TY - JOUR
T1 - Exposed thiols confer localization in the endoplasmic reticulum by retention rather than retrieval
AU - Isidoro, Ciro
AU - Maggioni, Claudia
AU - Demoz, Marina
AU - Pizzagalli, Antonella
AU - Fra, Anna M.
AU - Sitia, Roberte
PY - 1996
Y1 - 1996
N2 - The cysteine present in the Ig μ chain tailpiece (μtp) prevents the secretion of unpolymerized IgM intermediates and causes their accumulation in the endoplasmic reticulum (ER). In principle, this can be the consequence of actual retention in this organelle or of retrieval from the Golgi. To determine which of the two mechanisms underlies the cysteine-dependent ER localization, we analyze here the post-translational modifications of suitably engineered cathepsin D (CD) molecules. The glycans of this protease are phosphorylated by post-ER phosphotransferases and further modified in the trans-Golgi to generate a mannose 6-phosphate lysosome targeting signal. Only trace amounts of the μtp-tagged CD (CDMμtpCys) are phosphorylated, unless retention is reversed by exogenous reducing agents or the critical cysteine mutated (CDMμtpSer). In contrast, a KDEL-tagged CD, that is retrieved from the Golgi into the ER, acquires phosphates, though mainly resistant to alkaline phosphatase. Similarly to CDMμtpSer, the few CDMμtpCys molecules that escape retention and acquire phosphates in the cis-Golgi are transported beyond the KDEL retrieval compartment, as indicated by their sensitivity to alkaline phosphatase. These results demonstrate that the thiol-dependent ER localization arises primarily from true retention, without recycling through the Golgi.
AB - The cysteine present in the Ig μ chain tailpiece (μtp) prevents the secretion of unpolymerized IgM intermediates and causes their accumulation in the endoplasmic reticulum (ER). In principle, this can be the consequence of actual retention in this organelle or of retrieval from the Golgi. To determine which of the two mechanisms underlies the cysteine-dependent ER localization, we analyze here the post-translational modifications of suitably engineered cathepsin D (CD) molecules. The glycans of this protease are phosphorylated by post-ER phosphotransferases and further modified in the trans-Golgi to generate a mannose 6-phosphate lysosome targeting signal. Only trace amounts of the μtp-tagged CD (CDMμtpCys) are phosphorylated, unless retention is reversed by exogenous reducing agents or the critical cysteine mutated (CDMμtpSer). In contrast, a KDEL-tagged CD, that is retrieved from the Golgi into the ER, acquires phosphates, though mainly resistant to alkaline phosphatase. Similarly to CDMμtpSer, the few CDMμtpCys molecules that escape retention and acquire phosphates in the cis-Golgi are transported beyond the KDEL retrieval compartment, as indicated by their sensitivity to alkaline phosphatase. These results demonstrate that the thiol-dependent ER localization arises primarily from true retention, without recycling through the Golgi.
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U2 - 10.1074/jbc.271.42.26138
DO - 10.1074/jbc.271.42.26138
M3 - Article
C2 - 8824258
AN - SCOPUS:0029908325
VL - 271
SP - 26138
EP - 26142
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 42
ER -