RESUMO
p300 regulates the transcriptional activity of a variety of transcription factors by forming an activation complex and/or promoting histone acetylation. Here, we show a unique characteristic of orphan receptor TR3 in negatively regulating the function of p300. TR3 was found to interact with p300 and inhibited the acetylation of transcription factors induced by p300, resulting in the repression of their transcriptional activity. Further analysis revealed that both a conserved transcriptional adapter motif (TRAM) in p300 and a specific sequence FLELFIL in TR3 were critical for their interaction. TR3 binding completely covered the histone acetyltransferase (HAT) domain of p300 and resulted in suppression of the HAT activity, as the p300-induced histone H3 acetylation and transcription were inhibited with the presence TR3. Furthermore, an agonist of TR3, a natural octaketide isolated from Dothiorella sp. HTF3 of an endophytical fungus, was shown to be a potent compound for inhibiting p300 HAT activity (IC(50) = 1.5 microg/ml) in vivo. More importantly, this agonist could repress the transcriptional activity of transcription factors, and proliferation of cancer cells. Taken together, our results not only delineate a novel transcriptional repressor function for TR3, but also reveal its modulation on p300 HAT activity as the underlying mechanism.
Assuntos
Receptores de Esteroides/metabolismo , Receptores dos Hormônios Tireóideos/metabolismo , Proteínas Repressoras/metabolismo , Fatores de Transcrição de p300-CBP/antagonistas & inibidores , Acetilação , Sequência de Aminoácidos , Sítios de Ligação , Linhagem Celular , Regulação para Baixo , Regulação da Expressão Gênica , Humanos , Membro 1 do Grupo A da Subfamília 4 de Receptores Nucleares , Receptores de Esteroides/agonistas , Receptores de Esteroides/química , Receptores dos Hormônios Tireóideos/agonistas , Receptores dos Hormônios Tireóideos/química , Proteínas Repressoras/agonistas , Proteínas Repressoras/química , Fatores de Transcrição de p300-CBP/química , Fatores de Transcrição de p300-CBP/metabolismoRESUMO
Acetylation modification regulates the functions of histone and nonhistone proteins, including transcriptional activity, protein interaction, and subcellular localization. Although many nuclear receptors have been shown to be modified by acetylation, whether retinoid X receptors (RXRs) are acetylated and how the acetylation is regulated remains unknown. Here, we provide the first evidence of RXRalpha acetylation by p300 on lysine 145. Acetylation of RXRalpha by p300 facilitated its DNA binding and subsequently increased its transcriptional activity. Furthermore, we discovered that TR3, an orphan receptor, exerted a negative regulation on p300-induced RXRalpha acetylation. TR3 significantly reduced the p300-induced RXRalpha acetylation and transcriptional activity, and such inhibition required the interaction of TR3 with RXRalpha. Binding of TR3 to RXRalpha resulted in the sequestration of RXRalpha from p300. 9-cis retinoic acid, a ligand for RXRalpha, enhanced the association of RXRalpha with TR3, rather than acetylation of RXRalpha by p300. Biological function analysis revealed that the mitogenic activity of RXRalpha stimulated by p300 was acetylation dependent and could be repressed by TR3. Upon the treatment of 9-cis retinoic acid, RXRalpha was translocated with TR3 from the nucleus to the mitochondria, and apoptosis was induced. Taken together, our data demonstrate the distinct regulatory mechanisms of p300 and TR3 on RXRalpha acetylation and reveal a previously unrecognized role for orphan receptor in the transcriptional control of retinoid receptors.
Assuntos
Proteína p300 Associada a E1A/metabolismo , Receptores de Esteroides/metabolismo , Receptores dos Hormônios Tireóideos/metabolismo , Receptores X de Retinoides/metabolismo , Acetilação , Alitretinoína , Apoptose , Linhagem Celular , DNA/metabolismo , Humanos , Lisina/genética , Lisina/metabolismo , Membro 1 do Grupo A da Subfamília 4 de Receptores Nucleares , Ligação Proteica , Transporte Proteico , Receptores de Esteroides/genética , Receptores dos Hormônios Tireóideos/genética , Receptores X de Retinoides/genética , Transcrição Gênica/efeitos dos fármacos , Transcrição Gênica/genética , Tretinoína/farmacologiaRESUMO
MDM2 is an oncoprotein whose transforming potential is activated by overexpression. The expression level of MDM2 is negatively regulated by orphan receptor TR3 that mainly acts as a transcriptional factor to regulate gene expression. However, the underlying mechanism is largely unclear. Here, we present the first evidence that inhibition of TR3 on MDM2 is mediated by p53. We found that TR3 directly interacts with p53 but not MDM2, and such interaction is critical for TR3 to inhibit MDM2 expression. TR3 downregulates p53 transcriptional activity by blocking its acetylation, leading to a decrease on the transcription level of MDM2. Furthermore, TR3 binding to p53 obstructs its ubiquitination and degradation induced by MDM2, resulting in the MDM2 ubiquitination and degradation. In addition, TR3 could enhance p53-mediated apoptosis induced by UV irradiation. Taken together, our findings demonstrate that p53 mediates the suppression of TR3 on MDM2 at both transcriptional and post-transcriptional level and suggest TR3 as a potential target to develop new anticancer agents that restrict MDM2-induced tumor progression.