FTI-277抑制急性髓系白血病细胞增生及增强三氧化二砷诱导细胞凋亡的作用

  目的 研究法尼基转移酶抑制剂FTI-277单独或联合三氧化二砷（As2O3）对急性髓系白血病（AML）细胞增生和凋亡的影响及其作用机制。方法 以HL-60细胞株、31例初治AML患者骨髓标本为研究对象,用四甲基偶氮唑蓝（MTT）法检测细胞增生,用流式细胞术检测细胞周期、磷酸化ERK1／2表达,用AnnexinV-FITC法、DNA琼脂糖凝胶电泳检测细胞凋亡。结果 FTI-277可明显抑制AML细胞增生,对正常细胞无明显抑制增生作用。FTI-277使AML细胞G2／M期百分数显著升高,但亚G1期细胞百分数无明显变化。FTI-277显著下调AML细胞磷酸化ERK1／2的表达,但不影响正常细胞表达。联合组与单用组相比,AML细胞凋亡率明显增高,并可检出梯状DNA条带。结论 FTI-277通过阻断AML细胞ERK／MAPK途径,使细胞发生G2／M期阻滞,抑制细胞增生。FTI-277可增强As2O3对AML细胞的凋亡诱导作用。     

迷迭香酸通过MAPK/ERK信号通路对结肠癌细胞增殖及凋亡的影响

摘 要：［目的］ 探讨迷迭香酸通过丝裂原激活的蛋白激酶/胞外信号调节的蛋白激酶（MAPK/ERK）信号通路对结肠癌细胞增殖凋亡的影响。［方法］ 取对数生长期LS174T细胞,加入迷迭香酸（0、25、50和100μmol/L）处理24、48 和72h后,CCK-8法检测迷迭香酸对细胞增殖活性的影响。以100μmol/L迷迭香酸处理细胞,24、48 和72h后,采用流式细胞仪检测迷迭香酸对细胞周期和细胞凋亡率的影响;采用蛋白质印迹法检测细胞中Bax、Bcl-2和Cleaved Caspase-3蛋白的表达及ERK1/2磷酸化水平。［结果］ 迷迭香酸对LS174T细胞呈时间浓度依赖性抑制细胞增殖;100μmol/L迷迭香酸处理LS174T细胞不同时间后,与对照组相比,迷迭香酸组细胞中S期和G2/M期细胞所占比例明显降低,G0/G1期比例显著升高,但组间时间效应不显著（P>0.05）;而Bcl-2蛋白表达、ERK1/2磷酸化水平明显降低,细胞凋亡率、Bax和Cleaved Caspase-3蛋白表达量显著增强,均表现出明显的时效关系（P<0.05）。［结论］ 迷迭香酸能够抑制结肠癌LS174T细胞增殖,诱导细胞凋亡,其作用机制可能与抑制MAPK/ERK信号通路有关。     

ERK参与裸鼠体内辛伐他汀诱导K 562细胞凋亡的调控作用

目的：探讨辛伐他汀（simvastatin）作用于裸鼠体内K562细胞后Ras-MAPK信号转导通路胞外信号调节激酶（extracellular signal—regulated protein kinase，ERK）分子水平的变化，以说明ERK参与裸鼠体内辛伐他汀诱导K562细胞凋亡的调控作用。方法：体外培养慢性髓细胞白血病（CML）细胞株K562细胞，构建BALB／c-nu／nu裸鼠的K562细胞移植瘤模型。流式细胞术（FCM）检测对照组和两个辛伐他汀处理组的K562细胞周期变化，TUNEL法检测K562细胞晚期凋亡情况。采用RT-PCR检测K562细胞中Ras-MAPK信号通路N-Ras、ERK1mRNA的差异表达。免疫组织化学标记葡聚糖聚合物（labbled dextran polymer，LDP）法检测P-ERK蛋白水平变化。结果：辛伐他汀能够明显抑制裸鼠K562移植瘤组织的增长，随着辛伐他汀剂量的增加，K562细胞移植瘤体积和质量明显减小（P〈0．05，P〈0．01）。每次注射0．05mg的辛伐他汀能够诱导裸鼠体内K562细胞发生明显的G0／G1期停滞，不同剂量的辛伐他汀能够诱导K562细胞发生明显的凋亡，并随剂量的增加，凋亡率逐渐增高（P〈0．01）；不同剂量的辛伐他汀能够引起N-Ras、ERK1mRNA的表达下调（P〈0．01）。与对照组相比，两个处理组的p-ERK蛋白分别出现表达下调（P=0．01，P〈0．01）。结论：辛伐他汀在体内可能依赖Ras—MAPK信号转导通路ERK基因和蛋白水平的表达下调诱导K562细胞凋亡发生。     

