Malik Amal Idris, Storey Kenneth B
Institute of Biochemistry and Department of Biology, Carleton University, 1125 Colonel By Drive, Ottawa, Ontario, Canada K1S 5B6.
J Exp Biol. 2009 Aug;212(Pt 16):2595-603. doi: 10.1242/jeb.030627.
In its native environment the African clawed frog, Xenopus laevis, can experience seasonally arid conditions that impose dehydration stress. Activation of intracellular signal transduction cascades can mediate and coordinate biochemical responses to ameliorate dehydration stress. This study examines the extracellular signal-regulated kinase (ERK) signaling cascade, analyzing responses of both upstream and downstream components in six tissues of X. laevis experiencing medium and high levels of dehydration, 16.6+/-1.59 and 28.0+/-1.6% of total body water lost, respectively. Immunoblotting was used to assess the three tiers in this mitogen-activated protein kinase (MAPK) cascade: the initiating MAPK kinase kinases (c-Raf, MEKK), the MAPK kinase (MEK1/2), and finally the MAPK (ERK1/2). The amount of active phosphorylated c-Raf(Ser338) rose by 2- to 2.5-fold under high dehydration in muscle, lung and skin whereas MEKK protein levels rose in these organs and also increased 4-fold in liver. As a result, phosphorylated active MEK1/2(Ser217/221) increased significantly by 2- to 6-fold during dehydration which, in turn, led to 2- to 6-fold increases in phospho-ERK(Thr202/Tyr204) content in all tissues except skin. Given this clear demonstration of ERK cascade activation, two downstream targets of ERK2 were then evaluated. The amount of phosphorylated active transcription factor, STAT3(Ser727) and p90 ribosomal S6 kinase (RSK(Ser380)) increased particularly in muscle, lung and kidney. Furthermore, RSK activation was correlated with a 5- to 8-fold increase in phosphorylation of its target, S6 ribosomal protein. Overall, the results show a strong conserved activation of the ERK cascade in X. laevis tissues in response to dehydration.
在其原生环境中，非洲爪蟾（非洲爪蟾，学名：Xenopus laevis）会经历季节性干旱条件，从而面临脱水应激。细胞内信号转导级联反应的激活可以介导和协调生化反应，以缓解脱水应激。本研究检测了细胞外信号调节激酶（ERK）信号级联反应，分析了非洲爪蟾六个组织中上游和下游成分在中度和高度脱水情况下的反应，分别损失了全身水分的16.6±1.59%和28.0±1.6%。免疫印迹法用于评估这种丝裂原活化蛋白激酶（MAPK）级联反应中的三个层级：起始的MAPK激酶激酶（c-Raf、MEKK）、MAPK激酶（MEK1/2），以及最终的MAPK（ERK1/2）。在肌肉、肺和皮肤中，高脱水状态下活性磷酸化c-Raf（Ser338）的量增加了2至2.5倍，而MEKK蛋白水平在这些器官中升高，在肝脏中也增加了4倍。结果，在脱水过程中，磷酸化活性MEK1/2（Ser217/221）显著增加了2至6倍，进而导致除皮肤外的所有组织中磷酸化ERK（Thr202/Tyr204）含量增加了2至6倍。鉴于ERK级联反应激活的明确证明，随后评估了ERK2的两个下游靶点。磷酸化活性转录因子STAT3（Ser727）和p90核糖体S6激酶（RSK（Ser380））的量尤其在肌肉、肺和肾脏中增加。此外，RSK的激活与其靶点S6核糖体蛋白磷酸化增加5至8倍相关。总体而言，结果表明非洲爪蟾组织中的ERK级联反应在脱水时具有强烈的保守激活。
