Hepatocyte growth factor-induced expression of ornithine decarboxylase, c-met, and c-myc is differently affected by protein kinase inhibitors in human hepatoma cells HepG2

Molecular basis of anti-inflammatory action of platelet-rich plasma on human chondrocytes: mechanisms of NF-κB inhibition via HGF

Loss of articular cartilage through injury or disease presents major clinical challenges also because cartilage has very poor regenerative capacity, giving rise to the development of biological approaches. As autologous blood product, platelet-rich plasma (PRP) provides a promising alternative to surgery by promoting safe and natural healing. Here we tested the possibility that PRP might be effective as an anti-inflammatory agent, providing an attractive basis for regeneration of articular cartilage, and two principal observations were done. First, activated PRP in chondrocytes reduced the transactivating activity of NF-κB, critical regulator of the inflammatory process, and decreased the expression of COX-2 and CXCR4 target genes. By analyzing a panel of cytokines with different biological significance, in activated PRP we observed increases in hepatocyte growth factor (HGF), interleukin-4 and tumor necrosis factor-α (TNF-α). HGF and TNF-α, by disrupting NF-κB-transactivating activity, were important for the anti-inflammatory function of activated PRP. The key molecular mechanisms involved in PRP-inhibitory effects on NF-κB activity were for HGF the enhanced cellular IkBα expression, that contributed to NF-κB-p65 subunit retention in the cytosol and nucleo-cytoplasmic shuttling, and for TNF-α the p50/50 DNA-binding causing inhibition of target-gene expression. Second, activated PRP in U937-monocytic cells reduced chemotaxis by inhibiting chemokine transactivation and CXCR4-receptor expression, thus possibly controlling local inflammation in cartilage. In conclusion, activated PRP is a promising biological therapeutic agent, as a scaffold in micro-invasive articular cartilage regeneration, not only for its content of proliferative/differentiative growth factors, but also for the presence of anti-inflammatory agents including HGF.

Prognostic significance of c-Met expression in glioblastomas

BACKGROUND

The authors investigated whether expression of c-Met protein in glioblastomas is associated with overall survival and biologic features representing tumor invasiveness in patients with glioblastomas.

METHODS

Paraffin-embedded specimens of glioblastomas from 62 patients treated in a single institution were assessed by immunohistochemical (IHC) analysis of c-Met expression. On the basis of the clinical data for these patients, the association between c-Met expression and clinicobiologic features representing tumor invasiveness was analyzed.

RESULTS

c-Met overexpression was detected in 29.0% (18 of 62) of glioblastomas. In patients with c-Met overexpression, the median survival was 11.7 months (95% confidence interval [95% CI], 9.9 months-13.5 months), compared with a median survival of 14.3 months (95% CI, 7.6 months-21.0 months) for patients whose tumors had no or little expression of c-Met (P=.031). On the radiographic analysis, 9 of 18 patients (50%) with tumors overexpressing c-Met demonstrated invasive and multifocal lesions on the initial magnetic resonance images, whereas only 9 of 44 patients (20.5%) with tumors that expressed no or little c-Met demonstrated these features (P=.030). Using immunohistochemistry, we also found a significant association between c-Met expression and matrix metalloproteinase-2,-9 (P=.020 and P=.013). Furthermore, Myc overexpression was found to be closely correlated with c-Met overexpression on IHC analysis (P=.004).

CONCLUSIONS

The authors suggest that c-Met overexpression is associated with shorter survival time and poor treatment response in glioblastomas, the mechanism for which is elevated tumor invasiveness on the molecular and clinical phenotypes. This implies that more effective therapeutic strategies targeting c-Met receptors may have important clinical implication.