硼替佐米对伊马替尼耐药细胞株K562/G01增殖抑制和诱导凋亡作用的研究

 目的　探讨蛋白酶体抑制剂硼替佐米（BOR）对慢性粒细胞白血病（CML）伊马替尼耐药细胞株K562／G01的增殖抑制和诱导凋亡作用。方法　采用MTT法观察细胞的生长抑制效应;流式细胞术（FCM）检测细胞周期与凋亡。结果　K562／G01细胞对伊马替尼不敏感,伊马替尼对K562／G01和K562细胞的IC50分别是（20.09±1.38）、（0.54±0.13）μmol／L;BOR对K562／G01细胞具有增殖抑制作用,并于48 h时作用效果达高峰,IC50（23.10±2.71）nmol／L,随着BOR浓度和作用时间的增加,FCM检测可见G2／M 期细胞周期阻滞及明显的凋亡峰。结论　BOR对CML伊马替尼耐药细胞株具有增殖抑制和诱导凋亡的作用,其机制可能与细胞周期G2／M 期的阻滞有关。     

甘草查尔酮B对三阴性乳腺癌MDA-MB-231细胞的抑制作用及其机制

目的：探讨甘草查尔酮B（LCB）对三阴性乳腺癌（TNBC）MDA-MB-231 细胞的抑制作用及其机制。方法: 常规培养MDA-MB-231 细胞，用不同浓度LCB 处理后，采用CCK-8法、免疫荧光法、FCM 和WB法分别检测MDA-MB-231 细胞的增殖活力、细胞核内DNA双链断裂标志物γ-H2AX的表达，以及细胞周期和周期调控、丝裂原活化蛋白激酶（MAPK）、内质网应激信号途径相关蛋白的表达水平。结果: LCB能显著抑制乳腺癌MDA-MB-231 细胞的增殖活力（P<0.05），使γ-H2AX阳性细胞数和蛋白表达水平均显著升高（均P<0.05）、G2/M 和S 期的细胞数量均明显增加（均P<0.05）、MAPK 家族主要成员细胞外调节激酶1/2（ERK1/2）和p38MAPK蛋白的磷酸化水平均显著上调（均P<0.05），还使内质网应激途径相关蛋白Bip、ATF4和CHOP 的表达均显著上调（均P<0.05）。结论: LCB 能够显著抑制MDA-MB-231 细胞的增殖活力、诱导DNA损伤和细胞周期阻滞于G2/M 和S期，LCB对MDA-MB-231细胞的抑制作用可能与其激活MAPK和内质网应激信号通路相关。     

小檗碱通过调控IGF-1R信号通路抑制食管癌细胞增殖和诱导细胞凋亡的实验

目的 检测小檗碱对食管癌细胞增殖、周期和凋亡的影响,并探讨其作用机制。 方法 MTT法检测细胞的增殖抑制作用;碘化丙啶（Propidium iodide, PI）染色法检测细胞周期进程;Annexin V-FITC和PI双染法结合流式细胞技术检测小檗碱的凋亡诱导作用;Western blot技术检测小檗碱对胰岛素样生长因子1受体（IGF-1R）的活化及下游主要信号分子AKT和p44/42MAPK（ERK）磷酸化水平的影响。结果 小檗碱在体外可浓度依赖性地抑制四种食管癌细胞系的增殖,且其IC50值与细胞表面IGF-1R的表达水平呈负相关。小檗碱可使细胞阻滞在G₂/M期。细胞凋亡实验结果显示,小檗碱可浓度依赖性地诱导食管癌细胞发生凋亡,并且在相同浓度下KYSE450细胞（IGF-1R高表达）的凋亡率显著高于KYSE150细胞（IGF-1R低表达）。Western blot结果显示,小檗碱处理可显著抑制IGF-1R的磷酸化,并抑制AKT和ERK的活化,且抑制作用随着小檗碱浓度的增加而增强。结论 小檗碱可通过对IGF-1R及其介导的下游信号通路的调控来发挥抑制食管癌细胞增殖、阻断细胞周期进程以及诱导食管癌细胞凋亡的作用。     

