Promotes ciliogenesis in renal epithelial cells and therefore participates in the tubules formation and/or ensures the maintenance of the architecture of the lumen of the kidney (PubMed:18235088, PubMed:20875407). Has an impact on cellular symmetry by ensuring correct bipolar cell division through the regulation of centrosome duplication and mitotic spindle assembly and by maintaining oriented cell division (OCD) during tubular elongation through planar cell polarity (PCP) pathway (PubMed:19959710). During epithelial cell morphogenesis regulates also cell-cell and cell-matrix adhesion and participates in cell motility (By similarity). Promotes cell-cell contact through the positive regulation of PTK2 kinase activity leading to either positive regulation of epithelial cell proliferation through the HRAS/RAF1 pathways, or negative regulation of apoptosis through the PDK1/AKT1 pathway (PubMed:20875407). May act in collecting-duct and biliary differentiation (By similarity). May participate in the regulation of the cholangiocytes proliferation and the CCN2 production in an CXCL8-dependent manner (By similarity). Interacts with CAMLG (PubMed:16243292). Interacts with PKD2 (PubMed:18235088). Interacts (via CST) with ARF4; this interaction allows an efficient PKHD1 trafficking to the cilium (PubMed:24586199). Interacts (via CST) with RAB8A; this interaction controls trafficking through the endomembrane systeme and to the cilium (PubMed:20048263). Interacts (via CST) with TULP3; this interaction allows PKHD1 trafficking to the cilium (PubMed:28154160). The intra-cellular C-terminal fragment (ICD) translocates to the nucleus and is not detected in primary cilia (PubMed:16956880, PubMed:28729032). The extracellular domain (PECD) traffics beyond the mid-Golgi and localizes on exosome like vesicles (ELVs) attached to the primary cilium (PubMed:22021705, PubMed:28729032). In the urine, the extracellular domain (PECD) exists as an highly abundant secreted form and a less abundant PECD form that is either tethered to or shed with the C-terminal fragment (PTM) in ELVs (PubMed:28729032). The majority of full length PKHD1 protein resides at the endoplasmic reticulum and cannot pass beyond the mid-Golgi apparatus and is not detected in primary cilia (PubMed:28729032). Expressed in bile ducts and distal nephron segments but is absent from the proximal tubule (PubMed:18202188). Expressed in pancreas and kidney but also in the liver (PubMed:28729032). Expressed primarily in the distal tubule and thick ascending limb of the loop of Henle, and at low-level in the proximal tubule before renal development is complete at P0 (PubMed:28729032). Palmitoylated (PubMed:20048263). Palmitoylation facilitates the trafficking to the cilia and membrane targeting (PubMed:20048263). N-glycosylated. Several proteolytic cleavages occur within the extracellular domain, whereas at least one cleavage occurs within the cytoplasmic domain (PubMed:16956880). Cleaved by a probable proprotein convertase which produces an extracellular domain (polyductin extracellular domain, (PECD)) and a C-terminal fragment (polyductin transmembrane fragment (PTM)) which are tethered together by disulfide bonds (PubMed:17470460, PubMed:28729032). This extracellular domain (PECD) is then shed from the primary cilium by activation of a member of the ADAM metalloproteinase disintegrins family, resulting in concomitant release of an intra-cellular C-terminal fragment (ICD) via a gamma-secretase-dependent process (PubMed:17470460, PubMed:28729032). The proteolytic cleavage of the C-terminal intracellular fragment (ICD) is controlled by cytosolic calcium concentration and activation of PKC (PubMed:16956880). A mouse model, for human autosomal recessive polycystic kidney disease (ARPKD), where homozygous knockout mice for the Pkhd1 gene are born at a frequency lower than the expected Mendelian ratio (PubMed:18235088). Homozygous mice may lead to embryonic lethality (PubMed:18235088). Mice that escape embryonic lethality and survive into adulthood exhibit mild to severe tubular dilation or cyst formation in the kidney and liver accompanied by fibrosis and necrosis (PubMed:18235088). Homozygous mice for the Pkhd1 gene develop cysts and fibrosis in the liver at 1 month of age, and females develop proximal tubule (PT) dilation at 6 months of age whereas male mice never develop PT dilation (PubMed:22021705). Both male and female homozygous mice develop liver cysts and fibrosis at 3 months of age and this worsens with age until the liver is completely replaced by cysts at 12 mo of age (PubMed:22021705). A new mouse model, for ARPKD, where homozygous knockout mice for the Pkhd1 gene develop biliary dysgenesis accompanied by periportal fibrosis. Despite the progressive liver disease, these mice are viable at 12 months of age with no apparent decline in synthetic liver function. These mice also develop extrahepatic phenotypes involving the pancreas, extrahepatic bile ducts, and spleen, which occur in a more variable manner (PubMed:18202188). An other model, for ARPKD, where homozygous knockout mice for the Pkhd1 gene develop progressive renal cystic disease involving the proximal tubules, collecting ducts, and glomeruli. In the liver, mice show dilatation of the bile ducts and periportal fibrosis. Dilatation of pancreatic exocrine ducts is uniformly seen, with pancreatic cysts arising less frequently (PubMed:18286309).