Role of PPARgamma and EGFR signalling in the urothelial terminal differentiation programme

Recently, considerable interest has focused on the ability of activated peroxisome proliferator-activated receptor gamma (PPARgamma) to promote cytodifferentiation in adipocytes and some carcinoma cells; however, the role of PPARgamma in normal epithelial cytodifferentiation is unknown. Using uroplakin (UP) gene expression as a specific correlate of terminal urothelial cytodifferentiation, we investigated the differentiation-inducing effects of PPARgamma activation in normal human urothelial (NHU) cells grown as finite cell lines in monoculture. Two high-affinity activators of PPARgamma, troglitazone (TZ) and rosiglitazone (RZ) induced the expression of mRNA for UPII and UPIb and, to a lesser extent, UPIa. The specificity of the effect was shown by pretreating cells with a PPARgamma antagonist, GW9662, which attenuated the TZ-induced response in a dose-specific manner. The PPARgamma-mediated effect on UP gene expression was maximal when there was concurrent inhibition of autocrine-activated epidermal growth factor receptor (EGFR) signalling through either the phosphatidylinositol 3-kinase or extracellular signal-regulated kinase (ERK) pathways. The use of a specific EGFR tyrosine kinase inhibitor, PD153035, correlated with PPARgamma dephosphorylation and translocation to the nucleus, indicating a mechanism for regulating the balance between proliferation and differentiation. This is the first identification of specific factors involved in regulating differentiation-associated gene changes in urothelium and the first unambiguous evidence of a role for PPARgamma signalling in the terminal differentiation programme of a normal epithelium.

Abnormal expression of molecular markers for bladder impermeability and differentiation in the urothelium of patients with interstitial cystitis

PURPOSE

Despite a lack of consensus concerning the etiology of interstitial cystitis (IC) the loss of impermeability and other abnormalities of the urothelium are features of the disease. In this study the distribution of proteins involved with epithelial adhesion, cellular differentiation and bladder impermeability in urothelial biopsies were explored by the immunohistochemical assessment of E-cadherin, ZO-1, uroplakin and chondroitin sulfate.

MATERIALS AND METHODS

Biopsies obtained from 27 patients with IC and 7 controls were immediately fixed in formalin, immunohistochemically labeled for the described proteins and scored for protein expression, morphology and differentiation.

RESULTS

Only 3 IC samples appeared completely normal, while 24 of the 27 showed an abnormality in at least 1 marker and in 6 all 4 markers were abnormal. In patients vs controls findings were abnormal for uroplakin in 13 of 27 vs 1 of 7 (p = 0.085), for E-cadherin (over expressed) in 18 of 27 vs 0 of 7 (p = 0.0021), for ZO-1 in 11 of 27 vs 0 of 7 (p = 0.046) and for chondroitin sulfate in 15 of 27 vs 0 of 7 (p = 0.0054). The morphology/polarity score significantly correlated with ZO-1 (Pearson r = 0.3935, p = 0.0423) and chondroitin sulfate (Pearson r = 0.7079, p <0.0001) expression. Chondroitin sulfate and ZO-1 showed a high correlation with each other (Pearson r = 0.5587, p = 0.0025). Uroplakin and E-cadherin expression were independent of all other markers.

CONCLUSIONS

The findings reported strongly suggest abnormal differentiation in the IC bladder. The disruption of ZO-1 is similar to that reported in feline IC. Elevated E-cadherin may represent an adaptation to increased bladder permeability.

Roles of uroplakins in plaque formation, umbrella cell enlargement, and urinary tract diseases

The apical surface of mouse urothelium is covered by two-dimensional crystals (plaques) of uroplakin (UP) particles. To study uroplakin function, we ablated the mouse UPII gene. A comparison of the phenotypes of UPII- and UPIII-deficient mice yielded new insights into the mechanism of plaque formation and some fundamental features of urothelial differentiation. Although UPIII knockout yielded small plaques, UPII knockout abolished plaque formation, indicating that both uroplakin heterodimers (UPIa/II and UPIb/III or IIIb) are required for plaque assembly. Both knockouts had elevated UPIb gene expression, suggesting that this is a general response to defective plaque assembly. Both knockouts also had small superficial cells, suggesting that continued fusion of uroplakin-delivering vesicles with the apical surface may contribute to umbrella cell enlargement. Both knockouts experienced vesicoureteral reflux, hydronephrosis, renal dysfunction, and, in the offspring of some breeding pairs, renal failure and neonatal death. These results highlight the functional importance of uroplakins and establish uroplakin defects as a possible cause of major urinary tract anomalies and death.

