Nuclear 24 kD fibroblast growth factor (FGF)-2 confers metastatic properties on rat bladder carcinoma cells

A functional variant rs1464938 in the promoter of fibroblast growth factor 12 is associated with an increased risk of bladder transitional cell carcinoma

Increasing evidence shows that inflammation plays critical roles in the tumorigenesis of bladder cancer. Fibroblast growth factor 12 (FGF12), a kind of inflammatory cytokine, is located in the region of 3q28 that has been demonstrated to be a bladder cancer risk locus by genome wide association study (GWAS). In this study, we aimed to investigate the association of GWAS signal rs710521 and rs884309 and rs1464938 in the promoter of FGF12 with the risk of bladder transitional cell carcinoma (TCC). The polymorphisms were analyzed by using a Taqman assay in 331 TCC patients and 516 age-, gender-, and ethnicity-matched controls. The expression levels of FGF12 mRNA were examined in TCC and non-cancerous normal tissues by using quantitative real-time PCR and the luciferase activity was determined by using the Dual-Luciferase Assay System. The rs1464938 AA genotype and A allele were associated with a significantly increased risk of TCC (AA vs. GG: adjusted OR = 2.54, 95% CI, 1.49-4.35, P < 0.001; AA vs. AG/GG: adjusted OR = 2.25, 95% CI, 1.36-3.71, P = 0.002; A vs. G: adjusted OR = 1.44, 95% CI, 1.15-1.80, P = 0.001, respectively). Haplotype analysis showed that rs884309G- rs1464938A haplotype was associated with an increased risk of TCC (OR = 1.61, 95% CI, 1.23-2.11, P = 0.001). Functional analysis showed that the rs1464938 AG/AA genotypes exhibited higher levels of FGF12 mRNA in TCC tissues and the rs1464938 A allele enhanced FGF12 promoter activity (P < 0.05). These findings suggest that the rs1464938 A allele at the 3q28 locus contribute to the development of TCC by regulating FGF12 expression levels.

Variants in genes belonging to the fibroblast growth factor family are associated with lower extremity amputation in non-Hispanic whites: Findings from the chronic renal insufficiency cohort study

Diabetes is the major risk factor for nontraumatic lower extremity amputation (LEA). The role of genetic polymorphisms in predisposing diabetics to impaired wound healing leading to LEA has not been sufficiently explored. We investigated the association between a set of genes belonging to the angiogenesis/wound repair pathway with LEA in the Chronic Renal Insufficiency Cohort, a study of adults with chronic kidney disease (CKD) that includes a subgroup with diabetes. This study was performed on 3,772 Chronic Renal Insufficiency Cohort participants who were genotyped on the ITMAT-Broad-CARe array chip. A total of 1,017 single-nucleotide polymorphisms (SNPs) in 22 genes belonging to the angiogenesis/would repair pathway were investigated. LEA was determined from patient self-report. The association between genetic variants and LEA status was examined using logistic regression and additive genetic models after stratifying the cohort by race/ethnicity and diabetic status. Unadjusted analyses as well as analyses adjusted for age, sex, estimated glomerular filtration rate, body mass index, peripheral vascular disease, hemoglobin A1c, and population stratification were performed. In non-Hispanic white participants with diabetes, rs11938826 and rs1960669, both intronic SNPs in the gene basic fibroblast growth factor-2 (FGF2), were significantly associated with LEA in covariate-adjusted analysis (OR: 2.83 (95% CI: 1.73, 4.62); p-value: 0.000034; Bonferroni adjusted p-value: 0.0006) and (OR: 2.61 (95% CI: 1.48, 4.61); p-value: 0.00095; Bonferroni adjusted p-value: 0.02). In the same subgroup, rs10883688, an FGF8 SNP of unknown functional effect, was also associated with LEA (OR: 1.72 (95% Confidence Interval: 1.14, 2.6); p-value: 0.00999; Bonferroni adjusted p-value: 0.04). No statistically significant associations were identified in the other ethnic groups. In conclusion, variant/s in FGF2 and FGF8 may predispose diabetics with CKD to LEA. Dysregulation of the FGF2 gene represents an opportunity to understand further, and possibly intervene upon, mechanisms of wound healing in diabetics with CKD.

Nuclear basic fibroblast growth factor regulates triple-negative breast cancer chemo-resistance

INTRODUCTION

Chemotherapy remains the only available treatment for triple-negative (TN) breast cancer, and most patients exhibit an incomplete pathologic response. Half of patients exhibiting an incomplete pathologic response die within five years of treatment due to chemo-resistant, recurrent tumor growth. Defining molecules responsible for TN breast cancer chemo-resistance is crucial for developing effective combination therapies blocking tumor recurrence. Historically, chemo-resistance studies have relied on long-term chemotherapy selection models that drive genetic mutations conferring cell survival. Other models suggest that tumors are heterogeneous, being composed of both chemo-sensitive and chemo-resistant tumor cell populations. We previously described a short-term chemotherapy treatment model that enriches for chemo-residual TN tumor cells. In the current work, we use this enrichment strategy to identify a novel determinant of TN breast cancer chemotherapy resistance [a nuclear isoform of basic fibroblast growth factor (bFGF)].

