Novel E3 Ubiquitin Ligase Regulators of Parkinson's Protein LRRK2
Parkinson’s Disease (PD) is a neurodegenerative movement disorder affecting approximately 1% of the population over 60, with no existing treatments that slow, stop, prevent, or reverse neuron loss. Missense mutations in Leucine-Rich Repeat Kinase 2 (LRRK2) are the most common identified cause of PD; however, the disease-driving and normal cellular functions of LRRK2 are not fully defined. We used two screening approaches to gain insight into LRRK2 function and regulation: a proteomic screen to identify novel LRRK2 interactors, and a CRISPRi screen to identify modifiers of LRRK2 turnover. Our proteomic screen generated a quantitative global interactome of full-length LRRK2 that identified 48 novel interacting proteins, including Tripartite Motif-Containing Protein 1 (TRIM1), a microtubule-associated E3 ubiquitin ligase. We find that TRIM1 binds an unstructured regulatory domain on LRRK2 to recruit it to the microtubule. Furthermore, TRIM1 ubiquitinates LRRK2, leading to its proteasomal degradation. Expression of TRIM1 also modulates LRRK2 kinase activity and cytotoxicity: TRIM1 inhibits Rab29-mediated LRRK2 kinase activation and rescues the neurite outgrowth deficit caused by the most common PD-driving mutation, LRRK2 G2019S. In our second screen, we sought to identify additional novel regulators of LRRK2 turnover, focusing on proteasomal degradation caused by pharmacological LRRK2 kinase inhibition. LRRK2 kinase inhibitors are a promising therapeutic strategy for PD, but also lead to ubiquitination and degradation of LRRK2 by unknown ubiquitin ligases, which appears to cause pulmonary toxicity in non-human primates. We identified two additional E3 ubiquitin ligases that target LRRK2 for degradation downstream of kinase inhibition. Together, these findings identify LRRK2 localization, ubiquitination, and degradation as important regulatory events with relevance for kinase activity, cytotoxicity, and pharmacological intervention in PD.