The endoplasmic reticulum (ER) is the primary site for folding and quality control for proteins destined to the cell surface and intracellular organelles. A variety of cellular insults alter ER homeostasis to disrupt protein folding, cause the accumulation of misfolded protein and activate an autophagic response. However, the molecular signaling pathways required for ER stress-induced autophagy are largely unknown. Recently, we discovered that a novel-type protein kinase C family member (PKCθ) is required for ER stress-induced autophagy. We shown that ER stress, in a Ca2+-dependent manner, induces PKCθ phosphorylation within the activation loop and localization with LC3-II in punctate cytoplasmic structures. Pharmacological inhibition, siRNA-mediated knockdown, or transdominant-negative mutant expression of PKCθ block the ER stress-induced autophagic response. PKCθ activation is not required for autophagy induced by amino acid starvation, and PKCθ activation in response to ER stress does not require either the mTOR kinase or the unfolded protein response signaling pathways. Herein, we review and discuss the significance of these findings with respect to regulation of autophagy in response to ER stress.
Addendum to: Sakaki K, Wu J, Kaufman RJ. Protein kinase C-θ is required for autophagy in response to stress in the endoplasmic reticulum. J Biol Chem 2008; 283:15370-80.Full Text Options