2-甲氧基雌二醇对白血病细胞K562增生、凋亡及细胞周期的影响

 目的 探讨2-甲氧基雌二醇（2-ME）对体外培养的慢性粒细胞白血病（CML）急变期细胞系bcr-abl（+）K562细胞增生、凋亡及细胞周期的影响。方法 将不同浓度和作用时间的2-ME与K562细胞共同培养，采用相差显微镜观察细胞的形态学变化；四甲基偶氮唑蓝（MTT）法检测2-ME对K562细胞增生的抑制作用；流式细胞术分析2-ME对K562细胞凋亡及细胞周期的影响。结果 1~ 16μmol／L浓度的2-ME在24、36、48及60 h均可明显抑制K562细胞增生，并在一定范围内呈时间和剂量依赖性；2-ME作用后G0／G1期细胞增加，并伴随细胞凋亡峰和凋亡率的升高。结论 2-ME可抑制K562细胞增生，诱导其凋亡，为2-ME的临床应用提供实验依据。     

斑蝥素通过MAPK信号传导途径对A549细胞增殖抑制作用的研究

目的 :研究斑蝥素对人肺癌A5 49细胞的增殖抑制作用和有丝分裂原激活蛋白激酶 (mi togenactivatedproteinkinase ,MAPK)表达的影响。方法 :采用MTT法检测斑蝥素对A5 49细胞的增殖抑制作用 ;流式细胞仪分析A5 49细胞周期及斑蝥素对细胞周期的影响 ;蛋白印迹法检测斑蝥素作用后ERK1、ERK2 、phos ERK1、phos ERK2 表达的改变。结果 :斑蝥素对A5 49细胞有增殖抑制作用 ;A5 49细胞周期出现明显的G2 /M期阻滞 ,t检验P <0 0 5 ;ERK1、ERK2 、phos ERK1、phos ERK2表达下降。结论 :MAPK信号传导途径参与了斑蝥素对人肺癌A5 49细胞的增殖抑制作用。     

三氧化二砷对胃癌BGC-823细胞增殖及细胞周期的影响

[目的]探讨三氧化二砷（AS2O3）对胃癌BGC-823细胞增殖的抑制作用及对细胞周期的影响。[方法]应用MTT方法检测三氧化二砷对胃癌BGC-823细胞增殖的抑制作用，流式细胞仪进行细胞周期解析及凋亡检测．[结果]三氧化二砷对胃癌BGC823细胞具有杀伤作用，且呈时间-浓度依赖性抑制肿瘤细胞的增殖．72h抑制细胞50％增殖的药物浓度约为3．3μmol／L，与对照组比差异显著（P=0．0048）；5μmol／LAs2O3作用24h，细胞形态学可见典型的凋亡细胞及M期阻滞；流式细胞仪进行细胞周期解析结果提示，G2/M期细胞由正常对照的25％增加到46．3％，出现了明显的G2/M期阻滞，亚二倍体凋亡细胞由4％增加到18％。[结论]三氧化二砷抑制胃癌细胞的增殖．诱导细胞周期阻滞及凋亡。     

