MYELOMA LIGHT CHAINS INDUCE EPITHELIAL-MESENCHYMAL TRANSITION IN HUMAN RENAL PROXIMAL TUBULE EPITHELIAL CELLS: A POTENTIAL ROLE IN RENAL FIBROSIS AND POSSIBLE INTERVENTION BY BONE MORPHOGENETIC PROTEIN 7 AND PITUITARY ADENYLATE CYCLASE-ACTIVATING POLYPEPTIDE.: 269

The most common type of renal injury in patients with multiple myeloma is “myeloma kidney,” a predominantly tubulointerstitial kidney disease that is characterized by cast formation and marked interstitial fibrosis. We previously demonstrated that excessive endocytosis of myeloma light chains (LCs) induces inflammatory cytokines in human proximal tubule epithelial cells (PTECs). In the present studies, we examined whether LCs directly induce epithelial-mesenchymal transition (EMT) in human renal PTECs. Human LCs were purified from the urine of myeloma patients with modest renal insufficiency. We found that LCs induce marked cellular morphologic alterations in PTECs, accompanied with increased mRNA levels for the extracellular matrix components, collagen IV and fibronectin. Using semiquantative immunoblotting and RT-PCR analyses in human PTECs exposed to 25 μM LCs for up to 72 hours, we observed that the expression of E-cadherin decreases after 24 hours, whereas the expression of α-SMA increased, consistent with the acquisition of mesenchymal characteristics. In contrast, exposure to human serum albumin (160 μM) had no effect on the expression of EMT-related molecules, and its effect was not different from the cells without protein absorption. Human cytokine antibody arrays showed that human PTECs exposed to LCs have increased expressions of profibrotic IL-1, IL-6, IL-8, IL-1ra, MCP-1/4, M-CSF, and TIMP-1/2, as well as EGF, VEGF, TNF-α/β, sTNF-R, and TGF-β. However, the induction of EMT by LCs was not blocked by a neutralizing TGF-β1 antibody, suggesting that this action was TGF-β1 independent. In contrast, LC-induced EMT was markedly attenuated by silencing the p38 MAPK gene using a siRNA. The use of 500 ng/mL bone morphogenetic protein 7 (BMP-7) or 10−8 M pituitary adenylate cyclase-activating polypeptide (PACAP) induced the formation of cell aggregates and the reacquisition of E-cadherin expression and renal proximal tubule epithelial morphology within the confluent cell monolayer during LC treatment. These findings demonstrate that LCs are a direct stimulus for EMT in human renal PTECs. LC-induced EMT involves multiple cytokines and is modulated by p38 MAPK but appears to be independent of the action of TGF-β. LC-induced EMT may be an important mechanism for kidney involvement in myeloma and may be reversible upon administration of exogenous BMP-7 or PACAP.