SUMO1 and autosomal recessive polycystic kidney disease: Moreover, immunostaining of the liver showed an enrichment of SUMO1 (i.e., combination of free SUMO1 ligand and SUMO1-conjugated proteins) in the cystic epithelium of patients with ADPKD and ARPKD, as well as in PCK rats, compared to the biliary epithelium of healthy controls (Fig. 1C).