Loss of Grp170 results in catastrophic disruption of endoplasmic reticulum functions

Abstract

GRP170, a product of the Hyou1 gene, is required for mouse embryonic development, and its ablation in kidney nephrons leads to renal failure. Unlike most chaperones, GRP170 is the lone member of its chaperone family in the ER lumen. However, the cellular requirement for GRP170, which both binds non-native proteins and acts as nucleotide exchange factor for BiP, is poorly understood. Here, we report on the isolation of embryonic fibroblasts from mice in which LoxP sites were engineered in the Hyou1 loci (Hyou1LoxP/LoxP). A doxycycline-regulated Cre recombinase was also stably introduced into these cells. Induction of Cre resulted in excision of Hyou1 and depletion of Grp170 protein, culminating in apoptotic cell death. As Grp170 levels fell we observed increased steady-state binding of BiP to a client, slowed degradation of a misfolded BiP substrate, and BiP accumulation in NP40-insoluble fractions. Consistent with disrupted BiP functions, we observed reactivation of BiP storage pools and induction of the unfolded protein response (UPR) in futile attempts to provide compensatory increases in ER chaperones and folding enzymes. Together, these results provide insights into the cellular consequences of controlled Grp170 loss and insights into mutations in the Hyou1 locus and human disease.

Excess dietary sodium partially restores salt and water homeostasis caused by loss of the endoplasmic reticulum molecular chaperone, GRP170, in the mouse nephron

“…In addition, the GRP170 NT-/- animals developed albuminuria and glucosuria, hallmarks of PT injury, and renal histology revealed features consistent with PT injury. As predicted based on our prior work, the loss of GRP170 also altered nephron channel stability and trafficking, especially in the proximal nephron(22, 23, 38).…”

“…UPR activation and GRP170 expression have also been linked to numerous disease states, including ischemic injury, diabetes, diabetic nephropathy, cancer, and neurodegenerative disease (27, 32, 54–58). We also recently showed that the progressive loss of GRP170 is accompanied by UPR activation and induction of apoptotic markers in mouse embryo fibroblasts (38). Therefore, we asked if a HS diet tempers UPR activation as a result of the downstream consequence of the amelioration of select kidney injury markers in GRP170 NT-/- mice (see above).…”