Wen Dan Chen

Acetylation of Beclin 1 inhibits autophagosome maturation and promotes tumour growth

Beclin 1, a protein essential for autophagy, regulates autophagy by interacting with Vps34 and other cofactors to form the Beclin 1 complex. Modifications of Beclin 1 may lead to the induction, inhibition or fine-tuning of the autophagic response under a variety of conditions. Here we show that Beclin 1 is acetylated by p300 and deacetylated by SIRT1 at lysine residues 430 and 437. In addition, the phosphorylation of Beclin 1 at S409 by CK1 is required for the subsequent p300 binding and Beclin 1 acetylation. Beclin 1 acetylation inhibits autophagosome maturation and endocytic trafficking by promoting the recruitment of Rubicon. In tumour xenografts, the expression of 2KR mutant Beclin 1 (substitution of K430 and K437 to arginines) leads to enhanced autophagosome maturation and tumour growth suppression. Therefore, our study identifies an acetylation-dependent regulatory mechanism governing Beclin 1 function in autophagosome maturation and tumour growth.

ATM-mediated PTEN phosphorylation promotes PTEN nuclear translocation and autophagy in response to DNA-damaging agents in cancer cells

PTEN (phosphatase and tensin homolog), a tumor suppressor frequently mutated in human cancer, has various cytoplasmic and nuclear functions. PTEN translocates to the nucleus from the cytoplasm in response to oxidative stress. However, the mechanism and function of the translocation are not completely understood. In this study, topotecan (TPT), a topoisomerase I inhibitor, and cisplatin (CDDP) were employed to induce DNA damage. The results indicate that TPT or CDDP activates ATM (ATM serine/threonine kinase), which phosphorylates PTEN at serine 113 and further regulates PTEN nuclear translocation in A549 and HeLa cells. After nuclear translocation, PTEN induces autophagy, in association with the activation of the p-JUN-SESN2/AMPK pathway, in response to TPT. These results identify PTEN phosphorylation by ATM as essential for PTEN nuclear translocation and the subsequent induction of autophagy in response to DNA damage.

A diterpenoid compound, excisanin A, inhibits the invasive behavior of breast cancer cells by modulating the integrin β1/FAK/PI3K/AKT/β-catenin signaling.

AIM Excisanin A, a diterpenoid compound purified from Isodon macrocalyxin D, has anti-cancer properties with little toxicity. In this study, the anti-invasive effects of excisanin A on breast cancer cells and its molecular mechanism of action were investigated. MAIN METHODS MTT, wound healing, transwell chamber and cell adhesion assays were utilized to investigate the effects of excisanin A on MDA-MB-231 and SKBR3 cells. Western blotting, real-time PCR, RNA interference and luciferase reporter assays were employed to determine the molecular mechanism of action of excisanin A. KEY FINDINGS Treating MDA-MB-231 and SKBR3 cells with 10-40μM excisanin A significantly inhibited cell migration and invasion and suppressed the mRNA and protein levels of matrix metalloproteinase-2 (MMP-2) and matrix metalloproteinase-9 (MMP-9) in a dose-dependent manner. Excisanin A efficiently abolished integrin β1 expression and reduced the phosphorylation of the downstream kinases focal adhesion kinase (FAK) and Src. Excisanin A inhibited the phosphorylation of phosphoinositide 3-kinase (PI3K), AKT and glycogen synthase kinase 3 beta (GSK3β) and down-regulated β-catenin expression and the luciferase activity of the transcription factor LEF-1. Moreover, treating breast cancer cells with siRNA targeting integrin β1 inhibited cell invasion and migration. SIGNIFICANCE These results demonstrated that excisanin A inhibited invasion by suppressing MMP-2 and MMP-9 expression; the integrin β1/FAK/PI3K/AKT/β-catenin signaling pathway was involved in this process. Therefore, excisanin A might be a potential anti-metastatic chemotherapeutic agent for the treatment of breast cancer.

Hirsutanol A, a novel sesquiterpene compound from fungus Chondrostereum sp., induces apoptosis and inhibits tumor growth through mitochondrial-independent ROS production: hirsutanol A inhibits tumor growth through ROS production.

BackgroundHirsutanol A is a novel sesquiterpene compound purified from fungus Chondrostereum sp. in Sarcophyton tortuosum. Our previous studies had demonstrated that hirsutanol A exhibited potent cytotoxic effect on many kinds of cancer cell lines. In the current study, the antitumor activity of hirsutanol A and its molecular mechanisms were investigated.MethodsHirsutanol A induced growth inhibition and apoptotic cell death of human colon cancer SW620 cells and human breast cancer MDA-MB-231cells were determined using MTT assay and flow cytometry assay, respectively. The effect of hirsutanol A on intrinsic ROS level and change in mitochondrial membrane potential (△ψm) of different cell lines were also measured by flow cytometry assay. The function of JNK was compromised by JNK siRNA or JNK inhibitor SP600125. The expression of cytochrome c, p-JNK, p-c-Jun after treatment with hirsutanol A were detected by Western blot analysis. Finally, the in vivo anti-tumor effect of hirsutanol A was examined in human cancer cell SW620 xenograft model.ResultsThe results showed that hirsutanol A significantly induced apoptosis, mitochondrial-independent increase of Reactive Oxygen Species (ROS) level, change of mitochondrial membrane potential, release of cytochrome c in human cancer cells. Preventing increase of ROS level using the potent antioxidant N-acetyl-L-cysteine (NAC) markedly decreased hirsutanol A-induced apoptosis. In addition, JNK signaling pathway was activated by hirsutanol A through elevating ROS level. Blockade of JNK signaling pathway by JNK specific inhibitor SP600125 enhanced apoptosis and hirsutanol A-induced ROS accumulation. Also, hirsutanol A exhibited antitumor activity in human cancer cell SW620 xenograft model.ConclusionThese data suggested that hirsutanol A inhibited tumor growth through triggering ROS production and apoptosis.

