Mechanism of RACK1-dependent ZAKα activation at stalled and collided ribosomes

  • Mol Cell. 2026 Jun 18;86(12):2341-2357.e10. doi: 10.1016/j.molcel.2026.04.034.
Anna Constance Vind  1 ,  José Francisco Martínez  1 ,  Zhenzhen Wu  1 ,  Andrii Bugai  2 ,  Kelly Mordente  1 ,  Giancarlo Abis  3 ,  Sébastien Chamois  4 ,  Sofia Ramalho  1 ,  Catarina Pechincha  1 ,  Laura Ryder  1 ,  Qiuyan Chen  1 ,  Mads Rasmussen  1 ,  Xinyao Shi  1 ,  Dandan He  1 ,  Jesper Q Svejstrup  1 ,  Peter Haahr  1 ,  David Gatfield  4 ,  Maria R Conte  3 ,  Torben Heick Jensen  2 ,  Melanie Blasius  1 ,  Simon Bekker-Jensen  5
Affiliations
  • 1. Center for Gene Expression, Department of Cellular and Molecular Medicine, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark.
  • 2. Department of Molecular Biology and Genetics, Aarhus University, Aarhus, Denmark.
  • 3. Randall Centre for Cell and Molecular Biophysics, King's College London, London SE1 1UL, UK.
  • 4. Center for Integrative Genomics, University of Lausanne, 1015 Lausanne, Switzerland.
  • 5. Center for Gene Expression, Department of Cellular and Molecular Medicine, University of Copenhagen, Blegdamsvej 3, 2200 Copenhagen, Denmark. Electronic address: [email protected].
PMID: 42214329 DOI: 10.1016/j.molcel.2026.04.034
Abstract

Despite a growing interest in the ribotoxic stress response (RSR), it remains unknown how the upstream p38- and JNK-activating MAP3 kinase ZAKα senses translational impairment. Combining AlphaFold3 prediction and RNA crosslinking and immunoprecipitation (CLIP), we uncover that ZAKα dynamically monitors the mRNA exit channel of elongating ribosomes. This is accomplished by ZAKα via direct interactions with the ribosomal proteins RACK1 and RPS27 as well as 18S rRNA helix-26. In this conformation, the RNA-binding S (sensing) and C-terminal domain of ZAKα span across the mRNA exit channel. Loss of ribosome processivity and mRNA stasis stabilizes the interaction allowing for kinase activation. Prolonged binding of ZAKα to stalled and collided ribosomes is associated with sequestration of the sterile alpha-motif (SAM) domain on RACK1, which allows for transient ZAKα dimerization, activation loop trans-autophosphorylation, and RSR activation. Our findings highlight how ZAKα senses both stalled and collided ribosomes in human cells through overlapping mechanisms.

Keywords
ZAK-alpha; ribosome collision; ribosome stalling; ribotoxic stress response; translation surveillance.
Products