Defective repair of O6-methylguanine-DNA in primary Sjögren's syndrome patients predisposed to lymphoma

DNA Methylation of T Lymphocytes as a Therapeutic Target: Implications for Rheumatoid Arthritis Etiology

Rheumatoid arthritis (RA) is an autoimmune disease that can cause joint damage and disability. Epigenetic variation, especially DNA methylation, has been shown to be involved in almost all the stages of the pathology of RA, from autoantibody production to various self-effector T cells and the defects of protective T cells that can lead to chronic inflammation and erosion of bones and joints. Given the critical role of T cells in the pathology of RA, the regulatory functions of DNA methylation in T cell biology remain unclear. In this review, we elaborate on the relationship between RA pathogenesis and DNA methylation in the context of different T cell populations. We summarize the relevant methylation events in T cell development, differentiation, and T cell-related genes in disease prediction and drug efficacy. Understanding the epigenetic regulation of T cells has the potential to profoundly translate preclinical results into clinical practice and provide a framework for the development of novel, individualized RA therapeutics.

Cell-autonomous epithelial activation of AIM2 (absent in melanoma-2) inflammasome by cytoplasmic DNA accumulations in primary Sjögren's syndrome

Primary Sjögren's syndrome (SS) is characterized by chronic periductal inflammatory infiltrates in the salivary glands. Several previous studies have indicated that the ductal epithelia of SS patients play a pro-inflammatory role and manifest an intrinsically activated status, as demonstrated in cultured non-neoplastic ductal salivary gland epithelial cell (SGEC) lines. Herein, we investigated the activation of inflammasomes in the salivary epithelia of SS patients and non-SS controls, using salivary biopsy tissues and SGEC lines. The ductal epithelial cells of SS patients were found to display significant activation of the AIM2 (absent in melanoma-2) inflammasome. Such activation occurred in a cell-autonomous manner, as it was illustrated by the constitutively high expression of AIM2 activation-related genes, the presence of cytoplasmic ASC specks and the increased spontaneous IL-1β production observed in patients' SGEC lines. Since AIM2 activation is known to occur in response to cytoplasmic DNA, we further searched for the presence of undegraded extranuclear DNA in the SGEC lines and SG tissues of patients and controls. This investigation revealed marked cytoplasmic accumulations of damaged genomic DNA that co-localized with AIM2 in the specimens of SS patients (but not controls). The SGEC lines and the ductal tissues of SS patients were also found to manifest impaired DNase1 expression and activity, which possibly denotes defective cytoplasmic DNA degradation in patients' cells and AIM2 triggering thereof. In corroboration, DNase1-silencing in normal SGEC was shown to lead to high AIM2-related gene expression and IL-1β production. Our findings indicate that the cell-intrinsic activation status of ductal epithelia in SS patients owes to persistent epithelial AIM2 activation by aberrant cytoplasmic DNA build-up.

DNA repair deficiency as a susceptibility marker for spontaneous lymphoma in golden retriever dogs: a case-control study

There is accumulating evidence that an individual's inability to accurately repair DNA damage in a timely fashion may in part dictate a predisposition to cancer. Dogs spontaneously develop lymphoproliferative diseases such as lymphoma, with the golden retriever (GR) breed being at especially high risk. Mechanisms underlying such breed susceptibility are largely unknown; however, studies of heritable cancer predisposition in dogs may be much more straightforward than similar studies in humans, owing to a high degree of inbreeding and more limited genetic heterogeneity. Here, we conducted a pilot study with 21 GR with lymphoma, 20 age-matched healthy GR and 20 age-matched healthy mixed-breed dogs (MBD) to evaluate DNA repair capability following exposure to either ionizing radiation (IR) or the chemical mutagen bleomycin. Inter-individual variation in DNA repair capacity was evaluated in stimulated canine lymphoctyes exposed in vitro utilizing the G2 chromosomal radiosensitivity assay to quantify clastogen-induced chromatid-type aberrations (gaps and breaks). Golden retrievers with lymphoma demonstrated elevated sensitivity to induction of chromosome damage following either challenge compared to either healthy GR or MBD at multiple doses and time points. Using the 75(th) percentile of chromatid breaks per 1,000 chromosomes in the MBD population at 4 hours post 1.0 Gy IR exposure as a benchmark to compare cases and controls, GR with lymphoma were more likely than healthy GR to be classified as "sensitive" (odds ratio = 21.2, 95% confidence interval 2.3-195.8). Furthermore, our preliminary findings imply individual (rather than breed) susceptibility, and suggest that deficiencies in heritable factors related to DNA repair capabilities may be involved in the development of canine lymphoma. These studies set the stage for larger confirmatory studies, as well as candidate-based approaches to probe specific genetic susceptibility factors.

