Endocytosis of light chains induces cytokines through activation of NF-kappaB in human proximal tubule cells.
BACKGROUND
In proteinuric states increased cytokine production through endocytosis of filtered proteins by proximal tubule cells (PTCs) has been proposed as a major mechanism mediating tubulointerstitial injury and progressive kidney disease. We studied the effects of six different light chains (LCs) on the production of cytokines in cultured human PTCs.


METHODS
LCs were isolated and purified from the urine of patients with myeloma and human PTCs were exposed to either LC or human serum albumin (HSA) for up to 24 hours. LC endocytosis was monitored by immunocytochemistry. Cytokines were determined by enzyme-linked immunosorbent assay (ELISA) in the supernatants and activation of nuclear factor-kappa B (NF-kappaB) was detected by electrophoretic mobility shift assays (EMSA) and immunocytochemistry.


RESULTS
Endocytosis of LCs induced the release of interleukins (IL) IL-6, IL-8 and monocyte chemoattractant protein-1 (MCP-1); however, there was considerable variability among the six different LCs. In contrast, HSA had no effect on cytokine production even at very high concentrations. Removal of LC-containing media resulted in cessation of IL-6 release. LC-induced cytokine release was associated with nuclear translocation of NF-kappaB subunits p50 and p65, as demonstrated by both EMSA and immunocytochemistry. Inhibitors of NF-kappaB, aspirin and pyrrolidineditiocarbamate (PDTC) markedly suppressed LC-induced cytokine production.


CONCLUSIONS
LC endocytosis leads to production of inflammatory cytokines through activation of NF-kappaB. This may be an important mechanism of chronic tubulointerstitial inflammation process commonly seen in multiple myeloma. These findings also point out a potential role by filterable low-molecular-weight proteins, like LCs, in PTC injury during all proteinuric diseases.
Sengul
Sule
S
Department of Medicine, Section of Nephrology, Tulane Medical Center, Tulane Cancer Center, and Veterans Administration Medical Center, New Orleans, Louisiana, USA.
Zwizinski
Craig
C
Simon
Eric E
EE
Kapasi
Aditi
A
Singhal
Pravin C
PC
Batuman
Vecihi
V
D002478:Cells, Cultured; D018932:Chemokine CCL2 / Q000096:biosynthesis / Q000378:metabolism; D024202:Electrophoretic Mobility Shift Assay; D004705:Endocytosis; D019084:Fluorescent Antibody Technique, Indirect; D006801:Humans; D007147:Immunoglobulin Light Chains / Q000378:metabolism / Q000494:pharmacology*; D015850:Interleukin-6 / Q000096:biosynthesis / Q000378:metabolism; D016209:Interleukin-8 / Q000096:biosynthesis / Q000378:metabolism; D007687:Kidney Tubules, Proximal / Q000166:cytology* / Q000378:metabolism*; D009101:Multiple Myeloma / Q000378:metabolism; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D012709:Serum Albumin / Q000494:pharmacology
D018932:Chemokine CCL2; D007147:Immunoglobulin Light Chains; D015850:Interleukin-6; D016209:Interleukin-8; D016328:NF-kappa B; D012709:Serum Albumin