ACTH promotion of p27(Kip1) induction in mouse Y1 adrenocortical tumor cells is dependent on both PKA activation and Akt/PKB inactivation.
Here we report antimitogenic mechanisms activated by the adrenocorticotropic hormone (ACTH) in the mouse Y1 adrenocortical tumor cell line. ACTH receptors activate the Galphas/adenylate cyclase cAMP/PKA pathway to promote dephosphorylation of Akt/PKB enzymes, leading to induction of the cyclin-dependent kinases' (CDKs) inhibitor p27(Kip1). Y1 cells display high constitutive levels of phosphorylated Akt/PKB dependent on chronically elevated c-Ki-Ras.GTP and PI3K activity. Expression of the dominant negative mutant RasN17 in Y1 cells results in strong reduction of both c-Ki-Ras.GTP and phosphorylated Akt/PKB, which are restored by FGF2 treatments. Inhibitors of PI3K lead to rapid dephosphorylation of Akt/PKB and block phosphorylation of Akt/PKB promoted by FGF2. ACTH rapidly promotes dephosphorylation of Akt/PKB in Y1 adrenal cells, while constitutively high levels of c-Ki-Ras.GTP remain unchanged. ACTH and cAMP elevating agents fail to cause Akt/PKB dephosphorylation in PKA-deficient clonal mutants of Y1 cells. In addition, cholera toxin, forskolin, and 8BrcAMP all mimic ACTH, causing dephosphorylation of Akt/PKB in wild-type Y1 cells. ACTH is unable to prevent Akt/PKB phosphorylation, promoted by FGF2 in clonal lines of RasN17-Y1 transfectants displaying negligible levels of c-Ki-Ras.GTP. ACTH promotes strong p27(Kip1) protein induction in wild-type Y1 adrenocortical cells but not in PKA-deficient Y1-clonal mutants nor in RasN17-Y1 transfectants. PI3K inhibitors induce p27(Kip1) protein in all cells studied, i.e., wild type and transfectants. The inverse correlation between levels of phosphorylated Akt/PKB and of p27(Kip1) protein caused by ACTH suggests a novel antimitogenic pathway activated by ACTH and mediated by cAMP/PKA in the mouse Y1 adrenocortical tumor cell line.
Forti
Fábio L
FL
Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo-SP, 05508-900, Brazil.
Schwindt
Telma T
TT
Moraes
Miriam S
MS
Eichler
Claudia B
CB
Armelin
Hugo A
HA
D000306:Adrenal Cortex Neoplasms / Q000201:enzymology / Q000378:metabolism*; D000324:Adrenocorticotropic Hormone / Q000502:physiology*; D000818:Animals; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000096:biosynthesis* / Q000235:genetics; D051379:Mice; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D014407:Tumor Cells, Cultured
C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D011518:Proto-Oncogene Proteins; D000324:Adrenocorticotropic Hormone; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases