Regulation of cathepsin D dependent on the phenotype of colon carcinoma cells

Abstract

Int. J. Cancer: 68,479-484 (1996) 0 1996 Wilcy-Liss, Inc. In human skin fibroblasts, cathepsin D is synthesised as a glycosylated precursor form of M, 53,000 with 2 asparaginelinked oligosaccharide side chains in the rough endoplasmic reticulum (Hasilik and Von Figura, 1981; Gieselman et al., 1983). A portion of these N-linked oligosaccharides may become phosphorylated or converted into complex oligosaccharides in the Golgi apparatus (Hasilik and Von Figura, 1981; Giesclman et al., 1983). Phosphomannosyl residucs are lysosoma1 targcting signals which will bind to the mcmbrancassociated mannose-6-phosphate specific receptors (MPRs) in the trans-Golgi network (Dahms et al., 1989). During transport to lysosomes, the precursor form is successively converted into an intermediate M, 47,000 form by cleavage of the pro-peptide in a pre-lysosomal compartment and then into the mature M, 31,000 form found in lysosomes (Gieselman et al., 1983). REGULATION OF CATHEPSIN D DEPENDENT ON THE PHENOTYPE OF COLON CARCINOMA CELLSSylvianeThe oestrogen-stimulated over-cxprcssion of cathepsin D in breast cancer cells has becn suggested to induce a saturation of the mannose-6-phosphatc/IGF-II receptor that Icd to the abnormal secretion of the pro-enzyme (Rochefort et al., 1990). Subsequently, intracellular targeting of cathepsin D was also shown to occur in a mannose-6-phosphate indcpendent manner in HepG2 cells (Rijnboutt et al., 1991a, b ) and breast cancer cells (Capony et al., 1994). In the MPR indcpendent transport in HepG2 cells, cathepsin D also becomes transiently membrane-associated in the Golgi apparatus through binding to an M, 72,000 pro-saposin form (Zhu and Conner, 1994). After delivery to lysosomes and subsequent proteolytic processing, the complex is dissociated and both proteins are released from the membrane. In addition, pro-cathepsin D associates to an M, 68,000 pro-saposin to form a soluble complex.By Western blotting, we have previously shown that the HT-29 colon carcinoma cell line, which contains >95% undiffcrentiatcd HT-29 cclls, secretes pro-cathepsin D in the culture medium, whcreas a subpopulation derived from this cell line, which contains differentiated mucin-secreting HT-29 cells, appears unable to secrete the pro-enzyme. Furthermore, using immunocytochcmistry, we have found that cathepsin D is localised, like mucins, in the apical compartment of the cells, under the brush border (Huct et al., 1994).These observations Icd us to examine the synthesis and intracellular trafficking of cathepsin D in the HT-29 cell line, composed of > 95% undifferentiated cells, and in different types of differentiated colon carcinoma cells: differentiated mucin-secreting HT-29 goblet cells, obtained by a stepwise adaptation to the anti-cancer drug methotrcxatc ( M) (Ixsumeur et al., 1990); differentiated cnterocyte-like HT-29 cells, selected by hexose deprivation (Lcsumeur et al., 1991); and Caco-2 cells, which spontaneously display structural and functional differentiation characteristics of mature enterocytcs at late c...

Cell surface human α‐L‐fucosidase

“…In this sense it has been documented that a serine phosphorylation mechanism is involved in intracellular retention of α‐ l ‐fucosidase in lymphoid cells lacking the mannose 6‐phosphate that targets newly made hydrolases to lysosomes [34]. Another lysosomal enzyme, cathepsin D, shows a very complex intracellular trafficking, including a MPR–independent association to the membrane, and in fact it can be found at the periphery and processing some secreted proteins [35,36]. A different regulation for this enzyme was described for HT‐29 and Caco‐2 colorectal cells [35].…”

“…Another lysosomal enzyme, cathepsin D, shows a very complex intracellular trafficking, including a MPR–independent association to the membrane, and in fact it can be found at the periphery and processing some secreted proteins [35,36]. A different regulation for this enzyme was described for HT‐29 and Caco‐2 colorectal cells [35]. HT‐29 are about 95% undifferentiated whereas Caco‐2 cells differentiate spontaneously after confluence.…”