Overexpression of NGF in mouse urothelium leads to neuronal hyperinnervation, pelvic sensitivity, and changes in urinary bladder function

NGF has been suggested to play a role in urinary bladder dysfunction by mediating inflammation, as well as morphological and functional changes, in sensory and sympathetic neurons innervating the urinary bladder. To further explore the role of NGF in bladder sensory function, we generated a transgenic mouse model of chronic NGF overexpression in the bladder using the urothelium-specific uroplakin II (UPII) promoter. NGF mRNA and protein were expressed at higher levels in the bladders of NGF-overexpressing (NGF-OE) transgenic mice compared with wild-type littermate controls from postnatal day 7 through 12-16 wk of age. Overexpression of NGF led to urinary bladder enlargement characterized by marked nerve fiber hyperplasia in the submucosa and detrusor smooth muscle and elevated numbers of tissue mast cells. There was a marked increase in the density of CGRP- and substance P-positive C-fiber sensory afferents, neurofilament 200-positive myelinated sensory afferents, and tyrosine hydroxylase-positive sympathetic nerve fibers in the suburothelial nerve plexus. CGRP-positive ganglia were also present in the urinary bladders of transgenic mice. Transgenic mice had reduced urinary bladder capacity and an increase in the number and amplitude of nonvoiding bladder contractions under baseline conditions in conscious open-voiding cystometry. These changes in urinary bladder function were further associated with an increased referred somatic pelvic hypersensitivity. Thus, chronic urothelial NGF overexpression in transgenic mice leads to neuronal proliferation, focal increases in urinary bladder mast cells, increased urinary bladder reflex activity, and pelvic hypersensitivity. NGF-overexpressing mice may, therefore, provide a useful transgenic model for exploring the role of NGF in urinary bladder dysfunction.

Role of Ha-ras activation in superficial papillary pathway of urothelial tumor formation

Urothelial tumors develop along two distinctive phenotypic pathways (superficial papillary non-invasive tumors versus flat carcinoma in situ lesions), with markedly different biological behavior and prognosis. Although multiple genetic alterations have been identified in human bladder cancer, their cause-effect relationship with the two pathways has not been firmly established. Using a urothelium-specific promoter of the uroplakin II gene, we showed earlier in transgenic mice that the urothelial expression of SV40T antigen, which inactivates p53 and pRb, induced carcinoma in situ and invasive and metastatic bladder cancer. In striking contrast, we demonstrate here that the urothelial expression of an activated Ha-ras in transgenic mice caused urothelial hyperplasia and superficial papillary non-invasive bladder tumors. These results provide strong, direct experimental evidence that the two phenotypical pathways of bladder tumorigenesis are caused by distinctive genetic defects. Our results indicate that Ha-ras activation can induce urothelial proliferation in vivo; and that urothelial hyperplasia is a precursor of low-grade, superficial papillary bladder tumors. Our transgenic models provide unique opportunities to study the detailed molecular events underlying different types of bladder neoplasms, and can serve as useful preclinical models for evaluating the in vivo efficacy of preventive and therapeutic agents that act on various signaling pathways in bladder cancer.

Uroplakin gene expression by normal and neoplastic human urothelium

cDNA sequences for human uroplakins UPIa, UPIb, UPII, and UPIII were cloned and used to investigate uroplakin transcription by normal and neoplastic urothelial cells. Normal urothelium expressed mRNA for all four uroplakins, although UPIII could be detected only by ribonuclease protection assay. By in situ hybridization, UPIa and UPII were confined to superficial cells and UPIb was also expressed by intermediate cells. Cultured normal human urothelial cells showed a proliferative basal/intermediate cell phenotype and constitutive expression of UPIb only. Uroplakin expression by transitional cell carcinoma cell lines was related to their differentiated phenotype in vitro. RT4 cells expressed all uroplakins, VM-CUB-3 expressed three uroplakins, RT112 and HT1376 cells expressed only UPIb in high abundance, and COLO232, KK47, and EJ cells had no detectable expression. These results correlated with patterns of uroplakin expression in tumors. UPIa and UPII were detected superficially only in well differentiated transitional cell carcinoma papillae. UPIb was positive in seven of nine and overexpressed in five of nine noninvasive transitional cell carcinomas and was also present in four of eight invasive transitional cell carcinomas. Lymph node metastases retained the same pattern of UPIb expression as the primary tumor. Unlike the three differentiation-regulated uroplakins, UPIb may have an alternative role in urothelial cell/tissue processes.

