DIFFERENTIATION-INDUCED CHANGES IN THE CONTENT, SECRETION, AND SUBCELLULAR-DISTRIBUTION OF LYSOSOMAL CATHEPSINS IN THE HUMAN COLON-CANCER HT-29 CELL-LINE

Enterocyte-like differentiated HT-29 colon carcinoma cells were shown to contain far higher intracellular levels of activity of lysosomal ca thepsins B, D, and L than their undifferentiated counterparts. In the latter, inhibition of lysosomal functions by leupeptin or ammonium chl oride led to a marked increase in the cell-associated activity of the three cathepsins. High levels of pro-cathepsins B, D, and L were found in the culture media of both HT-29 cell populations. Ammonium chlo- r ide and chloroquine, which are known to impair the mannose-6-phosphate -dependent trafficking of lysosomal-targetted proteins, did not increa se the secretion of the three cathepsins in either undifferentiated or differentiated cultures of HT-29 cells. Analyses by cell fractionatio n revealed heterogeneities with regard to the density and the content of lysosomal cathepsins between the two cell populations. Leupeptin in duced the accumulation of mature lysosomal cathepsins B and L in light density organelles in undifferentiated HT-29 cells. Altogether, these data demonstrate that (1) the expression and subcellular distribution of cathepsins B, D, and L in HT-29 cells are influenced by their stat e of enterocytic differentiation, (2) the segregation of lysosomal cat hepsins is largely inefficient in this tumor cell line and does not in crease upon differentiation, and (3) the mannose-6-phosphate-receptor- dependent pathway plays a minor role in the sorting of the three cathe psins, both in undifferentiated and enterocytic-differentiated HT-29 c ells.