Cathepsin L is involved in cathepsin D processing and regulation of apoptosis in A549 human lung epithelial cells

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Cathepsins are implicated in a multitude of physiological and pathophysiological processes. The aim of the present study was to investigate the function of cathepsin L (catL) in the proteolytic network of human lung epithelial cells and its role in the regulation of apoptosis.

We found that catL-deficient A549 cells as well as lung tissue extracts of catL-/- mice express increased amounts of single-chain cathepsin D (catD). Degradation experiments indicate that catL specifically degrades the single-chain isoform of catD. Furthermore, we found that catL-deficient cells showed increased sensitivity to apoptosis. Finally, we demonstrate that the inhibition of catD activity by pepstatin A decreased the number of apoptotic cells in catL-deficient A549 cells after anti-Fas treatment.

In conclusion, catL is involved in catD processing and the accumulation of catD isoforms in catL-deficient cells is associated with increased rates of spontaneous and anti-Fas-induced apoptosis.

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