SIRT1 promotes proliferation and inhibits apoptosis of human malignant glioma cell lines

In mammalian cells, SIRT1 decreases PTEN acetylation and inactivates the AKT pathway in a SIRT1 deacetylase-dependent manner. However, the function of SIRT1 in glioma was unknown. SIRT1 reexpression or knockdown was induced in human glioma cell lines. The cell synchronization, BrdU labeling and mitotic index were detected. Subsequently, cell cycle, cell viability, apoptosis, cell growth and proliferation were analyzed. Our work identified that SIRT1-knockdown significantly delayed mitotic entry of glioma cells, inhibited its growth and proliferation, and promoted its apoptosis. The apoptosis was related to PTEN/PI3K/AKT signaling pathway. The results showed that SIRT1 might be a promoter factor on tumorigenesis of glioma through PTEN/PI3K/AKT signaling pathway.     

Knockdown of Akt1 promotes Akt2 upregulation and resistance to oxidative-stress-induced apoptosis through control of multiple signaling pathways

The Akt signaling pathway plays a key role in promoting the survival of various types of cells from stress-induced apoptosis, and different members of the Akt family display distinct physiological roles. Previous studies have shown that in response to UV irradiation, Akt2 is sensitized to counteract the induced apoptosis. However, in response to oxidative stress such as hydrogen peroxide, it remains to be elucidated what member of the Akt family would be activated to initiate the signaling cascades leading to resistance of the induced apoptosis. In the present study, we present the first evidence that knockdown of Akt1 enhances cell survival under exposure to 50 μM H(2)O(2). This survival is derived from selective upregulation and activation of Akt2 but not Akt3, which initiates 3 major signaling cascades. First, murine double minute 2 (MDM2) is hyperphosphorylated, which promotes p53 degradation and attenuates its Ser-15 phosphorylation, significantly attenuating Bcl-2 homologous antagonist killer (Bak) upregulation. Second, Akt2 activation inactivates glycogen synthase kinase 3 beta (GSK-3β) to promote stability of myeloid leukemia cell differentiation protein 1 (MCL-1). Finally, Akt2 activation promotes phosphorylation of FOXO3A toward cytosolic export and thus downregulates Bim expression. Overexpression of Bim enhances H(2)O(2)-induced apoptosis. Together, our results demonstrate that among the Akt family members, Akt2 is an essential kinase in counteracting oxidative-stress-induced apoptosis through multiple signaling pathways.     

Proteinase-activated receptor-1 mediates elastase-induced apoptosis of human lung epithelial cells

Apoptosis of distal lung epithelial cells plays a pivotal role in the pathogenesis of acute lung injury. In this context, proteinases, either circulating or leukocyte-derived, may contribute to epithelial apoptosis and lung injury. We hypothesized that apoptosis of lung epithelial cells induced by leukocyte elastase is mediated via the proteinase activated receptor (PAR)-1. Leukocyte elastase, thrombin, and PAR-1-activating peptide, but not the control peptide, induced apoptosis in human airway and alveolar epithelial cells as assessed by increases in cytoplasmic histone-associated DNA fragments and TUNEL staining. These effects were largely prevented by a specific PAR-1 antagonist and by short interfering RNA directed against PAR-1. To ascertain the mechanism of epithelial apoptosis, we determined that PAR-1AP, thrombin, and leukocyte elastase dissipated mitochondrial membrane potential, induced translocation of cytochrome c to the cytosol, enhanced cleavage of caspase-9 and caspase-3, and led to JNK activation and Akt inhibition. In concert, these observations provide strong evidence that leukocyte elastase mediates apoptosis of human lung epithelial cells through PAR-1-dependent modulation of the intrinsic apoptotic pathway via alterations in mitochondrial permeability and by modulation of JNK and Akt.     

