Functional Rac-1 and Nck signaling networks are required for FGF-2-induced DNA synthesis in MCF-7 cells

Transcriptional signaling pathways inversely regulated in Alzheimer's disease and glioblastoma multiform

Convincing epidemiological data suggest an inverse association between cancer and neurodegeneration, including Alzheimer's disease (AD). Since both AD and cancer are characterized by abnormal, but opposing cellular behavior, i.e., increased cell death in AD while excessive cell growth occurs in cancer, this motivates us to initiate the study into unraveling the shared genes and cell signaling pathways linking AD and glioblastoma multiform (GBM). In this study, a comprehensive bioinformatics analysis on clinical microarray datasets of 1,091 GBM and 524 AD cohorts was performed. Significant genes and pathways were identified from the bioinformatics analyses – in particular ERK/MAPK signaling, up-regulated in GBM and Angiopoietin Signaling pathway, reciprocally up-regulated in AD – connecting GBM and AD (P < 0.001), were investigated in details for their roles in GBM growth in an AD environment. Our results showed that suppression of GBM growth in an AD background was mediated by the ERK-AKT-p21-cell cycle pathway and anti-angiogenesis pathway.

FGF-2 prevents cancer cells from ER stress-mediated apoptosis via enhancing proteasome-mediated Nck degradation

Induction of ER (endoplasmic reticulum) stress-mediated apoptosis in cancer cells represents an alternative approach for cancer therapy. Whether FGF-2 (fibroblast growth factor 2)-induced survival signals may interact with ER stress signalling in cancer cells remains elusive. In the present study, we showed that pretreatment with FGF-2 decreased the inhibition of DNA synthesis and induction of apoptosis by two different ER stress inducers, TM (tunicamycin) and TG (thapsigargin), in both human hepatoblastoma HepG2 cells and breast cancer MCF-7 cells. Pretreatment with FGF-2 prevented ER stress-mediated apoptosis by decreasing ER stress-induced CHOP [C/EBP (CCAAT/enhancer-binding protein)-homologous protein] expression. We further demonstrated that pretreatment with FGF-2 mediated the decrease in TM-induced CHOP expression and apoptosis through ERK1/2 (extracellular-signal-regulated kinases 1 and 2) pathway. Finally, we demonstrated that FGF-2 promoted proteasome-mediated degradation of Nck (non-catalytic region of tyrosine kinase adaptor protein), an SH (Src homology) 2/SH3-containing adaptor protein. Whereas overexpression of Nck1 decreased FGF-2-induced ERK1/2 phosphorylation to inhibit the effect of FGF-2 on TM-induced CHOP expression and apoptosis, a decrease in Nck expression prevented TM-induced CHOP expression and apoptosis. Taken together, the findings of the present study provide the first evidence that Nck plays a pivotal role in integrating FGF-2 and ER stress signals to counteract the ER stress deleterious effect on cancer cell survival.

Roles of rho GTPases in intracellular transport and cellular transformation

Rho family GTPases belong to the Ras GTPase superfamily and transduce intracellular signals known to regulate a variety of cellular processes, including cell polarity, morphogenesis, migration, apoptosis, vesicle trafficking, viral transport and cellular transformation. The three best-characterized Rho family members are Cdc42, RhoA and Rac1. Cdc42 regulates endocytosis, the transport between the endoplasmic reticulum and Golgi apparatus, post-Golgi transport and exocytosis. Cdc42 influences trafficking through interaction with Wiskott-Aldrich syndrome protein (N-WASP) and the Arp2/3 complex, leading to changes in actin dynamics. Rac1 mediates endocytic and exocytic vesicle trafficking by interaction with its effectors, PI3kinase, synaptojanin 2, IQGAP1 and phospholipase D1. RhoA participates in the regulation of endocytosis through controlling its downstream target, Rho kinase. Interestingly, these GTPases play important roles at different stages of viral protein and genome transport in infected host cells. Importantly, dysregulation of Cdc42, Rac1 and RhoA leads to numerous disorders, including malignant transformation. In some cases, hyperactivation of Rho GTPases is required for cellular transformation. In this article, we review a number of findings related to Rho GTPase function in intracellular transport and cellular transformation.

