Inhibition of 5-HT1A receptor-dependent cell survival by cAMP/protein kinase A: Role of protein phosphatase 2A and Bax

Serotonergic 5-HT1A receptor signaling leading to nuclear factor-κB (NF-κB) activation appears to be critical for cell survival. Adenylyl cyclase and protein kinase A (AC/PKA) are effectors of the 5-HT1A receptor that are inhibited by Gαi subunits. Conversely, Gβγi subunits downstream from the 5-HT1A receptor participate in the activation of extracellular signal-regulated kinases (ERK1/2), phosphatidylinositol 3-kinase (PI3K), Akt, and NF-κB. To model the contribution of pro- and antiapoptotic signaling cascades downstream of activated 5-HT1A receptor in cell survival, Chinese hamster ovarian (CHO) cells were employed that exogenously overexpress 5-HT1A receptors. Stimulation with the 5-HT1A receptor agonist 8-OH-DPAT and pharmacological agonists of AC induced PKA and protein phosphatase 2A (PP2A) activity, which in turn inhibited: Akt activity, IκBα degradation, nuclear translocation of NF-κB, and expression of X-linked inhibitor of apoptosis protein (XIAP/BIRC4). Pharmacological inhibition of PP2A with calyculin A potentiated Akt activity while attenuating ERK1/2 signaling via increased inhibitory phosphorylation of Raf (pSer259). In contrast, increased cAMP levels enhanced Bax translocation to the mitochondria, resulting in the release of cytochrome c, caspase-3 activation, and apoptosis induction. Our data suggest a central role of cAMP/PKA-dependent PP2A in shifting the homeostasis of intracellular signaling downstream of activated 5-HT1A receptor toward cell death in biological systems linked to neuropsychiatric disorders. © 2008 Wiley-Liss, Inc.