Incidence of fibroblast growth factor receptor 3 gene (FGFR3) A248C, S249C, G372C, and T375C mutations in bladder cancer

Bladder cancer is the most frequent cancer of the urinary system. Fibroblast growth factor receptors (FGFR) belong to the tyrosine kinase family and have important roles in cell differentiation and proliferation and embryogenesis. FGFR3 is located on chromosome 4p16.3, and missense mutations of FGFR3 are associated with autosomal dominant human skeletal disorders and have some oncogenic effects. We examined the incidence of FGFR3 thanatophoric dysplasia mutations located in exon 7, A248C and S249C, and in exon 10, G372C and T375C, and their correlation with clinical-pathological parameters in bladder carcinoma patients. Fifty-six paraffin-embedded specimens of transitional cell carcinoma of the urinary bladder were included in this study. Analysis of FGFR3 thanatophoric dysplasia mutations located in exon 7, A248C and S249C, and in exon 10, G372C and T375C, was performed by PCR-restriction fragment length polymorphism (RFLP) analysis and DNA sequencing. FGFR3 thanatophoric dysplasia mutations located in exon 7, A248C and S249C, and in exon 10, G372C and T375C, were detected in 33 of the 56 patients (heterozygous mutant). Among the 56 transitional cell carcinomas, missense point mutations were detected in seven of them at codon A248C, 28 of them at codon S249C, and three of them at codon T375C, similar to data from previous reports. When the results of the FGFR3 thanatophoric dysplasia mutations located in exon 7, A248C and S249C and in exon 10, G372C and T375C, were analyzed one by one or as a group, despite the findings of previous research reports, our data suggest that these mutations are detected homogenously regardless of the tumor classification and tumor grade.     

The bovine fibroblast growth factor receptor 3 (FGFR3) gene is not the locus responsible for bovine chondrodysplastic dwarfism in Japanese brown cattle

Fibroblast growth factor receptor 3 (FGFR3) is one of the four distinct membrane-spanning tyrosine kinase receptors for fibroblast growth factors. The FGFR3 is a negative regulator of endochondral ossification and mutations in the FGFR3 gene have been found in patients of human hereditary diseases with chondrodysplastic phenotypes. Recently, we mapped the locus responsible for hereditary chondrodysplastic dwarfism in Japanese brown cattle to the distal region of bovine chromosome 6 close to the FGFR3 gene, suggesting that FGFR3 was a positional candidate gene for this disorder. In the present study, we isolated complementary DNA (cDNA) clones containing the entire coding region of the bovine FGFR3 gene. Comparison of the nucleotide sequence between affected and normal animals revealed no disease-specific differences in the deduced amino acid sequences. We further refined the localization of FGFR3 by radiation hybrid mapping, which is distinct from that of the disease locus. Therefore we conclude that bovine chondrodysplastic dwarfism in Japanese brown cattle is not caused by mutation in the FGFR3 gene.     

Human immortalized chondrocytes carrying heterozygous FGFR3 mutations: an in vitro model to study chondrodysplasias

Achondroplasia and thanatophoric dysplasia are human chondrodysplasias caused by mutations in the fibroblast growth factor receptor 3 (FGFR3) gene. We have developed an immortalized human chondrocyte culture model to study the regulation of chondrocyte functions. One control and eight mutant chondrocytic lines expressing different FGFR3 heterozygous mutations were obtained. FGFR3 signaling pathways were modified in the mutant lines as revealed by the constitutive activation of the STAT pathway and an increased level of P21(WAF1/CIP1) protein. This model will be useful for the study of FGFR3 function in cartilage studies and future therapeutic approaches in chondrodysplasias.     

Chimeras of the native form or achondroplasia mutant (G375C) of human fibroblast growth factor receptor 3 induce ligand-dependent differentiation of PC12 cells.

