Basic fibroblast growth factor-induced cell death is effected through sustained activation of p38MAPK and up-regulation of the death receptor p75NTR

Effects of a New Combination of Natural Extracts on Glaucoma-Related Retinal Degeneration

BACKGROUND

Glaucoma is currently the leading cause of irreversible blindness; it is a neuropathy characterized by structural alterations of the optic nerve, leading to visual impairments. The aim of this work is to develop a new oral formulation able to counteract the early changes connected to glaucomatous degeneration. The composition is based on gastrodin and vitamin D3 combined with vitamin C, blackcurrant, and lycopene.

METHODS

Cells and tissues of the retina were used to study biological mechanisms involved in glaucoma, to slow down the progression of the disease. Experiments mimicking the conditions of glaucoma were carried out to examine the etiology of retinal degeneration.

RESULTS

Our results show a significant ability to restore glaucoma-induced damage, by counteracting ROS production and promoting cell survival by inhibiting apoptosis. These effects were confirmed by the intracellular mechanism that was activated following administration of the compound, either before or after the glaucoma induction. In particular, the main results were obtained as a preventive action of glaucoma, showing a beneficial action on all selected markers, both on cells and on eyecup preparations. It is therefore possible to hypothesize both the preventive and therapeutic use of this formulation, in the presence of risk factors, and due to its ability to inhibit the apoptotic cycle and to stimulate cell survival mechanisms, respectively.

CONCLUSION

This formulation has exhibited an active role in the prevention or restoration of glaucoma damage for the first time.

SFPQ promotes an oncogenic transcriptomic state in melanoma

The multifunctional protein, splicing factor, proline- and glutamine-rich (SFPQ) has been implicated in numerous cancers often due to interaction with coding and non-coding RNAs, however, its role in melanoma remains unclear. We report that knockdown of SFPQ expression in melanoma cells decelerates several cancer-associated cell phenotypes, including cell growth, migration, epithelial to mesenchymal transition, apoptosis, and glycolysis. RIP-seq analysis revealed that the SFPQ-RNA interactome is reprogrammed in melanoma cells and specifically enriched with key melanoma-associated coding and long non-coding transcripts, including SOX10, AMIGO2 and LINC00511 and in most cases SFPQ is required for the efficient expression of these genes. Functional analysis of two SFPQ-enriched lncRNA, LINC00511 and LINC01234, demonstrated that these genes independently contribute to the melanoma phenotype and a more detailed analysis of LINC00511 indicated that this occurs in part via modulation of the miR-625-5p/PKM2 axis. Importantly, analysis of a large clinical cohort revealed that elevated expression of SFPQ in primary melanoma tumours may have utility as a prognostic biomarker. Together, these data suggest that SFPQ is an important driver of melanoma, likely due to SFPQ-RNA interactions promoting the expression of numerous oncogenic transcripts.

p38-MAPK-mediated translation regulation during early blastocyst development is required for primitive endoderm differentiation in mice

Successful specification of the two mouse blastocyst inner cell mass (ICM) lineages (the primitive endoderm (PrE) and epiblast) is a prerequisite for continued development and requires active fibroblast growth factor 4 (FGF4) signaling. Previously, we identified a role for p38 mitogen-activated protein kinases (p38-MAPKs) during PrE differentiation, but the underlying mechanisms have remained unresolved. Here, we report an early blastocyst window of p38-MAPK activity that is required to regulate ribosome-related gene expression, rRNA precursor processing, polysome formation and protein translation. We show that p38-MAPK inhibition-induced PrE phenotypes can be partially rescued by activating the translational regulator mTOR. However, similar PrE phenotypes associated with extracellular signal-regulated kinase (ERK) pathway inhibition targeting active FGF4 signaling are not affected by mTOR activation. These data indicate a specific role for p38-MAPKs in providing a permissive translational environment during mouse blastocyst PrE differentiation that is distinct from classically reported FGF4-based mechanisms.

Phenotypic profiling with a living biobank of primary rhabdomyosarcoma unravels disease heterogeneity and AKT sensitivity

Cancer therapy is currently shifting from broadly used cytotoxic drugs to patient-specific precision therapies. Druggable driver oncogenes, identified by molecular analyses, are present in only a subset of patients. Functional profiling of primary tumor cells could circumvent these limitations, but suitable platforms are unavailable for most cancer entities. Here, we describe an in vitro drug profiling platform for rhabdomyosarcoma (RMS), using a living biobank composed of twenty RMS patient-derived xenografts (PDX) for high-throughput drug testing. Optimized in vitro conditions preserve phenotypic and molecular characteristics of primary PDX cells and are compatible with propagation of cells directly isolated from patient tumors. Besides a heterogeneous spectrum of responses of largely patient-specific vulnerabilities, profiling with a large drug library reveals a strong sensitivity towards AKT inhibitors in a subgroup of RMS. Overall, our study highlights the feasibility of in vitro drug profiling of primary RMS for patient-specific treatment selection in a co-clinical setting.

Patient-specific precision medicine approaches are important for future cancer therapies. Here, the authors show that functional drug profiling with Rhabdomyosarcoma cells isolated from PDX and primary patient tumors uncovers patient-specific vulnerabilities.

Fibroblast Growth Factor 2 lethally sensitizes cancer cells to stress-targeted therapeutic inhibitors

In malignant transformation, cellular stress‐response pathways are dynamically mobilized to counterbalance oncogenic activity, keeping cancer cells viable. Therapeutic disruption of this vulnerable homeostasis might change the outcome of many human cancers, particularly those for which no effective therapy is available. Here, we report the use of fibroblast growth factor 2 (FGF2) to demonstrate that further mitogenic activation disrupts cellular homeostasis and strongly sensitizes cancer cells to stress‐targeted therapeutic inhibitors. We show that FGF2 enhanced replication and proteotoxic stresses in a K‐Ras‐driven murine cancer cell model, and combinations of FGF2 and proteasome or DNA damage response‐checkpoint inhibitors triggered cell death. CRISPR/Cas9‐mediated K‐Ras depletion suppressed the malignant phenotype and prevented these synergic toxicities in these murine cells. Moreover, in a panel of human Ewing's sarcoma family tumor cells, sublethal concentrations of bortezomib (proteasome inhibitor) or VE‐821 (ATR inhibitor) induced cell death when combined with FGF2. Sustained MAPK‐ERK1/2 overactivation induced by FGF2 appears to underlie these synthetic lethalities, as late pharmacological inhibition of this pathway restored cell homeostasis and prevented these described synergies. Our results highlight how mitotic signaling pathways which are frequently overridden in malignant transformation might be exploited to disrupt the robustness of cancer cells, ultimately sensitizing them to stress‐targeted therapies. This approach provides a new therapeutic rationale for human cancers, with important implications for tumors still lacking effective treatment, and for those that frequently relapse after treatment with available therapies.

