Myeloma light chains induce epithelial-mesenchymal transition in human renal proximal tubule epithelial cells.
BACKGROUND
To determine the role of epithelial-mesenchymal transition (EMT) as a potential mechanism contributing to the characteristic tubulointerstitial renal fibrosis in multiple myeloma, we examined whether myeloma light chains (LCs) directly induce EMT in human renal proximal tubule epithelial cells (PTECs).


METHODS
As positive controls we used TGF-beta1 and cyclosporine A (CsA), two agents known to induce EMT in PTECs. Human LCs were isolated and purified from the urine of myeloma patients with modest renal insufficiency without evidence of glomerular involvement. HK-2 cells were exposed to kappa LC (25 microM) for periods up to 72 h.


RESULTS
LCs induced marked cellular morphological alterations in PTECs, accompanied with increased expression levels of profibrotic TGF-beta1, FSP-1 and extracellular matrix components. Using semiquantitative immunoblotting and RT-PCR, we observed that the expression of E-cadherin decreased after 24 h, while the expression of alpha-SMA increased in PTEC after continuous exposure to kappa-LCs. Human serum albumin (HSA; 160 microM) had less potent effect on the expression of EMT-related molecules. Neutralizing TGF-beta1 antibody blocked CsA-induced EMT but had no effect on LC-exposed cells. LC-induced EMT and the secretions of IL-6 and MCP-1 were, however, markedly attenuated by p38 MAPK interference. The use of bone morphogenetic protein-7 or 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 and after LC exposure.


CONCLUSIONS
These findings demonstrate that LC is a direct stimulus for EMT in PTECs. LC-induced EMT involved multiple cytokines, is modulated by p38 MAPK, but appeared independent of the action of TGF-beta1. LC-induced EMT may be an important mechanism of kidney injury associated with myeloma and may be reversible upon the administration of exogenous PACAP.
Li
Min
M
Department of Medicine, Tulane University School of Medicine, 1430 Tulane Avenue, New Orleans, Louisiana 70112, USA.
Hering-Smith
Kathleen S
KS
Simon
Eric E
EE
Batuman
Vecihi
V
D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins / Q000494:pharmacology; D015820:Cadherins / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism; D002449:Cell Aggregation / Q000187:drug effects; D054338:Cell Transdifferentiation / Q000187:drug effects*; D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000378:metabolism; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D016326:Extracellular Matrix Proteins / Q000378:metabolism; D005355:Fibrosis / Q000378:metabolism / Q000473:pathology; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000378:metabolism* / Q000494:pharmacology*; D015850:Interleukin-6 / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D008648:Mesoderm / Q000187:drug effects / Q000378:metabolism / Q000473:pathology*; D009101:Multiple Myeloma / Q000378:metabolism*; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide / Q000494:pharmacology; D000071999:S100 Calcium-Binding Protein A4; D016212:Transforming Growth Factor beta / Q000494:pharmacology; D053773:Transforming Growth Factor beta1 / Q000378:metabolism; D048051:p38 Mitogen-Activated Protein Kinases / Q000378:metabolism
C525819:BMP7 protein, human; D055419:Bone Morphogenetic Protein 7; D019485:Bone Morphogenetic Proteins; C111835:CCL2 protein, human; D015820:Cadherins; D002135:Calcium-Binding Proteins; D018932:Chemokine CCL2; D016326:Extracellular Matrix Proteins; D007147:Immunoglobulin Light Chains; D015850:Interleukin-6; D051219:Pituitary Adenylate Cyclase-Activating Polypeptide; D000071999:S100 Calcium-Binding Protein A4; D016212:Transforming Growth Factor beta; D053773:Transforming Growth Factor beta1; C077591:S100A4 protein, human; D048051:p38 Mitogen-Activated Protein Kinases