Antifolate/folate-activated HGF/c-Met signalling pathways in mouse kidneys-the putative role of their downstream effectors in cross-talk with androgen receptor

This in vivo study of mouse kidneys was focused on the identification of protein mediators involved in the cross-talk between two signalling pathways. One pathway was triggered by testosterone via an androgen receptor, AR, and the other induced by CB 3717/folate via HGF, and its membrane receptor c-Met. Sequential activation of these pathways leads to a drastic decrease of testosterone-induced ornithine decarboxylase, ODC, expression. We proved that CB 3717/folate-induced ODC expression is Akt-dependent. CB 3717/folate activates Akt and ERK1/2 kinases, PTEN phosphatase and also up-regulates cyclin D2 and PCNA, but decreases GSK3beta and cyclin D1 protein levels. Testosterone activation of AR induces GSK3beta and PTEN. Results of the sequential activation of the studied signalling pathways suggest that Akt, GSK3beta and possibly ERK1/2 kinases may participate in the negative cross-talk and attenuation of AR transactivity, while the involvement of PTEN and cyclin D1 seems to be doubtful.

Hepatocyte growth factor regulates cyclooxygenase-2 expression via beta-catenin, Akt, and p42/p44 MAPK in human bronchial epithelial cells

Hepatocyte growth factor (HGF) is upregulated in response to lung injury and has been implicated in tissue repair through its antiapoptotic and proliferative activities. Cyclooxygenase-2 (COX-2) is an inducible enzyme in the biosynthetic pathway of prostaglandins, and its activation has been shown to play a role in cell growth. Here, we report that HGF induces gene transcription of COX-2 in human bronchial epithelial cells (HBEpC). Treatment of HBEpC with HGF resulted in phosphorylation of the HGF receptor (c-Met), activation of Akt, and upregulation of COX-2 mRNA. Adenovirus-mediated gene transfer of a dominant negative (DN) Akt mutant revealed that HGF increased COX-2 mRNA in an Akt-dependent manner. COX-2 promoter analysis in luciferase reporter constructs showed that HGF regulation required the beta-catenin-responsive T cell factor-4 binding element (TBE). The HGF activation of the COX-2 gene transcription was blocked by DN mutant of beta-catenin or by inhibitors that blocked activation of Akt. Inhibition of p42/p44 MAPK pathway blocked HGF-mediated activation of beta-catenin gene transcription but not Akt activation, suggesting that p42/p44 MAPK acts in a parallel mechanism for beta-catenin activation. We also found that inhibition of COX-2 with NS-398 blocked HGF-induced growth in HBEpC. Together, the results show that the HGF increases COX-2 gene expression via an Akt-, MAPK-, and beta-catenin-dependent pathway in HBEpC.

Nitric oxide-dependence of satellite stem cell activation and quiescence on normal skeletal muscle fibers

Satellite cells (quiescent precursors in normal adult skeletal muscle) are activated for growth and regeneration. Signaling by nitric oxide (NO) and hepatocyte growth factor (HGF) during activation has not been examined in a model that can distinguish quiescent from activated satellite cells. We tested the hypothesis that NO and HGF are required to regulate activation using the single-fiber culture model. In normal fibers, HGF and inhibition of NO synthase (NOS) each increased activation without stretching, and NOS inhibition reduced stretch-activation. Activation in unstretched mdx and NOS-I(-/-) fibers was three- to fourfold higher than normal, and was reduced by stretching. Distinctions were not due to different pax7-expressing populations on normal and mdx fibers. The population of c-met-expressing satellite cells on normal fibers was increased by stretch, demonstrating functional heterogeneity among normal satellite cells. Cycloheximide did not prevent the stretch-related increase in c-met expression, suggesting c-met may be an immediate-early gene in satellite cell activation. Results have important implications for designing new therapies that target the role of exercise in health, aging, and disease.

Increasing ornithine decarboxylase activity is another way of prolactin preventing methotrexate-induced apoptosis: Crosstalk between ODC and BCL-2

