RESUMO
Major histocompatibility complex (MHC) class I proteins are an essential component of the immune system allowing the organism to protect from viral infections and neoplastic transformation. Expression of the MHC class I genes is regulated by a variety of cis-regulatory promoter elements among which the enhancer A is of particular importance. This enhancer is synergistically activated through AP-1/ATF and NF-kappa B transcription factors. NF-kappa B recruits the histone acetyltransferase (HAT) p300/CREB-binding protein (CBP) to the multiprotein complex bound to the enhancer A. Here we present evidence that acetylation and deacetylation processes are involved in the activation of the enhancer A. The p300/CBP associated factor PCAF, but not p300/CBP, counteracts the repression of the enhancer A mediated by the histone deacetylase HDAC1. Furthermore, overexpression of PCAF results in an increase in the acetylation of histone H4 bound to the enhancer A and HDAC1 counteracts the PCAF-mediated H4 acetylation. The activation function of PCAF requires the p300/CBP binding motif indicating that PCAF might be recruited to the enhancer A through an association with p300/CBP. Moreover, PCAF and the Brahma/SWI2-related protein BRG-1, which is a key factor of the human ATP-dependent chromatin remodelling complex SWI/SNF, synergistically up-regulate the enhancer A. Synergistic activation requires the HAT domain of PCAF. Taken together our data suggest that members of two different groups of chromatin modifying complexes are involved in the activation of the enhancer A of the MHC class I promoter.
Assuntos
Acetiltransferases/metabolismo , Proteínas de Ciclo Celular/metabolismo , Elementos Facilitadores Genéticos/genética , Genes MHC Classe I/genética , Proteínas Nucleares/metabolismo , Regiões Promotoras Genéticas/genética , Proteínas de Saccharomyces cerevisiae , Fatores de Transcrição/metabolismo , Acetilação , Acetiltransferases/genética , Western Blotting , Proteínas de Ciclo Celular/genética , Cloranfenicol O-Acetiltransferase/genética , Cloranfenicol O-Acetiltransferase/metabolismo , DNA Helicases , Regulação da Expressão Gênica , Células HeLa , Histona Acetiltransferases , Histonas/metabolismo , Humanos , Proteínas Nucleares/genética , Plasmídeos/genética , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Fatores de Transcrição/genética , Transfecção , Células Tumorais Cultivadas , Fatores de Transcrição de p300-CBPRESUMO
Activation of the transcription unit early region 2 (E2) promoter of the oncogenic adenovirus serotype 12 (Ad12), which regulates the expression of proteins essential for viral replication, requires the assembly of a ternary complex consisting of cAMP response element-binding protein (CREB)-1/activating transcription factor (ATF)-1, the Ad12 12S oncogene product of early region 1A (E1A(12S)), and the co-activator p300/CBP on the E2(Ad12) cAMP response element (E2-CRE). Here we show that the active E2(Ad12) promoter is associated with acetylated histone H4 whereas an E2-CRE point-mutated promoter which is transcriptionally inactive due to its inability to assemble this ternary complex is not bound by acetylated histone H4. The histone deacetylase 1 as well as Roscovitine, which blocks the activation of the histone acetyltransferase (HAT) activity of CBP by cyclin E-Cdk2, prevents E2(Ad12) promoter activation through E1A(12S). p300/CBP counteracts the repressive function of histone deacetylase 1 in a HAT domain-dependent manner whereas the p300/CBP-associated factor PCAF failed to rescue E2(Ad12) promoter activity. E1A(12S) bound p300/CBP displays strong HAT activity. Most interestingly, E1A(12S)-mediated activation of the E2(Ad12) promoter correlates well with the ability of the viral protein to associate with the HAT activity of p300/CBP in vivo. Taken together these data indicate that the recruitment of the HAT activity of p300/CBP by E1A(12S) plays an important role in E2(Ad12) promoter activation.
