Selective phosphorylation of nuclear CREB by fluoxetine is linked to activation of CaM kinase IV and MAP kinase cascades.
Regulation of gene expression is purported as a major component in the long-term action of antidepressants. The transcription factor cAMP-response element-binding protein (CREB) is activated by chronic antidepressant treatments, although a number of studies reported different effects on CREB, depending on drug types used and brain areas investigated. Furthermore, little is known as to what signaling cascades are responsible for CREB activation, although cAMP-protein kinase A (PKA) cascade was suggested to be a central player. We investigated how different drugs (fluoxetine (FLX), desipramine (DMI), reboxetine (RBX)) affect CREB expression and phosphorylation of Ser(133) in the hippocampus and prefrontal/frontal cortex (PFCX). Acute treatments did not induce changes in these mechanisms. Chronic FLX increased nuclear phospho-CREB (pCREB) far more markedly than pronoradrenergic drugs, particularly in PFCX. We investigated the function of the main signaling cascades that were shown to phosphorylate and regulate CREB. PKA did not seem to account for the selective increase of pCREB induced by FLX. All drug treatments markedly increased the enzymatic activity of nuclear Ca2+/calmodulin (CaM) kinase IV (CaMKIV), a major neuronal CREB kinase, in PFCX. Activation of this kinase was due to increased phosphorylation of the activatory residue Thr196, with no major changes in the expression levels of alpha- and beta-CaM kinase kinase, enzymes that phosphorylate CaMKIV. Again in PFCX, FLX selectively increased the expression level of MAP kinases Erk1/2, without affecting their phosphorylation. Our results show that FLX exerts a more marked effect on CREB phosphorylation and suggest that CaMKIV and MAP kinase cascades are involved in this effect.
Tiraboschi
Ettore
E
Department of Pharmacological Sciences, Center of Neuropharmacology, University of Milano and Center of Excellence on Neurodegenerative Diseases, University of Milano, Milano, Italy.
Tardito
Daniela
D
Kasahara
Jiro
J
Moraschi
Stefania
S
Pruneri
Paolo
P
Gennarelli
Massimo
M
Racagni
Giorgio
G
Popoli
Maurizio
M
D018663:Adrenergic Agents / Q000494:pharmacology; D000818:Animals; D018687:Antidepressive Agents, Second-Generation / Q000494:pharmacology*; D015153:Blotting, Western; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D017362:Cyclic AMP Response Element-Binding Protein / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005473:Fluoxetine / Q000494:pharmacology*; D006624:Hippocampus / Q000187:drug effects / Q000201:enzymology; D047468:Immunoprecipitation; D008297:Male; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017397:Prefrontal Cortex / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects
D018663:Adrenergic Agents; D018687:Antidepressive Agents, Second-Generation; D054734:Calcium-Calmodulin-Dependent Protein Kinase Type 4; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D017362:Cyclic AMP Response Element-Binding Protein; D017868:Cyclic AMP-Dependent Protein Kinases; D005473:Fluoxetine; D020928:Mitogen-Activated Protein Kinases; D017367:Selective Serotonin Reuptake Inhibitors; C517686:Camk4 protein, rat