MDM2 is required for suppression of apoptosis by activated aktl in salivary acinar cells
MDM2 is required for suppression of apoptosis by activated aktl in salivary acinar cells
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DOI：
10.1128/mcb.01846-05
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发表时间：
2006-12-01
影响因子：
5.3
通讯作者：
Anderson, Steven M.
中科院分区：
文献类型：
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作者：
Limesand, Kirsten H.;Schwertfeger, Kathryn L.;Anderson, Steven M.
唾液腺的慢性损伤是头颈部照射后常见的副作用。人们假设，唾液腺在辐射后立即发生不可逆转的损伤；然而，以前对大鼠模型的研究并未显示细胞凋亡在辐射诱导的损伤中的因果作用。我们报道了足叶乙苷和伽马射线在体内外诱导FVB对照组小鼠唾液腺泡细胞的凋亡；然而，表达Akt1的组成性激活突变体(MYR-Akt1)的转基因小鼠的凋亡减少。在唾液腺中MYR-Aktl的表达导致原代唾液腺泡细胞在依托泊苷或伽马照射后，P53丝氨酸的磷酸化(18)、P53蛋白的总积聚以及p21(WAF1)或Bax mRNA的显著减少。MYR-Akt1唾液腺中P53蛋白水平的降低与体内MDM2磷酸化水平的增加相对应，提示Akt/MDM2/P53通路参与了细胞凋亡的抑制。显性阴性Akt阻断了MYR-Akt1转基因小鼠唾液腺泡细胞中MDM2的磷酸化。使用小干扰RNA降低MYR-Aktl原代唾液腺泡细胞中MDM2的水平会增加P53蛋白的水平，使这些细胞即使存在激活的Akt1也容易受到依托泊苷诱导的细胞凋亡的影响。这些结果表明，在体内，MDM2是激活Akt1抑制P53依赖的细胞凋亡的关键底物。
Chronic damage to the salivary glands is a common side effect following head and neck irradiation. It is hypothesized that irreversible damage to the salivary glands occurs immediately after radiation; however, previous studies with rat models have not shown a causal role for apoptosis in radiation-induced injury. We report that etoposide and gamma irradiation induce apoptosis of salivary acinar cells from FVB control mice in vitro and in vivo; however, apoptosis is reduced in transgenic mice expressing a constitutively activated mutant of Akt1 (myr-Akt1). Expression of myr-Aktl in the salivary glands results in a significant reduction in phosphorylation of p53 at serine(18), total p53 protein accumulation, and p21(WAF1) or Bax mRNA following etoposide or gamma irradiation of primary salivary acinar cells. The reduced level of p53 protein in myr-Aktl salivary glands corresponds with an increase in MDM2 phosphorylation in vivo, suggesting that the Akt/MDM2/p53 pathway is responsible for suppression of apoptosis. Dominant-negative Akt blocked phosphorylation of MDM2 in salivary acinar cells from myr-Aktl transgenic mice. Reduction of MDM2 levels in myr-Aktl primary salivary acinar cells with small interfering RNA increases the levels of p53 protein and renders these cells susceptible to etoposide-induced apoptosis in spite of the presence of activated Akt1. These results indicate that MDM2 is a critical substrate of activated Akt1 in the suppression of p53-dependent apoptosis in vivo.