Mutations in the gene for human fibroblast growth factor receptor 3 (hFGFR3) cause a variety of skeletal dysplasias, including the most common genetic form of dwarfism, achondroplasia (ACH). Evidence indicates that these phenotypes are not due to simple haploinsufficiency of FGFR3 but are more likely related to a role in negatively regulating skeletal growth. The effects of one of these mutations on FGFR3 signaling were examined by constructing chimeric receptors composed of the extracellular domain of human platelet-derived growth factor receptor beta (hPDGFR beta) and the transmembrane and intracellular domains of hFGFR3 or of an ACH (G375C) mutant. Following stable transfection in PC12 cells, which lack platelet-derived growth factor (PDGF) receptors, all clonal cell lines, with either type of chimera, showed strong neurite outgrowth in the presence of PDGF but not in its absence. Antiphosphotyrosine immunoblots showed ligand-dependent autophosphorylation, and both receptor types stimulated strong phosphorylation of mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase, an event associated with the differentiative response of these cells. In addition, ligand-dependent phosphorylation of phospholipase Cgamma and Shc was also observed. All of these responses were comparable to those observed from ligand activation, such as by nerve growth factor, of the native PC12 cells used to prepare the stable transfectants. The cells with the chimera bearing the ACH mutation were more rapidly responsive to ligand with less sustained MAPK activation, indicative of a preactivated or primed condition and consistent with the view that these mutations weaken ligand control of FGFR3 function. However, the full effect of the mutation likely depends in part on structural features of the extracellular domain. Although FGFR3 has been suggested to act as a negative regulator of long-bone growth in chrondrocytes, it produces differentiative signals similar to those of FGFR1, to which only positive effects have been ascribed, in PC12 cells. Therefore, its regulatory effects on bone growth likely result from cellular contexts and not the induction of a unique FGFR3 signaling pathway.     

Paternal origin of FGFR3 mutations in Muenke-type craniosynostosis

Muenke syndrome, also known as FGFR3-associated coronal synostosis, is defined molecularly by the presence of a heterozygous nucleotide transversion, c.749C>G, encoding the amino acid substitution Pro250Arg, in the fibroblast growth factor receptor type 3 gene (FGFR3). This frequently occurs as a new mutation, manifesting one of the highest documented rates for any transversion in the human genome. To understand the biology of this mutation, we have investigated its parental origin, and the ages of the parents, in 19 families with de novo c.749C>G mutations. All ten informative cases originated from the paternal allele (95% confidence interval 74–100% paternal); the average paternal age at birth overall was 34.7 years. An exclusive paternal origin of mutations, and increased paternal age, were previously described for a different mutation (c.1138G>A) of the FGFR3 gene causing achondroplasia, as well as for mutations of the related FGFR2 gene causing Apert, Crouzon and Pfeiffer syndromes. We conclude that similar biological processes are likely to shape the occurrence of this c.749C>G mutation as for other mutations of FGFR3 as well as FGFR2.S.V. Rannan-Eliya and I.B. Taylor contributed equally to this work.     

Effect of Thanatophoric Dysplasia Type I Mutations on FGFR3 Dimerization

Thanatophoric dysplasia type I (TDI) is a lethal human skeletal growth disorder with a prevalence of 1 in 20,000 to 1 in 50,000 births. TDI is known to arise because of five different mutations, all involving the substitution of an amino acid with a cysteine in fibroblast growth factor receptor 3 (FGFR3). Cysteine mutations in receptor tyrosine kinases (RTKs) have been previously proposed to induce constitutive dimerization in the absence of ligand, leading to receptor overactivation. However, their effect on RTK dimer stability has never been measured experimentally. In this study, we characterize the effect of three TDI mutations, Arg248Cys, Ser249Cys, and Tyr373Cys, on FGFR3 dimerization in mammalian membranes, in the absence of ligand. We demonstrate that the mutations lead to surprisingly modest dimer stabilization and to structural perturbations of the dimers, challenging the current understanding of the molecular interactions that underlie TDI.     

