Identification of PKDL, a Novel Polycystic Kidney Disease 2-Like Gene Whose Murine Homologue Is Deleted in Mice with Kidney and Retinal Defects

Abstract

Polycystin-1 and polycystin-2 are the products of PKD1 and PKD2, genes that are mutated in most cases of autosomal dominant polycystic kidney disease. Polycystin-2 shares ϳ46% homology with pore-forming domains of a number of cation channels. It has been suggested that polycystin-2 may function as a subunit of an ion channel whose activity is regulated by polycystin-1. Here we report the identification of a human gene, PKDL, which encodes a new member of the polycystin protein family designated polycystin-L. Polycystin-L has 50% amino acid sequence identity and 71% homology to polycystin-2 and has striking sequence and structural resemblance to the pore-forming ␣1 subunits of Ca 2؉ channels, suggesting that polycystin-L may function as a subunit of an ion channel. The full-length transcript of PKDL is expressed at high levels in fetal tissues, including kidney and liver, and down-regulated in adult tissues. PKDL was assigned to 10q24 by fluorescence in situ hybridization and is linked to D10S603 by radiation hybrid mapping. There is no evidence of linkage to PKDL in six ADPKD families that are unlinked to PKD1 or PKD2. The mouse homologue of PKDL is deleted in Krd mice, a deletion mutant with defects in the kidney and eye. We propose that PKDL is an excellent candidate for as yet unmapped cystic diseases in man and animals.Polycystin-1 and polycystin-2 are the respective gene products of PKD1 and PKD2, mutations in which account for ϳ95% of cases of ADPKD.1 ADPKD affects up to 1/1,000 individuals and is associated with a 50% incidence of end-stage renal failure by the sixth decade of life (1). At least one additional gene is known to be mutated in the ADPKD population (2, 3) but has yet to be identified.Polycystin-1 encodes a 4,303-amino acid plasma membrane protein with a large extracellular N-terminal domain that contains leucine-rich repeats, a C-type lectin domain, and an LDL-A-like domain, all three of which are involved in cell-cell or cell-matrix interactions in other proteins (4 -6). These domains are followed by 16 repeats of the so-called PKD domain and by an REJ (receptor for egg jelly in sea urchin sperm)-like domain. Polycystin-1 has 7 to 11 transmembrane domains. The short cytoplasmic tail (197 amino acids) of polycystin-1 contains a coiled-coil domain, which appears to interact with other proteins containing similar structures (7,8).The predicted amino acid sequence of the PKD2 gene is homologous to the C terminus of polycystin-1 (9, 10). Polycystin-2 is a 968-amino acid protein with ϳ46% sequence similarity to each domain of the pore-forming ␣1 subunits of Ca 2ϩ and other cation channels, and like these channel subunits, it is predicted to have six transmembrane domains. Polycystin-2 has a putative Ca 2ϩ binding structure (EF-hand) in its Cterminal cytoplasmic domain. It interacts biochemically with polycystin-1 and with itself (7,8).Here we report the identification, chromosomal localization, and expression of a third gene encoding a protein of the polycystin family. The product of this gene is ...

Genes homologous to the autosomal dominant polycystic kidney disease genes (PKD1 and PKD2)

“…Consequently, we identified one partial cDNA clone 35 and two genomic sequences with homology on protein level to polycystin-1 and polycystin-2. Here we describe the isolation of one novel gene, PKD2L2, and confirm and extend the findings of two recently published genes, PKD2L 36,37 and PKDREJ. 38 …”

“…The highest homology has been found in the region containing transmembrane domains 4, 5 and 6 (73% identity). Recently, a partial cDNA sequence (PKD2L, GenBank AF094827) 36 and a protein sequence (PKDL) 37 of a polycystin-like gene have been reported, which are identical to the sequence we obtained for testis cDNA sequence. Using brain Marathon cDNA for a 3' RACE with primer L1F3 (Table 3), we obtained an alternatively spliced product with an additional 85 bp compared with the testis cDNA sequence.…”

“…PCR on several cDNAs with a forward primer in exon 3 and a reverse primer in exon 8 resulted in a 1055 bp Figure 1 Comparison between polycystin-2 (PKD2, GenBank U50928), the PKD2-like protein 37 Genes homologous to the PKD1 and PKD2 genes B Veldhuisen et al t fragment in testis cDNA, but no product was seen in the other tissues (data not shown). The 1055 bp PCR product was used as a probe to hybridise adult and foetal northern blots.…”

Coordinate Expression of the Autosomal Dominant Polycystic Kidney Disease Proteins, Polycystin-2 And Polycystin-1, in Normal and Cystic Tissue

“…Recently a polycystin-2-like protein, PKDL, has been described but cross-reactivity with this molecule is unlikely because the antigenic region shows only a low level of identity (26%) and because PKDL appears to have a restricted tissue distribution. 25,26 The specificity of p30 was initially tested by Western blotting and dual immunofluorescent staining of COS-1 cells transiently transfected with the Pk epitope tagged PKD2 cDNA expression plasmid (PKD2Pk). Western blot analysis indicated high levels of a 110-kd protein in PKD2Pk transfected COS-1 cells with the p30 and Pk antibodies ( Figure 1A).…”

The Transient Receptor Potential Superfamily of Ion Channels

“…It contains a Ca 2ϩ -binding EF-hand motif and a coiled-coil domain in the C-terminus but does not include any ankyrin repeats or a TRP domain. PKD2L1 (TRPP3) and PKD2L2 (TRPP5) are homologues of PKD2 (42,43). No mutations in either PKD2L1 or PKD2L2 have been found in patients with autosomal dominant polycystic kidney disease.…”