SKAP2, a novel target of HSF4b, associates with NCK2/F-actin at membrane ruffles and regulates actin reorganization in lens cell

In addition to roles in stress response, heat shock factors (HSFs) play crucial roles in differentiation and development. Heat shock transcription factor 4 (HSF4) deficiency leads to defect in lens epithelial cell (LEC) differentiation and cataract formation. However, the mechanism remains obscure. Here, we identified Src kinase-associated phosphoprotein 2 (SKAP2) as a downstream target of HSF4b and it was highly expressed at the anterior tip of lens elongating fibre cells in vivo. The HSF4-deficient lenses showed reduced SKAP2 expression and defects in actin reorganization. The disassembly of stress fibres and formation of cortical actin fibres are critical for the initiation of LEC differentiation. SKAP2 localized at actin-rich ruffles in human LECs (SRA01/04 cells) and knockdown SKAP2 using RNA interference impaired the disassembly of cellular stress fibres in response to fibroblast growth factor (FGF)-b. Overexpression of SKAP2, but not the N-terminal deletion mutant of SKAP2, induced the actin remodelling. We further found that SKAP2 interacted with the SH2 domain of non-catalytic region of tyrosine kinase adaptor protein 2 (NCK2) via its N-terminus. The complex of SKAP2-NCK2-F-actin accumulated at the leading edge of the lamellipodium, where FGF receptors and focal adhesion were also recruited. These results revealed an essential role for HSF4-mediated SKAP2 expression in the regulation of actin reorganization during lens differentiation, likely through a mechanism that SKAP2 anchors the complex of NCK2/focal adhesion to FGF receptors at the lamellipodium in lens epithelial cells.

MUC4 Mucin Potentiates Pancreatic Tumor Cell Proliferation, Survival, and Invasive Properties and Interferes with Its Interaction to Extracellular Matrix Proteins

MUC4, a transmembrane mucin, is aberrantly expressed in pancreatic adenocarcinomas while remaining undetectable in the normal pancreas. Recent studies have shown that the expression of MUC4 is associated with the progression of pancreatic cancer and is inversely correlated with the prognosis of pancreatic cancer patients. In the present study, we have examined the phenotypic and molecular consequences of MUC4 silencing with an aim of establishing the mechanistic basis for its observed role in the pathogenesis of pancreatic cancer. The silencing of MUC4 expression was achieved by stable expression of a MUC4-specific short hairpin RNA in CD18/HPAF, a highly metastatic pancreatic adenocarcinoma cell line. A significant decrease in MUC4 expression was detected in MUC4-knockdown (CD18/HPAF-siMUC4) cells compared with the parental and scrambled short interfering RNA-transfected (CD18/HPAF-Scr) control cells by immunoblot analysis and immunofluorescence confocal microscopy. Consistent with our previous observation, inhibition of MUC4 expression restrained the pancreatic tumor cell growth and metastasis as shown in an orthotopic mouse model. Our in vitro studies revealed that MUC4-associated increase in tumor cell growth resulted from both the enhanced proliferation and reduced cell death. Furthermore, MUC4 expression was also associated with significantly increased invasiveness (P < or = 0.05) and changes in actin organization. The presence of MUC4 on the cell surface was shown to interfere with the tumor cell-extracellular matrix interactions, in part, by inhibiting the integrin-mediated cell adhesion. An altered expression of growth- and metastasis-associated genes (LI-cadherin, CEACAM6, RAC1, AnnexinA1, thrombomodulin, epiregulin, S100A4, TP53, TP53BP, caspase-2, caspase-3, caspase-7, plakoglobin, and neuregulin-2) was also observed as a consequence of the silencing of MUC4. In conclusion, our study provides experimental evidence that supports the functional significance of MUC4 in pancreatic cancer progression and indicates a novel role for MUC4 in cancer cell signaling.

