R. Urade et al., Accumulation and degradation in the endoplasmic reticulum of a truncated ER-60 devoid of C-terminal amino acid residues, J BIOCHEM, 127(2), 2000, pp. 211-220
The accumulation and degradation in the endoplasmic reticulum (ER) of a tru
ncated ER-60 protease, from which the C-terminal 89 amino acid residues hav
e been deleted (K 417 ochre), was examined. K 417 ochre overexpressed in CO
S-l cells is not secreted into the medium, but accumulates as insoluble agg
regates in non-ionic detergent without degradation in unusual clump membran
e structures. K 417 ochre, stably expressed, forms soluble aggregates in no
n-ionic detergent and is distributed in the reticular structures of ER, Und
er these conditions, K 417 ochre is not secreted into the medium but is deg
raded with a half-life time of more than 8 h, Since K 417 ochre/C all S, in
which all the Cys residues of K 417 ochre are replaced by Ser, also forms
aggregates, an inter-disulfide bond appears unnecessary for aggregation. In
both types of aggregates, Ig heavy chain binding protein, calnexin, glucos
e regulated protein 94, calreticulin, ERp72, and protein disulfide isomeras
e are scarcely found. Since degradation of the stably expressed K 417 ochre
was not inhibited by lactacystin, leupeptin, NH4Cl, or cytocharasin B, but
was inhibited by N-acetyl-leucyl-leucyl-norleucinal, the self-aggregated a
bnormal protein in the lumen of ER is assumed to be degraded by an unknown
protease system other than proteasome, lysosome or autophagy.