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CAMK2/CaMKII activates MLKL in short-term starvation to facilitate autophagic flux

Qionghui Zhan1,2,3, Jaepyo Jeon3, Ying Li4

  • 1Department of Anesthesiology, The First Affiliated Hospital of Soochow University, Suzhou, Jiangsu, China.

Autophagy
|July 20, 2021
PubMed

Insights

Mixed lineage kinase domain like pseudokinase (MLKL) is activated by calcium/calmodulin dependent protein kinase II (CAMK2) during nutrient deprivation. This CAMK2-MLKL pathway promotes autophagic flux and cell survival, independent of necroptosis.

Area of Science:

  • Cellular Biology
  • Molecular Signaling
  • Autophagy and Cell Death Pathways

Background:

  • Mixed lineage kinase domain like pseudokinase (MLKL) is a known effector of necroptosis, activated by RIPK3.
  • Emerging evidence suggests MLKL also participates in endosomal trafficking, independent of RIPK3.
  • The precise role of MLKL in cellular responses to nutrient stress remains largely unexplored.

Purpose of the Study:

  • To investigate the role of MLKL phosphorylation during nutrient deprivation (serum and amino acid starvation).
  • To elucidate the signaling pathway regulating MLKL activation under starvation conditions.
  • To determine the functional consequences of MLKL activation on autophagy and cell survival during starvation.

Main Methods:

  • Utilized mouse Neuro-2a and L929 cells, and human HEK293 and HT29 cells.
  • Employed pharmacological and genetic manipulations (knockout, shRNA, siRNA) to disrupt MLKL and CAMK2.
  • Assessed MLKL phosphorylation, autophagosome markers (MAP1LC3B/LC3B, SQSTM1/p62), and autophagic flux using biochemical assays.

Main Results:

  • MLKL phosphorylation was induced by serum and amino acid deprivation, dependent on CAMK2 but not RIPK3.
  • Starvation-induced MLKL activation correlated with decreased LC3-II lipidation and SQSTM1/p62 levels, indicating impaired autophagosome maturation.
  • Disruption of MLKL or CAMK2 inhibited autophagic flux and prevented cell death during starvation, highlighting a pro-survival role.

Conclusions:

  • A novel CAMK2-MLKL signaling axis is activated by nutrient deprivation, distinct from the necroptosis pathway.
  • This pathway facilitates autophagic flux by promoting autophagosome maturation and lysosomal fusion, contributing to cell survival.
  • MLKL possesses a previously unrecognized function in regulating cellular metabolism and survival under stress, independent of its role in necroptosis.
Keywords:
AutophagosomeCa2+/calmodulin-dependent kinase IIRIPK3lysosomemacroautophagynecroptosisnutrient deprivation

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