EXPRESSION AND POSTTRANSLATIONAL FATE OF CATHEPSIN-D IN HT-29 TUMOR-CELLS DEPEND ON THEIR ENTEROCYTIC DIFFERENTIATION STATE

In the present work, we analyzed the variations in the expression and trafficking of cathepsin D (CD), a lysosomal endopeptidase, associated with the enterocytic differentiation of the human colon carcinoma HT- 29 cell line. In spite of the fact that the abundance of CD mRNA was s everalfold higher in undifferentiated HT-29 cells than in their entero cytelike differentiated counterparts, the intracellular levels of CD a ctivity and protein were found to be much higher in the latter. The ki netic of transport of newly synthesized proCD was different in the two cell populations: (a) full conversion of proCD into the lysosomal mat ure form required more than 24 h in differentiated cells, whereas it w as almost complete within 8 h in undifferentiated HT-29 cells; and (b) the extracellular release of proCD was shown to occur more rapidly an d to a higher degree in undifferentiated than in differentiated cells. Most of the secreted proCD contained phosphomannoses. Secretion of be ta-hexosaminidase activity doubled, whereas that of CD activity was un changed, upon vacuolar alkalinization with ammonium chloride or chloro quine. Inhibition of the lysosomal-autophagic degradative pathway resu lted in the accumulation of proCD molecules in undifferentiated HT-29 cells. Altogether these data suggest that: (a) the expression and the posttranslational fate of CD in HT-29 colon cancer cells are largely a ffected by the state of their enterocytic differentiation; and (b) in this cell line the acid-dependent mannose 6-phosphate receptor pathway is, at best, little involved in the trafficking of CD.