Shingo Yogosawa

A combination of indole-3-carbinol and genistein synergistically induces apoptosis in human colon cancer HT-29 cells by inhibiting Akt phosphorylation and progression of autophagy

BackgroundThe chemopreventive effects of dietary phytochemicals on malignant tumors have been studied extensively because of a relative lack of toxicity. To achieve desirable effects, however, treatment with a single agent mostly requires high doses. Therefore, studies on effective combinations of phytochemicals at relatively low concentrations might contribute to chemopreventive strategies.ResultsHere we found for the first time that co-treatment with I3C and genistein, derived from cruciferous vegetables and soy, respectively, synergistically suppressed the viability of human colon cancer HT-29 cells at concentrations at which each agent alone was ineffective. The suppression of cell viability was due to the induction of a caspase-dependent apoptosis. Moreover, the combination effectively inhibited phosphorylation of Akt followed by dephosphorylation of caspase-9 or down-regulation of XIAP and survivin, which contribute to the induction of apoptosis. In addition, the co-treatment also enhanced the induction of autophagy mediated by the dephosphorylation of mTOR, one of the downstream targets of Akt, whereas the maturation of autophagosomes was inhibited. These results give rise to the possibility that co-treatment with I3C and genistein induces apoptosis through the simultaneous inhibition of Akt activity and progression of the autophagic process. This possibility was examined using inhibitors of Akt combined with inhibitors of autophagy. The combination effectively induced apoptosis, whereas the Akt inhibitor alone did not.ConclusionAlthough in vivo study is further required to evaluate physiological efficacies and toxicity of the combination treatment, our findings might provide a new insight into the development of novel combination therapies/chemoprevention against malignant tumors using dietary phytochemicals.

Cucurbitacin B induces G2 arrest and apoptosis via a reactive oxygen species-dependent mechanism in human colon adenocarcinoma SW480 cells.

Cucurbitacin B (cucB) is a triterpenoid constituent of Cucurbitaceae vegetables and a promising phytochemical for cancer prevention. However, the mechanism of anti-tumor activity of cucB remains unknown, especially in colon cancers. Here, we demonstrate for the first time that cucB inhibited growth of human colon cancer SW480 cells through a reactive oxygen species (ROS)-dependent mechanism. CucB induced G(2) phase arrest and apoptosis in a dose-dependent manner. At the molecular level, cucB reduced the expression of cyclin B1 and cdc25C proteins and activated caspases in SW480 cells. On the other hand, the state of phosphorylation of signaling transducer and activator of transcription 3 (STAT3) was unchanged. We found that cucB increased intracellular ROS levels, and N-acetylcysteine, a well-known antioxidant, reduced the changes in expression of the molecules, and suppressed both G(2) arrest and apoptosis. These results suggested that cucB induced G(2) arrest and apoptosis through a STAT3-independent but ROS-dependent mechanism in SW480 cells.

Dehydrozingerone, a Structural Analogue of Curcumin, Induces Cell-Cycle Arrest at the G2/M Phase and Accumulates Intracellular ROS in HT-29 Human Colon Cancer Cells

Dehydrozingerone (1) is a pungent constituent present in the rhizomes of ginger (Zingiber officinale) and belongs structurally to the vanillyl ketone class. It is a representative of half the chemical structure of curcumin (2), which is an antioxidative yellow pigment obtained from the rhizomes of turmeric (Curcuma longa). Numerous studies have suggested that 2 is a promising phytochemical for the inhibition of malignant tumors, including colon cancer. On the other hand, there have been few studies on the potential antineoplastic properties of 1, and its mode of action based on a molecular mechanism is little known. Therefore, the antiproliferative effects of 1 were evaluated against HT-29 human colon cancer cells, and it was found that 1 dose-dependently inhibited growth at the G2/M phase with up-regulation of p21. Dehydrozingerone additionally led to the accumulation of intracellular ROS, although most radical scavengers could not clearly repress the cell-cycle arrest at the G2/M phase. Furthermore, two synthetic isomers of 1 (iso-dehydrozingerone, 3, and ortho-dehydrozingerone, 4) were also examined. On comparing of their activities, accumulation of intracellular ROS was found to be interrelated with growth-inhibitory effects. These results suggest that analogues of 1 may be potential chemotherapeutic agents for colon cancer.

Multiple mammalian proteasomal ATPases, but not proteasome itself, are associated with TATA-binding protein and a novel transcriptional activator, TIP120.

SUG1 belongs to proteasomal ATPase. Previous studies have demonstrated that SUG1 is associated with TBP. It is assumed to be involved in transcriptional regulation in addition to proteolysis. In this study, we investigated the association of mammalian SUG1 with TBP in more detail.

