Cytosolic sequestration of spatacsin by Protein Kinase A and 14-3-3 proteins

RAF1 kinase contributes to autophagic lysosome reformation

Autophagic lysosome reformation (ALR) is crucial for lysosomal homeostasis and therefore for different autophagic processes. Despite recent advances, the signaling mechanisms regulating ALR are incompletely understood. We show that RAF1, a member of the RAS/RAF/MEK/ERK pathway initiated by growth factors, has an essential, kinase-dependent role in lysosomal biology. RAF1 ablation impairs autophagy, and a proxisome screen identifies several proteins involved in autophagic and lysosomal pathways in the RAF1 molecular space. Two of these, SPG11 and the lipid phosphatase MTMR4, are RAF1 substrates. RAF1 ablation causes the appearance of enlarged autolysosomes and alters the phosphoinositide composition of autolysosomes. RAF1 and MTMR4 colocalize on autolysosomes, and overexpression of a MTMR4 mutant mimicking phosphorylation of the RAF1-dependent site rescues the lysosomal phenotypes induced by RAF1 ablation. Our data identify an RAF1 function in lysosomal homeostasis and a substrate through which the kinase regulates phospholipid metabolism at the lysosome, ALR, and autophagy.

Prospective Role of PAK6 and 14-3-3γ as Biomarkers for Parkinson's Disease

Background

Parkinson's disease is a progressive neurodegenerative disorder mainly distinguished by sporadic etiology, although a genetic component is also well established. Variants in the LRRK2 gene are associated with both familiar and sporadic disease. We have previously shown that PAK6 and 14-3-3γ protein interact with and regulate the activity of LRRK2.

Objective

The aim of this study is to quantify PAK6 and 14-3-3γ in plasma as reliable biomarkers for the diagnosis of both sporadic and LRRK2-linked Parkinson's disease.

Methods

After an initial quantification of PAK6 and 14-3-3γ expression by means of Western blot in post-mortem human brains, we verified the presence of the two proteins in plasma by using quantitative ELISA tests. We analyzed samples obtained from 39 healthy subjects, 40 patients with sporadic Parkinson's disease, 50 LRRK2-G2019S non-manifesting carriers and 31 patients with LRRK2-G2019S Parkinson's disease.

Results

The amount of PAK6 and 14-3-3γ is significantly different in patients with Parkinson's disease compared to healthy subjects. Moreover, the amount of PAK6 also varies with the presence of the G2019S mutation in the LRRK2 gene. Although the generalized linear models show a low association between the presence of Parkinson's disease and PAK6, the kinase could be added in a broader panel of biomarkers for the diagnosis of Parkinson's disease.

Conclusions

Changes of PAK6 and 14-3-3γ amount in plasma represent a shared readout for patients affected by sporadic and LRRK2-linked Parkinson's disease. Overall, they can contribute to the establishment of an extended panel of biomarkers for the diagnosis of Parkinson's disease.