PTEN modulates hepatitis B virus-X protein induced survival signaling in Chang liver cells

PTEN gene, a novel tumor suppressor is frequently mutated or deleted in several malignancies including human hepatocellular carcinoma (HCC). We report previously that human hepatitis B virus-X (HBx) protein achieves protection from apoptotic cell death through-PI3K-Akt-Bad signaling that is p53-independent in liver cells (JBC; 276, 16969 (2000)). In this report, we demonstrated the PTEN effect on HBx induced anti-apoptotic signaling in Chang liver cells (CHL). Expression of PTEN in CHL cells downregulate HBx induced PI3K, Akt activities, Akt, Bad phosphorylations, decreased caspase 3 activity and protection from DNA fragmentations. PTEN suppression of CHL cell growth at G1 phase (JBC;278,4057(2003)) in cell cycle analysis, which is overcome by HBx activated Akt/PKB further confirmed that same PI3K/Akt pathway is involved in cell survival and apoptosis by HBx and PTEN. PTEN suppression of HBx-mediated cell survival through PI3K pathway is specific, since PTEN does not suppress the effect of HBx on the protection from Fas-mediated apoptosis. Taken together, these findings demonstrate that PTEN potently modulate HBx-mediated signaling and is a viable target in therapeutic approaches to inhibit the formation of HCC caused by HBV infections.     

Cyclooxygenase-2-derived prostaglandin e2 protects mouse embryonic stem cells from apoptosis

Little is known about prostaglandin synthesis and function in embryonic stem cells. We postulated that mouse embryonic stem (mES) cells possess enzymes to synthesize protective prostaglandins. Compared with differentiated adult cells, mES cells were less susceptible to H(2)O(2)-induced apoptosis. However, their apoptosis was enhanced by indomethacin or SC-236, a selective inhibitor of cyclooxygenase (COX)-2. Analysis of COX pathway enzymes by Western blotting revealed expression of COX-2 and cytosolic and microsomal prostaglandin E(2) (PGE(2)) synthases. COX-1 and prostacyclin (PGI(2)) synthases were undetectable. mES cells produced PGE(2) but not PGI(2). Importantly, PGE(2) rescued mES cells from apoptosis. To elucidate the signaling mechanism by which PGE(2) inhibits apoptosis, we analyzed E-type prostaglandin (EP) receptors by Western blots. All EP isoforms were detected except EP4. Butaprost, a specific EP2 agonist, rescued mES cells from apoptosis, whereas sulprostone, an EP1/EP3 agonist, had no effect, suggesting selective interaction of PGE(2) with EP2. The antiapoptotic effect of PGE(2) was abrogated by Ly-294002 or wortmannin but not H-89 or a specific inhibitor of protein kinase A, suggesting signaling via phosphatidylinositol-3 kinase (PI-3K). Akt was constitutively active in mES cells, which were inhibited by indomethacin and rescued by PGE(2). The rescuing effect of PGE(2) was abrogated by Ly-294002. These results indicate that mES cells constitutively express COX-2 and PGE synthases and produce PGE(2), which confers resistance to apoptosis via EP2-mediated activation of PI-3K to the Akt pathway. Disclosure of potential conflicts of interest is found at the end of this article.     

X射线诱导NSCLC组织Axin表达并通过p53或JNK途径促进细胞凋亡

目的研究X-射线对非小细胞肺癌(non-smallcelllungcancer,NSCLC)组织中Axin表达的作用,以及X射线上调Axin表达的机制。方法应用Westernblot、RT-PCR方法检测15例经过X射线照射后NSCLC组织中Axin在蛋白水平及RNA水平的表达变化情况以及caspase-3活化情况。转染Axin及AxinΔp53ΔHIPK2至A549、BE1细胞中,并施加p53或JNK抑制剂,细胞经X线照射后用流式细胞仪(FCM)检测细胞凋亡,研究Axin上调细胞凋亡的机制。结果经X射线照射后,在15例NSCLC肺癌组织中,有8例Axin在RNA水平和蛋白水平上表达上调,与Axin未上调组相比,细胞凋亡显著增加(P<0.05)。转染Axin能使A549、BE1细胞凋亡明显增加,AxinΔp53ΔHIPK2不能上调A549细胞凋亡,p53抑制剂和JNK抑制剂分别抑制A549和BE1细胞凋亡。结论 X射线诱导部分NSCLC组织Axin表达增加并促进细胞凋亡,Axin通过p53或JNK途径促进X射线诱导的细胞凋亡。检测NSCLC组织中是否存在p53基因突变并不能作为判定是否对X射线敏感的指标。     

