The mitogenic signaling pathway of fibroblast growth factor is not mediated through polyphosphoinositide hydrolysis and protein kinase C activation in hamster fibroblasts

Mesenchymal stem cell-conditioned media recovers lung fibroblasts from cigarette smoke-induced damage

Cigarette smoking causes apoptotic death, senescence, and impairment of repair functions in lung fibroblasts, which maintain the integrity of alveolar structure by producing extracellular matrix (ECM) proteins. Therefore, recovery of lung fibroblasts from cigarette smoke-induced damage may be crucial in regeneration of emphysematous lung resulting from degradation of ECM proteins and subsequent loss of alveolar cells. Recently, we reported that bone marrow-derived mesenchymal stem cell-conditioned media (MSC-CM) led to angiogenesis and regeneration of lung damaged by cigarette smoke. In this study, to further investigate reparative mechanisms for MSC-CM-mediated lung repair, we attempted to determine whether MSC-CM can recover lung fibroblasts from cigarette smoke-induced damage. In lung fibroblasts exposed to cigarette smoke extract (CSE), MSC-CM, not only inhibited apoptotic death, but also induced cell proliferation and reversed CSE-induced changes in the levels of caspase-3, p53, p21, p27, Akt, and p-Akt. MSC-CM also restored expression of ECM proteins and collagen gel contraction while suppressing CSE-induced expression of cyclooxygenase-2 and microsomal PGE(2) synthase-2. The CSE-opposing effects of MSC-CM on cell fate, expression of ECM proteins, and collagen gel contraction were partially inhibited by LY294002, a phosphatidylinositol 3-kinase (PI3K) inhibitor. In rats, MSC-CM administration also resulted in elevation of p-Akt and restored proliferation of lung fibroblasts, which was suppressed by exposure to cigarette smoke. Taken together, these data suggest that MSC-CM may recover lung fibroblasts from cigarette smoke-induced damage, possibly through inhibition of apoptosis, induction of proliferation, and restoration of lung fibroblast repair function, which are mediated in part by the PI3K/Akt pathway.

Modeling species-specific diacylglycerol dynamics in the RAW 264.7 macrophage

A mathematical model of the G protein signaling pathway in RAW 264.7 macrophages downstream of P2Y(6) receptors activated by the ubiquitous signaling nucleotide uridine 5'-diphosphate is developed. The model, which is based on time-course measurements of inositol trisphosphate, cytosolic calcium, and diacylglycerol, focuses particularly on differential dynamics of multiple chemical species of diacylglycerol. When using the canonical pathway representation, the model predicted that key interactions were missing from the current network structure. Indeed, the model suggested that accurate depiction of experimental observations required an additional branch to the signaling pathway. An intracellular pool of diacylglycerol is immediately phosphorylated upon stimulation of an extracellular receptor for uridine 5'-diphosphate and subsequently used to aid replenishment of phosphatidylinositol. As a result of sensitivity analysis of the model parameters, key predictions can be made regarding which of these parameters are the most sensitive to perturbations and are therefore most responsible for output uncertainty.

Quantification of diacylglycerol species from cellular extracts by electrospray ionization mass spectrometry using a linear regression algorithm

Diacylglycerols (DAGs) play significant roles in both intermediate metabolism and signal transduction. These lipid species are second messengers involved in modulating a plethora of cellular processes. Evaluation of DAG species concentrations has been hampered by the lack of a reliable method for molecular species analysis within a complex mixture of cellular lipids. We describe a new method for quantitative analysis of DAG species from complex biological extracts based on positive mode electrospray ionization mass spectrometry without prior derivatization. Quantification is achieved using internal standards and calibration curves constructed by spiking cell extracts with different concentrations of DAG species containing various acyl chain lengths and degrees of unsaturation. The new mass spectral data processing algorithm incorporates a multiple linear regression model including a factor accountable for possible interactions between experimental preparations and the slope of the curve for the standards, allowing the examinations of the effects of sample origin conditions (such as cell types, phenotypes, etc.) and instrument variability on this slope. Internal standards provide a basis for quantification of 28 DAG molecular species detected in RAW 264.7 cells after stimulation of a G-protein coupled receptor with platelet activating factor. This method displays excellent reproducibility over the established range of concentrations with variations of < or =10% and is highly sensitive with a detection limit of 0.1-0.4 pmol/microL depending upon acyl chain composition. We have shown differential effects on various DAGs in response to a ligand which illustrates the importance of examining lipids at the molecular species level rather than as a single homogeneous entity.

Differences of Cell Growth and Cell Cycle Regulators Induced by Basic Fibroblast Growth Factor Between Nifedipine Responders and Non-responders

Differences of cell proliferation, cell cycle, and G(1)/S transition regulatory proteins of gingival fibroblasts derived from nifedipine-reactive patient (NIFr) and nifedipine-non-reactive patient (NIFn) in the presence of basic fibroblast growth factor (bFGF) were investigated to elucidate the mechanism of gingival overgrowth associated with nifedipine, one of the Ca(2+)-channel blockers. The proliferation rate of NIFr cells in the presence of bFGF significantly increased than NIFn cells. The proportion of NIFr cells that had undergone progression to the S and G(2)/M phases from the G(0)/G(1) phase significantly increased compared to that in NIFn cells. Increases of pRB (Ser807/811), pCDK2 (Thr160), CDK2, and cyclin E protein levels in NIFr cells were greater than those in NIFn cells. The elevations of pRB (Ser780), RB, and cyclin A protein levels in NIFr cells did not differ from those of NIFn cells. The growth of NIFr cells was greater than that of NIFn cells as a result of the active G(1)/S transition of NIFr cells, as assessed by the increments of cyclin E, pCDK2, and pRB (ser807/811) protein in NIFr cells.

Angiogenic therapy for the chronically ischemic lower limb in a rabbit model

The purpose of this study was to evaluate the long-term effectiveness of basic fibroblast growth factor (bFGF) in achieving neovascularization following ischemia from arterial ligation and to determine an optimal dosage level. We used an Ameroid constrictor to produce progressive occlusion of the left femoral artery of rabbits. At 2 weeks, the rabbits were randomized to receive intravenous injection of vehicle (group A, n = 15); 3 microg/kg/day bFGF (group B, n = 12); 10 microg/kg/day bFGF (group C, n = 12); or 16 microg/kg/day bFGF (group D, n = 15) for 3 days. At 1 to 37 days after surgery, we assessed limb neovascularization by transcutaneous oximetry (TCPO(2)), angiography, heart rate, arterial pressure, peripheral vascular resistance (PRU), and muscle blood flow (MBF) during steady-state intra-arterial infusion of saline (basal), acetylcholine, papaverine, or serotonin under anesthesia and capillary density (cap/mm(2)) and capillary per muscle fiber ratio (cap/F). Groups B and C showed significantly greater change in TCPO(2) over time than groups A and D (P < 0.0001). Group D showed the lowest TCPO(2) values from days 14 to 37 and group C the highest. Groups B and C showed a higher number of vessels filled with contrast agent than groups A and D (P < 0.0001). Calf cap/mm(2) and cap/F were significantly higher in groups B and C than groups A and D (P < 0.0001). Calf basal MBF values were higher in groups B and C than in groups A and D, but were not statistically significant. Group D showed the highest level in basal PRU. There were no significant differences in heart rate or blood pressure among the groups. These results show (1) treatment with bFGF has no adverse hemodynamic effects, (2) bFGF enhances angiogenesis and circulation at moderate doses, and these effects persist at least several weeks, and (3) high doses of bFGF may inhibit angiogenesis and collateral circulation.

