Polycystic kidney disease protein fibrocystin localizes to the mitotic spindle and regulates spindle bipolarity

Autosomal recessive polycystic kidney disease (ARPKD) is a significant hereditary renal disease occurring in infancy and childhood, which presents with greatly enlarged echogenic kidneys, ultimately leading to renal insufficiency and end-stage renal disease. ARPKD is caused by mutations in a single gene PKHD1, which encodes fibrocystin/polyductin (FPC), a large single transmembrane protein generally known to be on the primary cilium, basal body and plasma membrane. Here, using our newly generated antibody raised against the entire C-terminal intracellular cytoplasmic domain (ICD) of FPC, as well as our previously well-characterized antibody against a peptide of ICD, we report for the first time that at least one isoform of FPC is localized to the centrosome and mitotic spindle of dividing cells in multiple cell lines, including MDCK, mIMCD3, LLCPK1, HEK293, RCTEC and HFCT cells. Using short-hairpin-mediated RNA interference, we show that the inhibition of FPC function in MDCK and mIMCD3 cells leads to centrosome amplification, chromosome lagging and multipolar spindle formation. Consistent with our in vitro findings, we also observed centrosome amplification in the kidneys from human ARPKD patients. These findings demonstrate a novel function of FPC in centrosome duplication and mitotic spindle assembly during cell division. We propose that mitotic defects due to FPC dysfunction contribute to cystogenesis in ARPKD.