SCID mice and the cell lines. In accord with DNA histogram patterns, SCID cell lines (SD/SD-eA and SC3VA2) expressing extremely low level of DNA-PK activity grew faster than a normal mouse cell line (CB/CB-eB) and SC3VA2 complemented with human p470 gene (RD13B2). In regenerating liver after partial hepatectomy, de novo DNA synthesis determined by [(3)H]thymidine incorporation started at 30h in C.B-17/Icr-SCID (SCID) mice and at around 36h in C.B-17/Icr (C.B-17) mice. Compared with normal cells, SCID cells contained slightly higher levels of transcripts of cyclin A, cyclin E, B-Myb and dihydrofolate reductase, which are regulated by E2F-1. E2F-1 playing a key role in G1- to S-phase progression was phosphorylated in vitro by DNA-PK. Importantly, the E2F-1 promoter transcriptional activity in SCID cell lines (SD/SD-eA and SC3VA2) was 4-5-fold higher than that in CB/CB-eB and RD13B2. These results suggest that p470 is involved in down-regulation of cell cycle progression through E2F-1-responsible genes.