The unfolded protein response regulator GRP78/BiP is required for endoplasmic reticulum integrity and stress-induced autophagy in mammalian cells

Abstract

In mammalian cells, endoplasmic reticulum (ER) stress has recently been shown to induce autophagy and the induction requires the unfolded protein response (UPR) signaling pathways. However, little is known whether autophagy regulates UPR pathways and how specific UPR targets might control autophagy. Here, we demonstrated that although ER stress-induced autophagy was suppressed by class III phosphatidylinositol-3 0 -kinase (PI3KC3) inhibitor 3-methyladenine (3-MA), wortmannin and knockdown of Beclin1 using small interfering RNA (siRNA), only 3-MA suppressed UPR activation. We discovered that the UPR regulator and ER chaperone GRP78/BiP is required for stress-induced autophagy. In cells in which GRP78 expression was knocked down by siRNA, despite spontaneous activation of UPR pathways and LC3 conversion, autophagosome formation induced by ER stress as well as by nutrition starvation was inhibited. GRP78 knockdown did not disrupt PI3KC3-Beclin1 association. However, electron microscopic analysis of the intracellular organelle structure reveals that the ER, a putative membrane source for generating autophagosomal double membrane, was massively expanded and disorganized in cells in which GRP78 was knocked down. ER expansion is known to be dependent on the UPR transcription factor XBP-1. Simultaneous knockdown of GRP78 and XBP-1 recovered normal levels of stress-induced autophagosome formation. Thus, these studies uncover 3-MA as an inhibitor of UPR activation and establish GRP78 as a novel obligatory component of autophagy in mammalian cells.

Redox-Sensitive Endoplasmic Reticulum Stress and Autophagy at Rostral Ventrolateral Medulla Contribute to Hypertension in Spontaneously Hypertensive Rats

“…Apart from its beneficial functions of abrogating ER stress, 39,50 GRP78 is reported recently as an obligatory component of ER stress-induced autophagy. 24 Gene knockdown of GRP78 has been demonstrated to block ER stress-induced autophagosome formation in human cells. 24,51 These results are in line with our finding that treatment with siGRP78 attenuated the augmented expression of LC3-II in RVLM of SHR.…”

“…24 Gene knockdown of GRP78 has been demonstrated to block ER stress-induced autophagosome formation in human cells. 24,51 These results are in line with our finding that treatment with siGRP78 attenuated the augmented expression of LC3-II in RVLM of SHR. Together with our finding of an involvement of ER stress-associated autophagy in hypertension phenotype of SHR, it is conceivable that under the scenario of chronic ER stress, as in RVLM of SHR, ER stress-associated autophagy might play a predominant role in the pathogenesis of hypertension.…”

“…SHR received an ER stress protector, 18 salubrinal; a superoxide dismutase (SOD) mimetic, 19 tempol; an autophagy inhibitor, 20,21 3-methyladenine (3-MA); bafilomycin A1 or small interfering RNA against GRP78 (siGRP78) 22 or light chain 3 (LC3; siLC3) 23 to inhibit ER stress-induced autophagy. 24 WKY rats received an ER stress inducer, 25 tunicamycin, or Ang II, alone or with additional treatment of tempol. These test agents were infused into the cisterna magna or microinjected directly into the bilateral RVLM.…”

Omi/HtrA2 is a positive regulator of autophagy that facilitates the degradation of mutant proteins involved in neurodegenerative diseases

“…The upregulation of Omi by ER stress is similar to that observed for other prosurvival stress response proteins such as Grp78, which is also upregulated in response to ER stress; its knockdown also spontaneously activates UPR and upregulates CHOP. 30 Omi is a key component needed to maintain mitochondrial integrity and the function of the respiratory chain, and loss of Omi produces a large number of damaged mitochondria. 10,29 We report here that Omi is responsible for the maintenance of constitutive autophagy (Figure 2).…”

The Expression of the Endoplasmic Reticulum Stress Sensor BiP/GRP78 Predicts Response to Chemotherapy and Determines the Efficacy of Proteasome Inhibitors in Diffuse Large B-Cell Lymphoma

“…25 Therefore, BiP/GRP78 expression is widely used as a marker for ER stress. 26,27 Because of its antiapoptotic role, the expression of BiP/GRP78 is important for tumor cell survival under ER stress. 28 Nevertheless, the role of BiP/GRP78 in B-cell lymphomas remains to be determined.…”