Role of MAPK pathways in light chain-induced cytokine production in human proximal tubule cells.

We previously demonstrated that light chain (LC) endocytosis by human proximal tubule cells (PTCs) leads to production of cytokines through activation of NF-kappaB. Here, we examined the role of MAPK pathways in these responses using four species of myeloma LCs (kappa(1), kappa(2), kappa(3), and lambda(1)) previously shown to induce cytokine production by PTCs. Among these, kappa(1)-LC, which yielded the strongest cytokine responses, was selected for detailed studies. Activation of MAPKs was probed by Western blot analysis for the active kinases, ERK 1/2, JNK 1/2, and p38 in kappa(1)-LC-exposed human PTCs. To evaluate the functional role of MAPKs in LC-induced cytokine responses, we tested the effects of U-0126, an ERK inhibitor; SP-600125, an inhibitor of JNK; SB-203580, a p38 inhibitor; and curcumin, a JNK-AP-1 inhibitor, all added to media before 4-h exposure to 1.5 mg/ml kappa(1)-LC. IL-6 and monocyte chemotactic protein-1 (MCP-1) were determined by ELISA. Both LC and human serum albumin (HSA) activated ERK, although the HSA effect was weaker. kappa(1)-LC stimulated all three MAPKs, although phosphorylation of ERK was more pronounced and sustained than others. Inhibitors of ERK, JNK, and p38 reduced LC-induced IL-6 and MCP-1 production. These findings suggest that activation of MAPKs plays a role in LC-induced cytokine responses in PTCs. Activation of MAPKs may be involved in cytokine responses induced by other proteins as well as LCs and may be pivotal in the pathophysiology of tubulointerstitial injury in proteinuric diseases.