Regulation of calnexin sub-cellular localization modulates endoplasmic reticulum stress-induced apoptosis in MCF-7 cells

The endoplasmic reticulum (ER) is the cellular compartment where proteins enter the secretory pathway, undergo post-translational modifications and acquire a correct conformation. If these functions are chronically altered, specific ER stress signals are triggered to promote cell death through the intrinsic apoptotic pathway. Here, we show that tunicamycin causes significant alteration of calnexin sub-cellular distribution in MCF-7 cells. Interestingly, this correlates with the absence of both tunicamycin-induced calnexin phosphorylation as well as tunicamycin-induced cell death. Under these conditions, calnexin-associated Bap31, an ER integral membrane protein, is subjected to a caspase-8 cleavage pattern within a specific sub-compartment of the ER. These results suggest that MCF-7 resistance to ER stress-induced apoptosis is partially mediated by the expression level of calnexin which in turn controls its sub-cellular localization, and its association with Bap31. These data may delineate a resistance mechanism to the ER stress-induced intrinsic apoptotic pathway.

Proteomic analysis of tyrosine phosphorylation during human liver transplantation

Background

Ischemia-reperfusion (I/R) causes a dramatic reprogramming of cell metabolism during liver transplantation and can be linked to an alteration of the phosphorylation level of several cellular proteins. Over the past two decades, it became clear that tyrosine phosphorylation plays a pivotal role in a variety of important signalling pathways and was linked to a wide spectrum of diseases. Functional profiling of the tyrosine phosphoproteome during liver transplantation is therefore of great biological significance and is likely to lead to the identification of novel targets for drug discovery and provide a basis for novel therapeutic strategies.

Results

Using liver biopsies collected during the early phases of organ procurement and transplantation, we aimed at characterizing the global patterns of tyrosine phosphorylation during hepatic I/R. A proteomic approach, based on the purification of tyrosine phosphorylated proteins followed by their identification using mass spectrometry, allowed us to identify Nck-1, a SH₂/SH₃ adaptor, as a potential regulator of I/R injury. Using immunoblot, cell fractionation and immunohistochemistry, we demonstrate that Nck-1 phosphorylation, expression and localization were affected in liver tissue upon I/R. In addition, mass spectrometry identification of Nck-1 binding partners during the course of the transplantation also suggested a dynamic interaction between Nck-1 and actin during I/R.

Conclusion

Taken together, our data suggest that Nck-1 may play a role in I/R-induced actin reorganization, which was previously reported to be detrimental for the hepatocytes of the transplanted graft. Nck-1 could therefore represent a target of choice for the design of new organ preservation strategies, which could consequently help to reduce post-reperfusion liver damages and improve transplantation outcomes.

Multifaceted role of Rho proteins in angiogenesis

The Rho family of GTPases is part of the Ras superfamily. The Rho, Rac, and Cdc42 members of the family are present in mammalian cells and have been the subject of attention of researchers due to their vast spectrum of functions. Rac 1, Cdc42, and RhoA are well-known for their role in the regulation of the actin cytoskeleton in promoting the formation of lamellipodia, filopodia, and stress fibers, respectively. The Rho proteins also participate in the control of cell growth, motility, cell-cell adhesions, morphogenesis, cytoskeletal dynamics, and cellular trafficking. The mechanisms for eliciting these functions have become clearer during the last decade. Concordant with their roles in multiple processes of cellular control, the Rho proteins have been shown to be involved in tumor growth, progression, metastasis, and now angiogenesis.

p66SHC: the apoptotic side of Shc proteins

Initially identified as components of the signaling pathways triggered by receptor tyrosine kinases and leading to Ras activation, Shc proteins have been more recently implicated in the regulation of signals controlling not only cell proliferation, but also cell survival and apoptosis. Here we briefly review the current understanding of Shc proteins as promoters of apoptosis. Specifically, we focus on the 66 kDa isoform of ShcA, whose paramount importance in the regulation of oxidative stress responses leading to cell apoptosis and ageing has been by now firmly established.

