FGFR3IIIS: a novel soluble FGFR3 spliced variant that modulates growth is frequently expressed in tumour cells

Role of FGFR3 in bladder cancer: Treatment landscape and future challenges

Bladder cancer is a heterogeneous malignancy and is responsible for approximately 3.2% of new diagnoses of cancer per year (Sung et al., 2021). Fibroblast Growth Factor Receptors (FGFRs) have recently emerged as a novel therapeutic target in cancer. In particular, FGFR3 genomic alterations are potent oncogenic drivers in bladder cancer and represent predictive biomarkers of response to FGFR inhibitors. Indeed, overall ∼50% of bladder cancers have somatic mutations in the FGFR3 -coding sequence (Cappellen et al., 1999; Turner and Grose, 2010). FGFR3 gene rearrangements are typical alterations in bladder cancer (Nelson et al., 2016; Parker et al., 2014). In this review, we summarize the most relevant evidence on the role of FGFR3 and the state-of-art of anti-FGFR3 treatment in bladder cancer. Furthermore, we interrogated the AACR Project GENIE to investigate clinical and molecular features of FGFR3-altered bladder cancers. We found that FGFR3 rearrangements and missense mutations were associated with a lower fraction of mutated genome, compared to the FGFR3 wild-type tumors, as also observed in other oncogene-addicted cancers. Moreover, we observed that FGFR3 genomic alterations are mutually exclusive with other genomic aberrations of canonical bladder cancer oncogenes, such as TP53 and RB1. Finally, we provide an overview of the treatment landscape of FGFR3-altered bladder cancer, discussing future perspectives for the management of this disease.

High expression of FGFR3 predicts a better prognosis for patients with non-small cell lung cancer in a Chinese population

Background

This study sought to examine the expression and mutation status of fibroblast growth factor receptor 3 (FGFR3) in non-small cell lung cancer (NSCLC) tissues and explore the prognostic potential of FGFR3 in NSCLC.

Methods

Immunohistochemistry (IHC) was used to evaluate the FGFR3 protein expression of 116 NSCLC tissues. Sanger sequencing was used to examine the mutation status of exons 7, 10, and 15 in FGFR3. A Kaplan‑Meier survival analysis was conducted to evaluate the association between the expression level of FGFR3 and the overall survival (OS) and disease-free survival (DFS) of NSCLC patients. Univariate and multivariate Cox analyses were conducted to examine the association between the risk score and clinical features.

Results

FGFR3 was immunoreactive in 26 of the 86 NSCLC cases. Further, FGFR3 was positively expressed in 84.6% of the lung adenocarcinoma (AC) cases and 15.4% of the lung squamous cell carcinoma (SCC) cases. FGFR3 mutations were detected in 2 NSCLC patients (2/72, 2.8%), who both harbored the T450M mutation, a novel mutation in exon 10 of FGFR3. In NSCLC, a high expression of FGFR3 was positively correlated with gender, smoking, histology type, T stage, and the epidermal growth factor receptor (EGFR) mutation (P<0.05). FGFR3 expression was also correlated with better OS and DFS. The multivariate analysis revealed that FGFR3 served as an independent prognostic factor (P=0.024) for the OS of NSCLC patients.

Conclusions

This study showed that FGFR3 was highly expressed in NSCLC tissues, and the frequency rate for the FGFR3 mutation at T450 M in NSCLC tissues was low. The survival analysis suggested that FGFR3 may be a useful prognostic biomarker in NSCLC.

Differential expression profiling of onco and tumor-suppressor genes from major-signaling pathways in Wilms' tumor

PURPOSE

Wilms' tumor is the most-frequent malignant-kidney tumor in children under 3-4 years of age and is caused by genetic alterations of oncogenes (OG) and tumor-suppressor genes (TG). Wilms' tumor has been linked to many OG-&-TG. However, only WT1 has a proven role in the development of this embryonic-tumor.

