Lysosomotropic agents including azithromycin, chloroquine and hydroxychloroquine activate the integrated stress response

The integrated stress response manifests with the phosphorylation of eukaryotic initiation factor 2 alpha (eIF2 alpha) on serine residue 51 and plays a major role in the adaptation of cells to endoplasmic reticulum stress in the initiation of autophagy and in the ignition of immune responses. Here, we report that lysosomotropic agents, including azithromycin, chloroquine, and hydroxychloroquine, can trigger eIF2 alpha phosphorylation in vitro (in cultured human cells) and, as validated for hydroxychloroquine, in vivo (in mice). Cells bearing a non-phosphorylatable eIF2 alpha mutant (S51A) failed to accumulate autophagic puncta in response to azithromycin, chloroquine, and hydroxychloroquine. Conversely, two inhibitors of eIF2 alpha dephosphorylation, nelfinavir and salubrinal, enhanced the induction of such autophagic puncta. Altogether, these results point to the unexpected capacity of azithromycin, chloroquine, and hydroxychloroquine to elicit the integrated stress response.

Automated summary

This study revealed that azithromycin, chloroquine, and hydroxychloroquine can induce eIF2 alpha phosphorylation, triggering the integrated stress response in cells. In contrast, cells unable to phosphorylate eIF2 alpha in response to these drugs fail to accumulate autophagic puncta, highlighting the importance of eIF2 alpha phosphorylation in autophagy induction.