Possible Mechanisms of Lymphoma Development in Sjögren's Syndrome

Primary Sjögren's syndrome (pSS) is a systemic as well as an organ-specific autoimmune disease characterized by lymphocytic infiltration of the glandular epithelial tissue. SS patients have been reported to be at highest risk of developing lymphoproliferative neoplasms, when compared with patients with other rheumatoid diseases. Factors such as cytokine stimulation, environmental factors, viral infection and genetic events as well as vitamin deficiency may contribute to the development of lymphoma. Over the past few decades, numerous efforts have been made to assess the relationship between lymphoma and SS. These include epidemiological surveys, molecular biologic assessments of clonality and well-linked register cohort studies evaluating the predictive value of clinical, laboratory and histological findings. Nevertheless, the mechanisms and factors predictive of lymphoma development in pSS patients remain to be defined. This review summarizes updated knowledge on the incidence of and risk factors for lymphoma development in pSS patients, as well as discussing the most recent findings on the development and treatment of lymphoma in pSS patients and the possible mechanism of lymphoma development.

Incidence of cancer in a cohort of patients with primary Sjogren's syndrome

OBJECTIVE

To compare the incidence of subsequent cancers in a cohort of patients with primary Sjögren's syndrome (pSS) with that of the general population in the same region of England.

METHODS

A retrospective analysis was carried out on 112 patients who had attended the out-patients department at University College Hospital, London, from 1979 onwards. Patients were followed up from diagnosis of pSS to diagnosis of first subsequent cancer, death, loss to follow-up or 31 December 2003 (the censoring date) to determine the person-years at risk for each individual. The expected numbers of subsequent cancers were calculated from sex-/age-/period-specific rates for the general population of southeast England, derived from registrations at the Thames Cancer Registry. Standardized incidence ratios (SIRs) were then calculated as the ratio of observed to expected numbers of cancers, along with 95% confidence intervals (CIs). Separate analyses were performed for all malignant cancers combined, lymphomas and non-lymphoid cancers.

RESULTS

Among the 112 patients with pSS, 25 developed cancer (either before or after development of pSS), with lymphoma occurring in 11 cases. Nine patients had two cancers. There was a significantly elevated incidence of lymphomas in pSS patients compared with the general population (SIR 37.5, 95% CI 20.7-67.6). For non-lymphoid cancer, the observed increase in incidence was small and not statistically significant (SIR 1.5, 95% CI 0.9-2.6).

CONCLUSION

This study confirms that there is an increased incidence of lymphoma in patients with pSS. An increase in the incidence of other cancers was not proven but the observation that some patients developed more than one cancer raises the possibility that there may be a subgroup of patients who are at greater risk of developing cancer.