[Relationship between FGFR1 Gene Regulation of Circulating Tumor Cells and Clinical Features of Non-small Cell Lung Cancer]

背景与目的

目前检测非小细胞肺癌（non-small cell lung cancer, NSCLC）术后患者复发转移的方法均具有一定的滞后性及片面性。本研究总结分析了30例NSCLC患者外周血循环肿瘤细胞（circulating tumor cell, CTC）及成纤维细胞生长因子受体1（fibroblast growth factor receptor 1, FGFR1）表达情况与临床病理之间的关系，以期能够为肿瘤复发转移的检测提供新思路。

方法

分析北京协和医院胸外科2016年11月-2017年6月30例NSCLC患者临床资料及CTC检测数据并进行相关性分析。

结果

相关性数据分析可得，外周血CTC细胞阳性率与吸烟史相关（P=0.016），病理类型与CTC阳性率及FGFR1表达情况之间无明显关联（P=0.202, P=0.806），不同类型CTC细胞FGFR1表达情况并无明显差异（P=0.094）。

结论

CTC阳性率与NSCLC患者吸烟史相关，不同病理类型NSCLC中CTC分类及FGFR1表达情况无明显差异，不同类型CTC之间FGFR1表达情况无明显差异。我们期待着更大样本量及纳入随访数据后可得出与CTC及FGFR1基因表达相关的更多具有临床应用意义的结论。

Salvianolic acid B suppresses cell proliferation and induces apoptosis in osteosarcoma through p38-mediated reactive oxygen species generation

The present study aimed to investigate the potential anticancer effect and mechanisms of salvianolic acid B on osteosarcoma. Salvianolic acid B suppressed osteosarcoma cell proliferation and induced apoptosis in the osteosarcoma MG63 cell line, and activated the expressions of cleaved caspase-3, phosphorylated-tumor protein (p)38 mitogen-activated protein kinase (p-p38 MAPK) and phosphorylated-p53 (p-p53) proteins in the MG63 cells. Additionally, Salvianolic acid B also increased the level of reactive oxygen species (ROS) generation in the MG63 cells. The silencing of p38 expression inhibited the anticancer effect of salvianolic acid B on the levels of cell proliferation, p-p53 protein expression and ROS generation level in the MG63 cells. All these data supported the hypothesis that the anticancer effect of salvianolic acid B includes the suppression of cell proliferation and induces apoptosis in MG63 cells, and that p38 is important in the anticancer effect of salvianolic acid B on osteosarcoma cells due to the direct regulation of ROS generation. These data suggest that salvianolic acid B is important in the proliferation of osteosarcoma cells due to the direct regulation of p38-mediated ROS signaling.

Sprouty2 is involved in the control of osteoblast proliferation and differentiation through the FGF and BMP signaling pathways

Fibroblast growth factor (FGF) and bone morphogenetic protein (BMP) play essential roles in bone formation and osteoblast activity through the extracellular signal-regulated kinase 1/2 (ERK1/2) and Smad pathways. Sprouty family members are intracellular inhibitors of the FGF signaling pathway, and four orthologs of Sprouty have been identified in mammals. In vivo analyses have revealed that Sprouty2 is associated with bone formation. However, the mechanism by which the Sprouty family controls bone formation has not been clarified. In this study, we investigated the involvement of Sprouty2 in osteoblast proliferation and differentiation. We examined Sprouty2 expression in MC3T3-E1 cells, and found that high levels of Sprouty2 expression were induced by basic FGF stimulation. Overexpression of Sprouty2 in MC3T3-E1 cells resulted in suppressed proliferation compared with control cells. Sprouty2 negatively regulated the phosphorylation of ERK1/2 after basic FGF stimulation, and of Smad1/5/8 after BMP stimulation. Furthermore, Sprouty2 suppressed the expression of osterix, alkaline phosphatase, and osteocalcin mRNA, which are markers of osteoblast differentiation. Additionally, Sprouty2 inhibited osteoblast matrix mineralization. These results suggest that Sprouty2 is involved in the control of osteoblast proliferation and differentiation by downregulating the FGF-ERK1/2 and BMP-Smad pathways, and suppresses the induction of markers of osteoblast differentiation.

SRC Family Kinase Inhibition in Ewing Sarcoma Cells Induces p38 MAP Kinase-Mediated Cytotoxicity and Reduces Cell Migration

Ewing sarcoma (ES) is a highly aggressive bone and soft tissue cancer, representing the second most common primary malignant bone tumor in children and adolescents. Although the development of a multimodal therapy, including both local control (surgery and/or radiation) and systemic multidrug chemotherapy, has determined a significant improvement in survival, patients with metastatic and recurrent disease still face a poor prognosis. Moreover, considering that ES primarily affects young patients, there are concerns about long-term adverse effects of the therapy. Therefore, more rational strategies, targeting specific molecular alterations underlying ES, are required. Recent studies suggest that SRC family kinases (SFKs), which are aberrantly activated in most cancer types, could represent key therapeutic targets also for ES. Here, we challenged ES cell lines with a recently developed selective SFK inhibitor (a pyrazolo[3,4-d]pyrimidine derivative, called SI221), which was previously shown to be a valuable proapoptotic agent in other tumor types while not affecting normal cells. We observed that SI221 significantly reduced ES cell viability and proved to be more effective than the well-known SFK inhibitor PP2. SI221 was able to induce apoptosis in ES cells and also reduced ES cell clonogenic potential. Furthermore, SI221 was also able to reduce ES cell migration. At the molecular level, our data suggest that SFK inhibition through SI221 could reduce ES cell viability at least in part by hindering an SFK-NOTCH1 receptor-p38 mitogen-activated protein kinase (MAPK) axis. Overall, our study suggests a potential application of specific SFK inhibition in ES therapy. J. Cell. Physiol. 232: 129-135, 2017. © 2016 Wiley Periodicals, Inc.

