RESUMEN
Histone chaperones prevent promiscuous histone interactions before chromatin assembly. They guarantee faithful deposition of canonical histones and functionally specialized histone variants into chromatin in a spatial- and temporally-restricted manner. Here, we identify the binding partners of the primate-specific and H3.3-related histone variant H3.Y using several quantitative mass spectrometry approaches, and biochemical and cell biological assays. We find the HIRA, but not the DAXX/ATRX, complex to recognize H3.Y, explaining its presence in transcriptionally active euchromatic regions. Accordingly, H3.Y nucleosomes are enriched in the transcription-promoting FACT complex and depleted of repressive post-translational histone modifications. H3.Y mutational gain-of-function screens reveal an unexpected combinatorial amino acid sequence requirement for histone H3.3 interaction with DAXX but not HIRA, and for H3.3 recruitment to PML nuclear bodies. We demonstrate the importance and necessity of specific H3.3 core and C-terminal amino acids in discriminating between distinct chaperone complexes. Further, chromatin immunoprecipitation sequencing experiments reveal that in contrast to euchromatic HIRA-dependent deposition sites, human DAXX/ATRX-dependent regions of histone H3 variant incorporation are enriched in heterochromatic H3K9me3 and simple repeat sequences. These data demonstrate that H3.Y's unique amino acids allow a functional distinction between HIRA and DAXX binding and its consequent deposition into open chromatin.
Asunto(s)
Proteínas Adaptadoras Transductoras de Señales/genética , Proteínas de Ciclo Celular/genética , Chaperonas de Histonas/genética , Código de Histonas , Histonas/genética , Proteínas Nucleares/genética , Factores de Transcripción/genética , Proteínas Adaptadoras Transductoras de Señales/metabolismo , Secuencia de Aminoácidos , Animales , Sitios de Unión , Proteínas de Ciclo Celular/metabolismo , Línea Celular Transformada , Cromatina/química , Cromatina/metabolismo , Proteínas Co-Represoras , Proteínas de Unión al ADN/genética , Proteínas de Unión al ADN/metabolismo , Células Epiteliales/citología , Células Epiteliales/metabolismo , Células HeLa , Proteínas del Grupo de Alta Movilidad/genética , Proteínas del Grupo de Alta Movilidad/metabolismo , Chaperonas de Histonas/metabolismo , Histonas/metabolismo , Humanos , Células Madre Mesenquimatosas/citología , Células Madre Mesenquimatosas/metabolismo , Repeticiones de Microsatélite , Chaperonas Moleculares , Proteínas Nucleares/metabolismo , Nucleosomas/genética , Nucleosomas/metabolismo , Cultivo Primario de Células , Unión Proteica , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Factores de Transcripción/metabolismo , Transcripción Genética , Factores de Elongación Transcripcional/genética , Factores de Elongación Transcripcional/metabolismoRESUMEN
Histone variants have emerged as important contributors to the regulation of chromatin structure and therefore of almost all DNA-based processes. Hence, these specialized proteins play important roles in transcriptional regulation, cell cycle progression, DNA repair, chromatin stability, chromosome segregation and apoptosis. Due to their evident biological significance, it is not surprising that mutations or the deregulation of their expression levels can have severe implications for cellular functions that ultimately might contribute to or even drive disease development, most notably cancer. Besides the histones themselves, their respective chaperone/remodeling complexes needed for precise variant chromatin deposition, are consequently frequent targets in neoplasms and diverse diseases. In this review, we briefly summarize current understanding on the function of human/mammalian histone variants and their regulatory networks and highlight their roles in cancer development.