Basic fibroblast growth factor-stimulated arachidonic acid release in rat pancreatic acini: sequential action of tyrosine kinase, phospholipase C, protein kinase C and diacylglycerol lipase

This study was performed to evaluate the effect of human recombinant basic fibroblast growth factor on arachidonic acid release from rat pancreatic acini and to determine the cellular mechanism involved. From enzymatic assays, basic fibroblast growth factor did not significantly stimulate phospholipase A2 activity, whereas it significantly increased diacylglycerol lipase activity. Validity of phospholipase A2 or diacylglycerol lipase inhibitors was confirmed by their ability to inhibit phospholipase A2 or diacylglycerol lipase activities. Basic fibroblast growth factor increased intracellular accumulation and extracellular release of arachidonic acid from metabolically labelled acinar cells in a concentration- and time-dependent manner. This effect was maximal with 50 pM basic fibroblast growth factor and became significant after a 5-min incubation period. The protein tyrosine kinase inhibitor, 0.5 mM genistein, inhibited arachidonic acid release in basic fibroblast growth factor-stimulated acini, whereas 100 microM vanadate, a protein tyrosine phosphatase inhibitor, enhanced arachidonic acid release. Two phospholipase A2 inhibitors, mepacrine and aristolochic acid, failed to attenuate basic fibroblast growth factor-stimulated arachidonic acid release. A diacylglycerol lipase inhibitor RHC 80267 at 150 microM and 50 microM completely inhibited 50 pM basic fibroblast growth factor-induced intracellular accumulation and extracellular release of arachidonic acid, respectively. Furthermore, basic fibroblast growth factor stimulated arachidonic acid release was also inhibited by 10 microM U73122 and by 100 nM staurosporine, phospholipase C and protein kinase C respective inhibitors. Wortmannin, an inhibitor of basic fibroblast growth factor-stimulated phospholipase D, did not affect arachidonic acid release. 100 nM 4 beta-phorbol 12-myristate 13-acetate also increased arachidonic acid release, an effect also inhibited by staurosporine. Taken together, these data demonstrate activation of diacylglycerol lipase and arachidonic acid release in pancreatic acini upon stimulation by basic fibroblast growth factor, and strongly indicate that arachidonic acid release in response to basic fibroblast growth factor depends upon the sequential action of tyrosine kinase, phospholipase C, protein kinase C and diacylglycerol lipase but not from phospholipase A2 not phospholipase D activation.

Interleukin-1 and endothelin stimulate distinct species of diglycerides that differentially regulate protein kinase C in mesangial cells

Diglycerides are phospholipid-derived second messengers that serve as cofactors for protein kinase C activation. We have previously shown that, in rat glomerular mesangial cells, the cytokine, interleukin-1 alpha, and the vasoactive peptide, endothelin, generate diglycerides from unique phospholipid precursors. However, neither the molecular species of these diglycerides nor their biological actions were determined. It is now hypothesized that interleukin-1- and endothelin-treated mesangial cells form distinct molecular species of diglycerides which may serve different roles as intracellular signaling molecules. Diglyceride molecular species were resolved and quantified by TLC and high performance liquid chromatography as diglyceride-[14C]acetate derivatives. Endothelin stimulates predominantly ester-linked species (diacylglycerols) in contrast to interleukin-1 which stimulates only ether-linked species (alkyl, acyl- and alkenyl,acylglycerols). In support of these data, interleukin-1-treated mesangial cells hydrolyze ethanolamine plasmalogens, vinyl ether-linked phospholipids. It has been reported that ether-linked, in contrast to ester-linked, diglyceride species do not activate protein kinase C activity. Thus, we next assessed membrane protein kinase C activity in endothelin- or interleukin-1-treated mesangial cells. Even though interleukin-1 has no effect upon basal protein kinase C activity, this cytokine, through the formation of ether-linked diglyceride second messengers, inhibits endothelin, platelet-activating factor, or arginine vasopressin-stimulated protein kinase C activity. We further demonstrate that ester-linked diacylglycerols but not alkyl,acyl- or alkenyl,acylglycerols substitute for phorbol esters in a cell-free protein kinase C assay. In addition, alkenyl,acylglycerols inhibit diacylglycerol-stimulated immunoprecipitated protein kinase C alpha activity in vitro and total protein kinase C activity in permeabilized mesangial cells ex vivo. Taken together, these data suggest that interleukin-1-induced formation of ether-linked diglycerides may physiologically serve to down-regulate receptor-mediated protein kinase C activity and that individual molecular species of diglycerides may serve different roles as intracellular signaling molecules.

EGF-induced increase in diacylglycerol, choline release, and DNA synthesis is extracellular calcium dependent

Previous studies have demonstrated a strict extracellular Ca2+ dependence for the G0 to G1 and G1 to S transition in growth factor-treated T51B rat liver cells that is associated with increased levels of protein kinase C activity. Consequently, we have examined these cells for changes in phospholipid-derived second messengers in response to epidermal growth factor (EGF) and thrombin in order to determine which signals are generated during the initiation of the G0 to G1 transition. Thrombin is coupled to a phosphoinositide hydrolyzing phospholipase C, as we have found a rapid Ca(2+)-independent increase in the levels of inositol 1,4,5-trisphosphate (Ins[1,4,5]P3), inositol 1,4-bisphosphate (Ins[1,4]P2), and inositol 4-monophosphate (Ins[4]P), as well as a concomitant, transient elevation in diacylglycerol. No changes in either intracellular or extracellular choline metabolites, or an increase in DNA synthesis, were found in response to thrombin. By contrast, treatment of T51B cells with EGF results in a slower, more prolonged extracellular Ca(2+)-dependent increase in both [3H]-glycerol radiolabeled diacyl-glycerol, and diacylglycerol mass, an increase in choline release into the extracellular medium, and eventually a substantial DNA synthesis. We were, however, unable to detect any changes in phosphatidylinositol (PtdIns) turnover, either by accumulation of inositol phosphates or by changes in phospholipids in response to EGF. These results indicate that DNA synthesis can readily occur in the absence of stimulated PtdIns turnover, and that PtdIns turnover is not sufficient in itself or necessary to induce DNA synthesis and is not necessary for a Ca(2+)-dependent increase in diacylglycerol. Moreover, we have demonstrated that the extracellular Ca(2+)-dependent increase in diacylglycerol levels in response to EGF is associated with an increase in extracellular choline release, which is indicative of an activation of a phosphatidylcholine-linked phospholipase D. These results suggest that diacylglycerol sources other than PtdIns's may be important in the extracellular Ca(2+)-dependent regulation of EGF-mediated cell replication.

