Cell cycle and apoptosis regulator protein 2

Cell cycle and apoptosis regulator protein 2 (CCAR2) is a 923-amino acid core component of the DBIRD complex that integrates transcript elongation with alternative splicing regulation in (A+T)-rich genomic regions (UniProt: Q8N163). Beyond splicing, CCAR2 functions as a multifaceted transcriptional regulator, inhibiting SIRT1 deacetylase activity to enhance p53-mediated apoptosis, regulating circadian clock components NR1D1 and BMAL1, and modulating nuclear hormone receptor signaling. It also stabilizes p53 by preventing its interaction with the MDM2 ubiquitin ligase, supporting tumor suppression and genomic stability.

CCAR2 participates in multiple cellular pathways including apoptosis, circadian rhythm regulation, gluconeogenesis, and the Wnt/beta-catenin signaling cascade (UniProt: Q8N163). The protein exhibits diverse regulatory interactions with histone deacetylases, methyltransferases, and transcriptional regulators, positioning it as a hub in cellular stress response and metabolic control.

In Alzheimer's disease, CCAR2 is significantly downregulated in post-mortem AD brain tissue compared to age-matched controls (Chaparral AD proteomics, mean log2FC: −0.78, direction: down). This reduction may impair p53-dependent apoptotic pathways and transcriptional regulation of protective cellular processes, potentially contributing to the pathophysiological cascade in AD neurodegeneration.