RESUMO
Cellular senescence, a state of sustained cell cycle arrest, has been identified as an important anti-tumor barrier. Senescent cells secrete various growth factors and cytokines, such as IL6 and IL8, which collectively constitute the senescence-associated secretory phenotype (SASP). The SASP can signal to the tumor environment and elicit the immune-mediated clearance of tumor cells or, depending on the context, could potentially promote tumor progression. Despite the importance of the SASP to tumor biology, its regulation remains relatively unknown. Here, we show that IκBζ, an atypical member of the inhibitor of NFκB proteins and selective coactivator of particular NFκB target genes, is an important regulator of SASP expression. Several models of DNA damage- and oncogene-induced senescence revealed a robust induction of IκBζ expression. RNAi-mediated knockdown of IκBζ impaired IL6 and IL8 expression, whereas transgenic IκBζ expression resulted in enhanced SASP cytokine expression. Importantly, during senescence of IκBζ knockout cells induction of IL6 and IL8, but not of the cell cycle inhibitor p21(WAF/CIP1), was completely abolished. Thus, we propose an important and hitherto unappreciated role of IκBζ in SASP formation in both DNA damage- and oncogene-induced senescence.
Assuntos
Dano ao DNA , Proteínas I-kappa B/metabolismo , Pontos de Checagem do Ciclo Celular , Linhagem Celular Tumoral , Senescência Celular/genética , Senescência Celular/fisiologia , Citocinas/metabolismo , Humanos , Proteínas I-kappa B/biossíntese , Proteínas I-kappa B/genética , Células MCF-7 , Oncogenes , Fenótipo , Transdução de SinaisRESUMO
CCL2, also referred to as MCP-1, is critically involved in directing the migration of blood monocytes to sites of inflammation. Consequently, excessive CCL2 secretion has been linked to many inflammatory diseases, whereas a lack of expression severely impairs immune responsiveness. We demonstrate that IκBζ, an atypical IκB family member and transcriptional coactivator required for the selective expression of a subset of NF-κB target genes, is a key activator of the Ccl2 gene. IκBζ-deficient macrophages exhibited impaired secretion of CCL2 when challenged with diverse inflammatory stimuli, such as LPS or peptidoglycan. These findings were reflected at the level of Ccl2 gene expression, which was tightly coupled to the presence of IκBζ. Moreover, mechanistic insights acquired by chromatin immunoprecipitation demonstrate that IκBζ is directly recruited to the proximal promoter region of the Ccl2 gene and is required for transcription-enhancing histone H3 at lysine-4 trimethylation. Finally, IκBζ-deficient mice showed significantly impaired CCL2 secretion and monocyte infiltration in an experimental model of peritonitis. Together, these findings suggest a distinguished role of IκBζ in mediating the targeted recruitment of monocytes in response to local inflammatory events.
Assuntos
Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Quimiocina CCL2/genética , Quimiocina CCL2/metabolismo , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Transcrição Gênica/genética , Proteínas Adaptadoras de Transdução de Sinal/imunologia , Animais , Células Cultivadas , Quimiocina CCL2/imunologia , Feminino , Expressão Gênica/genética , Expressão Gênica/imunologia , Histonas/genética , Histonas/imunologia , Histonas/metabolismo , Inflamação/genética , Inflamação/imunologia , Inflamação/metabolismo , Lipopolissacarídeos/imunologia , Macrófagos/imunologia , Macrófagos/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Monócitos/imunologia , Monócitos/metabolismo , NF-kappa B/genética , NF-kappa B/imunologia , NF-kappa B/metabolismo , Proteínas Nucleares/imunologia , Peritonite/genética , Peritonite/imunologia , Peritonite/metabolismo , Regiões Promotoras Genéticas/genética , Regiões Promotoras Genéticas/imunologia , Transcrição Gênica/imunologiaRESUMO
Previous efforts to develop drugs that directly inhibit the activity of mutant KRAS, the most commonly mutated human oncogene, have not been successful. Cancer cells driven by mutant KRAS require expression of the serine/threonine kinase STK33 for their viability and proliferation, identifying STK33 as a context-dependent therapeutic target. However, specific strategies for interfering with the critical functions of STK33 are not yet available. Here, using a mass spectrometry-based screen for STK33 protein interaction partners, we report that the HSP90/CDC37 chaperone complex binds to and stabilizes STK33 in human cancer cells. Pharmacologic inhibition of HSP90, using structurally divergent small molecules currently in clinical development, induced proteasome-mediated degradation of STK33 in human cancer cells of various tissue origin in vitro and in vivo, and triggered apoptosis preferentially in KRAS mutant cells in an STK33-dependent manner. Furthermore, HSP90 inhibitor treatment impaired sphere formation and viability of primary human colon tumor-initiating cells harboring mutant KRAS. These findings provide mechanistic insight into the activity of HSP90 inhibitors in KRAS mutant cancer cells, indicate that the enhanced requirement for STK33 can be exploited to target mutant KRAS-driven tumors, and identify STK33 depletion through HSP90 inhibition as a biomarker-guided therapeutic strategy with immediate translational potential.