Conus N M, Hemmings B A, Pearson R B
Trescowthick Research Laboratories, Peter MacCallum Cancer Institute, Locked Bag 1, A'Beckett Street, Melbourne, Victoria 3000, Australia.
J Biol Chem. 1998 Feb 20;273(8):4776-82. doi: 10.1074/jbc.273.8.4776.
Activation of the phosphatidylinositol 3-kinase (PI3K) plays an important role in the mitogenic response of many cell types. Recently, two serine/threonine kinases Akt and p70(S6k) have been identified as physiological targets of PI3K. Observations that expression of activated forms of Akt led to the activation of p70(S6k) implied Akt might mediate mitogenic signaling through activation of p70(S6k). To clarify the relationship between signaling through these two kinases, we have examined their regulation by various mitogenic stimuli. In this study we have focused on the role of calcium in the regulation of each kinase in Balb/c-3T3 fibroblasts. Depletion of intracellular calcium stores by EGTA pretreatment has no effect on growth factor-induced Akt activation but completely abolishes p70(S6k) stimulation. Increase of intracellular calcium induced by ionomycin or thapsigargin results in a full activation of p70(S6k), whereas little or no activation of Akt is observed. Furthermore, although PI3K in anti-phosphotyrosine immunoprecipitates is only very weakly activated by ionomycin, the calcium-induced stimulation of p70(S6k) is completely inhibited by the specific PI3K inhibitor wortmannin. We conclude Akt and p70(S6k) lie on separate signaling pathways. Activation of signaling to Akt is insufficient for the activation of p70(S6k), which can be achieved independently of Akt. p70(S6k) requires a separate calcium-dependent and wortmannin-sensitive process that is likely to be independent of type IA PI3K family members.
磷脂酰肌醇3激酶（PI3K）的激活在许多细胞类型的促有丝分裂反应中起着重要作用。最近，两种丝氨酸/苏氨酸激酶Akt和p70（S6k）已被确定为PI3K的生理靶点。有观察表明，活化形式的Akt的表达导致p70（S6k）的激活，这意味着Akt可能通过激活p70（S6k）介导促有丝分裂信号传导。为了阐明通过这两种激酶的信号传导之间的关系，我们研究了它们受各种促有丝分裂刺激的调节情况。在本研究中，我们重点关注了钙在Balb/c - 3T3成纤维细胞中对每种激酶调节的作用。用乙二醇双四乙酸（EGTA）预处理耗尽细胞内钙储存对生长因子诱导的Akt激活没有影响，但完全消除了对p70（S6k）的刺激。离子霉素或毒胡萝卜素诱导的细胞内钙增加导致p70（S6k）完全激活，而观察到Akt几乎没有或没有激活。此外，尽管抗磷酸酪氨酸免疫沉淀物中的PI3K仅被离子霉素非常微弱地激活，但钙诱导的p70（S6k）刺激被特异性PI3K抑制剂渥曼青霉素完全抑制。我们得出结论，Akt和p70（S6k）位于不同的信号传导途径上。激活到Akt的信号不足以激活p70（S6k），p70（S6k）的激活可以独立于Akt实现。p70（S6k）需要一个独立的钙依赖性和渥曼青霉素敏感的过程，这个过程可能独立于IA型PI3K家族成员。
