The role of endoplasmic reticulum stress in disease
Studying the consequences of protein misfolding in the endoplasmic reticulum (ER), termed ER stress, particularly on cell growth and survival.
Proteins destined for secretion or for insertion into the cell membrane are first folded within the endoplasmic reticulum. The process of protein folding can become defective in many disease states such as hypoxia, malignancy and some forms of diabetes. When the level of misfolded proteins within the endoplasmic reticulum increases, the cell is said to experience 'endoplasmic reticulum stress'.
We wish to understand the cellular consequences of endoplasmic reticulum stress, in particular its effects on tissue growth and cell survival. In doing so, we hope to identify targets for the development of novel therapies. During endoplasmic reticulum stress, protein biosynthesis is initially attenuated through phosphorylation of the translation initiation factor eIF2α by the kinase PERK. Subsequent dephosphorylation of eIF2α following the induction of the phosphatase PPP1R15a (GADD34) restores protein translation. We previously discovered that this recovery of translation can contribute to the toxic effects of endoplasmic reticulum stress. This raises the exciting possibility that modulation of eIF2α phosphorylation may provide a useful target for the development of novel drugs to protect tissues from cell death.
Cellular stresses frequently impair cell cycle progression, which can prejudice tissue growth. Using mammalian cell biology and Drosophila genetics we recently described a novel G2 cell cycle checkpoint initiated by translation attenuation during endoplasmic reticulum stress. This too provides potential targets for the development of new therapies.
This movie shows CHO cell expressing YFP-Z-α1-antitrypsin subjected to serial blockface scanning electron microscopy. The surface of antitrypsin-containing inclusions were traced in 2D images and combined to generate a 3D projection by isosurface rendering with a surface area detail of 36nm. Distinct coloration of physically separated inclusions showed that many of these structures contacted one another, but inspection of the original 3View stack revealed that inclusion membrane contacts were almost never accompanied by evidence of inter-luminal connectivity.
van‘t WoutEFA, van Schadewijk A, van Boxtel R, Dalton LE, Clarke HJ, Tommassen J, Marciniak SJ* & Hiemstra PS*. Virulence factors of Pseudomonas aeruginosa induce both the unfolded protein and integrated stress responses in airway epithelial cells. PLoS Pathogens 11(6): e1004946 (2015). *Joint senior authors
Chambers JE, Dalton LE, Clarke HJ, Malzer E, Dominicus CS, Patel V, Moorhead G, Ron D, Marciniak SJ. Actin dynamics tune the integrated stress response by regulating eukaryotic initiation factor 2α dephosphorylation. Elife 4, doi: 10.7554/eLife.04872 (2015).
Chen R, Rato C, Yan Y, Crespillo-Casado A, Clarke HJ, Harding HP, Marciniak SJ*, Read RJ*, Ron D*. G-actin provides substrate-specificity to eukaryotic initiation factor 2α holophosphatases. Elife 4, doi: 10.7554/eLife.04871 (2015). *Joint corresponding authors.
van ‘t Wout, E.F.A., Dickens, J.A., van Schadewijk, A., Haq, I., Kwok, H.F., Ordóñez, A., Murphy, G., Stolk, J., Lomas, D.A., Hiemstra, P.S. and Marciniak, S.J. Increased ERK signalling promotes inflammatory signalling in primary airway epithelium expressing Z α1-antitrypsin. Hum. Mol. Gen. 23, 929–941 (2014).
Malzer, E, Szajewska-Skuta, M., Dalton, L.E., Thomas, S.E., Hu, N., Skaer, H., Lomas, D.A., Crowther, D.C., and Marciniak, S.J. Coordinate regulation of eIF2α phosphorylation by dPPP1R15 and dGCN2 is required during Drosophila development. J. Cell Sci. 126, 1406–1415 (2013).
Ordóñez, A., Snapp, E.L., Tan, L., Miranda, E., Marciniak, S.J.§* and Lomas, D.A.* Endoplasmic reticulum polymers impair luminal protein mobility and sensitise to cellular stress in α1-antitrypsin deficiency. Hepatology 57, 2049–2060 (2013). *Joint senior authors §Corresponding author