Intercellular adhesion molecule 1 underlies the functional heterogeneity of synovial cells in patients with rheumatoid arthritis: involvement of cell cycle machinery

p53 Levels positively correlate with carotid intima-media thickness in patients with subclinical atherosclerosis

BACKGROUND

The level of circulating p53 is related to inflammation in asymptomatic subjects with cardiovascular risk factors. Whether p53 is associated with the severity of atherosclerosis remains to be determined.

HYPOTHESIS

This study examines the relationship of systemic p53 levels with atherosclerotic risk factors and subclinical atherosclerosis.

METHODS

Circulating levels of p53 and markers of inflammation were measured in 356 subjects with cardiovascular risk factors but who were free from clinical cardiovascular disease. Subclinical atherosclerosis was evaluated by both the mean carotid intima-media thickness (IMT) and the presence of atherosclerotic plaques with the use of B-mode ultrasound in all subjects.

RESULTS

p53 levels were positively correlated with age (r = 0.382, P < 0.001), intercellular adhesion molecular-1 (ICAM-1; r = 0.510, P < 0.01), vascular cell adhesion molecular-1 (VCAM-1; r = 0.497, P < 0.01), E-selectin (r = 0.337, P < 0.01), and carotid IMT (r = 0.594, P < 0.01). The association between p53 and IMT remained significant in multiple regression analysis (P < 0.01) when controlling for traditional atherosclerotic risk factors and inflammatory markers.

CONCLUSION

Higher plasma p53 levels were associated with an increase in inflammatory markers, as well as increased carotid IMT. Circulating p53 may be useful in identifying subclinical atherosclerosis in subjects symptomatically free from cardiovascular disease.

Local cell proliferation in rheumatoid synovial tissue: analysis by cyclin expression

The immunohistochemical staining of cyclins was done to evaluate the proliferating cells in synovial tissue of rheumatoid arthritis (RA). Synovial specimens obtained from 18 patients with RA, 12 with osteoarthritis (OA), and 8 with traumatic arthritis (TA) were used for immunostaining of cyclins A and B1 and proliferating cell nuclear antigen (PCNA). The positive cells in lining layer (synoviocytes) and sublining layer (lymphoid and nonlymphoid cells) were counted. Moreover, the relationship between the frequency of their positive cells and clinical data of RA patients was analyzed statistically. In general, cyclin-A-, cyclin-B1-, and PCNA-positive cells in RA were more frequently observed as compared with those in OA and TA. Significant differences were found between RA and OA or TA in cyclin-A-, cyclin-B1-, and PCNA-positive sublining lymphoid cells, between RA and OA or TA in cyclin-B1- and PCNA-positive sublining nonlymphoid cells, and between RA and OA in cyclin-B1-positive synoviocytes. The ratio of cyclin-A- or cyclin-B1-positive cells per PCNA-positive cells was significantly higher in sublining lymphoid cells in RA than TA and in sublining lymphoid and nonlymphoid cells of RA than OA or TA. Moreover, a better relationship was observed between the frequency of cyclin-A-positive synoviocytes and age and between cyclin-A-positive sublining nonlymphoid cells and duration of the disease in RA patients. Our data demonstrated clearly that synoviocytes, as well as sublining lymphoid and nonlymphoid cells, could divide in situ, and more frequent cell division and a higher ratio of cyclin-A- or cyclin-B1-positive/PCNA-positive sublining cells could occur in RA than OA and TA.

beta1 integrin-mediated signaling induces intercellular adhesion molecule 1 and Fas on rheumatoid synovial cells and Fas-mediated apoptosis

OBJECTIVE

Rheumatoid arthritis (RA) synovial cells interact with inflammatory cells, as well as extracellular matrices, through integrins. However, the relevance of beta1 integrin to inflammatory processes in RA remains unclear. We examined the role of beta1 integrin-mediated signaling in RA.

METHODS

Expression of cell-surface molecules was assessed by FACScan. Engagement of beta1 integrins was performed by crosslinking using a specific monoclonal antibody (mAb) and ligand matrices such as fibronectin or collagen. To determine the involvement of tyrosine kinases in beta1 integrin-mediated signaling, the cells were pretreated with various inhibitors of intracytoplasmic signaling or were transfected with a wild-type focal adhesion kinase (FAK) or a dominant negative truncation of the FAK expression plasmid via cationic liposome-mediated transfection. Apoptosis of synovial cells was detected by double staining with propidium iodide and annexin V.

RESULTS

beta1 integrin was highly expressed on RA synovial cells. Engagement of beta1 integrins by crosslinking as well as by ligand matrices markedly up-regulated expression of intercellular adhesion molecule 1 (ICAM-1) and Fas. Up-regulation of ICAM-1 and Fas induced by beta1 integrin was mediated by the tyrosine kinase signaling pathway, especially involving FAK. Fas-mediated early apoptotic change in the cells was amplified by beta1 crosslinking.

CONCLUSION

Our results suggest that interaction of beta1 integrins with extracellular matrix augments expression of ICAM-1 and Fas on RA synovial cells, as well as Fas-mediated apoptosis of synovial cells. This might lead to the spontaneous growth arrest through the Fas/Fas ligand pathway observed in RA synovitis.

p53 activates ICAM-1 (CD54) expression in an NF-kappaB-independent manner

Intercellular adhesion molecule-1 (ICAM-1) is a crucial receptor in the cell-cell interaction, a process central to the reaction to all forms of injury. Its expression is upregulated in response to a variety of inflammatory/immune mediators, including cellular stresses. The NF-kappaB signalling pathway is known to be important for activation of ICAM-1 transcription. Here we demonstrate that ICAM-1 induction represents a new cellular response to p53 activation and that NF-kappaB inhibition does not prevent the effect of p53 on ICAM-1 expression after DNA damage. Induction of ICAM-1 is abolished after treatment with the specific p53 inhibitor pifithrin-alpha and is abrogated in p53-deficient cell lines. Furthermore, we map two functional p53-responsive elements to the introns of the ICAM-1 gene, and show that they confer inducibility to p53 in a fashion similar to other p53 target genes. These results support an NF-kappaB-independent role for p53 in ICAM-1 regulation that may link p53 to ICAM-1 function in various physiological and pathological settings.