TATA-Binding Protein-Interacting Protein 120, TIP120, Stimulates Three Classes of Eukaryotic Transcription via a Unique Mechanism

ABSTRACT We previously identified a novel TATA-binding protein (TBP)-interacting protein (TIP120) from the rat liver. Here, in an RNA polymerase II (RNAP II)-reconstituted transcription system, we demonstrate that recombinant TIP120 activates the basal level of transcription from various kinds of promoters regardless of the template DNA topology and the presence of TFIIE/TFIIH and TBP-associated factors. Deletion analysis demonstrated that a 412-residue N-terminal domain, which includes an acidic region and the TBP-binding domain, is required for TIP120 function. Kinetic studies suggest that TIP120 functions during preinitiation complex (PIC) formation at the step of RNAP II/TFIIF recruitment to the promoter but not after the completion of PIC formation. Electrophoretic mobility shift assays showed that TIP120 enhanced PIC formation, and TIP120 also stimulated the nonspecific transcription and DNA-binding activity of RNAP II. These lines of evidence suggest that TIP120 is able to activate basal transcription by overcoming a kinetic impediment to RNAP II/TFIIF integration into the TBP (TFIID)-TFIIB-DNA-complex. Interestingly, TIP120 also stimulates RNAP I- and III-driven transcription and binds to RPB5, one of the common subunits of the eukaryotic RNA polymerases, in vitro. Furthermore, in mouse cells, ectopically expressed TIP120 enhances transcription from all three classes (I, II, and III) of promoters. We propose that TIP120 globally regulates transcription through interaction with basal transcription mechanisms common to all three transcription systems.

Identification of JTP‐70902, a p15INK4b‐inductive compound, as a novel MEK1/2 inhibitor

The INK4 family members p16INK4a and p15INK4b negatively regulate cell cycle progression by inhibition of cyclin‐dependent kinase (CDK) 4/6. Loss of p16INK4a functional activity is frequently observed in tumor cells, and is thought to be one of the primary causes of carcinogenesis. In contrast, despite the biochemical similarity to p16INK4a, the frequency of defects in p15INK4b was found to be lower than in p16INK4a, suggesting that p15INK4b‐inductive agents may be useful for tumor suppression. Here we report the discovery of a novel pyrido‐pyrimidine derivative, JTP‐70902, which exhibits p15INK4b‐inducing activity in p16INK4a‐inactivated human colon cancer HT‐29 cells. JTP‐70902 also induced another CDK‐inhibitor, p27KIP1, and downregulated the expression of c‐Myc and cyclin D1, resulting in G1 cell cycle arrest. MEK1/2 was identified by compound‐immobilized affinity chromatography as the molecular target of JTP‐70902, and this was further confirmed by the inhibitory activity of JTP‐70902 against MEK1/2 in kinase assays. JTP‐70902 suppressed the growth of most colorectal and some other cancer cell lines in vitro, and showed antitumor activity in an HT‐29 xenograft model. However, JTP‐70902 did not inhibit the growth of COLO320 DM cells; in these, constitutive extracellular signal‐regulated kinase phosphorylation was not detected, and neither p15INK4b nor p27KIP1 induction was observed. Moreover, p15INK4b‐deficient mouse embryonic fibroblasts were found to be more resistant to the growth‐inhibitory effect of JTP‐70902 than wild‐type mouse embryonic fibroblasts. These findings suggest that JTP‐70902 restores CDK inhibitor‐mediated cell cycle control by inhibiting MEK1/2 and exerts a potent antitumor effect. (Cancer Sci 2007; 98: 1809–1916)

ZD1839 induces p15INK4b and causes G1 arrest by inhibiting the mitogen-activated protein kinase/extracellular signal–regulated kinase pathway

Inactivation of the retinoblastoma protein pathway is the most common abnormality in malignant tumors. We therefore tried to detect agents that induce the cyclin-dependent kinase inhibitor p15INK4b and found that ZD1839 (gefitinib, Iressa) could up-regulate p15INK4b expression. ZD1839 has been shown to inhibit cell cycle progression through inhibition of signaling pathways such as phosphatidylinositol 3′-kinase-Akt and mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) cascades. However, the mechanism responsible for the differential sensitivity of the signaling pathways to ZD1839 remains unclear. We here showed that ZD1839 up-regulated p15INK4b, resulting in retinoblastoma hypophosphorylation and G1 arrest in human immortalized keratinocyte HaCaT cells. p15INK4b induction was caused by MAPK/ERK kinase inhibitor (PD98059), but not by Akt inhibitor (SH-6, Akt-III). Moreover, mouse embryo fibroblasts lacking p15INK4b were resistant to the growth inhibitory effects of ZD1839 compared with wild-type mouse embryo fibroblasts. Additionally, the status of ERK phosphorylation was related to the antiproliferative activity of ZD1839 in human colon cancer HT-29 and Colo320DM cell lines. Our results suggest that induction of p15INK4b by inhibition of the MAPK/ERK pathway is associated with the antiproliferative effects of ZD1839. [Mol Cancer Ther 2007;6(5):1579–1587]

p53 inactivation upregulates p73 expression through E2F-1 mediated transcription.

