Fig. 5: PAR-binding deficient cancer SNPs of PARP13 exhibit smaller and more numerous stress granules.

A Structural model of PARP13.2-WWE domains (PDB: 7TGQ). The positively charged surface highlighted in blue indicates the potential “PAR path” that stabilizes PAR-binding. B ZnF5-WWE1&2 protein fragments of wild-type PARP13.2 or R681K mutant were incubated with 20-mer FAM-PAR to examine protein-PAR binding by fluorescence polarization. The mean ± SD was reported from three biological replicates; p < 0.005; two-tailed unpaired Student’s t-test. C Wild-type HeLa cells expressing GFP-tagged wild-type or mutant PARP13.2 constructs were treated with 250 µM sodium arsenite for 30 min. Cells were fixed and stained for eIF3b (red) and DAPI (blue). Transfecetd cells were shown in green. Scale bar, 10 µm. D Quantification of panel C. GFP channel was used to quantify stress granule number, mean area, and total area. The mean ± s.e. of each parameter was reported from three biological replicates; ***p < 0.001, ****p < 0.0001, ns = not significant, two-tailed unpaired Mann–Whitney U test for SG number analysis and two-tailed unpaired Student’s t test for the rest. Number of cells analyzed was provided in Source data. E Working model: The dual-binding ability of PARP13 allows it to act as a hub of multivalent interactions, linking the PAR interactome (PARylated proteins and PAR-binding proteins) with the RNA interactome (RNA-binding proteins and RNA-RNA interactions) in addition to protein-protein interactions. Notably, stress granule core components such as G3BP1, G3BP2 and UBAP2L are ADP-ribosylated⁶⁴, and G3BP1 and G3BP2 bind to PAR⁵⁰.