FLI1 and ERG protein degradation is regulated via Cathepsin B lysosomal pathway in Human Dermal Microvascular Endothelial Cells.

OBJECTIVES FLI1 and ERG, important regulators of endothelial cell homeostasis, are reduced in microvascular endothelial cells (MVEC) in scleroderma patients and their deficiency has been implicated in disease pathogenesis. The goal of this study was to identify the mechanisms involved in the protein turnover of FLI1 and ERG in MVECs. METHODS The effects of lysosome and proteosome inhibitors on FLI1 and ERG levels was assessed by western blotting and capillary morphogenesis. The effect of scleroderma and control sera on the levels of FLI1 and ERG was examined. RESULTS The reduction of the protein levels of FLI1 and ERG in response to IFNα or Poly:(IC) was reversed by blocking either lysosomal (leupeptin and Cathepsin B inhibitor) or proteosomal degradation (MG132). MG132, leupeptin or CTSB-(i) also counteracted the anti-angiogenic effects of Poly:(IC) or IFNα. Scleroderma sera reduced protein levels of FLI1 and ERG in comparison to control sera. Treatment with CTSB(i) increased the levels of FLI1 and ERG in a majority of serum-treated samples. CONCLUSIONS Inhibition of cathepsin B was effective in reversing the reduction of FLI1 and ERG protein levels after treatment with IFNα or SSc sera, suggesting that targeting cathepsin B may have a beneficial effect in SSc vascular disease.