茯苓多糖对人宫颈癌HeLa细胞增殖、迁移、促凋亡的影响及其机制

目的 探讨茯苓多糖（Pachymaran）对人宫颈癌HeLa细胞增殖、迁移、促凋亡的作用及其相关机制。方法 MTT法检测细胞增殖率并筛选出适宜的茯苓多糖低、中、高浓度用于后续实验；不同浓度的茯苓多糖处理细胞后，倒置相差显微镜观察细胞形态学变化；Hoechst 33342染色观察细胞核的变化；平板克隆实验检测细胞克隆形成能力；细胞划痕实验检测细胞迁移能力；流式细胞术检测细胞凋亡率及细胞周期；Western blot法检测凋亡、迁移及ERK通路相关蛋白的表达。结果 茯苓多糖浓度对HeLa细胞活力的影响实验得出，取30、40、50 mg/ml茯苓多糖作为低、中、高浓度进行后续实验；中、高浓度茯苓多糖处理细胞后，细胞和细胞核发生显著的凋亡形态学变化，低浓度下形态学变化不显著；不同浓度茯苓多糖均能降低细胞克隆形成能力；降低细胞迁移率（P<0.05）；使细胞凋亡率增加（P<0.05）；使S期细胞减少并阻滞于G₂/M期（P<0.05）；Cleaved Caspase 3、Cleaved Caspase 8、Cleaved Caspase 9、Bax表达较对照组明显增多，Bcl-2、MMP-9、VEGFA、p-ERK1/2表达明显减少（P<0.05）。ERK1/2表达无明显变化。结论 茯苓多糖能显著抑制HeLa细胞增殖，并诱导其凋亡。其促凋亡机制可能与下调p-ERK1/2表达，抑制ERK信号通路磷酸化有关。同时，茯苓多糖对抑制HeLa细胞的迁移也有一定的作用。     

Cross-talk between extracellular S1P/S1P2 and P42/44 MAPK in bcr/abl positive chronic myeloid leukemia cells

Objective: BCR/ABL oncoprotein-expression is associated with uncontrolled cell growth. Sphingosine kinase 1 (SPK1) regulates the production of sphingosine 1-phosphate (S1P), a key lipid signal molecular in cell proliferation and survival. The objective of this study was to elucidate the roles of S1P and its receptors in bcr/abl positive chronic myeloid leukemia (CML) cells.Methods: The expressions of S1P receptors: S1P1, S1P2 and S1P3 in CML cells were detected by RT-PCR. SPK1 expression, activity and extracellular S1P were determined in ECV304 and HL-60 cells which were transfected with bcr/abl gene. To elucidate the relationship between the BCR/ABL, ERK/MAPK (extracellular signal-regulated kinase/mitogen-activated protein kinase), SPK/S1P and S1P/S1P2 signal pathways, bcr/abl positive CML cell line K562 was treated with STI571, PD98059, N,N-dimethyl sphingosine (DMS) and JTE-013.Results: Retrovirus-mediated overexpression of bcr/abl gene in ECV304 and HL-60 cells resulted in upregulation of the expression, activity of SPK1 and increase of the secretion of S1P, whereas treatment of STI571 and PD98059 decreased the BCR/ABL-induced S1P secretion. Treatment of DMS reduced S1P secretion and P42/44MAPK phosphorylation. S1P2-selective antagonist JTE-013 could also decrease P42/44MAPK phosphorylation. Conclusion: These results suggest that BCR/ABL up-regulates extracellular sphingosine 1-phosphate through sphingosine kinase 1 and there is cross-talk between SPK1/S1P/S1P2 and P42/44MAPK in bcr/abl positive CML cells.     

Mitogen-activated protein kinase pathway-dependent tumor-specific survival signaling in melanoma cells through inactivation of the proapoptotic protein bad

Mitogen-activated protein kinase (MAPK) signaling regulates fundamental cellular functions including proliferation, differentiation, and survival. We have demonstrated previously that inhibiting MAPK signaling induces apoptosis in melanoma cells but not in normal melanocytes, suggesting that the MAPK pathway propagates essential survival signals in melanoma cells. Here, we report that the 90-kDa ribosomal S6 kinase (RSK), a downstream effector in the MAPK signaling cascade, phosphorylates and inactivates the Bcl-2 homology 3-only proapoptotic protein Bad, thereby mediating a MAPK-dependent tumor-specific survival signal in melanoma cells. The MAPK kinase (MEK)/extracellular signal-regulated kinase (ERK)/RSK MAPK signaling module is constitutively hyperactivated, and Bad is maintained in its inactive state by phosphorylation at Ser(75) in a MEK/ERK/RSK-dependent manner in melanoma cells. In contrast, in normal melanocytes, Bad is highly phosphorylated at multiple residues (Ser(75), Ser(99), and Ser(118)) in a MAPK pathway-independent manner. Importantly, ectopic expression of a constitutively activated RSK mutant abrogates Bad activation and renders melanoma cells resistant to apoptosis induced by a MEK inhibitor. Furthermore, overexpressing alanine-substituted (S75A) Bad further sensitizes melanoma cells to MEK inhibitor-induced apoptosis. Our results suggest that the MAPK pathway mediates melanoma-specific survival signaling by differentially regulating RSK-mediated phosphorylation of the proapoptotic protein Bad and may present potentially selective therapeutic targets for the treatment of melanomas.     