Uroplakin gene expression in normal human tissues and locally advanced bladder cancer

The uroplakins are widely regarded as urothelium-specific markers of terminal urothelial cytodifferentiation. This study investigated the expression of the four uroplakin genes, UPIa, UPIb, UPII and UPIII, in a wide range of normal human tissues to determine tissue specificity and in advanced transitional cell carcinoma (TCC) to examine gene expression in primary and metastatic disease. In the urinary tract, all four uroplakins were expressed by urothelium and UPIII was also expressed by prostatic glandular epithelium. UPIa and UPII appeared to be urothelium-specific, but UPIb was detected in several non-urothelial tissues, including the respiratory tract, where it was associated with squamous metaplasia of tracheal and bronchial epithelia. The ten cases of primary TCC and corresponding lymph node metastases demonstrated that each uroplakin gene could be expressed at the mRNA level. No single uroplakin gene was expressed in all primary tumours or metastases, but 80% of the primary tumours and 70% of the lymph node metastases expressed at least one uroplakin gene. UPIII mRNA was often expressed in the absence of UPIII protein. These results confirm that in human tissues the expression of UPIa and UPII genes is highly specific to urothelium and suggest that the tight differentiation-restricted expression of uroplakin genes in normal urothelium is lost following malignant transformation.

Structural basis for tetraspanin functions as revealed by the cryo-EM structure of uroplakin complexes at 6-A resolution

Tetraspanin uroplakins (UPs) Ia and Ib, together with their single-spanning transmembrane protein partners UP II and IIIa, form a unique crystalline 2D array of 16-nm particles covering almost the entire urothelial surface. A 6 Å–resolution cryo-EM structure of the UP particle revealed that the UP tetraspanins have a rod-shaped structure consisting of four closely packed transmembrane helices that extend into the extracellular loops, capped by a disulfide-stabilized head domain. The UP tetraspanins form the primary complexes with their partners through tight interactions of the transmembrane domains as well as the extracellular domains, so that the head domains of their tall partners can bridge each other at the top of the heterotetramer. The secondary interactions between the primary complexes and the tertiary interaction between the 16-nm particles contribute to the formation of the UP tetraspanin network. The rod-shaped tetraspanin structure allows it to serve as stable pilings in the lipid sea, ideal for docking partner proteins to form structural/signaling networks.

Specific heterodimer formation is a prerequisite for uroplakins to exit from the endoplasmic reticulum

Much of the lower urinary tract, including the bladder, is lined by a stratified urothelium forming a highly differentiated, superficial umbrella cell layer. The apical plasma membrane as well as abundant cytoplasmic fusiform vesicles of the umbrella cells is covered by two-dimensional crystals that are formed by four membrane proteins named uroplakins (UPs) Ia, Ib, II, and III. UPs are synthesized on membrane-bound polysomes, and after several co- and posttranslational modifications they assemble into planar crystals in a post-Golgi vesicular compartment. Distension of the bladder may cause fusiform vesicles to fuse with the apical plasma membrane. We have investigated the early stages of uroplakin assembly by expressing the four uroplakins in 293T cells. Transfection experiments showed that, when expressed individually, only UPIb can exit from the endoplasmic reticulum (ER) and move to the plasma membrane, whereas UPII and UPIII reach the plasma membrane only when they form heterodimeric complexes with UPIa and UPIb, respectively. Heterodimer formation in the ER was confirmed by pulse-chase experiment followed by coimmunoprecipitation. Our results indicate that the initial building blocks for the assembly of crystalline uroplakin plaques are heterodimeric uroplakin complexes that form in the ER.

Assembly of urothelial plaques: tetraspanin function in membrane protein trafficking

The apical surface of mammalian urothelium is covered by 16-nm protein particles packed hexagonally to form 2D crystals of asymmetric unit membranes (AUM) that contribute to the remarkable permeability barrier function of the urinary bladder. We have shown previously that bovine AUMs contain four major integral membrane proteins, i.e., uroplakins Ia, Ib, II, and IIIa, and that UPIa and Ib (both tetraspanins) form heterodimers with UPII and IIIa, respectively. Using a panel of antibodies recognizing different conformational states of uroplakins, we demonstrate that the UPIa-dependent, furin-mediated cleavage of the prosequence of UPII leads to global conformational changes in mature UPII and that UPIb also induces conformational changes in its partner UPIIIa. We further demonstrate that tetraspanins CD9, CD81, and CD82 can stabilize their partner protein CD4. These results indicate that tetraspanin uroplakins, and some other tetraspanin proteins, can induce conformational changes leading to the ER-exit, stabilization, and cell surface expression of their associated, single-transmembrane-domained partner proteins and thus can function as "maturation-facilitators." We propose a model of AUM assembly in which conformational changes in integral membrane proteins induced by uroplakin interactions, differentiation-dependent glycosylation, and the removal of the prosequence of UPII play roles in regulating the assembly of uroplakins to form AUM.

