JAZF1: a novel p400/TIP60/NuA4 complex member involved in the acetylation of H2A.Z

Abstract

In the nucleus of eukaryotic cells, the DNA occurs with histone proteins that package the DNA into the repeating subunit of chromatin, the nucleosome. This basic functional entity consists of two copies of each canonical histone H2A, H2B, H3 and H4, where the DNA is wrapped around. In order to allow DNA-related processes to gain access to the compacted DNA, different epigenetic regulatory mechanisms have evolved, in which the exchange of canonical histones with their specific variants is one possibility. The evolutionary conserved histone protein H2A.Z is one of the most intensively studied H2A variants that is involved in several biological processes such as transcriptional regulation with sometimes contrasting functions. To accomplish its diverse and at the same time controversial roles, H2A.Z requires the concerted action of unique multi-subunit histone variant-specific exchangers, responsible for its dedicated loading – and removal – into specific chromatin regions. In metazoans, H2A.Z incorporation is tightly regulated by the multifunctional p400/TIP60/NuA4 (p400) and SRCAP chaperone/remodelling complexes. However, it is still unclear, whether other, not yet identified proteins, are also implicated in the chromatin deposition of H2A.Z. Hence, a quantitative mass spectrometry (qMS) approach was employed to gain more insights into H2A.Z’s chromatin-free interactome. Besides all members of both known chaperone complexes, also new interactors were identified that were formerly not related to H2A.Z deposition. Among others, the proposed transcriptional regulator Juxtaposed with another zinc finger 1 (JAZF1) was discovered as a novel member of an H2A.Z-specific p400 sub-complex that contains MBTD1 but excludes ANP32E. Since JAZF1 is functionally poorly characterized and has frequently been linked to human diseases such as sarcomas, I aimed to unravel the functions of JAZF1, especially with regard to the role it may play within the H2A.Z-specific p400 complex. First preliminary data hint towards a role of JAZF1 in the regulation of DNA damage repair processes, as it has already been shown for other p400 complex components. Moreover, RNA-seq experiments demonstrated that depletion of the putative transcription factor JAZF1 results in the deregulation of several genes involved not only in DNA repair, but also above all in ribosome biogenesis. To identify the underlying molecular mechanism by which JAZF1 might control transcriptional regulation of genes, the genome-wide level of H2A.Z and H2A.Zac upon JAZF1 depletion via ChIP-seq analyses were evaluated. Remarkably, ˃1.000 genomic sites that were significantly deregulated in H2A.Zac levels upon loss of JAZF1 were identified, while H2A.Z levels and locations remained unaffected. Since depletion of TIP60, the histone acetyltransferase of the p400 complex, also causes decreased acetylation of H2A.Z at some JAZF1-targeted regulatory enhancer regions, it is possible that JAZF1’s function in gene regulation might depend on the enzymatic activity of the TIP60-containing p400 complex. Therefore, I propose JAZF1 as a chromatin modulator, which orchestrates acetylation of the histone variant H2A.Z via recruiting the enzymatic active p400 complex to respective sites, thereby controlling expression of target genes. Altogether, this study contributes to a better understanding of the largely unknown functions of JAZF1 and may thus provide a starting point for future research to clarify its putative role in the development of diseases such as human sarcomas.