Requirement for protein kinase C activation in basic fibroblast growth factor-induced human endothelial cell proliferation

The intracellular signaling mechanisms that mediate basic fibroblast growth factor (bFGF)-induced angiogenesis have not been fully identified. In particular, whether activation of the intracellular enzyme protein kinase C (PKC) is necessary or sufficient for bFGF-induced mitogenesis of human endothelial cells is not clear. Accordingly, the effect of bFGF stimulation on the Ca2+ increase and PKC activity of normal human endothelial cells (HEC) was studied, as was the effect of inhibition of PKC and the distribution of PKC isoenzymes in these cells. The addition of bFGF to cultured HEC increased overall PKC activity in the absence of an increase in intracellular Ca2+ and markedly stimulated their proliferation, as did the addition of PKC-activating phorbol esters. bFGF-induced proliferation was prevented by the PKC inhibitors chelerythrine and H-7 and by downregulation of PKC after prolonged incubation with phorbol esters. In contrast, these inhibitors did not prevent HEC proliferation induced by epidermal growth factor. Because of the failure of bFGF to increase Ca2+, we determined whether bFGF-induced proliferation could be mediated by novel or atypical PKC isoenzymes (which are not regulated by Ca2+). Investigation of the isoenzyme distribution of confluent and subconfluent HEC by immunoblotting, Northern transfer analysis, and polymerase chain reaction of reverse-transcribed RNA revealed the presence of several novel and atypical isoenzymes (PKC-delta, -eta, -theta, and -zeta) as well as small amounts of the conventional (Ca(2+)-regulated) isoenzymes PKC-alpha and -beta. Activation of PKC by bFGF, in the absence of an increase in intracellular Ca2+, suggests that one or more of these Ca(2+)-independent PKC isoenzymes are both necessary and sufficient for HEC proliferation after bFGF.

The mitogenic action of recombinant basic FGF in Swiss 3T3 cells is independent of early diradylglycerol production and downregulatable protein kinase C activity

In this study we have investigated the requirement for phosphoinositide metabolism, diradylglycerol (DG) production and protein kinase C (PKC) activation in recombinant basic fibroblast growth factor (rbFGF)-mediated reinitiation of DNA synthesis in Swiss 3T3 cells. We have assessed the involvement of PKC activation in rbFGF-induced DNA synthesis by two approaches; enzymic inhibition by H7 and down-regulation by prolonged phorbol-ester treatment. In both conditions we observed that rbFGF was able to sustain a significant component of its mitogenic response, therefore denying an exclusive role for the activation of downregulatable and H7-sensitive PKC isoforms in rbFGF-induced reinitiation of DNA synthesis. Moreover, we have found no evidence for diacylglycerol accumulation in response to rbFGF by 3T3 cells. In previous studies, we observed that rbFGF caused a moderate and slow accumulation of total inositol phosphates. This effect was significant only after a 60 min incubation. It is our contention that rbFGF, in our culture system, does not exert a direct effect on phosphoinositide metabolism.

Phospholipase D activation in fibroblast membranes by the alpha and beta isoforms of protein kinase C

The regulation of phosphatidylcholine-hydrolyzing phospholipase D (PLD) by protein kinase C (PRC) in membranes of Chinese hamster lung fibroblasts (CCL39) was studied using conventional PKC isoforms alpha, beta and gamma isolated from rat brain and recombinant PKC isoforms. Cells were incubated with [14C]choline to label endogenous phosphatidylcholine before membranes were prepared and assayed for release of [14C]choline. PKC alpha was the most potent activator of PLD, producing a maximal effect at approximately 0.1 microgram/ml. PKC beta also stimulated PLD but was less potent and less efficacious, whereas PKC gamma was ineffective. Stimulation required addition of a PKC activator, but the isoform specificity was the same whether phorbol 12-myristate 13-acetate (PMA) or Ca2+ was used. Recombinant Ca(2+)-independent PKC isoforms delta, epsilon, and zeta failed to stimulate PLD, but recombinant PKC beta 1 stimulated PLD in a manner similar to the purified brain PKC beta. Immunoblot analysis of the soluble fraction of CCL 39 fibroblasts detected only the alpha and zeta isoforms of PKC. The results suggest that PKC alpha and beta are activators of PLD and that PKC alpha is responsible for the activation in these fibroblasts.

Stimulation of arachidonic-acid release from Swiss 3T3 cells by recombinant basic fibroblast growth factor: independence from phosphoinositide turnover

In this study we have attempted to characterize the mechanism of recombinant bovine basic fibroblast growth factor (rbFGF)-induced release of arachidonic acid from prelabelled Swiss 3T3 fibroblasts. Recombinant bFGF caused the release of [3H]arachidonic acid from metabolically labelled cells in a dose- and time-dependent manner. This effect was maximal with 10 ng rbFGF/ml and became significant after a 30-min incubation. Although rbFGF was able to cause a modest increase in total inositol phosphate accumulation, an examination of the time-course of the latter effect revealed that enhanced [3H]arachidonic-acid release could not have been derived from phosphoinositide metabolism. Evidence suggesting that rbFGF-induced release of [3H]arachidonic acid was being mediated via a PLA2 pathway was obtained by pharmacological antagonism using mepacrine, a putative PLA2 inhibitor. Moreover, treatment of cells with neomycin failed to attenuate rbFGF-mediated release of [3H]arachidonic acid. Chelation of extracellular calcium by EGTA was found to abrogate rbFGF-induced liberation of [3H]arachidonic add. Down-regulation of protein kinase C (PKC) by prolonged treatment of cells with the phorbol ester, PMA, was observed to have no effect on the action of rbFGF on [3H]arachidonic add release from Swiss 3T3 fibroblasts. While rbFGF was found to cause the indomethacin-sensitive production of prostaglandin E2 (PGE2) in a dose-dependent manner, this effect was independent of rbFGF-induced reinitiation of DNA synthesis. Clearly, the effect of rbFGF on cellular DNA synthesis was being mediated independently of PGE2 biosynthesis. We discuss the potential importance of the PLA2-signalling pathway in the mechanism of action of fibroblast growth factors.

Involvement of Ca(2+)-calmodulin in platelet-derived growth factor-, fibroblast growth factor-, and insulin-induced ornithine decarboxylase in NIH-3T3 cells

Ornithine decarboxylase (ODC) was induced by platelet-derived growth factor (PDGF), fibroblast growth factor (FGF), and insulin at doses ranging from 0.125 to 0.5 U/mL, 25 to 500 ng/mL, and 10(-8) to 10(-7) mol/L, respectively, in NIH-3T3 cells. The induction of ODC reached a plateau approximately 4 to 6 hours after addition of each mitogen. PDGF exerted a synergistic action with 10(-7) mol/L insulin until the concentration of PDGF reached 0.5 U/mL and exerted an additive action at concentrations greater than 0.5 U/mL. FGF also accelerated ODC induction by insulin (10(-7) mol/L) synergistically when it was added at doses up to 500 ng/mL. PDGF added to the intact monolayer cells caused a spike-and-plateau increase in cytosolic Ca2+ concentration ([Ca2+]i); the spike was independent of extracellular Ca2+, whereas the plateau formation was dependent on extracellular Ca2+. On the other hand, FGF caused a plateau-like increase in [Ca2+]i, exclusively dependent on extracellular Ca2+. Insulin did not affect [Ca2+]i in NIH-3T3 cells. Trifluoperazine (15 to 30 mumol/L) inhibited the induction of ODC by PDGF and FGF, but did not inhibit the effect of insulin to induce ODC. N-(6-aminohexyl)-5-chloro-1-Naphthalenesulfonamide ([W-7] 30 to 40 mumol/L) showed a more profound suppressive effect on ODC induced by PDGF and FGF than N-(6-aminohexyl)-naphthalenesulfonamide (W-5) did. There was no difference between the effects of W-7 and W-5 on ODC induction by insulin.(ABSTRACT TRUNCATED AT 250 WORDS)

Basic FGF activates phospholipase D in endothelial cells in the absence of inositol-lipid hydrolysis

