Transcriptional Activation of Histone Genes Requires NPAT-Dependent Recruitment of TRRAP-Tip60 Complex to Histone Promoters during the G₁/S Phase Transition

Abstract

Transcriptional activation of histone subtypes is coordinately regulated and tightly coupled with the onset of DNA replication during S-phase entry. The underlying molecular mechanisms for such coordination and coupling are not well understood. The cyclin E-Cdk2 substrate NPAT has been shown to play an essential role in the transcriptional activation of histone genes at the G 1 /S-phase transition. Here, we show that NPAT interacts with components of the Tip60 histone acetyltransferase complex through a novel amino acid motif, which is functionally conserved in E2F and adenovirus E1A proteins. In addition, we demonstrate that transformation/transactivation domain-associated protein (TRRAP) and Tip60, two components of the Tip60 complex, associate with histone gene promoters at the G 1 /S-phase boundary in an NPAT-dependent manner. In correlation with the association of the TRRAP-Tip60 complex, histone H4 acetylation at histone gene promoters increases at the G 1 /S-phase transition, and this increase involves NPAT function. Suppression of TRRAP or Tip60 expression by RNA interference inhibits histone gene activation. Thus, our data support a model in which NPAT recruits the TRRAP-Tip60 complex to histone gene promoters to coordinate the transcriptional activation of multiple histone genes during the G 1 /S-phase transition.Histone proteins are integral components of eukaryotic chromatin and play crucial roles in virtually all cellular processes that involve chromosomal DNA, such as DNA replication, transcription, DNA repair, recombination, and chromosome segregation (27,28). The bulk of the histones are assembled with genomic DNA into chromosomes, and the biosynthesis of multiple histone subtypes (replication-dependent histones) is tightly coordinated and coupled with DNA synthesis during the S phase of the cell cycle (20,36,45,51). Perturbation of such coordination and coupling can lead to the loss of chromosomes, DNA damage, and developmental arrest (39,55,62,64), underscoring the importance of the proper regulation of these events.The rate of histone synthesis in S phase is regulated at both the transcriptional and the posttranscriptional levels (20,36,45,51). Histone gene transcription increases from 3-to 10-fold as cells enter S phase (20). The transcription of each histone subtype (H1, H2A, H2B, H3, and H4) in S phase is likely regulated by proteins or protein complexes that interact directly with the subtype-specific regulatory elements (SSREs) in the promoters of replication-dependent histone genes (20, 45). Indeed, it has been shown that Oct1 and its coactivator complex OCA-S interact with the H2B SSRE to activate H2B transcription, while HiNF-P interacts with the H4 SSRE to stimulate H4 expression (14,40,67). Components of OCA-S include nuclear p38/glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and lactate dehydrogenase, and the activity of OCA-S is regulated by NAD ϩ and NADH, suggesting a link between the histone gene transcription and the cellular metabolic state/redox status (67). The molecular m...

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