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 (By similarity). 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 (By similarity). During epithelial cell morphogenesis regulates also cell-cell and cell-matrix adhesion and participates in cell motility (PubMed:32698519, PubMed:31398719). 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 (By similarity). 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. Interacts with PKD2. Interacts (via CST) with ARF4; this interaction allows an efficient PKHD1 trafficking to the cilium. Interacts (via CST) with RAB8A; this interaction controls trafficking through the endomembrane systeme and to the cilium. Interacts (via CST) with TULP3; this interaction allows PKHD1 trafficking to the cilium. The intra-cellular C-terminal fragment (ICD) translocates to the nucleus and is not detected in primary cilia (By similarity). The extracellular domain (PECD) traffics beyond the mid-Golgi and localizes on exosome like vesicles (ELVs) attached to the primary cilium (By similarity). 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 (By similarity). 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 (By similarity). The intra-cellular C-terminal fragment of 21-kDa translocates to the nucleus. The extracellular domain traffics beyond the mid-Golgi and localizes on exosome like vesicles (ELVs) attached to the primary cilium (By similarity). Palmitoylated. Palmitoylation facilitates the trafficking to the cilia and membrane targeting. N-glycosylated. Several proteolytic cleavages occur within the extracellular domain, whereas at least one cleavage occurs within the cytoplasmic domain. 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. 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. The proteolytic cleavage of the C-terminal intracellular fragment (ICD) is controlled by cytosolic calcium concentration and activation of PKC.