In the absence of inositol-lipid hydrolysis, mitogenic concentrations of basic fibroblast growth factor (bFGF) stimulated phosphatidylbutanol formation in the presence of butan-1-ol in [3H]myristate-labeled human umbilical vascular endothelial (HUVE) cells, indicating that the fibroblast growth factor receptor was able to couple to the activation of phospholipase D (PLD). The ability of bFGF and 12-O-tetradecanoylphorbol-13-acetate (TPA) to stimulate PLD activity was completely abolished in cells pretreated with 400 nM TPA for 48 h to downregulate protein kinase C (PKC). bFGF-stimulated PLD activity was inhibited by genistein (5 microM; P < 0.02) and the PKC inhibitor 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7, 5 microM; P < 0.001) as well as by the removal of calcium from extracellular environment. bFGF induced DNA synthesis in a dose-dependent manner, and pretreatment of cells with H-7 inhibited the mitogenic activity of bFGF. These results indicate that activation of PKC is responsible for bFGF-induced PLD activation and the mitogenic activity of bFGF in HUVE cells. A coupled PLD/3-sn-phosphatidate phosphohydrolase pathway may play a role in the regulation of endothelial cell proliferation.

Colocalization of acidic and basic fibroblast growth factor (FGF) in human placenta and the cellular effects of bFGF in trophoblast cell line JEG-3

The placenta undergoes extensive angiogenesis and cellular proliferation to establish adequate blood supply to the fetus. The aim of this study was to compare and contrast the immunolocalization of acidic and basic fibroblast growth factor (FGF) in both first trimester and term placenta and gestational decidua. Human choriocarcinoma cell line JEG-3 were employed as a model of cytotrophoblast and the effect of basic FGF on cell proliferation and phospholipase C and D activation investigated. Basic FGF-immunoreactivity (IR) was detected in or around cytotrophoblast cells and in extravillous trophoblast in first trimester placenta by immunohistochemistry using primary polyclonal rabbit antibodies. Identical staining patterns were produced by acidic FGF antibodies indicating colocalization of acidic FGF and basic FGF. At term, weaker and more diffuse staining was seen in the syncytiotrophoblast surrounding the placenta villi and strong staining was present in the smooth muscle cells of mid and large size placental vessels and in some endothelial cells. Endothelial cells and extravillous trophoblast stained strongly within the decidua at first trimester, whereas the glandular epithelium was weakly stained. Basic FGF induced [3H]thymidine incorporation in JEG-3 cells in a dose dependent manner and caused an increase in inosital phosphate accumulation in cells pre-labelled with myo-[3H]inosital at similar concentrations, suggesting a role of phospholipase C in JEG-3 cell proliferation. However, basic FGF failed to stimulate phospholipase D activity in cells pre-labelled with [3H]myristic acid. The detection of acid FGF and basic FGF on both maternal and fetal side of the placenta during early pregnancy suggests a role for FGF in angiogenesis, whereas localisation of the growth factor at term, when extensive angiogenesis has diminished, would indicate that FGF may be associated with more differentiated functions of the trophoblast. The nuclear localization of basic FGF in dividing but not non-dividing placental cells together with the effect of basic FGF on JEF-3 cells, strongly supports a role for basic FGF in cytotrophoblast proliferation in vivo.

Induction of phosphatidic acid by fibroblast growth factor in cultured baby hamster kidney fibroblasts

Basic fibroblast growth factor (bFGF/FGF-2) is a strong mitogenic inducer of cultured baby hamster kidney (BHK) cells. When cultured BHK cells were stimulated with FGF-2, phosphatidic acid (PA) was induced within 2 min, peaked at 5 min and gradually decreased. Phospholipase D (PLD) was also mitogenic for cultured BHK cells and this effect was mediated via PA. The possibility that PA induction by FGF-2 is an essential signaling step for BHK cell proliferation is discussed.

Basic fibroblast growth factor-induced increase in zif/268 and c-fos mRNA levels is Ca2+ dependent in primary cultures of hippocampal neurons

Basic fibroblast growth factor (bFGF) is present in the developing rat brain and has been shown to provide critical trophic support for hippocampal neurons in culture. The influence of bFGF on the expression of mRNAs encoding the transcription factors zif/268 and c-fos was studied in primary cultures of hippocampal neurons (derived from rat embryos) using reverse transcription-coupled PCR. In these cultures grown for 3 days in the absence of serum, bFGF causes a dramatic and transient increase in the levels of zif/268 and c-fos, within 15 and 30 min, respectively. A similar induction of these two early genes occurs following activation of protein kinase C (PKC). The bFGF-induced activation persists after PKC desensitization but is inhibited by chelation of intracellular Ca2+. These results suggest that in primary cultures of hippocampal neurons, bFGF induces the expression of immediate early genes through a pathway that requires Ca2+ mobilization.

Biphasic effect of basic fibroblast growth factor on 125I-human chorionic gonadotropin binding to cultured immature Leydig cells

The present studies examined the effects of basic fibroblast growth factor (bFGF or FGF-2) on 125I-human chorionic gonadotropin (hCG) binding to cultured immature rat Leydig cells. We found that low concentrations of bFGF (0.1-1.0 ng/ml) inhibited 125I-hCG binding to cultured immature Leydig cells in a dose- and time-dependent manner; however, this inhibition was reversed partially at higher bFGF concentrations (10-200 ng/ml). The decline in 125I-hCG binding by bFGF was due to a reduction in the number of binding sites per cell and not to a change in receptor affinity for the ligand. The inclusion of 10 micrograms/ml heparin (a concentration that is reported to block bFGF binding to heparan sulfate proteoglycans) with increasing bFGF concentrations had no effect on the inhibition of 125I-hCG binding by low bFGF concentrations, but completely blocked the secondary increase in binding by higher bFGF concentrations. In addition, neither varying heparin concentrations (0.1-25 micrograms/ml) nor insulin or insulin-like growth factor-I had any effect on the inhibition of 125I-hCG binding by 1 ng/ml bFGF. These studies suggest that receptor-mediated actions of bFGF (inhibition of hCG binding by low bFGF concentrations) on cultured immature Leydig cells are unaffected by heparin; however, the secondary increase in 125I-hCG binding observed with higher bFGF concentrations (mediated by bFGF binding to heparan sulfate proteoglycans) is blocked by heparin.

Modulation of the epidermal growth factor receptor by basic fibroblast growth factor

Treatment of Swiss 3T3 fibroblasts with basic fibroblast growth factor (bFGF) lead to a rapid reduction in epidermal growth factor (EGF) binding and a slower inhibition of EGF receptor autophosphorylation. The reduction in binding was due to a complete loss of the highest affinity EGF binding sites and a reduction in the lower affinity binding sites. Neither the inhibition of EGF binding nor the inhibition of EGF receptor autophosphorylation required protein kinase C. Treatment of cells with bFGF stimulated the phosphorylation of the EGF receptor, which persisted for several hours. The inhibition of EGF receptor autophosphorylation by bFGF was reduced in the presence of cycloheximide. However, cycloheximide had no effect on the reduction of EGF binding by bFGF. In contrast to these results with Swiss 3T3 fibroblasts, treatment of PC12 cells with bFGF lead to a reduction in EGF binding but no inhibition of EGF receptor autophosphorylation. Thus inhibition of EGF receptor autophosphorylation and inhibition of EGF binding can be uncoupled.