Biochemical clustering of monomeric GTPases of the Ras superfamily

To date phylogeny has been used to compare entire families of proteins based on their nucleotide or amino acid sequence. Here we developed a novel analytical platform allowing a systematic comparison of protein families based on their biochemical properties. This approach was validated on the Rho subfamily of GTPases. We used two high throughput methods, referred to as AlphaScreen and FlashPlate, to measure nucleotide binding capacity, exchange, and hydrolysis activities of small monomeric GTPases. These two technologies have the characteristics to be very sensitive and to allow homogenous and high throughput assays. To analyze and integrate the data obtained, we developed an algorithm that allows the classification of GTPases according to their enzymatic activities. Integration and hierarchical clustering of these results revealed unexpected features of the small Rho GTPases when compared with primary sequence-based trees. Hence we propose a novel phylobiochemical classification of the Ras superfamily of GTPases.

Fibroblast growth factors regulate prolactin transcription via an atypical Rac-dependent signaling pathway

Fibroblast growth factors (FGFs) play a critical role in pituitary development and in pituitary tumor formation and progression. We have previously characterized FGF signal transduction and regulation of the tissue-specific rat prolactin (rPRL) promoter in GH4 pituitary cells. FGF induction of rPRL transcription is independent of Ras, but mediated by a protein kinase C-delta (PKCdelta)-dependent activation of MAPK (ERK). Here we demonstrate a functional role for the Rho family monomeric G protein, Rac1, in FGF regulation of PRL gene expression via an atypical signaling pathway. Expression of dominant negative Rac, but not RhoA or Cdc42, selectively inhibited FGF-induced rPRL promoter activity. Moreover, expression of dominant negative Rac also attenuated FGF-2 and FGF-4 stimulation of MAPK (ERK). However, in contrast to other Rac-dependent signaling pathways, FGF activation of rPRL promoter activity was independent of the c-Jun N-terminal kinase (JNK) and phosphoinositide 3-kinase/Akt cascades. FGFs failed to activate JNK1 or JNK2, and expression of dominant negative JNK or Akt constructs did not block FGF-induced PRL transcription. Consistent with the role of PKCdelta in FGF regulation of PRL gene expression, activation of the rPRL promoter was blocked by an inhibitor of phospholipase Cgamma (PLCgamma) activity. FGF treatment also induced rapid tyrosine phosphorylation of PLCgamma in a Rac-dependent manner. These results suggest that FGF-2 and FGF-4 activate PRL gene expression via a novel Rac1, PLCgamma, PKCdelta, and ERK cascade, independent of phosphoinositol-3-kinase and JNK.

An endogenous inhibitor of focal adhesion kinase blocks Rac1/JNK but not Ras/ERK-dependent signaling in vascular smooth muscle cells

Humoral factors and extracellular matrix are critical co-regulators of smooth muscle cell (SMC) migration and proliferation. We reported previously that focal adhesion kinase (FAK)-related non-kinase (FRNK) is expressed selectively in SMC and can inhibit platelet-derived growth factor BB homodimer (PDGF-BB)-induced proliferation and migration of SMC by attenuating FAK activity. The goal of the current studies was to identify the mechanism by which FAK/FRNK regulates SMC growth and migration in response to diverse mitogenic signals. Transient overexpression of FRNK in SMC attenuated autophosphorylation of FAK at Tyr-397, reduced Src family-dependent tyrosine phosphorylation of FAK at Tyr-576, Tyr-577, and Tyr-881, and reduced phosphorylation of the FAK/Src substrates Cas and paxillin. However, FRNK expression did not alter the magnitude or dynamics of ERK activation induced by PDGF-BB or angiotensin II. Instead, FRNK expression markedly attenuated PDGF-BB-, angiotensin II-, and integrin-stimulated Rac1 activity and attenuates downstream signaling to JNK. Importantly, constitutively active Rac1 rescued the proliferation defects in FRNK expressing cells. Based on these observations, we hypothesize that FAK activation is required to integrate integrin signals with those from receptor tyrosine kinases and G protein-coupled receptors through downstream activation of Rac1 and that in SMC, FRNK may control proliferation and migration by buffering FAK-dependent Rac1 activation.

