Goruppi S, Ruaro E, Varnum B, Schneider C
L.N.C.I.B. Laboratorio Nazionale Consorzio Interuniversitario Biotecnologie AREA Science Park, Trieste, Italy.
Oncogene. 1999 Jul 22;18(29):4224-36. doi: 10.1038/sj.onc.1202788.
Gas6 is a growth factor membrane of the vitamin K-dependent family of proteins which is preferentially expressed in quiescent cells. Gas6 was identified as the ligand for Axl tyrosine kinase receptor family. Consistent with this, Gas6 was previously reported to induce cell cycle re-entry of serum-starved NIH3T3 cells and to prevent cell death after complete growth factor withdrawal, the survival effect being uncoupled from Gas6-induced mitogenesis. We have previously demonstrated that both Gas6 mitogenic and survival effects are mediated by Src and the phosphatidylinositol3-OH kinase (PI3K). Here we report that Ras is required for Gas6 mitogenesis but is dispensable for its survival effect. Gas6-induced survival requires the activity of the small GTPases of the Rho family, Rac and Rho, together with the downstream kinase Pak. Overexpression of the respective dominant negative constructs abrogates Gas6-mediated survival functions. Addition of Gas6 to serum starved cells results in the activation of AKT/PKB and in the phosphorylation of the Bcl-2 family member, Bad. By ectopic expression of a catalytically inactive form of AKT/PKB, we demonstrate that AKT/PKB is necessary for Gas6-mediated survival functions. We further show evidence that Gas6 stimulation of serum starved NIH3T3 cells results in a transient ERK, JNK/SAPK and p38 MAPK activation. Blocking ERK activation did not influence Gas6-induced survival, suggesting that such pathway is not involved in Gas6 protection from cell death. On the contrary we found that the late constitutive increase of p38 MAPK activity associated with cell death was downregulated in Gas6-treated NIH3T3 cells thus suggesting that Gas6 might promote survival by interfering with this pathway. Taken together the evidence here provided identity elements involved in Gas6 signalling more specifically elucidating the pathway responsible for Gas6-induced cell survival under conditions that do not allow cell proliferation.
Gas6是维生素K依赖性蛋白家族的一种生长因子膜蛋白，在静止细胞中优先表达。Gas6被鉴定为Axl酪氨酸激酶受体家族的配体。与此一致的是，先前有报道称Gas6可诱导血清饥饿的NIH3T3细胞重新进入细胞周期，并在完全撤除生长因子后防止细胞死亡，其存活效应与Gas6诱导的有丝分裂无关。我们先前已证明，Gas6的促有丝分裂和存活效应均由Src和磷脂酰肌醇3 - OH激酶（PI3K）介导。在此我们报告，Ras是Gas6促有丝分裂所必需的，但对其存活效应则是可有可无的。Gas6诱导的存活需要Rho家族的小GTP酶Rac和Rho以及下游激酶Pak的活性。各自显性负性构建体的过表达消除了Gas6介导的存活功能。向血清饥饿细胞中添加Gas6会导致AKT/PKB激活以及Bcl - 2家族成员Bad的磷酸化。通过异位表达催化失活形式的AKT/PKB，我们证明AKT/PKB是Gas6介导的存活功能所必需的。我们进一步表明，Gas6刺激血清饥饿的NIH3T3细胞会导致ERK、JNK/SAPK和p38 MAPK的短暂激活。阻断ERK激活并不影响Gas6诱导的存活，这表明该途径不参与Gas6对细胞死亡的保护作用。相反，我们发现与细胞死亡相关的p38 MAPK活性的晚期组成性增加在Gas6处理的NIH3T3细胞中被下调，因此表明Gas6可能通过干扰该途径来促进存活。综上所述，这里提供的证据确定了Gas6信号传导中涉及的元件，更具体地阐明了在不允许细胞增殖的条件下负责Gas6诱导细胞存活的途径。