Immunohistochemical Analysis of 1,25-dihydroxyvitamin D3 Receptor in Cervical Carcinoma

The immunohistochemical localization and expression of 1,25-dihydroxyvitamin D₃ receptors (VDR) has been investigated in normal human cervical tissue (n = 15) and in cervical carcinomas (n = 23). VDR immunoreactivity (monoclonal antibody 9A7r354;) was compared with the staining patterns of transglutaminase K, cytokeratin 10 and Ki-67 in these tumours. Moderate to strong nuclear immunoreactivity for VDR was detected in almost all cervical carcinomas analysed. VDR staining was homogeneous, with no visual differences between individual tumour cells. Some 60% of normal cervical tissues revealed weak immunoreactivity for VDR. In normal cervical tissue, nuclear VDR staining was confined to the lower cervical layers, predominantly to the basal cell layer. Both the intensity of VDR immunostaining and the number of VDR-positive cells were up-regulated in cervical carcinomas compared with normal cervical tissue. No visual correlation wa s found for the coexpression of VDR with markers of proliferation and differentiation. Our findings indicate that: (1) cervical tissue may be a new target organ for therapeutically applied vitamin D analogues; (2) VDR is up-regulated at the protein level in cervical carcinomas compared with normal cervical tissue; (3) up-regulation of VDR in cervical carcinoma is induced not exclusively by alterations in epithelial differentiation or proliferation, but by different, unknown mechanisms; and (4) calcitriol and new vitamin D analogues exerting fewer calcaemic side-effects may be promising new drugs for the treatment or chemoprevention of metastasizing cervical carcinomas as well as of cervical precancerous lesions.     

Immunohistochemical Analysis of 1,25-dihydroxyvitamin D3 Receptor in Cervical Carcinoma

The immunohistochemical localization and expression of 1,25-dihydroxyvitamin D₃ receptors (VDR) has been investigated in normal human cervical tissue (n = 15) and in cervical carcinomas (n = 23). VDR immunoreactivity (monoclonal antibody 9A7r354;) was compared with the staining patterns of transglutaminase K, cytokeratin 10 and Ki-67 in these tumours. Moderate to strong nuclear immunoreactivity for VDR was detected in almost all cervical carcinomas analysed. VDR staining was homogeneous, with no visual differences between individual tumour cells. Some 60% of normal cervical tissues revealed weak immunoreactivity for VDR. In normal cervical tissue, nuclear VDR staining was confined to the lower cervical layers, predominantly to the basal cell layer. Both the intensity of VDR immunostaining and the number of VDR-positive cells were up-regulated in cervical carcinomas compared with normal cervical tissue. No visual correlation wa s found for the coexpression of VDR with markers of proliferation and differentiation. Our findings indicate that: (1) cervical tissue may be a new target organ for therapeutically applied vitamin D analogues; (2) VDR is up-regulated at the protein level in cervical carcinomas compared with normal cervical tissue; (3) up-regulation of VDR in cervical carcinoma is induced not exclusively by alterations in epithelial differentiation or proliferation, but by different, unknown mechanisms; and (4) calcitriol and new vitamin D analogues exerting fewer calcaemic side-effects may be promising new drugs for the treatment or chemoprevention of metastasizing cervical carcinomas as well as of cervical precancerous lesions.     

Dwarfism in Dexter cattle is not caused by the mutations in FGFR3 responsible for achondroplasia in humans

Dexter cattle carry a genetic defect causing a dwarf phenotype in the heterozygotes (Dx +/–), while homozygotes (Dx +/+) are stillborn with extreme shortening of limbs and gross craniofacial defects and are described as 'bulldog' calves. The heterozygous phenotype has been likened to achondroplastic dwarfism in humans (ACH), which has recently been shown to be the result of mutations in the transmembrane region of the fibroblast growth factor receptor 3 (FGFR3) gene. We have sequenced the transmembrane region of bovine FGFR3 from normal Dexter cattle (Dx -/-) and bulldog calves (Dx +/+). The sequence from both is identical and therefore excludes mutations in the transmembrane region of FGFR3 as the cause of Dexter dwarfism.     