Overexpression of miR-100 inhibits cancer growth, migration, and chemosensitivity in human NSCLC cells through fibroblast growth factor receptor 3

Nonsmall cell lung cancer (NSCLC) is a commonly occurring lung cancer. A combination of molecular biological treatments with regular chemotherapy may result in improved therapeutic outcome. Here, we reported significantly higher levels of fibroblast growth factor receptor 3 (FGFR3) and significantly lower levels of miR-100 in the NSCLC specimen, compared to the paired NSCLC-adjacent normal lung tissues. Moreover, the levels of FGFR3 and miR-100 were inversely correlated. Bioinformatics analyses followed by luciferase reporter assay showed that miR-100 bound to the 3'-UTR of FGFR3 messenger RNA (mRNA) to inhibit its translation. Overexpression of miR-100 in NSCLC cells decreased FGFR3 protein levels, whereas inhibition of miR-100 increased FGFR3 protein levels, without affecting FGFR3 mRNA levels. Furthermore, overexpression of miR-100 suppressed cancer growth, migration, and chemosensitivity in NSCLC cells, while inhibition of miR-100 significantly facilitated them. Taken together, our data demonstrate that miR-100 may inhibit NSCLC through FGFR3.

Heparan sulfation is essential for the prevention of cellular senescence

Cellular senescence is considered as an important tumor-suppressive mechanism. Here, we demonstrated that heparan sulfate (HS) prevents cellular senescence by fine-tuning of the fibroblast growth factor receptor (FGFR) signaling pathway. We found that depletion of 3'-phosphoadenosine 5'-phosphosulfate synthetase 2 (PAPSS2), a synthetic enzyme of the sulfur donor PAPS, led to premature cell senescence in various cancer cells and in a xenograft tumor mouse model. Sodium chlorate, a metabolic inhibitor of HS sulfation also induced a cellular senescence phenotype. p53 and p21 accumulation was essential for PAPSS2-mediated cellular senescence. Such senescence phenotypes were closely correlated with cell surface HS levels in both cancer cells and human diploid fibroblasts. The determination of the activation of receptors such as FGFR1, Met, and insulin growth factor 1 receptor β indicated that the augmented FGFR1/AKT signaling was specifically involved in premature senescence in a HS-dependent manner. Thus, blockade of either FGFR1 or AKT prohibited p53 and p21 accumulation and cell fate switched from cellular senescence to apoptosis. In particular, desulfation at the 2-O position in the HS chain contributed to the premature senescence via the augmented FGFR1 signaling. Taken together, we reveal, for the first time, that the proper status of HS is essential for the prevention of cellular senescence. These observations allowed us to hypothesize that the FGF/FGFR signaling system could initiate novel tumor defenses through regulating premature senescence.

Overexpression of miR-100 inhibits growth of osteosarcoma through FGFR3

Osteosarcoma (OS) is a prevalent, fast growing cancer. Identification of molecular regulation of OS growth may result in development of a novel therapy. Previous studies have highlighted a role of microRNAs (miRNAs) in the regulation of the carcinogenesis of OS, whereas the underlying mechanisms are not completely understood. Moreover, a role of miR-100 in the growth control of OS is not clear. Here we reported significantly higher levels of fibroblast growth factor receptor 3 (FGFR3) and significantly lower levels of miR-100 in the OS specimen, compared to those in the paired normal bone tissues. Bioinformatics analysis and luciferase reporter assay suggest that miR-100 binds to the 3'UTR of FGFR3 mRNA to prevent its translation. To prove it, we modified miR-100 levels in OS cells. We found that overexpression of miR-100 in OS cells decreased FGFR3 protein levels, whereas inhibition of miR-100 increased FGFR3 protein levels, without affecting FGFR3 transcripts. Moreover, overexpression of miR-100 suppressed the OS growth in vitro and in vivo, while inhibition of miR-100 significantly increased OS growth. Taken together, our data demonstrate that miR-100 may inhibit the growth of OS through FGFR3.

Activation of FGF receptor signaling promotes invasion of non-small-cell lung cancer

The molecular regulation of metastasis of non-small-cell lung cancer (NSCLC) remains not completely defined. Here we showed significant higher MMP26 in the resected NSCLC than adjacent healthy tissue from the patients. Moreover, a strong correlation between MMP26 and the phosphorylated fibroblast growth factor receptor 1 (FGFR1) was detected. To examine the causal relationship between activated FGFR signaling and MMP26, we studied a human NSCLC cell line, A549. We found that FGF1-induced FGFR1 phosphorylation in A549 cells activated MMP26, resulting in an increase in cancer invasiveness. Inhibition of FGFR1 phosphorylation abolished FGF1-stimulated MMP26 activation, suggesting that activation of FGFR signaling pathway in NSCLC promotes cancer metastasis through MMP26. To define the signal transduction cascades downstream of FGFR1 activation for MMP26 activation, we used specific inhibitors for PI3K, ERK/MAPK, and JNK, respectively, to the FGF1-stimulated A549 cells. We found that only inhibition of JNK significantly decreased the activation of MMP26 in response to FGF1 stimulation, suggesting that activation of FGFR1 signaling may activate JNK to activate MMP26 in NSCLC. Our study thus highlights FGFR signaling pathway and MMP26 as novel therapeutic targets for NSCLC therapy.

Inhibition of fibroblast growth factor receptor signaling impairs metastasis of hepatocellular carcinoma

The molecular mechanism underlying metastasis of hepatocellular carcinoma (HCC) remains elusive. Here, we showed that matrix metalloproteinase (MMP) 7 and MMP26 levels are significantly higher in the resected HCC than in the adjacent healthy hepatic cells from the patients. Moreover, a strong correlation of the levels of MMP7 or MMP26 with the phosphorylated fibroblast growth factor receptor 2 (FGFR2) was detected. To prove a causal link between the activation of FGFR signaling pathway and expression of MMP7 and MMP26, we used two human HCC lines, HepG2 and HuH-7, to study the underlying molecular basis. We found that FGF1-induced FGFR2 phosphorylation in either line resulted in significant activation of MMP7 and MMP26 and consequently an increase in cancer invasiveness. Inhibition of FGFR2 phosphorylation in HCC abolished FGF1-stimulated MMP7 and MMP26 expression, suggesting that activation of the FGFR signaling pathway in HCC may promote cancer metastasis by inducing MMP7 and MMP26 expression. To define the signal transduction cascades downstream of FGFR2 activation for MMP7 and MMP26 activation, we applied specific inhibitors for phosphatidylinositol-3 kinase (PI3K), extracellular signal-related kinase/mitogen-activated protein kinase (ERK/MAPK), and Jun N-terminal kinase (JNK), respectively, to the FGF1-stimulated HCC cells. We found that only inhibition of JNK significantly decreased the activation of MMP26 in response to FGF1 stimulation, and only inhibition of PI3K significantly decreased the activation of MMP7 in response to FGF1 stimulation, suggesting that the activation of the FGFR2 signaling may activate PI3K to activate MMP7 and activate JNK to activate MMP26, in HCC. Our study thus highlights the FGFR2 signaling pathway and MMP7 and MMP26 as novel therapeutic targets for HCC.

