|
|
|
|
|
|
|
||
© The Rockefeller University Press,
0021-9525/2002/11/685 $5.00
The Journal of Cell Biology, Volume 159, Number 4, 685-694
Article |
Uroplakin IIIb, a urothelial differentiation marker, dimerizes with uroplakin Ib as an early step of urothelial plaque assembly
Address correspondence to Tung-Tien Sun, Dept. of Dermatology, New York University School of Medicine, 550 First Ave., New York, NY 10016. Tel.: (212) 263-5685. Fax: (212) 263-8561. E-mail: sunt01{at}med.nyu.edu
 |
Abstract |
|---|
 Top Abstract IntroductionResultsDiscussionMaterials and methodsReferences |
|---|
Urothelial plaques consist of four major uroplakins (Ia, Ib, II, and III) that form two-dimensional crystals covering the apical surface of urothelium, and provide unique opportunities for studying membrane protein assembly. Here, we describe a novel 35-kD urothelial plaque-associated glycoprotein that is closely related to uroplakin III: they have a similar overall type 1 transmembrane topology; their amino acid sequences are 34% identical; they share an extracellular juxtamembrane stretch of 19 amino acids; their exit from the ER requires their forming a heterodimer with uroplakin Ib, but not with any other uroplakins; and UPIII-knockout leads to p35 up-regulation, possibly as a compensatory mechanism. Interestingly, p35 contains a stretch of 80 amino acid residues homologous to a hypothetical human DNA mismatch repair enzyme-related protein. Human p35 gene is mapped to chromosome 7q11.23 near the telomeric duplicated region of Williams-Beuren syndrome, a developmental disorder affecting multiple organs including the urinary tract. These results indicate that p35 (uroplakin IIIb) is a urothelial differentiation product structurally and functionally related to uroplakin III, and that p35–UPIb interaction in the ER is an important early step in urothelial plaque assembly.
Key Words: bladder; urothelium; tetraspanin; membrane; DNA mismatch repair enzyme
|
Introduction |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
Urothelial plaques (also known as asymmetric unit membranes [AUM]) are structurally unique in that they consist of 16-nm protein particles arranged hexagonally, forming two-dimensional crystals (Hicks and Ketterer, 1969; Vergara et al., 1969; Brisson and Wade, 1983; Walz et al., 1995; Kachar et al., 1999). These plaques represent the major differentiation products of mammalian urothelia; thus, they can be readily isolated with an extraordinary yield of 10–20 mg of highly purified two-dimensional crystals from 
100 bovine bladders within 2 d (Wu et al., 1990). Consistent with their crystalline structure, urothelial plaques have a relatively simple protein composition consisting of four known uroplakin (UP)* subunits, i.e., UPIa (27 kD), UPIb (28 kD), UPII (15 kD), and UPIII (47 kD; Wu and Sun, 1993; Lin et al., 1994; Yu et al., 1994; Sun et al., 1999). Cultured urothelial cells form stratified cell layers and continue to synthesize uroplakins, which, however, fail to assemble into two-dimensional crystals, thus providing unique opportunities to study the regulation of membrane assembly (Surya et al., 1990). Uroplakins Ia and Ib have four transmembrane domains, are 40% identical in their amino acid sequences, and belong to the "tetraspanin" gene family that contains many leukocyte- and cancer-associated cell surface proteins including CD9, CD37, CD53, and CD63 (Yu et al., 1994; Maecker et al., 1997; Hemler, 2001). On the other hand, uroplakins II and III have only a single transmembrane domain. UPII is synthesized as a precursor containing a signal peptide and a pro-sequence; the mature protein anchors into the membrane via its COOH-terminal transmembrane domain (Lin et al., 1994). Uroplakin III also has a signal peptide and a single transmembrane domain that separates a long (200 amino acids) extracellular from a short (50 amino acids) intracellular domain (Wu and Sun, 1993). Interestingly, the two tetraspanin-type uroplakins (UPIa and UPIb) are cross-linked selectively to UPII and UPIII, respectively, suggesting the existence of two separate uroplakin pairs (Wu et al., 1995). Together, these results indicate that urothelial plaque provides an excellent model for studying membrane protein assembly (Sun et al., 1999).
