Transformation by oncogenic ras-p21 alters the processing and subcellular localization of the lysosomal protease cathepsin D.

The expression, processing, and intracellular localization of cathepsin D (CD), an endosomal-lysosomal protease involved in malignancy, were studied in rat embryo fibroblasts transformed with an active mutant of c-Ha-ras oncogene. The pattern of the processed molecular forms of CD, comprising two single-chain mature forms of 45 and 43 kDa and two double-chain mature forms of 34 + 9 kDa and 30 + 14 kDa, expressed by the parental cell line was similar to that found in normal rat liver cells. By contrast, in the ras-transfected counterpart this pattern was profoundly altered in that the 45 kDa species was much less represented and the 30 + 14 kDa species virtually absent. In both untransformed and ras-transformed cells the conversion of proCD into mature forms was not inhibited by ammonium chloride, which is known to increase the intravacuolar pH of post-Golgi compartments. Yet, this drug induced the accumulation of the 43 and 45 kDa molecular forms of mature CD in ras-transformed cells and of the 34 kDa molecule in untransformed cells. As compared to controls, in ras-transformed fibroblasts vacuolar compartments containing CD were reduced in number and mostly located toward the periphery of the cell. This contrasted with the perinuclear distribution of CD-positive granules in untransformed cells. Serum deprivation did not affect the growth, nor the intra- and extracellular accumulation of CD activity in ras-transformed cultures, while it blocked the growth and strongly stimulated the accumulation of CD in the medium in cultures of control fibroblasts. Altogether these data are indicative for a crucial role of ras GTPase in the regulation of the transport between post-Golgi organelles.