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

Regulation of tumor suppressor PDCD4 by novel protein kinase C isoforms

Transforming growth factor-beta1 (TGF-beta1) induces apoptosis in normal hepatocytes and hepatoma cells. PDCD4 is involved in TGF-beta1-induced apoptosis via the Smad pathway. The tumor promoter 12-O-tetradecanoylphorbor-13-acetate (TPA), a protein kinase C stimulator, inhibits TGF-beta1-induced apoptosis. However, the mechanisms of TPA action on PDCD4 expression remain to be elucidated. Therefore. the regulatory mechanism of PDCD4 expression by PKC was investigated. The treatment of the human hepatoma cell line, Huh7 with TPA suppressed PDCD4 protein expression and TGF-beta1 failed to increase the PDCD4 protein expression. PKC inhibitors Ro-31-8425 or bisindolylmaleimide-1-hydrocholoride (pan-PKC inhibitors) and rottlerin (PKCdelta inhibitor), but not Go6976 (PKCalpha inhibitor), enhanced the induction of PDCD4 protein by TGF-beta1. Furthermore, siRNA-mediated knockdown of PKCdelta and epsilon, but not PKCalpha, augmented the TGF-beta1-stimulated PDCD4 protein expression. However, TPA or pan-PKC inhibitor did not alter the PDCD4 mRNA expression either under basal- and TGF-beta1-treated conditions. The down-regulation of PDCD4 by TPA was restored by treatment with the proteasome inhibitor MG132. These data suggest that two isoforms of PKCs are involved in the regulation of the PDCD4 protein expression related to the proteasomal degradation pathway.

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.

Differential phosphorylation of p38 induced by apoptotic and anti-apoptotic stimuli in murine hepatocytes

AIM: To investigate the differential phosphorylation and activation of p38 in hepatocytes by pro-apoptotic Transforming Growth Factor-β1 (TGF-β1), pro-survival factors Epidermal Growth Factor (EGF) and 12-O-tetradecanoylphorbol-13-acetate (TPA) and the potential mechanisms.

METHODS: The phosphorylation and activation of p38 were determined by immunoblotting. Apoptosis was analyzed by morphological staining and observation, FACS analysis of sub-G1 content and DNA fragmentation assay. To quantitatively determine caspase activation, caspase activity assay was performed in vitro.

RESULTS: TGF-β1-induced apoptosis was associated with the phosphorylation of p38, and SB202190, a specific inhibitor of p38, which was able to inhibit TGF-β1-induced caspase activation and apoptosis. TPA and EGF also blocked apoptosis induced by TGF-β1. Both of them induced the phosphorylation of p38. The results showed SB202190 had no effect on TGF-β1-induced phosphorylation of p38, but effectively inhibited both EGF and TPA-induced phosphorylation of p38.

CONCLUSION: Pro-apoptotic TGF-β1, anti-apoptotic TPA and EGF induce the phosphorylation of p38 through different mechanisms that can be distinguished by SB202190. The data suggest that TPA and EGF-induced p38 phosphorylation is through an autophosphorylation-dependent mechanism. Since p38 phosphorylation induced by TGF-β1 plays an important role in caspase activation and apoptosis, TPA and EGF-induced p38 phosphorylation may not be requisite for their anti-apoptotic function.

Effects of difluoromethylornithine on growth inhibition and apoptosis in human cervical epithelial and cancerous cell lines

OBJECTIVE

Difluoromethylornithine(DFMO), an irreversible inhibitor of ornithine decarboxylase and an angiogenesis inhibitor, has been used in phase I cervical intraepithelial neoplasia (CIN) trials, producing a 50% regression of CIN 3 lesions. DFMO is currently in phase II trials. In the experiments reported here, DFMO's growth inhibition and apoptosis induction were explored in an in vitro model to elucidate mechanisms of action.

METHODS

Four immortalized cervical epithelial cell lines, serving as in vitro models of precancerous CIN lesions, and nine cervical carcinoma cell lines were studied. DFMO's growth inhibitory effect was tested in monolayer culture and in semisolid medium, and concentrations required for a 50% growth inhibition (IC(50)) with a 5-day treatment were determined. Apoptosis induction was analyzed using the terminal deoxynucleotidyl transferase assay of DNA fragmentation.

RESULTS

DFMO inhibited growth of immortalized cervical epithelial cell lines and cervical cancer cell lines in monolayer culture and in semisolid medium. The immortalized cervical epithelial cell lines were more sensitive than the cervical cancer cell lines to DFMO's growth inhibitory effect. Concentrations required for 50% growth inhibition after a 5-day treatment ranged from 100 microM to >5 mM for cervical carcinoma cell lines and from 100 microM to 1 mM for immortalized cervical epithelial cell lines. DFMO induced apoptosis in precancerous and cancerous cell lines at a concentration of 5 mM, regardless of the cells' human papillomavirus status.

CONCLUSION

DFMO inhibits the growth of cervical precancerous and cancerous cells in vitro in a dose-dependent and time-dependent manner, partially through inducing apoptosis.

Growth inhibitory effect of green tea extract in Ehrlich ascites tumor cells involves cytochrome c release and caspase activation

We reported previously that the mechanism by which Green tea extract (GTE) elicited growth-inhibitory effects in Ehrlich ascites tumor cells involved a decrease in ornithine decarboxylase (ODC) activity and in cell viability. Decrease in ODC activity has been associated with apoptotic cell death and we therefore studied changes in cytochrome c release and caspase activation, which characterize apoptosis. GTE caused a dose- and time-dependent increase in caspase-3-like protease activation, preceded by a release of cytochrome c from the mitochondria. Inhibiting the activation of caspase-3 with acetyl-Asp-Glu-Val-Asp-alpha-aldehyde (caspase inhibitor) caused a reversal in the effect on cell viability.

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.