METHODS

Studies are conducted using our in vitro model of chemotherapy resistance. Short-term chemotherapy treatment enriches for a chemo-residual TN subpopulation that over time resumes proliferation. By western blotting and real-time polymerase chain reaction, we show that this chemotherapy-enriched tumor cell subpopulation expresses nuclear bFGF. The importance of bFGF for survival of these chemo-residual cells is interrogated using short hairpin knockdown strategies. DNA repair capability is assessed by comet assay. Immunohistochemistry (IHC) is used to determine nuclear bFGF expression in TN breast cancer cases pre- and post- neoadjuvant chemotherapy.

RESULTS

TN tumor cells surviving short-term chemotherapy treatment express increased nuclear bFGF. bFGF knockdown reduces the number of chemo-residual TN tumor cells. Adding back a nuclear bFGF construct to bFGF knockdown cells restores their chemo-resistance. Nuclear bFGF-mediated chemo-resistance is associated with increased DNA-dependent protein kinase (DNA-PK) expression and accelerated DNA repair. In fifty-six percent of matched TN breast cancer cases, percent nuclear bFGF-positive tumor cells either increases or remains the same post- neoadjuvant chemotherapy treatment (compared to pre-treatment). These data indicate that in a subset of TN breast cancers, chemotherapy enriches for nuclear bFGF-expressing tumor cells.

CONCLUSION

These studies identify nuclear bFGF as a protein in a subset of TN breast cancers that likely contributes to drug resistance following standard chemotherapy treatment.

The potential of fibroblast growth factor/fibroblast growth factor receptor signaling as a therapeutic target in tumor angiogenesis

INTRODUCTION

Fibroblast growth factors (FGFs) are endowed with a potent pro-angiogenic activity. Activation of the FGF/FGF receptor (FGFR) system occurs in a variety of human tumors. This may lead to neovascularization, supporting tumor progression and metastatic dissemination. Thus, a compelling biologic rationale exists for the development of anti-FGF/FGFR agents for the inhibition of tumor angiogenesis in cancer therapy.

AREAS COVERED

A comprehensive search on PubMed was performed to identify studies on the role of the FGF/FGFR system in angiogenesis. Endothelial FGFR signaling, the pro-angiogenic function of canonical FGFs, and their role in human tumors are described. In addition, experimental approaches aimed at the identification and characterization of nonselective and selective FGF/FGFR inhibitors and their evaluation in clinical trials are summarized.

EXPERT OPINION

Different approaches can be envisaged to inhibit the FGF/FGFR system, a target for the development of 'two-compartment' anti-angiogenic/anti-tumor agents, including FGFR selective and nonselective small-molecule tyrosine kinase inhibitors, anti-FGFR antibodies, and FGF ligand traps. Further studies are required to define the correlation between tumor vascularization and activation of the FGF/FGFR system and for the identification of cancer patients more likely to benefit from anti-FGF/FGFR treatments. In addition, advantages and disadvantages about the use of selective versus non-selective FGF inhibitors remain to be elucidated.

Role of fibroblast growth factor in squamous cell carcinoma of the bladder: prognostic biomarker and potential therapeutic target

BACKGROUND

We evaluated the association of fibroblast growth factor (FGF2) expression with pathologic features and clinical outcomes of squamous cell carcinoma (SCC) of the urinary bladder.

METHODS

Immunohistochemistry of FGF2 was performed on radical cystectomy specimens with pure SCC from 1997 to 2003. The relationship between FGF2 and pathologic parameters and oncological outcome was assessed.

RESULTS

The study included 151 patients with SCC (98 men) with a median age of 52 years (range: 36-74 y). Schistosomal infection was found in 81% of patients. Pathologic category was T2 and T3 in 88% of patients and the grade was low in>50%. Lymph node invasion and lymphovascular invasion were found in 30.5% and 16%. Altered FGF2 was associated with tumor grade (P = 0.014), lymph node invasion, and lymphovascular invasion (P = 0.042). Altered FGF2 was associated with both disease recurrence and cancer-specific mortality (P≤0.001) in Kaplan-Meier analyses and was an independent predictor of cancer recurrence (hazard ratio = 2.561, P = 0. 009) and cancer-specific mortality (hazard ratio = 2.679, P = 0. 033) in multivariate Cox regression analyses. Adding FGF2 to a model including standard clinicopathologic prognostics (pathologic T category, lymph node status, and grade) showed a significant improvement (6%) in accuracy of prediction poor oncological outcome.

CONCLUSIONS

FGF2 overexpression is associated with aggressive pathologic features and worse outcomes after radical cystectomy for SCC, suggesting a good prognostic and possible therapeutic role.

Utility of biomarkers in the prediction of oncologic outcome after radical cystectomy for squamous cell carcinoma

PURPOSE

We evaluated the association of multiple biomarkers with clinical outcomes in patients treated with radical cystectomy for squamous cell carcinoma of the bladder to identify the best prognostic panel of markers.

