Expression of the myc-family proto-oncogenes and related genes max and mad in synovial tissue

TP53 mutations coincide with the ectopic expression of activation-induced cytidine deaminase in the fibroblast-like synoviocytes derived from a fraction of patients with rheumatoid arthritis

Main features of rheumatoid arthritis (RA), hyperplasia of fibroblast-like synoviocytes (FLS) and joint destruction are caused by inflammatory cytokines produced in chronic autoimmune inflammation. Cell-intrinsic acquisition of tumour-like phenotypes of RA-FLS could also be responsible for the aggressive proliferation and invasion, which are supported by the fact that in some cases RA-FLS has mutations of a tumour suppressor gene TP53. However, the underlying molecular mechanism for TP53 mutations in RA-FLS has not yet been clarified. Recently it has been reported that the non-lymphoid cells in the inflammatory tissues express ectopically the activation-induced cytidine deaminase (AID) gene that induces somatic hypermutations, not only at the immunoglobulin (Ig) gene variable regions in germinal centre B lymphocytes but also at coding regions in TP53. Real-time polymerase chain reaction (PCR) analyses revealed more than half (five of nine) of the RA-FLS lines we established showed the markedly increased expression of AID. AID transcription in RA-FLS was augmented by tumour necrosis factor (TNF)-alpha and even by physiological concentration of beta-oestradiol that could not induce AID transcription in osteoarthritis-FLS. Furthermore, AID-positive RA-FLS presented a higher frequency of somatic mutations in TP53. Cytological and immunohistochemical analyses demonstrated clearly the ectopic expression of AID in the FLS at the RA synovium. These data suggested strongly a novel consequence of RA; the ectopic expression of AID in RA-FLS causes the somatic mutations and dysfunction of TP53, leading to acquisition of tumour-like properties by RA-FLS.

Interferon-induced sensitization to apoptosis is associated with repressed transcriptional activity of the hTERT promoter in multiple myeloma

The aim of the present study was to explore hTERT as a target for IFN-induced sensitization to apoptosis in multiple myeloma (MM). IFN-alpha and IFN-gamma downregulated telomerase activity in the IL-6-dependent MM cell line U-266-1970. In MM cells undergoing IFN-induced sensitization to Fas-mediated apoptosis, the repression of telomerase was increased as compared to IFN-alpha treatment alone. Similar to the sensitization effect of IFN, the use of a dominant negative IkappaBalpha vector inhibiting hTERT activity via transcriptional targeting resulted in augmentation of Fas-mediated apoptosis. The mechanism underlying the reduction of telomerase activity by IFN was shown to be transcriptional repression of the hTERT gene. The present study does not support a direct effect of IFN on NF-kappaB binding to the hTERT promoter as underlying the transcriptional repression. We conclude that one potential mechanism whereby IFNs induce apoptosis sensitization is by repressing hTERT transcription and telomerase activity, thereby constituting attractive targets for MM therapy.

Differential effects of TGF-β1 on telomerase activity in thyroid carcinoma cell lines

The aim of the present study was to investigate the effect of transforming growth factor-beta1 (TGF-beta1) on telomerase activity in a panel of human anaplastic thyroid carcinoma (ATC) cell lines. Addition of TGF-beta1 decreased the telomerase activity in HTh 74 and KTC-1 cells, while in C 643 and HTh 7 an increased activity was observed. The decreased telomerase activity appeared to be due to transcriptional repression of the hTERT promoter. Addition of a PI-3 kinase inhibitor (LY294002) abrogated the stimulatory effect of TGF-beta1 on the telomerase activity, indicating the possible involvement of hTERT activation via phosphorylation. Furthermore, the MEK-inhibitor U0126 had similar effects suggesting dual regulatory mechanisms. Interestingly, the cell lines differed genetically in that ATC cell lines responding with increased telomerase activity harbored a p53 mutation. In conclusion, TGF-beta1 exerts opposing effects on telomerase activity in ATC cell lines, possibly reflecting deregulation of TGF-beta1 signaling in a more malignant genotype.

TRAIL-R2 (DR5) mediates apoptosis of synovial fibroblasts in rheumatoid arthritis

TRAIL has been proposed as an anti-inflammatory cytokine in animal models of rheumatoid arthritis (RA). Using two agonistic mAbs specific for TRAIL-R1 (DR4) and TRAIL-R2 (DR5), we examined the expression and function of these death receptors in RA synovial fibroblast cells. The synovial tissues and primary synovial fibroblast cells isolated from patients with RA, but not those isolated from patients with osteoarthritis, selectively expressed high levels of cell surface DR5 and were highly susceptible to anti-DR5 Ab (TRA-8)-mediated apoptosis. In contrast, RA synoviocytes did not show increased expression of TRAIL-R1 (DR4), nor was there any difference in expression of Fas between RA and osteoarthritis synovial cells. In vitro TRA-8 induced apoptosis of RA synovial cells and inhibited production of matrix metalloproteinases induced by pro-inflammatory cytokines. In vivo TRA-8 effectively inhibited hypercellularity of a SV40-transformed RA synovial cell line and completely prevented bone erosion and cartilage destruction induced by these cells. These results indicate that increased DR5 expression and susceptibility to DR5-mediated apoptosis are characteristic of the proliferating synovial cells in RA. As highly proliferative transformed-appearing RA synovial cells play a crucial role in bone erosion and cartilage destruction in RA, the specific targeting of DR5 on RA synovial cells with an agonistic anti-DR5 Ab may be a potential therapy for RA.

Gene expression induced by interleukin-17 in fibroblast-like synoviocytes of patients with rheumatoid arthritis: upregulation of hyaluronan-binding protein TSG-6

Interleukin-17 (IL-17) has been characterized as a proinflammatory cytokine produced by CD4+ CD45RO+ memory T cells. Overproduction of IL-17 was detected in the synovium of patients with rheumatoid arthritis (RA) compared with patients with osteoarthritis. This study examines differentially expressed genes after the stimulation of fibroblast-like synoviocytes of RA patients by IL-17. Among these genes we identified the following: tumor necrosis factor-stimulated gene-6 (TSG-6), IL-6, IL-8, GRO-beta, and bone morphogenetic protein-6 with an expression 3.6-10.6-fold that in the unstimulated control. IL-17 augmented the expression of TSG-6, a hyaluronan-binding protein, in a time- and dose-dependent manner. IL-17 showed additive effects with IL-1beta and tumour necrosis factor-alpha on the expression of TSG-6, IL-6 and IL-8. The mitogen-activated protein kinase p38 seems to be necessary for the regulation of TSG-6 expression by IL-17, as shown by inhibition with SB203580. Our results support the hypothesis that IL-17 is important in the pathogenesis of RA, contributing to an unbalanced production of cytokines as well as participating in connective tissue remodeling.