Lipopolysaccharide inhibits translation of iron chaperone PCBP1 to regulate inflammatory cytokine response in macrophage.

Macrophages play a key role in maintaining systemic iron homeostasis and immunity. During pro-inflammatory stage macrophages retain iron due to the decrease of the unique iron exporter ferroportin. Increased cellular iron is sequestered in to storage protein ferritin by iron chaperone poly(rC)-binding protein 1 (PCBP1). However, the fate of PCBP1 and its interaction with ferritin in pro-inflammatory macrophages has not been studied so far. Here we report that PCBP1 protein level is down-regulated in lipopolysaccharide (LPS) treated macrophages. LPS did not alter PCBP1 mRNA and protein stability suggesting inhibition of translation as a mechanism of PCBP1 down-regulation that was confirmed by 35S-methionine incorporation assay. PCBP1 interacts with ferritin-H (Ft-H) subunit to load iron into ferritin. We detected a decreased interaction between PCBP1 and Ft-H after LPS-stimulation. As a result iron loading in to ferritin was affected with simultaneous increase in labile iron pool (LIP). Pre-treatment of cells with iron chelator dampened LPS-induced expression of TNF-α, IL-1β and IL-6 mRNA. Silencing of PCBP1 increased the magnitude of expression of these cytokines compared to control siRNA transfected LPS-treated macrophages. In contrast, overexpression of PCBP1 resulted a decrease in expression of these cytokines compared to vector transfected macrophages. Our results reveal a novel regulation of PCBP1 and its role in expression of cytokines in LPS-induced pro-inflammatory macrophages.