Overexpression of BiP in Tobacco Alleviates Endoplasmic Reticulum Stress

Abstract

To study the role of the lumenal binding protein (BiP) in the transport and secretion of proteins, we have produced plants with altered BiP levels. Transgenic plants overexpressing BiP showed dramatically increased BiP mRNA levels but only a modest increase in BiP protein levels. The presence of degradation products in BiP overproducers suggests a regulatory mechanism that increases protein turnover when BiP is abundant. Antisense inhibition of BiP synthesis was not successful, demonstrating that even a minor reduction in the basal BiP level is deleterious to cell viability. Overexpression of BiP leads to downregulation of the basal transcript levels of endogenous BiP genes and greatly reduces the unfolded protein response. The data confirm that BiP transcription is regulated via a feedback mechanism that involves monitoring of BiP protein levels. To test BiP activity in vivo, we designed a functional assay, using the secretory protein alpha-amylase and a cytosolic enzyme as a control for cell viability. During tunicamycin treatment, an overall reduction of alpha-amylase synthesis was observed when compared with the cytosolic marker. We show that the tunicamycin effect is due to the depletion of BiP in the endoplasmic reticulum because coexpressed BiP alone is able to restore efficient alpha-amylase synthesis. This is a novel assay to monitor BiP activity in promoting secretory protein synthesis in vivo.

Restoration of visual function in P23H rhodopsin transgenic rats by gene delivery of BiP/Grp78

“…Part of the reason for this moderate elevation was incomplete transduction of the retina (60%) by AAV-BiP. It is also possible that expression of BiP from the AAV-delivered gene down-regulates the synthesis of endogenous BiP mRNA (29). The level of endogenous BiP protein was not elevated more than 20-40% when it was induced by BiP inducer X (BIX) (20).…”

AtBAG7 , an Arabidopsis Bcl-2–associated athanogene, resides in the endoplasmic reticulum and is involved in the unfolded protein response

“…During ER stress, BiP and other Ca 2 + -dependent folding proteins, including calreticulin (CRT) and calnexin (CNX), are expressed as part of the UPR to create an optimal environment for proper protein folding (17,19,21,(27)(28)(29)(30)(31). Because AtBAG7 interacts with a major mediator of ER stress, AtBiP, we considered whether it plays a role within the UPR.…”

“…In contrast to yeast and mammals, the underlying mechanisms of the UPR in plants are not well documented. Recent data, however, suggest that the UPR is important in plants, particularly in response to both abiotic and biotic stimuli where it triggers a variety of processes, including attenuation of protein translation, activation of the ER-associated degradation pathway, or the induction of ER chaperones (17)(18)(19)(20)(21)(22)(23).…”

Functional analysis of Hsp70 superfamily proteins of rice (Oryza sativa)

“…In rice, ER Hsp70 (BiP) is found to associate with nascent polypeptides that emerge into the ER lumen during prolamin translocation and facilitate peptide folding and assembly (Muench et al 1997). Over-expression of BiP relieves "ER stress" (Leborgne-Castel et al 1999).…”