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Abstract: Peroxisome proliferator-activated receptor γ (PPARγ) ligands inhibit cell proliferation and induce apoptosis in cancer cells. Here we wished to determine whether the PPARγ ligand induces apoptosis and cell cycle arrest of the MDA-MB-231 cell, an estrogen receptor α negative breast cancer cell line. The treatment of MDA-MB-231 cell with PPARγ ligands was shown to induce inhibition of cell growth in a dose-dependent manner as determined by MTT assay. Cell cycle analysis showed a G1 arrest in MDA-MB-231 cells exposed to troglitazone. An apoptotic effect by troglitazone demonstrated that apoptotic cells elevated by 2.5-fold from the control level at 10μM, to 3.1-fold at 50μM and to 3.5-fold at 75μM. Moreover, troglitazone treatment, applied in a dose-dependent manner, caused a marked decrease in pRb, cyclin D1, cyclin D2, cyclin D3, Cdk2, Cdk4 and Cdk6 expression as well as a significant increase in p21 and p27 expression. These results indicate that troglitazone causes growth inhibition, G1 arrest and apoptotic death of MDA-MB-231 cells. [Copyright &y& Elsevier]

The differentiation of promyelocytic leukemic cells into mature cells is the major strategy for drug-based treatment of leukemia. Higher efficient methods to differentiate promyelocytic leukemic cells have been developed using various differentiation inducers including interferon-alpha, interleukin-4, tumor necrosis factor-alpha (TNF-alpha), and dimethyl sulfoxide (DMSO) as a single agent or in combination with each other. Here, we show that a combination of TNF-alpha with DMSO shows a synergic effect on HL-60 cell differentiation through the activation of ERK pathway. TNF-alpha enhanced CD11b expression and percent of cell population in the G1 phase induced by DMSO, which are hallmarks for HL-60 cell differentiation. Inhibition of ERK pathway abolished the synergic effect of TNF-alpha in combination with DMSO on HL-60 differentiation, but the inhibition NF-kappaB pathway did not. These results suggest that TNF-alpha synergistically increases DMSO-induced differentiation of HL-60 cells through the activation of ERK/MAPK-signaling pathway. [ABSTRACT FROM AUTHOR]

Peroxisome proliferator-activated receptor gamma (PPARgamma) and retinoic acid receptors (RARs) have been a focus in chemotherapy for human cancers. The tumor suppressor PTEN plays a pivotal role in the growth of human cancer cells. We investigated whether costimulation of PPARgamma and RAR could synergistically up-regulate PTEN in human leukemia cells and consequently potentiate the inhibition of growth and cell cycle progression of these cells. We found that overexpression of PTEN with the adenoviral vector Ad/PTEN caused growth arrest at the G1 phase of the cell cycle of HL-60 cells. HL-60 cells treated with either a PPARgamma ligand (ciglitazone) or a RAR ligand (all-trans retinoic acid [ATRA]) up-regulated PTEN in HL-60 cells. The 2 compounds in combination showed synergistic effects on PTEN expression at the protein and messenger RNA levels. Moreover, the combination of ciglitazone and ATRA synergistically reduced cell growth rates and cell cycle arrest at the G1 phase. Our results suggest that, PPARgamma and RAR play an important role in controlling the growth of leukemia cells via the up-regulation of PTEN. [ABSTRACT FROM AUTHOR]

Docosahexaenoic acid (DHA) is an omega-3 fatty acid that is considered to have applications in cancer prevention and treatment. The beneficial effects of DHA against cancer metastasis are well established; however, the mechanisms underlying these effects in breast cancer are not clear. Cell invasion is critical for neoplastic metastasis, and involves the degradation of the extracellular matrix by matrix metalloproteinase (MMP)-9. The present study investigated the inhibitory effect of DHA on MMP-9 expression and cell invasion induced by 12- O -tetradecanoylphorbol-13-acetate (TPA) in the MCF-7 breast cancer cell line. DHA inhibited the TPA-induced activation of mitogen-activated protein kinase (MAPK) and the transcription of nuclear factor (NF)-κB, but did not inhibit the transcription of activator protein-1. DHA increased the activity of peroxisome proliferator-activated receptor (PPAR)-γ, an effect that was reversed by the application of the PPAR-γ antagonist GW9662. In addition, combined treatment with GW9662 and DHA increased NF-κB-related protein expression. These results indicate that DHA regulates MMP-9 expression and cell invasion via modulation of the MAPK signaling pathway and PPAR-γ/NF-κB activity. This suggests that DHA could be a potential therapeutic agent for the prevention of breast cancer metastasis.