METHODS

The study investigates the level of mRNA expression of 16 OGs and 20 TGs involved in key-signaling pathways, including chromatin modification; RAS; APC; Cell Cycle/Apoptosis; Transcriptional Regulation; PI3K; NOTCH-&-HH; PI3K & RAS of 24-fresh Wilms'-tumor cases by capture-and-reporter probe Code-Sets chemistry, as CNVs in these pathway genes have been reported.

RESULTS

Upon extensively investigating, MEN1, MLL2, MLL3, PBRM1, PRDM1, SMARCB1, SETD2, WT1, PTPN11, KRAS, HRAS, NF1, APC, RB1, FUBP1, BCOR, U2AF1, PIK3CA, PTEN, EBXW7, SMO, ALK, CBL, EP300-and-GATA1 were found to be significantly up-regulated in 58.34, 62.5, 79.17, 91.67, 58, 66.66,54, 58.34, 66.67, 75, 62.5, 62.5, 58, 79.17, 79.17, 75, 70.84, 50, 50, 75, 66.66, 62.50, 61.66, 58.34-and-62.50% of cases respectively, whereas BRAF, NF2, CDH1, BCL2, FGFR3, ERBB2, MET, RET, EGFR-and-GATA2 were significantly down regulated in 58, 87.50, 79.16, 54.16, 79.17, 91.66, 66.66, 58.33, 91.66-and-62.50% of cases, respectively. Interestingly, the WT1 gene was five-fold down regulated in 41.66% of cases only.

CONCLUSION

Hence, extensive profiling of OGs and TGs association of major-signaling pathways in Wilms' tumor cases may aid in disease diagnosis. PBRM1 (up-regulated in 91.67% of cases), ERBB2 and EGFR (down-regulated in 91.66 and 91.66% of cases, respectively) could be marker genes. However, validation of all relevant results in a larger number of samples is required.

Members of the Fibroblast Growth Factor Receptor Superfamily Are Proteolytically Cleaved by Two Differently Activated Metalloproteases

Fibroblast growth factor receptors (FGFRs) are a family of receptor tyrosine kinases that have been associated not only with various cellular processes, such as embryonic development and adult wound healing but also enhanced tumor survival, angiogenesis, and metastatic spread. Proteolytic cleavage of these single-pass transmembrane receptors has been suggested to regulate biological activities of their ligands during growth and development, yet little is known about the proteases responsible for this process. In this study, we monitored the release of membrane-anchored FGFRs 1, 2, 3, and 4 in cell-based assays. We demonstrate here that metalloprotease-dependent metalloprotease family, ADAM10 and ADAM17. Loss- and gain-of-function studies in murine embryonic fibroblasts showed that constitutive shedding as well as phorbol-ester-induced processing of FGFRs 1, 3, and 4 is mediated by ADAM17. In contrast, treatment with the calcium ionophore ionomycin stimulated ADAM10-mediated FGFR2 shedding. Cell migration assays with keratinocytes in the presence or absence of soluble FGFRs suggest that ectodomain shedding can modulate the function of ligand-induced FGFR signaling during cell movement. Our data identify ADAM10 and ADAM17 as differentially regulated FGFR membrane sheddases and may therefore provide new insight into the regulation of FGFR functions.

Targeting FGF receptors in colorectal cancer: from bench side to bed side

Successful management of advanced colorectal cancer has been a challenging job for practicing oncologists as well as a priority for the oncology research community. The better understanding of the underlying patho-biology and critical pathway targets in this disease has contributed to major developments in that direction. In this review, we will revise the different biological and clinical aspects related to the use of FGFR pathway-targeted therapies in advanced colorectal cancer with particular focus on future perspectives in that regard.

