Epac, in synergy with cAMP-dependent protein kinase (PKA), is required for cAMP-mediated mitogenesis.
cAMP stimulates proliferation in many cell types. For many years, cAMP-dependent protein kinase (PKA) represented the only known cAMP effector. PKA, however, does not fully mimic the action of cAMP, indicating the existence of a PKA-independent component. Since cAMP-mediated activation of the G-protein Rap1 and its phosphorylation by PKA are strictly required for the effects of cAMP on mitogenesis, we hypothesized that the Rap1 activator Epac might represent the PKA-independent factor. Here we report that Epac acts synergistically with PKA in cAMP-mediated mitogenesis. We have generated a new dominant negative Epac mutant that revealed that activation of Epac is required for thyroid-stimulating hormone or cAMP stimulation of DNA synthesis. We demonstrate that Epac's action on cAMP-mediated activation of Rap1 and cAMP-mediated mitogenesis depends on the subcellular localization of Epac via its DEP domain. Disruption of the DEP-dependent subcellular targeting of Epac abolished cAMP-Epac-mediated Rap1 activation and thyroid-stimulating hormone-mediated cell proliferation, indicating that an Epac-Rap-PKA signaling unit is critical for the mitogenic action of cAMP.
Hochbaum
Daniel
D
Department of Pharmacology, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15261, USA.
Hong
Kyoungja
K
Barila
Guillermo
G
Ribeiro-Neto
Fernando
F
Altschuler
Daniel L
DL
D000818:Animals; D002460:Cell Line; D049109:Cell Proliferation / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism* / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism*; D004247:DNA / Q000096:biosynthesis / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D020662:Guanine Nucleotide Exchange Factors / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D010766:Phosphorylation / Q000187:drug effects; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000187:drug effects / Q000502:physiology; D051381:Rats; D015398:Signal Transduction / Q000502:physiology*; D013972:Thyrotropin / Q000378:metabolism / Q000494:pharmacology; D020827:rap1 GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*
D020662:Guanine Nucleotide Exchange Factors; D013972:Thyrotropin; D004247:DNA; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D020827:rap1 GTP-Binding Proteins