| TRRAP is a large ATM‑related adaptor protein within the phosphatidylinositol 3‑kinase–related kinase family that lacks kinase activity but serves as a common scaffold in several nuclear histone acetyltransferase complexes, where it connects transcription factors to chromatin remodeling machinery and coordinates acetylation‑dependent regulation of gene expression, DNA replication and repair. The protein contains an ATM‑like C‑terminal domain and extended HEAT‑repeat regions that mediate stable incorporation into STAGA/SAGA‑like and Tip60/NuA4 HAT assemblies; this structural arrangement allows TRRAP to bind activation domains of c‑Myc and E2F‑1 and simultaneously recruit GCN5 or Tip60 catalytic subunits to specific promoters, establishing localized histone H3 and H4 acetylation and opening chromatin for RNA polymerase II engagement. In Myc signaling, TRRAP interacts directly with the N‑terminal transactivation/transforming domain of c‑Myc and brings hGCN5 HAT activity to Myc‑responsive genes, including tRNA and 5S rRNA polymerase III targets and telomerase reverse transcriptase, so Myc‑dependent transcriptional activation and oncogenic transformation require TRRAP‑dependent histone acetylation of promoter nucleosomes and are blocked by dominant‑negative TRRAP fragments or antisense TRRAP expression. TRRAP also binds E2F‑1 and is necessary for transformation by adenovirus E1A/E2F pathways: E1A mutants that retain RB and p300/CBP binding but fail to engage TRRAP are defective in immortalization and transformation, indicating that TRRAP‑mediated recruitment of HAT complexes is a shared mechanism by which c‑Myc and E1A/E2F oncoproteins drive cell‑cycle progression and override checkpoint control. As a central component of Tip60‑related HAT complexes, TRRAP participates in DNA double‑strand break repair by associating with the MRN complex (MRE11–RAD50–NBS1) at damaged chromatin; TRRAP depletion reduces histone acetylation near breaks, impairs MRN‑dependent end processing and homologous recombination, and disrupts mitotic checkpoint signaling, placing TRRAP at the interface between histone modification, checkpoint activation and genome stability. TRRAP‑containing HAT assemblies also act at replication origins and developmental promoters, where TRRAP recruitment is required to establish acetylated chromatin states that support origin firing or lineage‑specific transcription, and genome‑wide expression studies identify sets of cell‑cycle, metabolic and stress‑response genes whose transcription is dependent on TRRAP‑linked HAT activity, underscoring its broad regulatory reach. In cancer models, TRRAP interacts with oncogenic chromatin modifiers such as SMYD3 and with transcription factors including HSF1 and Sp1, contributing to non‑mutational epigenetic reprogramming: TRRAP–Tip60 complexes help maintain active chromatin at oncogenic loci, while TRRAP can also repress interferon‑stimulated genes in colorectal cancer cells via Sp1‑mediated promoter association, shaping both proliferative and inflammatory transcriptional programs. TRRAP depletion in hepatocellular carcinoma cells induces p53‑independent apoptosis and cell‑cycle arrest, and genetic or expression alterations of TRRAP are linked with breast, colorectal and liver tumors, consistent with its role as an essential cofactor for Myc/E2F‑driven proliferation and a coordinator of chromatin‑based processes that, when deregulated, favor malignant growth. |
