PLK2-mediated phosphorylation of SQSTM1 S349 promotes aggregation of polyubiquitinated proteins upon proteasomal dysfunction

ABSTRACT

Dysregulation in protein homeostasis results in accumulation of protein aggregates, which are sequestered into dedicated insoluble compartments so-called inclusion bodies or aggresomes, where they are scavenged through different mechanisms to reduce proteotoxicity. The protein aggregates can be selectively scavenged by macroautophagy/autophagy called aggrephagy, which is mediated by the autophagic receptor SQSTM1. In this study, we have identified PLK2 as an important regulator of SQSTM1-mediated aggregation of polyubiquitinated proteins. PLK2 is upregulated following proteasome inhibition, and then associates with and phosphorylates SQSTM1 at S349. The phosphorylation of SQSTM1 S349 strengthens its binding to KEAP1, which is required for formation of large SQSTM1 aggregates/bodies upon proteasome inhibition. Our findings suggest that PLK2-mediated phosphorylation of SQSTM1 S349 represents a critical regulatory mechanism in SQSTM1-mediated aggregation of polyubiquitinated proteins.

KEYWORDS:

• Phosphorylation
• PLK2
• polyubiquitination
• proteasome
• protein aggregation
• SQSTM1/p62

Acknowledgements

We would like to thank Yixian Cui, Huan Lian, Ru Zang, Li Zhong and Heng Lin for technical help and discussions. We thank SpecAlly Life Technology for proteomic data analysis.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Abbreviations

APP: amyloid beta precursor protein; CCCP: carbonyl cyanide m-chlorophenylhydrazone; EBSS: Earle’s balanced salt solution; 3-MA: 3-methyladenine; MEFs: murine embryonic fibroblasts; MLFs: murine lung fibroblasts; NaAsO₂: sodium arsenite; NH₄Cl: lysosome inhibitor ammonium chloride; SNCA/α-Syn: synuclein alpha; UPS: ubiquitin-proteasome system.

Data availability statement

The materials described in the study are either commercially available or available upon request from the corresponding author.

Supplementary material

Supplemental data for this article can be accessed online at https://doi.org/10.1080/15548627.2024.2361574.

Additional information

Funding

This work was supported by the National Natural Science Foundation of China (32188101 and 32070775), the CAMS Innovation Fund for Medical Sciences (2019-I2M-5-071), the Major Scientific and Technological Project of Hubei Province (2022ACA005), and the Fundamental Research Funds for the Central Universities (2042022dx0003).