C. Isidoro et al., EXPRESSION AND POSTTRANSLATIONAL FATE OF CATHEPSIN-D IN HT-29 TUMOR-CELLS DEPEND ON THEIR ENTEROCYTIC DIFFERENTIATION STATE, Cell growth & differentiation, 8(9), 1997, pp. 1029-1037
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.