Functional proteomics of breast cancer for signal pathway profiling and target discovery

The near completion of human genome sequencing and the introduction of mass spectrometry combined with advanced bioinformatics for protein identification have led to the emergence of proteomics as a powerful tool for characterizing new markers and therapeutic targets. Breast cancer proteomics has already identified proteins of potential clinical interest, such as the molecular chaperone 14-3-3 sigma and the heat shock protein HSP90, and technological innovations such as large scale and high throughput analysis are now driving the field. Methods in functional proteomics have also been developed to study the intracellular signaling pathways that underlie the development of breast cancer cells. As illustrated by fibroblast growth factor-2 and the H19 noncoding oncogenic mRNA, proteomics is a pertinent approach to identify signaling proteins and to decipher the complex signaling circuitry involved in tumor growth and metastasis. Together with genomics, proteomics is now providing a way to define molecular processes involved in breast carcinogenesis and to identify new therapeutic targets. The next challenge will be the introduction of proteomics as a tool for the clinic, for the establishment of diagnosis, prognosis, and the monitoring of treatment; however, this ambitious goal still requires further technological progress in the field.

Growth signaling in breast cancer cells: outcomes and promises of proteomics

Methods in functional proteomics are now used to study the intracellular signaling pathways that underlie the development of breast cancer. As shown with fibroblast growth factor-2, the oncogenic/non-coding mRNA H19 and 14-3-3 proteins, proteomics is a powerful approach to identify signaling proteins and to decipher the complex signaling circuitry involved in growth of breast cancer cells. Together with genomics, proteomics is now providing a way to define molecular processes involved in breast cancerogenesis and to identify new therapeutic targets.

A novel role for farnesyl pyrophosphate synthase in fibroblast growth factor-mediated signal transduction

Farnesyl pyrophosphate synthase (FPPS) catalyses the formation of a key cellular intermediate in isoprenoid metabolic pathways. Here we describe a novel role for this enzyme in fibroblast growth factor (FGF)-mediated signalling. We demonstrate the binding of FPPS to FGF receptors (FGFRs) using the yeast two-hybrid assay, pull-down assays and co-immunoprecipitation. The interaction between FPPS and FGFR is regulated by the cellular metabolic state and by treatment with FGF-2. Overexpression of FPPS inhibits FGF-2-induced cell proliferation, accompanied by a failure of the FGF-2-mediated induction of cyclins D1 and E. Overexpression of FPPS in fibroblasts also promotes increased farnesylation of Ras, and temporally extends FGF-2-stimulated activation of the Ras/ERK (extracellular-signal-regulated kinase) cascade. These data suggest that, in addition to its role in isoprenoid biosynthesis, FPPS may function as a modulator of the cellular response to FGF treatment.

Proteomics of breast cancer: outcomes and prospects

Breast cancer is a major public health problem. The identification of new markers to differentiate neoplastic from the normal cells, more thorough understanding of different stages of the pathology, as well as the definition of new therapeutic targets, are all of critical importance. With the completion of human genome sequencing and the introduction of mass spectrometry, combined with protein identification via advanced bioinformatics, proteomics has emerged as a valuable tool for the discovery of new molecular markers. New methods in functional proteomics have also been developed to study the intracellular signaling pathways that underline the development of breast cancer. As illustrated with the examples of fibroblast growth factor-2 and H19, an oncogenic, noncoding mRNA, proteomics have become a powerful approach for deciphering the complex signaling circuitry involved in tumor growth. Breast cancer proteomics have already identified proteins of potential clinical interest (such as the molecular chaperone 14-3-3 sigma) and technological innovations in large scale/high throughput analysis are now ushering in new prospects.

