Phosphorylation by casein kinase 2 induces PACS-1 binding of nephrocystin and targeting to cilia

Abstract

Mutations in proteins localized to cilia and basal bodies have been implicated in a growing number of human diseases. Access of these proteins to the ciliary compartment requires targeting to the base of the cilia. However, the mechanisms involved in transport of cilia proteins to this transitional zone are elusive. Here we show that nephrocystin, a ciliary protein mutated in the most prevalent form of cystic kidney disease in childhood, is expressed in respiratory epithelial cells and accumulates at the base of cilia, overlapping with markers of the basal body area and the transition zone. Nephrocystin interacts with the phosphofurin acidic cluster sorting protein (PACS)-1. Casein kinase 2 (CK2)-mediated phosphorylation of three critical serine residues within a cluster of acidic amino acids in nephrocystin mediates PACS-1 binding, and is essential for colocalization of nephrocystin with PACS-1 at the base of cilia. Inhibition of CK2 activity abrogates this interaction and results in the loss of correct nephrocystin targeting. These data suggest that CK2-dependent transport processes represent a novel pathway of targeting proteins to the cilia.

Role of Primary Cilia in the Pathogenesis of Polycystic Kidney Disease

“…Recently, these proteins were localized to the cilium or the basal body (68,69). In the case of NPHP-1, this localization depends on its ability to interact with the phosphofurin acidic cluster sorting protein-1, which is regulated by the phosphorylation of NPHP1 by casein kinase 2 (70).…”

Caught in the act – protein adaptation and the expanding roles of the PACS proteins in tissue homeostasis and disease

“…Thus, PACS-1, which interacts with the clathrin adaptors AP-1 and AP-3, as well as the monomeric adaptor GGA3, mediates localization of furin and other client proteins to the trans-Golgi network (TGN) and also targets a subset of client proteins to the primary cilium, including the adaptor protein nephrocystin (also known as NPHP1) and the olfactory cyclic-nucleotide-gated ion channel (CNG), the latter by binding to the β1 subunit (CNGB1) (Fig. 3A) (Wan et al, 1998;Schermer et al, 2005;Jenkins et al, 2009;Youker et al, 2009). PACS-1 acquired a CK2-phosphorylated acidic cluster of its own, which is located in the disordered MR (see Fig.…”

Hypomorphic CEP290/NPHP6 mutations result in anosmia caused by the selective loss of G proteins in cilia of olfactory sensory neurons

“…Nephrocystins are a family of ciliary proteins that are likely involved in cargo sorting during transport from the basal body to the ciliary axoneme (16)(17)(18)(19)(20). Loss-of-function mutations in CEP290 are associated with Joubert syndrome, which is characterized by nephronophthisis, retinal degeneration, and cerebellar vermis hypoplasia (21,22).…”

“…CEP290 is localized to the connecting cilium of retinal photoreceptors, the basal body of an inner medullary collecting duct cell line (IMCD-3), and the centro-some of mitotic cells (21)(22)(23). Furthermore, the basal body of mammalian olfactory cilia is enriched in ␥-tubulin and resembles the Caenorhabditis elegans transition zone, which is enriched in nephrocystin proteins (7,(16)(17)(18). Hence, mutations in CEP290 may alter ciliary microtubule transport.…”