MAPK1/3 kinase-dependent ULK1 degradation attenuates mitophagy and promotes breast cancer bone metastasis

Autophagy. 2021 Oct;17(10):3011-3029. doi: 10.1080/15548627.2020.1850609. Epub 2020 Dec 7.

Abstract

The function of mitophagy in cancer is controversial. ULK1 is critical for induction of macroautophagy/autophagy and has a more specific role in mitophagy in response to hypoxia. Here, we show that ULK1 deficiency induces an invasive phenotype of breast cancer cells under hypoxia and increases osteolytic bone metastasis. Mechanistically, ULK1 depletion attenuates mitophagy ability during hypoxia. As a result, the accumulation of damaged, ROS-generating mitochondria leads to activation of the NLRP3 inflammasome, which induces abnormal soluble cytokines secretion, then promotes the differentiation and maturation of osteoclasts, and ultimately results in bone metastasis. Notably, phosphorylation of ULK1 by MAPK1/ERK2-MAPK3/ERK1 kinase triggers its interaction with BTRC and subsequent K48-linked ubiquitination and proteasome degradation. Also, a clearly negative correlation between the expression levels of ULK1 and p-MAPK1/3 was observed in human breast cancer tissues. The MAP2K/MEK inhibitor trametinib is sufficient to restore mitophagy function via upregulation of ULK1, leading to inhibition of NLRP3 inflammasome activation, thereby reduces bone metastasis. These results indicate that ULK1 knockout-mediated mitophagy defect promotes breast cancer bone metastasis and provide evidence to explore MAP2K/MEK- MAPK1/3 pathway inhibitors for therapy, especially in cancers displaying low levels of ULK1.Abbreviations: ATG: autophagy-related; Baf A1: bafilomycin A1; BTRC/β-TrCP: beta-transducin repeat containing E3 ubiquitin protein ligase; CHX: cycloheximide; CM: conditioned media; FBXW7/FBW7: F-box and WD repeat domain containing 7; MAPK1: mitogen-activated protein kinase 1; MTDR: MitoTracker Deep Red; mtROS: mitochondrial reactive oxygen species; microCT: micro-computed tomography; mtROS: mitochondrial reactive oxygen species; OCR: oxygen consumption rate; SQSTM1: sequestosome 1; ACP5/TRAP: acid phosphatase, tartrate resistant; ULK1: unc-51 like autophagy activating kinase 1.

Keywords: Bone metastasis; MAPK1/3 kinase; NLRP3 inflammasome; ULK1; breast cancer; mitophagy deficiency.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Autophagy-Related Protein-1 Homolog* / metabolism
  • Bone Neoplasms* / secondary
  • Breast Neoplasms* / pathology
  • Female
  • Humans
  • Intracellular Signaling Peptides and Proteins* / metabolism
  • Mitogen-Activated Protein Kinase 1* / metabolism
  • Mitogen-Activated Protein Kinase 3* / metabolism
  • Mitophagy*
  • X-Ray Microtomography

Substances

  • Intracellular Signaling Peptides and Proteins
  • Autophagy-Related Protein-1 Homolog
  • ULK1 protein, human
  • MAPK1 protein, human
  • MAPK3 protein, human
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3

Grant support

This study was supported by the Natural Science Foundation of China (81630079, 81772624, 81803006, 81972855, 81772835, 81972481, 81802789, 81972442), the Science and Technology Project of Guangzhou (201803010007), the Natural Science Foundation of Guangdong Province (2019A1515011209), the National Key R&D Program of China (2017YFC0908501).