Variation in the salivary proteomes of differentially virulent greenbug (Schizaphis graminum Rondani) biotypes

Greenbug (Schizaphis graminum Rondani) biotypes are classified by their differential virulence to wheat, barley, and sorghum varieties possessing greenbug resistance genes. Virulent greenbug biotypes exert phytotoxic effects upon their hosts during feeding, directly inducing physiological and metabolic alterations and accompanying foliar damage. Comparative analyses of the salivary proteomes of four differentially virulent greenbug biotypes C, E, G, and H showed significant proteomic divergence between biotypes. Thirty-two proteins were identified by LC-MS/MS; the most prevalent of which were three glucose dehydrogenase paralogs (GDH), lipophorin, complementary sex determiner, three proteins of unknown function, carbonic anhydrase, fibroblast growth factor receptor, and abnormal oocyte (ABO). Seven nucleotide-binding proteins were identified, including ABO which is involved in mRNA splicing. Quantitative variation among greenbug biotypes was detected in six proteins; two GDH paralogs, carbonic anhydrase, ABO, and two proteins of unknown function. Our findings reveal that the greenbug salivary proteome differs according to biotype and diverges substantially from those reported for other aphids. The proteomic profiles of greenbug biotypes suggest that interactions between aphid salivary proteins and the plant host result in suppression of plant defenses and cellular transport, and may manipulate transcriptional regulation in the plant host, ultimately allowing the aphid to maintain phloem ingestion.

BIOLOGICAL SIGNIFICANCE

Greenbug (Schizaphis graminum Rondani, GB) is a major phytotoxic aphid pest of wheat, sorghum, and barley. Unlike non-phytotoxic aphids, GB directly damages its host, causing uniformly characteristic symptoms leading to host death. As saliva is the primary interface between the aphid and its plant host, saliva is also the primary aphid biotypic determinant, and differences in biotypic virulence are the result of biotypic variations in salivary content. This study analyzed the exuded saliva of four distinct Greenbug biotypes with a range of virulence to crop lines containing greenbug resistance traits in order to identify differences between salivary proteins of the examined biotypes. Our analyses confirmed that the salivary proteomes of the examined greenbug biotypes differ widely, identified 32 proteins of the greenbug salivary proteome, and found significant proteomic variation between six identified salivary proteins. The proteomic variation identified herein is likely the basis of biotypic virulence, and the proteins identified can serve as the basis for functional studies into both greenbug-induced phytotoxic damage and into the molecular basis of virulence in specific GB biotypes. This article is part of a Special Issue entitled: SI: Proteomics of non-model organisms.

Identification of fibroblast growth factor receptor 3 (FGFR3) as a protein receptor for botulinum neurotoxin serotype A (BoNT/A)

Botulinum neurotoxin serotype A (BoNT/A) causes transient muscle paralysis by entering motor nerve terminals (MNTs) where it cleaves the SNARE protein Synaptosomal-associated protein 25 (SNAP25₂₀₆) to yield SNAP25₁₉₇. Cleavage of SNAP25 results in blockage of synaptic vesicle fusion and inhibition of the release of acetylcholine. The specific uptake of BoNT/A into pre-synaptic nerve terminals is a tightly controlled multistep process, involving a combination of high and low affinity receptors. Interestingly, the C-terminal binding domain region of BoNT/A, H_C/A, is homologous to fibroblast growth factors (FGFs), making it a possible ligand for Fibroblast Growth Factor Receptors (FGFRs). Here we present data supporting the identification of Fibroblast Growth Factor Receptor 3 (FGFR3) as a high affinity receptor for BoNT/A in neuronal cells. H_C/A binds with high affinity to the two extra-cellular loops of FGFR3 and acts similar to an agonist ligand for FGFR3, resulting in phosphorylation of the receptor. Native ligands for FGFR3; FGF1, FGF2, and FGF9 compete for binding to FGFR3 and block BoNT/A cellular uptake. These findings show that FGFR3 plays a pivotal role in the specific uptake of BoNT/A across the cell membrane being part of a larger receptor complex involving ganglioside- and protein-protein interactions.