Regulation of metastasis of pediatric multiple myeloma by MMP13

The molecular mechanism underlying metastasis of pediatric multiple myeloma (MM) remains elusive. Here, we showed that the levels of MMP13 are significantly higher in MM from young patients than those from adult patients. Moreover, a strong correlation of the MMP13 and phosphorylated fibroblast growth factor receptor 4 (FGFR4) levels was detected in MM from young patients. To prove a causal link between activation of fibroblast growth factor receptors (FGFR) signaling pathway and MMP13 expression, we used a human MM line, RPMI-8226 (8226), to study the underlying molecular basis. We found that FGF1-induced FGFR4 phosphorylation in 8,226 cells resulted in significant activation of MMP13, and consequently, an increase in cancer invasiveness. FGFR4 inhibition in 8,226 cells abolished FGF1-stimulated MMP13 expression, suggesting that activation of FGFR signaling pathway in MM may promote cancer metastasis by inducing MMP13 expression. To define the signaling cascades downstream of FGFR4 activation for MMP13 activation, we applied specific inhibitors for PI3K, Jun N-terminal kinase (JNK), and ERK/MAPK, respectively, to the FGF1-stimulated 8,226 cells. We found that only inhibition of ERK1/2 significantly decreased the activation of MMP13 in response to FGF stimulation, suggesting that activation of FGFR signaling may activate ERK/MAPK, rather than JNK or PI3K pathway to activate MMP13 expression in 8,226 cells. Our study thus highlights FGFR4 signaling pathway and MMP13 as novel therapeutic targets for MM.

Fibroblast growth factor 2 causes G2/M cell cycle arrest in ras-driven tumor cells through a Src-dependent pathway

We recently reported that paracrine Fibroblast Growth Factor 2 (FGF2) triggers senescence in Ras-driven Y1 and 3T3^Ras mouse malignant cell lines. Here, we show that although FGF2 activates mitogenic pathways in these Ras-dependent malignant cells, it can block cell proliferation and cause a G2/M arrest. These cytostatic effects of FGF2 are inhibited by PD173074, an FGF receptor (FGFR) inhibitor. To determine which downstream pathways are induced by FGF2, we tested specific inhibitors targeting mitogen-activated protein kinase (MEK), phosphatidylinositol 3 kinase (PI3K) and protein kinase C (PKC). We show that these classical mitogenic pathways do not mediate the cytostatic activity of FGF2. On the other hand, the inhibition of Src family kinases rescued Ras-dependent malignant cells from the G2/M irreversible arrest induced by FGF2. Taken together, these data indicate a growth factor-sensitive point in G2/M that likely involves FGFR/Ras/Src pathway activation in a MEK, PI3K and PKC independent manner.

Sir2 histone deacetylase prevents programmed cell death caused by sustained activation of the Hog1 stress-activated protein kinase

Exposure of yeast to high osmolarity induces a transient activation of the Hog1 stress-activated protein kinase (SAPK), which is required for cell survival under these conditions. However, sustained activation of the SAPK results in a severe growth defect. We found that prolonged SAPK activation leads to cell death, which is not observed in nma111 cells, by causing accumulation of reactive oxygen species (ROS). Mutations of the SCF(CDC4) ubiquitin ligase complex suppress cell death by preventing the degradation of Msn2 and Msn4 transcription factors. Accumulation of Msn2 and Msn4 leads to the induction of PNC1, which is an activator of the Sir2 histone acetylase. Sir2 is involved in protection against Hog1-induced cell death and can suppress Hog1-induced ROS accumulation. Therefore, cell death seems to be dictated by the balance of ROS induced by Hog1 and the protective effect of Sir2.

Induction of Id-1 by FGF-2 involves activity of EGR-1 and sensitizes neuroblastoma cells to cell death

Inhibitor of differentiation-1 (Id-1) is a member of helix-loop-helix (HLH) family of proteins that regulate gene transcription through their inhibitory binding to basic-HLH transcription factors. Similarly to other members of this family, Id-1 is involved in the repression of cell differentiation and activation of cell growth. The dual function of Id-1, inhibition of differentiation, and stimulation of cell proliferation, might be interdependent, as cell differentiation is generally coupled with the exit from the cell cycle. Fibroblast growth factor-2 (FGF-2) has been reported to play multiple roles in different biological processes during development of the central nervous system (CNS). In addition, FGF-2 has been described to induce "neuronal-like" differentiation and trigger apoptosis in neuroblastoma SK-N-MC cells. Although regulation of Id-1 protein by several mitogenic factors is well-established, little is known about the role of FGF-2 in the regulation of Id-1. Using human neuroblastoma cell line, SK-N-MC, we found that treatment of these cells with FGF-2 resulted in early induction of both Id-1 mRNA and protein. The induction occurs within 1 h from FGF-2 treatment and is mediated by ERK1/2 pathway, which in turn stimulates expression of the early growth response-1 (Egr-1) transcription factor. We also demonstrate direct interaction of Egr-1 with Id-1 promoter in vitro and in cell culture. Finally, inhibition of Id-1 expression results in G(2) /M accumulation of FGF-2-treated cells and delayed cell death.

Fenretinide-dependent upregulation of death receptors through ASK1 and p38α enhances death receptor ligand-induced cell death in Ewing's sarcoma family of tumours

Background:

Sustained p38^MAPK phosphorylation upregulates p75 neurotrophin (p75^NTR) and induces apoptosis in Ewing's sarcoma family of tumours (ESFT). As fenretinide induces ESFT death through sustained p38^MAPK phosphorylation, we hypothesised that this may be effected through upregulation of death receptors (DRs) and that treatment of fenretinide plus DR ligands may enhance apoptosis.

Methods:

DR expression was determined by flow cytometry. Trypan blue exclusion assays, caspase-8 flow cytometry and immunoblotting for Bid were used to measure cell death.