蛇床子素通过抑制SIRT1的表达增强阿霉素对p53野生型前列腺癌细胞的凋亡诱导活性

目的:探讨中药活性成分蛇床子素对阿霉素抗前列腺癌作用的影响及机制。方法:MTT法检测前列腺癌细胞系LNCaP在阿霉素和蛇床子素处理下的细胞活力。Western blot实验检测阿霉素和蛇床子素对LNCaP细胞中沉默信息调节因子1(SIRT1)、p53、乙酰化p53和Puma的表达水平、细胞色素C的释放水平及caspase-9和caspase-3活化水平的影响。流式细胞术检测阿霉素和蛇床子素对LNCaP细胞凋亡的影响。结果:蛇床子素联合治疗能明显提高阿霉素对p53野生型前列腺癌细胞系LNCaP的杀伤力。蛇床子素处理能显著抑制LNCaP细胞中SIRT1的表达,转染SIRT1过表达质粒后,蛇床子素、阿霉素联合治疗对LNCaP细胞的杀伤力受到显著抑制(P0.05)。蛇床子素联合阿霉素显著升高LNCaP细胞p53蛋白的表达水平和乙酰化水平,转染p53 si RNA后,蛇床子素对阿霉素的协同作用明显减弱。蛇床子素联合阿霉素显著诱导LNCaP细胞细胞色素C从线粒体释放到细胞质中,增强细胞中的caspase-9及下游caspase-3的活性并诱导细胞发生凋亡。结论:蛇床子素通过下调前列腺癌LNCaP细胞中SIRT1的表达促进阿霉素诱导的p53依赖的细胞凋亡。     

WISP-1 attenuates p53-mediated apoptosis in response to DNA damage through activation of the Akt kinase.

WISP-1 (Wnt-1-induced secreted protein) was identified as an oncogene regulated by the Wnt-1-beta-catenin pathway. WISP-1 belongs to the CCN family of growth factors, which are cysteine-rich, heparin-binding, secreted proteins associated with the extracellular matrix, and can interact with cellular integrins. Expression of WISP-1 in some cells results in transformation and tumorigenesis. Here it is shown that WISP-1 can activate the antiapoptotic Akt/PKB signaling pathway. It also is demonstrated that WISP-1 can prevent cells from undergoing apoptosis following DNA damage through inhibition of the mitochondrial release of cytochrome c and up-regulation of antiapoptotic Bcl-X(L). Furthermore, the results show that WISP-1 protects cells from p53-dependent cell death, but not Fas-ligand activated cell death, suggesting that there may be cross talk between the tumor suppressor protein p53 and WISP-1 signaling pathways. WISP-1 acts to block cell death at a late stage in the p53-mediated apoptosis pathway.     

Mechanical stress-activated immune response genes via Sirtuin 1 expression in human periodontal ligament cells

Recently, Sirtuin 1 (SIRT1) has been implicated in the molecular control of ageing and immune response. Although the remodelling of periodontal ligament (PDL) in response to mechanical stress (MS) is mediated by several host factors, including cytokines and chemokines, the transmission of mechanical stimuli into specific cellular activity is still not understood fully. This study aimed to investigate the effects of MS, particularly cyclic strain, on immune response genes, as well as SIRT1 and its signal transduction pathways, in human PDL cells. MS up-regulated the expression of SIRT1 and immune response genes encoding cytokines [tumour necrosis factor (TNF)-α, interleukin (IL)-1β], chemokines [IL-8, monocyte cheoattractant protein (CCL)-20], defensins [human β-defensin (hBD)-2, hBD-3] and Toll-like receptors (TLR-2 and TLR-4) in a force- and time-dependent manner. The SIRT1 inducers resveratrol and isonicotinamide attenuated MS-induced cytokine and chemokine expression, but enhanced the expression of defensins and TLRs. Blockade of SIRT1 activity by the SIRT1 inhibitors sirtinol and nicotinamide and down-regulation of SIRT1 expression by SIRT1 siRNA reduced the stimulatory effects of MS on defensins and TLRs, but increased its effects on cytokines and chemokines. MS induced activation of protein kinase B (Akt), protein kinase C (PKC), nuclear factor (NF)-κB and p38 mitogen-activated protein kinase (MAPK), c-Jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK). Treatment with the anti-oxidants N-acetylcysteine and glutathione inhibited MS-induced reactive oxygen species production and expression of cytokines, chemokines, defensins and TLRs. These results suggest that MS activates human PDL cells to express immune/defence genes encoding cytokines, chemokines, defensins and TLRs via a SIRT1 pathway.     

