The role of MAPK signalling pathways in the response to endoplasmic reticulum stress

• MAPK signalling acts as an effector and modulator for the unfolded protein response.
• MAPK signalling promotes cell cycle progression or arrest and survival or death.
• Cell fate determination following ER stress and MAPK signalling is context-specific.
• Cross-talk between MAPKs and UPR is evident in cancer, atherosclerosis and ischemia.
• UPR inhibitors have potential as single and combined therapies with MAPK inhibitors.

Perturbations in endoplasmic reticulum (ER) homeostasis, including depletion of Ca2 + or altered redox status, induce ER stress due to protein accumulation, misfolding and oxidation. This activates the unfolded protein response (UPR) to re-establish the balance between ER protein folding capacity and protein load, resulting in cell survival or, following chronic ER stress, promotes cell death. The mechanisms for the transition between adaptation to ER stress and ER stress-induced cell death are still being understood. However, the identification of numerous points of cross-talk between the UPR and mitogen-activated protein kinase (MAPK) signalling pathways may contribute to our understanding of the consequences of ER stress. Indeed, the MAPK signalling network is known to regulate cell cycle progression and cell survival or death responses following a variety of stresses. In this article, we review UPR signalling and the activation of MAPK signalling pathways in response to ER stress. In addition, we highlight components of the UPR that are modulated in response to MAPK signalling and the consequences of this cross-talk. We also describe several diseases, including cancer, type II diabetes and retinal degeneration, where activation of the UPR and MAPK signalling contribute to disease progression and highlight potential avenues for therapeutic intervention. This article is part of a Special Issue entitled: Calcium Signaling In Health and Disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.