RESUMO
It is widely assumed that decreasing transcription factor DNA-binding affinity reduces transcription initiation by diminishing occupancy of sequence-specific regulatory elements. However, in vivo transcription factors find their binding sites while confronted with a large excess of low-affinity degenerate motifs. Here, using the melanoma lineage survival oncogene MITF as a model, we show that low-affinity binding sites act as a competitive reservoir in vivo from which transcription factors are released by mitogen-activated protein kinase (MAPK)-stimulated acetylation to promote increased occupancy of their regulatory elements. Consequently, a low-DNA-binding-affinity acetylation-mimetic MITF mutation supports melanocyte development and drives tumorigenesis, whereas a high-affinity non-acetylatable mutant does not. The results reveal a paradoxical acetylation-mediated molecular clutch that tunes transcription factor availability via genome-wide redistribution and couples BRAF to tumorigenesis. Our results further suggest that p300/CREB-binding protein-mediated transcription factor acetylation may represent a common mechanism to control transcription factor availability.
Assuntos
Regulação Neoplásica da Expressão Gênica , Genoma , Melanoma/genética , Fator de Transcrição Associado à Microftalmia/genética , Processamento de Proteína Pós-Traducional , Neoplasias Cutâneas/genética , Acetilação , Sequência de Aminoácidos , Animais , Sítios de Ligação , Linhagem Celular Tumoral , Sequência Conservada , Elementos Facilitadores Genéticos , Feminino , Xenoenxertos , Humanos , Masculino , Melanócitos/metabolismo , Melanócitos/patologia , Melanoma/metabolismo , Melanoma/patologia , Camundongos , Camundongos Nus , Fator de Transcrição Associado à Microftalmia/química , Fator de Transcrição Associado à Microftalmia/metabolismo , Motivos de Nucleotídeos , Regiões Promotoras Genéticas , Ligação Proteica , Domínios e Motivos de Interação entre Proteínas , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Neoplasias Cutâneas/metabolismo , Neoplasias Cutâneas/patologia , Peixe-ZebraRESUMO
Whether cell types exposed to a high level of environmental insults possess cell type-specific prosurvival mechanisms or enhanced DNA damage repair capacity is not well understood. BRN2 is a tissue-restricted POU domain transcription factor implicated in neural development and several cancers. In melanoma, BRN2 plays a key role in promoting invasion and regulating proliferation. Here we found, surprisingly, that rather than interacting with transcription cofactors, BRN2 is instead associated with DNA damage response proteins and directly binds PARP1 and Ku70/Ku80. Rapid PARP1-dependent BRN2 association with sites of DNA damage facilitates recruitment of Ku80 and reprograms DNA damage repair by promoting Ku-dependent nonhomologous end-joining (NHEJ) at the expense of homologous recombination. BRN2 also suppresses an apoptosis-associated gene expression program to protect against UVB-, chemotherapy- and vemurafenib-induced apoptosis. Remarkably, BRN2 expression also correlates with a high single-nucleotide variation prevalence in human melanomas. By promoting error-prone DNA damage repair via NHEJ and suppressing apoptosis of damaged cells, our results suggest that BRN2 contributes to the generation of melanomas with a high mutation burden. Our findings highlight a novel role for a key transcription factor in reprogramming DNA damage repair and suggest that BRN2 may impact the response to DNA-damaging agents in BRN2-expressing cancers.
Assuntos
Apoptose , Reparo do DNA por Junção de Extremidades/genética , Proteínas de Homeodomínio/metabolismo , Melanoma/genética , Melanoma/fisiopatologia , Mutação/genética , Fatores do Domínio POU/metabolismo , Linhagem Celular Tumoral , Regulação Neoplásica da Expressão Gênica/genética , Proteínas de Homeodomínio/genética , Humanos , Autoantígeno Ku/metabolismo , Fatores do Domínio POU/genética , Poli(ADP-Ribose) Polimerase-1/metabolismo , Ligação Proteica , Domínios Proteicos , Transporte ProteicoRESUMO
S-carboxymethylcysteine (S-CMC) is a mucolytic agent that can prevent respiratory infection by decreasing the attachment of respiratory pathogens to human pharyngeal epithelial cells (HPECs). Streptococcus pneumoniae is a major cause of respiratory infections. A previous study revealed that treatment of S. pneumoniae with S-CMC caused a decrease in the attachment of this bacterium to HPECs. In the present study we found that the effect of S-CMC varied according to hosts and strains. S-CMC treatment altered the surface structure of S. pneumoniae, resulting in a decrease of attachment, without affecting the virulence of the bacteria.