Results:

Fenretinide upregulated cell surface expression of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors, FAS and p75^NTR, in an ASK1- and p38α-dependent manner. Cotreatment with fenretinide and DR ligands resulted in synergistic death compared with either agent alone; caspase-8 and Bid were cleaved in a time-dependent manner. Fenretinide did not increase DR expression in non-malignant cells. Furthermore, fenretinide, TRAIL or a combination of both agents was non-cytotoxic to non-malignant cells. Etoposide and actinomycin D increased expression of all DRs examined, whereas vincristine increased FAS alone. Only actinomycin D and TRAIL, and etoposide with TRAIL or FasL, enhanced death compared with either agent alone.

Conclusion:

The synergistic death observed with fenretinide and DR ligands suggests that this combination may be an attractive strategy for the treatment of ESFT.

Basic fibroblast growth factor in the bone microenvironment enhances cell motility and invasion of Ewing's sarcoma family of tumours by activating the FGFR1-PI3K-Rac1 pathway

Background:

Ewing's sarcoma family of tumours (ESFT) is a malignant small round-cell tumour of the bone and soft tissues. It is characterised by a strong tendency to invade and form metastases. The microenvironment of the bone marrow is a large repository for many growth factors, including the basic fibroblast growth factor (bFGF). However, the role of bFGF in the invasive and metastatic phenotype of ESFT has not been investigated.

Methods:

The motility and invasion of ESFT cells were assessed by a wound-healing assay, chemotaxis assay, and invasion assay. The expression and activation of FGF receptors (FGFRs) in ESFT cell lines and clinical samples were detected by RT–PCR, western blotting, and immunohistochemistry. The morphology of ESFT cells was investigated by phase-contrast microscopy and fluorescence staining for actin. Activation of Rac1 was analysed by a pull-down assay.

Results:

bFGF strongly induced the motility and invasion of ESFT cells. Furthermore, FGFR1 was found to be expressed and activated in clinical samples of ESFT. Basic FGF-induced cell motility was mediated through the FGFR1–phosphatidylinositol 3-kinase (PI3K)–Rac1 pathway. Conditioned medium from bone marrow stromal cells induced the motility of ESFT cells by activating bFGF/FGFR1 signalling.

Conclusion:

The bFGF–FGFR1–PI3K–Rac1 pathway in the bone microenvironment may have a significant role in the invasion and metastasis of ESFT.

The myelin protein MAL affects peripheral nerve myelination: a new player influencing p75 neurotrophin receptor expression

The myelin and lymphocyte protein (MAL) is a raft-associated membrane protein predominantly expressed by oligodendrocytes and Schwann cells. Here we show that MAL regulates myelination in the peripheral nervous system. In mice overexpressing MAL, myelination was retarded and fibers were hypomyelinated, whereas myelination in MAL knockout mice was accelerated. This was not due to impaired Schwann cell proliferation, differentiation or axonal sorting. We found that the expression level of p75 neurotrophin receptor mRNA and protein was strongly reduced in developing sciatic nerves in MAL-overexpressing mice. This reduction is well correlated with the observed alterations in myelination initiation, speed of myelination and alterations in Remak bundle development. Our results suggest a functional role for MAL in peripheral myelination by influencing the expression of membrane components that mediate axon-glia interaction during ensheathment and myelin wrapping.

3-Nitrofluoranthene (3-NF) but not 3-aminofluoranthene (3-AF) elicits apoptosis as well as programmed necrosis in Hepa1c1c7 cells

In this study, we show that the environmental pollutant, 3-nitrofluoranthene (3-NF) but not its amine form, 3-aminofluoranthene (3-AF), induces apoptosis as well as regulated necrosis with necroptotic features in Hepa1c1c7 cells. Upon exposure to 3-NF, both typical apoptotic and necrotic cells were observed. A large number of the cells exhibited a characteristic partial nuclear chromatin condensation. Cycloheximide completely attenuated 3-NF-induced cell death. Activation of caspase-8, -9, and -3 were observed. Moreover, Z-VAD-FMK decreased the apoptotic cells, whereas the number of propidium iodide (PI)-positive cells with partial chromatin condensation was reduced by Nec-1, an inhibitor of receptor interacting protein (RIP-1). Cyp1a1, but not nitric oxide synthase (NOS), appears to be involved in activation of 3-NF to reactive metabolites. Increase in the number as well as size of lysosomes, myelinosomes, and activation of autophagy were also observed. 3-NF induced phosphorylation of ERK1/2, JNK and p38 MAPKs. Interestingly, while inhibitors of ERK1/2 and JNK reduced apoptotic as well as necrotic cell death, the p38 inhibitor, SB202190 reduced only the necrotic cell death. Taken together, 3-NF elicits both apoptosis and a caspase-independent programmed cell death (PCD) with autophagic characteristics. Conversely, with 3-AF, no apparent cytotoxic effects besides a reduction in cell proliferation was observed.

BAY 11-7082 induces cell death through NF-kappaB-independent mechanisms in the Ewing's sarcoma family of tumours

The role of NF-kappaB in the Ewing's sarcoma family of tumours (ESFT) and their response to fenretinide has been investigated. Basal levels of phosphorylated NF-kappaB were low in all ESFT cells. BAY 11-7082 decreased cell viability, which was accompanied by caspase-3 cleavage. This was independent of the increase in reactive oxygen species, p38(MAPK) phosphorylation and expression of NF-kappaB target proteins. NF-kappaB knockdown did not induce death under normal growth conditions, but did reduce TNFalpha-dependent cell survival. Fenretinide-induced apoptosis was independent of NF-kappaB. BAY 11-7082-induced cell death through an NF-kappaB-independent mechanism and enhanced cell death when combined with fenretinide.