To understand the assembly of urothelial plaques, it is crucial to fully characterize all the protein subunits of the plaques, including some minor components that can potentially play regulatory functions. In this regard, it should be noted that highly purified bovine urothelial plaques contain, in addition to the four known uroplakins that account for >90% of the total protein mass, another protein of 35 kD (p35) that remained uncharacterized (Liang et al., 1999). In this paper, we show that p35 represents a novel urothelial differentiation marker that is homologous to uroplakin III in sequence and transmembrane topography. Interestingly, p35 also shares a stretch of 80 amino acid residues (78–157) that is >90% identical to a portion of a human DNA mismatch repair (MMR) enzyme-related PMSR6 protein (Horii et al., 1994; Nicolaides et al., 1995). The human p35 gene is mapped to chromosome 7q11.23 near a region that is frequently deleted in patients with the Williams-Beuren syndrome (WBS; Online Mendelian Inheritance in Man [OMIM], 2002, MIM no. 194050, available at http://www.ncbi.nlm.nih.gov/omim; Francke, 1999), a developmental disorder affecting multiple systems including the urinary tract (Babbitt et al., 1979; Morris et al., 1990; Francke, 1999).
|
Results |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
30 kD in size and were 34% identical (Fig. 2
b), and they adopted a similar transmembrane topography. Both p35 and UPIII were type 1 transmembrane proteins with a signal peptide and a single transmembrane domain (Fig. 2, a, b, and d). Both had a long NH2-terminal extracellular domain (200 amino acid residues) harboring several N-glycosylation sites (one for p35 and 4 for UPIII), and a short COOH-terminal cytoplasmic domain (50 amino acids; Fig. 2, b and d). In addition, both possessed a domain of 19 amino acid residues (190-IDTWPGRRSGDMIIITSIL-208 for p35; 197-IDTWPGRRSGGMIVITSIL-215 for uroplakin III) that was located in a juxtamembrane position immediately NH2-terminal to the transmembrane domain (Fig. 2, b, c, and d). However, the p35 was unique in that its NH2-terminal extracellular domain contained a stretch of 80 amino acid residues (78–157) that were 74% identical and 83% similar to a hypothetical human DNA MMR enzyme-related protein (the "PMSR6" gene; Figs. 1 c and 2 d; Horii et al., 1994; Nicolaides et al., 1995). RT-PCR using primers corresponding to the PMSR6- and UPIII-related regions yielded the expected p35 PCR products, thus proving the colinear existence of these two domains in bovine p35 (Fig. 2 a and unpublished data).
|
|
|
|
|
|
20-fold in total cell lysates, suggesting lower translational efficiency and/or degradation possibly due to suboptimal subunit stabilization (Fig. 7 b). Within the putative p35/UPIb pair, both mRNAs increased approximately sixfold (Fig. 7 a), whereas the proteins decreased three- to 10-fold (Fig. 7 b), indicating that p35 and UPIb were coordinately regulated. Immunohistochemical staining results showed that although much of UPIb was mistargeted to the basal–lateral surface (Hu et al., 2000), small amounts of UPIb and p35 were associated with the apical urothelial surface (Fig. 7 c; see Discussion).
|
5 kb (Fig. 8
a), which was 0.5 Mb centromeric to the PMSR6 gene. The sequence of p35 gene was distally homologous with uroplakin III gene (Fig. 8 a), but was highly related to PMSR6 gene that encoded a hypothetical DNA MMR enzyme-related protein (Horii et al., 1994; Nicolaides et al., 1995). The close relationship between p35 and PMSR6 gene (Fig. 8 a) was indicated by the fact that (1) a large stretch (25 kb) of the 5' upstream sequence of p35 gene was >90% identical to the 5' half of PMSR6 gene containing its first 5 exons; (2) the p35 genomic sequence starting from the first intron to the end of third intron was >90% identical to the sixth exon of PMSR6 and its surrounding intron sequences; (3) the third exon of p35 gene, which corresponded to exon 6 of the PMSR6 gene (Fig. 8 a, arrowhead), encoded the 80 amino acid residues shared by these two proteins (Fig. 2 b); and (4) the 3' downstream sequence of p35 (>20 kb downstream from the sixth or last exon) was >90% identical to the 3' downstream sequence of PMSR6 gene (Fig. 8 b). Therefore, it seemed likely that p35 and PMSR6 genes were evolved by gene duplication (see Discussion); given the more conserved and perhaps primitive nature of the DNA MMR function, we speculate that PMSR6 gene was the precursor of p35 gene. Southern analysis of human genomic DNA using a partial human p35 cDNA probe (corresponding to the second and third exons of p35; a sequence shared by the two genes) showed two equal intensity bands in DNA digested by five different restriction enzymes, suggesting the existence of two closely related genes (p35 and PMSR6; Fig. 8 b). PCR products generated using primers based on the second and third exons of p35 gene contained the sequence of not only p35, but also that of PMSR6 (Fig. 8 c), thus confirming the close relationship between these two genes. BLAST analysis of the HTGS database showed that p35 and R6 genes are present in BAC clone RP11-340A14 and RP11-506L7, respectively. Based on Peoples et al. (2000), Valero et al. (2000), and the HTGS-derived data, these two clones are localized on chromosome 7q11.23 immediately telomeric to HIP1, a single-copy gene that maps telomeric to the frequent distal breakpoint of the WBS (OMIM 194050; see Discussion and Fig. 8 d).