Prolactin has more than 300 separate functions including affecting mammary growth, differentiation, secretion and anti-apoptosis. In the previous studies, prolactin induced Bcl-2 expression to prevent apoptosis and also provoked the activity of ornithine decarboxylase (ODC). Our previous data showed that ODC overexpression upregulates Bcl-2 and prevents tumor necrosis factor alpha (TNF-alpha)- and methotrexate (MTX)-induced apoptosis. Here, we further investigate whether prolactin prevents MTX-induced apoptosis through inducing ODC activity and the relationship between ODC and Bcl-2 upon prolactin stimulation. Prolactin prevented MTX-induced apoptosis in a dose-dependent manner in HL-60 cells. Following prolactin stimulation, ODC enzyme activity also shows an increase in a dose-dependent manner, expressing its maximum level at 3 h, and rapidly declining thereafter. Prolactin-induced ODC activity is completely blocked by a protein kinase C delta (PKCdelta) inhibitor, rottlerin. However, there are no changes in the expressions of ODC mRNA and protein level after prolactin stimulus. It indicates that prolactin may induce ODC activity through the PCKdelta pathway. Besides, Bcl-2 expresses within 1 h of prolactin treatment and this initiating effect of prolactin is not inhibited by alpha-difluoromethylornithine (DFMO). However, Bcl-2 is further enhanced following prolactin stimulation for 4 h and this enhancement is blocked by DFMO. Bcl-2 has no effect on ODC activity and protein levels, but ODC upregulates Bcl-2, which is inhibited by DFMO. Overall, there are two different forms of prolactin effect, it induces Bcl-2 primarily, and following this it stimulates ODC activity. Consequently induced ODC activity further enhances the expression of Bcl-2. The anti-apoptotic effect of prolactin is diminished by DFMO and recovered by putrescine. Obviously, ODC activity is one basis for the anti-apoptotic mechanisms of prolactin. A Bcl-2 inhibitor, HA14-1, together with DFMO, completely blocks the anti-apoptotic effects of prolactin. These results suggest that increasing ODC activity is another way of prolactin preventing MTX-induced apoptosis and that this induction of ODC activity enhances the expression of Bcl-2 strongly enough to bring about the anti-apoptotic function.

Glutathione depletion modulates gene expression in HepG2 cells via activation of protein kinase C alpha

Buthionine sulphoximine (BSO; 1mM) resulted in the depletion of glutathione (GSH) in HepG2 cells to 17+/-1.5% within 24h. This was not associated with apoptotic or necrotic cell death over this time period. Use of a human (Phase 1) cDNA custom toxicology-array and a larger scale (>10,000 gene) Affymetrix U95Av2 array identified a total of 48 and 104 genes, respectively, with a statistically significant (and >1.5-fold) change in expression. A total of 64 differentially expressed genes (6 of which were confirmed by real-time polymerase chain reaction) were suggestive of protein kinase C (PKC) activation. Activation of PKC-alpha (but not betaI or delta) was demonstrated at 24 h through activity measurements and through Western blot analysis of membrane-associated PKC-alpha protein. Activation did not occur in the presence of additional gamma-glutamylcysteine to prevent GSH depletion. Activation of PKC-alpha by GSH-depletion may, at least in part, be mediated by thiol oxidation and may contribute to a survival signal. If sustained, the activation may be important in non-genotoxic carcinogenesis.

HSG cells differentiated by culture on extracellular matrix involves induction of S-adenosylmethione decarboxylase and ornithine decarboxylase

The human salivary gland (HSG) epithelial cell line can differentiate when cultured on extracellular matrix preparations. We previously identified >30 genes upregulated by adhesion of HSG cells to extracellular matrix. In the current studies, we examined the role of one of these genes, the polyamine pathway biosynthetic enzyme S-adenosylmethionine decarboxylase (SAM-DC) and the related enzyme, ornithine decarboxylase (ODC), on HSG cell differentiation during culture on extracellular matrix. HSG cells cultured on fibronectin-, collagen I gel-, and Matrigel-coated substrates for 12-24 h upregulated SAM-DC and ODC mRNA expression and enzyme activity compared to cells cultured on non-precoated substrates. After 3-5 days, HSG cells grown on Matrigel- or collagen I gel-coated substrates acquired a differentiated phenotype: the cells showed changes in culture morphology and increased expression of salivary gland differentiation markers (vimentin, SN-cystatin, and alpha-amylase). Further, culturing the cells on substrates precoated with an anti-beta1-integrin-antibody promoted differentiation-like changes. HSG cells cultured on collagen I- or Matrigel-coated substrates rapidly entered the cell cycle but showed decreased cell proliferation at longer times. In contrast, cell proliferation was enhanced on fibronectin-coated substrates compared to cells on non-precoated substrates. Treatment with the polyamine synthesis inhibitors, difluoromethylornithine (DFMO), and methylglyoxal bis-(guanylhydrazone) (MGBG), inhibited cell proliferation and delayed (3)H-thymidine incorporation in HSG cells cultured on all of the substrates. Further, inclusion of DFMO and MGBG inhibited or delayed acquisition of the differentiated phenotype in HSG cells cultured on Matrigel- or collagen I gel-coated substrates. This suggests that the adhesion-dependent expression of SAM-DC and ODC contributes to extracellular matrix-dependent HSG cell differentiation.