Botulinum neurotoxin serotype A (BoNT/A) is one of seven neurotoxins (BoNT/A-G), produced by the bacteria Clostridium botulinum that are both poisons and versatile therapeutics. These toxins enter motor neurons where they prevent the release of acetylcholine at the neuromuscular junction. The specific uptake of BoNT/A across the neuronal cell membrane is dependent on specific receptor interactions. Binding to high density ganglioside GT1b mediates the initial binding step and via a low affinity interaction concentrates BoNT/A on the cell surface. Once anchored in the membrane, lateral movements within the plasma membrane facilitate intermolecular interactions of BoNT/A with additional lower density but higher affinity protein receptors. Here we present data supporting the identification of Fibroblast Growth Factor Receptor 3 (FGFR3) as a high affinity receptor for BoNT/A. We show that BoNT/A binds to FGFR3 with high affinity and functions as an agonist ligand for FGFR3. The identification of this novel receptor for BoNT/A represents an important advance in the understanding of the mechanism of action of BoNT/A, especially on the initial steps of neuronal uptake, and can be the basis for the development of new specific countermeasures and new BoNT/A-based therapeutics.

Cancer-Associated Perturbations in Alternative Pre-messenger RNA Splicing

For most of our 25,000 genes, the removal of introns by pre-messenger RNA (pre-mRNA) splicing represents an essential step toward the production of functional messenger RNAs (mRNAs). Alternative splicing of a single pre-mRNA results in the production of different mRNAs. Although complex organisms use alternative splicing to expand protein function and phenotypic diversity, patterns of alternative splicing are often altered in cancer cells. Alternative splicing contributes to tumorigenesis by producing splice isoforms that can stimulate cell proliferation and cell migration or induce resistance to apoptosis and anticancer agents. Cancer-specific changes in splicing profiles can occur through mutations that are affecting splice sites and splicing control elements, and also by alterations in the expression of proteins that control splicing decisions. Recent progress in global approaches that interrogate splicing diversity should help to obtain specific splicing signatures for cancer types. The development of innovative approaches for annotating and reprogramming splicing events will more fully establish the essential contribution of alternative splicing to the biology of cancer and will hopefully provide novel targets and anticancer strategies. Metazoan genes are usually made up of several exons interrupted by introns. The introns are removed from the pre-mRNA by RNA splicing. In conjunction with other maturation steps, such as capping and polyadenylation, the spliced mRNA is then transported to the cytoplasm to be translated into a functional protein. The basic mechanism of splicing requires accurate recognition of each extremity of each intron by the spliceosome. Introns are identified by the binding of U1 snRNP to the 5' splice site and the U2AF65/U2AF35 complex to the 3' splice site. Following these interactions, other proteins and snRNPs are recruited to generate the complete spliceosomal complex needed to excise the intron. While many introns are constitutively removed by the spliceosome, other splice junctions are not used systematically, generating the phenomenon of alternative splicing. Alternative splicing is therefore the process by which a single species of pre-mRNA can be matured to produce different mRNA molecules (Fig. 1). Depending on the number and types of alternative splicing events, a pre-mRNA can generate from two to several thousands different mRNAs leading to the production of a corresponding number of proteins. It is now believed that the expression of at least 70 % of human genes is subjected to alternative splicing, implying an enormous contribution to proteomic diversity, and by extension, to the development and the evolution of complex animals. Defects in splicing have been associated with human diseases (Caceres and Kornblihtt, Trends Genet 18(4):186-93, 2002, Cartegni et al., Nat Rev Genet 3(4):285-98, 2002, Pagani and Baralle, Nat Rev Genet 5(5):389-96, 2004), including cancer (Brinkman, Clin Biochem 37(7):584-94, 2004, Venables, Bioessays 28(4):378-86, 2006, Srebrow and Kornblihtt, J Cell Sci 119(Pt 13):2635-2641, 2006, Revil et al., Bull Cancer 93(9):909-919, 2006, Venables, Transworld Res Network, 2006, Pajares et al., Lancet Oncol 8(4):349-57, 2007, Skotheim and Nees, Int J Biochem Cell Biol 39:1432-1449, 2007). Numerous studies have now confirmed the existence of specific differences in the alternative splicing profiles between normal and cancer tissues. Although there are a few cases where specific mutations are the primary cause for these changes, global alterations in alternative splicing in cancer cells may be primarily derived from changes in the expression of RNA-binding proteins that control splice site selection. Overall, these cancer-specific differences in alternative splicing offer an immense potential to improve the diagnosis and the prognosis of cancer. This review will focus on the functional impact of cancer-associated alternative splicing variants, the molecular determinants that alter the splicing decisions in cancer cells, and future therapeutic strategies.

