The PKARIalpha subunit of protein kinase A modulates the activation of p90RSK1 and its function.
Previously, we showed that interactions between p90(RSK1) (RSK1) and the subunits of type I protein kinase A (PKA) regulate the activity of PKA and cellular distribution of active RSK1 (Chaturvedi, D., Poppleton, H. M., Stringfield, T., Barbier, A., and Patel, T. B. (2006) Mol. Cell Biol. 26, 4586-4600). Here we examined the role of the PKARIalpha subunit of PKA in regulating RSK1 activation and cell survival. In mouse lung fibroblasts, silencing of the PKARIalpha increased the phosphorylation and activation of RSK1, but not of RSK2 and RSK3, in the absence of any stimulation. Silencing of PKARIalpha also decreased the nuclear accumulation of active RSK1 and increased its cytoplasmic content. The increased activation of RSK1 in the absence of any agonist and changes in its subcellular redistribution resulted in increased phosphorylation of its cytoplasmic substrate BAD and increased cell survival. The activity of PKA and phosphorylation of BAD (Ser-155) were also enhanced when PKARIalpha was silenced, and this, in part, contributed to increased cell survival in unstimulated cells. Furthermore, we show that RSK1, PKA subunits, D-AKAP1, and protein phosphatase 2A catalytic subunit (PP2Ac) exist in a complex, and dissociation of RSK1 from D-AKAP1 by either silencing of PKARIalpha, depletion of D-AKAP1, or by using a peptide that competes with PKARIalpha for binding to AKAPs, decreased the amount of PP2Ac in the RSK1 complex. We also demonstrate that PP2Ac is one of the phosphatases that dephosphorylates RSK, but not ERK1/2. Thus, in unstimulated cells, the increased phosphorylation and activation of RSK1 after silencing of PKARIalpha or depletion of D-AKAP1 are due to decreased association of PP2Ac in the RSK1 complex.
Chaturvedi
Deepti
D
Department of Pharmacology, Stritch School of Medicine, Loyola University Chicago, Maywood, Illinois 60153, USA.
Cohen
Michael S
MS
Taunton
Jack
J
Patel
Tarun B
TB
D000818:Animals; D002460:Cell Line; D002470:Cell Survival; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit / Q000235:genetics / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D051379:Mice; D010766:Phosphorylation; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism*; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*; D051025:bcl-Associated Death Protein / Q000235:genetics / Q000378:metabolism
C494820:Bad protein, mouse; D054756:Cyclic AMP-Dependent Protein Kinase RIalpha Subunit; D021122:Protein Subunits; D051025:bcl-Associated Death Protein; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse; D017868:Cyclic AMP-Dependent Protein Kinases