Towards the molecular architecture of the asymmetric unit membrane of the mammalian urinary bladder epithelium: a closed "twisted ribbon" structure

The asymmetric unit membrane (AUM) forms numerous plaques covering the apical surface of mammalian urinary bladder epithelium. These plaques contain four major integral membrane proteins called uroplakins Ia, Ib, II and III, which form particles arranged in a well-ordered hexagonal lattice with p6 symmetry and a lattice constant of 16.5 nm. Bovine AUM plaques negatively stained with anionic sodium silicotungstate revealed structural detail to 3.1 nm resolution. Correlation averaging resolved each particle into 12 stain-excluding domains arranged in two concentric rings (inner ring radius (rm) = 3.7 nm, outer ring radius (rout) = 6.6 nm), each with six domains which were rotated by roughly 30 degrees relative to each other. Negative staining with cationic uranyl formate increased the resolution to 2.2 nm and unveiled distinct connections between adjacent AUM particles. These connections may provide a molecular basis for the observed insolubility of the plaques in many detergents. Examination of the luminal face of freeze-dried/unidirectionally metal-shadowed AUM plaques established a left-handed vorticity of the 16 nm protein particles, whereas the cytoplasmic face exhibited no significant surface corrugations. Three-dimensional reconstruction from sodium silicotungstate-stained specimens revealed the AUM particles to be built of six "V-shaped" subunits anchored upright in the membrane. The mass density distribution within uranyl formate-stained AUM particles was similar except that the inner tip of each V was bridged to the outer tip of an adjacent V, so that the 16 nm AUM particle appeared as a continuous, "twisted ribbon" embracing a central cavity. Finally, mass measurements of unstained/freeze-dried plaques by scanning transmission electron microscopy yielded a total mass of 1,120 kDa per membrane-bound AUM particle. By imposing constraints on the possible uroplakin stoichiometries within AUM plaques, these data provide a first glimpse of the molecular architecture of the 16 nm particles constituting the plaques.

Structural basis of urothelial permeability barrier function as revealed by Cryo-EM studies of the 16 nm uroplakin particle

The apical surface of terminally differentiated mammalian urothelial umbrella cells is covered by numerous plaques consisting of two-dimensional (2D) crystals of hexagonally packed 16 nm uroplakin particles, and functions as a remarkable permeability barrier. To determine the structural basis of this barrier function, we generated, by electron cryo microscopy, a projection map of the isolated mouse urothelial plaques at 7 A and a 3D structure at 10 A resolution. Our results indicate that each 16 nm particle has a central 6 nm lipid-filled 'hole' surrounded by 6 inverted U-shaped subunits, each consisting of an inner and an outer subdomain connected via a distal joint. The transmembrane portion of each subdomain can fit about 5 helices. This finding, coupled with our STEM and EM data, suggests that uroplakin pairs Ia/II and Ib/III are associated with the inner and outer subdomains, respectively. Since the inner subdomains interconnect to form a ring, which can potentially segregate the lipids of the central hole from those outside, the 2D crystalline uroplakin network may impose an organized state and a severely restricted freedom of movement on the lipid components, thus reducing membrane fluidity and contributing to the barrier function of urothelial plaques. Our finding that distinct uroplakin substructures are in contact with the cytoplasmic and exoplasmic leaflets of the plaque suggests that the two leaflets may have different lipid composition and contribute asymmetrically to the barrier function. We propose that the crystalline lattice structure of uroplakin, through its interactions with specialized lipids, plays a major role in the remarkable permeability barrier function of urothelial apical surface. Our results also have implications for the transmembrane signal transduction in urothelial cells as induced by the binding of uropathogenic E. coli to its uroplakin receptor.