|
|
Discussion |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
|
Possible functions of UPIIIb
Existing data suggest that UPIIIb plays a urothelial-specific function most likely involved in urothelial plaque formation. First, UPIIIb is associated with the differentiated urothelial cells (Fig. 3 and Fig. 4, d–i). Second, the amino acid sequences of human, mouse, and bovine UPIIIb are >90% identical (Fig. 2 a), suggesting that the protein plays a highly conserved biological function. Third, the fact that UPIIIb is highly enriched in purified bovine urothelial plaques suggests that it is a plaque component (Fig. 4 a). Fourth, the relatively large cytoplasmic domains of UPIIIb and UPIIIa suggest these may mediate membrane–cytoskeletal interactions serving to anchor the urothelial plaque to an underlying cytoskeletal network (Wu and Sun, 1993). The fact that UPIIIa and UPIIIb exhibit a much higher degree of homology in their luminal domains (36%) than their cytoplasmic tails (18%; Fig. 2 b) suggests that their conserved luminal domains interact with a common target, i.e., UPIb, whereas their cytoplasmic tails play chain-specific functions (Liang et al., 1999). A potentially important difference between the cytoplasmic tails of UPIIIa and UPIIIb is that only the former harbors several potential phosphorylation sites (Wu and Sun, 1993). Fifth, unlike UPIIIa that is present as a major component in purified urothelial plaques, UPIIIb is present at a much lower level amounting usually to <10% of UPIIIa (Fig. 1a and Fig. 4 a, lane 1) and this level is somewhat variable. Recently, we have shown by EM localization that UPIIIa is associated with almost all urothelial plaques in mouse and bovine urothelial umbrella cells (Liang et al., 2001), suggesting that UPIIIa is a constant component of both cytoplasmic and apical plaques. The low stoichiometry of UPIIIb suggests that this protein is associated with a subpopulation of urothelial plaques, possibly conferring special structural or functional properties to these plaques.
A puzzling phenotype of uroplakin III knockout mice is the presence of some normal-looking (albeit much smaller) urothelial plaques (0.05-µm-diam vs. 0.2–1-µm in normal urothelium; Hu et al., 2000). There are two possible explanations for this UPIIIa-independent plaque formation. One is that the ablation of UPIIIa abolished the UPIIIa/UPIb pair; but the remaining UPII/UPIa pair can still form small urothelial plaques. Another possibility is that all four uroplakins are required for plaque formation, but a small amount of UPIIIa homologue, i.e., UPIIIb, can rescue some of the other three uroplakins and is thus responsible for the formation of the observed small plaques. Our current finding that UPIIIb is up-regulated relative to other uroplakins in the UPIIIa-deficient urothelium (Fig. 7, a and b) supports the latter interpretation.
Possible significance of the CD and hPMSR6-related domains
It is interesting that UPIIIa and UPIIIb share 19 amino acid residues (IDTWPGRRSGDMIIITSIL) located proximal to their single transmembrane domain (Fig. 2, b and d). The structural significance of this conserved domain (CD) is unclear, although our preliminary data indicate that mutations in this domain do not affect UPIIIb–UPIb interaction in the ER as assayed by cotransfection (unpublished data). Additional studies are needed to determine whether the CD plays a role in subsequent steps of asymmetric unit membrane assembly.
A surprising feature of human UPIIIb protein is that it contains a domain of 80 amino acid residues that are >95% identical to a portion of hPMSR6, a hypothetical DNA MMR enzyme–related protein. That this hPMSR6-related domain is a part of the UPIIIb molecule is supported by several findings. First, the cDNA sequence of UPIIIb has been validated by the fact that it can account for all five partial protein sequences of electrophoretically purified p35 (Fig. 1 c), and that antibodies raised against several p35 peptide recognized the correct p35 protein (Fig. 4 a). Second, sequencing of a PCR product between the hPMSR6 and CDs confirmed the colinear existence of these two domains in a single p35 cDNA. Third, the segment of 80 amino acids that are shared by P35 and hPMSR6 is encoded by a single exon (exon 2 of the p35 gene and exon 6 of the hPMSR6 gene; Fig. 8 a). Fourth, both human p35 and hPMSR6 genes are localized on chromosome 7q11.23, and the genomic structures of these two genes show striking conservations, suggesting the derivation of one from another by gene duplication (Fig. 8 a).