1-Nitropyrene (1-NP) induces apoptosis and apparently a non-apoptotic programmed cell death (paraptosis) in Hepa1c1c7 cells

Mechanistic studies of nitro-PAHs (polycyclic aromatic hydrocarbons) of interest might help elucidate which chemical characteristics are most important in eliciting toxic effects. 1-Nitropyrene (1-NP) is the predominant nitrated PAH emitted in diesel exhaust. 1-NP-exposed Hepa1c1c7 cells exhibited marked changes in cellular morphology, decreased proliferation and different forms of cell death. A dramatic increase in cytoplasmic vacuolization was observed already after 6 h of exposure and the cells started to round up at 12 h. The rate of cell proliferation was markedly reduced at 24 h and apoptotic as well as propidium iodide (PI)-positive cells appeared. Electron microscopic examination revealed that the vacuolization was partly due to mitochondria swelling. The caspase inhibitor Z-VAD-FMK inhibited only the apoptotic cell death and Nec-1 (an inhibitor of necroptosis) exhibited no inhibitory effects on either cell death or vacuolization. In contrast, cycloheximide markedly reduced both the number of apoptotic and PI-positive cells as well as the cytoplasmic vacuolization, suggesting that 1-NP induced paraptotic cell death. All the MAPKs; ERK1/2, p38 and JNK, appear to be involved in the death process since marked activation was observed upon 1-NP exposure, and their inhibitors partly reduced the induced cell death. The ERK1/2 inhibitor PD 98057 completely blocked the induced vacuolization, whereas the other MAPKs inhibitors only had minor effects on this process. These findings suggest that 1-NP may cause apoptosis and paraptosis. In contrast, the corresponding amine (1-aminopyrene) elicited only minor apoptotic and necrotic cell death, and cells with characteristics typical of paraptosis were absent.

Interaction between ERK and GSK3beta mediates basic fibroblast growth factor-induced apoptosis in SK-N-MC neuroblastoma cells

The Ewing's sarcoma family of tumors (ESFT) includes Ewing's sarcoma (ES), Askin's tumor of the chest wall, and peripheral primitive neuroectodermal tumor. Basic fibroblast growth factor (FGF2) suppresses the growth of ESFT cells and causes their apoptosis. The underlying mechanism is unclear. Using a human peripheral primitive neuroectodermal tumor cell line, SK-N-MC, we demonstrated FGF2 stimulated phosphorylation of ERK1 and ERK2 (pERK1/2) and GSK3beta (pGSK3beta(Tyr-216)), all of which were primarily retained in the cytoplasm. FGF2 promoted the association between ERK and pGSK3beta(Tyr-216). Inhibitors for GSK3beta (TDZD and LiCl) and ERK (PD98059) protected cells from FGF2-induced apoptosis. On the other hand, inhibitors of GSK3beta, but not PD98059 decreased ERK/pGSK3beta(Tyr-216) association and caused a nuclear translocation of pERK1/2. Similarly, expression of a kinase-deficient (K85R) GSK3beta or GSK3beta-small interfering RNA inhibited FGF2-regulated ERK/pGSK3beta(Tyr-216) association and translocated pERK to the nucleus. Both K85R GSK3beta and small interfering RNA offered protection against FGF2-induced cell death. In contrast, overexpression of wild-type GSK3beta sensitized cells to FGF2 cytotoxicity. Hydrogen peroxide and ethanol enhanced FGF2-stimulated pGSK3beta(Tyr-216), ERK/pGSK3beta(Tyr-216) association, and cytoplasmic retention of pERK1/2. As a result, they potentiated FGF2-induced cell death. Taken together, our results suggested that FGF2-induced accumulation of pERK1/2 in the cytoplasm is toxic for SK-N-MC cells. The formation of an ERK.GSK3beta complex retained pERK1/2 in the cytoplasm. In contrast, disruption of the ERK.GSK3beta complex resulted in nuclear translocation of pERK1/2 and offered protection.

The p38 MAPK pathway mediates aryl propionic acid induced messenger rna stability of p75 NTR in prostate cancer cells

The p75(NTR) acts as a tumor suppressor in the prostate, but its expression is lost as prostate cancer progresses and is minimal in established prostate cancer cell lines such as PC-3, DU-145, and LNCaP. Previously, we showed that treatment with R-flurbiprofen or ibuprofen induced p75(NTR) expression in PC-3 and DU-145 cells leading to p75(NTR)-mediated decreased survival. Here, we investigate the mechanism by which these drugs induce p75(NTR) expression. We show that the observed increase in p75(NTR) protein due to R-flurbiprofen and ibuprofen treatment was accompanied by an increase in p75(NTR) mRNA, and this increase in mRNA was the result of increased mRNA stability and not by an up-regulation of transcription. In addition, we show that treatment with R-flurbiprofen or ibuprofen led to sustained activation of the p38 mitogen-activated protein kinase (MAPK) pathway. Furthermore, inhibition of the p38 MAPK pathway with the p38 MAPK-specific inhibitor SB202190 or by small interfering RNA (siRNA) knockdown of p38 MAPK protein prevented induction of p75(NTR) by R-flurbiprofen and ibuprofen. We also observed that siRNA knockdown of MAPK-activated protein kinase (MK)-2 and MK3, the kinases downstream of p38 MAPK that are responsible for the mRNA stabilizing effects of the p38 MAPK pathway, also prevented an induction of p75(NTR) by R-flurbiprofen and ibuprofen. Finally, we identify the RNA stabilizing protein HuR and the posttranscriptional regulator eukaryotic translation initiation factor 4E as two possible mechanisms by which the p38 MAPK pathway may increase p75(NTR) expression. Collectively, the data suggest that R-flurbiprofen and ibuprofen induce p75(NTR) expression by increased mRNA stability that is mediated through the p38 MAPK pathway.

Specific inhibitor of MEK-mediated cross-talk between ERK and p38 MAPK during differentiation of human osteosarcoma cells

Osteosarcoma is the most common primary malignant bone tumor, accounting for approximately 20% of all primary sarcomas in bone. Although treatment modalities have been improved over the past decades, it is still a tumor with a high mortality rate in children and young adults. Based on histological considerations, osteosarcoma arises from impaired differentiation of these immature cells into more mature types and that correction of this impairment may reduce malignancy and increase the efficiency of chemotherapy. The purpose of this study was to determine the effect of specific inhibitors of MAPK extracellular signaling-regulated kinase (ERK) kinase (MEK) and p38 on the differentiation of human osteosarcoma cell line SaOS-2 cells. We found that PD98059, a specific inhibitor of MEK, inhibited the serum-stimulated proliferation of SaOS-2 cells; whereas SB203580, a specific inhibitor of p38 MAPK, had little effect on it. SB203580 suppressed ALPase activity, gene expression of type I collagen, and expression of ALP and BMP-2 mRNAs; whereas PD98059 upregulated them dose dependently. In addition, immunoblot and immunostaining analysis revealed that phosphorylation of ERK was increased by treatment with SB203580; whereas PD98059 increased the phosphorylation of p38, which implies a seesaw-like balance between ERK and p38 phosphorylation. We suggest that osteosarcoma cell differentiation is regulated by the balance between the activities of the ERK and p38 pathways and that the MEK/ERK pathway negatively regulates osteosarcoma cell differentiation, whereas the p38 pathway does so positively. MEK inhibitor may thus be a good candidate for altering the expression of the osteosarcoma malignant phenotype.