O(6)-methylguanine DNA methyltransferase activity in diabetic patients

In the present study, we evaluated O(6)-methylguanine-DNA methyltransferase (MGMT) activity in diabetic patients. The study was performed on 27 patients with Type 1 diabetes, and 42 with Type 2 diabetes. Patients with complications were excluded from the study. 36 non-diabetic volunteers, non-smokers who do not consume alcoholic beverage, were chosen from the medical staff as control subjects. MGMT activity was measured by the transfer of radiolabeled methyl groups from a prepared methylguanine-DNA substrate to the enzyme fraction of leukocyte extract. Leukocyte MGMT activity was significantly reduced in both Type 1 and Type 2 diabetes patients as compared with control subjects (P<0.001). The present study demonstrates decreased MGMT activity in leukocytes from patients with Type 1 and Type 2 diabetes.

Glutathione S-transferase and O6-methylguanine DNA methyl transferase activities in patients with thyroid papillary carcinoma

Alkylating agents, which are metabolized by glutathione S-transferase (GST), have an important role in the etiology of cancer by forming mutagenic DNA adducts. Previous studies have shown that DNA repair protein, O6-methylguanine DNA methyltransferase, repairs these mutagenic DNA adducts and its activity is correlated with the resistance of human tumors to alkylating agent-based anti-cancer drugs. However, little is known about GST and O6-methylguanine DNA methyltransferase activities in patients with thyroid cancer in vivo. We measured the activities of GST and O6-methylguanine DNA methyltransferase in the leukocytes from patients with papillary thyroid carcinoma and healthy controls. The GST activity was significantly higher in men than in women, and it was negative correlated with age in men whereas it was unchanged in women in the control group. Both GST and O6-methylguanine DNA methyltransferase activities were significantly increased in the patient group. There were no age and sex-related changes in the O6-methylguanine DNA methyltransferase activity in both the control and patient groups. These results suggest that leukocyte GST and O6-methylguanine DNA methyltransferase activities were increased with thyroid cancer. This may be related to the resistance to chemotherapy exhibited by patients with thyroid cancer.

Enhanced DNA damage-induced p53 peptide phosphorylation and cell-cycle arrest in Sjögren's syndrome cells

BACKGROUND

Cells from primary Sjögren's syndrome (SS) patients have been reported to show alterations in DNA repair and p53 expression. The DNA-dependent protein kinase (DNA-PK) autoantigen may be involved in both of these alterations in relation to cellular DNA damage responses. We conducted this study of cell-cycle kinetics and p53 to find additional evidence for an abnormal stress response role in the pathogenesis of SS.

DESIGN

DNA-dependent protein kinase activity, p53 peptide phosphorylation and p53 protein levels were determined in gamma-irradiated long-term T lymphocyte cultures. Cell-cycle progression of peripheral blood mononuclear cells was analysed with flow cytometry.

RESULTS

No significant differences in the DNA-PK activities or p53 protein levels appeared between the SS patients and the healthy individuals. However, patients with the SS hallmark Ro/SS-A and La/SS-B autoantibodies showed enhancement of both p53 peptide phosphorylation (P = 0.036) and G1 cell-cycle arrest (P = 0.015) in response to gamma radiation.

CONCLUSIONS

Sjögren's syndrome cells express an enhanced G1 checkpoint function which may be mediated partly by p53 phosphorylation, suggesting that an abnormal stress response in SS is of relevance for the development of this autoimmune disease.

Exposure of HEp-2 cells to stress conditions influences antinuclear antibody reactivity

This study of stress-related antinuclear antibody (ANA) reactivity was undertaken with the objective of improving clinical ANA testing. ANA was determined by parallel enzyme-linked immunosorbent assays of crude nuclear protein antigen extracted from HEp-2 cells either grown under optimal conditions (providing nonstress ANA antigen) or exposed to stress (providing stress ANA antigen). The stress stimuli used were gamma radiation (causing DNA damage) and a hypertonic environment (causing apoptosis). Signs of stress-related ANA reactivity were seen among connective tissue disease (CTD) patients (including patients with systemic lupus erythematosus; mixed CTD; calcinosis, Reynaud's phenomenon, esophageal motility disorders, sclerodactyly, and telangiectasia; scleroderma; and Sjögren's syndrome): 11% showed stress-positive ANA (i.e., a significantly stronger ANA reactivity with the extract from stressed cells), whereas 21% showed a markedly weaker reaction with the stress antigen. In contrast, among ANA screening patient sera, with no diagnosis of CTD, the fraction showing stress-positive ANA was higher (7 to 8%, depending on the type of stress) than among those showing a lower reactivity with stress antigen (1.5 to 2.5%). Only one serum among 89 (1%) tested sera from healthy individuals showed a stress-related ANA reaction. This demonstration of stress-related ANA suggests a means to improve the performance of clinical ANA testing.