In vitro chemopreventive activity of Camellia sinensis, Ilex paraguariensis and Ardisia compressa tea extracts and selected polyphenols

Several herbal teas contain bioactive compounds that have been associated with a lower risk of chronic diseases including cancer. The aim of this study was to evaluate the chemopreventive activity of tea aqueous extracts and selected constituent pure polyphenols using a battery of in vitro marker systems relevant for the prevention of cancer. The effects of (-) epigallocatechin gallate (EGCG), quercetin (Q), gallic acid (GA), green tea (GT, Camellia sinensis), ardisia tea (AT, Ardisia compressa) and mate tea (MT, Ilex paraguariensis) extracts were tested. Cytotoxicity, TPA-induced ornithine decarboxylase (ODC) and quinone reductase (QR) activities were evaluated in vitro using HepG2 cells. The topoisomerase inhibitory activity was also tested, using the Saccharomyces cerevisiae yeast system. Results suggest that MT, AT and GT are cytotoxic to the HepG2 cells, with MT demonstrating dominant cytotoxicity. EGCG showed greater cytotoxicity than Q and GA against HepG2 cells. The greatest inhibition (82%) of TPA-induced ODC activity was shown by Q, with 25 microM (IC50 = 11.90 microM). Topoisomerase II, but not topoisomerase I, was the cellular target of MT, AT, EGCG, Q and GA, which acted mainly as true catalytic inhibitors. The cytotoxic activity and the inhibition of topoisomerase II may contribute to the overall chemopreventive activity of AT and MT extracts. Ardisia and mate teas may thus share a public health potential as chemopreventive agents.

Contribution of spermidine to stimulation by hepatocyte growth factor in repair after damage of rabbit gastric mucosal cells in primary culture

Wound-healing of the gastric mucosa is suggested to be stimulated by hepatocyte growth factor (HGF). Polyamines are shown to contribute to repair after damage in the gastric mucosa. The present study was designed to elucidate whether HGF can stimulate wound-healing of the gastric mucosa via polyamine production, using rabbit gastric mucosal cells in primary culture. A wound was made as a round cell-free area in the cell sheet of confluent cultured cells. When HGF was added to the culture medium, such denuded area was significantly reduced in size compared with the control, but the reduction was inhibited by addition of D,L-alpha-difluoromethylornithine (DFMO), an inhibitor of a rate-limiting enzyme (ornithine decarboxylase) of polyamine biosynthesis, to the culture medium. However, the inhibitory effect by DFMO was reversed by pretreatment with spermidine, but not with putrescine. Intracellular levels of polyamines in the whole confluent cells including the cells around the denuded area were not changed by addition of HGF, but putrescine and spermidine levels were decreased by further addition of DFMO. We conclude that spermidine may be involved in stimulation by HGF in the repair after damage of gastric mucosal cells.

A cluster region of AP-1 responsive elements is required for transcriptional activity of mouse ODC gene by hepatocyte growth factor

Ornithine decarboxylase (ODC) activity is regulated by a variety of mechanisms including transcription, translation, and RNA and protein half-life. Since in mouse B16-F1 melanoma cells an early and remarkable (about 6-fold) increase in steady state mRNA levels was observed after hepatocyte growth factor (HGF) treatment, we investigated the transcriptional regulation of mouse ODC promoter. Transient transfection of various ODC-luciferase promoter constructs into the B16-Fl cells in combination with electrophoretic mobility shift assays identified the HGF-responsive element as a cluster of three AP-1 binding sites (-1660 to -1572). Even if each site differs from the canonical TPA responsive element for one nucleotide, only the first two AP-1 consensus sequences seemed to be functional since allowed DNA-binding activity of nuclear proteins after HGF treatment. Comparison of the results of transfection assays with the pOD2.5-luc (2.5 kb gene fragment) and with the construct deprived of the AP-1 cluster pOD-B-luc showed that this 50 bp region was required for ODC transactivating activity in response to HGF. Since in B16-F1 cells HGF increased AP-1 activity and the mRNA expression of various AP-1 subunits, we may conclude that HGF-induced transcription of mouse ODC was largely due to triggering of AP-1 pathway.

