cAMP signaling selectively influences Ras effectors pathways.
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.
Ciullo
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I
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.
Diez-Roux
G
G
Di Domenico
M
M
Migliaccio
A
A
Avvedimento
E V
EV
D002453:Cell Cycle / Q000187:drug effects*; D002454:Cell Differentiation; D002455:Cell Division / Q000502:physiology; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D004247:DNA / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism; D015151:Immunoblotting; D015689:Oncogene Protein p21(ras) / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D015398:Signal Transduction; D013954:Thyroglobulin / Q000235:genetics / Q000378:metabolism*; D018631:ras Proteins / Q000235:genetics / Q000378:metabolism*
D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D004247:DNA; D019204:GTP-Binding Proteins; D015689:Oncogene Protein p21(ras); D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf; D013954:Thyroglobulin; D018631:ras Proteins