The sensitivity of the Ewing's sarcoma family of tumours to fenretinide-induced cell death is increased by EWS-Fli1-dependent modulation of p38MAPK activity

The Ewing's sarcoma family of tumours (ESFT) are small round cell tumours characterized by the non-random EWS-ETS gene rearrangements. We have previously demonstrated that ESFT are highly sensitive to fenretinide-induced death, effected in part through a reactive oxygen species (ROS)-dependent pathway. Here, we demonstrate for the first time that the sensitivity of ESFT cells to fenretinide-induced cell death is decreased following downregulation of the oncogenic fusion protein EWS-Fli1; siRNA targeting EWS-Fli1 attenuated fenretinide-induced cell death in cell lines expressing EWS-Fli1, but not EWS-ERG. This decrease in cell death was independent of the level of ROS produced following exposure to fenretinide, but was effected through EWS-Fli1-dependent modulation of p38(MAPK) activity. Furthermore, inhibition of p38(MAPK) activity and knockdown of EWS-Fli1 reduced fenretinide-induced mitochondrial permeabilization, cytochrome c release, caspase and PARP cleavage, consistent with the hypothesis that p38(MAPK) is critical for activation of the death cascade by fenretinide in ESFT cells. These data demonstrate that expression of EWS-Fli1 enhances fenretinide-induced cell death in ESFT and that this is effected at least in part through modulation of p38(MAPK) activity.

The cardioprotective effect of the low molecular weight isoform of fibroblast growth factor-2: the role of JNK signaling

Our laboratory showed that overexpression of fibroblast growth factor-2 (FGF2) protected the heart against ischemia-reperfusion injury. FGF2 has different protein isoforms (low [LMW] and high [HMW] molecular weight isoforms) produced from alternative translation start sites. However, which FGF2 isoform(s) mediates this cardioprotection, and which signaling pathway (i.e., mitogen-activated protein kinase (MAPK)) elicits FGF2 isoform-induced cardioprotection remains to be elucidated.

METHODS AND RESULTS

Wildtype, Fgf2 KO (absence of all FGF2 isoforms) and FGF2 LMWKO (absence of LMW isoform) hearts were subjected to an ex vivo work-performing heart ischemic model of 60 min ischemia and 120 min reperfusion. There was a significant decrease in the recovery of post-ischemic contractile function (p<0.05) in Fgf2 KO and FGF2 LMWKO mouse hearts compared to wildtype hearts. Following ischemia-reperfusion injury, MKK4/7, JNK, and c-Jun were significantly phosphorylated (i.e., activated), and the levels of TUNEL-positive nuclei and caspase 3 cleavage were significantly increased in vehicle-treated Fgf2 KO and FGF2 LMWKO compared to wildtype hearts (p<0.05). A novel JNK pathway inhibitor, CEP11004 (50 nM), significantly restored the post-ischemic contractile function and reduced myocardial cell death, as measured by CK release and apoptotic markers, compared to DMSO-treated cohorts (p<0.05). Overall, our data indicate that the LMW isoform has an important role in restoring cardiac function after ischemia-reperfusion (I/R) injury. These results provide unequivocal evidence that inhibition of JNK signaling is involved in FGF2 LMW isoform-mediated cardioprotection and that the potential mechanism may be through inhibition of the apoptotic process.

Inter- and intracellular signaling in amyotrophic lateral sclerosis: role of p38 mitogen-activated protein kinase

The pathogenetic processes underlying the selective motor neuron degeneration in amyotrophic lateral sclerosis (ALS) are complex and still not completely understood even in the cases of inherited disease caused by mutations in the Cu/Zn superoxide dismutase-dependent (SOD1) gene. Recent evidence supports the view that ALS is not a cell-autonomous disease and that glial-neuron cross-talk, throughout cytokines and other toxic factors like the nitric oxide and superoxide, is a crucial determinant for the induction of motor neuron death. This cell-cell interaction may determine the progression of the disease through processes that are likely independent of the initial trigger and that may converge on the activation of intracellular death pathways in the motor neurons. In this review we provide support to the hypothesis that aberrant expression and activity of p38 mitogen protein-activated kinases cascade (p38MAPK) in motor neurons and glial cells may play a role in the development and progression of ALS. Increased activation of p38MAPK may phosphorylate neuron-specific substrates altering their physiological properties and it may turn on responsive genes leading to neurotoxicity.

Regulation of apoptosis and proliferation in Ewing's sarcoma--opportunities for targeted therapy

The Ewing's sarcoma family of tumors are malignant tumors of bone and soft tissue which occur predominantely in children and adolescents. Whereas cure rates for patients with localized tumors are around 70%, survival rates for patients with metastases or relapse are poor in spite of intensive chemo- and radiation therapy, demonstrating a clear need for new, more effective therapies. Insights into the biology of the tumors of the Ewing's sarcoma family with identification of the EWS/ETS gene rearrangement as the key event in malignant transformation and its influence on the regulation of various pathways involved in proliferation, differentiation and apoptosis has led to the identification of potential targets for the development of new molecular therapeutics. This review will focus on the regulation of major pathways of proliferation and apoptosis in tumors of the Ewing's sarcoma family and point out how modulation of these pathways might be of potential use for future therapy.

Unraveling the differential expression of the two isoforms of myelin-associated glycoprotein in a mouse expressing GFP-tagged S-MAG specifically regulated and targeted into the different myelin compartments

The two myelin-associated glycoprotein (MAG) isoforms are cell adhesion molecules that differ only in their cytoplasmic domains, but their specific roles are not well understood. In this study, we present a transgenic mouse line that specifically expresses GFP-tagged S-MAG correctly regulated and targeted into the myelin sheath allowing the specific discrimination of L- and S-MAG on the subcellular level. Here, we describe the differential expression pattern and spatial distribution of L- and S-MAG during development as well as in the adult central and peripheral nervous system. In peripheral nerves, where S-MAG is the sole isoform, we observed S-MAG concentrated in different ring-like structures such as periaxonal and abaxonal rings, and discs spanning through the compact myelin sheath perpendicular to the axon. In summary, our data provide new insight in the subcellular distribution of the two isoforms fundamental for the understanding of their specific functions in myelin formation and maintenance.