Molecular markers associated with nonepithelial ovarian cancer in formalin-fixed, paraffin-embedded specimens by genome wide expression profiling

Nonepithelial ovarian cancer (NEOC) is a rare cancer that is often misdiagnosed as other malignant tumors. Research on this cancer using fresh tissues is nearly impossible because of its limited number of samples within a limited time provided. The study is to identify potential genes and their molecular pathways related to NEOC using formalin-fixed paraffin embedded samples. Total RNA was extracted from eight archived NEOCs and seven normal ovaries. The RNA samples with RNA integrity number >2.0, purity >1.7 and cycle count value <28 cycles were hybridized to the Illumina Whole-Genome DASL assay (cDNA-mediated annealing, selection, extension, and ligation). We analyzed the results using the GeneSpring GX11.0 and FlexArray software to determine the differentially expressed genes. Microarray results were validated using an immunohistochemistry method. Statistical analysis identified 804 differentially expressed genes with 443 and 361 genes as overexpressed and underexpressed in cancer, respectively. Consistent findings were documented for the overexpression of eukaryotic translation elongation factor 1 alpha 1, E2F transcription factor 2, and fibroblast growth factor receptor 3, except for the down-regulated gene, early growth response 1 (EGR1). The immunopositivity staining for EGR1 was found in the majority of cancer tissues. This finding suggested that the mRNA level of a transcript did not always match with the protein expression in tissues. The current gene profile can be the platform for further exploration of the molecular mechanism of NEOC.

Alternative Splicing of Fibroblast Growth Factor Receptor IgIII Loops in Cancer

Alternative splicing of the IgIII loop of fibroblast growth factor receptors (FGFRs) 1–3 produces b- and c-variants of the receptors with distinctly different biological impact based on their distinct ligand-binding spectrum. Tissue-specific expression of these splice variants regulates interactions in embryonic development, tissue maintenance and repair, and cancer. Alterations in FGFR2 splicing are involved in epithelial mesenchymal transition that produces invasive, metastatic features during tumor progression. Recent research has elucidated regulatory factors that determine the splice choice both on the level of exogenous signaling events and on the RNA-protein interaction level. Moreover, methodology has been developed that will enable the in depth analysis of splicing events during tumorigenesis and provide further insight on the role of FGFR 1–3 IIIb and IIIc in the pathophysiology of various malignancies. This paper aims to summarize expression patterns in various tumor types and outlines possibilities for further analysis and application.

Antitumor activity of fibroblast growth factor receptor 3-specific immunotoxins in a xenograft mouse model of bladder carcinoma is mediated by apoptosis

