Abstract
Expression of the glucose-regulated proteins (GRPs), GRP78 and GRP94, is induced by a variety of stress conditions including treatment of cells with tunicamycin or the calcium ionophore A23187. The stimulus for induction of these resident endoplasmic reticulum (ER) proteins appears to be accumulation of misfolded or underglycosylated protein within the ER. We have studied the induction of mRNAs encoding two other resident ER proteins, ERp72 and protein disulfide isomerase (PDI), during the stress response in Chinese hamster ovary cells. ERp72 shares amino acid sequence homology with PDI within the presumed catalytic active sites. ERp72 mRNA and, to a lesser degree, PDI mRNA were induced by treatment of Chinese hamster ovary cells with tunicamycin or A23187. These results identify ERp72 as a member of the GRP family. Stable high level overproduction of ERp72 or PDI from recombinant expression vectors did not alter the constitutive or induced expression of other GRPs. High level overexpression resulted in secretion of the overproduced protein specifically but not other resident ER proteins. This suggests that the ER retention mechanism is mediated by more specific interactions than just KDEL sequence recognition.
Highlights
Expression of the glucose-regulated proteins (GRPs), GRP’78 and GRP94, is induced by a variety of stress conditions including treatment of cells with tunicamycin or the calcium ionophore A23 187
We have studied the induction of mRNAs -encoding two other resident endoplasmic reticulum (ER) proteins, ERp72 and protein disulfide isomerase (PDI), during the stress response in Chinese hamster ovary cells
To ascertain whether PDI or ERp72 mRNAs were induced by this stress condition, Chinese hamster ovary (CHO) cells were treated with tunicamycin for 8 or 24 h
Summary
Expression of the glucose-regulated proteins (GRPs), GRP’78 and GRP94, is induced by a variety of stress conditions including treatment of cells with tunicamycin or the calcium ionophore A23 187. We have studied the induction of mRNAs -encoding two other resident ER proteins, ERp72 and protein disulfide isomerase (PDI), during the stress response in Chinese hamster ovary cells. ERp72 mRNA and, to a lesser degree, PDI mRNA were induced by treatment of Chinese hamster ovary cells with tunicamycin or A23187. These results identify ERp72 as a member of the GRP family. GRP78 and GRP94 are resident ER proteins induced by a variety of stress conditions associated with increased secretory protein traffic (Dorner et al, 1989) or the accumulation of misfolded or unglycosylated protein in the ER (Chang et al, 1987; Kozutsumi et al, 1988; Watowich and Morimoto, 1988). Stable association of GRP78 with misfolded, unglycosylated, or incompletely assembled proteins correlates with a block in efficient secretion (Bole et al, 1986; Dorner et al, 1987; Hurtley et al, 1989), while transient association may be part of the normal secretory pathway (Kaufman et al, 1989; Machamer et al, 1990; Ng et al, 1989)
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