MATERIALS AND METHODS

Immunohistochemistry for 14 biomarkers was performed on tissue microarray sections of 151 radical cystectomy specimens showing squamous cell carcinoma. Biomarker alterations, pathological features and oncologic outcomes were evaluated. The panel of biomarkers that best predicted the oncologic outcome was determined. Outcomes were stratified based on a prognostic score according to the number of altered biomarkers. The accuracy of oncologic outcome prediction was evaluated by ROC curves.

RESULTS

The study included 151 patients. Pathological stage was T2 in 50%, T3 in 38%, T1 in 6% and T4 in 6% of patients. Median followup was 63.2 months. The best prognostic panel of markers included COX-2, FGF-2, p53, Bax and EGFR. On multivariate Cox regression analysis a prognostic score based on marker alterations was an independent predictor of intermediate and high risk of disease recurrence (HR 3.2, p = 0.008 and HR 15.5, p ≤ 0.001) and bladder cancer specific mortality (HR 5.2, p = 0.009 and HR 19.4, p ≤ 0.001, respectively). A multivariate prognostic model incorporating the prognostic score demonstrated significantly better performance to predict the outcome compared to clinicopathological parameters only (0.78 vs 0.64).

CONCLUSIONS

Biomarkers have significant potential to predict the outcome of radical cystectomy for squamous cell carcinoma. An increased number of altered markers may identify patients at high risk who might benefit from multimodal treatment approaches.

Internal ribosome entry site of bFGF is the target of thalidomide for IMiDs development in multiple myeloma

Although new analogues of immunomodulatory drugs (IMiDs) are being developed for MM, the molecular mechanism of these drugs remains unclear. In the current study, we used MM cell lines as a model to investigate the molecular mechanism of thalidomide and to compare its potency with IMiDs such as pomalidomide. We determined that thalidomide did not inhibit cell proliferation of RPMI8226 and U266 MM cells, whereas pomalidomide showed a significant inhibitory effect on these two MM cell lines. Interestingly, we further demonstrated that although thalidomide down-regulated bFGF translation through the inhibition of IRES even at 0.1 μg/ml, pomalidomide did not have a similar affect bFGF levels. A colony formation assay demonstrated that thalidomide and the bFGF knock-down clones caused a significant reduction in the clonogenic ability of MM cells, and treatment with exogenous bFGF can recover the clonogenic ability of thalidomide-treated cells and knock-down clones, but not that of pomalidomide-treated cells. This implies that thalidomide, but not pomalidomide, targets the IRES of FGF-2.

In conclusion, our results highlight a non-cytotoxic anticancer drug target for thalidomide, the IRES of bFGF, and provide the mechanistic rationale for developing IMiDs as anti-cancer therapeutics in MM patients, with improved potency and fewer side effects.

Inhibition of RUNX2 transcriptional activity blocks the proliferation, migration and invasion of epithelial ovarian carcinoma cells

Previously, we have identified the RUNX2 gene as hypomethylated and overexpressed in post-chemotherapy (CT) primary cultures derived from serous epithelial ovarian cancer (EOC) patients, when compared to primary cultures derived from matched primary (prior to CT) tumors. However, we found no differences in the RUNX2 methylation in primary EOC tumors and EOC omental metastases, suggesting that DNA methylation-based epigenetic mechanisms have no impact on RUNX2 expression in advanced (metastatic) stage of the disease. Moreover, RUNX2 displayed significantly higher expression not only in metastatic tissue, but also in high-grade primary tumors and even in low malignant potential tumors. Knockdown of the RUNX2 expression in EOC cells led to a sharp decrease of cell proliferation and significantly inhibited EOC cell migration and invasion. Gene expression profiling and consecutive network and pathway analyses confirmed these findings, as various genes and pathways known previously to be implicated in ovarian tumorigenesis, including EOC tumor invasion and metastasis, were found to be downregulated upon RUNX2 suppression, while a number of pro-apoptotic genes and some EOC tumor suppressor genes were induced. Taken together, our data are indicative for a strong oncogenic potential of the RUNX2 gene in serous EOC progression and suggest that RUNX2 might be a novel EOC therapeutic target. Further studies are needed to more completely elucidate the functional implications of RUNX2 and other members of the RUNX gene family in ovarian tumorigenesis.

FGF2 mediates DNA repair in epidermoid carcinoma cells exposed to ionizing radiation

Purpose

Fibroblast growth factor 2 (FGF2) is a well-known survival factor. However, its role in DNA repair is poorly documented. The present study was designed to investigate in epidermoid carcinoma cells the potential role of FGF2 in DNA repair.

Materials and methods

The side population (SP) with cancer stem cell-like properties and the main population (MP) were isolated from human A431 squamous carcinoma cells. Radiation-induced DNA damage and repair were assessed using the alkaline comet assay. FGF2 expression was quantified by enzyme linked immunosorbent assay (ELISA).

