The polycystic kidney disease protein PKD2 interacts with Hax-1, a protein associated with the actin cytoskeleton

Abstract

Despite the recent positional cloning of the PKD1 and PKD2 genes, which are mutated in the great majority of patients with autosomal-dominant polycystic kidney disease (PKD), the pathogenic mechanism for cyst formation is still unclear. The finding, that the PKD1 and PKD2 proteins interact with each other through their COOH termini, suggests that both proteins are part of the same protein complex or signal transduction pathway. Using a yeast two-hybrid screen with the PKD2 protein, we isolated the PKD2-interacting protein Hax-1. The specificity of the interaction was demonstrated by the fact that PKD2L, a protein closely related to PKD2, failed to interact with Hax-1. Immunofluorescence experiments showed that in most cells PKD2 and Hax-1 colocalized in the cell body, but in some cells PKD2 and Hax-1 also were sorted into cellular processes and lamellipodia. Furthermore we demonstrated an association between Hax-1 and the F-actin-binding protein cortactin, which suggests a link between PKD2 and the actin cytoskeleton. We speculate that PKD2 is involved in the formation of cell-matrix contacts, which are dysfunctional without a wildtype PKD2 protein, thus leading to cystic enlargement of tubular structures in the kidney, liver, and pancreas.polycystin-2 ͉ cortactin ͉ focal adhesion ͉ cell-matrix contact ͉ cell-cell contact W ith an incidence of Ϸ1:1,000 autosomal-dominant polycystic kidney disease (ADPKD) is one of the most common monogenetic human diseases (1). The positional cloning of two genes, which are mutated in the vast majority of patients with ADPKD, has opened new opportunities for a better understanding of cyst formation (2, 3). Whereas the PKD1 protein contains a number of motifs suggesting it is involved in cell-cell or cell-matrix interactions (4, 5), the homology between PKD2 and the ␣ 1 -subunits of voltage-activated calcium channels has led to the hypothesis that PKD2 influences calcium fluxes (3), but so far no experimental evidence has been presented for both assumptions. Meanwhile it could be demonstrated that PKD1 and PKD2 interact with each other through their COOH termini (6, 7), indicating that both proteins are part of the same protein complex or signal transduction pathway. The picture becomes even more complex by the recent identification of two PKD2-related proteins, the first of which has been named PKD2L (8, 9) and PKDL (10), the second PKD2L2 (9). The genomic location of the genes coding for PKD2L and PKD2L2 makes it unlikely that one of them is involved in renal cyst formation.The PKD2 gene encodes a protein of 968 aa with six putative transmembrane domains, both the NH 2 and COOH terminus have been suggested to extend into the cytoplasm (3). So far the characterization of the PKD2 protein has focused on its COOH terminus, which contains a calcium-binding EF-hand and a coiled-coil domain and represents the interface for the interaction with PKD1 (6, 7). Other domains in the COOH terminus of PKD2 are responsible for the association with TRPC1 (11), a member of the family of store-o...

Regulation of HAX-1 Anti-apoptotic Protein by Omi/HtrA2 Protease during Cell Death

“…This experiment clearly shows that Omi is solely responsible for HAX-1 cleavage, which is essential for apoptosis under the conditions used in these experiments. HAX-1 subcellular localization depends on cell type (21,30) and has been reported to be present in the mitochondria, cytoplasm, or plasma membrane (10,21,22,30). We performed subcellular fractionation to investigate where HAX-1 cleavage by Omi takes place.…”

“…Omi-induced HAX-1 Degradation Occurs in the Mitochondria-HAX-1 protein is reported to be present in the mitochondria as well as in the cytoplasm (10,21). We investigated where in the cell Omi-induced degradation of HAX-1 occurs.…”

Pkd1 Haploinsufficiency Increases Renal Damage and Induces Microcyst Formation following Ischemia/Reperfusion

“…7 In addition, the cellular effects of polycystins seem to rely on interaction with the cytoskeleton and mediation of cell-cell adhesion. 8,9 PC1 and PC2 activate a number of other pathways. PC1 may function as a G protein-coupled receptor.…”

HS1-Associated Protein X-1 Interacts with Membrane-Bound IgE: Impact on Receptor-Mediated Internalization

“…However, the subcellular localization of HAX-1 depends on the cell type. Accordingly, HAX-1 was localized in the cytoplasm (13) and even in mitochondria (14), and was found along the endoplasmic reticulum and the nuclear envelope as well (15). HAX-1 displays a weak homology to the intracellular mammalian protein, BNip3 (13), and similarity to the functionally important domains BH1 and BH2 of Bcl-2 family member proteins.…”

“…2) Association of HAX-1 with cortactin (or EMS1) (15), polycystic kidney disease protein 2 (15), ATP-binding cassette transporters BSEP, MDR1, and MDR2 (22) and G␣-13, a cell migration-stimulating component (23) emphasizes the involvement of HAX-1 in cell motility processes.…”