Because little is known about the protein encoded by the hPMSR6 gene, we do not know the functional significance of the hPMSR6-related domain in UPIIIb. However, we do know that because this domain is not present in UPIIIa, the entire R6 domain is unlikely to be essential for p35 to form heterodimer with UPIb. DNA MMR enzymes, including hPMS2, play a key role in promoting genetic stability by repairing DNA replication errors, inhibiting recombination between nonidentical DNA sequences, and participating in cellular responses to DNA damage (Modrich and Lahue, 1996; Harfe and Jinks-Robertson, 2000). Defects in hPMS2 have been shown to play a role in hereditary nonpolyposis colon cancer (Nicolaides et al., 1994; Hamilton et al., 1995). Moreover, ablation of mouse PMS2 gene leads to the formation of sarcomas, lymphomas, and intestinal adenomatous polyp (Baker et al., 1998). PCR amplification led to the identification of >17 human PMS2-related cDNAs, and hPMSR6 is one of them (Horii et al., 1994; Nicolaides et al., 1995). All these PMS2-related genes are mapped to chromosome 7, are homologous with the 5' portion of PMS2, and contain several motifs highly conserved among various DNA MMR enzymes, such as KELVEN and GFRGEAL (Prolla et al., 1994), suggesting possible enzymatic domains. However, no data are as yet available about the expression of hPMSR6 in terms of its tissue distribution and protein function.
UPIIIb gene is telomeric of the frequently deleted region of the WBS
WBS is a neurodevelopmental disorder affecting multiple organs with distinctive facial features, congenital cardiovascular anomalies, mental retardation, growth deficiency, and occasional infantile hypercalcemia. Importantly, WBS patients have an increased prevalence of urinary symptoms and voiding dysfunctions (Babbitt et al., 1979; Morris et al., 1990; Blane et al., 1994; Perez Jurado et al., 1996). For example, Schulman et al. (1996) reported that 10% of WBS patients had bladder diverticula and uninhibited detrusor contraction. Pankau et al. (1996) reported that 17.7% of the WBS patients had bladder diverticula and renal abnormalities. Other genitourinary manifestations include urethral stenosis, vesicoureteral reflux, and recurrent urinary tract infection (Lashkari et al., 1999). Stoermer et al. (1984) reported that 12 out of 14 of children with all signs of WBS had renal and lower urinary tract abnormalities, but only 1 out of 5 of children with only typical cardiovascular findings (without pathognomonic faces or major mental retardation) showed urinary tract problems. WBS is caused by the heterozygous deletion of parts of chromosome subband 7q11.23 amounting to 1.5 to 2 Mb (Francke, 1999; Hockenhull et al., 1999; Peoples et al., 2000). Such deletions occur due to the presence of long stretches of duplicated sequences flanking this subband, thus facilitating inter- or intra-chromosomal crossover events (Dutly and Schinzel, 1996; Urban et al., 1996; Baumer et al., 1998). Because p35 gene is localized near the telomeric duplicated sequence of the WBS and because UPIIIa knockout led to widespread anomalies in the lower urinary tract, including vesicoureteral reflux (Hu et al., 2000), it is important to determine whether p35 deletion plays a role in causing some of the observed urinary tract defects in WBS.
|
Materials and methods |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
phage DNA from all positive clones. DNA sequencing was performed using the dideoxynucleotide chain termination method (Sanger et al., 1977) with a DNA sequence kit (US Biochemical Corp.).
Mass spectrometry
The Coomassie blue–stained band was excised from the gel, and the protein was digested in-gel (Shevchenko et al., 1996). Digested peptides were analyzed by LC/MS and LC/MS/MS on a mass spectrometer (API III+; MDS Sciex) as described previously (Resing et al., 1993). De novo sequencing was done manually, with a complete set of b and y ions observed for most of the identified sequence.
RT-PCR and Northern and Southern blotting
Total RNAs from various tissues were isolated using an RNAgent® system (Promega). For Northern blotting, 10 µg total RNA was electrophoretically transferred onto a nylon membrane and hybridized with different 32P-labeled probes. For RT-PCR, cDNA was synthesized using a SuperScriptTM first-strand synthesis system (GIBCO BRL). Primers for bovine p35 were forward, 5'-CGTGCTTAGGGTGGGCAATG-3', and reverse, 5'-ATCATGTCTCCACTCCGCCG-3'. Primers for mouse p35 were forward, 5'-ACCTGGAAGGGAAGATCAC-3', and reverse, 5'-AACGTTTTCCCATGAAGGAG-3'. 10 µg of human blood genomic DNA was digested with various restriction enzymes for 16 h, size-fractionated on an 0.8% agarose gel, transferred to a nylon membrane, and probed with a 300-bp 5' end of human p35 cDNA (Lin et al., 1994).
Generation and purification of antibodies against synthetic peptides
Three peptides, (1) VLDRHSSAADTVW, (2) TNSRGSPQAETRWSD, and (3) EPGLERFPSLSP were synthesized (Genemed Synthesis, Inc.) based on the cDNA-deduced amino acid sequence of bovine p35. An additional cysteine residue was placed at the COOH terminus of peptide b and NH2 terminus of peptides a and c. These peptides were conjugated to keyhole limpet hemocyanin. 100 µg of each conjugated peptide was used to prime each rabbit and 50 µg for booster injections at 2-wk intervals. Antibodies were affinity-purified using a peptide-conjugated Ultralink Iodoacetyl column (Pierce Chemical Co.). The eluted antibodies were concentrated using Centricon-30 (Amicon).
