MOAP-1 associates with p62 to promote dissociation of the p62 bodies.Figure 5A MOAP-1 associates with p62 and their interaction is enhanced by DEN-mediated stress. LO2 cells transfected with Myc-MOAP-1 were treated with or without diethylnitrosamine (DEN) (200 µM) for 12 h and subjected to Duolink proximity ligation assay using anti-p62 and anti-Myc antibodies. Red dots represent MOAP-1/p62 interaction. B Alanine substitution of positively charged residues in the KYKKLR sequence of MOAP-1 abolishes its interaction with p62. Replacement of the positively charged residues in the KYKKLR sequence of MOAP-1 with alanine (referred to as the M3 mutant) disrupts MOAP-1/p62 interaction, whereas alanine substitution in the neighboring region of positively charged KRRR (M1 mutant) and negatively charged EEE (M2 mutant) has no effect. LO2 cells were transfected with plasmid encoding Myc-MOAP-1 or the indicated alanine mutants together with plasmid encoding Flag-p62. The cells were then subjected to co-IP assay with anti-Myc antibody. C Schematics of the amino acid (aa) residues in the aa115-208 region of MOAP-1 across the indicated mammalian species. Red boxes depicting location of positively or negatively charged residues of MOAP-1 subjected to mutagenesis to alter positively charged residues in the KYKKLR sequence (aa161-166.) (MOAP-1-M3), the KRRR sequence (aa202-205) (MOAP-1-M1) and the negatively charged residues in the EEE sequence (aa178-180) (MOAP-1-M2) to alanine. D MOAP-1, but not its p62-binding defective mutant, MOAP-1-M3, localizes at the p62 bodies. MOAP-1 KO LO2 cells were transfected with plasmid encoding Myc-MOAP-1 or Myc-MOAP-1-M3 mutant. The transfected cells were harvested at 14 hours post-transfection, which is the time point that localization of MOAP-1 at the p62 bodies is readily detected. IF analysis was performed on these cells using anti-p62 (red) and anti-Myc (green) antibodies. Arrowheads indicate colocalization between Myc-MOAP-1 and p62 bodies. E MOAP-1 but not the MOAP-1-M3-mutant promotes the exchange of RFP-p62 in the p62 bodies. WT LO2 cells transfected with expression vector encoding RFP-tagged p62 and GFP-tagged MOAP-1 or MOAP-1-M3. At 14 hours post-transfection, cells were subjected to FRAP assay. Scale bar: 2 µm. F Quantification of the rate of fluorescence recovery of RFP-p62 in cells co-expressing GFP-MOAP-1 or GFP-MOAP-1-M3 mutant. n = 6 samples. Error bars represent S.E.M. *P<0.05, **P<0.01, ns, not significant, two-way ANOVA. G Western analysis of lysates of the WT LO2 cells transfected with expression vector encoding RFP-tagged p62 and GFP-tagged MOAP-1 or MOAP-1-M3 as described in (E). H Re-expression of MOAP-1, but not the MOAP-1-M3 mutant, reduces the levels of p62 bodies. MOAP-1 KO LO2 cells were transfected with plasmid encoding Myc-MOAP-1 or Myc-MOAP-1-M3. The transfected cells were harvested at 24 hours post-transfection, which is the time point that MOAP-1 was found to effectively downregulate p62 bodies, followed by IF analysis as in (D). Cells expressing Myc-MOAP-1 or Myc-MOAP-1-M3 were marked by dashed lines.J Western blotting of MOAP-1 KO LO2 cells transfected with plasmid encoding Myc-MOAP-1 or Myc-MOAP-1-M3 mutant as described in (H).