Dual blockade of EGFR and ERK1/2 phosphorylation potentiates growth inhibition of breast cancer cells

One of the major targets for breast cancer therapy is the epidermal growth factor receptor (EGFR) and related receptors, which signal via different signal transduction pathways including the mitogen-activated protein kinase (MAPK) pathway. This study determined whether there is a correlation between EGFR/HER2 status and MAPK (ERK1/2) phosphorylation in breast cancer cells, and how this affects the response to an inhibitor of the receptors. Expression of EGFR, HER2 and phosphorylated ERK1/2 were measured by immunoblotting in a panel of breast cancer cell lines. Several lines expressed high levels of pERK1/2, with no obvious correlation with the level of EGFR/HER2. The EGFR tyrosine kinase inhibitor PKI166 inhibited growth and induced apoptosis in some cells with high levels of growth factor receptors (MDA-MB-468, SUM149, SKBR3), but was less effective in cells that also had high basal ERK1/2 activity (MDA-MB-231). The combination of an inhibitor of MAPK signalling (U0126) and PKI166 produced significantly more inhibition and apoptosis than either agent alone. This suggests that constitutive activation of the MAPK pathway may bypass inhibition of EGFR/HER2 tyrosine kinases, and lead to insensitivity to agents targeting the receptors. However, inhibiting both EGFR/HER2 and MAPK signalling can result in significant growth inhibition and apoptosis of EGFR-expressing breast cancer cells.     

Constitutive activation of MAPK/ERK inhibits prostate cancer cell proliferation through upregulation of BRCA2

BRCA2 is central to an utterly diverse biological behavior elicited after integrin-mediated normal and prostate cancer cell adhesion to basement membrane (BM) and extracellular matrix (ECM) proteins. Unlike normal cells, adhesive stimuli in cancer cells activate PI 3-kinase/AKT signaling resulting in BRCA2 degradation and unchecked cancer cell proliferation and metastasis. However, the precise mechanisms involved in normal BRCA2 homeostasis are unknown. We investigated ERK and AKT phosphorylation in normal (PNT1A) and cancer (PC-3) prostate cells after adhesion to ECM and the effects upon BRCA2 and cell proliferation. PNT1A cell adhesion to ECM triggered MAPK/ERK signaling resulting in upregulation of BRCA2 mRNA and protein, with negligible effects upon cell proliferation. Disruption of MAPK/ERK with PD98059 prevented any BRCA2 upregulation inhibiting DNA synthesis below basal levels. PC-3 cells exhibited a defective MAPK/ERK pathway that was unresponsive to adhesion to the ECM, which instead triggered PI 3-kinase/AKT signaling leading to BRCA2 protein depletion and cell proliferation. Reconstitution of MAPK/ERK by recombinant expression of a constitutively active form of MAPK kinase 1 (MEK1) effectively reversed the neoplastic phenotype by increasing BRCA2 expression and preventing any aberrant cell proliferation at rest and upon interaction with ECM proteins. Our results suggest that aberrant loss of MAPK/ERK activity in prostate cancer may play a pivotal role in the malignant phenotype, and provide evidence that interventions aimed at bypassing the signaling block are able to effectively reverse neoplastic unchecked cell proliferation.     

BRAF mutation associated with dysregulation of apoptosis in human colorectal neoplasms