Immunoblotting and enzymatic deglycosylation
Proteins were separated by SDS-PAGE on 17% polyacrylamide gels with an acrylamide/bisacrylamide ratio of 120:1, and were electrophoretically transferred onto a nitrocellulose membrane. The membrane was briefly stained with Fast Green (Sigma-Aldrich) to reveal protein bands. After blocking with 2% nonfat milk in PBS, the blots were incubated with specific primary antibodies. The primary antibodies were detected with a goat anti–rabbit or anti–mouse IgG conjugated with HRP (ICN Biomedicals). After washing with PBS, the membrane was developed by the enhanced chemiluminescence Western blotting detecting system (Pierce Chemical Co.) and exposed to Fuji x-ray film at RT. For enzymatic deglycosylation, bovine urothelial plaques were solubilized in 0.5% SDS at RT for 15 min, and then incubated with endoglycosidase H or with N-glycosidase F (Roche). Glycosidase was omitted in negative control incubation. After incubation at 37°C for 16 h, the reaction mixtures were resolved by SDS-PAGE and electrophoretically transferred onto a nitrocellulose membrane. P35 was detected by immunoblotting using a peptide antibody against bovine p35.
Urothelial cell culture
Bovine urothelial cells were isolated from bovine bladder epithelial cells and cultured in the presence of mitomycin C–treated NIH 3T3 feeder cells in DME containing 15% FCS, 0.5 µg/ml hydrocortisone, 5 ng/ml cholera toxin, 5 µg/ml insulin, and 15 ng/ml EGF as described previously (Surya et al., 1990). 3T3 feeder cells and any contaminating fibroblasts were removed by spraying the culture with 0.01% EDTA in PBS after the cell reached 70% confluence. Urothelium were collected at different stages of differentiation and stored at -70°C for further analysis.
Immunohistochemistry
Paraffin sections were treated with 1% hydrogen peroxide in methanol to block the endogenous peroxidase, and incubated with normal 1:50 goat serum in 2% BSA, followed by overnight incubation at 4°C with a peptide antibody against bovine p35 and AU1, an mAb against UPIII (Liang et al., 2001; Riedel et al., 2001). Primary antibodies were detected with specific HRP-conjugated secondary antibodies (RCN). Preimmune serum and 2% BSA were used as negative controls. After counterstaining with hematoxylin, sections were mounted using glycerin gelatin and observed under a Zeiss Axiophot microscope.
Transient transfection of 293T cells
cDNAs of all four uroplakins and p35 were isolated by PCR using bovine urothelial cDNA as the template. Additional EcoRI and XhoI restriction sites were introduced to the forward and reverse primers, respectively. The cDNAs were cloned into the pcDNA3 vector using the EcoRI and XhoI sites (Invitrogen). An HA tag was inserted into the small extracellular loop region of the UPIb cDNA. 293T cells were maintained in DME supplemented with 10% FBS. The FuGENE6 reagent (Roche) was used for transient transfection. 18 h before transfection, 293T cells were plated in 6-well plates (6 x 105/well). cDNA was mixed with FuGENE6 (Roche; 1:3, wt/vol) in serum-free DME, incubated at RT for 30 min, and added dropwise to the 293T cells. 24 h after transfection, cells were rinsed with ice-cold PBS and lysed in lysis buffer (50 mM Tris-HCl, pH 7.5, 150 mM NaCl, 0.5% sodium deoxylcholate, 1% NP-40, 10 µg/ml aprotinin, 10 µg/ml leupeptin, and 1 mM PMSF) on ice. The total cell lysates were centrifuged at 13,000 g for 10 min at 4°C, and the supernatants were stored at -20°C or used for experiments directly.
Metabolic labeling and immunoprecipitation
24 h after transfection, cells were rinsed twice with PBS prewarmed to 37°C and incubated for 30 min in a methionine-free DME containing 5% dialyzed bovine serum. The cells were then pulse-labeled for 10 min with [35S]methionine (ICN Biomedicals) at 0.05 mCi/ml. Chase was done at 37°C for the indicated periods with DME containing an excess of unlabeled methionine (30 µg/ml). The labeled cells were washed with 4°C PBS and extracted with lysis buffer for immunoprecipitation.
For immunoprecipitation, protein G–agarose beads (Roche) were preconjugated with primary antibodies or preimmune serum for 2 h at 4°C. After being precleaned with protein G–agarose beads, the supernatants of total cell lysates were incubated overnight at 4°C, with gentle agitation, with the antibody-conjugated protein G–agarose beads. The beads were sedimented (5,000 g for 2 min) and washed four times with cold lysis buffer. The antigens were then eluted with 0.2% SDS sample buffer.