Negative regulation of mitogen-stimulated, anchorage-independent cell growth by a tumor-suppressor gene function

Immortal, nontumorigenic cell lines of Syrian hamster embryo (SHE) cells with different tumor-suppressing activity were isolated. Subclones from the parental cells were isolated that either had retained (supB+) or lost (supB-) the ability to suppress tumorigenicity after hybridization with tumor cells. The growth properties of these cells were studied to determine how this tumor-suppressor gene function influences cell growth. When the cells were grown on plastic, their growth properties were similar, and neither cell type grew in soft agar containing 10% serum, which supported the growth of tumorigenic cells. However, in agar supplemented with growth factors and 10% serum, supB- cells formed colonies whereas supB+ cells did not. Efficient growth (colony-forming efficiencies greater than 20%) of supB- cells was obtained in agar supplemented with serum and a combination of epidermal growth factor (EGF), platelet-derived growth factor (PDGF), and insulin (EPI) or with serum and basic fibroblast growth factor (bFGF). The effect of EPI and bFGF together was additive. supB+ cells failed to grow under any of these conditions, suggesting that the suppressor gene function blocked the growth response of the cells to multiple growth factors when the cells were suspended in agar. In SupB- cells, transforming growth factor-beta 1 and retinoic acid inhibited anchorage-independent growth response to EPI but not the growth response to bFGF. These observations are consistent with the hypothesis that bFGF stimulates the growth of supB- cells by a signal transduction pathway that differs from the pathway stimulated by EGF or PDGF. Thus, this suppressor gene function may regulate anchorage-independent growth at some common point in signal transduction for multiple mitogens.

Evidence for basic fibroblast growth factor receptors in cultured immature Leydig cells

Previous studies have shown that basic fibroblast growth factor (bFGF) can modulate basal and luteinizing hormone/human chorionic gonadotropin (LH/hCG)-stimulated Leydig cell functions. It has not been ascertained whether these actions are due to direct or indirect effects on Leydig cells. To resolve this question, a multi-step procedure was used to isolate highly-purified Leydig cells from immature rats. 125I-bFGF binding studies were performed on cultured cells. Scatchard analysis of the data indicated a single binding site with an apparent Kd of 82 pM and a binding capacity of approximately 2800 sites per cell. Both bFGF and acidic FGF similarly were effective in displacing 125I-bFGF, suggesting that the receptor binds both bFGF and aFGF. However, neither hCG, follicle-stimulating hormone (FSH), insulin, insulin-like growth factor-1 (IGF-1), prolactin, platelet-derived growth factor (PDGF) or epidermal growth factor (EGF) were effective competitors. When binding studies were conducted on cultured testicular interstitial cellular fractions that are normally discarded during Leydig cell purification, bFGF receptors were identified in these fractions. These results demonstrate that bFGF can have direct effects on Leydig cells through specific receptors; however, because other interstitial cell type(s) also have bFGF receptors, they stress the importance of using highly purified cells when evaluating bFGF actions on Leydig cells.

Allergic contact dermatitis releases soluble factors that stimulate melanogenesis through activation of protein kinase C-related signal-transduction pathway

Phenylazo-naphthol (PAN) allergy induces visibly well-defined and late-appearing hyperpigmentation of brownish yellow guinea pig skin in clear contrast to dinitrochlorobenzene (DNCB) allergy, which has very low incidence of hyperpigmentation. Skin extract from PAN allergy at 20-29 d post-challenge exhibited marked melanogenic stimulatory effects (3H2O release and 14C-thiouracil incorporation) when added to cultured guinea pig melanocytes. The time course in the appearance of melanogenic factor was definitely consistent with the induction pattern of visible pigmentation. By contrast, the addition of DNCB-challenged skin extract demonstrated no significant stimulating effect on melanogenesis in either assay system on any of the post-challenge days tested. Assay of intracellular inositol 1,4,5-trisphosphate formed through incubation with the melanocytes demonstrated that the PAN-allergy skin extract at day 28, which contains definite melanogenic factors, stimulated the formation of inositol 1,4,5-trisphosphate that occurs around 50 seconds in contrast to no or little increase with extracts obtained at days 0 and 1 post-challenge. Gel chromatographic analysis revealed that the PAN-allergy skin extract at day 28 contained a newly generated melanogenic fraction with a molecular weight of approximately 9000 Da which was also capable of stimulating DNA synthesis and activating the signal-transduction process (inositol trisphosphate formation) when added to guinea pig melanocytes. Both stimulations of melanogenesis and DNA synthesis by the 9000 Da fraction were completely abolished by the prior and simultaneous addition of protein kinase C (PKC) inhibitor (H-7) or its down-regulatory agent, phorbol 12,13-dibutyrate (PdBu). Taken together, these results suggest that PAN allergy provides a new mechanism of hypermelanization in which endogenous factors synthesized within skin induce the activation of signal-transduction pathways such as phosphoinositide turnover through ligands-receptor binding, resulting in the stimulation of melanocytes possibly through the activation of PKC.

Lithium mimics dexamethasone in stimulating DNA synthesis by WI-38 cells

Lithium interferes with the responses of neural and secretory cells to calcium-mobilizing agonists by blocking the generation of phospholipase C-dependent second messengers. However, the mechanism by which lithium stimulates the proliferation of other cells in response to agonists that do not activate phospholipase C remains obscure. We investigated the pathways that mediate the mitogenic action of lithium on WI-38 cells in a defined, serum-free medium. Lithium, like dexamethasone (Dex), potentiated DNA synthesis in response to the combination of insulin+epidermal growth factor (EGF) (+50%), but not in response to either growth factor alone or with Dex. As in the case of Dex, lithium could be added as late as 8 h following stimulation of quiescent cells by insulin+EGF without loss of potentiating activity. While DNA synthesis in control cultures was essentially complete by 24 h, lithium and Dex stimulated "late" DNA synthesis (24-30 h) 10-fold and 5-fold, respectively. The potentiating activity of Dex, but not that of lithium, was blocked by the specific glucocorticoid receptor antagonist, RU486. Both lithium and Dex stimulated log-phase growth, but only Dex increased saturation density. These data indicate that both lithium and Dex recruit into the cell cycle a subpopulation of cells with a longer mean prereplicative phase (G1). The effect of lithium on DNA synthesis in WI-38 cells may be mediated by the glucocorticoid response pathway at some point distal to activation of the glucocorticoid receptor, or by an independent mechanism that can be switched on late in G1.

Mechanism of carbachol-stimulated diacylglycerol formation in rat parotid acinar cells

We studied the relationship between phosphoinositide hydrolysis, phosphatidylcholine hydrolysis, and sn-1,2-diacylglycerol (DAG) formation in response to carbachol stimulation in rat parotid acinar cells. Previously, we demonstrated that DAG formation stimulated with 1 microM carbachol was biphasic: the first peak occurred at 5 min and the second one at 20 min. It was also demonstrated that the second peak was regulated in part by a calmodulin/protein kinase C-dependent mechanism. Based on the kinetic analysis of DAG formation and [32P]phosphoinositide breakdown, the first peak of carbachol (1 microM)-stimulated DAG accumulation was found to be related to the breakdown of [32P]phosphatidylinositol 4-monophosphate ([32P]PIP) and [32P]phosphatidylinositol 4,5-bisphosphate ([32P]PIP2). The second peak was found to be related to [32P]PIP2 breakdown. Carbachol stimulated the release of [3H]phosphocholine into the medium, indicating that the predominant pathway for phosphatidylcholine hydrolysis was via phospholipase C. Moreover, carbachol stimulated the release of [3H]choline metabolites in a time- and dose-dependent manner. This agonist slightly stimulated the release of [3H]ethanolamine metabolites. A calmodulin/protein kinase C-dependent mechanism was also studied and was found to be involved in carbachol-stimulated phosphatidylcholine hydrolysis; W-7, a calmodulin inhibitor and staurosporine, a protein kinase C inhibitor, inhibited the carbachol (1-microM)-induced release of [3H]choline metabolites at 20 min in a dose-dependent manner, but did not have inhibitory effects at 5 min. These results suggest that the first peak of DAG accumulation induced by carbachol is predominantly associated with the breakdown [32P]PIP and of [32P]PIP2 and that the second peak is predominantly associated with [32P]PIP2 breakdown and phosphatidylcholine hydrolysis.

