Polycystin 2 Interacts with Type I Inositol 1,4,5-Trisphosphate Receptor to Modulate Intracellular Ca2+ Signaling

Abstract

Autosomal dominant polycystic kidney disease, a common cause of renal failure, arises from mutations in either the PKD1 or the PKD2 gene. The precise function of both PKD gene products polycystins (PCs) 1 and 2 remain controversial. PC2 has been localized to numerous cellular compartments, including the endoplasmic reticulum, plasma membrane, and cilia. 2؉ transients. However, overexpressing the disease-associated PC2 mutants, the point mutation D511V, and the C-terminally truncated mutation R742X did not alter the t1 ⁄ 2 . In addition, we found that D511V overexpression significantly reduced the amplitude of IP 3 -induced Ca 2؉ transients. Interestingly, overexpression of the C terminus of PC2 not only significantly reduced the amplitude but also prolonged the t1 ⁄ 2 . Coimmunoprecipitation assays indicated that PC2 physically interacts with IP 3 R through its C terminus. Taken together, our data suggest that PC2 and IP 3 R functionally interact and modulate intracellular Ca 2؉ signaling. Therefore, mutations in either PC1 or PC2 could result in the misregulation of intracellular Ca 2؉ signaling, which in turn could contribute to the pathology of autosomal dominant polycystic kidney disease. Autosomal dominant polycystic kidney disease (ADPKD)2 is one of the most common causes of renal failure (1). It arises from mutations in either the PKD1 or the PKD2 genes (1-5). The primary phenotype of ADPKD is the presence of numerous fluid-filled cysts in the kidney, liver, pancreas, and intestine (4). Mutations in PKD1 account for the majority (ϳ85%) of ADPKD cases and are associated with more severe clinical presentations and an earlier onset of renal failure (1, 2, 4, 5). Although both PKD genes have been identified, the molecular mechanisms leading to these clinical symptoms are still not fully clear. Hence, it is important to understand the biological roles of the PKD gene products polycystins (PCs) 1 and 2.PC1 is a 4,302-amino-acid integral membrane protein that has 11 putative transmembrane domains, a long extracellular N terminus, and a short intracellular C terminus (6). The large extracellular portion contains a novel combination of motifs originally found in other proteins that are predicted to be involved in cell-cell and cell-matrix interactions (1-3, 6, 7). Its C terminus contains a coiled-coil domain responsible for interacting with PC2 (8, 9). PC2 is a 968-amino-acid protein containing six transmembrane domains (10). Transmembrane domains 5 and 6 share a significant similarity with TRPC1, a member of the transient receptor potential cation channel family (10 -12). Both the N and the C termini are cytosolic. The C terminus of PC2 contains an ER retention signal, an EF-hand motif, and a coiled-coil domain (10, 11, 13). Electrophysiological studies indicate that PC2 is a Ca 2ϩ -activated, non-selective cation channel with multiple subconductance states and a high permeability to Ca 2ϩ (14 -17). Although it is well accepted that PC1 is expressed in the plasma membrane, the subcellular localization of PC2 has ...

Cell biology of polycystin-2

“…However, PKD2 overexpression augmented mostly the duration rather than the amplitude of the Ca 2+ release transient. Moreover, overexpression of the naturally occurring mutant PKD2-D511V had a dominant negative effect on Ca 2+ release transients [46] lending support to the idea that endogenous PKD2 was likely to function as an intracellular Ca 2+ -induced Ca 2+ release channel. Experiments in vascular smooth muscle cells [47] and immortalized lymphoblasts [48] from PKD2 knock out mice and ADPKD patients, respectively, showed that PKD2 played a role in G protein coupled receptor-induced Ca 2+ signaling, but the possibility that PKD2 could have also contributed to Ca 2+ signaling through Ca 2+ influx was not clearly addressed in these studies.…”

“…The implication of these findings was that it could enhance local intracellular Ca 2+ concentration in response to an initial rise in Ca 2+ and therefore, PKD2 could regulate intracellular Ca 2+ concentration in a localized fashion. Subsequent reports confirmed the role of PKD2 in intracellular Ca 2+ release and further showed that it interacted with the isoform 1 of the IP 3 receptor (IP 3 R1) [46]. However, PKD2 overexpression augmented mostly the duration rather than the amplitude of the Ca 2+ release transient.…”

“…Therefore, based on these mutants, it is not clear whether mutations in PKD2 result in ADPKD because of loss of channel activity or loss of protein-protein interactions. In contrast, the PKD2-D511V mutation, which has not only been described at the genomic level but also at the mRNA level [78], does not affect the expression, subcellular targeting, or protein-protein interactions but only channel activity [36,46]. Then, what are consequences of impaired PKD2 channel activity in ADPKD?…”

“…PKD1 overexpression somehow enhanced the phosphorylation state of PKD2 and subsequently increased binding of PKD2 to Id2. Therefore, Li et al [46] proposed that naturally occurring mutations in PKD2 would result in insufficient cytosolic sequestration of Id2 and subsequent increase in nuclear import of Id2. Similarly, PKD1 mutations would enhance the nuclear translocation of Id2 by reducing the phosphorylation state of PKD2 and thereby allowing Id2 to travel to the nucleus.…”

“…Interestingly, I-mfa does not inhibit the function of the E47 subset of bHLHs [93,94]. Therefore, it is quite intriguing that two independent unbiased screens [46,92] using the C-termini of structurally related and interacting channels identified two structurally unrelated proteins with complementary functions. The data clearly indicate the existence of a novel signal transduction pathway linking TRP ion channel and bHLH functional regulation (Fig.…”