IRE1α governs cytoskeleton remodelling and cell migration through a direct interaction with filamin A

The large number of candidate genes made available by comprehensive genome analysis requires that relatively rapid techniques for the study of function be developed. Here, we report a rapid and convenient electroporation method for both gain- and loss-of-function studies in vivo and in vitro in the rodent retina. Plasmid DNA directly injected into the subretinal space of neonatal rodent pups was taken up by a significant fraction of exposed cells after several pulses of high voltage. With this technique, GFP expression vectors were efficiently transfected into retinal cells with little damage to the operated pups. Transfected GFP allowed clear visualization of cell morphologies, and the expression persisted for at least 50 days. DNA-based RNA interference vectors directed against two transcription factors important in photoreceptor development led to photoreceptor phenotypes similar to those of the corresponding knockout mice. Reporter constructs carrying retinal cell type-specific promoters were readily introduced into the retina in vivo, where they exhibited the appropriate expression patterns. Plasmid DNA was also efficiently transfected into retinal explants in vitro by high-voltage pulses.

Accumulation of misfolded protein in the endoplasmic reticulum (ER) triggers an adaptive stress response-termed the unfolded protein response (UPR)-mediated by the ER transmembrane protein kinase and endoribonuclease inositol-requiring enzyme-1alpha (IRE1alpha). We investigated UPR signaling events in mice in the absence of the proapoptotic BCL-2 family members BAX and BAK [double knockout (DKO)]. DKO mice responded abnormally to tunicamycin-induced ER stress in the liver, with extensive tissue damage and decreased expression of the IRE1 substrate X-box-binding protein 1 and its target genes. ER-stressed DKO cells showed deficient IRE1alpha signaling. BAX and BAK formed a protein complex with the cytosolic domain of IRE1alpha that was essential for IRE1alpha activation. Thus, BAX and BAK function at the ER membrane to activate IRE1alpha signaling and to provide a physical link between members of the core apoptotic pathway and the UPR.

Endoplasmic reticulum (ER) stress is a common feature of several physiological and pathological conditions affecting the function of the secretory pathway. To restore ER homeostasis, an orchestrated signaling pathway is engaged that is known as the unfolded protein response (UPR). The UPR has a primary function in stress adaptation and cell survival; however, under irreversible ER stress a switch to pro-apoptotic signaling events induces apoptosis of damaged cells. The mechanisms that initiate ER stress-dependent apoptosis are not fully understood. Several pathways have been described where we highlight the participation of the BCL-2 family of proteins and ER calcium release. In addition, recent findings also suggest that microRNAs and oxidative stress are relevant players on the transition from adaptive to cell death programs. Here we provide a global and integrated overview of the signaling networks that may determine the elimination of a cell under chronic ER stress. This article is part of a Special Section entitled: Cell Death Pathways. © 2013.