RB·E2F1 Complex Mediates DNA Damage Responses through Transcriptional Regulation of ZBRK1*

Abstract

RB plays an essential role in DNA damage-induced growth arrest and regulates the expression of several factors essential for DNA repair machinery. However, how RB coordinates DNA damage response through transcriptional regulation of genes involved in growth arrest remains largely unexplored. We examined whether RB can mediate the response to DNA damage through modulation of ZBRK1, a zinc finger-containing transcriptional repressor that can modulate the expression of GADD45A, a DNA damage response gene, to induce cell cycle arrest in response to DNA damage. We found that the ZBRK1 promoter contains an authentic E2F-recognition sequence that specifically binds E2F1, but not E2F4 or E2F6, together with chromatin remodeling proteins CtIP and CtBP to form a repression complex that suppresses ZBRK1 transcription. Furthermore, loss of RB-mediated transcriptional repression led to an increase in ZBRK1 transcript levels, correlating with increased sensitivity to ultraviolet (UV) and methyl methanesulfonate-induced DNA damage. Taken together, these results suggest that the RB⅐CtIP (CtBP interacting protein)/CtBP (C terminus-binding protein) /E2F1 complex plays a critical role in ZBRK1 transcriptional repression, and loss of this repression may contribute to cellular sensitivity of DNA damage, ultimately leading to carcinogenesis.The DNA damage response that responds to genotoxic stress induced by radiation, chemicals, and endogenous reactive oxygen species is highly conserved in higher eukaryotes (1, 2). The cellular responses to DNA damage include activation of cell-cycle arrest, apoptosis, and DNA damage repair (3). In mammals, multiple partially overlapping DNA repair mechanisms, including base excision, recombination, and mismatch repair, are required for proper DNA damage repair. Defects in these repair pathways frequently lead to irreparable DNA damage, aging, and cancer.RB, a prototypic tumor suppressor (4), is essential for regulating cell cycle progression through interaction with binding partners such as E2F (5). In quiescent and early G 1 cells, RB associates with the E2F family of transcription factors to repress the expression of E2F-responsive genes involved in cell cycle progression (6). As cells progress toward S-phase, RB is phosphorylated by cyclin-dependent kinases, releasing E2F, which opens the DNA replication origin, and induces transcription of S-phase genes (7). When RB is lost or inactivated, DNA replication origins become readily accessible, resulting in uncontrolled transcription of S-phase genes and ultimately leading to premature S-phase progression (8). RB also plays an essential role in DNA damage-induced growth arrest (9) and transcriptional regulation of several DNA damage-repair factors involved in the ultraviolet (UV) damage repair process, including FEN1, XPC, RPA2-3, RFC4, and proliferating cell nuclear antigen (10). Although previous studies have established that phosphorylation of RB inactivates its binding activity with its interacting partners and promotes cell cycle progression (1...

Effect of hypoxia, glutamine and glucose deprivation on the expression of mRNA of the retinoblastoma binding proteins in glioma cells

“…Moreover, the growing tumor requires the endoplasmic reticulum stress, as well as ischemia and hypoxia which initiate the endoplasmic reticulum stress for its own neovascularization and growth, for apoptosis inhibition [15]. It is well known that retinoblastoma proteins, retinoblastoma binding and associated proteins, as well as E2F transcription factors, cyclins, cyclin-dependent kinases and its inhibitors participate in controling cell cycling and proliferation and are the components of endoplasmic reticulum stress system [14,15,[18][19][20][21].…”

“…This protein negatively regulates the G1-S transition by binding to the E2F transcription factors, until cyclin-dependent kinases phosphorylate retinoblastoma protein, causing E2F release. Moreover, retinoblastoma-E2F1 complex plays a critical role in ZBRK1 transcriptional repression, and loss of this repression may contribute to cellular sensitivity of DNA damage, ultimately leading to carcinogenesis [20]. Active E2F1/DP1 promotes apoptosis in both p53-dependent and independent manner, induces the expression of ADP rybosylation factor which, in turn, blocks MDM2-mediated ubiquination of p53, or enhances p53 transcriptional activity via direct binding of E2F1 to p53 [21].…”

Proteomic Approaches to Unraveling the RB/E2F Regulatory Pathway

“…In agreement with the original findings, it has been recently shown that CtIP/CtBP plays a transcriptional co-repressor role in ZBRK1 expression. ZBRK1 is a zinc finger-containing transcriptional repressor that can modulate the expression of GADD45A to induce cell cycle arrest in response to DNA damage (Liao et al 2010). It has been proposed that the contribution of RB to DNA damageinduced growth arrest may depend on the formation of this complex and loss of CtIP/CtBPmediated repression could affect the cellular sensitivity to DNA damage.…”

Post-Transcriptional Regulation of E2F Transcription Factors: Fine-Tuning DNA Repair, Cell Cycle Progression and Survival in Development & Disease

“…The latter is involved in induction of cell cycle arrest in response to DNA damage (Siafakas and Richardson, 2009). E2F-1, but not other E2F proteins, binds to the ZBRK1 promoter, together with pRb, CtIP and CtBP, forming repressor complexes that interfere with ZBRK1 expression (Liao et al, 2010). In pRbdeficient cells, increased susceptibility to DNA damage induced by UV radiation or methylating agents occurs, partly as a result of abnormal cell cycle arrest and DNA repair.…”