Inflammatory cytokines increase extracellular procathepsin D in permanent and primary endothelial cell cultures

The protease cathepsin D (Cath D) and its proteolytically inactive proform, procathepsin D (ProCath D), turned out to be multifunctional within and outside the cell. Elevated levels of ProCath D occur in malignant tumors and in organs under chronic inflammation. One important source for this increase of ProCath D might be endothelial cells. Here we examined the expression of Cath D in the human endothelial cell line EA.hy 926 and in primary endothelial cells isolated from human umbilical cord veins (HUVEC). After serum-free incubation with or without human interferon-γ (hIFN-γ) and/or human tumor necrosis factor-α (hTNF-α) immature and mature Cath D forms were examined in cell extracts and in cell-conditioned medium concentrates by Western blotting. Lysates of EA.hy 926 cells as well as of HUVEC contained active Cath D as two-chain form, but only negligible amounts of ProCath D and Cath D intermediates. Yet both endothelial cell cultures accumulated ProCath D in their conditioned media in the absence of any stimulus. The treatment with hIFN-γ and/or hTNF-α had little effect on intracellular levels of Cath D, whereas the cytokine stimulation increased the extracellular presence of ProCath D in both endothelial cell cultures. The extracellular increase of ProCath D was not related to induction of apoptosis, as validated by cleaved caspase-3 in cell lysates. Acidification of cytokine-treated media converted ProCath D into Cath D, which was associated with cathepsin-like activity using a fluorogenic substrate-linked assay. We conclude, in vitro, endothelial cells are a cytokine-dependent source for extracellular ProCath D.