Ku protein and DNA strand breaks in lip glands of normal and primary Sjögren's syndrome subjects: lack of correlation with apoptosis

The aim was to examine tissue expression of Ku protein in lower lip salivary gland (LSG) biopsies from cases of primary Sjögren's syndrome (SS) and from normal subjects.

METHODS

immunohistochemistry was used with antibodies to Ku70/86 and also Ki67, PCNA and p53. In addition, the Klenow method was applied in order to detect evidence of apoptosis. Sections of hyperplastic tonsil served as additional controls.

RESULTS

in normal controls, LSG acinar cells stained negatively whereas LSG excretory duct cell nuclei stained positively with Ku and Klenow and occasionally with PCNA but negatively with Ki67 and p53. In LSG focal sialadenitis of SS cases, some lymphocytic cells showed staining with Ku, Ki67, PCNA, Klenow and p53. In addition to duct cell Ku and Klenow as well as PCNA staining which was not much different from normals, a few ductal epithelial and also mononuclear cells stained with p53. In focal sialadenitis, some acinar cells showed staining with PCNA as well as with Klenow.

CONCLUSIONS

our findings in LSG biopsies of SS cases added little to an increased understanding about the pathogenetic mechanisms in the development of focal sialadenitis in SS. However, in normal LSG, ductal epithelial but not acinar cells seem to express a constitutively specific Ku protein and Klenow profile, suggestive of DNA strand breaks but not clearly associated with ongoing apoptotic events. It may reflect an enhanced stress response, which may be pathogenetically important in the early events of focal sialadenitis development in primary Sjögren's syndrome.

Circadian variation in O6-alkylguanine-DNA alkyltransferase activity in circulating blood mononuclear cells of healthy human subjects

Cytotoxic agents such as chloroethylnitrosoureas (CENUs) mostly alkylate DNA on the O6-guanine position. This highly mutagenic lesion can be repaired by O6-alkylguanine-DNA alkyltransferase (AGT), which removes the alkyl group by accepting it to the cysteine residue of its active site. AGT activity displayed a circadian rhythm in mouse liver, coincident with that of CENU tolerability. We investigated whether AGT activity displayed a circadian rhythm in human circulating mononuclear cells (MNCs). The study was performed in 12 healthy volunteers aged 19 to 31 years. Circadian synchronization was verified with rest/activity cycle as assessed with wrist actigraphy and plasma cortisol and melatonin rhythms. Subjects were hospitalized for 24 hr and blood samples were obtained at 08:00, 12:00, 16:00, 20:00, 22:00, 00:00, 02:00, 04:00 and 08:00 overnight. MNCs were isolated on Ficoll immediately after blood sampling and frozen at -196 degrees C until AGT activity determination by HPLC. Mean AGT activity (+/- SEM) varied from 821 +/- 67 fmol/mg of total proteins at noon (trough), up to 1,055 +/- 80 fmol/mg at midnight (peak), i.e., by approximately 30%. A circadian rhythm was statistically validated with both analysis of variance (p < 0.009) and cosinor (p < 0.02) for AGT activity in MNCs (acrophase +/- SD at 00:30 +/- 210 min) as well as for MNC circulating count and for plasma cortisol and melatonin concentrations. Despite individual variations in the extent of AGT activity rhythm (more or less pronounced according to subject), AGT activity displayed a circadian rhythm in human MNCs of our healthy study group subjects. The results warrant to further investigate AGT rhythmicity both in circulating MNCs and in target tissues of cancer patients, as a prerequisite for clinical testing of chronotherapy with alkylating agents.

