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J. Cell Biol.,
Volume 142, Number 2, July 27, 1998 377-389
Department of Pharmacology, Biozentrum, University of Basel, CH-4056 Basel, Switzerland
ERGIC-53, a homo-oligomeric recycling
protein associated with the ER-Golgi intermediate
compartment (ERGIC), has properties of a mannose-selective lectin in vitro, suggesting that it may function
as a transport receptor for glycoproteins in the early secretory pathway. To investigate if ERGIC-53 is involved in glycoprotein secretion, a mutant form of this
protein was generated that is incapable of leaving the
ER. If expressed in HeLa cells in a tetracycline-inducible manner, this mutant accumulated in the ER and
retained the endogenous ERGIC-53 in this compartment, thus preventing its recycling. Mistargeting of
ERGIC-53 to the ER did not alter the gross morphology of the early secretory pathway, including the distribution of 
'-COP. However, it impaired the secretion of
one major glycoprotein, identified as the precursor of the
lysosomal enzyme cathepsin C, while overexpression of
wild-type ERGIC-53 had no effect on glycoprotein
secretion. Transport of two other lysosomal enzymes and three post-Golgi membrane glycoproteins was unaffected by inactivating the recycling of ERGIC-53. The
results suggest that the recycling of ERGIC-53 is required for efficient intracellular transport of a small
subset of glycoproteins, but it does not appear to be essential for the majority of glycoproteins.
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