FGF-2 and TPA induce matrix metalloproteinase-9 secretion in MCF-7 cells through PKC activation of the Ras/ERK pathway

Matrix metalloproteinases (MMPs) play an important role in cancer metastasis. Here, we investigated the effect of fibroblast growth factor-2 (FGF-2) and 12-O-tetradecanoylphorbol-13-acetate (TPA) on the secretion of type IV collagenases (MMP-2, MMP-9) in breast cancer MCF-7 cells. As shown by gelatin zymography, both FGF-2 and TPA stimulated the secretion of MMP-9 in MCF-7 cells while they did not change the level of MMP-2 secretion. Signaling cascade studies indicated that both FGF-2 and TPA induced Ras activation, c-Raf phosphorylation, mitogen-activated protein kinase/ERK kinase (MEK(1/2)) phosphorylation, and extracellular signal-regulated kinase (ERK(1/2)) phosphorylation. The FGF-2- and TPA-induced MMP-9 secretion was significantly inhibited by transient transfection of MCF-7 cells with dominant negative Ras (Ras-N17) and by treatment with MEK(1/2) inhibitor PD98059. A pan-protein kinase C (PKC) inhibitor, GF109203X, was found to totally abolish the FGF-2- and TPA-induced MMP-9 secretion and ERK(1/2) phosphorylation. Use of isoform-specific PKC inhibitors such as Rotllerin and Gö6976 suggested, moreover, that the PKC-delta isoform is a likely component of FGF-2 and TPA trophic signaling. These results demonstrated that FGF-2 and TPA induce MMP-9 secretion in MCF-7 cells mainly through PKC-dependent activation of the Ras/ERK(1/2) signaling pathway.

Mesodermal patterning defect in mice lacking the Ste20 NCK interacting kinase (NIK)

We have previously shown that the Drosophila Ste20 kinase encoded by misshapen (msn) is an essential gene in Drosophila development. msn function is required to activate the Drosophila c-Jun N-terminal kinase (JNK), basket (Bsk), to promote dorsal closure of the Drosophila embryo. Later in development, msn expression is required in photoreceptors in order for their axons to project normally. A mammalian homolog of msn, the NCK-interacting kinase (NIK) (recently renamed to mitogen-activated protein kinase kinase kinase kinase 4; Map4k4), has been shown to activate JNK and to bind the SH3 domains of the SH2/SH3 adapter NCK. To determine whether NIK also plays an essential role in mammalian development, we created mice deficient in NIK by homologous recombination at the Nik gene. Nik(−/−) mice die postgastrulation between embryonic day (E) 9.5 and E10.5. The most striking phenotype in Nik(−/−) embryos is the failure of mesodermal and endodermal cells that arise from the anterior end of the primitive streak (PS) to migrate to their correct location. As a result Nik(−/−)embryos fail to develop somites or a hindgut and are truncated posteriorly. Interestingly, chimeric analysis demonstrated that NIK has a cell nonautonomous function in stimulating migration of presomitic mesodermal cells away from the PS and a second cell autonomous function in stimulating the differentiation of presomitic mesoderm into dermomyotome. These findings indicate that despite the large number of Ste20 kinases in mammalian cells, members of this family play essential nonredundant function in regulating specific signaling pathways. In addition, these studies provide evidence that the signaling pathways regulated by these kinases are diverse and not limited to the activation of JNK because mesodermal and somite development are not perturbed in JNK1-, and JNK2-deficient mice.

Overexpression of FGF-2 increases cardiac myocyte viability after injury in isolated mouse hearts

We generated transgenic (TG) mice overexpressing fibroblast growth factor (FGF)-2 protein (22- to 34-fold) in the heart. Chronic FGF-2 overexpression revealed no significant effect on heart weight-to-body weight ratio or expression of cardiac differentiation markers. There was, however, a significant 20% increase in capillary density. Although there was no change in FGF receptor-1 expression, relative levels of phosphorylated c-Jun NH(2)-terminal kinase and p38 kinase as well as of membrane-associated protein kinase C (PKC)-alpha and total PKC-epsilon were increased in FGF-2-TG mouse hearts. An isolated mouse heart model of ischemia-reperfusion injury was used to assess the potential of increased endogenous FGF-2 for cardioprotection. A significant 34-45% increase in myocyte viability, reflected in a decrease in lactate dehydrogenase released into the perfusate, was observed in FGF-2 overexpressing mice and non-TG mice treated exogenously with FGF-2. In conclusion, FGF-2 overexpression causes augmentation of signal transduction pathways and increased resistance to ischemic injury. Thus, stimulation of endogenous FGF-2 expression offers a potential mechanism to enhance cardioprotection.

