Ciullo I, Diez-Roux G, Di Domenico M, Migliaccio A, Avvedimento E V
Dipartimento di Biologia e Patologia Molecolare e Cellulare, Centro di Endocrinologia ed Oncologia Sperimentale del C.N.R., Facoltà di Medicina, Università "Federico II" via S.Pansini 5, Napoli, Italy.
Oncogene. 2001 Mar 8;20(10):1186-92. doi: 10.1038/sj.onc.1204219.
Thyrotropin (TSH) stimulates survival and growth of thyroid cells via a seven transmembrane G protein-coupled receptor. TSH elevates the intracellular cyclic AMP (cAMP) levels activating protein kinase A (PKA). Recent evidence indicates that p21 Ras is required for TSH-induced mitogenesis, but the molecular mechanism(s) is not known. Here we report that Ras p21 activity is necessary for the Go- G1 transition in TSH induced cycle and that the downstream effector of Ras upon TSH signaling is p85-p110 PI3K. We show that PI3K inhibitors block TSH-induced DNA synthesis, cAMP-PKA stimulate the formation of the complex PI3K-p21 Ras and reduce the complex Ras-Raf1 in thyroid and other cells types. Moreover, PKA phosphorylates immunoprecipitated p85 and PKA phosphorylation of cell extracts significantly stimulates the formation of the complex PI3K-Ras. We suggest that PKA phosphorylates p85 and stabilizes the complex p110-p85, enhancing the interaction PI3K and p21 Ras. Simultaneously, cAMP inhibits Raf-1-ERK signaling by decreasing Raf1 availability to Ras. Under these circumstances PI3K signaling is favored. These results indicate that PI3K is an important mediator of Ras effects in cAMP-induced proliferation and illustrates how cAMP can selectively influence Ras effector pathways.
促甲状腺激素（TSH）通过七跨膜G蛋白偶联受体刺激甲状腺细胞的存活和生长。TSH提高细胞内环状AMP（cAMP）水平，激活蛋白激酶A（PKA）。最近的证据表明，p21 Ras是TSH诱导的有丝分裂所必需的，但分子机制尚不清楚。在这里，我们报告Ras p21活性对于TSH诱导的细胞周期中从G0期到G1期的转变是必需的，并且TSH信号传导时Ras的下游效应器是p85-p110 PI3K。我们表明，PI3K抑制剂可阻断TSH诱导的DNA合成，cAMP-PKA刺激PI3K-p21 Ras复合物的形成，并减少甲状腺和其他细胞类型中的Ras-Raf1复合物。此外，PKA使免疫沉淀的p85磷酸化，细胞提取物的PKA磷酸化显著刺激PI3K-Ras复合物的形成。我们认为PKA使p85磷酸化并稳定p110-p85复合物，增强PI3K与p21 Ras的相互作用。同时，cAMP通过降低Raf1与Ras的结合能力来抑制Raf-1-ERK信号传导。在这种情况下，PI3K信号传导受到青睐。这些结果表明，PI3K是cAMP诱导的增殖中Ras效应的重要介质，并说明了cAMP如何选择性地影响Ras效应途径。