二氢青蒿素通过抑制SIRT1的表达而增强5-氟尿嘧啶对胃癌的抗肿瘤活性

目的:探讨二氢青蒿素对5-氟尿嘧啶治疗胃癌的辅助作用并研究其机制。方法:实验分为对照组、二氢青蒿素组、5-氟尿嘧啶组、5-氟尿嘧啶联合二氢青蒿素组和5-氟尿嘧啶+二氢青蒿素+SIRT1质粒组。MTT法检测胃癌细胞系BGC-823在5-氟尿嘧啶联合二氢青蒿素处理下的细胞活力。Western blot实验检测5-氟尿嘧啶联合二氢青蒿素对BGC-823细胞SIRT1和NADPH氧化酶表达水平,caspase-9和caspase-3活化水平及凋亡信号调节激酶1(ASK1)和c-Jun氨基末端激酶(JNK)蛋白磷酸化水平的影响。流式细胞术检测BGC-823细胞在5-氟尿嘧啶和二氢青蒿素联合处理下的活性氧簇(ROS)生成水平和细胞凋亡率。结果:二氢青蒿素处理能显著抑制BGC-823细胞SIRT1的表达并增加NADPH氧化酶的蛋白水平,明显提高BGC-823细胞对5-氟尿嘧啶的敏感性,降低5-氟尿嘧啶的半数抑制浓度;转染SIRT1表达质粒后,二氢青蒿素联合5-氟尿嘧啶对BGC-823细胞的杀伤活性受到显著抑制(P0.05)。二氢青蒿素能明显促进5-氟尿嘧啶对BGC-823细胞生成ROS的诱导效应和ASK1及JNK的磷酸化(P0.05)。用ROS清除剂N-乙酰半胱氨酸(NAC)或JNK特异性抑制剂SP600125处理后,二氢青蒿素联合5-氟尿嘧啶对BGC-823细胞的杀伤活性和caspase-9及caspase-3的活化均受到明显抑制(P0.05)。另外,NAC能显著抑制二氢青蒿素联合5-氟尿嘧啶对JNK磷酸化的促进作用,而SP600125却不能影响BGC-823细胞ROS的产生,表明JNK是ROS的下游分子。结论:二氢青蒿素联合5-氟尿嘧啶通过SIRT1/NADPH氧化酶/ROS/JNK通路诱导胃癌细胞发生caspase依赖的凋亡。     

二氢杨梅素联合顺铂显著诱导PC3细胞中Noxa和Bim过表达

目的:探讨二氢杨梅素对前列腺癌顺铂化疗的辅助作用并研究其机制。方法:MTT法检测前列腺癌细胞系LNCaP和PC3在不同浓度二氢杨梅素和顺铂处理下的细胞活力。Western blot实验检测顺铂和二氢杨梅素联用对PC3细胞FOXO1、Noxa和Bim表达水平、细胞色素C从线粒体中的释放及caspase-9和caspase-3活化水平的影响。免疫共沉淀实验检测PC3细胞中凋亡蛋白酶激活因子1(Apaf-1)和caspase-9的相互作用。流式细胞术检测PC3细胞的凋亡率。结果:二氢杨梅素辅助治疗可明显提高顺铂对前列腺癌的体外抗肿瘤活性(P0.05)。二氢杨梅素处理能显著促进PC3细胞FOXO1的表达,转染FOXO1小干扰RNA(siRNA)后,二氢杨梅素对顺铂的辅助治疗效果受到明显抑制。二氢杨梅素联合顺铂能显著诱导PC3细胞中Noxa和Bim的过表达,细胞色素C的释放,Apaf-1和caspase-9的相互作用,caspase-9和caspase-3的活化及凋亡的发生。转染FOXO1 siRNA后,二氢杨梅素联合顺铂对PC3细胞的凋亡诱导途径受到显著抑制。结论:二氢杨梅素可能通过FOXO1-Bim/Noxa途径增强顺铂对前列腺癌细胞的体外杀伤活性。     

