Hypoxia Enhances Sphingosine Kinase 2 Activity and Provokes Sphingosine-1-Phosphate-Mediated Chemoresistance in A549 Lung Cancer Cells
Hypoxia Enhances Sphingosine Kinase 2 Activity and Provokes Sphingosine-1-Phosphate-Mediated Chemoresistance in A549 Lung Cancer Cells
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DOI：
10.1158/1541-7786.mcr-08-0156
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发表时间：
2009-03-01
影响因子：
5.2
通讯作者：
Bruene, Bernhard
中科院分区：
文献类型：
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作者：
Schnitzer, Steffen E.;Welgert, Andreas;Bruene, Bernhard
缺氧和缺氧诱导因子-1(HIF-1)是实体瘤的一个重要特征，与肿瘤的进展和治疗失败有关。虽然人们普遍认为HIF-1在低氧条件下刺激肿瘤细胞存活并诱导化疗耐药，但HIF-1不依赖于HIF-1的机制也起作用。我们提供的证据表明，从A549细胞获得的条件培养液，在低氧条件下孵育24小时，可以保护未成熟的A549细胞免受依托泊苷诱导的细胞死亡。低氧条件培养液中产生的脂类提取物仍能使细胞免于依托泊苷诱导的细胞凋亡。具体地说，生物活性脂鞘氨醇-1-磷酸(S1P)不仅是A549细胞存活所必需的，而且还能保护细胞免受凋亡。我们注意到，在低氧条件下，鞘氨醇激酶2(SphK2)蛋白水平和酶活性增加，这与S1P释放到培养液中有关。SphK2基因敲除可减轻A549细胞对低氧耐药的耐药，而SphK2基因敲除细胞的条件培养液只能起到部分保护作用。将条件培养液与S1P(1)/S1P(3)拮抗剂VPC23019共同孵育，可降低条件培养液的保护作用，并进一步认为p42/44丝裂原激活蛋白激酶在S1P(1)/S1P(3)受体下游传递自分泌或旁分泌生存信号。我们的结果提示，缺氧激活SphK2促进S1P的合成和释放，而S1P又与S1P(1)/S1P(3)受体结合，从而激活P42/44丝裂原激活的蛋白激酶，传递A549细胞的自分泌或旁分泌保护。(摩尔癌症研究2009；7(3)：393-401)
Hypoxia and signaling via hypoxia-Inducible factor-1 (HIF-1) is a key feature of solid tumors and Is related to tumor progression as well as treatment failure. Although it is generally accepted that HIF-1 provokes tumor cell survival and Induces chemoresistance under hypoxia, HIF-1-independent mechanisms operate as well. We present evidence that conditioned medium obtained from A549 cells, Incubated for 24 h under hypoxia, protected naive A549 cells from etoposide-Induced cell death. Lipid extracts generated from hypoxia-conditioned medium still rescued cells from apoptosis induced by etoposide. Specifically, the bioactive lipid sphingosine-1-phosphate (S1P) not only was essential for cell viability of A549 cells but also protected cells from apoptosis. We noticed an Increase in sphingosine kinase 2 (SphK2) protein level and enzymatic activity under hypoxia, which correlated with the release of S1P into the medium. Knockdown of SphK2 using specific small Interfering RNA relieved chemoresistance of A549 cells under hypoxia and conditioned medium obtained from SphK2 knockdown cells was only partially protective. Coincubations of conditioned medium with VPC23019, a S1P(1)/S1P(3) antagonist, reduced protection of conditioned medium, with the further notion that p42/44 mitogen-activated protein kinase transmits autocrine or paracrine survival signaling downstream of S1P(1)/S1P(3) receptors. Our data suggest that hypoxia activates SphK2 to promote the synthesis and release of S1P, which In turn binds to S1P(1)/S1P(3) receptors, thus activating p42/44 mitogen-activated protein kinase to convey autocrine or paracrine protection of A549 cells. (Mol Cancer Res 2009;7(3):393-401)