RESUMO
RAS proteins are GTPases that lie upstream of a signaling network impacting cell fate determination. How cells integrate RAS activity to balance proliferation and cellular senescence is still incompletely characterized. Here, we identify ZNF768 as a phosphoprotein destabilized upon RAS activation. We report that ZNF768 depletion impairs proliferation and induces senescence by modulating the expression of key cell cycle effectors and established p53 targets. ZNF768 levels decrease in response to replicative-, stress- and oncogene-induced senescence. Interestingly, ZNF768 overexpression contributes to bypass RAS-induced senescence by repressing the p53 pathway. Furthermore, we show that ZNF768 interacts with and represses p53 phosphorylation and activity. Cancer genomics and immunohistochemical analyses reveal that ZNF768 is often amplified and/or overexpressed in tumors, suggesting that cells could use ZNF768 to bypass senescence, sustain proliferation and promote malignant transformation. Thus, we identify ZNF768 as a protein linking oncogenic signaling to the control of cell fate decision and proliferation.
Assuntos
Senescência Celular/genética , Genes ras/genética , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismo , Carcinogênese , Ciclo Celular , Diferenciação Celular , Proliferação de Células , Transformação Celular Neoplásica , Replicação do DNA , Regulação Neoplásica da Expressão Gênica , Técnicas de Silenciamento de Genes , Genômica , Células HeLa , Humanos , Oncogenes , Fenótipo , Fosfoproteínas , Fosforilação , Repressão Psicológica , Transdução de Sinais , Proteínas ras/genéticaRESUMO
The phosphoinositide-3-kinase (PI3K)/protein kinase B (Akt) axis plays a central role in attenuating inflammation upon macrophage stimulation with toll-like receptor (TLR) ligands. The mechanistic target of rapamycin complex 2 (mTORC2) relays signal from PI3K to Akt but its role in modulating inflammation in vivo has never been investigated. To evaluate the role of mTORC2 in the regulation of inflammation in vivo, we have generated a mouse model lacking Rictor, an essential mTORC2 component, in myeloid cells. Primary macrophages isolated from myeloid-specific Rictor null mice exhibited an exaggerated response to TLRs ligands, and expressed high levels of M1 genes and lower levels of M2 markers. To determine whether the loss of Rictor similarly affected inflammation in vivo, mice were either fed a high fat diet, a situation promoting chronic but low-grade inflammation, or were injected with lipopolysaccharide (LPS), which mimics an acute, severe septic inflammatory condition. Although high fat feeding contributed to promote obesity, inflammation, macrophage infiltration in adipose tissue and systemic insulin resistance, we did not observe a significant impact of Rictor loss on these parameters. However, mice lacking Rictor exhibited a higher sensitivity to septic shock when injected with LPS. Altogether, these results indicate that mTORC2 is a key negative regulator of macrophages TLR signalling and that its role in modulating inflammation is particularly important in the context of severe inflammatory challenges. These observations suggest that approaches aimed at modulating mTORC2 activity may represent a possible therapeutic approach for diseases linked to excessive inflammation.
Assuntos
Proteínas de Transporte/genética , Deleção de Genes , Macrófagos Peritoneais/patologia , Obesidade/patologia , Animais , Proteínas de Transporte/imunologia , Dieta Hiperlipídica , Fibroblastos/imunologia , Fibroblastos/patologia , Regulação da Expressão Gênica , Inflamação/induzido quimicamente , Inflamação/genética , Inflamação/imunologia , Inflamação/patologia , Resistência à Insulina , Lipopolissacarídeos , Macrófagos Peritoneais/imunologia , Alvo Mecanístico do Complexo 2 de Rapamicina , Camundongos , Camundongos Knockout , Complexos Multiproteicos/genética , Complexos Multiproteicos/imunologia , Obesidade/induzido quimicamente , Obesidade/genética , Obesidade/imunologia , Fosfatidilinositol 3-Quinases/genética , Fosfatidilinositol 3-Quinases/imunologia , Cultura Primária de Células , Proteínas Proto-Oncogênicas c-akt/genética , Proteínas Proto-Oncogênicas c-akt/imunologia , Proteína Companheira de mTOR Insensível à Rapamicina , Transdução de Sinais , Serina-Treonina Quinases TOR/genética , Serina-Treonina Quinases TOR/imunologia , Receptores Toll-Like/genética , Receptores Toll-Like/imunologiaRESUMO
PURPOSE OF REVIEW: The implication of the mammalian target of rapamycin (mTOR) complex 1 (mTORC1) in promoting protein synthesis has been well described. Over the past years, several studies revealed that mTORC1 also plays a crucial role in promoting lipid biosynthesis and that such connection could be linked to diseases including obesity, nonalcoholic fatty liver disease (NAFLD), and cancer. Here, we review the mechanisms by which mTORC1 regulates lipid synthesis by focusing on the key signaling events that trigger hepatic de-novo lipogenesis in response to nutrients and insulin. RECENT FINDINGS: mTORC1 promotes lipid synthesis by activating the transcription factor sterol regulatory element binding protein 1 (SREBP-1). Recent studies indicate that mTORC1 regulates SREBP-1 activation at multiple levels. Although mTORC1 was originally shown to be necessary and sufficient to activate SREBP-1 in vitro, new studies indicate that hyperactivation of mTORC1 is insufficient to trigger SREBP-1 activation and lipid biogenesis in vivo. These findings reveal that the molecular connection between mTORC1 and SREBP-1 is more complex than originally envisioned. SUMMARY: The discovery of a connection between mTORC1 and SREBP-1 opens a new chapter in our understanding of the molecular mechanisms regulating de-novo lipogenesis. A better comprehension of these mechanisms is key for the development of new tools to treat NAFLD and its complications.