Disruption of the human Cystin-1 myristoyl-electrostatic switch causes autosomal recessive polycystic kidney disease (ARPKD)

ABSTRACT: Autosomal recessive polycystic kidney disease (ARPKD; MIM#263200) is primarily caused by pathogenic variants in PKHD1, which encodes fibrocystin/polyductin (FPC). The Cys1cpk/cpk (cpk) mouse expresses a renal lesion that closely phenocopies ARPKD. Cys1-encoded cystin is a myristoylated protein that traffics to the primary cilium and the nucleus, where it regulates gene expression. We recently described the first human patient with ARPKD due to a homozygous CYS1 splicing variant. Here we present two siblings with ARPKD and homozygosity for a CYS1 c.4G>A (p.G2S) variant, which disrupts the G2 myristoylation site within the predicted N-terminal myristylation motif, MGxxxSx. Alignment of 97 vertebrate cystin protein sequences showed high conservation of a putative myristoyl-electrostatic switch that can regulate reversible protein binding to membranes. The conserved region includes the N-myristylation site and an adjacent arginine-rich stretch flanked by serine-8 (S8) and -17 (S17) residues. Using immunofluorescence and site-directed mutagenesis, we confirmed that S17 phosphorylation modulates cystin membrane association and intracellular trafficking. In turn, optogenetic activation of ciliary cAMP signaling reduced the cystin ciliary localization in a PKA-dependent manner. Tandem affinity purification (TAP) and mass spectroscopy identified the protein phosphatase PPM1A as a cystin-interacting partner. Inhibition of PPM1A with sanguinarine impeded cystin S17 de-phosphorylation confirming functional interaction. Our study demonstrates that cystin intracellular trafficking and nuclear function are regulated by a myristoyl-electrostatic switch mechanism, and further supports CYS1 as a disease-causing gene for human ARPKD, providing the first mechanistic insight for disease pathogenesis.

INSTRUMENT(S):

ORGANISM(S): Mus Musculus (mouse)

TISSUE(S): Kidney

DISEASE(S): Autosomal Recessive Polycystic Kidney Disease

SUBMITTER: Landon Wilson  

LAB HEAD: Lisa Guay-Woodford

PROVIDER: PXD048013 | Pride | 2026-04-13

REPOSITORIES: Pride