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 end osomal and lysosomal functions was studied by following procathepsin D maturation and epidermal growth factor (EGF) degradation in HeLa cell s 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 p artly secreted in the extracellular medium via the constitutive secret ion pathway, Intracellular degradation of EGF was also inhibited by Va cA 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 usi ng transferrin, diphtheria toxin, and ricin as tracers, Subcellular fr actionation of intoxicated cells showed that procathepsin D and non-de graded EGF accumulate in lysosomes, Measurements of intracellular acid ification with fluorescein isothiocyanate-dextran revealed a partial n eutralization of the lumen of endosomes and lysosomes, sufficient to a ccount for both mistargeting of procathepsin D outside the cell and th e decreased activity of lysosomal proteases.