Immunostaining
293T cells were plated on coverslips 24 h before transfection. 24 h after transfection, the cells were fixed with 3% PFA in PBS, pH 7.5, and incubated with 5% nonfat milk in PBS. Some cells were permeabilized by adding 0.05% saponin to milk solution. The fixed cells were incubated at 37°C for 90 min with a rabbit antibody against p35 (1:100) and a mouse mAb against the HA tag of the UPIb, followed by a secondary antibody (1:200, Texas red–conjugated donkey anti–mouse IgG and FITC-conjugated donkey anti–rabbit IgG; Jackson ImmunoResearch Laboratories). Immunostained cells were scanned using a confocal microscope (model LSM510; Carl Zeiss MicroImaging, Inc.).
|
Footnotes |
|---|
|
Acknowledgments |
|---|
This work was supported by National Institutes of Health grants DK39753, DK52206, and DK57269.
Submitted: 19 April 2002
Revised: 9 October 2002
Accepted: 9 October 2002
|
References |
|---|
|
TopAbstractIntroductionResultsDiscussionMaterials and methodsReferences |
|---|
Babbitt, D.P., J. Dobbs, and R.A. Boedecker. 1979. Multiple bladder diverticula in Williams "Elfin-Facies" syndrome. Pediatr. Radiol. 8:29–31.[CrossRef][Medline]
Baker, S.M., A.C. Harris, J.L. Tsao, T.J. Flath, C.E. Bronner, M. Gordon, D. Shibata, and R.M. Liskay. 1998. Enhanced intestinal adenomatous polyp formation in Pms2-/-;Min mice. Cancer Res. 58:1087–1089.
Baumer, A., F. Dutly, D. Balmer, M. Riegel, T. Tukel, M. Krajewska-Walasek, and A.A. Schinzel. 1998. High level of unequal meiotic crossovers at the origin of the 22q11. 2 and 7q11.23 deletions. Hum. Mol. Genet. 7:887–894.
Blane, C.E., J.M. Zerin, and D.A. Bloom. 1994. Bladder diverticula in children. Radiology. 190:695–697.
Brisson, A., and R.H. Wade. 1983. Three-dimensional structure of luminal plasma membrane protein from urinary bladder. J. Mol. Biol. 166:21–36.[Medline]
Deng, F.M., M. Ding, R.M. Lavker, and T.T. Sun. 2001. Urothelial function reconsidered: A role in urinary protein secretion. Proc. Natl. Acad. Sci. USA. 98:154–159.
Diatchenko, L., Y.F. Lau, A.P. Campbell, A. Chenchik, F. Moqadam, B. Huang, S. Lukyanov, K. Lukyanov, N. Gurskaya, E.D. Sverdlov, and P.D. Siebert. 1996. Suppression subtractive hybridization: a method for generating differentially regulated or tissue-specific cDNA probes and libraries. Proc. Natl. Acad. Sci. USA. 93:6025–6030.
Dutly, F., and A. Schinzel. 1996. Unequal interchromosomal rearrangements may result in elastin gene deletions causing the Williams-Beuren syndrome. Hum. Mol. Genet. 5:1893–1898.
Ellgaard, L., M. Molinari, and A. Helenius. 1999. Setting the standards: quality control in the secretory pathway. Science. 286:1882–1888.
Francke, U. 1999. Williams-Beuren syndrome: genes and mechanisms. Hum. Mol. Genet. 8:1947–1954.
Green, W.N. 1999. Ion channel assembly: creating structures that function. J. Gen. Physiol. 113:163–170.
Hamilton, S.R., B. Liu, R.E. Parsons, N. Papadopoulos, J. Jen, S.M. Powell, A.J. Krush, T. Berk, Z. Cohen, B. Tetu, et al. 1995. The molecular basis of Turcot's syndrome. N. Engl. J. Med. 332:839–847.
Harfe, B.D., and S. Jinks-Robertson. 2000. DNA mismatch repair and genetic instability. Annu. Rev. Genet. 34:359–399.[CrossRef][Medline]
Hemler, M.E. 2001. Specific tetraspanin functions. J. Cell Biol. 155:1103–1107.
Hicks, R.M., and B. Ketterer. 1969. Hexagonal lattice of subunits in the thick luminal membrane of the rat urinary bladder. Nature. 224:1304–1305.[Medline]
Hockenhull, E.L., M.J. Carette, K. Metcalfe, D. Donnai, A.P. Read, and M. Tassabehji. 1999. A complete physical contig and partial transcript map of the Williams syndrome critical region. Genomics. 58:138–145.[CrossRef][Medline]
Horii, A., H.J. Han, S. Sasaki, M. Shimada, and Y. Nakamura. 1994. Cloning, characterization and chromosomal assignment of the human genes homologous to yeast PMS1, a member of mismatch repair genes. Biochem. Biophys. Res. Commun. 204:1257–1264.[CrossRef][Medline]
Hu, P., F.M. Deng, F.X. Liang, C.M. Hu, A.B. Auerbach, E. Shapiro, X.R. Wu, B. Kachar, and T.T. Sun. 2000. Ablation of uroplakin III gene results in small urothelial plaques, urothelial leakage, and vesicoureteral reflux. J. Cell Biol. 151:961–972.
