Expression of the serum- and glueocorticoid-inducible protein kinase, Sgk, is a cell survival response to multiple types of environmental stress stimuli in mammary epithelial cells
Expression of the serum- and glueocorticoid-inducible protein kinase, Sgk, is a cell survival response to multiple types of environmental stress stimuli in mammary epithelial cells
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DOI：
10.1074/jbc.m211649200
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发表时间：
2003-02-21
影响因子：
4.8
通讯作者：
Firestone, GL
中科院分区：
文献类型：
--
作者：
Leong, MLL;Maiyar, AC;Firestone, GL
在NMuMG乳腺上皮细胞中，观察了多种应激刺激对血清和糖皮质激素诱导蛋白激酶(SGK)利用的影响。NMuMG乳腺上皮细胞暴露于有机渗透压山梨醇、热休克、紫外线照射、过氧化氢诱导的氧化应激或地塞米松(一种合成的糖皮质激素，代表一类生理应激激素)诱导的高渗透应激。每种应激刺激诱导SGK蛋白表达的动力学、诱导持续时间和亚细胞定位不同。环境压力，而不是地塞米松，通过依赖p38/MAPK的途径刺激SGK的表达。在每种情况下，在SGK的同源物Akt保持其非磷酸化状态的条件下，都产生了过度磷酸化的活性SGK蛋白。野生型SGK或模拟磷酸化的T256D/S422D突变体SGK的异位表达对NMuMG细胞的应激诱导的细胞死亡具有保护作用。相反，T256A/S422A SGK磷酸化位点突变体的表达对细胞存活没有影响。已知SGK能磷酸化并负调控促凋亡叉头转录因子FKHRL1。诱导SGK的环境应激刺激强烈地抑制了FKHRL1的核转录活性，增加了FKHRL1的胞质滞留，而不是地塞米松。此外，条件IPTG可诱导野生型SGK的表达，但不能诱导激酶死亡的T256A突变体SGK的表达，从而保护Con8乳腺上皮肿瘤细胞免受血清饥饿诱导的凋亡。综上所述，我们的研究证实，在不同的环境应激刺激下，酶活性SGK的诱导发挥着关键的细胞生存成分的作用。
The effects of multiple stress stimuli on the cellular utilization of the serum- and glucocorticoid-inducible protein kinase (Sgk) were examined in NMuMg mammary epithelial cells exposed to hyperosmotic stress induced by the organic osmolyte sorbitol, heat shock, ultraviolet irradiation, oxidative stress induced by hydrogen peroxide, or to dexamethasone, a synthetic glucocorticoid that represents a general class of physiological stress hormones. Each of the stress stimuli induced Sgk protein expression with differences in the kinetics and duration of induction and in subcellular localization. The environmental stresses, but not dexamethasone, stimulated Sgk expression through a p38/ MAPK-dependent pathway. In each case, a hyperphosphorylated active Sgk protein was produced under conditions in which Akt, the close homolog of Sgk, remained in its non-phosphorylated state. Ectopic expression of wild type Sgk or of the T256D/S422D mutant Sgk that mimics phosphorylation conferred protection against stress-induced cell death in NMuMg cells. In contrast, expression of the T256A/S422A Sgk phosphorylation site mutant has no effect on cell survival. Sgk is known to phosphorylate and negatively regulate proapoptotic forkhead transcription factor FKHRL1. The environmental stress stimuli that induce Sgk, but not dexamethasone, strongly inhibited the nuclear transcriptional activity and increased the cytoplasmic retention of FKHRL1. Also, the conditional IPTG inducible expression of wild type Sgk, but not of the kinase dead T256A mutant Sgk, protected Con8 mammary epithelial tumor cells from serum starvation-induced apoptosis. Taken together, our study establishes that induction of enzymatically active Sgk functions as a key cell survival component in response to different environmental stress stimuli.