Systemic lupus erythematosus (SLE) is a representative systemic autoimmune disease characterized by activated T cells and polyclonally activated B cells that produce autoantibodies. Activation of autoreactive T and B cells plays a pivotal role in the pathogenesis of this disease. A role of focal adhesion kinase (FAK) in the pathogenesis has been suggested. Proline-rich tyrosine kinase2 (PYK2) is structurally related to FAK, however, the functional activation of PYK2 in SLE remains unclear. In the present study, we showed that PYK2 is significantly increased and activated in peripheral blood mononuclear cells (PBMCs) of patients with SLE. In addition, we showed the involvement of PYK2 proteins in the up-regulation of CD40L and CTLA4 expression and PBMC proliferation.
Freshly isolated PBMCs from 48 SLE patients, 32 patients with rheumatoid arthritis(RA) and 24 healthy individuals were analyzed for the expression and activation of PYK2 by western-blotting and immunocytochemistry. The other isolated PBMCs from patients with this condition were cultured and stimulated with PMA or TyrA9, and then the expression of costimulatory molecules CD40L and CTLA4 was evaluated using flow cytometry, PBMCs proliferation was determined with [3H]-thymidine incorporation (CPM).
Compared with RA patients and healthy donors, PBMCs from SLE patients expressed more of both the total PYK2 protein and its activated/phosphorylated form. The increase of activated PYK2 protein in SLE PBMCs was correlated with the complication of nephritis and inversly associated the level of serum complements. In active SLE patients, activation of PYK2 in PBMCs is accompanying the increased cell proliferation and the induced expression of costimulatory molecules CD40L and CTLA4.
Our findings indicate that phosphorylated PYK2 in SLE PBMCs may induce the expression of CD40L and CTLA4, and subsequently the cell proliferation. PYK2 signaling enhances the autoreactive lymphocyte activation and plays an important role in the pathogenesis of SLE.