The selective degradation of intracellular components by autophagy involves sequential interactions of the cargo with a receptor, which also binds the autophagosomal protein Atg8 and a scaffold protein. Here, we demonstrated that mutations in C. elegans epg-11, which encodes an arginine methyltransferase homologous to PRMT1, cause the defective removal of PGL-1 and PGL-3 (cargo)-SEPA-1 (receptor) complexes, known as PGL granules, from somatic cells during embryogenesis. Autophagic degradation of the PGL granule scaffold protein EPG-2 and other protein aggregates was unaffected in epg-11/prmt-1 mutants. Loss of epg-11/prmt-1 activity impairs the association of PGL granules with EPG-2 and LGG-1 puncta. EPG-11/PRMT-1 directly methylates arginines in the RGG domains of PGL-1 and PGL-3. Autophagic removal of PGL proteins is impaired when the methylated arginines are mutated. Our study reveals that posttranslational arginine methylation regulates the association of the cargo-receptor complex with the scaffold protein, providing a mechanism for modulating degradation efficiency in selective autophagy.

SUMMARYThe arginine methylation status of histones dynamically changes during many cellular processes, including hematopoietic stem/progenitor cell (HSPC) development. The arginine methyltransferases and the readers that transduce the histone codes have been defined. However, whether arginine demethylation actively occurs in cells and what enzyme demethylates the methylarginine residues during various cellular processes are unknown. We report that JMJD1B, previously identified as a lysine demethylase for H3K9me2, mediates arginine demethylation of H4R3me2s and its intermediate, H4R3me1. We show that demethylation of H4R3me2s and H3K9me2s in promoter regions is correlated with active gene expression. Furthermore, knockout of JMJD1B blocks demethylation of H4R3me2s and/or H3K9me2 at distinct clusters of genes and impairs the activation of genes important for HSPC differentiation and development. Consequently, JMJD1B−/− mice show defects in hematopoiesis. Altogether, our study demonstrates that demethylase-mediated active arginine demethylation process exists in eukaryotes and that JMJD1B demethylates both H4R3me2s and H3K9me2 for epigenetic programming during hematopoiesis.

Protein synthesis is essential for cell growth, proliferation, and survival. Protein synthesis is a tightly regulated process that involves multiple mechanisms. Deregulation of protein synthesis is considered as a key factor in the development and progression of a number of diseases, such as cancer. Here we show that the dynamic modification of proteins by O-linked β-N-acetyl-glucosamine (O-GlcNAcylation) regulates translation initiation by modifying core initiation factors eIF4A and eIF4G, respectively. Mechanistically, site-specific O-GlcNAcylation of eIF4A on Ser322/323 disrupts the formation of the translation initiation complex by perturbing its interaction with eIF4G. In addition, O-GlcNAcylation inhibits the duplex unwinding activity of eIF4A, leading to impaired protein synthesis, and decreased cell proliferation. In contrast, site-specific O-GlcNAcylation of eIF4G on Ser61 promotes its interaction with poly(A)-binding protein (PABP) and poly(A) mRNA. Depletion of eIF4G O-GlcNAcylation results in inhibition of protein synthesis, cell proliferation, and soft agar colony formation. The differential glycosylation of eIF4A and eIF4G appears to be regulated in the initiation complex to fine-tune protein synthesis. Our study thus expands the current understanding of protein synthesis, and adds another dimension of complexity to translational control of cellular proteins.protein synthesis | translation initiation | glycosylation