Results

SP cells exhibited rapid repair of radiation induced DNA damage and a high constitutive level of nuclear FGF2. Blocking FGF2 signaling abrogated the rapid DNA repair. In contrast, in MP cells, a slower repair of damage was associated with low basal expression of FGF2. Moreover, the addition of exogenous FGF2 accelerated DNA repair in MP cells. When irradiated, SP cells secreted FGF2, whereas MP cells did not.

Conclusions

FGF2 was found to mediate DNA repair in epidermoid carcinoma cells. We postulate that carcinoma stem cells would be intrinsically primed to rapidly repair DNA damage by a high constitutive level of nuclear FGF2. In contrast, the main population with a low FGF2 content exhibits a lower repair rate which can be increased by exogenous FGF2.

Targeting fibroblast-growth-factor-receptor-dependent signaling for cancer therapy

INTRODUCTION

Fibroblast growth factors (FGF) exert a combination of biological effects that contribute to four of the six essential hallmarks of cancer. It is no surprise that FGF-dependent signaling has increasingly moved to the center of cancer therapy research during the past decade. This is illustrated by the large number of publications focusing on various aspects of this theme that have been published in the past 5 years.

AREAS COVERED

Information from these sources as well as ongoing work from the authors' groups is used to outline the physiological functions of FGF signaling and to highlight how the high oncogenic effects of deregulated FGFs and FGFRs derive from their physiological functions. The biological effect of deregulated FGFR signaling in malignant diseases is described and the current state of therapeutic targeting of FGFR is summarized.

EXPERT OPINION

Strategies for targeting FGFR-signaling for cancer therapy are very promising, but need to be carefully developed based on the physiological roles of FGF signaling. Preventive measures may be necessary for protection from FGF-related side effects. Combined targeting of several receptor tyrosine kinases or combination with other therapies may be a useful way of avoiding or ameliorating side effects. FGF-related markers of prognosis and therapy response still need to be investigated.

Growth factors as active participants in carcinogenesis: a perspective

Growth factors are low molecular peptides active in the stimulation of cell proliferation and in the regulation of embryonic development and cellular differentiation. Significant progress has been made in developing effective strategies to treat human malignancies with new chemical compounds based on a rationale directed against various components of signaling pathways. Many of these drugs target a growth factor receptor--for instance, in the form of monoclonal antibodies or inhibitors of tyrosine kinases, such as monoclonal antibodies against epidermal growth factor receptors used in treating certain types of breast cancer. Imatinib mesylate [Gleevec]) is an excellent example of mediators of signal transduction, such as tyrosine kinases. Growth factors proper are used to ameliorate various and sometimes fatal side effects of cytotoxic and/or myelosuppressive chemotherapy. Basic characteristics of several growth families are discussed with therapeutic modalities based on growth factor activity or, more often, inhibition of such activity.

The influence of FGF2 high molecular weight (HMW) isoforms in the development of cardiac ischemia-reperfusion injury

Fibroblast growth factor 2 (FGF2) consists of multiple protein isoforms (low [LMW] and high molecular weight [HMW]), which are localized to different cellular compartments, indicating unique biological activity. We previously showed that the LMW isoform is important in protecting the heart from myocardial dysfunction associated with ischemia-reperfusion (I/R) injury, but the roles of the HMW isoforms remain unknown. To elucidate the role of HMW isoforms in I/R and cardioprotection, hearts from novel mouse models, in which the murine FGF2 HMWs are knocked out (HMWKO) or the human FGF2 24 kDa HMW isoform is overexpressed (HMW Tg) and their wildtype (Wt) or non-transgenic (NTg) cohorts were subjected to an ex vivo work-performing heart model of I/R. There was a significant improvement in post-ischemic recovery of cardiac function in HMWKO hearts (76+/-5%, p<0.05) compared to Wt hearts (55+/-5%), with a corresponding decrease in HMW Tg function (line 20: 38+/-6% and line 28: 33+/-4%, p<0.05) compared to non-transgenic hearts (68+/-9%). FGF2 LMW isoform was secreted from Wt and HMWKO hearts during I/R, and a FGF receptor (FGFR) inhibitor, PD173074 caused a decrease in cardiac function when administered in I/R in Wt and FGF2 HMWKO hearts (p<0.05), indicating that FGFR is involved in FGF2 LMW isoform's biological effect in ischemia-reperfusion injury. Moreover, overexpression of HMW isoform reduced FGFR1 phosphorylation/activation with no further decrease in the phosphorylation state in the presence of the FGFR inhibitor. Overall, our data indicate that HMW isoforms have a detrimental role in the development of post-ischemic myocardial dysfunction.

High molecular weight FGF2: the biology of a nuclear growth factor

Fibroblast growth factor 2 (FGF2) is one of the most studied growth factors to date. Most attention has been dedicated to the smallest, 18 kDa FGF2 variant that is released by cells and acts through activation of cell-surface FGF-receptor tyrosine kinases. There are, however, several higher molecular weight (HMW) variants of FGF2 that rarely leave their producing cells, are retained in the nucleus and act independently of FGF-receptors (FGFR). Despite significant evidence documenting the expression and intracellular trafficking of HMW FGF2, many important questions remain about the physiological roles and mechanisms of action of HMW FGF2. In this review, we summarize the current knowledge about the biology of HMW FGF2, its role in disease and areas for future investigation.