Altered phenotype of cultured urothelial and other stratified epithelial cells: implications for wound healing

The differentiation of cultured stratified epithelial cells can deviate significantly from that of normal epithelium, leading to suggestions that cultured cells undergo abnormal differentiation, or a truncated differentiation. Thus cultured epidermal and corneal epithelial cells stop synthesizing their tissue-specific keratin pair K1/K10 and K3/K12, respectively. The replacement of these keratins in the suprabasal compartment by K6/K16 keratins that are made by all stratified squamous epithelia during hyperplasia rules out a truncated differentiation. Importantly, the keratin pattern of in vivo corneal epithelium undergoing wound repair mimics that of cultured rabbit corneal epithelial cells. Although cultured urothelial cells continue to synthesize uroplakins, which normally form two-dimensional crystalline urothelial plaques covering almost the entire apical urothelial surface, these proteins do not assemble into crystals in cultured cells. Cultured epithelial cells can, however, rapidly regain normal differentiation on the removal of mitogenic stimuli, the use of a suitable extracellular matrix, or the transplantation of the cells to an in vivo, nonmitogenic environment. These data suggest that cultured epithelial cells adopt altered differentiation patterns mimicking in vivo regenerating or hyperplastic epithelia. Blocking the synthesis of tissue-specific differentiation products, such as the K1 and K10 keratins designed to form extensive disulfide cross-links in cornified cells, or the assembly of uroplakin plaques allows epithelial cells to better migrate and proliferate, activities that are of overriding importance during wound repair. Cultured urothelial and other stratified epithelial cells provide excellent models for studying the regulation of the synthesis and assembly of differentiation products, a key cellular process during epithelial wound repair.

The bladder as a bioreactor: urothelium production and secretion of growth hormone into urine

Uroplakin genes are expressed in a bladder-specific and differentiation-dependent fashion. Using a 3.6-kb promoter of mouse uroplakin II gene, we have generated transgenic mice that express human growth hormone (hGH) in their bladder epithelium, resulting in its secretion into the urine at 100-500 ng/ml. The levels of urine hGH concentration remain constant for longer than 8 months. hGH is present as aggregates mostly in the uroplakin-delivering cytoplasmic vesicles that are targeted to fuse with the apical surface. Using the bladder as a bioreactor offers unique advantages, including the utility of all animals throughout their lives. Using urine, which contains little protein and lipid, as a starting material facilitates recombinant protein purification.

Formation of asymmetric unit membrane during urothelial differentiation

Mammalian urothelium undergoes unique membrane specialization during terminal differentiation making numerous rigid-looking membrane plaques (0.3-0.5 micron diameter) that cover the apical cell surface. The outer leaflet of these membrane plaques is almost twice as thick as the inner leaflet hence the name asymmetric unit membrane (AUM). Ultrastructural studies established that the outer leaflet of AUM is composed of 16 nm particles forming two dimensional crystals, and that each particle forms a 'twisted ribbon' structure. We showed recently that highly purified bovine AUMs contain four major integral membrane proteins: uroplakins Ia (27 kD), Ib (28 kD), II (15 kD) and III (47 kD). Studies of the protease sensitivity of the different subdomains of uroplakins and other considerations suggest that UPIa and UPIb have 4 transmembrane domains, while UPII and UPIII have only one transmembrane domain. Chemical crosslinking studies showed that UPIa and UPIb, which share 39% amino acid sequence, are topologically adjacent to UPII and UPIII, respectively, thus raising the possibility that there exist two biochemically distinct AUM particles, i.e., those containing UPIa/UPII vs. UPIb/UPIII. Bovine urothelial cells grown in the presence of 3T3 feeder cells undergo clonal growth forming stratified colonies capable of synthesizing and processing all known uroplakins. Transgenic mouse studies showed that a 3.6 kb 5'-flanking sequence of mouse uroplakin II gene can drive the expression of bacterial LacZ gene to express in the urothelium. Further studies on the biosynthesis, assembly and targeting of uroplakins will offer unique opportunities for better understanding the structure and function of AUM as well as the biology of mammalian urothelium.

A survivin gene signature predicts aggressive tumor behavior

Gene signatures that predict aggressive tumor behavior at the earliest stages of disease, ideally before overt tissue abnormalities, are urgently needed. To search for such genes, we generated a transgenic model of survivin, an essential regulator of cell division and apoptosis overexpressed in cancer. Transgenic expression of survivin in the urinary bladder did not cause histologic abnormalities of the urothelium. However, microarray analysis revealed that survivin-expressing bladders exhibited profound changes in gene expression profile affecting extracellular matrix and inflammatory genes. Following exposure to a bladder carcinogen, N-butyl-N-(4-hydroxybutyl) nitrosamine (OH-BBN), survivin transgenic animals exhibited accelerated tumor progression, preferential incidence of tumors as compared with premalignant lesions, and dramatically abbreviated survival. Conversely, transgenic expression of a survivin Thr34-->Ala dominant-negative mutant did not cause changes in gene expression or accelerated tumor progression after OH-BBN treatment. Therefore, survivin expression induces global transcriptional changes in the tissue microenvironment that may promote tumorigenesis. Detection of survivin or its associated gene signature may provide an early biomarker of aggressive tumor behavior before the appearance of tissue abnormalities.

