The presence of malfolded proteins in the endoplasmic reticulum signals the induction of glucose-regulated proteins

Abstract

Two glucose-regulated proteins, GRP78 and GRP94, are major constituents of the endoplasmic reticulum (ER) of mammalian cells. These proteins are synthesized constitutively in detectable amounts under normal growth conditions; they can also be induced under a variety of conditions of stress including glucose starvation and treatment with drugs that inhibit cellular glycosylation, with calcium ionophores or with amino-acid analogues. Unlike the closely-related heat shock protein (HSP) family, the GRPs are not induced significantly by high temperature. Recently, GRP78 has been identified as the immunoglobulin heavy chain binding protein (BiP) (ref. 5 and Y.K. et al., in preparation) which binds transiently to a variety of nascent, wild-type secretory and transmembrane proteins and permanently to malfolded proteins that accumulate within the ER. We have tested the hypothesis that the presence of malfolded proteins may be the primary signal for induction of GRPs by expressing wild-type and mutant forms of influenza virus haemagglutinin (HA) in simian cells. Only malfolded HAs, whose transport from the ER is blocked, induced the synthesis of GRPs 78 and 94. Additional evidence is presented that malfolding per se, rather than abnormal glycosylation, is the proximal inducer of this family of stress proteins.

Acidosis Causes Endoplasmic Reticulum Stress and Caspase-12-Mediated Astrocyte Death

“…Western blotting showed that acidosis exposure increased levels of procaspase-12 as well as the active 46 and 35 kDa caspase-12 fragments, with peak expression levels at 6 to 12 hours after acidosis ( Figures 3A and 3C). Increased expression of the ER chaperone protein GRP-78 was also observed, consistent with an ER stress response (Kozutsumi et al, 1988). Astrocytes incubated with agents known to induce ER stress, tunicamycin, brefeldin A, and thapsigargin , showed a similar pattern of increased expression of procaspase-12 and the active caspase-12 fragments ( Figures 3B and 3D).…”

“…Acidosis in this range also can reduce the activity of ER Ca 2 þ ATPase (Wolosker et al, 1997). Since protein misfolding and reduced ER Ca 2 þ are both known to cause ER stress (Kozutsumi et al, 1988;Paschen and Frandsen, 2001), acidosis could be an important factor contributing to the ER stress response after ischemia.…”

The protein disulphide-isomerase family: unravelling a string of folds

“…ERp72 is an abundant, ubiquitous, stress-inducible protein with calcium-binding capacity [132,135,136,[162][163][164][165] that differs from other PDI-like proteins in having three active thioredoxin domains rather than two. The domain distribution is c-a o -a-b-bh-ah (see Figure 3).…”

Roles of CHOP/GADD153 in endoplasmic reticulum stress

“…6 The second response is upregulation of genes encoding ER chaperone proteins such as BiP/GRP78 and GRP94, enzymes including protein disulfide isomerase (PDI) and peptidyl-prolyl isomerase, and structural components of the ER including sarcoplasmic ER Ca 2 þ -ATPase 2 (SERCA2), to increase the protein-folding capacity in ER. [7][8][9] In addition to these genes, recent studies revealed that genes involved in translational recovery, amino-acid import, glutathione biosynthesis and protection against oxidative stress are also upregulated. 10 In a later phase, components of ER-associated degradation (ERAD), including ER degradation-enhancing a-mannosidase-like protein (EDEM), are transcriptionally induced to eliminate misfolded proteins in the ER by the ubiquitin-proteasome system.…”