To understand the role of BRAF dysfunction in the carcinogenesis and progression/development of colorectal tumors, the authors investigated genetic alterations in the BRAF gene in human colorectal neoplasms as well as the effects of an RAS inhibitor in BRAF-mutant cells. Seven colon cancer cell lines and 116 colorectal tumors (34 adenomas and 82 adenocarcinomas) were analyzed. Genetic alterations in the BRAF and K-ras genes were examined using polymerase chain reaction-single strand conformation polymorphism and direct sequencing analyses. The growth-inhibitory and apoptosis-inducing effects of the FTI-277 RAS inhibitor in colon cancer cell lines were analyzed as well. An immunohistochemical study was also performed to investigate the correlations between the clinicopathologic parameters involved in the Ki-67 labeling index and the number of apoptotic bodies in tumor cells. FTI-277 did not suppress the proliferation of BRAF-mutant cells (WiDr and TCO), but remarkably inhibited the growth of K-ras mutant cells (LoVo). Interestingly, LoVo cells underwent apoptosis by FTI-277 in a dose-dependent manner, whereas WiDr cells were resistant to this agent. In tumor samples, BRAF mutations were found in 1 (3.0%) of 33 adenomas and 6 (7.2%) of 83 adenocarcinomas. No tumor exhibited mutations in both the BRAF and K-ras genes. Neither BRAF nor K-ras mutations correlated with the Ki-67 labeling index immunohistochemically. However, the number of apoptotic bodies was significantly decreased in the BRAF-mutant tumors. Mutation in the BRAF gene may contribute to colorectal carcinogenesis by upregulating the antiapoptotic role of the RAS/RAF/MEK/ERK pathway.     

Multiple signal pathways are involved in the mitogenic effect of 5(S)-HETE in human pancreatic cancer

Pancreatic carcinoma is characterized by poor prognosis and lack of response to conventional therapy. The reasons for this are not fully understood. We have reported that inhibition of 5-lipoxygenase abolished proliferation and induced apoptosis in pancreatic cancer cells while the 5-lipoxygenase metabolite, 5(S)-hydroxyeicosatetraenoic acid [5(S)-HETE] stimulated pancreatic cancer cell proliferation. The current study was designed to investigate the underlying mechanisms for 5(S)-HETE-stimulated proliferation of pancreatic cells. Two human pancreatic cancer cell lines, PANC-1 and HPAF, were used. Cell proliferation was monitored by thymidine incorporation and cell counting. Phosphorylation of P42/44(MAPK) (mitogen activated protein kinase, ERK), MEK (MAPK/ERK kinase), P38 kinase, JNK/SAPK (c-Jun N-terminal kinase/ stress-activated protein kinase), AKT and tyrosine residues of intracellular proteins was measured by Western blot using their corresponding phospho-specific antibodies. The results showed that (1) 5(S)-HETE markedly stimulated pancreatic cancer cell proliferation in a time- and concentration-dependent manner; (2) 5(S)-HETE induced tyrosine phosphorylation of multiple intracellular proteins while the tyrosine kinase inhibitor, genestein, blocked 5(S)-HETE-stimulated cell proliferation; (3) 5(S)-HETE significantly stimulated both MEK and P42/44(MAPK) phosphorylation and the MEK inhibitors, PD098059 and U0126, inhibited 5(S)-HETE-stimulated proliferation in these two cell lines; (4) 5(S)-HETE also stimulated P38 kinase phosphorylation but the P38 inhibitor, SB203580, did not effect 5(S)-HETE-stimulated cell proliferation; (5) 5(S)-HETE markedly stimulated AKT phosphorylation while the phosphatidylinositide-3 (PI3)-kinase inhibitor, wortmannin, blocked 5(S)-HETE-stimulated cell proliferation; (6) phosphorylation of JNK/SAPK was not induced by 5(S)-HETE, and (7) the general protein kinase C (PKC) inhibitor, GF109203X, did not affect 5(S)-HETE-stimulated cancer cell proliferation. These findings suggest that intracellular tyrosine kinases, MEK/ERK and PI3 kinase/AKT pathways are involved in 5(S)-HETE-stimulated pancreatic cancer cell proliferation but P38 kinase, JNK/SAPK and PKC are not involved in this mitogenic effect.     