Urothelial injuries and the early wound healing response: tight junctions and urothelial cytodifferentiation

Using primary explant cultures of mouse bladder, the early response of the urothelium after superficial and full-thickness injuries was investigated. In such an in vitro wound healing model, explant surfaces with a mostly desquamated urothelial superficial layer represented superficial wounds, and the exposed lamina propria at the cut edges of the explants represented full-thickness wounds. The urothelial cell ultrastructure, the expression and subcellular distribution of the tight junctional protein occludin, and differentiation-related proteins CK 20, uroplakins, and actin were followed. Since singular terminally differentiated superficial cells remained on the urothelium after superficial injury (i.e., original superficial cells), we sought to determine their role during the urothelial wound-healing process. Ultrastructural and immunocytochemical studies have revealed that restored tight junctions are the earliest cellular event during the urothelial superficial and full-thickness wound-healing process. Occludin-containing tight junctions are developed before the new superficial cells are terminally differentiated. New insights into the urothelium wound-healing process were provided by demonstrating that the original superficial cells contribute to the urothelium wound healing by developing tight junctions with de novo differentiated superficial cells and by stretching, thus providing a large urothelial surface with asymmetric unit membrane plaques.

The epidermal differentiation-associated Grainyhead gene Get1/Grhl3 also regulates urothelial differentiation

Skin and bladder epithelia form effective permeability barriers through the activation of distinct differentiation gene programs. Using a genome-wide gene-expression study, we identified transcriptional regulators whose expression correlates highly with that of differentiation markers in both the bladder and skin, including the Grainyhead factor Get1/Grhl3, which is already known to be important for epidermal barrier formation. In the bladder, Get1 is most highly expressed in the differentiated umbrella cells and its mutation in mice leads to a defective bladder epithelial barrier formation due to the failure of apical membrane specialization. Genes encoding components of the specialized urothelial membrane, the uroplakins, were downregulated in Get1(-/-) mice. At least one of these genes, uroplakin II, is a direct target of Get1. The urothelial-specific activation of the uroplakin II gene is due to selective binding of Get1 to the uroplakin II promoter in urothelial cells, which is most likely regulated by histone modifications. These results show a crucial role for Get1 in urothelial differentiation and barrier formation.

A tissue-specific promoter that can drive a foreign gene to express in the suprabasal urothelial cells of transgenic mice

Uroplakins are a group of integral membrane proteins that are synthesized as the major differentiation products of urothelium. The luminal portions of these proteins form 12-nm protein particles arranged in a two-dimensional crystalline array. The expression of uroplakin genes is bladder specific and differentiation dependent; little is known, however, about their molecular regulation. Here we describe the cloning of mouse uroplakin II gene and demonstrate, in transgenic mouse experiments, that a 3.6-kb 5'-flanking sequence of this gene can drive a bacterial lacZ (reporter) gene to express in the suprabasal cell layers of the urothelium. The transgene was not expressed in any tested (nonurothelial) epithelial and other tissues (except hypothalamus). These results suggest that most of the cis elements that confer the bladder-specific and differentiation-dependent expression of mouse uroplakin II gene must reside in the 3.6-kb sequence. The availability of a promoter capable of delivering a foreign molecule to the differentiated cell layers of bladder epithelium opens avenues for studying normal and pathological urothelial differentiation in transgenic mice.

Detection of Micrometastases in Pelvic Lymph Nodes in Patients Undergoing Radical Cystectomy for Focally Invasive Bladder Cancer by Real-time Reverse Transcriptase-PCR for Cytokeratin 19 and Uroplakin II

PURPOSE

The objective of this study was to clarify the significance of micrometastases in pelvic lymph nodes in patients who underwent radical cystectomy for bladder cancer.

EXPERIMENTAL DESIGN

We included 40 patients with locally invasive bladder cancer who underwent radical cystectomy and pelvic lymphadenectomy. Expression of cytokeratin 19 (CK19), uroplakin II (UP II), and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in 760 lymph nodes were assessed by a fully quantitative real-time reverse transcription-PCR (RT-PCR) assay. The quantification value of CK19 or UP II mRNA was described as each value relative to GAPDH mRNA. In this study, we regarded specimen in which either CK19 or UP II mRNA was positive as "presence of micrometastasis."