Proteomic detection of changes in protein synthesis induced by fibroblast growth factor-2 in MCF-7 human breast cancer cells

Fibroblast growth factor-2 (FGF-2) is a potent regulator of breast cancer cell growth through stimulation of tyrosine kinase receptors and activation of the mitogen-activated protein kinase cascade. In the present study, we have investigated changes in protein synthesis induced by FGF-2 stimulation of the prototypic human breast cancer cell line MCF-7. Using high-resolution two-dimensional electrophoresis of (35)S amino acid metabolically labeled proteins and computerized analysis of 2D autoradiograms, we found that four proteins were up-regulated within the first 12 h of FGF-2 stimulation. Mass spectrometry analysis (MALDI-TOF and MS-MS) of tryptic fragments and database searches allowed the identification of these FGF-2-regulated proteins as the heat shock proteins HSP90 and HSP70, the proliferating cell nuclear antigen (PCNA), and the transcriptionaly controlled tumor protein (TCTP). We then analyzed the distribution of these proteins in various cancerous and normal breast epithelial cells. Interestingly, the four FGF-2-regulated proteins were found to be constitutively up-regulated in ras-transfected MCF-7 cells, indicating their relevance to the up-regulation of cellular proliferation. Moreover, HSP90 and PCNA were found at higher levels in cancerous cells than in normal cells. The role of HSP90 was further investigated using the specific inhibitor geldanamycin. We showed that the functionality of HSP90 is strictly required in order to obtain FGF-2 mitogenic stimulation in MCF-7 cells, indicating the crucial role played by this molecular chaperone in the control of breast cancer cell growth. Finally, these results show that proteomic analysis is a valuable method for identifying potential markers or therapeutic targets related to cancer growth.

The mitogenic signaling pathway for fibroblast growth factor-2 involves the tyrosine phosphorylation of cyclin D2 in MCF-7 human breast cancer cells

Fibroblast growth factor-2 (FGF-2) is mitogenic for the human breast cancer cell line MCF-7; here we investigate some of the signaling pathways subserving this activity. FGF-2 stimulation of MCF-7 cells resulted in a global increase of intracellular tyrosine phosphorylation of proteins, particularly FGF receptor substrate-2, the protooncogene product Src and the mitogen-activated protein kinase (MAP kinase) cascade. A major increase in the tyrosine phosphorylation of a 30-kDa protein species was also found. This protein was identified as cyclin D2 by mass spectrometry after trypsin digestion. Immunoprecipitation of cyclin D2 and immunoblotting with anti-phosphotyrosine antibodies confirmed that the tyrosine phosphorylation of cyclin D2 was indeed induced by FGF-2 stimulation. In addition, pharmacological inhibition of Src (with herbimycin A and PP2), and of the MAP kinase cascade (with PD98059), confirmed that Src activity is required for the FGF-2-induced phosphorylation of cyclin D2 whereas MAP kinase activity is not. Thus, tyrosine phosphorylation of cyclin D2 may be a key regulatory target for FGF-2 signaling.

Vitamin D induced up-regulation of keratinocyte growth factor (FGF-7/KGF) in MCF-7 human breast cancer cells

Keratinocyte growth factor (FGF-7/KGF) is a secreted member of the fibroblast growth factor family, which functions primarily as an important paracrine mediator of cell growth and differentiation. Inhibitory pathways of vitamin D may also involve participation of some growth factors. To determine whether vitamin D may play a role in the expression of FGF-7, we investigated FGF-7 expression in human breast cancer cells treated with 1,25-dihydroxyvitamin D3, which inhibited the growth of the cells. By means of cDNA microarray, RT-PCR, and Western blot analysis, we have shown an increase in expression of FGF-7 on both mRNA and protein levels after vitamin D exposure. This is the first demonstration of vitamin D regulation of FGF-7 expression and its possible involvement in mediating growth and differentiation by vitamin D.