Kachar, B., F. Liang, U. Lins, M. Ding, X.R. Wu, D. Stoffler, U. Aebi, and T.T. Sun. 1999. Three-dimensional analysis of the 16 nm urothelial plaque particle: luminal surface exposure, preferential head-to-head interaction, and hinge formation. J. Mol. Biol. 285:595–608.[CrossRef][Medline]
Kozak, M. 1984. Compilation and analysis of sequences upstream from the translational start site in eukaryotic mRNAs. Nucleic Acids Res. 12:857–872.
Kozak, M. 2000. Do the 5' untranslated domains of human cDNAs challenge the rules for initiation of translation (or is it vice versa)? Genomics. 70:396–406.[CrossRef][Medline]
Lashkari, A., A.K. Smith, and J.M. Graham. 1999. Williams-Beuren syndrome: an update and review for the primary physician. Clin. Pediatr. (Phila.). 38:189–208.
Liang, F., B. Kachar, M. Ding, Z. Zhai, X.R. Wu, and T.T. Sun. 1999. Urothelial hinge as a highly specialized membrane: detergent-insolubility, urohingin association, and in vitro formation. Differentiation. 65:59–69.[CrossRef][Medline]
Liang, F.X., I. Riedel, F.M. Deng, G. Zhou, C. Xu, X.R. Wu, X.P. Kong, R. Moll, and T.T. Sun. 2001. Organization of uroplakin subunits: transmembrane topology, pair formation and plaque composition. Biochem. J. 355:13–18.[CrossRef][Medline]
Lin, J.H., X.R. Wu, G. Kreibich, and T.T. Sun. 1994. Precursor sequence, processing, and urothelium-specific expression of a major 15-kDa protein subunit of asymmetric unit membrane. J. Biol. Chem. 269:1775–1784.
Lin, J.H., H. Zhao, and T.T. Sun. 1995. A tissue-specific promoter that can drive a foreign gene to express in the suprabasal urothelial cells of transgenic mice. Proc. Natl. Acad. Sci. USA. 92:679–683.
Maecker, H.T., S.C. Todd, and S. Levy. 1997. The tetraspanin superfamily: molecular facilitators. FASEB J. 11:428–442.[Abstract]
Modrich, P., and R. Lahue. 1996. Mismatch repair in replication fidelity, genetic recombination, and cancer biology. Annu. Rev. Biochem. 65:101–133.[CrossRef][Medline]
Morris, C.A., C.O. Leonard, C. Dilts, and S.A. Demsey. 1990. Adults with Williams syndrome. Am. J. Med. Genet. Suppl. 6:102–107.[Medline]
Nicolaides, N.C., N. Papadopoulos, B. Liu, Y.F. Wei, K.C. Carter, S.M. Ruben, C.A. Rosen, W.A. Haseltine, R.D. Fleischmann, C.M. Fraser, et al. 1994. Mutations of two PMS homologues in hereditary nonpolyposis colon cancer. Nature. 371:75–80.[CrossRef][Medline]
Nicolaides, N.C., K.C. Carter, B.K. Shell, N. Papadopoulos, B. Vogelstein, and K.W. Kinzler. 1995. Genomic organization of the human PMS2 gene family. Genomics. 30:195–206.[CrossRef][Medline]
Pankau, R., C.J. Partsch, M. Winter, A. Gosch, and A. Wessel. 1996. Incidence and spectrum of renal abnormalities in Williams-Beuren syndrome. Am. J. Med. Genet. 63:301–304.[CrossRef][Medline]
Peoples, R., Y. Franke, Y.K. Wang, L. Perez-Jurado, T. Paperna, M. Cisco, and U. Francke. 2000. A physical map, including a BAC/PAC clone contig, of the Williams-Beuren syndrome–deletion region at 7q11.23. Am. J. Hum. Genet. 66:47–68.[CrossRef][Medline]
Perez Jurado, L.A., R. Peoples, P. Kaplan, B.C. Hamel, and U. Francke. 1996. Molecular definition of the chromosome 7 deletion in Williams syndrome and parent-of-origin effects on growth. Am. J. Hum. Genet. 59:781–792.[Medline]
Prolla, T.A., Q. Pang, E. Alani, R.D. Kolodner, and R.M. Liskay. 1994. MLH1, PMS1, and MSH2 interactions during the initiation of DNA mismatch repair in yeast. Science. 265:1091–1093.
