Mutations in LRRK2 are the most common genetic causes of Parkinson's disease (PD). While the enzymatic activity of LRRK2 has been linked to PD, previous work has also provided support for an important role of elevated LRRK2 protein levels, independent of enzymatic activity, in PD pathogenesis. However, the mechanisms underlying the regulation of LRRK2 protein levels remain unclear.Here, we identify a role for the purine biosynthesis pathway enzyme ATIC in the regulation of LRRK2 levels and toxicity. AICAr, the precursor of ATIC substrate, regulates LRRK2 levels in a celltype-specific manner in vitro and in mouse tissue. AICAr regulates LRRK2 levels through AUF1-mediated mRNA decay. Upon AICAr treatment, the RNA binding protein AUF1 is recruited to the AUrich elements (ARE) of LRRK2 mRNA leading to the recruitment of the decapping enzyme complex DCP1/2 and decay of LRRK2 mRNA. AICAr suppresses LRRK2 expression and rescues LRRK2-induced dopaminergic neurodegeneration and neuroinflammation in PD Drosophila and mouse models. Together, this study provides insight into a novel regulatory mechanism of LRRK2 protein levels and function via LRRK2 mRNA decay that is distinct from LRRK2 enzymatic functions.

The Hippo pathway is an evolutionarily conserved developmental pathway that controls organ size by integrating diverse regulatory inputs, including actomyosin-mediated cytoskeletal tension. Despite established connections between the actomyosin cytoskeleton and the Hippo pathway, the upstream regulation of actomyosin in the Hippo pathway is less defined. Here, we identify the phosphoinositide-3-phosphatase Myotubularin (Mtm) as a novel upstream regulator of actomyosin that functions synergistically with the Hippo pathway during growth control. Mechanistically, Mtm regulates membrane phospholipid PI(3)P dynamics, which, in turn, modulates actomyosin activity through Rab11mediated vesicular trafficking. We reveal PI(3)P dynamics as a novel mode of upstream regulation of actomyosin and establish Rab11-mediated vesicular trafficking as a functional link between membrane lipid dynamics and actomyosin activation in the context of growth control. Our study also shows that MTMR2, the human counterpart of Drosophila Mtm, has conserved functions in regulating actomyosin activity and tissue growth, providing new insights into the molecular basis of MTMR2-related peripheral nerve myelination and human disorders.

In higher eukaryotes, post-transcriptional regulation of gene expression, which is accomplished by an ensemble of RNA-binding proteins (RBPs), is critical for cellular homeostasis. Unkempt (UNK) is an evolutionarily conserved Zinc Finger/RING domain RNA-binding protein that was originally identified as a developmental regulator in Drosophila. Recent studies suggest that UNK targets specific mRNAs through its two compact zinc finger clusters and regulates their translation. However, the underlying molecular mechanisms by which UNK represses translation remain unclear. To examine UNK interactions, we purified Flag-tagged UNK and subjected the preparations to Mass spectrometry (MS) and identified an enriched protein Cytoplasmic poly(A)-binding protein(PABPC1), a key component of the translation machinery that binds to the poly(A) tail of mRNAs to promote translation and mRNA turnover. GST Pull down assay and reciprocal immunoprecipitations in HEK293 cells further confirmed the strong interaction between UNK and PABPC1 and showed that the interaction is RNA-dependent. Notably, the structural analysis, along with mutational studies proved that the interaction is mediated by the C-terminal MLLE domain of PABPC1 and the C-terminal Domain of UNK both in vitro and in vivo. Further MS2 tethering assay indicated that UNK inhibits PABPC1-stimulated translation activity. Our studies identified Unkempt as a novel partner of PABPC1 that functions to represses PABPC1-stimulated translation. The findings provide novel insight into the molecular function of Unkempt and PABPC1-mediated translational machinery. Citation Format: Naren Li, Liang Hu, Qinfang Liu, Yulan Xiong, Jianzhong Yu. Translational repression by a novel partner of human cytoplasmic poly(A) binding protein [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 866.