Mitogenic growth factors regulate differentially early gene mRNA expression: a study on two clones of 3T3 fibroblasts

The relationship between cell proliferation and mRNA levels of the immediate early genes c-fos, c-jun, and jun B has been investigated in two clones of 3T3 fibroblasts (D1-3T3 and N2-3T3) upon treatment with basic fibroblast growth factor (bFGF), thrombin, phorbol 12-myristate 13-acetate (PMA) and dibutyryl cyclic AMP (Bt2cAMP). The 3T3-derived clone D1-3T3 almost stops dividing upon serum deprivation, while the N2-3T3 clone does not. The proliferation of the two clones was stimulated by thrombin and PMA and inhibited by Bt2cAMP. Basic FGF stimulated the growth of D1-3T3 but partly inhibited that of N2-3T3 cells. In spite of variable mitogenic response, immediate early genes, c-fos, c-jun, jun B, and c-myc, were induced by the growth factors and by PMA in both cell clones. In our experimental conditions the early gene mRNAs were expressed independently; i.e., the expression of one protooncogene had no bearing on the expression of the other. The cell growth was not directly related to the expression of a particular protooncogene mRNA. Data are presented showing that early gene mRNA expression induced by bFGF or thrombin was not mediated by protein kinase C activation while thrombin-induced mitosis was. Basic FGF induced a part of c-jun mRNA expression, but not mitosis, through a pertussis toxin-sensitive mechanism.

Phosphorylation of the MARCKS protein (P87), a major protein kinase C substrate, is not an obligatory step in the mitogenic signaling pathway of basic fibroblast growth factor in rat oligodendrocytes

Basic fibroblast growth factor (bFGF) is a well-characterized peptide hormone that has mitogenic activity for various cell types and elicits a characteristic set of responses on the cell types investigated. In this report we confirmed that bFGF is a potent mitogen for rat brain-derived oligodendrocyte (OL) precursor cells as well as for differentiated OL in secondary culture. bFGF was shown to induce expression of the protooncogene c-fos in OL. The role of protein kinase C (PKC) in mediating bFGF-stimulated proliferation as well as c-fos expression in OL was investigated. The PKC activator phorbol 12-myristate 13-acetate (PMA) stimulated c-fos expression but did not trigger cell proliferation. When PKC was down-regulated by pretreatment of OL with PMA for 20 h, the bFGF-mediated stimulations of OL proliferation and c-fos mRNA expression were still observed, whereas the induction of c-fos mRNA by PMA was totally inhibited. These data demonstrate that the bFGF mitogenic signaling pathway in OLs does not require PKC. On the other hand, bFGF was found to stimulate specifically the phosphorylation of a limited number of PKC substrates in oligodendroglial cells, including the MARCKS protein. The bFGF-dependent phosphorylation of MARCKS protein was totally inhibited when PKC was first down-regulated, indicating that the phosphorylation of this protein is PKC dependent. Tryptic digestion of the phosphorylated MARCKS protein revealed that bFGF stimulated specifically the phosphorylation of the MARCKS protein on a single phosphopeptide. We provide evidence that bFGF also stimulated fatty acylation of the MARCKS protein, which might explain the observed specific bFGF-dependent phosphorylation of this protein in OL. We propose that bFGF-dependent fatty acylation and phosphorylation of the MARCKS protein are not essential for the transduction of the bFGF mitogenic signal but are probably linked to differentiation processes elicited by bFGF on OL.

An IGF binding protein is an inhibitor of FGF stimulation

We purified to homogeneity a growth inhibiting diffusible factor (IDF45) secreted by dense cultures of mouse 3T3 cells and which was able to inhibit 100% of DNA synthesis stimulated by serum in chick embryo fibroblasts (CEF) (Blat et al., 1989a). We then demonstrated that this factor was an IGF-binding protein (Blat et al., 1989b). Indeed, its N-terminal amino acid sequence was homologous to that of rat IGFBP-3. Our present results show that basic fibroblast growth factor (bFGF) induced, respectively, a fivefold and threefold increase in DNA synthesis in mouse embryo fibroblasts (MEF) and CEF. IDF-45 inhibited the stimulation induced by bFGF by about 65%, while stimulation induced by insulin, PDGF, or EGF was only weakly or not at all inhibited by IDF45. When bFGF stimulation was determined in the presence of a high concentration of insulin in conditions which minimize the effect of endogenous IGF-I or -II, this stimulation was decreased by about 50% in the presence of IDF45. This result suggests that addition of bFGF stimulates IGF secretion, thereby resulting in partial loss of inhibition, by IDF45, of bFGF stimulation.

Mitogenic effects of fibroblast growth factors in cultured fibroblasts. Interaction with the G-protein-mediated signaling pathways

We have shown that FGF (basic or acidic) is mitogenic for quiescent hamster lung fibroblasts (CCL39 line). It is active alone but is much more efficient in synergistic combinations with G-protein-activating agents. When used alone, FGF appears to exert its mitogenic effects without involving any of the major G-protein-mediated signaling pathways. It causes no significant hydrolysis of phosphoinositides, it does not alter the activity of adenylate cyclase, and its mitogenicity is insensitive to pertussis toxin. It therefore seems likely that all pleiotropic actions of FGF are primarily mediated by the intrinsic protein tyrosine kinase of its receptors. However, FGF, acting through its receptor tyrosine kinase, and thrombin, acting through G-protein-coupled receptors, induce a common set of early responses detected within seconds or minutes at the level of membranes, cytoplasm, and nuclei. Typical examples of early responses are activation of Na/H antiporter and Na/K/Cl cotransporter, phosphorylation of ribosomal protein S6, and increased transcription of early-immediate genes (c-fos, c-jun, and c-myc). Not only various classes of growth factors acting via distinct transducing mechanisms activate common targets, but also their synergistic effects on reinitiation of DNA synthesis is reflected on the early responses. How does the coordination of these signaling events take place? A partial answer to this question is illustrated in Figure 6 in which "switch kinases" play the role of integrators of multiple extracellular signals. Raf and, perhaps more convincingly, MAP kinases that are activated by dual phosphorylation on tyrosine and threonine residues are potential good candidates for this integration. This hypothetical scheme could therefore explain, in part, the coordination and the synergy commonly observed in the mitogenic response. The synergy could be generated at the level of MAP kinases simply by dual activating phosphorylations. With the recent cloning of MAP kinases, these questions will be more easily addressed. Another important gap that will have to be filled in future studies is the identification of all the members of the kinase cascade. When used in synergistic combinations with G-protein-activating agents, FGF does exert in contrast some effects on the G-protein-mediated pathways. It potentiates the G-protein-mediated activations of both PIP2-PLC and adenylate cyclase.(ABSTRACT TRUNCATED AT 400 WORDS)

