Transient Aggregation of Ubiquitinated Proteins Is a Cytosolic Unfolded Protein Response to Inflammation and Endoplasmic Reticulum Stress

• Published in: The Journal of biological chemistry 2012-06, Vol.287 (23), p.19687-19698
• Main Authors: Liu, Xian-De, Ko, Soyoung, Xu, Yi, Fattah, Elmoataz Abdel, Xiang, Qian, Jagannath, Chinnaswamy, Ishii, Tetsuro, Komatsu, Masaaki, Eissa, N. Tony
• Format: Article
• Language: English
• Subjects: Adaptor Proteins, Signal Transducing - genetics; Adaptor Proteins, Signal Transducing - metabolism; Aggresome-like Induced Structures; Aggresomes; Animals; Autophagy; Cell Line; Cytosol - metabolism; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Down-Regulation - physiology; Endoplasmic Reticulum Stress - physiology; ER Stress; Inflammation; Mice; Mice, Knockout; NF-kappa B - genetics; NF-kappa B - metabolism; NF-κB (NF-κB); p62; Protein Synthesis and Degradation; Regulatory Factor X Transcription Factors; Sequestosome-1 Protein; TOR Serine-Threonine Kinases - genetics; TOR Serine-Threonine Kinases - metabolism; Transcription Factors - genetics; Transcription Factors - metabolism; Transcription, Genetic - physiology; Ubiquitinated Proteins - genetics; Ubiquitinated Proteins - metabolism; Ubiquitination; Unfolded Protein Response - physiology; Up-Regulation - physiology; X-Box Binding Protein 1
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M112.350934

Failure to maintain protein homeostasis (proteostasis) leads to accumulation of unfolded proteins and contributes to the pathogenesis of many human diseases. Accumulation of unfolded proteins in the endoplasmic reticulum (ER) elicits unfolded protein response (UPR) that serves to attenuate protein translation, and increase protein refolding or degradation. In contrast to UPR in the ER, the regulatory molecules operative in cytosolic responses and their potential relation to ER stress are not well elucidated. Aggresome-like induced structures (ALIS) have been described as transient aggregation of ubiquitinated proteins in the cytosol. In this study, we show that cells respond to inflammation, infection or ER stress by cytosolic formation of ALIS, indicating that ALIS formation represents an early event in cellular adjustment to altered proteostasis that occurs under these conditions. This response was aided by rapid transcriptional up-regulation of polyubiqutin-binding protein p62. NF-κB and mTOR activation were also required for ALIS formation. Importantly, we show a cross talk between UPR in the ER and cytosolic ALIS. Down-regulation of ER UPR in XBP1 deficient cells increases cyotosolic ALIS formation. Furthermore, lysosomal activity but not macroautophagy is responsible for ALIS clearance. This study reveals the underlying regulatory mechanisms of ALIS formation and clearance, and provides a previously unrecognized common adaptive mechanism for cellular responses against inflammation and ER stress. ALIS are transient aggregation of ubiquitinated proteins. p62, NF-κB and mTOR were required for ALIS formation. Lysosomal activity is responsible for ALIS clearance. There is a cross talk between UPR in the ER and cytosolic ALIS. There is an adaptive mechanism for cellular responses against inflammation and ER stress.