Reddy, P.S., and R.B. Corley. 1998. Assembly, sorting, and exit of oligomeric proteins from the endoplasmic reticulum. Bioessays. 20:546–554.[CrossRef][Medline]
Resing, K.A., R.S. Johnson, and K.A. Walsh. 1993. Characterization of protease processing sites during conversion of rat profilaggrin to filaggrin. Biochemistry. 32:10036–10045.[CrossRef][Medline]
Riedel, I., B. Czernobilsky, B. Lifschitz-Mercer, L.M. Roth, X.R. Wu, T.T. Sun, and R. Moll. 2001. Brenner tumors but not transitional cell carcinomas of the ovary show urothelial differentiation: immunohistochemical staining of urothelial markers, including cytokeratins and uroplakins. Virchows Arch. 438:181–191.[CrossRef][Medline]
Sanger, F., S. Nicklen, and A.R. Coulson. 1977. DNA sequencing with chain-terminating inhibitors. Proc. Natl. Acad. Sci. USA. 74:5463–5467.
Schulman, S.L., S. Zderic, and P. Kaplan. 1996. Increased prevalence of urinary symptoms and voiding dysfunction in Williams syndrome. J. Pediatr. 129:466–469.[CrossRef][Medline]
Shevchenko, A., M. Wilm, O. Vorm, and M. Mann. 1996. Mass spectrometric sequencing of proteins silver-stained polyacrylamide gels. Anal. Chem. 68:850–858.[Medline]
Stoermer, J., H. Olbing, F. Hentrich, K. Even, O. Galal, and J. Bachmann. 1984. [Syndrome of supravalvular aortic stenosis (Williams-Beuren syndrome) in association with changes in the kidney and efferent urinary tract]. Monatsschr. Kinderheilkd. 132:110–112
Sun, T.T., F.X. Liang, and X.R. Wu. 1999. Uroplakins as markers of urothelial differentiation. Adv. Exp. Med. Biol. 462:7–18.[Medline]
Surya, B., J. Yu, M. Manabe, and T.T. Sun. 1990. Assessing the differentiation state of cultured bovine urothelial cells: elevated synthesis of stratification-related K5 and K6 keratins and persistent expression of uroplakin I. J. Cell Sci. 97:419–432.
Tu, L., T.-T. Sun, and G. Kreibich. 2002. Formation of uroplakin heterodimers is a prerequisite for exit from the endoplasmic reticulum. Mol. Biol. Cell. In press.
Urban, Z., C. Helms, G. Fekete, K. Csiszar, D. Bonnet, A. Munnich, H. Donis-Keller, and C.D. Boyd. 1996. 7q11.23 deletions in Williams syndrome arise as a consequence of unequal meiotic crossover. Am. J. Hum. Genet. 59:958–962.[Medline]
Valero, M.C., O. de Luis, J. Cruces, and L.A. Perez Jurado. 2000. Fine-scale comparative mapping of the human 7q11.23 region and the orthologous region on mouse chromosome 5G: the low-copy repeats that flank the Williams-Beuren syndrom deletion arose at breakpoint sites of an evolutionary inversion(s). Genomics. 69:1–13.[CrossRef][Medline]
Vergara, J., W. Longley, and J.D. Robertson. 1969. A hexagonal arrangement of subunits in membrane of mouse urinary bladder. J. Mol. Biol. 46:593–596.[CrossRef][Medline]
Walz, T., M. Haner, X.R. Wu, C. Henn, A. Engel, T.T. Sun, and U. Aebi. 1995. Towards the molecular architecture of the asymmetric unit membrane of the mammalian urinary bladder epithelium: a closed "twisted ribbon" structure. J. Mol. Biol. 248:887–900.[CrossRef][Medline]
Wu, X.R., and T.T. Sun. 1993. Molecular cloning of a 47 kDa tissue-specific and differentiation-dependent urothelial cell surface glycoprotein. J. Cell Sci. 106:31–43.[Abstract]
Wu, X.R., M. Manabe, J. Yu, and T.T. Sun. 1990. Large scale purification and immunolocalization of bovine uroplakins I, II, and III. Molecular markers of urothelial differentiation. J. Biol. Chem. 265:19170–19179.
Wu, X.R., J.J. Medina, and T.T. Sun. 1995. Selective interactions of UPIa and UPIb, two members of the transmembrane 4 superfamily, with distinct single transmembrane-domained proteins in differentiated urothelial cells. J. Biol. Chem. 270:29752–29759.
Yu, J., J.H. Lin, X.R. Wu, and T.T. Sun. 1994. Uroplakins Ia and Ib, two major differentiation products of bladder epithelium, belong to a family of four transmembrane domain (4TM) proteins. J. Cell Biol. 125:171–182.
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Facebook 
Reddit 
Technorati 
Twitter What's this?
This article has been cited by other articles:
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|