Signal transduction by bFGF, but not TGF beta 1, involves arachidonic acid metabolism in endothelial cells

We investigated the stimulation of early cellular events resulting from the interaction of the growth factor basic FGF (bFGF) and of the growth inhibitor transforming growth factor beta-type 1 (TGF beta 1), with their specific receptors on bovine endothelial cells. At mitogenic concentrations, bFGF stimulated the rapid release of arachidonic acid and its metabolites from (3H)-arachidonic acid labeled cells. When arachidonic acid metabolism was stimulated by addition of the calcium ionophore A23187, the effect of bFGF was amplified. Nordihydroguaïaretic acid, an inhibitor of the lipoxygenase pathway of arachidonic acid metabolism, decreased the mitogenic effect of bFGF, whereas indomethacin, an inhibitor of the cyclooxygenase pathway, was ineffective. These findings suggest that metabolism of arachidonic acid to lipoxygenase products may be necessary for the mitogenic effect of bFGF. Basic FGF did not stimulate the production of inositol phosphates from cells labelled with myo-(2-3H)-inositol nor did it induce calcium mobilization, as measured by fura-2 fluorescence, indicating that bFGF does not activate phosphoinositide-specific phospholipase C in endothelial cells, but rather, that bFGF-induced arachidonic acid metabolism is mediated by another phospholipase. TGF beta 1, which inhibits basal and bFGF-induced endothelial cell growth, had no effect on arachidonic acid metabolism and inositol phosphate formation and did not prevent bFGF-induced arachidonic acid metabolism. These results suggest that the inhibitory action of TGF beta 1 on endothelial cell growth occurs through different mechanisms.

Differential regulation of gamma and delta T cell antigen receptor gene expression by phorbol esters and Ca2+ ionophores in the acute lymphocyte leukemia DND41 cell line

We have investigated the role of two signal transduction pathways on the regulation of the gamma and delta T cell antigen receptor (TcR) gene expression, in the acute lymphocytic leukemic cell line DND41. Protein kinase C (PKC) activation, and intracellular free Ca2+ mobilization, initiated by phorbol esters and calcium ionophores, respectively, not only acted independently but, more interestingly, their effects were antagonistic, suggesting a role for these signals during T cell differentiation. The Ca2+ ionophore, ionomycin, increased the levels of intracellular free Ca2+ and induced the expression of the gamma and delta chains of the T cell antigen receptor in a concentration-dependent manner. The phorbol ester 12-myristate 13-acetate down-regulated the basal gamma TcR expression with marginal effect on delta TcR mRNA, but diminished the induction of both gamma and delta TcR, initiated by the Ca2+ ionophore. These antagonistic effects of the two arms of the phospholipase C-mediated signal transduction pathways, i.e. PKC activation and increased intracellular free Ca2+, were specific to the regulation of the gamma and delta TcR, since the same signals exerted a synergistic effect on the mRNA levels of interleukin 2 receptor. These data confirm our hypothesis that the antagonistic regulation on the gamma and delta TcR gene expression by phorbol esters and calcium ionophores occurs in the same cell, and stresses the biological significance of PKC activation and intracellular free calcium mobilization during intrathymic differentiation and selection.

Basic fibroblast growth factor and somatomedin C in human medulloepithelioma

Two published cases of medulloepithelioma, a rare malignant pediatric brain tumor composed of a mixture of primitive neuroepithelium and its differentiated neuronal and glial descendants, were examined by immunohistochemical staining for the presence of growth factors. From a panel of antibodies, those identifying basic fibroblast growth factor and insulin-like growth factor I, formerly known as somatomedin C, were strongly immunoreactive within the neuroepithelial cell population of the tumors. Immunoblots of purified recombinant basic fibroblast growth factor and insulin-like growth factor I showed antibody specificity without cross-reactivity. In controls, immunostaining of tissue sections was abolished by preabsorption of primary antibodies with the appropriate growth factor polypeptide antigen. Preabsorption with inappropriate growth factor did not reduce the intensity or alter the distribution of staining. The congruent histologic patterns of immunoreactivities suggest that more than one type of growth factor may be produced by the neuroepithelial component of medulloepithelioma. These growth factors may stimulate proliferation and differentiation of tumor cells by autocrine molecular mechanisms.

Protein kinase C-dependent diacylglycerol formation is mediated via Ca2+/calmodulin in parotid cells

The kinetics of carbachol-induced sn-1,2-diacylglycerol (DAG) formation and the underlying mechanism(s) involved in parotid acinar cells were investigated. Supramaximal concentrations of carbachol for amylase secretion (10 microM) caused a transient rise in DAG levels at 10 s. In contrast, this rapid rise was not elicited by 1 microM carbachol, which is the maximally effective concentration for amylase secretion. Carbachol (10 microM) also increased DAG levels linearly up to 20 min, which were sustained for up to a further 10 min. DAG formation stimulated by 1 microM carbachol was biphasic; the first peak was observed after 5 min and the second after 20 min. DAG formation induced by 0.01-0.1 microM carbachol was concentration-dependent and monophasic, peaking at 5 min. The second peak evoked by carbachol was partly inhibited by Ca2+ deprivation from the extracellular space, whereas the first peak was not. Similar results were obtained in experiments using Ca2+ antagonists such as verapamil and LaCl3. The protein kinase C inhibitors, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7) and staurosporine, and a calmodulin antagonist, N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), significantly inhibited the second DAG peak produced by 1 microM carbachol, but did not alter the first peak. The degree of inhibition of the second peak by these antagonists was comparable. Furthermore, the inhibitory effect of staurosporine and W-7 was concentration-dependent. The A23187-induced accumulation of DAG also was abolished by both staurosporine and W-7. These data indicate that a protein kinase C-dependent mechanism(s) is involved in mediating the second DAG accumulation peak induced by 1 microM carbachol and is mainly regulated by the Ca(2+)-calmodulin complex.

MCF7 mammary cancer cells respond to bFGF and internalize it following its release from extracellular matrix: a permissive role of cathepsin D

High and low affinity receptors for basic fibroblast growth factor (bFGF) were detected by binding experiments on MCF7 breast cancer cells. These cells were stimulated for growth by physiological concentrations of bFGF. However, in contrast to endothelial cells, these MCF7 cells did not produce detectable amounts of biologically active bFGF or related heparin-binding growth factor(s) of the FGF family. In vitro, the cathepsin D (cath-D) secreted by MCF7 cells was able to digest extracellular matrix (ECM) and to release ECM-bound 125I-bFGF. When MCF7 cells were cultured on ECM containing bound bFGF, they internalized bFGF, which was slowly and partially proteolyzed in the cells. Processing occurred in acidic compartments and was inhibited by leupeptin. Pepstatin A, an inhibitor of aspartyl proteases, had no effect on the processing but reduced internalization of matrix-bound bFGF by MCF7 cells. Taken together, these results suggest a cooperation between cath-D and bFGF, by which the protease could facilitate the release of bFGF from ECM and its subsequent use by breast cancer cells and/or adjacent cells involved in angiogenesis.