Synergy between truncated c-Met (cyto-Met) and c-Myc in liver oncogenesis: importance of TGF-beta signalling in the control of liver homeostasis and transformation

The c-Met tyrosine kinase receptor and its ligand, Hepatocyte Growth Factor/ Scatter Factor, have been implicated in human cancer. We have previously described that the transgenic expression of a truncated form of human c-Met (cyto-Met) in the liver confers resistance to several apoptotic stimuli. Here we show the impact of cyto-Met expression on liver proliferation and transformation. Despite a sixfold increase of hepatocyte proliferation, adult transgenic livers displayed normal size and architecture. We present evidence showing that activation of TGF-beta1 signalling controls the liver mass in cyto-Met mice. The oncogenic potential of cyto-Met was further assessed in the context of c-Myc-induced hepatocarcinogenesis, using WHV/c-Myc transgenic mice. Co-expression of cyto-Met and c-Myc further enhanced hepatocyte proliferation and caused a dramatic acceleration of the Myc-induced tumorigenesis, leading to the emergence of hepatocarcinomas in 3-4-month-old animals. Importantly, the TGF-beta receptor type II expression was strongly downregulated in most tumours, indicating that impairment of TGF-beta1-mediated growth inhibition plays a major role in accelerated neoplastic development. The strong potential of cyto-Met for oncogenic cooperation without direct transforming activity designates cyto-Met mice as an ideal tool for studying the early steps of multistage hepatocarcinogenesis and for identification of prognostic markers of transformation.

HGF upregulates and modifies subcellular distribution of proteins in colon cancer cell enterocytic differentiation

Hepatocyte growth factor (HGF) and its receptor, c-Met, are involved in cell transformation. To study their role in intestinal cell differentiation, we used Caco-2 colon cancer cells, which differentiate spontaneously into enterocytes during culture. Cells grown continuously in the presence of HGF reached confluence more quickly than control cells. Markers of enterocytic differentiation, such as alkaline phosphatase and sucrase-isomaltase activities, adhesion molecules, and structural proteins such as E-cadherin, villin, and F-actin were upregulated by HGF throughout the 35 days of culture, and actin fibers were reorganized. HGF also stimulated expression and tyrosine phosphorylation of c-Met and Gab-1 as well as protein kinase C (PKC)-alpha expression. PKC-alpha has been shown to be involved in intestinal differentiation. We therefore investigated the possibility that increases in PKC-alpha protein levels were responsible for the HGF-promoted events. We did this by incubating cells with Gö-6976, an inhibitor of PKC-alpha and -beta1, concomitantly with HGF. This inhibitor abolished the HGF-induced increase in villin levels before, but not after, confluence. Thus HGF accelerates Caco-2 cell differentiation and stimulates the metabolic and structural events accompanying this process. These HGF-promoted events may be mediated partly by Gab-1, and the effects of HGF on villin before confluence seem to involve PKC.

Invasiveness of hepatocellular carcinoma cell lines: contribution of hepatocyte growth factor, c-met, and transcription factor Ets-1

To understand the mechanism of invasion and metastasis of hepatocellular carcinoma (HCC), the expression of c-met and Ets-1, and the effect of HGF on these cell's motility and invasion ability were examined in four hepatoma cell lines. The analysis revealed that the overexpression of c-met and Ets-1 is closely connected with the motility and invasion ability of the HCC cell lines. Invasion activity of HepG2 and HLE cells were enhanced by the addition of HGF to medium. HGF regulated c-met transcription in HepG2 and Bel-7402 cells, HGF also induced Ets-1 transcription in Bel-7402 cell. Bel-7402 cells stably transduced with the human Ets-1 gene showed significantly increased invasion potentials compared to parental and mock-transfected cells. The expression level of c-met, MMP1, MMP9, and u-PA in Bel-7402 cells transfected with Ets-1 were markedly increased, and as a consequence of c-met expression increase. Bel-7402 cells transfected with Ets-1 were more responsive to exogenous HGF stimulation in invasiveness and motility ability. In addition, conditioned by antisense Ets-1 oligonucleotide-treat-Bel-7402 cells transfected with Ets-1 gene and HLE hepatoma cells showed markedly reduced invasion activity, and down-regulated the transcription of Ets-1, c-met, u-PA, MMP-1, and MMP-9. These results strongly suggest that Ets-1 has a crucial role in the invasive property in hepatoma cell lines, and there may exist a loop to enhance the invasive ability of hepatoma cell lines.

