INDUCTION OF MONOCYTE CHEMOATTRACTANT PROTEIN-1 IN PROXIMAL TUBULE CELLS BY URINARY PROTEIN

Cytokines play a pivotal role in synthesis and deposition of extracell ular matrix in chronic renal failure (CRF). The proinflammatory proper ties of monocyte chemoattractant protein (MCP)-1 make it an ideal cand idate cytokine for the production of interstitial inflammation in CRF. To investigate the possible role of proteinuria in inducing proximal tubular (PT) MCP-1, MCP-1 mRNA levels were measured by Northern blot a nd reverse transcription PCR in confluent monolayers of PT cells in pr imary culture in media containing a variety of proteins. PT cells prod uced MCP-1 mRNA in response to bovine serum albumin (BSA), delipidated BSA (dBSA; 0.5 to 30 mg/ml), holotransferrin, and apotransferrin (1 t o 8 mg/ml). Unstimulated PT cells expressed very low levels of MCP-1 m RNA, detectable by reverse transcription PCR but not by Northern blot. The expression of MCP-1 mRNA reached a peak (sixfold greater than con trol) within 4 h of exposure to dBSA and was maintained for at least 2 4 h with continued exposure. Removal of dBSA from the media led to a r apid decline in MCP-1 mRNA expression, dBSA-induced MCP-1 expression w as inhibited by lysine, an inhibitor of protein uptake, and reproduced by dBSA purified by gel and size-selective filtration. dBSA influence d MCP-1 expression at the level of transcription and probably translat ion, as evidenced by abrogation of MCP-1 by actinomycin D and superind uction with the protein synthesis inhibitor cycloheximide. The concent ration of MCP-1 protein in response to dBSA added to the apical surfac e of PT cells was 2.4-fold greater in basolateral than in apical media , indicating basolateral secretion of MCP-1 protein. In summary, PT ce ll MCP-1 mRNA and protein expression are upregulated by albumin and tr ansferrin, in concentrations similar to those of proteinuric urine. Th is effect could explain the link between proteinuria and interstitial inflammation in CRF.