A calcium-activated, calcium-permeable ion channel in human retinal glial cells: modulation by basic fibroblast growth factor

A calcium-permeable, voltage-insensitive non-specific cation channel that is activated by cytoplasmic calcium was found in approximately 50% of the cell-attached patches in cultured human retinal glial cells sampled by the patch clamp technique. Spontaneous openings of this channel were infrequent, but increased markedly when glial cells were exposed to basic fibroblast growth factor. Although the role of these cation channels is uncertain, they provide a mechanism to perpetuate a transient rise in cytosolic calcium induced by the release of calcium from intracellular stores.

Unitary model of cell activation, growth control, cancer and other diseases: 1. Activated oxygen species and arachidonic acid modulation of solute permeabilities, internal Ca, Na and AOS levels and DNA transcription and synthesis

A comprehensive model of cellular activation and proliferation is developed. The model has arachidonic acid (ARA) produced mainly from PLA2 on both sides of the membrane, and superoxide and other activated oxygen species (AOS) formed from O2 by electrons passing out through membrane NANPH and NADH oxidases, as the immediate stimulants of solute permeability. Both ARA and AOS interact with the various solute channel proteins especially their external thiols and disulfides, to increase influx of metabolic substrates, Na, Ca and O2. PLA2 and NADPH oxidase are turned on by growth factors at their receptors acting through tyrosine kinase phosphorylations of messenger proteins GP and ras p-21, stimulated proteases, and by Ca-calmodulin. The adenylate cyclase system has opposite, deactivating character as it increases efflux of Ca and desensitizes growth factor receptors by phosphorylation to shut down the increased solute permeability. Most cancer types are due to carcinogen binding to cell membrane channel and mitochondrial sites for increased solute influx with excessive AOS production inside the cell from mitochondria and other vesicles. High Ca, Na and AOS stimulate proliferation with extra high levels causing transformation to the autogenic, more embryonic-type cancer cell.

Colony stimulating factor-1 stimulates diacylglycerol generation in murine bone marrow-derived macrophages, but not in resident peritoneal macrophages

Colony stimulating factor-1 (CSF-1) stimulates DNA synthesis in murine bone marrow-derived macrophages (BMM); however, unlike BMM, murine resident peritoneal macrophages (RPM) undergo a poor proliferative response. It has previously been shown that phosphatidylinositol-4,5-bisphosphate hydrolysis is not associated with CSF-1 action in BMM. In this report we demonstrate that, despite a lack of inositol trisphosphate generation, CSF-1 transiently elevated both [3H]myristoyl- and [3H]arachidonyl-diacylglycerol (DAG) in BMM in a dose-dependent fashion. CSF-1 failed, however, to stimulate an increase in either species of DAG in RPM. Thus, DAG could be a second messenger for the proliferative action of CSF-1 in macrophages. Other mitogenic agents, 12-0-tetradecanoyl phorbol 13-acetate (TPA) and exogenous phospholipase C, also increased BMM levels of [3H]myristoyl- and [3H]arachidonyl-DAG. The nonmitogenic agents, lipopolysaccharide (LPS), tumor necrosis factor-alpha (TNF-alpha) and zymosan, had different effects on the generation of either species of DAG in BMM. LPS failed to elevate either form, TNF-alpha increased only [3H]arachidonyl-DAG, while zymosan stimulated levels of both species of DAG. It therefore appears that increased diacylglycerol generation may be necessary, but perhaps not sufficient, for macrophage proliferation.

Response to growth factors of human dermal fibroblasts in a quiescent state owing to cell-matrix contact inhibition

Mitogenic responses to various growth factors were compared for quiescent human dermal fibroblasts cultured under three different conditions; serum depletion, cell-cell contact inhibition and cell-matrix contact inhibition. The non-dividing fibroblasts cultured under a low serum condition (0.2% fetal bovine serum, FBS) or in a confluent culture with 10% FBS resumed multiplying upon exposure to any one of or any combination of the growth factors examined; epidermal growth factor (EGF), basic fibroblast growth factor (b-FGF), platelet-derived growth factor (PDGF) and transforming growth factor beta (TGF-beta). The only exception was the lack of effect of TGF-beta on the cell under a low serum condition. In contrast, the proliferation of fibroblasts which were growth-arrested in contracted collagen gel by cell-matrix contact inhibition was not stimulated by any of the growth factors examined except for PDGF. It is currently accepted that the mechanism of growth stimulation or signal transduction after binding of each growth factor to the specific receptor depends on the kind of growth factor. The results suggest that the signal transductions delivered by EGF, b-FGF or TGF-beta are inactivated by a high level of interaction of collagen fibrils with the cell membrane (under the condition of cell-matrix contact inhibition); whereas the signal transduction by PDGF is unaffected. The finding supports the existence of a specific growth stimulation pathway for PDGF.

Induction of 5-deiodinase activity in astroglial cells by 12-O-tetradecanoylphorbol 13-acetate and fibroblast growth factors

In the brain, 5'-deiodinase (5'-D) is responsible for the metabolic activation of thyroxine (T4) into 3,5,3'-triiodothyronine (T3) and 5-deiodinase (5-D) deiodinates T4 and T3 into inactive metabolites. This study examines the effects of factors known to induce astroglial 5'-D activity on the 5-D activity in cultured rat astroglial cells. The potencies of these factors were compared after 8 h of incubation, when stimulations by these factors near their maximal effects. 12-O-Tetradecanoylphorbol 13-acetate (TPA) at 10(-7) M was a potent inducer of 5-D activity, producing a 30- to 80-fold increase after 8 h. The maximal effect of TPA was observed after about 14 h. The TPA stimulation of 5-D activity was not dependent on glucocorticoids, unlike 5'-D activity. In comparison with TPA, 8-bromo-cyclic AMP (10(-3) M) was a poor inducer of 5-D activity whereas it is an excellent inducer of 5'-D activity. It produced a 2- to 20-fold increase in 5-D activity after 8 h. Natural acidic fibroblast growth factor (20 ng/ml) produced a degree of stimulation similar to that of TPA after 8 h. The maximal effect of acidic fibroblast growth factor was observed after about 16 h (until a 120-fold increase). Recombinant acidic fibroblast growth factor also induced 5-D activity. Basic fibroblast growth factor was less potent than acidic fibroblast growth factor for increasing 5-D activity (maximal increase by 40- to 50-fold after 8 h).(ABSTRACT TRUNCATED AT 250 WORDS)

Phorbol ester TPA inhibits the stimulation of bumetanide-sensitive Na+/K+/Cl- transporter by different mitogens in quiescent BALB/c 3T3 mouse fibroblasts

In this study we examined the effect of the phorbol ester 12-O-tetradecanoyl-phorbol-13-acetate (TPA) on the bumetanide-sensitive Na+/K+/Cl- transporter in quiescent BALB/c 3T3 cells. We have shown that exposure of quiescent BALB/c 3T3 cultures to phorbol ester did not inhibit the basal bumetanide-sensitive Rb+ influx or efflux. In fact, at high concentration (100 ng/ml), TPA slightly stimulated the bumetanide-sensitive Rb+ influx and efflux. However, when the quiescent cultures were stimulated by serum or by defined growth factors, the stimulated fraction of the bumetanide-sensitive Rb+ influx was drastically inhibited by exposure of the cells to the phorbol ester TPA. Based on the above findings, we propose that activation of protein kinase C by the phorbol ester TPA does not inhibit the Na+/K+/Cl- cotransport activity; however it does suppress only the growth-factors-stimulated fraction of the cotransport in quiescent BALB/c 3T3 cells. These data propose that activation of kinase C has a regulatory feedback effect on the stimulation of the Na+/K+/Cl- cotransport activity by growth factors.