Blocking the Raf/MEK/ERK pathway sensitizes acute myelogenous leukemia cells to lovastatin-induced apoptosis

The statin family of drugs are well-established inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase and are used clinically in the control of hypercholesterolemia. Recent evidence, from ourselves and others, shows that statins can also trigger tumor-specific apoptosis by blocking protein geranylgeranylation. We and others have proposed that statins disrupt localization and function of geranylgeranylated proteins responsible for activating signal transduction pathways essential for the growth and/or survival of transformed cells. To explore this further, we have investigated whether the mitogen-activated protein kinase (MAPK) signaling cascades play a role in regulating statin-induced apoptosis. Cells derived from acute myelogenous leukemia (AML) are used as our model system. We show that p38 and c-Jun NH2-terminal kinase/stress-activated kinase MAPK pathways are not altered during lovastatin-induced apoptosis. By contrast, exposure of primary and established AML cells to statins results in significant disruption of basal extracellular signal-regulated kinase (ERK) 1/2 phosphorylation. Addition of geranylgeranyl PPi reverses statin-induced loss of ERK1/2 phosphorylation and apoptosis. By establishing and evaluating the inducible Raf-1:ER system in AML cells, we show that constitutive activation of the Raf/MAPK kinase (MEK)/ERK pathway significantly represses but does not completely block lovastatin-induced apoptosis. Our results strongly suggest statins trigger apoptosis by regulating several signaling pathways, including the Raf/MEK/ERK pathway. Indeed, down-regulation of the Raf/MEK/ERK pathway potentiates statin-induced apoptosis because exposure to the MEK1 inhibitor PD98059 sensitizes AML cells to low, physiologically achievable concentrations of lovastatin. Our study suggests that lovastatin, alone or in combination with a MEK1 inhibitor, may represent a new and immediately available therapeutic approach to combat tumors with activated ERK1/2, such as AML.     

Heterogeneity of receptor function in colon carcinoma cells determined by cross-talk between type I insulin-like growth factor receptor and epidermal growth factor receptor

This study identifies a novel cross-talk paradigm between the type I insulin-like growth factor receptor (IGF1R) and epidermal growth factor receptor (EGFR) in colon cancer cells. IGF1R activation by ligand exposure in growth factor-deprived cells induces Akt activation in the FET, CBS, and GEO colon cancer cell lines. Investigation of IGF1R-mediated signaling pathways using small interfering RNA approaches indicated that, as expected, phosphatidylinositol 3'-kinase (PI3K) was activated by IGF1R. Mitogen-activated protein kinase (MAPK) activity as reflected by phospho-extracellular signal-regulated kinase (ERK) induction was not significantly activated until later times following release of these cells from growth factor deprivation stress. The appearance of phospho-ERK was proximal to EGFR activation. Treatment of cells with the PI3K inhibitor LY294002 before release from stress resulted in a concentration-dependent loss of EGFR activation, whereas treatment with the MAPK inhibitor PD98059 did not block EGFR activation, indicating that EGFR activation was downstream of the IGF1R/PI3K pathway. PD98059 inhibition of MAPK was associated with a concentration-dependent reduction in EGFR-mediated phospho-ERK. EGFR inhibitor blocked induction of phospho-ERK, showing that MAPK activity was a consequence of EGFR-mediated signaling. On the other hand, a small-molecule IGF1R inhibitor, PQIP, blocked Akt phosphorylation. The divergent signaling functions of IGF1R and EGFR suggested the potential for synergism by a combination of therapy directed at the two receptors. Combination treatment with PQIP and EGFR inhibitor Tarceva resulted in synergistic effects as indicated by combination index analysis in all three cell lines tested.     

Regulation of mixed lineage kinase 3 is required for Neurofibromatosis-2-mediated growth suppression in human cancer

The Neurofibromatosis-2 (NF2) tumor suppressor merlin negatively regulates cell proliferation in numerous cell types. We have previously shown that the NF2 protein (merlin/schwannomin) associates with mixed lineage kinase 3 (MLK3), a mitogen-activated protein kinase (MAPK) kinase kinase that is required for the proliferation of normal and neoplastic cells. In this study, we show that merlin inhibits MLK3 activity, as well as the activation of its downstream effectors, B-Raf, extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK). The ability of merlin to regulate MLK3 activity requires a direct association between MLK3 and residues in the C-terminal region of merlin. Merlin integrates Rho GTPase family signaling with MAPK activity by inhibiting the binding between MLK3 and its upstream activator, Cdc42. Furthermore, we demonstrate that MLK3 is required for merlin-mediated suppression of cell proliferation and invasion. Collectively, these results establish merlin as a potent inhibitor of MLK3, ERK and JNK activation in cancer, and provide a mechanistic link between deregulated MAPK and Rho GTPase signaling in NF2 growth control.