RESULTS

Routine pathologic examinations detected tumor cells in 29 lymph nodes from six patients. Real-time RT-PCR identified positive expression of CK19 and UP II mRNAs in 49 lymph nodes from 10 patients and 98 lymph nodes from 16 patients, respectively. Of 633 lymph nodes from 34 patients with no pathologic evidence of nodal involvement, 13 nodes from five patients and 58 nodes from 10 patients were diagnosed as positive for CK19 and UP II mRNAs expression, respectively, by real-time RT-PCR. Presence of micrometastases was significantly associated with other conventional prognostic variables, including pathologic stage and microvascular invasion. Disease recurrence was occurred in eight patients, among whom four patients were negative for lymph node metastasis by routine pathologic examination and diagnosed as having micrometastasis by real-time RT-PCR assay. Furthermore, cause-specific survival rate in patients without micrometastasis was significantly higher than that in those with micrometastasis, irrespective of the presence of pathologic-positive nodes.

CONCLUSIONS

Approximately 30% of locally invasive bladder cancer shed cancer cells to pelvic lymph nodes, and disease recurrence after radical cystectomy could be explained, at least in part, by micrometastases in pelvic lymph nodes.

All-trans retinoic acid directs urothelial specification of murine embryonic stem cells via GATA4/6 signaling mechanisms

The urinary bladder and associated tract are lined by the urothelium, a transitional epithelium that acts as a specialized permeability barrier that protects the underlying tissue from urine via expression of a highly specific group of proteins known as the uroplakins (UP). To date, our understanding of the developmental processes responsible for urothelial differentiation has been hampered due to the lack of suitable models. In this study, we describe a novel in vitro cell culture system for derivation of urothelial cells from murine embryonic stem cells (ESCs) following cultivation on collagen matrices in the presence all trans retinoic acid (RA). Upon stimulation with micromolar concentrations of RA, ESCs significantly downregulated the pluripotency factor OCT-4 but markedly upregulated UP1A, UP1B, UP2, UP3A, and UP3B mRNA levels in comparison to naïve ESCs and spontaneously differentiating controls. Pan-UP protein expression was associated with both p63- and cytokeratin 20-positive cells in discrete aggregating populations of ESCs following 9 and 14 days of RA stimulation. Analysis of endodermal transcription factors such as GATA4 and GATA6 revealed significant upregulation and nuclear enrichment in RA-treated UP2-GFP+ populations. GATA4-/- and GATA6-/- transgenic ESC lines revealed substantial attenuation of RA-mediated UP expression in comparison to wild type controls. In addition, EMSA analysis revealed that RA treatment induced formation of transcriptional complexes containing GATA4/6 on both UP1B and UP2 promoter fragments containing putative GATA factor binding sites. Collectively, these data suggest that RA mediates ESC specification toward a urothelial lineage via GATA4/6-dependent processes.

Serial cloning of pigs by somatic cell nuclear transfer: restoration of phenotypic normality during serial cloning

Somatic cell nuclear transfer (scNT) is a useful way to create cloned animals. However, scNT clones exhibit high levels of phenotypic instability. This instability may be due to epigenetic reprogramming and/or genomic damage in the donor cells. To test this, we produced transgenic pig fibroblasts harboring the truncated human thrombopoietin (hTPO) gene and used them as donor cells in scNT to produce first-generation (G1) cloned piglets. In this study, 2,818 scNT embryos were transferred to 11 recipients and five G1 piglets were obtained. Among them, a clone had a dimorphic facial appearance with severe hypertelorism and a broad prominent nasal bridge. The other clones looked normal. Second-generation (G2) scNT piglets were then produced using ear cells from a G1 piglet that had an abnormal nose phenotype. We reasoned that, if the phenotypic abnormality of the G1 clone was not present in the G2 and third-generation (G3) clones, or was absent in the G2 clones but reappeared in the G3 clones, the phenotypic instability of the G1 clone could be attributed to faulty epigenetic reprogramming rather than to inherent/accidental genomic damage to the donor cells. Blastocyst rates, cell numbers in blastocyst, pregnancy rates, term placenta weight and ponderal index, and birth weight between G1 and G2 clones did not differ, but were significantly (P < 0.05) lower than control age- and sex-matched piglets. Next, we analyzed global methylation changes during development of the preimplantation embryos reconstructed by donor cells used for the production of G1 and G2 clones and could not find any significant differences in the methylation patterns between G1 and G2 clones. Indeed, we failed to detect the phenotypic abnormality in the G2 and G3 clones. Thus, the phenotypic abnormality of the G1 clone is likely to be due to epigenetic dysregulation. Additional observations then suggested that expression of the hTPO gene in the transgenic clones did not appear to be the cause of the phenotypic abnormality in the G1 clones and that the abnormality was acquired by only a few of the G1 clone's cells during its gestational development.

