Caspase-dependent proteolytic cleavage of STAT3alpha in ES cells, in mammary glands undergoing forced involution and in breast cancer cell lines.

BACKGROUND: The STAT (Signal Transducers and Activators of Transcription) transcription factor family mediates cellular responses to a wide range of cytokines. Activated STATs (particularly STAT3) are found in a range of cancers. Further, STAT3 has anti-apoptotic functions in a range of tumour cell lines. After observing a proteolytic cleavage in STAT3alpha close to a potential apoptotic caspase protease cleavage site we investigated whether STAT3alpha might be a caspase substrate. METHODS: STAT3alpha status was investigated in vitro in several cell systems:- HM-1 murine embryonic stem (ES) cells following various interventions; IOUD2 murine ES cells following induction to differentiate along neural or adipocyte lineages; and in a number of breast cancer cell lines. STAT3alpha status was also analysed in vivo in wild type murine mammary glands undergoing controlled, forced involution. RESULTS: Immunoblotting for STAT3alpha in HM-1 ES cell extracts detected amino and carboxy terminal species of approximately 48 kDa and 43 kDa respectively--which could be diminished dose-dependently by cell treatment with the nitric oxide (NO) donor drug sodium nitroprusside (SNP). UV irradiation of HM-1 ES cells triggered the STAT3alpha cleavage (close to a potential caspase protease cleavage site). Interestingly, the pan-caspase inhibitor z-Val-Ala-DL-Asp-fluoromethylketone (z-VAD-FMK) and the JAK2 tyrosine kinase inhibitor AG490 both inhibited cleavage dose-dependently, and cleavage was significantly lower in a heterozygous JAK2 knockout ES cell clone. STAT3alpha cleavage also occurred in vivo in normal murine mammary glands undergoing forced involution, coinciding with a pulse of phosphorylation of residue Y705 on full-length STAT3alpha. Cleavage also occurred during IOUD2 ES cell differentiation (most strikingly along the neural lineage) and in several human breast cancer cell lines, correlating strongly with Y705 phosphorylation. CONCLUSION: This study documents a proteolytic cleavage of STAT3alpha into 48 kDa amino and 43 kDa carboxyl terminal fragments in a range of cell types. STAT3alpha cleavage occurs close to a potential caspase site, and can be inhibited dose-dependently by SNP, AG490 and z-VAD-FMK. The cleavage seems to be caspase-dependent and requires the phosphorylation of STAT3alpha at the Y705 residue. This highly regulated STAT3alpha cleavage may play an important role in modulating STAT3 transcriptional activity.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

The novel curcumin analog FLLL32 decreases STAT3 DNA binding activity and expression, and induces apoptosis in osteosarcoma cell lines

<p>Abstract</p> <p>Background</p> <p>Curcumin is a naturally occurring phenolic compound shown to have a wide variety of antitumor activities; however, it does not attain sufficient blood levels to do so when ingested. Using structure-based design, a novel compound, FLLL32, was generated from curcumin. FLLL32 possesses superior biochemical properties and more specifically targets STAT3, a transcription factor important in tumor cell survival, proliferation, metastasis, and chemotherapy resistance. In our previous work, we found that several canine and human osteosarcoma (OSA) cell lines, but not normal osteoblasts, exhibit constitutive phosphorylation of STAT3. Compared to curcumin, we hypothesized that FLLL32 would be more efficient at inhibiting STAT3 function in OSA cells and that this would result in enhanced downregulation of STAT3 transcriptional targets and subsequent death of OSA cells.</p> <p>Methods</p> <p>Human and canine OSA cells were treated with vehicle, curcumin, or FLLL32 and the effects on proliferation (CyQUANT^®), apoptosis (SensoLyte^®Homogeneous AMC Caspase- 3/7 Assay kit, western blotting), STAT3 DNA binding (EMSA), and vascular endothelial growth factor (VEGF), survivin, and matrix metalloproteinase-2 (MMP2) expression (RT-PCR, western blotting) were measured. STAT3 expression was measured by RT-PCR, qRT- PCR, and western blotting.</p> <p>Results</p> <p>Our data showed that FLLL32 decreased STAT3 DNA binding by EMSA. FLLL32 promoted loss of cell proliferation at lower concentrations than curcumin leading to caspase-3- dependent apoptosis, as evidenced by PARP cleavage and increased caspase 3/7 activity; this could be inhibited by treatment with the pan-caspase inhibitor Z-VAD-FMK. Treatment of OSA cells with FLLL32 decreased expression of survivin, VEGF, and MMP2 at both mRNA and protein levels with concurrent decreases in phosphorylated and total STAT3; this loss of total STAT3 occurred, in part, via the ubiquitin-proteasome pathway.</p> <p>Conclusions</p> <p>These data demonstrate that the novel curcumin analog FLLL32 has biologic activity against OSA cell lines through inhibition of STAT3 function and expression. Future work with FLLL32 will define the therapeutic potential of this compound <it>in vivo</it>.</p