Houttuyninum, an active constituent of Chinese herbal medicine, inhibits phosphorylation of HER2/neu receptor tyrosine kinase and the tumor growth of HER2/neu-overexpressing cancer cells.

AIMS The overexpression of HER2/neu receptor plays a key role in tumorigenesis and tumor progression. Small molecules targeting HER2/neu have therapeutic value in cancers that overexpress HER2. In this present study, the effect of houttuyninum, a component in the Chinese herbal medicine Houttuynia cordata Thunb, on HER2/neu tyrosine phosphorylation and its in vivo antitumour activity was investigated. MAIN METHODS The phosphorylation and expression of proteins were determined by Western blot analysis. The MTT assay was employed to examine the inhibition of cell proliferation in vitro. Xenografts were established in nude mice for evaluating the antitumour activity of houttuyninum in vivo. KEY FINDINGS Houttuyninum inhibited phosphorylation of HER2 in a dose-dependent manner with an IC50 of 5.52 μg/ml without reducing HER2/neu protein expression in MDA-MB-453 cells. Houttuyninum also inhibited the activation of ERK1/2 and AKT, downstream molecules in the HER2/neu-mediated signal transduction pathway. In contrast, tyrosine phosphorylation of EGFR was unaffected when the concentration of houttuyninum was increased to 40 μg/ml in both A431 cells and MDA-MB-468 cells. Additionally, houttuyninum preferentially inhibited the growth of MDA-MB-453 cells that overexpressed HER2/neu; the MDA-MB-468 cells that overexpress EGFR remained unaffected. Administration of houttuyninum in vivo resulted in a significant reduction of phosphorylated HER2 levels and in tumor volumes of the BT474 and N87 xenografts, which both overexpress HER2/neu. SIGNIFICANCE Our findings showed that houttuyninum can inhibit the HER2/neu signalling pathway and the tumor growth of cancer cells that overexpress HER2/neu. This drug may provide therapeutic value in the treatment of cancers that involve overexpression of HER2/neu.

Isolation and structural elucidation of chondrosterins F-H from the marine fungus Chondrostereum sp.

The marine fungus Chondrostereum sp. was collected from a soft coral of the species Sarcophyton tortuosum from the South China Sea. Three new compounds, chondrosterins F–H (1, 4 and 5), together with three known compounds, incarnal (2), arthrosporone (3), and (2E)-decene-4,6,8-triyn-1-ol (6), were isolated. Their structures were elucidated primarily based on NMR and MS data. Incarnal (2) exhibited potent cytotoxic activity against various cancer cell lines.

Hirsutanol A, a novel sesquiterpene compound from fungus Chondrostereum sp., induces apoptosis and inhibits tumor growth through mitochondrial-independent ROS production

BackgroundHirsutanol A is a novel sesquiterpene compound purified from fungus Chondrostereum sp. in Sarcophyton tortuosum. Our previous studies had demonstrated that hirsutanol A exhibited potent cytotoxic effect on many kinds of cancer cell lines. In the current study, the antitumor activity of hirsutanol A and its molecular mechanisms were investigated.MethodsHirsutanol A induced growth inhibition and apoptotic cell death of human colon cancer SW620 cells and human breast cancer MDA-MB-231cells were determined using MTT assay and flow cytometry assay, respectively. The effect of hirsutanol A on intrinsic ROS level and change in mitochondrial membrane potential (△ψm) of different cell lines were also measured by flow cytometry assay. The function of JNK was compromised by JNK siRNA or JNK inhibitor SP600125. The expression of cytochrome c, p-JNK, p-c-Jun after treatment with hirsutanol A were detected by Western blot analysis. Finally, the in vivo anti-tumor effect of hirsutanol A was examined in human cancer cell SW620 xenograft model.ResultsThe results showed that hirsutanol A significantly induced apoptosis, mitochondrial-independent increase of Reactive Oxygen Species (ROS) level, change of mitochondrial membrane potential, release of cytochrome c in human cancer cells. Preventing increase of ROS level using the potent antioxidant N-acetyl-L-cysteine (NAC) markedly decreased hirsutanol A-induced apoptosis. In addition, JNK signaling pathway was activated by hirsutanol A through elevating ROS level. Blockade of JNK signaling pathway by JNK specific inhibitor SP600125 enhanced apoptosis and hirsutanol A-induced ROS accumulation. Also, hirsutanol A exhibited antitumor activity in human cancer cell SW620 xenograft model.ConclusionThese data suggested that hirsutanol A inhibited tumor growth through triggering ROS production and apoptosis.