While p73 overexpression has been associated with increased apoptosis in cancer tissues, p73 overexpressing tumors appear to be of high grade malignancy. Why this putative tumor suppressor is overexpressed in cancer cells and what the function of overexpressed p73 is in breast cancers are critical questions to be addressed. By investigating the effect of p53 inactivation on p73 expression, we found that both protein and mRNA levels of TAp73 were increased in MCF-7/p53siRNA cells, MCF-7/p53mt135 cells and HCT-116/p53−/− cells, as compared to wild type control, suggesting that p53 inactivation by various forms upregulates p73. We showed that p53 knockdown induced p73 was mainly regulated at the transcriptional level. However, although p53 has a putative binding site in the TAp73 promoter, deletion of this binding site did not affect p53 knockdown mediated activation of TAp73 promoter. Chromatin immuno-precipitation (ChIP) data demonstrated that loss of p53 results in enhanced occupancy of E2F-1 in the TAp73 promoter. The responsive sequence of p53 inactivation mediated p73 upregulation was mapped to the proximal promoter region of the TAp73 gene. To test the role of E2F-1 in p53 inactivation mediated regulation of p73 transcription, we found that p53 knockdown enhanced E2F-1 dependent p73 transcription, and mutations in E2F-1 binding sites in the TAp73 promoter abrogated p53 knockdown mediated activation of TAp73 promoter. Moreover, we demonstrated that p21 is a mediator of p53-E2F crosstalk in the regulation of p73 transcription. We concluded that p53 knockdown/inactivation may upregulate TAp73 expression through E2F-1 mediated transcriptional regulation. p53 inactivation mediated upregulation of p73 suggests an intrinsic rescuing mechanism in response to p53 mutation/inactivation. These findings support further analysis of the correlation between p53 status and p73 expression and its prognostic/predictive significance in human cancers.

Histone Deacetylase Inhibitors and 15-Deoxy-Δ12,14-Prostaglandin J2 Synergistically Induce Apoptosis

Purpose: The clinically relevant histone deacetylase inhibitors (HDI) valproic acid (VPA) and suberoylanilide hydroxamic acid exert variable antitumor activities but increase therapeutic efficacy when combined with other agents. The natural endogenous ligand of peroxisome proliferator–activated receptor γ 15-deoxy-Δ12,14-prostaglandin J2 (15d-PGJ2) is a potent antineoplastic agent. Therefore, we investigated whether these HDIs in combination with 15d-PGJ2 could show synergistic antitumor activity in colon cancer DLD-1 cells. Experimental Design: Cell viability was determined using a Cell Counting Kit-8 assay. Apoptosis and reactive oxygen species (ROS) generation were determined using flow cytometry analysis. Western blotting and real-time reverse transcription-PCR analysis were carried out to investigate the expression of apoptosis-related molecules. Mice bearing DLD-1 xenograft were divided into four groups (n = 5) and injected everyday (i.p.) with diluent, VPA (100 mg/kg), 15d-PGJ2 (5 mg/kg), or a combination for 25 days. Results: HDI/15d-PGJ2 cotreatments synergistically induced cell death through caspase-dependent apoptosis in DLD-1 cells. Moreover, HDIs/15d-PGJ2 caused histone deacetylase inhibition, leading to subsequent ROS generation and endoplasmic reticulum stress to decrease the expression of antiapoptotic molecules Bcl-XL and XIAP and to increase that of proapoptotic molecules CAAT/enhancer binding protein homologous protein and death receptor 5. Additionally, VPA/15d-PGJ2 cotreatment induced ROS-dependent apoptosis in other malignant tumor cells and was more effective than a VPA or 15d-PGJ2 monotherapy in vivo. Conclusions: Cotreatments with the clinically relevant HDIs and the endogenous peroxisome proliferator–activated receptor γ ligand 15d-PGJ2 are promising for the treatment of a broad spectrum of malignant tumors. Clin Cancer Res; 16(8); 2320–32. ©2010 AACR.

A serine residue in the N-terminal acidic region of rat RPB6, one of the common subunits of RNA polymerases, is exclusively phosphorylated by casein kinase II in vitro ☆

RPB6 is one of the common subunits of all eukaryotic RNA polymerases and is indispensable for the enzyme function. Here, we isolated a rat cDNA encoding RPB6. It contained 127 amino acid (a.a.) residues. From alignment of RPB6 homologues of various eukaryotes, we defined two conserved regions, i.e. an N-terminal acidic region and a C-terminal core. In this study, we investigated in vitro phosphorylation of rat RPB6 by casein kinase II (CKII), a pleiotropic regulator of numerous cellular proteins. Three putative CKII-phosphorylated a.a. within rat RPB6 were assigned. We found that serines were phosphorylated by CKII in vitro. Mutagenesis studies provided evidence that a serine at a.a. position 2 was exclusively phosphorylated. Finally, an RPB6-engaged in-gel kinase assay clarified that CKII was a prominent protein kinase in rat liver nuclear extract that phosphorylates RPB6. Therefore, RPB6 was implied to be phosphorylated by CKII in the nucleus. We postulate that the N-terminal acidic region of the RPB6 subunit has some phosphorylation-coupled regulatory functions.