X-irradiation-induced changes of the prelysosomal and lysosomal compartments and proteolysis in HT-29 cells

As a consequence of external and internal ionizing radiation, lysosome-like bodies have been observed to increase both in size and number in some cell types. We investigated this process by morphological methods (electron microscopy, cationized ferritin uptake, acid phosphatase histochemistry, morphometry) in cultured HT-29 cells. In parallel with these studies, we measured the rate of protein degradation on the basis of 14C-valine release from prelabeled cellular proteins. We found that at 2 and 4 Gy doses of X-irradiation the volume of the vacuolar (probably lysosomal) compartment increased without detectable changes of acid phosphatase activity. A 2 Gy irradiation dose did not change protein degradation rate. However, 4 Gy caused a significant inhibition of 14C-valine release from prelabeled proteins. Our results indicate, that the radiation induced expansion of the lysosomal compartment is not necessarily accompanied by increased lytic activity of HT-29 cells.