Golgi apparatus fragmentation as a mechanism responsible for uniform delivery of uroplakins to the apical plasma membrane of uroepithelial cells

BACKGROUND INFORMATION

The GA (Golgi apparatus) has an essential role in membrane trafficking, determining the assembly and delivery of UPs (uroplakins) to the APM (apical plasma membrane) of superficial UCs (uroepithelial cells) of urinary bladder. UPs are synchronously and uniformly delivered from the GA to the APM by DFVs (discoidal- or fusiform-shaped vesicles); however, the mechanism of UP delivery is not known. We have used the culture model of UCs with the capacity to undergo terminal differentiation to study the process of uniform delivery of DFVs to the APM and to elucidate the mechanisms involved.

RESULTS

By three-dimensional localization using confocal microscopy of immunofluorescence-labelled GA-related markers [GM130 (cis-Golgi matrix protein of 130 kDa), GS15 (Golgi Snare 15 kDa), GS28 and giantin], uroepithelial differentiation-related markers (UPs), MTs (microtubules; α-tubulin) and intermediate filaments [CK7 (cytokeratin 7) and CK20], we found that in non-differentiated, UP-negative UCs the GA is mostly organized as a single ribbon-like structure close to the nucleus, whereas in differentiated, UP-positive UCs the GA is fragmented and spread almost through the entire cell. The FRAP (fluorescence recovery after photobleaching) experiments on the UCs transfected with GalT (trans-Golgi/TGN enzyme β1,4-galactosyltransferase) fused to fluorescent protein showed that Golgi-resident enzyme cycles freely within ribbon-like GA but not within fragmented GA. By CLEM (correlative light-electron microscopy), we examined the GA fragments in cells expressing UPs. We found that GA fragments are fully functional and similar to the GA fragments that are formed after nocodazole treatment. Furthermore, we demonstrated that the reorganization of GA into a fragmented form is associated with the impairment of the MT organization in the basal, central and subapical cytoplasm and the accumulation of intermediate filaments in the apical cytoplasm that could affect the kinetics of MT star leading to the peripheral fragmentation of the GA in the differentiated UCs.

CONCLUSIONS

The fragmentation of the GA and the subsequent spreading of GA to the cell periphery represent one of the key events that promote the uniform delivery of UPs over the entire APM of differentiating UCs and thus are of major importance in the final proper formation and maintenance of the blood-urine barrier.

Detection of circulating uroplakin-positive cells in patients with transitional cell carcinoma of the bladder

PURPOSE

Although transitional cell carcinoma of the bladder (TCC) metastasizes frequently with devastating consequences, no marker has been available to monitor this process. Uroplakins are a group of specific markers for normal urothelium and are continuously expressed by the majority of TCCs. Detection of uroplakin-positive cells in the circulation would be a strong indication of hematogenous dissemination of tumor cells in patients with TCC.

MATERIALS AND METHODS

Total RNAs were extracted from peripheral blood of 60 patients with TCC (50 non-metastatic and 10 metastatic) and 10 healthy controls, reverse-transcribed and subjected to polymerase chain reaction amplification (RT-PCR) using oligonucleotide primers of human uroplakin II gene. A uroplakin-expressing human bladder cancer cell line (RT4) was used as a positive control to establish the sensitivity of the RT-PCR assay.

RESULTS

We showed that the PCR-amplification of the mRNA encoding uroplakin II (UPII), a 15-kDa urothelium-specific marker, constitutes a highly sensitive and specific assay for detecting 100% of transitional cell carcinoma tissue, and that this assay can detect a single bladder cancer cell in a 5-ml. blood sample. UPII mRNA was detected in the blood samples of 2 patients with metastatic bladder cancer without chemotherapy and 1 out of 8 such patients with chemotherapy, but not in those of 50 non-metastatic patients or normal controls.

CONCLUSIONS

Uroplakin II is a highly specific marker for human TCC and the detection of uroplakin II in the peripheral blood is associated with metastatic spread of bladder cancer cells. The specific and sensitive detection of uroplakin II provides a useful adjunct for detecting bladder cancer metastasis, staging, and monitoring chemotherapeutic response.