The tumor suppressor protein, PTEN (phosphatase and tensin homologue), has been reported to play a crucial role in a variety of tumor cells. Recent studies indicate that the transcription factor, PPARgamma (peroxisome proliferator-activated receptor gamma) up-regulates PTEN expression transcriptionally through the binding of two response elements in the genomic sequence upstream of PTEN in tumor cells. Here, we determined the PTEN and PPARgamma expression in human leiomyomas, and whether estrogen can change their protein expressions in cultured leiomyoma cells. Immunohistochemical staining and Western blot analysis revealed that PTEN protein levels in leiomyomas were higher than that the adjacent normal myometrial tissues, which was paralleled with decrease in phospho-Akt (ser-473) and phosphatidylinositol 3,4,5-tris phosphate (PIP3) level. Interestingly, leiomyomas exhibit high PPARgamma expression compared to the adjacent normal myometrial tissues. In addition, we found that 17beta-estradiol (E2) significantly stimulated PTEN and PPARgamma expression in cultured leiomyoma cells, but did not change both protein levels in normal cells. This report shows the first evidence that PTEN and PPARgamma are up-regulated in leiomyoma tissues, and estrogen stimulates expression of PTEN and PPARgamma in leiomyoma cells, but not in normal cells.

Peroxisome proliferator-activated receptor gamma (PPARgamma) ligands inhibit cell proliferation and induce apoptosis in cancer cells. Here we wished to determine whether the PPARgamma ligand induces apoptosis and cell cycle arrest of the MDA-MB-231 cell, an estrogen receptor alpha negative breast cancer cell line. The treatment of MDA-MB-231 cell with PPARgamma ligands was shown to induce inhibition of cell growth in a dose-dependent manner as determined by MTT assay. Cell cycle analysis showed a G1 arrest in MDA-MB-231 cells exposed to troglitazone. An apoptotic effect by troglitazone demonstrated that apoptotic cells elevated by 2.5-fold from the control level at 10 microM, to 3.1-fold at 50 microM and to 3.5-fold at 75 microM. Moreover, troglitazone treatment, applied in a dose-dependent manner, caused a marked decrease in pRb, cyclin D1, cyclin D2, cyclin D3, Cdk2, Cdk4 and Cdk6 expression as well as a significant increase in p21 and p27 expression. These results indicate that troglitazone causes growth inhibition, G1 arrest and apoptotic death of MDA-MB-231 cells.

TNF-alpha plays a variety of biological functions such as apoptosis, inflammation and immunity. PTEN also has various cellular function including cell growth, proliferation, migration and differentiation. Thus, possible relationships between the two molecules are suggested. TNF-alpha has been known to downregulate PTEN via NF-kappaB pathway in the human colon cell line, HT-29. However, here we show the opposite finding that TNF-alpha upregulates PTEN via activation of NF-kappaB in human leukemic cells. TNF-alpha increased PTEN expression at HL-60 cells in a time- and dose-dependent manner, but the response was abolished by disruption of NF-kappaB with p65 antisense phosphorothioate oligonucleotide or pyrrolidine dithiocarbamate. We found that TNF-alpha activated the NF-kappaB pathways, evidenced by the translocation of p65 to the nucleus in TNF-alpha-treated cells. We conclude that TNF-alpha induces upregulation of PTEN expression through NF-kappaB activation in human leukemic cells.

Estrogen stimulates cell proliferation in breast cancer. The biological effects of estrogen are mediated through two intracellular receptors, estrogen receptor-alpha (ERalpha) and estrogen receptor-beta (ERbeta). However, the role of ERs in the proliferative action of estrogen is not well established. Recently, it has been known that ER activates phosphatidylinositol-3-OH kinase (PI3K) through binding with the p85 regulatory subunit of PI3K. Therefore, possible mechanisms may include ER-mediated phosphoinositide metabolism with subsequent formation of phosphatidylinositol-3,4,5-trisphosphate (PIP(3)), which is generated from phosphatidylinositol 4,5-bisphosphate via PI3K activation. The present study demonstrates that 17beta-estradiol (E2) up-regulates PI3K in an ERalpha-dependent manner, but not ERbeta, and stimulates cell growth in breast cancer cells. In order to study this phenomenon, we have treated ERalpha-positive MCF-7 cells and ERalpha-negative MDA-MB-231 cells with 10nM E2. Treatment of MCF-7 cells with E2 resulted in a marked increase in PI3K (p85) expression, which paralleled an increase in phospho-Akt (Ser-473) and PIP(3) level. These observations also correlated with an increased activity to E2-induced cell proliferation. However, these effects of E2 on breast cancer cells were not observed in the MDA-MB-231 cell line, indicating that the E2-mediated up-regulation of PI3K/Akt pathway is ERalpha-dependent. These results suggest that estrogen activates PI3K/Akt signaling through ERalpha-dependent mechanism in MCF-7 cells.