Effect of Helicobacter pylori vacuolating toxin on maturation and extracellular release of procathepsin D and on epidermal growth factor degradation

The effect of vacuolating toxin (VacA) from Helicobacter pylori on endosomal and lysosomal functions was studied by following procathepsin D maturation and epidermal growth factor (EGF) degradation in HeLa cells exposed to the toxin, VacA inhibited the conversion of procathepsin D (53 kDa) into both the intermediate (47 kDa) and the mature (31 kDa) form, Nonprocessed cathepsin D was partly retained inside cells and partly secreted in the extracellular medium via the constitutive secretion pathway, Intracellular degradation of EGF was also inhibited by VacA with a similar dose-response curve, VacA did not alter endocytosis, cell surface recycling, and retrograde transport from plasma membrane to trans-Golgi network and endoplasmic reticulum, as estimated by using transferrin, diphtheria toxin, and ricin as tracers, Subcellular fractionation of intoxicated cells showed that procathepsin D and non-degraded EGF accumulate in lysosomes, Measurements of intracellular acidification with fluorescein isothiocyanate-dextran revealed a partial neutralization of the lumen of endosomes and lysosomes, sufficient to account for both mistargeting of procathepsin D outside the cell and the decreased activity of lysosomal proteases.