Gene expression analysis of cell death induction by Taurolidine in different malignant cell lines

<p>Abstract</p> <p>Background</p> <p>The anti-infective agent Taurolidine (TRD) has been shown to have cell death inducing properties, but the mechanism of its action is largely unknown. The aim of this study was to identify potential common target genes modulated at the transcriptional level following TRD treatment in tumour cell lines originating from different cancer types.</p> <p>Methods</p> <p>Five different malignant cell lines (HT29, Chang Liver, HT1080, AsPC-1 and BxPC-3) were incubated with TRD (100 μM, 250 μM and 1000 μM). Proliferation after 8 h and cell viability after 24 h were analyzed by BrdU assay and FACS analysis, respectively. Gene expression analyses were carried out using the <it>Agilent </it>-microarray platform to indentify genes which displayed conjoint regulation following the addition of TRD in all cell lines. Candidate genes were subjected to <it>Ingenuity Pathways Analysis </it>and selected genes were validated by qRT-PCR and Western Blot.</p> <p>Results</p> <p>TRD 250 μM caused a significant inhibition of proliferation as well as apoptotic cell death in all cell lines. Among cell death associated genes with the strongest regulation in gene expression, we identified pro-apoptotic transcription factors (EGR1, ATF3) as well as genes involved in the ER stress response (PPP1R15A), in ubiquitination (TRAF6) and mitochondrial apoptotic pathways (PMAIP1).</p> <p>Conclusions</p> <p>This is the first conjoint analysis of potential target genes of TRD which was performed simultaneously in different malignant cell lines. The results indicate that TRD might be involved in different signal transduction pathways leading to apoptosis.</p

Benzylacyclouridine reverses azidothymidine-induced marrow suppression without impairment of anti-human immunodeficiency virus activity

Abstract Increased extracellular concentrations of uridine (Urd) have been reported to reduce, in vitro, azidothymidine (AZT)-induced inhibition of human granulocyte-macrophage progenitor cells without impairment of its antihuman immunodeficiency virus (HIV) activity. Because of the clinical toxicities associated with chronic Urd administration, the ability of benzylacyclouridine (BAU) to effect, in vivo, AZT-induced anemia and leukopenia was assessed. This agent inhibits Urd catabolism and, in vivo, increases the plasma concentration of Urd in a dose- dependent manner, without Urd-related toxicity. In mice rendered anemic and leukopenic by the administration of AZT for 28 days in drinking water (1.5 mg/mL), the continued administration of AZT plus daily BAU (300 mg/kg, orally) partially reversed AZT-induced anemia and leukopenia (P less than .05), increased peripheral reticulocytes (to 4.9%, P less than .01), increased cellularity in the marrow, and improved megaloblastosis. When coadministered with AZT from the onset of drug administration, BAU reduced AZT-induced marrow toxicity. In vitro, at a concentration of 100 mumol/L, BAU possesses minimal anti- HIV activity and has no effect on the ability of AZT to reverse the HIV- induced cytopathic effect in MT4 cells. The clinical and biochemical implications of these findings are discussed.</jats:p

Different effect of benzylacyclouridine on the toxic and therapeutic effects of azidothymidine in mice