腺病毒介导的shRNA下调PTEN表达对体外活化肝星状细胞增殖与凋亡的影响

目的:探讨腺病毒介导的shRNA下调第10号染色体缺失的磷酸酶和张力蛋白同源物基因(PTEN)表达对体外培养的大鼠活化肝星状细胞(HSCs)增殖和凋亡的影响及其信号转导机制。方法:体外培养活化HSCs,以腺病毒为载体将靶向PTEN的shRNA干扰重组体转染至体外活化的大鼠HSCs;四甲基偶氮唑盐(MTT)法检测HSCs增殖;末端转移酶标记技术(TUNEL)及流式细胞术测定HSCs凋亡;Western blotting方法检测PTEN、Bax、Bcl-2、Akt、p-Akt、ERK1/2及p-ERK1/2蛋白表达情况;实时荧光定量PCR方法检测PTEN、Akt及ERK1 mRNA表达情况。结果:(1)靶向PTEN的RNA干扰重组腺病毒成功感染体外活化HSCs,并在一定范围内呈时间依赖性地促进HSCs增殖,腺病毒感染HSCs后72 h,HSCs凋亡率显著下降(P<0.05);(2)Bax表达降低,Bcl-2表达增加(P<0.05);(3)p-Akt和p-ERK1/2蛋白表达显著增加(P<0.05);而Akt蛋白及其mRNA、ERK1蛋白及其mRNA表达均无显著改变(P>0.05)。结论:RNA干扰下调PTEN基因表达可能通过Bcl-2/Bax途径促进体外活化HSCs增殖并抑制其凋亡,此外,RNA干扰下调PTEN基因表达促进p-Akt和p-ERK1/2表达增多,提示PTEN可能通过影响PI3K/Akt和ERK1/2信号通路而在调控HSCs增殖和凋亡中发挥重要作用。     

Insulin-like growth factor-1 activates Akt and Jun N-terminal kinases (JNKs) in promoting the survival of T lymphocytes

Insulin-like growth factor 1 receptor (IGF-1R) expression is augmented on T cells upon ligation of CD28, and this promotes IGF-1-mediated protection from Fas-induced cell death for up to 6 days. To determine the mechanism of action of IGF-1R in T-cell expansion, we investigated the signalling pathways activated by IGF-1 in T cells and in Jurkat cells. We found that IGF-1 transiently induces Akt, jun N-terminal kinases (JNK), and c-Jun phosphorylation in activated T cells, with JNK and c-Jun phosphorylation occurring faster than Akt phosphorylation. To mimic IGF-1R expression levels in CD28-stimulated Jurkat cells these cells were stably transfected to over-express the IGF-1R. Jurkat/IGF-1R cells exhibited enhanced constitutive Akt phosphorylation compared with mock-transfected controls, but IGF-1 induced transient phosphorylation of MKK4, JNKs, and c-Jun. Inhibition of PI-3 kinase activity and Akt phosphorylation with LY294002 totally suppressed IGF-1-mediated protection from Fas killing in activated T cells, but only partially suppressed IGF-1-mediated protection in Jurkat/IGF-1R cells. However, either dicumarol in T cells or a dominant negative JNK1 (APF) in Jurkat/IGF-1R cells greatly suppressed IGF-1-mediated protection from Fas killing. Together, these data demonstrate that IGF-1-mediated activation of JNKs and PI-3 kinase contributes to normal T-cell survival, whereas the JNK pathway may be more important in Jurkat leukaemia cells.     

Differential effects of phosphatidylinositol-3/Akt-kinase inhibition on apoptotic sensitization to cytokines in LNCaP and PCc-3 prostate cancer cells.

Alterations in phosphatidylinositol 3'-kinase (PI3'-kinase) and Akt activation frequently occur in prostate cancer and may disrupt apoptotic induction by such cytokines as tumor necrosis factor (TNF) and TNF-related apoptosis-inducing ligand (TRAIL). To examine the role of PI3' phosphorylation in the cellular response to cytokines, two prostate cancer cell lines with constitutively activated PI3'-kinase cascades (LNCaP and PC-3) were examined for direct sensitivity to cytokines. TNF or TRAIL alone failed to activate apoptosis in either LNCaP or PC-3 cells, and drug-mediated inhibition of the PI3k/Akt cascade caused only minimal activation of apoptosis in either cell line. Suppression of PI3'-kinase/Akt signaling markedly enhanced the apoptotic activity of both TNF and TRAIL in LNCaP cells but not in PC-3 cells. Adenovirus-mediated PTEN/MMAC1 expression in LNCaP cells reduced Akt activation, activated apoptosis, and sensitized cells to TNF but not to TRAIL. Together, these results suggest that PI3'-kinase signaling inhibits both TNF-mediated and TRAIL-mediated apoptosis but may represent one of several apoptotic resistance mechanisms that inhibit cytokine-mediated killing of prostate cancer cells.