Basic fibroblast growth factor impact on retinoblastoma progression and survival

PURPOSE

Chemotherapy resistance is a problem in the treatment of advanced retinoblastoma (RB). Since basic fibroblast growth factor (bFGF) is a survival factor for neural precursor cells, bFGF was evaluated as a growth and chemoresistance factor in RB.

METHODS

bFGF expression was analyzed in the LH-betaTag transgenic mouse model of RB and human RB cell lines by immunofluorescence, RT-PCR, and Western blot. Proliferation and apoptosis (TUNEL) assays were performed.

RESULTS

bFGF levels significantly increased during tumorigenesis in transgenic RB, as a function of tumor status (P = 0.005). PCR and confocal microscopy confirmed that the human cell lines and primary tumors expressed bFGF. bFGF was localized to vascular and tumor cells and rarely to glial cells. Exogenous 18-kDa bFGF induced proliferation in two RB cell lines (WERI and Y79). Western blot analysis demonstrated 34-, 22-, and 18-kDa isoforms in transgenic RB and both cell lines. In TUNEL assays, chemoresistance to carboplatin-induced apoptosis was observed in the Y79 line, which expressed a higher ratio of high (34 kDa)- to low-molecular-weight bFGF isoforms, compared with the WERI line. Similar to other bFGF tumor studies, exogenous low-molecular-weight (18 kDa) bFGF (1 ng) significantly enhanced carboplatin-induced apoptosis in the more chemosensitive WERI, but not the chemoresistant Y79 line.

CONCLUSIONS

RB tumors produce significant amounts of bFGF, and the differential production and response to isoforms of bFGF may have implications for invasive tumor growth and chemoresistance.

The Tumor Microenvironment: Key to Early Detection

The tumor microenvironment plays an important role equal to the tumor cell population in the progression of cancer. Consisting of stromal fibroblasts, inflammatory cells, components of the vasculature, normal epithelia, and extracellular matrix, the surrounding environment interacts or "cross-talks" with tumor cells through the release of growth factors, cytokines, proteases, and other bioactive molecules. Tumor growth, formation of new vascular networks, evasion of the host immune system, and invasion and metastasis are processes that co-evolve and become finely optimized and regulated within the tumor microenvironment. However, relatively recent reports on three areas of study have come together to add new levels of complexity to the tumor microenvironment. These include ectodomain shedding of proteins, shedding of membrane-derived vesicles, and novel roles for phospholipids. These dynamic changes that take place in the tumor microenvironment provide new avenues for study and for the early detection of cancer, whereas proteomic technologies provide the means to detect these unique proteins and lipids. Here we review the evolving concepts of the tumor microenvironment that, together with advances in proteomic technologies, hold the promise to facilitate the detection of early-stage cancer.

Aberrant fibroblast growth factor receptor signaling in bladder and other cancers

Fibroblast growth factors (FGFs) are potent mitogens, morphogens, and inducers of angiogenesis, and FGF signaling governs the genesis of diverse tissues and organs from the earliest stages. With such fundamental embryonic and homeostatic roles, it follows that aberrant FGF signaling underlies a variety of diseases. Pathological modifications to FGF expression are known to cause salivary gland aplasia and autosomal dominant hypophosphatemic rickets, while mutations in FGF receptors (FGFRs) result in a range of skeletal dysplasias. Anomalous FGF signaling is also associated with cancer development and progression. Examples include the overexpression of FGF2 and FGF6 in prostate cancer, and FGF8 overexpression in breast and prostate cancers. Alterations in FGF signaling regulators also impact tumorigenesis, which is exemplified by the down-regulation of Sprouty 1, a negative regulator of FGF signaling, in prostate cancer. In addition, several FGFRs are mutated in human cancers (including FGFR2 in gastric cancer and FGFR3 in bladder cancer). We recently identified intriguing alterations in the FGF pathway in a novel model of bladder carcinoma that consists of a parental cell line (TSU-Pr1/T24) and two sublines with increasing metastatic potential (TSU-Pr1-B1 and TSU-Pr1-B2), which were derived successively through in vivo cycling. It was found that the increasingly metastatic sublines (TSU-Pr1-B1 and TSU-Pr1-B2) had undergone a mesenchymal to epithelial transition. FGFR2IIIc expression, which is normally expressed in mesenchymal cells, was increased in the epithelial-like TSU-Pr1-B1 and TSU-Pr1-B2 sublines and FGFR2 knock-down was associated with the reversion of cells from an epithelial to a mesenchymal phenotype. These observations suggest that modified FGF pathway signaling should be considered when studying other cancer types.

