Cyclic AMP Signaling Reduces Sirtuin 6 Expression in Non-small Cell Lung Cancer Cells by Promoting Ubiquitin-Proteasomal Degradation via Inhibition of the Raf-MEK-ERK (Raf/Mitogen-activated Extracellular Signal-regulated Kinase/Extracellular Signal-regulated Kinase) Pathway

• Published in: The Journal of biological chemistry 2015-04, Vol.290 (15), p.9604-9613
• Main Authors: Kim, Eui-Jun, Juhnn, Yong-Sung
• Format: Article
• Language: English
• Subjects: Apoptosis; Apoptosis - radiation effects; Blotting, Western; Cell Line, Tumor; Cyclic AMP (cAMP); Cyclic AMP - metabolism; Dinoprostone - pharmacology; Enzyme Inhibitors - pharmacology; Extracellular Signal-regulated Kinase (ERK); Gene Expression Regulation, Neoplastic - drug effects; GTP-Binding Protein alpha Subunits, Gs - genetics; GTP-Binding Protein alpha Subunits, Gs - metabolism; Humans; Isoquinolines - pharmacology; Leupeptins - pharmacology; Lung Cancer; MAP Kinase Kinase 1 - metabolism; MAP Kinase Signaling System - drug effects; Mitogen-Activated Protein Kinase 1 - metabolism; Mitogen-Activated Protein Kinase 3 - metabolism; Models, Biological; Phosphorylation - drug effects; Proteasome Endopeptidase Complex - metabolism; Protein Kinase A (PKA); Proteolysis - drug effects; Proto-Oncogene Proteins c-raf - metabolism; Reverse Transcriptase Polymerase Chain Reaction; Signal Transduction; Signal Transduction - drug effects; Sirtuin; Sirtuins - genetics; Sirtuins - metabolism; Sulfonamides - pharmacology; Ubiquitin - metabolism
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M114.633198

Background: cAMP signaling augments radiation-induced apoptosis of lung cancer cells. Results: cAMP signaling reduces the expression of sirtuin 6 deacetylase in non-small cell lung cancer cells by promoting ubiquitin-proteasomal degradation via inhibition of the Raf-MEK-ERK pathway. Conclusion: cAMP signaling reduces sirtuin 6, which augments radiation-induced apoptosis in lung cancer cells. Significance: cAMP signaling augments radiation-induced apoptosis by modulating epigenetic control. The cAMP signaling system regulates various cellular functions, including metabolism, gene expression, and death. Sirtuin 6 (SIRT6) removes acetyl groups from histones and regulates genomic stability and cell viability. We hypothesized that cAMP modulates SIRT6 activity to regulate apoptosis. Therefore, we examined the effects of cAMP signaling on SIRT6 expression and radiation-induced apoptosis in lung cancer cells. cAMP signaling in H1299 and A549 human non-small cell lung cancer cells was activated via the expression of constitutively active Gαs plus treatment with prostaglandin E2 (PGE2), isoproterenol, or forskolin. The expression of sirtuins and signaling molecules were analyzed by Western blotting. Activation of cAMP signaling reduced SIRT6 protein expression in lung cancer cells. cAMP signaling increased the ubiquitination of SIRT6 protein and promoted its degradation. Treatment with MG132 and inhibiting PKA with H89 or with a dominant-negative PKA abolished the cAMP-mediated reduction in SIRT6 levels. Treatment with PGE2 inhibited c-Raf activation by increasing inhibitory phosphorylation at Ser-259 in a PKA-dependent manner, thereby inhibiting downstream MEK-ERK signaling. Inhibiting ERK with inhibitors or with dominant-negative ERKs reduced SIRT6 expression, whereas activation of ERK by constitutively active MEK abolished the SIRT6-depleting effects of PGE2. cAMP signaling also augmented radiation-induced apoptosis in lung cancer cells. This effect was abolished by exogenous expression of SIRT6. It is concluded that cAMP signaling reduces SIRT6 expression by promoting its ubiquitin-proteasome-dependent degradation, a process mediated by the PKA-dependent inhibition of the Raf-MEK-ERK pathway. Reduced SIRT6 expression mediates the augmentation of radiation-induced apoptosis by cAMP signaling in lung cancer cells.