Activation and cross-talk between Akt, NF-kappaB, and unfolded protein response signaling in 1-LN prostate cancer cells consequent to ligation of cell surface-associated GRP78

Binding of activated forms of the proteinase inhibitor alpha2-macroglobulin (alpha2M*) to cell surface-associated GRP78 on 1-LN human prostate cancer cells causes their proliferation. We have now examined the interplay between Akt activation, regulation of apoptosis, the unfolded protein response, and activation of NF-kappaB in alpha2M*-induced proliferation of 1-LN cells. Exposure of cells to alpha2M* (50 pM) induced phosphatidylinositol 3-kinase-dependent activation of Akt by phosphorylation at Thr-308 and Ser-473 with a concomitant 60-80% increase in Akt-associated kinase activity. ERK1/2 and p38 MAPK were also activated, but there was only a marginal effect on JNK activation. Treatment of 1-LN cells with alpha2M* down-regulated apoptosis and promoted NF-kappaB activation as shown by increases of Bcl-2, p-Bad(Ser-136), p-FOXO1(Ser-253), p-GSK3beta(Ser-9), XIAP, NF-kappaB, cyclin D1, GADD45beta, p-ASK1(Ser-83), and TRAF2 in a time of incubation-dependent manner. alpha2M* treatment of 1-LN cells, however, showed no increase in the activation of caspase -3, -9, or -12. Under these conditions, we observed increased unfolded protein response signaling as evidenced by elevated levels of GRP78, IRE1alpha, XBP-1, ATF4, ATF6, p-PERK, p-eIF2alpha, and GADD34 and reduced levels of GADD153. Silencing of GRP78 gene expression by RNAi suppressed activation of Akt(Thr-308), Akt(Ser-473), and IkappaB kinase alpha kinase. The effects of alpha2M* on the NF-kappaB activation, antiapoptotic signaling, unfolded protein response signaling, and proapoptotic signaling were also reversed by this treatment. In conclusion, alpha2M* promotes cellular proliferation of 1-LN prostate cancer cells by activating MAPK and Akt-dependent signaling, down-regulating apoptotic signaling, and activating unfolded protein response signaling.

Differential susceptibility to TRAIL of normal versus malignant human urothelial cells

Comparing normal human urothelial (NHU) cells to a panel of six representative urothelial cell carcinoma (UCC)-derived cell lines, we showed that while TRAIL receptor expression patterns were similar, susceptibility to soluble recombinant crosslinked TRAIL fell into three categories. 4/6 carcinoma lines were sensitive, undergoing rapid and extensive death; NHU and 253J cells were partially resistant and HT1376 cells, like normal fibroblasts, were refractory. Both normal and malignant urothelial cells underwent apoptosis via the same caspase-8/9-mediated mechanism. Rapid receptor downregulation was a mechanism for evasion by some UCC cells. TRAIL resistance in malignant urothelial cells was partially dependent on FLIP(L) and was differentially mediated by p38(MAPK), whereas in normal cells, resistance was mediated by NF-kappaB. Importantly, extensive killing of UCC cells could be induced using noncrosslinked TRAIL after prolonged exposure, with no damage to their homologous, normal urothelial cell counterparts.

p38MAPK-Dependent Sensitivity of Ewing's Sarcoma Family of Tumors to Fenretinide-Induced Cell Death

PURPOSE

There is an urgent need for new therapeutic strategies in Ewing's sarcoma family of tumors (ESFT). In this study, we have evaluated the effect of fenretinide [N-(4-hydroxyphenyl)retinamide] in ESFT models.

EXPERIMENTAL DESIGN

The effect of fenretinide on viable cell number and apoptosis of ESFT cell lines and spheroids and growth of s.c. ESFT in nu/nu mice was investigated. The role of the stress-activated kinases p38(MAPK) and c-Jun NH(2)-terminal kinase in fenretinide-induced death was investigated by Western blot and inhibitor experiments. Accumulation of reactive oxygen species (ROS) and changes in mitochondrial transmembrane potential were investigated by flow cytometry.

RESULTS

Fenretinide induced cell death in all ESFT cell lines examined in a dose- and time-dependent manner. ESFT cells were more sensitive to fenretinide than the neuroblastoma cell lines examined. Furthermore, fenretinide induced cell death in ESFT spheroids and delayed s.c. ESFT growth in mice. p38(MAPK) was activated within 15 minutes of fenretinide treatment and was dependent on ROS accumulation. Inhibition of p38(MAPK) activity partially rescued fenretinide-mediated cell death in ESFT but not in SH-SY5Y neuroblastoma cells. c-Jun NH(2)-terminal kinase was activated after 4 hours and was dependent on ROS accumulation but not on activation of p38(MAPK). After 8 hours, fenretinide induced mitochondrial depolarization (Deltapsi(m)) and release of cytochrome c into the cytoplasm in a ROS- and p38(MAPK)-dependent manner.

CONCLUSIONS

These data show that the high sensitivity of ESFT cells to fenretinide is dependent in part on the rapid and sustained activation of p38(MAPK). The efficacy of fenretinide in preclinical models demands the evaluation of fenretinide as a potential therapeutic agent in ESFT.

Mechanisms underlying differential responses to FGF signaling

Fibroblast growth factors (FGFs) are key regulators of several developmental processes in which cell fate and differentiation to various tissue lineages are determined. The importance of the proper spatial and temporal regulation of FGF signals is evident from human and mouse genetic studies which show that mutations leading to the dysregulation of FGF signals cause a variety of developmental disorders including dominant skeletal diseases and cancer. The FGF ligands signal via a family of receptor tyrosine kinases and, depending on the cell type or stage of maturation, produce diverse biological responses that include proliferation, growth arrest, differentiation or apoptosis. A central issue in FGF biology is to understand how these diverse cellular responses are determined and how similar signaling inputs can generate distinct patterns of gene expression that govern the specificity of the cellular response. In this review we draw upon studies from the past fifteen years and attempt to construct a molecular picture of the different levels of regulation by which such specific cellular responses could be achieved by FGF signals. We discuss whether specificity could lie in the nature of the ligand, the particular receptor, the signal transduction pathways utilized, or the transcriptional regulation of specific genes. Finally, we also discuss how the interplay of FGF signals with other signaling systems could contribute to the cellular response. In particular we focus on the interaction with the Wnt pathway since FGF/Wnt cross-talk is emerging as an important nexus in regulating a variety of biological processes.