FGFR3 intracellular mutations induce tyrosine phosphorylation in the Golgi and defective glycosylation

Mutations of the Fibroblast Growth Factor Receptor 3 (FGFR3) gene have been implicated in a series of skeletal dysplasias including hypochondroplasia, achondroplasia and thanatophoric dysplasia. The severity of these diseases ranges from mild dwarfism to severe dwarfism and to perinatal lethality, respectively. Although it is considered that the mutations give rise to constitutively active receptors, it remains unclear how the different mutations are functionally linked to the severity of the different pathologies. By examining various FGFR3 mutations in a HEK cell culture model, including the uncharacterized X807R mutation, it was found that only the mutations affecting the intracellular domain, induced premature receptor phosphorylation and inhibited receptor glycosylation, suggesting that premature receptor tyrosine phosphorylation of the native receptor inhibits its glycosylation. Moreover, these mutations appeared to be associated with elevated receptor signaling in the Golgi apparatus. In conclusion, although pathological severity could not be correlated with a single factor arising from FGFR3 mutations, these results suggest that intracellular domain mutations define a distinct means by which mutated FGFR3 could disrupt bone development.     

Interaction of fibroblast growth factor receptor 3 and the adapter protein SH2-B. A role in STAT5 activation

Fibroblast growth factor receptor 3 (FGFR3) influences a diverse array of biological processes, including cell growth, differentiation, and migration. Activating mutations in FGFR3 are associated with multiple myeloma, cervical carcinoma, and bladder cancer. To identify proteins that interact with FGFR3 and which may mediate FGFR3-dependent signaling, a yeast two-hybrid screen was employed using the cytoplasmic kinase domain of FGFR3 as bait. We identified the adapter protein SH2-B as an FGFR3-interacting protein. Coimmunoprecipitation experiments demonstrate binding of the SH2-B beta isoform to FGFR3 in 293T cells. Tyrosine phosphorylation of SH2-B beta was observed when coexpressed with activated FGFR3 mutants such as the weakly activated mutant N540K or the strongly activated mutant K650E, both associated with human developmental syndromes. The extent of tyrosine phosphorylation of SH2-B beta correlates with receptor activation, suggesting that FGFR3 activation mediates tyrosine phosphorylation of SH2-B beta. Furthermore, two tyrosine phosphorylation sites of FGFR3, Tyr-724 and Tyr-760, are required for optimal binding of the Src homology-2 (SH2) domain of SH2-B beta. We also demonstrate the phosphorylation and nuclear translocation of Stat5 by activated FGFR3, which increases in response to overexpression of SH2-B beta. Taken together, our results identify SH2-B beta as a novel FGFR3 binding partner that mediates signal transduction.     

A single-base change in the tyrosine kinase II domain of ovine FGFR3 causes hereditary chondrodysplasia in sheep

Ovine hereditary chondrodysplasia, or spider lamb syndrome (SLS), is a genetic disorder that is characterized by severe skeletal abnormalities and has resulted in substantial economic losses for sheep producers. Here we demonstrate that a non-synonymous T>A transversion in the highly conserved tyrosine kinase II domain of a positional candidate gene, fibroblast growth factor receptor 3 (FGFR3), is responsible for SLS. We also demonstrate that the mutant FGFR3 allele has an additive effect on long-bone length, calling into question the long-standing belief that SLS is inherited as a strict monogenic, Mendelian recessive trait. Instead, we suggest that SLS manifestation is determined primarily by the presence of the mutant FGFR3 allele, but it is also influenced by an animal's genetic background. In contrast to FGFR3 mutations causing dwarfism in humans, this single-base change is the only known natural mutation of FGFR3 that results in a skeletal overgrowth phenotype in any species.     

Structural basis for epidermal growth factor receptor function

The receptor for epidermal growth factor (EGF) has been the subject of intense study primarily as a consequence of the pioneering studies of Cohen on growth factors and also because of its homology to the transforming protein encoded by the avian oncogene v-erbB, which is a truncated receptor, and its consequent role in cancer. Although similar structural mutation of the EGF receptor has not yet been found in human tumours, aberrant overexpression of both EGF receptors and c-erbB2, a closely related putative receptor [1], have been found to occur in squamous cell carcinomas and glial tumours, and mammary carcinomas respectively [2–4]. In addition to EGF, the related polypeptides transforming growth factor α (TGFα) and vaccinia virus growth factor [5] are also ligands for the EGF receptor. Expression of TGFα occurs during embryonal development and in specific adult tissues; it may also play a role in cellular transformation (reviewed in Ref. 6). These important properties, as well as the potential roles of both TGFα and EGF in wound repair, have emphasized the need to understand EGF receptor structure, function and regulation. This review discusses the structural properties of the EGF receptor and how these can be related to receptor function and regulation.     

