Effect of leucine-rich repeat kinase 2 (LRRK2) on protein synthesis

Mutations in the leucine-rich repeat kinase 2 (LRRK2) cause Parkinson's disease (PD) in an autosomal dominant manner. Pathogenic mutations of LRRK2 such as G2019S and R1441C have been observed as common genetic causes of PD. Recently, LRRK2 has been reported to increase the reporter protein synthesis in both cap-dependent and -independent manners via phosphorylation of the ribosomal protein RPS15. In this study, we tested whether LRRK2 recombinant protein would directly increase protein synthesis using a well-defined in vitro coupled transcription/translation system. Addition of commercial full-length LRRK2 or GST-fused N-terminal-deleted LRRK2 recombinant proteins to the system showed no change of protein synthesis, as measured by luciferase reporter activity. In addition, the SUnSET assay to measure newly synthesized cellular proteins showed that G2019S overexpression had a minimal effect on the total protein amount. However, we confirmed the previous result that G2019S overexpression increased the amount of protein synthesized from an exogenous gene, Flag-VAMP2, which was transfected as a reporter, whereas there was no significant change in the amount of the Flag-VAMP2 mRNA. Inhibition of protein degradation showed that protein accumulation in the vector control was higher than that of the G2019S overexpression vector. Our results suggest that LRRK2 protein influences the amount of protein by inhibiting protein degradation rather than by directly stimulating translation.