Sjogren's syndrome

Sjogren's syndrome is a chronic progressive autoimmune disorder manifested predominately by xerostomia (dry mouth) and keratoconjunctivitis sicca (dry eyes). It can also affect many body systems. Up to 5% of people over the age of 60 years have primary Sjogren's syndrome, and approximately one third of patients present with extraglandular (systemic) manifestations. This disease is seen mostly in middle-aged women, with a small but significant proportion of these women developing lymphoid neoplasia. The exact etiology is still unknown. This autoimmune disorder is characterized by B-cell activation, the production of numerous auto-antibodies, and the loss of immune tolerance. Salivary gland biopsy remains the most helpful diagnostic test. Treatment is aimed at moisture replacement, which alleviates the discomfort and slows the destructive process. Because of its prevalence in older women, the obstetrician-gynecologist must be aware of the diagnostic and therapeutic approach to Sjogren's syndrome.

Rheumatic syndromes: clues to occult neoplasia

OBJECTIVES

Rheumatic disorders associated with cancer include a variety of conditions, most of which have no features distinguishing them from idiopathic rheumatic disorders. It is generally held that an extensive search for occult malignancy in most rheumatic syndromes is not recommended unless accompanied by specific findings suggestive of malignancy. The objective of this review are to identify rheumatic syndromes associated with cancer, to call attention to features that may suggest the presence of a hidden cancer, and to examine the role to additional clinical and laboratory data as clues to the possible neoplastic cause of those syndromes.

METHODS

A MEDLINE search of the literature dealing with cancer-associated rheumatic syndromes was conducted.

RESULTS

Review of the literature identified significant progress in this area. First, the association of malignancy with certain rheumatic syndromes was convincingly established, such as asymmetric polyarthritis presenting in the elderly with an explosive onset, rheumatoid arthritis with monoclonal gammopathy, Sjögren's syndrome with monoclonality, hypertrophic osteoarthropathy, dermatomyositis, polymyalgia rheumatica with atypical features, Lambert-Eaton myasthenic syndrome, palmar fasciitis and arthritis, eosinophilic fasciitis poorly responsive to corticosteroid therapy, erythema nodosum lasting more than 6 months, and onset of Raynaud's phenomenon or cutaneous leukocytoclastic vasculitis after age 50 years. Second, the list of cancer-associated rheumatic syndromes was extended by including additional entities such as benign edematous polysynovitis, sacroiliitis, adult-onset Still's disease, dermatomyositis sine myositis, systemic sclerosis, Sweet's syndrome, osteomalacia, skeletal hyperostosis, antiphospholipid syndrome, and essential mixed cryoglobulinemia. Third, evidence was provided substantiating that certain long-standing rheumatic syndromes, in particular rheumatoid arthritis, Felty's syndrome, Sjögren's syndrome, dermatomyositis, systemic sclerosis, systemic lupus erythematosus, and temporal arteritis behave like "premalignant conditions." Fourth, it was shown that the recognized tumor markers alpha-fetoprotein, prostate-specific antigen, CA-125, CA 19-9, and CA-3 have low sensitivity and specificity in screening for occult cancer in a population of rheumatic patients, whereas the presence of a monoclonal gammopathy in rheumatoid arthritis and the monoclonal antibody 17-109 in Sjögren's syndrome are reliable signs of malignant transformation.

CONCLUSIONS

The presence of specific rheumatic syndromes and certain clinical and laboratory findings may justify a workup for hidden cancer. Studies of the epidemiology of the cancer-associated rheumatic syndromes and evaluation of the validity of aforementioned clues in prospective studies are goals for future investigations.

