Starting Mechanisms of Signal Transduction by Trk Family Receptors

培养的小脑颗粒神经元维持在含有26 mM钾的培养基中（高K^+或HK^<>）在转换到含5 mM钾的培养基时发生细胞死亡这种低K ^+诱导的细胞死亡具有典型的细胞凋亡特征，在K^+剥夺后2 ~ 5 h，小脑颗粒神经元开始发生凋亡，尽管大多数mRNA的水平随着定型而显著下降，但c-jun mRNA的表达在K^+剥夺后2-3 h增加。在caspase家族中，一种半胱天冬酶-3样蛋白酶在K^+浓度降低后4小时内被激活。LY 294002和渥曼青霉素均可诱导小脑颗粒神经元凋亡，LY 294002诱导小脑颗粒神经元凋亡的细胞内信号转导途径研究表明，LY 294002诱导小脑颗粒神经元凋亡的细胞内信号转导途径为：在低K^+培养液中加入LY 294002后，高K ^+培养液中加入LY 294002 8 h后，c-Jun N-末端激酶（JNK）活性升高低K^+诱导的小脑颗粒神经元凋亡可被高K^+所阻止，而高K^+则可抑制小脑颗粒神经元凋亡（高K^+引起的膜去极化），BDNF或cAMP。这些药物阻止低K^+诱导的细胞凋亡的细胞内信号通路已经被研究过。高K^+和BDNF通过PI 3-抑制细胞凋亡。cAMP对PI 3-K-Akt通路的促存活作用不受PI 3-K-Akt通路的影响。

Cultured cerebellar granule neurons maintained in medium containing 26 mM potassium (high K^+ or HK^<>) undergo cell death when switched to medium with 5 mM potassium (low K^+ or LK^+).This low K^+-induced cell death has typical features of apoptosis has been investigated.Cerebellar granule neurons become committed to undergo apoptosis between 2 and 5 h after K^+ deprivation, judging from the inability of high K^+ to rescue them after this time.Although the levels of most mRNAs decrease markedly concomitant with commitment, expression of c-jun mRNA increases 2-3 h after K^+ deprivation.Among the family of caspases, a caspase-3-like protease is activated within 4 h of lowering the K^+ concentration.Inhibition of phosphatidylinositol 3-kinase (PI3-K) activity by LY294002 or wortmannin also induces apoptosis in cerebellar granule neurons.The intracellular signaling pathway of LY294002-induced apoptosis has been investigated.The activity of c-Jun N-terminal kinase (JNK) increases 8 h after addition of LY294002 to high K^+ medium of low K^+ medium containing BDNF.Expression of c-Jun protein also increases almost simultaneously.The low K^+-induced apoptosis of cerebellar granule neurons is prevented by high K^+ (membrane depolarization by high K^+), BDNF or cAMP.The intracellular signaling pathways by which these agents prevent low K^+-induced apoptosis have been investigated.High K^+ and BDNF prevent apoptosis through PI3-K and Ser/Thr kinase, Akt/PKB.The survival-promoting effect of cAMP does not on the PI3-K-Akt pathway.