Abstract It has been reported that in vitro uridine (Urd) can reverse azidothymidine (AZT) cytotoxicity without decreasing anti-human immunodeficiency virus (HIV) activity. Our studies in mice have shown that daily oral doses of benzylacyclouridine (BAU), an inhibitor of Urd breakdown, also reduces AZT hematologic toxicity, presumably by elevating the plasma concentration of Urd. We now extend these murine studies and report the effect of various doses of exogenous Urd, various doses of BAU, or the combination of BAU and Urd, administered daily, on AZT-induced toxicity. In mice receiving concomitant AZT, daily doses of Urd of 1,000 to 2,000 mg/kg increase peripheral reticulocytes and slightly reduce AZT-induced hematologic toxicity. However, the range of effective doses is narrow, and higher doses of Urd (greater than 3,000 mg/kg/d) significantly enhance hematologic toxicity. At its most effective dose, (2,000 mg/kg/d), Urd produces 28% mortality. In contrast, BAU doses up to 300 mg/kg/d reduced AZT-related hematologic toxicity in a dose-dependent manner without mortality. Higher daily doses of BAU and the combination of BAU with low doses of Urd were not more effective. Studies conducted in mice infected with the Rauscher murine leukemia virus (RLV) indicate that BAU does not impair the antiretroviral effect of AZT when administered at doses that reduce AZT-induced anemia and leukopenia. These findings may be significant for the treatment of patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex.</jats:p

Benzylacyclouridine reverses azidothymidine-induced marrow suppression without impairment of anti-human immunodeficiency virus activity

Increased extracellular concentrations of uridine (Urd) have been reported to reduce, in vitro, azidothymidine (AZT)-induced inhibition of human granulocyte-macrophage progenitor cells without impairment of its antihuman immunodeficiency virus (HIV) activity. Because of the clinical toxicities associated with chronic Urd administration, the ability of benzylacyclouridine (BAU) to effect, in vivo, AZT-induced anemia and leukopenia was assessed. This agent inhibits Urd catabolism and, in vivo, increases the plasma concentration of Urd in a dose- dependent manner, without Urd-related toxicity. In mice rendered anemic and leukopenic by the administration of AZT for 28 days in drinking water (1.5 mg/mL), the continued administration of AZT plus daily BAU (300 mg/kg, orally) partially reversed AZT-induced anemia and leukopenia (P less than .05), increased peripheral reticulocytes (to 4.9%, P less than .01), increased cellularity in the marrow, and improved megaloblastosis. When coadministered with AZT from the onset of drug administration, BAU reduced AZT-induced marrow toxicity. In vitro, at a concentration of 100 mumol/L, BAU possesses minimal anti- HIV activity and has no effect on the ability of AZT to reverse the HIV- induced cytopathic effect in MT4 cells. The clinical and biochemical implications of these findings are discussed.</jats:p

Different effect of benzylacyclouridine on the toxic and therapeutic effects of azidothymidine in mice

It has been reported that in vitro uridine (Urd) can reverse azidothymidine (AZT) cytotoxicity without decreasing anti-human immunodeficiency virus (HIV) activity. Our studies in mice have shown that daily oral doses of benzylacyclouridine (BAU), an inhibitor of Urd breakdown, also reduces AZT hematologic toxicity, presumably by elevating the plasma concentration of Urd. We now extend these murine studies and report the effect of various doses of exogenous Urd, various doses of BAU, or the combination of BAU and Urd, administered daily, on AZT-induced toxicity. In mice receiving concomitant AZT, daily doses of Urd of 1,000 to 2,000 mg/kg increase peripheral reticulocytes and slightly reduce AZT-induced hematologic toxicity. However, the range of effective doses is narrow, and higher doses of Urd (greater than 3,000 mg/kg/d) significantly enhance hematologic toxicity. At its most effective dose, (2,000 mg/kg/d), Urd produces 28% mortality. In contrast, BAU doses up to 300 mg/kg/d reduced AZT-related hematologic toxicity in a dose-dependent manner without mortality. Higher daily doses of BAU and the combination of BAU with low doses of Urd were not more effective. Studies conducted in mice infected with the Rauscher murine leukemia virus (RLV) indicate that BAU does not impair the antiretroviral effect of AZT when administered at doses that reduce AZT-induced anemia and leukopenia. These findings may be significant for the treatment of patients with acquired immunodeficiency syndrome (AIDS) and AIDS-related complex.</jats:p