Background: Parkinson disease (PD) is characterized by a slow, progressive degeneration of dopaminergic neurons in the substantianigra. The cause of neuronal loss in PD is not well understood, but several genetic loci, including PTEN-induced putative kinase 1 (PINK1), have been linked to early-onset autosomal recessive forms of familial PD. Neuroinflammation greatly contributes to PD neuronal degeneration and pathogenesis. IL-1 is one of the principal cytokines that regulates various immune and inflammatory responses via the activation of the transcription factors NF-κB and activating protein-1. Despite the close relationship between PD and neuroinflammation, the functional roles of PD-linked genes during inflammatory processes remain poorly understood.Methods: To explore the functional roles of PINK1 in response to IL-1β stimulation, HEK293 cells, mouse embryonic fibroblasts derived from PINK1-null (PINK1 -/- ) and control (PINK1 +/+ ) mice, and 293 IL-1RI cells stably expressing type 1 IL-1 receptor were used. Immunoprecipitation and western blot analysis were performed to detect protein-protein interaction and protein ubiquitination. To confirm the effect of PINK1 on NF-κB activation, NF-κB-dependent firefly luciferase reporter assay was conducted.Results: PINK1 specifically binds two components of the IL-1-mediated signaling cascade, Toll-interacting protein (Tollip) and IL-1 receptor-associated kinase 1 (IRAK1). The association of PINK1 with Tollip, a negative regulator of IL-1β signaling, increases upon IL-1β stimulation, which then facilitates the dissociation of Tollip from IRAK1 as well as the assembly of the IRAK1-TNF receptor-associated factor 6 (TRAF6) complex. PINK1 also enhances Lys63-linked polyubiquitination of IRAK1, an essential modification of recruitment of NF-κB essential modulator and subsequent IκB kinase activation, and increases formation of the intermediate signalosome including IRAK1, TRAF6, and transforming growth factor-β activated kinase 1. Furthermore, PINK1 stimulates IL-1β-induced NF-κB activity via suppression of Tollip inhibitory action.Conclusions: These results suggest that PINK1 upregulates IL-1β-mediated signaling through the functional modulation of Tollip and IRAK1. These results further suggest that PINK1 stimulates the ubiquitination of proximal molecules and increases signalosome formation in the IL-1β-mediated signaling pathway. The present study therefore supports the idea of the close relationship between neuroinflammation and PD.
Bibliographical noteFunding Information:
The authors thank J Chung, K Nakayama, and G Takaesu for providing plasmids. They are also grateful to G Takaesu for providing 293 IL-1RI cells and to J Shen for the PINK1−/− and PINK1+/+ MEFs. This work was supported by grants from the Basic Science Research Program through the National Research Foundation (NRF) of Korea (2012–0000810 to KCC) and from the Brain Research Center of the 21st Century Frontier Research Program (2009K-001251 to KCC), all funded by the Ministry of Education, Science and Technology, Republic of Korea. This work was also supported by a NRF grant (2012R1A1A2021749 to KCC), and partially by grants from the Korea Healthcare Technology R&D Project (A092004 and A111653 to KCC), Ministry for Health, Welfare & Family Affairs, Republic of Korea.
All Science Journal Classification (ASJC) codes
- Cellular and Molecular Neuroscience