Functional diversity of FGF-2 isoforms by intracellular sorting

Regulation of the subcellular localization of certain proteins is a mechanism for the regulation of their biological activities. FGF-2 can be produced as distinct isoforms by alternative initiation of translation on a single mRNA and the isoforms are differently sorted in cells. High molecular weight FGF-2 isoforms are not secreted from the cell, but are transported to the nucleus where they regulate cell growth or behavior in an intracrine fashion. 18 kDa FGF-2 can be secreted to the extracellular medium where it acts as a conventional growth factor by binding to and activation of cell-surface receptors. Furthermore, following receptor-mediated endocytosis, the exogenous FGF-2 can be transported to the nuclei of target cells, and this is of importance for the transmittance of a mitogenic signal. The growth factor is able to interact with several intracellular proteins. Here, the mode of action and biological role of intracellular FGF-2 are discussed.

Fibroblast growth factor signaling in embryonic and cancer stem cells

Cancer stem cells are cancer cells that originate from the transformation of normal stem cells. The most important property of any stem cell is the ability to self-renew. Through this property, there are striking parallels between normal stem cells and cancer stem cells. Both cell types share various markers of "stemness". In particular, normal stem cells and cancer stem cells utilize similar molecular mechanisms to drive self-renewal, and similar signaling pathways may induce their differentiation. The fibroblast growth factor 2 (FGF-2) pathway is one of the most significant regulators of human embryonic stem cell (hESC) self-renewal and cancer cell tumorigenesis. Here we summarize recent data on the effects of FGF-2 and its receptors on hESCs and leukemic stem/progenitor cells. Also, we discuss the similarities of these findings with stem cell renewal and differentiation phenotypes.

Nuclear fibroblast growth factor-2 interacts specifically with splicing factor SF3a66

Fibroblast growth factor 2 (FGF-2) has a dual role as a classical extracellular signaling protein and as an intracellular factor. Isoforms of FGF-2, resulting from alternatively used start codons on one mRNA species, locate differentially to nuclear compartments. In this study we aimed to analyze functions of intracellular FGF-2 by identification of interacting proteins. We identified the 66-kDa subunit of splicing factor 3a (SF3a66) as a binding partner in a yeast two-hybrid screen and confirmed this interaction by pull-down assays. The splicing factor interacted with the 18-kDa (FGF-2(18)) and with the 23-kDa (FGF-2(23)) isoforms, indicating an interaction with a domain common to both isoforms. Moreover, FGF-2 interacted with the C-terminus of SF3a66, a sequence that has not previously been assigned a functional role. In a functional neurite outgrowth assay, SF3a66 enhanced neurite lengths similar to FGF-2(18). We have previously identified the spliceosomal assembly factor survival of motoneuron (SMN) protein as a protein interacting specifically with the FGF-2(23) isoform [Claus et al., J. Biol. Chem. 278 (2003), 479-485]. The identification of two FGF-2 interacting proteins from the same biochemical pathway suggests a novel intranuclear role of FGF-2.

Dipeptidyl Peptidase Inhibits Malignant Phenotype of Prostate Cancer Cells by Blocking Basic Fibroblast Growth Factor Signaling Pathway

Dipeptidyl peptidase IV (DPPIV) is a serine protease with tumor suppressor function. It regulates the activities of mitogenic peptides implied in cancer development. Progression of benign prostate cancer to malignant metastasis is linked to increased production of basic fibroblast growth factor (bFGF), a powerful mitogen. In this study, using in vitro model system we show that DPPIV loss is associated with increased bFGF production in metastatic prostate cancer cells. DPPIV reexpression in prostate cancer cells blocks nuclear localization of bFGF, reduces bFGF levels, inhibits mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase (ERK)1/2 activation, and decreases levels of urokinase-type plasminogen activator, known downstream effectors of bFGF signaling pathway. These molecular changes were accompanied by induction of apoptosis, cell cycle arrest, inhibition of in vitro cell migration, and invasion. Silencing of DPPIV by small interfering RNA resulted in increased bFGF levels and restoration of mitogen-activated protein kinase (MAPK)-extracellular signal-regulated kinase (ERK)1/2 activation. These results indicate that DPPIV inhibits the malignant phenotype of prostate cancer cells by blocking bFGF signaling pathway.

Fibroblast growth factor signaling in tumorigenesis

Fibroblast growth factors and their signaling receptors have been associated with multiple biological activities, including proliferation, differentiation and motility. Consequently, they have evoked interest as candidate oncogenes with the potential to initiate and/or promote tumorigenesis. This has resulted in a large literature describing the presence of these growth factors and their receptors in cancer cell lines and primary tumors of diverse origin. However, it is only recently that compelling evidence has emerged to implicate the fibroblast growth factors (Fgfs) and their receptors in the genesis of human cancers. Here, we outline the model systems that demonstrate the potential oncogenic nature of Fgf signaling and summarise recent evidence that implicates aberrant Fgf signaling as important in the natural history of some common human cancers.