Human single-chain Fv directed against fibroblast growth factor receptor 3 (FGFR3) have been shown to block proliferation of RT112 bladder carcinoma cells in vitro. Here, we examined the ability of the recombinant gelonin toxin (rGel) to enhance this inhibitory effect in vitro and in vivo on the bladder cancer cell line RT112 and the corresponding xenografts. Immunotoxins were genetically engineered by fusing FGFR3-specific Fv fragments (3C) to the NH(2) terminus of rGel and expressed as a soluble protein in Escherichia coli. The 3C/rGel fusion construct showed an IC(50) of 200 nmol/L against log-phase RT112 cells compared with 1,500 nmol/L for free rGel. Immunofluorescence studies showed that the 3C/rGel construct internalized rapidly into the cytoplasm of RT112 cells within 1 h of exposure. The mechanism of immunotoxin-induced cell death was found to be mediated by apoptosis. RT112 tumor xenografts in severe combined immunodeficient mice treated with 50 mg/kg 3C/rGel exhibited considerable growth delay relative to control tumors and a significant reduction of 55% to 70% in mean tumor size. Immunohistochemical analysis showed that tumors from mice treated with 3C/rGel displayed considerable apoptotic damage compared with control groups. Subcellular location of FGFR3 in immunotoxin-treated tumors indicated a translocation of FGFR3 to the nuclear membrane in contrast to tumors from saline-treated controls. These results show that FGFR3-driven immunotoxins may be an effective therapeutic agent against human bladder and other tumor types overexpressing FGFR3.

Entropy measures quantify global splicing disorders in cancer

Most mammalian genes are able to express several splice variants in a phenomenon known as alternative splicing. Serious alterations of alternative splicing occur in cancer tissues, leading to expression of multiple aberrant splice forms. Most studies of alternative splicing defects have focused on the identification of cancer-specific splice variants as potential therapeutic targets. Here, we examine instead the bulk of non-specific transcript isoforms and analyze their level of disorder using a measure of uncertainty called Shannon's entropy. We compare isoform expression entropy in normal and cancer tissues from the same anatomical site for different classes of transcript variations: alternative splicing, polyadenylation, and transcription initiation. Whereas alternative initiation and polyadenylation show no significant gain or loss of entropy between normal and cancer tissues, alternative splicing shows highly significant entropy gains for 13 of the 27 cancers studied. This entropy gain is characterized by a flattening in the expression profile of normal isoforms and is correlated to the level of estimated cellular proliferation in the cancer tissue. Interestingly, the genes that present the highest entropy gain are enriched in splicing factors. We provide here the first quantitative estimate of splicing disruption in cancer. The expression of normal splice variants is widely and significantly disrupted in at least half of the cancers studied. We postulate that such splicing disorders may develop in part from splicing alteration in key splice factors, which in turn significantly impact multiple target genes.

Role of FGFR3 in urothelial cell carcinoma: biomarker and potential therapeutic target

Although non-invasive bladder tumours (pTa) are the most common group of bladder tumours at presentation, there has until recently been relatively little information on their molecular biology. Thus it was of great interest when mutations in the FGF receptor 3 (FGFR3) were identified in bladder tumours and it became apparent that these were most common in tumours of low grade and stage. Since the initial description of activating mutations of FGFR3, there have been numerous studies confirming the frequency and spectrum of these mutations in bladder cancers of all grades and stages. Mutation screening techniques have evolved and improved. FGFR3 mutation has been assessed as a predictive biomarker in tumour tissues and as a diagnostic biomarker in urine. Efforts have been made to understand the function of FGFR3 in urothelial and other cells. Although our understanding of FGFR3 function is incomplete, it is already apparent that this may represent an important therapeutic target not only in non-invasive bladder cancer but also in a significant number of invasive tumours. This review summarises the current state of knowledge of this interesting receptor in urothelial carcinoma (UC).

Unbalanced alternative splicing and its significance in cancer

Alternative pre-mRNA splicing leads to distinct products of gene expression in development and disease. Antagonistic splice variants of genes involved in differentiation, apoptosis, invasion and metastasis often exist in a delicate equilibrium that is found to be perturbed in tumours. In several recent examples, splice variants that are overexpressed in cancer are expressed as hyper-oncogenic proteins, which often correlate with poor prognosis, thus suggesting improved diagnosis and follow up treatment. Global gene expression technologies are just beginning to decipher the interplay between alternatively spliced isoforms and protein-splicing factors that will lead to identification of the mutations in these trans-acting factors responsible for pathogenic alternative splicing in cancer.