A gene trap vector system for identifying transcriptionally responsive genes

We present a method for fast and efficient trapping of genes whose transcription is regulated by exogenous stimuli. We constructed a promoterless retroviral vector transducing a green fluorescent protein-nitroreductase (GFNR) fusion protein downstream from a splice acceptor site. Flow cytometric analysis of the infected population allows identification and sorting of cells in which the trap is integrated downstream from an active promoter. Conversely, the nitroreductase (NTR) moiety allows pharmacological selection against constitutive GFNR expression. Using hepatocyte growth factor (HGF) stimulation of liver cells combined with either positive or negative selection, we recovered cell populations carrying traps in induced or suppressed genes, respectively. Several distinct responsive clones were isolated, and regulated expression of the trapped gene was confirmed at the RNA level. Positive and negative selection can be calibrated to recover traps in genes showing different levels of basal expression or transcriptional regulation. The flexibility and efficiency of the GFNR-based trap screening procedure make it suitable for wide surveys of transcriptionally regulated genes.

Hepatocyte growth factor induces pro-apoptotic genes in HepG2 hepatoma but not in B16-F1 melanoma cells

Hepatocyte growth factor (HGF) exerts a cytostatic effect on HepG2 and B16-F1 cell lines. To evaluate the possible involvement of the apoptotic process in this effect, we performed studies at cellular and molecular levels. HGF induced apoptosis only in HepG2 hepatoma cells at day 3 in about 20% of the cells undergoing growth inhibition, while hallmarks of apoptosis did not occur in B16-F1 melanoma cells. During the first 24 h after HGF treatment, enhanced expression of the pro-apoptotic genes bax and c-Myc was observed at level of mRNA and protein. Concomitant induction of antizyme (AZ) might lower ornithine decarboxylase (ODC) protein level though a huge increase in ODC mRNA level took place. This was suggested as a signal for apoptosis decisional phase. The levels of the proteins examined except that of AZ fell down thereafter when HepG2 cells underwent apoptosis. In B16-F1 cells, only ODC and AZ protein levels were elevated probably in relation to the initial elevated growth rate and the absence of apoptosis involvement in the following cytostatic effect of HGF in melanoma cells. Consistent with this hypothesis, bax mRNA and protein levels were unchanged or even lower relative to control values.

Cross-talk between steroid-receptor-mediated and cell-membrane-receptor-mediated signalling pathways results in the in vivo modulation of c-Met and ornithine decarboxylase gene expression in mouse kidney

The cross-talk in vivo between two signalling pathways activated by testosterone via intracellular androgen receptor, and induced by damage to renal tubules evoked by anti-folate [N(10)-propargyl-5,8-dideazafolic acid (CB 3717)] or folate is reported. We show that CB 3717/folate induces the expression of the hepatocyte growth factor (HGF)/c-Met signalling system in injured kidneys in which a significant, but transient, elevation of the HGF mRNA level occurs. It is followed by a severalfold increase in the c-Met transmembrane receptor message that persists for up to 24 h. The c-Met expression is also positively controlled by testosterone, which induces a significant increase in its mRNA level that is abolished by an anti-androgen, casodex. However, when testosterone and anti-folate/folate are administered sequentially, a substantial (3.5-4.0-fold) decrease in the increase of c-Met expression caused by CB 3717/folate alone occurs. Similarly, testosterone-induced ornithine decarboxylase (ODC) mRNA level and activity are decreased 2.8-7.7-fold when the androgen is applied together with CB 3717. Antagonism between these pathways is also visible under physiological conditions in the kidneys of male mice in which, owing to elevated endogenous testosterone levels, neither the ODC activity nor the mRNA level is induced by anti-folate/folate, whereas the c-Met message response to these drugs is significantly decreased. Our results document a substantial negative regulation of c-Met and ODC gene expression as a result of the cross-talk between testosterone-activated and HGF-activated pathways and suggest a sex-differentiated response to injury of mouse kidneys.