Enhanced ultrasensitive detection of structurally diverse antigens using a single immuno-PCR assay protocol

Our studies of DNA damage and repair in autoimmune disease, lymphomagenesis, and carcinogenesis, require identification of an immunoassay approach that is capable of ultrasensitive detection in a routine human tissue biopsy of several physicochemically diverse antigens, some of which will be present at very low level. Immuno-polymerase chain reaction (immuno-PCR) is a recently described method for ultrasensitive antigen detection that combines the amplification power of PCR with a method similar to a standard antibody capture, enzyme-linked immunosorbent assay (ELISA). As a test of the universality of immuno-PCR, and as an assessment of the suitability of this method for our studies, we used a single immuno-PCR protocol to assay purified forms of the following physicochemically diverse antigens: oligomeric pyruvate dehydrogenase complex (PDC; Mr 8.5 x 10(6)), the promutagenic DNA base adduct O(6)-methylguanosine (Mr 298) and its monomeric repair enzyme, O(6)-methylguanine-DNA methyltransferase (MGMT; Mr 22,000), and a peptide from the N-terminus of MGMT (Mr 2310). We found that all antigens could be ultrasensitively assayed using the single immuno-PCR protocol. Assay limits observed using antigen-specific (primary) antibodies at 1 microg/ml, were in the approximate range of 10(2)-10(9) molecules, with O(6)-methylguanosine being detected most sensitively. Sensitivity of the antigen assay appeared to positively correlate with primary antibody titres determined by ELISA. Furthermore, we observed a substantial increase in detection sensitivity for all antigens by the use of primary antibodies at the higher level of 10 microg/ml. The latter approach permitted antigen assay within the approximate range of 10(0)-10(7) molecules. The combination of higher titre primary antibodies and their use at higher input level, produced an increase of immuno-PCR assay sensitivity of up to four orders of magnitude greater than those previously reported through the use of this assay to measure other antigens. This represents up to a nine order of magnitude increase in immunoassay sensitivity compared to ELISA. Our findings provide compelling evidence that immuno-PCR is indeed a universal ultrasensitive antigen detection method. Using the indicated assay enhancements. immuno-PCR performed as detailed here can offer greatly increased sensitivity for antigen measurement compared to other methods. Thus, our findings suggest that parallel quantitation of several different antigens in very small samples of human tissue will be readily attainable using immuno-PCR.

[Gougerot-Sjögren syndrome and malignant lymphoproliferative syndromes]

INTRODUCTION

This review is aimed at defining the frequency, anatomical and clinical presentation, pathogenesis, predictive factors and treatment of malignant lymphoproliferative diseases occurring in the course of Sjögren's syndrome.

CURRENT KNOWLEDGE AND KEY POINTS

The frequency of non-Hodgkin's lymphoma (NHL) is estimated to be about 7%. Other malignant lymphoproliferative diseases (Waldenstrom's macroglobulinemia, multiple myeloma, Hodgkin's disease) are rarely observed. NHL is most frequently extranodal (affecting the salivary glands, stomach, lung, etc) in low grade malignancy (MALT lymphoma [mucosa associated lymphoid tissue]). The pathogenesis of NHL in Sjögren's syndrome is a multi-step process, including B cell monoclonal proliferation, oncogenic and/or infectious agents, and/or cytokines. Various predictive factors such as persistent enlargment of parotid glands, adenopathy, splenomegaly, mixed cryoglobulinemia, monoclonal gammopathy, suggest potential lymphoma evolution. The treatment of Sjögren's syndrome-associated NHL depends on the type of lymphoma. Moreover, in patients with low-grade lymphoma therapeutical strategies varies according to the stage and evolution of the disease.

FUTURE PROSPECTS AND PROJECTS

Future prospective longitudinal studies should permit to define the best criteria for malignant transformation and to improve therapeutical strategies.