Role of Fibroblast Growth Factor-2 Isoforms in the Effect of Estradiol on Endothelial Cell Migration and Proliferation

Both 17beta-estradiol (E2) and fibroblast growth factor-2 (FGF2) stimulate angiogenesis and endothelial cell migration and proliferation. The first goal of this study was to explore the potential link between this hormone and this growth factor. E2-stimulated angiogenesis in SC Matrigel plugs in Fgf2+/+ mice, but not in Fgf2-/- mice. Cell cultures from subcutaneous Matrigel plugs demonstrated that E2 increased both migration and proliferation in endothelial cells from Fgf2+/+ mice, but not from in Fgf2-/- mice. Several isoforms of fibroblast growth factor-2 (FGF2) are expressed: the low molecular weight 18-kDa protein (FGF2lmw) is secreted and activates tyrosine kinase receptors (FGFRs), whereas the high molecular weight (21 and 22 kDa) isoforms (FGF2hmw) remains intranuclear, but their role is mainly unknown. The second goal of this study was to explore the respective roles of FGF2 isoforms in the effects of E2. We thus generated mice deficient only in the FGF2lmw (Fgf2lmw-/-). E2 stimulated in vivo angiogenesis and in vitro migration in endothelial cells from Fgf2lmw-/- as it did in Fgf2+/+ mice. E2 increased FGF2hmw protein abundance in endothelial cell cultures from Fgf2+/+ and Fgf2lmw-/- mice. As shown using siRNA transfection, these effects were FGFR independent but involved FGF2-Interacting Factor, an intracellular FGF2hmw partner. This is the first report for a physiological role for the intracellular FGF2hmw found to mediate the effect of E2 on endothelial cell migration via an intracrine action.

Nuclear FGF-2 facilitates cell survival in vitro and during establishment of metastases

Nuclear-targeted high molecular weight 24 kDa fibroblast growth factor 2 (FGF-2) may induce specific cell functions through intracrine mechanisms. The role of nuclear FGF-2 on the metastatic potential of carcinoma cells was examined by conditional FGF-2 expression, which demonstrated that spontaneous metastasis in nude mice is a direct consequence of its expression. The lung colonizing capacities of fluorescent nuclear FGF-2-expressing cells following intravenous injection was also investigated. All cells reaching the lung extravasated as soon as 5 min following injection with similar in vivo behavior during the first 24 h. However, after 2 days, dramatic differences were observed between the FGF-2 and parental cells: most control cells underwent apoptosis, while the FGF-2-producing cells instigated a survival program and proliferated. Therefore, sustained apoptosis in vivo prevents growth of metastatic foci, while nuclear FGF-2 induction of a survival program is responsible for growth of the lung metastases. In vitro serum deprivation assays also established that 24 kDa FGF-2 expression improves carcinoma cell survival. This study provides both in vitro and in vivo evidence that the role of the nuclear 24 kDa FGF-2 isoform in carcinoma is the promotion of cell survival, thereby defining its association with poor prognosis in some human carcinomas.

Signaling, internalization, and intracellular activity of fibroblast growth factor

The fibroblast growth factor (FGF) family contains 23 members in mammals including its prototype members FGF-1 and FGF-2. FGFs have been implicated in regulation of many key cellular responses involved in developmental and physiological processes. These includes proliferation, differentiation, migration, apoptosis, angiogenesis, and wound healing. FGFs bind to five related, specific cell surface receptors (FGFRs). Four of these have intrinsic tyrosine kinase activity. Dimerization of the receptor is a prerequisite for receptor transphosphorylation and activation of downstream signaling molecules. All members of the FGF family have a high affinity for heparin and for cell surface heparan sulfate proteoglycans, which participate in formation of stable and active FGF-FGFR complexes. FGF-mediated signaling is an evolutionarily conserved signaling module operative in invertebrates and vertebrates. It seems that some members of the family have a dual mode of action. FGF-1, FGF-2, FGF-3, and FGF-11-14 have been found intranuclearly as endogenous proteins. Exogenous FGF-1 and FGF-2 are internalized by receptor-mediated endocytosis, in a clathrin-dependent and -independent way. Internalized FGF-1 and FGF-2 are able to cross cellular membranes to reach the cytosol and the nuclear compartment. The role of FGF internalization and the intracellular activity of some FGFs are discussed in the context of the known signaling induced by FGF.

Clinical, cellular, and molecular aspects of cancer invasion

Invasion causes cancer malignancy. We review recent data about cellular and molecular mechanisms of invasion, focusing on cross-talk between the invaders and the host. Cancer disturbs these cellular activities that maintain multicellular organisms, namely, growth, differentiation, apoptosis, and tissue integrity. Multiple alterations in the genome of cancer cells underlie tumor development. These genetic alterations occur in varying orders; many of them concomitantly influence invasion as well as the other cancer-related cellular activities. Examples discussed are genes encoding elements of the cadherin/catenin complex, the nonreceptor tyrosine kinase Src, the receptor tyrosine kinases c-Met and FGFR, the small GTPase Ras, and the dual phosphatase PTEN. In microorganisms, invasion genes belong to the class of virulence genes. There are numerous clinical and experimental observations showing that invasion results from the cross-talk between cancer cells and host cells, comprising myofibroblasts, endothelial cells, and leukocytes, all of which are themselves invasive. In bone metastases, host osteoclasts serve as targets for therapy. The molecular analysis of invasion-associated cellular activities, namely, homotypic and heterotypic cell-cell adhesion, cell-matrix interactions and ectopic survival, migration, and proteolysis, reveal branching signal transduction pathways with extensive networks between individual pathways. Cellular responses to invasion-stimulatory molecules such as scatter factor, chemokines, leptin, trefoil factors, and bile acids or inhibitory factors such as platelet activating factor and thrombin depend on activation of trimeric G proteins, phosphoinositide 3-kinase, and the Rac and Rho family of small GTPases. The role of proteolysis in invasion is not limited to breakdown of extracellular matrix but also causes cleavage of proinvasive fragments from cell surface glycoproteins.

