Selective, potent blockade of the IRE1 and ATF6 pathways by 4‐phenylbutyric acid analogues

• Published in: British journal of pharmacology 2013-10, Vol.170 (4), p.822-834
• Main Authors: Zhang, Hui, Nakajima, Shotaro, Kato, Hironori, Gu, Liubao, Yoshitomi, Tatsuya, Nagai, Kaoru, Shinmori, Hideyuki, Kokubo, Susumu, Kitamura, Masanori
• Format: Article
• Language: English
• Subjects: 4‐phenylbutyric acid; Animals; ATF6; Cell Line; chemical chaperone; DNA-Binding Proteins - genetics; DNA-Binding Proteins - metabolism; Dose-Response Relationship, Drug; eIF-2 Kinase - metabolism; endoplasmic reticulum (ER) stress; Endoplasmic Reticulum Stress - drug effects; Eukaryotic Initiation Factor-2 - metabolism; Heat-Shock Proteins - metabolism; IRE1; JNK Mitogen-Activated Protein Kinases - metabolism; LIM Domain Proteins - antagonists & inhibitors; LIM Domain Proteins - metabolism; Membrane Proteins - antagonists & inhibitors; Membrane Proteins - metabolism; Microfilament Proteins - antagonists & inhibitors; Microfilament Proteins - metabolism; NF-kappa B - genetics; NF-kappa B - metabolism; PERK–eIF2α; Phenylbutyrates - pharmacology; Phosphorylation; Protein folding; Protein Kinase Inhibitors - pharmacology; Protein-Serine-Threonine Kinases - antagonists & inhibitors; Protein-Serine-Threonine Kinases - metabolism; Proto-Oncogene Proteins c-akt - metabolism; Rats; Regulatory Factor X Transcription Factors; Research Papers; Signal Transduction - drug effects; Transcription Factor CHOP - metabolism; Transcription Factors - genetics; Transcription Factors - metabolism; Transfection; unfolded protein response (UPR); Unfolded Protein Response - drug effects; X-Box Binding Protein 1
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/bph.12306

Background and Purpose 4‐Phenylbutyric acid (4‐PBA) is a chemical chaperone that eliminates the accumulation of unfolded proteins in the endoplasmic reticulum (ER). However, its chaperoning ability is often weak and unable to attenuate the unfolded protein response (UPR) in vitro or in vivo. To develop more potent chemical chaperones, we synthesized six analogues of 4‐PBA and evaluated their pharmacological actions on the UPR. Experimental Approach NRK‐52E cells were treated with ER stress inducers (tunicamycin or thapsigargin) in the presence of each of the 4‐PBA analogues; the suppressive effects of these analogues on the UPR were assessed using selective indicators for individual UPR pathways. Key Results 2‐POAA‐OMe, 2‐POAA‐NO2 and 2‐NOAA, but not others, suppressed the induction of ER stress markers GRP78 and CHOP. This suppressive effect was more potent than that of 4‐PBA. Of the three major UPR branches, the IRE1 and ATF6 pathways were markedly blocked by these compounds, as indicated by suppression of XBP1 splicing, inhibition of UPRE and ERSE activation, and inhibition of JNK phosphorylation. Unexpectedly, however, these agents did not inhibit phosphorylation of PERK and eIF2α triggered by ER stress. These compounds dose‐dependently inhibited the early activation of NF‐κB in ER stress‐exposed cells. 2‐POAA‐OMe and 2‐POAA‐NO2 also inhibited ER stress‐induced phosphorylation of Akt. Conclusion and Implications The 4‐PBA analogues 2‐POAA‐OMe, 2‐POAA‐NO2 and 2‐NOAA strongly inhibited activation of the IRE1 and ATF6 pathways and downstream pathogenic targets, including NF‐κB and Akt, in ER stress‐exposed cells. These compounds may be useful for therapeutic intervention in ER stress‐related pathological conditions.