TGF-beta 1 inhibits polyamine biosynthesis in K 562 leukemic cells

The Interplay Between TGF-β Signaling and Cell Metabolism

The transforming growth factor-β (TGF-β) signaling plays a critical role in the development and tissue homeostasis in metazoans, and deregulation of TGF-β signaling leads to many pathological conditions. Mounting evidence suggests that TGF-β signaling can actively alter metabolism in diverse cell types. Furthermore, metabolic pathways, beyond simply regarded as biochemical reactions, are closely intertwined with signal transduction. Here, we discuss the role of TGF-β in glucose, lipid, amino acid, redox and polyamine metabolism with an emphasis on how TGF-β can act as a metabolic modulator and how metabolic changes can influence TGF-β signaling. We also describe how interplay between TGF-β signaling and cell metabolism regulates cellular homeostasis as well as the progression of multiple diseases, including cancer.

Isothiocyanate sulforaphane inhibits protooncogenic ornithine decarboxylase activity in colorectal cancer cells via induction of the TGF-β/Smad signaling pathway

SCOPE

The objective of this study was to elucidate molecular mechanisms behind the antitumor activities of the isothiocyanate sulforaphane (SFN) in colorectal cancer cells.

METHODS AND RESULTS

Cell growth was determined by BrdU incorporation and crystal violet staining. Protein levels were examined by Western blot analysis. Ornithine decarboxylase (ODC) activity was assayed radiometrically. Reverse transcriptase-PCR was used for measuring mRNA expression. For reporter gene assays plasmids were transfected into cells via lipofection and luciferase activity was measured luminometrically. Acetyl-histone H3 and H4 chromatin immunoprecipitation (ChIP) assays were performed followed by PCR with TGF-β-receptor II promoter specific primers. We could show that SFN-mediated cell growth inhibition closely correlates with a dose-dependent reduction of protein expression and enzymatic activity of ODC. This effect seems to be due to reduced protein levels and transactivation activity of transcription factor c-myc, a direct regulator of ODC expression, as a consequence of SFN-induced TGF-β/Smad signaling. The coherency of these results was further confirmed by using TGF-β receptor kinase inhibitor SB431542, which largely abolishes inhibitory effects of SFN on both, ODC activity and cell growth.

CONCLUSION

Since elevated ODC enzyme activity is associated with enhanced tumor development, SFN may be a dietary phytochemical with potential to prevent carcinogenesis.

Comparison of skeletal muscle transcriptional profiles in dairy and beef breeds bulls

A cDNA microarray (18 263 probes) was used for transcriptome analysis of bovine skeletal muscle (m. semitendinosus) in 12-month-old bulls of the beef breed Limousin (LIM) and the typical dairy breed Holstein-Friesian (HF, used as a reference). We aimed to identify the genes whose expression may reflect the muscle phenotype of beef bulls. A comparison of muscle transcriptional profiles revealed significant differences in expression of 393 genes between HF and LIM. We classified biological functions of 117 genes with over 2-fold differences in expression between the examined breeds. Among them, 72 genes were up-regulated and 45 genes were down-regulated in LIM vs. HF. The genes were involved in protein metabolism and modifications (22 genes), signal transduction (15), nucleoside, nucleotide and nucleic acid metabolism (13), cell cycle (9), cell structure and motility (9), developmental processes (9), intracellular protein traffic (7), cell proliferation and differentiation (6), cell adhesion (6), lipid, fatty acid and steroid metabolism (5), transport (5), and other processes. For the purpose of microarray data validation, we randomly selected 4 genes: trip12, mrps30, pycrl, and c-erbb3. Real-time RT-PCR results showed similar trends in gene expression changes as those observed in microarray studies. Basing on results of the present study, we proposed a model of the regulation of skeletal muscle growth and differentiation, with a principal role of the somatotropic pathway. It may explain at least in part the development of muscle phenotype in LIM bulls. We assume that the growth hormone directly or indirectly (through IGF-1) activates the calcium-signaling pathway with calcineurin, which stimulates myogenic regulatory factors (MRFs) and inhibits early growth response gene. The inhibition results in indirect activation of MRFs and impaired activation of TGF-beta1 and myostatin, which finally facilitates terminal muscle differentiation.