The Gly571Arg mutation, associated with the autonomic and sensory disorder congenital insensitivity to pain with anhidrosis, causes the inactivation of the NTRK1/nerve growth factor receptor

Point mutations affecting the NTRK1/TRKA gene, encoding one of the receptors for the nerve growth factor (NGF), have been detected in congenital insensitivity to pain with anhidrosis (CIPA), a human hereditary sensory neuropathy characterized by absence of reaction to noxious stimuli and anhidrosis. To define the defect of NTRK1 in CIPA patients, we have introduced one of the previously reported mutations (Gly571Arg) into both the NTRK1 and the TRK-T3 oncogene cDNAs. The expression of the mutated constructs into COS1 cells revealed that the introduced mutation, while not affecting its correct membrane localization, rendered the NTRK1 protein unable to undergo activation upon stimulation with NGF. Similarly, the mutation abolished the constitutive activation of the TRK-T3 oncogene. Transfection into NIH3T3 and PC12 cells showed the loss of transforming and differentiating activity by the mutated constructs. Our results demonstrate clearly that the CIPA mutations cause the inactivation of the NTRK1 receptor, thus exerting a loss of function effect, and provide an experimental approach to distinguish functional mutations from genetic polymorphisms.     

Identification of tyrosine residues in constitutively activated fibroblast growth factor receptor 3 involved in mitogenesis, Stat activation, and phosphatidylinositol 3-kinase activation

Fibroblast growth factor receptor 3 (FGFR3) mutations are frequently involved in human developmental disorders and cancer. Activation of FGFR3, through mutation or ligand stimulation, results in autophosphorylation of multiple tyrosine residues within the intracellular domain. To assess the importance of the six conserved tyrosine residues within the intracellular domain of FGFR3 for signaling, derivatives were constructed containing an N-terminal myristylation signal for plasma membrane localization and a point mutation (K650E) that confers constitutive kinase activation. A derivative containing all conserved tyrosine residues stimulates cellular transformation and activation of several FGFR3 signaling pathways. Substitution of all nonactivation loop tyrosine residues with phenylalanine rendered this FGFR3 construct inactive, despite the presence of the activating K650E mutation. Addition of a single tyrosine residue, Y724, restored its ability to stimulate cellular transformation, phosphatidylinositol 3-kinase activation, and phosphorylation of Shp2, MAPK, Stat1, and Stat3. These results demonstrate a critical role for Y724 in the activation of multiple signaling pathways by constitutively activated mutants of FGFR3.     

Sensitive detection of FGFR3 mutations in bladder cancer and urine sediments by peptide nucleic acid-mediated real-time PCR clamping

Somatic mutations of the fibroblast growth factor receptor 3 (FGFR3) gene were detected by peptide nucleic acid (PNA)-mediated real-time PCR clamping. Mutation was detected in negative control containing only wild-type DNA due to a misincorporation of dNTPs to PNA binding sites when the amount of template DNA was decreased to 1 ng. Thus, the amount of template DNA was critical determinant of the assay sensitivity in PNA-mediated PCR clamping. Assay conditions were optimized to detect FGFR3 mutations in exons 7, 10, and 15, at a concentration of more than 1% mutated DNA using 50 ng of genomic DNA as the template. Mutations were detected in 12 of 13 (92.3%) tumor tissues and 11 of 13 (84.6%) urine samples from patients with superficial bladder cancer, while no mutations were detected in tissues and/or urine samples from patients with muscle-invasive bladder cancer or chronic cystitis.     