Rapid tumor development and potent vascularization are independent events in carcinoma producing FGF-1 or FGF-2

FGF-1 and FGF-2 are pleiotropic growth factors for many cell types, operating through the activation of specific transmembrane FGF receptors (FGFRs). The role of these factors in tumor progression was investigated, with specific discrimination between their autocrine and non autocrine cellular activity. The rat bladder carcinoma NBT-II cells were engineered to produce FGF-1 or 18 kDa FGF-2 in the presence or absence of their specific receptor. Non-autocrine cells that produced FGF-1 or FGF-2 but lacked FGFRs were epithelial and reminiscent of the parental NBT-II cells. Whilst autocrine cells, which both constitutively produced and secreted the growth factor and expressed FGFRs, had a highly invasive mesenchymal phenotype. Correspondingly, the autocrine cells were highly tumorigenic in vivo compared to the parental and non-autocrine cells, which correlated with the increased production of uPAR and active uPA and increased in vitro invasive potential. Although all cells produced VEGF, only tumors derived from cells that produced FGF-1 or FGF-2 were highly vascularized, suggesting that these two growth factors could be involved in the angiogenic process by activating host endothelial cells. As a result of activation of the FGFR in autocrine cells, changes in cell morphology and an increase in the invasive and tumorigenic properties were observed, however no in vitro or in vivo differential functions between FGF-1 and FGF-2 could be identified in this system. In conclusion, our data demonstrates that rapid tumor development is not dependent upon increased tumor vascularization, suggesting that 'basal' angiogenesis, probably mediated by VEGF, is sufficient to support tumor growth.

FIF [fibroblast growth factor-2 (FGF-2)-interacting-factor], a nuclear putatively antiapoptotic factor, interacts specifically with FGF-2

Numerous evidence indicates that some of the activities of fibroblast growth factor 2 (FGF-2) depend on an intracrine mode of action. Recently, we showed that three high molecular mass (HMM) nuclear forms of FGF-2 are part of a 320-kDa protein complex while the cytoplasmic AUG-initiated form is included in a 130-kDa complex. Consequently, the characterization of FGF endogenous targets has become crucial to allow the elucidation of their endogenous activities. Through the screening of GAL4-based yeast two-hybrid expression libraries, we have isolated a gene encoding a nuclear protein of 55 kDa, FIF (FGF-2-interacting-factor), which interacts specifically with FGF-2 but not with FGF-1, FGF-3, or FGF-6. In this system, FIF interacts equally well with the NH2-extended 24-kDa FGF form as with the 18-kDa form, indicating that the FIF-binding motif is located in the last 155 amino acids of FGF-2. Nevertheless, coimmunoprecipitation experiments showed an exclusive association with HMM FGF-2. The predicted protein contains a canonical leucine zipper domain and three overlapping hydrophobic heptad repeats. The region spanning these repeats is, together with a region located in the N-terminal part of the FIF protein, implicated in the binding to FGF-2. In contrast to the full-length FIF protein, several deletion constructs were able to transactivate a lac-Z reporter gene. Furthermore, the COOH-terminal part, but not the full-length FIF protein, has previously been shown to exhibit antiapoptotic properties. Thus we discuss the possibility that these activities could reflect a physiological function of FIF through its interaction with FGF-2.

Fibroblast growth factor-2

Fibroblast growth factor-2 (FGF-2) is a heparin-binding growth factor which occurs in several isoforms resulting from alternative initiations of translation: an 18 kD cytoplasmic isoform and four larger molecular weight nuclear isoforms (22, 22.5, 24 and 34 kD). FGF-2 has pleiotropic roles in many cell types and tissues; it is a motogenic, angiogenic and survival factor which is involved in cell migration, cell differentiation and in a variety of developmental processes. Although devoid of signal peptide, it could be secreted. It acts mainly through a paracrine/autocrine mechanism involving high affinity transmembrane receptors and heparan sulfate proteoglycan low affinity receptors, but also through still unknown intracrine process(es) on intracellular targets. FGF-2 has many biological functions which are probably isoform-specific. Nevertheless, FGF-2 is not essential for embryonic development as knock-out mice for the growth factor are viable and fertile although they exhibit abnormalities in neuronal differentiation. Use of FGF-2 as therapeutic agent for the treatment of ischemic cardiovascular disease is promising and clinical trials are in progress.