Involvement of polyamines in retinoblastoma protein phosphorylation

Hepatocyte growth factor (HGF) increased both levels of phosphorylated and non-phosphorylated forms of retinoblastoma protein (RB) in primary cultured rat hepatocytes. Combined treatment of HGF and a specific inhibitor of ornithine decarboxylase (ODC), alpha-difluoromethylornithine (DFMO), reduced the levels of hyper-phosphorylated and hypo-phosphorylated forms of RB and increased the levels of the non-phosphorylated form, compared to HGF alone, but did not affect the total level of RB. Polyamines added exogenously overcame the effects of DFMO; they increased hyper- and hypo-phosphorylated forms and decreased non-phosphorylated RB. TGF-beta1 inhibited the increases in ODC activity, RB phosphorylation, and DNA synthesis induced by HGF. However, polyamines added exogenously could not overcome the inhibition by RB phosphorylation and DNA synthesis by TGF-beta1. These results suggest that polyamines are involved in the phosphorylation of RB, but the inhibition of polyamine biosynthesis by TGF-beta1 did not result in the inhibition of RB phosphorylation and DNA synthesis.

Expression of bcl-2 and bax in TGF-beta 1-induced apoptosis of L1210 leukemic cells

TGF-beta1 is a multifunctional regulatory peptide (25 kDa) inducing growth arrest and apoptosis in many normal and neoplastic cells. In the present study, the involvement of proapoptotic (bax) and antiapoptotic (bcl-2) genes in the molecular mechanism of TGF-beta1-induced apoptosis of L1210 leukemic cells was investigated. Bax transcript was measured using the RT-PCR method with GAPDH as a "housekeeping gene" control, whereas Bcl-2 protein was determined using flow cytometry (FITC-conjugated monoclonal anti-Bcl-2 antibody and FITC-conjugated mouse anti-IgG1 antibody as a negative control). Apoptosis was evaluated using fluorescence microscopy and flow cytometry after cell staining with DAPI and sulforhodamine or propidium iodide and Hoechst 33342. ROS generation was assessed by flow cytometry using the oxidation-sensitive fluorescent marker C-DCDHF-DA. The response of L1210 leukemic cells to TGF-beta1 was two-directional: 1) partial arrest of the cell cycle at G1-S transition, and 2) induction of apoptotic cell death. TGF-beta1 increased the number of leukemic cells with typical morphological features of apoptosis: cell shrinkage, condensation of chromatin, pyknosis and fragmentation of nuclei, followed by secondary necrosis. DNA cleavage led to a decrease of the nuclear DNA content and the appearance of a hypodiploid peak sub-G1 in the DNA histogram. The extraction of low-molecular weight DNA fragments from apoptotic cells showed that TGF-beta1-induced apoptosis concerned first of all the cells from G1 phase. Two phases of intracellular ROS generation in TGF-beta1-treated cultures were observed: the first (rapid, 60 min after TGF-beta1 administration), and the second (slow, occurring between 24 and 48h of experiment, respectively). The increase of apoptotic cell number in TGF-beta1-treated cultures (2% FCS/RPMI 1640) was associated with the decrease of cell number expressing bcl-2, and with a significant drop of Bcl-2 level in the remaining cells after 24 h. The dose-dependent relationship between TGF-beta1 concentration and Bcl-2 level was nonlinear and described by power series regression. The lowest Bcl-2 level was noted at 1 ng/ml of TGF-beta1 concentration. The increase of Bax mRNA:GAPDH mRNA ratio was observed 3h after TGF-beta1 (1 ng/ml) administration to both the maintenance (2% FCS/RPMI) and growth promoting (10% FCS/RPMI) medium. Regardless of TGF-beta1 treatment, the quantity of Bax transcript was dependent on FCS concentration, being higher in the growth promoting medium. The results of this study indicate that bax may function as a primary response gene and together with lowered Bcl-2 level may determine the induction of apoptotic process in L1210 leukemic cells exposed to TGF-beta1.

Inhibition of spermidine synthase gene expression by transforming growth factor-beta 1 in hepatoma cells

We screened genes responsive to transforming growth factor-beta (TGF-beta 1) protein in a human hepatoma cell line (Hep3B) using a PCR-mediated differential display technique, in order to investigate the mechanisms involved in TGF-beta-induced growth suppression. We found a gene that was down-regulated by TGF-beta 1 to be completely identical in an approx. 620 bp segment to the gene for the enzyme spermidine synthase, which mediates the conversion of putrescine into spermidine. Both spermidine synthase mRNA expression and its enzyme activity were decreased after TGF-beta 1 treatment of Hep3B cells. The inhibition of spermidine synthase gene expression by TGF-beta 1 protein was also observed in other hepatoma cell lines. The expression of genes for other biosynthetic enzymes in polyamine metabolism (ornithine decarboxylase and S-adenosylmethionine decarboxylase) was also inhibited to the same extent as for spermidine synthase, while the gene expression of spermidine/spermine N1-acetyltransferase, a catabolic enzyme, was relatively resistant to TGF-beta 1. Spermine levels in Hep3B cells were decreased by TGF-beta 1 treatment, although the levels of spermidine and putrescine were unchanged, probably due to compensation by remaining spermidine/spermine N1-acetyltransferase activity. Exogenously added spermidine or spermine, but not putrescine, partially antagonized the growth-inhibitor effects of TGF-beta 1 on Hep3B cells. Our data suggest that down-regulation of gene expression of the enzymes involved in polyamine metabolism, including spermidine synthase, may be associated with the mechanism of TGF-beta-induced growth suppression.