Protooncogenes as mediators of apoptosis

Apoptosis has been well established as a vital biological phenomenon that is important in the maintenance of cellular homeostasis. Three major protooncogene families and their encoded proteins function as mediators of apoptosis in various cell types and are the subject of this chapter. Protooncogenic proteins such as c-Myc/Max, c-Fos/c-Jun, and Bcl-2/Bax utilize a synergetic effect to enhance their roles in the pro- or antiapoptotic action. These family members activate and repress the expression of their target genes, control cell cycle progression, and execute programmed cell death. Repression or overproduction of these protooncogenic proteins induces apoptosis, which may vary as a result of either cell type specificity or the nature of the apoptotic stimuli. The proapoptotic and antiapoptotic proteins exert their effects in the membrane of cellular organelles. Here they generate cell-type-specific signals that activate the caspase family of proteases and their regulators for the execution of apoptosis.

Hepatocyte growth factor signal coupling to various transcription factors depends on triggering of Met receptor and protein kinase transducers in human hepatoma cells HepG2

Hepatocyte growth factor (HGF) regulates a wide variety of biological activities by binding to the tyrosine kinase receptor Met. In HGF-treated hepatocarcinoma cells, we observed a biphasic activation of AP-1 and AP-2 transcription factors. For NF-kappaB complex the p50-p50 homodimer was activated before the p50-p65 heterodimer, and c-Myc/Max DNA-binding activity increased thereafter. Since these transcription factors are responders to mitogenic stimulation through protein kinase transducers, we tested the effects of inhibitors of these enzymes on the DNA binding after HGF treatment. Inhibition of protein kinase C (PKC) with H7 strikingly activated NF-kappaB above the values observed after HGF alone. Under this inhibitory condition, Met tyrosine phosphorylation was elevated as though the phosphorylation-dependent activity of the receptor was partially blocked by activation of PKC due to HGF. NF-kappaB DNA binding seems to be related to Met triggering by HGF since it was largely prevented by genistein treatment, which blocks receptor activity. Phosphatidylinositol 3-kinase seems to be involved in AP-1 binding activity stimulated by HGF. It is noteworthy that Met is responsive to HGF stimulating postreceptor signaling, which converges on the activation of transcription factors acting coordinately to regulate target gene expression.

Catecholamines participate in the induction of ornithine decarboxylase gene expression in normal and hyperplastic mouse kidney

In the quinazoline antifolate (CB 3717)-induced hyperplastic kidney model, a remarkable increase of ornithine decarboxylase (ODC) activity was paralleled by a smaller, but highly significant augmentation of the ODC transcript level. Catecholamine depletion, evoked by reserpine, strongly impaired antifolate-induced ODC expression; the enzyme activity was almost completely abolished while the mRNA level decreased by 60%. Moreover, under conditions of a depleted catecholamine pool, kidney enlargement was significantly reduced confirming our earlier reports on the indispensability of ODC induction for renal hyperplasia (M. Manteuffel-Cymborowska et al. , Biochim. Biophys. Acta, 1182 (1993) 133-141[1]). In normal mouse kidney catecholamines appeared to be inducers of ODC expression. Use of selective agonists of catecholamine receptors demonstrated the importance of dopamine D2 receptors, and to a lower extent beta adrenoreceptors, in the catecholamine mediation of induction of ODC activity and of ODC mRNA levels. These increases were not abolished by an antiandrogen, casodex, suggesting that catecholamine control of ODC expression is an androgen receptor-independent process. The results obtained point to the critical role of renal catecholamines; these biogenic amines are not only involved in the regulation of ODC expression in normal kidney but are also required for the induction of ODC in hyperplastic kidney evoked by antifolate and, as shown recently (M. Manteuffel-Cymborowska et al., Biochim. Biophys. Acta, 1356 (1997) 292-298[2]), in testosterone-induced hypertrophic kidney.