Alternative splicing of fibroblast growth factor receptor 3 produces a secreted isoform that inhibits fibroblast growth factor-induced proliferation and is repressed in urothelial carcinoma cell lines

Fibroblast growth factor receptors (FGFRs) are a family of receptor tyrosine kinases that play key roles in proliferation, differentiation, and tumorigenesis. FGFR3 was identified as the major family member expressed in both normal human urothelium and cultured normal human urothelial (NHU) cells and was expressed as the IIIb isoform. We also identified a splice variant, FGFR3 Delta8-10, lacking exons encoding the COOH-terminal half of immunoglobulin-like domain III and the transmembrane domain. Previous reports have assumed that this is a cancer-specific splice variant. We showed that FGFR3 Delta8-10 is a normal transcript in NHU cells and is translated, N-glycosylated, and secreted. Primary urothelium expressed high levels of FGFR3 transcripts. In culture, levels were reduced in actively proliferating cells but increased at confluence and as cells approached senescence. Cells overexpressing FGFR3 IIIb showed FGF1-induced proliferation, which was inhibited by the addition of FGFR3 Delta8-10. In bladder tumor cell lines derived from aggressive carcinomas, there were significant alterations in the relative expression of isoforms including an overall decrease in the proportion of FGFR3 Delta8-10 and predominant expression of FGFR3 IIIc in some cases. In summary, alternative splicing of FGFR3 IIIb in NHU cells represents a normal mechanism to generate a transcript that regulates proliferation and in bladder cancer, the ratio of FGFR3 isoforms is significantly altered.

Differential detergent fractionation for non-electrophoretic eukaryote cell proteomics

Differential detergent fractionation (DDF), which relies on detergents to sequentially extract proteins from eukaryotic cells, has been used to increase proteome coverage of 2D-PAGE. Here, we used DDF extraction in conjunction with the nonelectrophoretic proteomics method of liquid chromatography and electrospray ionization tandem mass spectrometry. We demonstrate that DDF can be used with 2D-LC ESI MS2 for comprehensive cellular proteomics, including a large proportion of membrane proteins. Compared to some published methods designed to isolate membrane proteins specifically, DDF extraction yields comprehensive proteomes which include twice as many membrane proteins. Two-thirds of these membrane proteins have more than one trans-membrane domain. Since DDF separates proteins based upon their physicochemistry and subcellular localization, this method also provides data useful for functional genome annotation. As more genome sequences are completed, methods which can aid in functional annotation will become increasingly important.

Cell responses to FGFR3 signalling: growth, differentiation and apoptosis

FGFR3 is a receptor tyrosine kinase (RTK) of the FGF receptor family, known to have a negative regulatory effect on long bone growth. Fgfr3 knockout mice display longer bones and, accordingly, most germline-activating mutations in man are associated with dwarfism. Somatically, some of the same activating mutations are associated with the human cancers multiple myeloma, cervical carcinoma and carcinoma of the bladder. How signalling through FGFR3 can lead to either chondrocyte apoptosis or cancer cell proliferation is not fully understood. Although FGFR3 can be expressed as two main splice isoforms (IIIb or IIIc), there is no apparent link with specific cell responses, which may rather be associated with the cell type or its differentiation status. Depending on cell type, differential activation of STAT proteins has been observed. STAT1 phosphorylation seems to be involved in inhibition of chondrocyte proliferation while activation of the ERK pathway inhibits chondrocyte differentiation and B-cell proliferation (as in multiple myeloma). The role of FGFR3 in epithelial cancers (bladder and cervix) is not known. Some of the cell specificity may arise via modulation of signalling by crosstalk with other signalling pathways. Recently, inhibition of the ERK pathway in achondroplastic mice has provided hope for an approach to the treatment of dwarfism. Further understanding of the ability of FGFR3 to trigger different responses depending on cell type and cellular context may lead to treatments for both skeletal dysplasias and cancer.