Phorbol ester (12-O-tetradecanoylphorbol 13-acetate) prevents ornithine decarboxylase inhibition and apoptosis and L1210 leukemic cells exposed to TGF-beta 1

Previous studies have shown that growth suppression and apoptosis of leukemic cells exposed to TGF-beta 1 is associated with the inhibition of ornithine decarboxylase (ODC)--the key enzyme of polyamine pathway. The aim of the present study was to evaluate the influence of 12-O-tetradecanoylphorbol 13-acetate (TPA)--a potent ODC inducer on antiproliferative and apoptotic effects of TGF-beta 1 in L1210 leukemic cells. Cells were incubated in 2% FCS/RPMI-1640 medium, supplemented with TGF-beta 1 (2 ng/ml). TPA (100 ng/ml) or alpha-difluoromethylornithine (DFMO) (5 mM). Cell proliferation, apoptosis and necrosis were evaluated using [methyl-3H] thymidine, electron microscopy, electrophoresis of DNA and trypan blue exclusion. Expression and activity of ODC were determined by RT-PCR and measurement of 14CO2 release from L-1-14C ornithine, respectively. TGF-beta 1 inhibited proliferation and induced apoptotic and necrotic cell death in L1210 leukemic cells. The above effects were associated with the inhibition of ODC expression and activity, measured 2 and 4 hr after TGF-beta 1 administration, respectively. The presence of DFMO, an irreversible inhibitor of ODC, led to apoptotic fragmentation of DNA, similar to that observed in TGF-beta 1-treated cultures. Administration of TPA simultaneously with TGF-beta 1 significantly reduced antiproliferative, apoptotic and necrotic effects of TGF-beta 1, and prevented its inhibitory action of ODC expression and activity. It is concluded that: down-regulation of ODC expression may be one of the early events associated with TGF-beta 1-evoked suppression of growth and apoptosis; ODC is involved in the mechanism of protective action of TPA on TGF-beta 1-related growth inhibition of L1210 leukemic cells.

Membrane modifications in human erythroleukemia K562 cells during induction of programmed cell death by transforming growth factor beta 1 or cisplatin

Transforming growth factor beta 1 (TGF beta 1) and cisplatin induce apoptosis (programmed cell death, PCD) in human erythroleukemia K562 cells in an additive manner. After PCD was induced in K562 cells, analysis of phospholipid composition, fatty acids and cholesterol content in their membranes showed a decrease in phosphatidylethanolamine and an increase in phosphatidylserine, cardiolipin and phosphatidic acid. Moreover, cisplatin but not TGF beta 1 enhanced sphingomyeline levels in apoptotic cells, whereas TGF beta 1 increased the amount of linoleic acid and, more remarkably, of cholesterol. The combination TGF beta 1 + cisplatin produced membrane changes similar to those provoked by each inducer individually. Furthermore, the specific activities of 5-lipoxygenase and cytosolic phospholipase A2, both modulating the physical properties of membranes and membrane-lipid-mediated intracellular signalling, were enhanced by treatment with TGF beta 1 or TGF beta 1 + cisplatin. These findings highlight the profound changes in cell membranes during the biochemical events of the apoptotic pathway.

Involvement of polyamines in epidermal growth factor (EGF), transforming growth factor (TGF)-alpha and -beta 1 action on culture of L6 and fetal bovine myoblasts

1. alpha-Difluoromethylornithine, an irreversible inhibitor of ornithine decarboxylase significantly abolished stimulation of protein synthesis evoked by EGF, TGF-alpha or -beta 1 in L6 and fetal bovine myoblasts. 2. The participation of polyamines in early events evoked by growth factors was shown by a significant stimulation of ornithine decarboxylase and S-adenosylmethionine decarboxylase activity as well as increased concentration of spermidine and spermine in L6 cells exposed to TGF-alpha and EGF. 3. TGF-beta 1 at a high concentration (1 ng/ml) increased protein synthesis in L6 myoblasts but inhibited it in fetal bovine myoblasts. Metabolic effects of TGF-beta 1 in L6 cells was associated with an enhancement of decarboxylase activities, however there were no significant changes in cellular polyamine concentrations. Presented data suggest that polyamines are involved in the signal transduction pathway of EGF, TGF-alpha, and -beta 1 in L6 and fetal bovine myoblasts.