The c-MYC oncoprotein, the NAMPT enzyme, the SIRT1-inhibitor DBC1, and the SIRT1 deacetylase form a positive feedback loop.
Proc Natl Acad Sci U S A
; 109(4): E187-96, 2012 Jan 24.
Article
em En
| MEDLINE
| ID: mdl-22190494
ABSTRACT
Silent information regulator 1 (SIRT1) represents an NAD(+)-dependent deacetylase that inhibits proapoptotic factors including p53. Here we determined whether SIRT1 is downstream of the prototypic c-MYC oncogene, which is activated in the majority of tumors. Elevated expression of c-MYC in human colorectal cancer correlated with increased SIRT1 protein levels. Activation of a conditional c-MYC allele induced increased levels of SIRT1 protein, NAD(+), and nicotinamide-phosphoribosyltransferase (NAMPT) mRNA in several cell types. This increase in SIRT1 required the induction of the NAMPT gene by c-MYC. NAMPT is the rate-limiting enzyme of the NAD(+) salvage pathway and enhances SIRT1 activity by increasing the amount of NAD(+). c-MYC also contributed to SIRT1 activation by sequestering the SIRT1 inhibitor deleted in breast cancer 1 (DBC1) from the SIRT1 protein. In primary human fibroblasts previously immortalized by introduction of c-MYC, down-regulation of SIRT1 induced senescence and apoptosis. In various cell lines inactivation of SIRT1 by RNA interference, chemical inhibitors, or ectopic DBC1 enhanced c-MYC-induced apoptosis. Furthermore, SIRT1 directly bound to and deacetylated c-MYC. Enforced SIRT1 expression increased and depletion/inhibition of SIRT1 reduced c-MYC stability. Depletion/inhibition of SIRT1 correlated with reduced lysine 63-linked polyubiquitination of c-Myc, which presumably destabilizes c-MYC by supporting degradative lysine 48-linked polyubiquitination. Moreover, SIRT1 enhanced the transcriptional activity of c-MYC. Taken together, these results show that c-MYC activates SIRT1, which in turn promotes c-MYC function. Furthermore, SIRT1 suppressed cellular senescence in cells with deregulated c-MYC expression and also inhibited c-MYC-induced apoptosis. Constitutive activation of this positive feedback loop may contribute to the development and maintenance of tumors in the context of deregulated c-MYC.
Texto completo:
1
Coleções:
01-internacional
Base de dados:
MEDLINE
Assunto principal:
Citocinas
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Proteínas Proto-Oncogênicas c-myc
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Senescência Celular
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Apoptose
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Proteínas Supressoras de Tumor
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Retroalimentação Fisiológica
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Nicotinamida Fosforribosiltransferase
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Sirtuína 1
Limite:
Humans
Idioma:
En
Ano de publicação:
2012
Tipo de documento:
Article