Phosphorylation of LRRK2 serines 955 and 973 is disrupted by Parkinson’s disease mutations and LRRK2 pharmacological inhibition

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial Parkinson's disease. An amino terminal cluster of constitutively phosphorylated residues, serines 860, 910, 935, 955, and 973, appears to be biologically relevant. Phosphorylation of serines 910 and 935 is regulated in response to LRRK2 kinase activity and is responsible for interaction with 14-3-3 and maintaining LRRK2 in a non-aggregated state. We examined the phosphorylation status of two other constitutive phosphorylation sites, serines 955 and 973. Treatment of LRRK2 expressing cells with the selective LRRK2 inhibitor LRRK2-IN1 revealed that, like Ser910/Ser935, phosphorylation of Ser955 and Ser973 is disrupted by acute inhibition of LRRK2 kinase activity. Additionally, phosphorylation of Ser955 and 973 is disrupted in the context of several Parkinson's disease associated mutations [R1441G/C, Y1699C, and I2020T]. We observed that modification of Ser973 is dependent on the modification of Ser910/Ser935. Ser955Ala and Ser973Ala mutations do not induce relocalization of LRRK2; however, all phosphomutants exhibited similar localization patterns when exposed to LRRK2-IN1. We conclude that the mechanisms of regulation of Ser910/935/955/973 phosphorylation are similar and physiologically relevant. These sites can be utilized as biomarkers for LRRK2 activity as well as starting points for the elucidation of upstream and downstream enzymes that regulate LRRK2.