Activation of MAPKs by Light Chains 1 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-κB. Here, we examined the role of MAPK pathways in these responses using four species of myeloma LCs (κ 1 , κ 2 , κ 3 and λ 1) previously shown to induce cytokine production by PTCs.. Among these, κ 1-LC that yielded the strongest cytokine responses was selected for detailed studies. Activation of MAPKs was probed by Western-blots for the active kinases, ERK 1/2, JNK 1/2 and p38 in κ 1-LC-exposed human PTCs. To evaluate the functional role of MAPKs in LC-induced cytokine responses, we tested the effects of U0126, an ERK inhibitor, SP600125, an inhibitor of JNK, SB203580, a p38 inhibitor, and curcumin, a JNK-AP-1 inhibitor, all added to media prior to 4 h exposure to 1.5 mg/ml κ 1-LC. IL-6 and MCP-1 were determined by ELISA. Both LC and human serum albumin (HSA) activated ERK, although the HSA effect was weaker. κ 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 play 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.