Absence of the c-Ha-ras and c-Ki-ras oncogene mutations in the hermaphroditic fish Rivulus marmoratus papillary thyroid carcinomas induced by N-methyl-N'-nitro-N-nitrosoguanidine

Previously we reported that papillary thyroid carcinomas were predominantly induced at high frequency by a low dose of N -methyl- N' -nitro- N -nitrosoguanidine (MNNG) in the hermaphroditic fish Rivulus marmoratus . In the current study, polymerase chain reaction (PCR) amplification and direct sequencing were used to examine the point mutations of Ha- and Ki- ras genes, which may be associated with papillary thyroid tumour development in rivulus. Thirty-three tumour samples were tested, however, no mutations were detected in rivulus Ha- and Ki- ras genes. In human and rodent models, it has been reported that ras gene mutations in papillary thyroid tumours occurred preferentially in the N- ras gene in general, while follicular tumours contained activated Ha- or Ki- ras gene mutations. This may explain why papillary thyroid carcinomas in rivulus were not mutated at codon 12, 13 or 61 of exon 1 or exon 2 of the rivulus Ha- or Ki- ras gene. These results imply that another oncogene, such as the N- ras gene and others, may be preferentially activated in rivulus papillary thyroid carcinomas, and also give valuable information for comparative studies of papillary thyroid carcinogenesis.     

The Pathogenic A391E Mutation in FGFR3 Induces a Structural Change in the Transmembrane Domain Dimer

Fibroblast growth factor receptor 3 (FGFR3) is a single-pass membrane protein and a member of the receptor tyrosine kinase family of proteins that is involved in the regulation of skeletal growth and development. FGFR3 has three distinct domains: the ligand binding extracellular domain, the cytosolic kinase domain and the transmembrane domain (TMD). Previous work with the isolated FGFR3 TMD has shown that it has the ability to dimerize. Clinical and genetic studies have also correlated mutations in the TMD with a variety of skeletal and cranial dysplasias and cancer. Although the structures of the extracellular and cytosolic domains of FGFR3 have been solved, the structure of the TMD dimer is still unknown. Furthermore, very little is known regarding the effects of pathogenic mutations on the TMD dimer structure. We, therefore, carried out ToxR activity assays to determine the role of the SmXXXSm motif in the dimerization of the FGFR3 TMD. This motif has been shown to drive the association of many transmembrane proteins. Our results indicate that the interaction between wild-type FGFR3 TMDs is not mediated by two adjacent SmXXXSm motifs. In contrast, studies using the TMD carrying the pathogenic A391E mutation suggest that the motifs play a role in the dimerization of the mutant TMD. Based on these observations, here we report a new mechanistic model in which the pathogenic A391E mutation induces a structural change that leads to the formation of a more stable dimer.     

Extracellular point mutations in FGFR2 elicit unexpected changes in intracellular signalling

An understanding of cellular signalling from a systems-based approach has to be robust to assess the effects of point mutations in component proteins. Outcomes of these perturbations should be predictable in terms of downstream response, otherwise a holistic interpretation of biological processes or disease states cannot be obtained. Two single, proximal point mutations (S252W and P253R) in the extracellular region of FGFR2 (fibroblast growth factor receptor 2) prolong growth factor engagement resulting in dramatically different intracellular phenotypes. Following ligand stimulation, the wild-type receptor undergoes rapid endocytosis into lysosomes, whereas (SW)FGFR2 (the S252W FGFR2 point mutation) and (PR)FGFR2 (the P253R FGFR2 point mutation) remain on the cell membrane for an extended period of time, modifying protein recruitment and elevating downstream ERK (extracellular-signal-regulated kinase) phosphorylation. FLIM (fluorescent lifetime imaging microscopy) reveals that direct interaction of FRS2 (FGFR substrate 2) with wild-type receptor occurs primarily at the vesicular membrane, whereas the interaction with the P253R receptor occurs exclusively at the plasma membrane. These observations suggest that the altered FRS2 recruitment by the mutant receptors results in an abnormal cellular signalling mechanism. In the present study these profound intracellular phenotypes resulting from extracellular receptor modification reveal a new level of complexity which will challenge a systems biology interpretation.