The secreted Ly-6/uPAR related protein-1 (SLURP1) stabilizes epithelial cell junctions and suppresses TNF-α-induced cytokine production

Abstract

The secreted Ly-6/uPAR related protein-1 (SLURP1) is an anti-angiogenic and anti-inflammatory peptide highly expressed by the mucosal epithelial cells. SLURP1 is abundantly expressed by the corneal epithelial cells and is significantly downregulated when these cells are transformed and adapted for culture in vitro. Here we studied the effect of overexpressing SLURP1 in Human Corneal Limbal Epithelial (HCLE) cells cultured in vitro. The expression of DSP1, DSG1, TJP1 and E-Cadherin was significantly upregulated in two different SLURP1-overexpressing HCLE cell (HCLE-SLURP1) clones. HCLE-SLURP1 cells also displayed a significant decrease in tumor necrosis factor-α (TNF-α)-induced upregulation of (i) IL-8 from 7.4- to 2.9- and 2.1-fold, (ii) IL-1β from 4.9- to 3.9- and 2.9-fold, (iii) CXCL1 from 9- to 3.3- and 5.5-fold, and (iv) CXCL2 from 4.8- to 2.1- and 2.8-fold. ELISAs revealed a concomitant decrease in IL-8 levels in cell culture supernatants from 789 pg/ml in the control, to 503 and 352 pg/ml in HCLE-SLURP1 cells. Consistently, cytosolic IκB expression was elevated in HCLE-SLURP1 cells with a concurrent suppression of TNF-α-activated nuclear translocation of NF-κB. Collectively, these results elucidate the beneficial effects of SLURP1 in stabilizing the HCLE intercellular junctions and suppressing the TNF-α-induced upregulation of inflammatory cytokines by suppressing NF-κB nuclear translocation.