CCAR2/DBC1 is required for Chk2-dependent KAP1 phosphorylation and repair of DNA damage

Abstract

Cell cycle and apoptosis regulator 2 (CCAR2, formerly known as DBC1) is a nuclear protein largely involved in DNA damage response, apoptosis, metabolism, chromatin structure and transcription regulation. Upon DNA lesions, CCAR2 is phosphorylated by the apical kinases ATM/ATR and this phosphorylation enhances CCAR2 binding to SIRT1, leading to SIRT1 inhibition, p53 acetylation and p53-dependent apoptosis. Recently, we found that also the checkpoint kinase Chk2 and the proteasome activator REGγ are required for efficient CCAR2-mediated inhibition of SIRT1 and induction of p53-dependent apoptosis.Here, we report that CCAR2 is required for the repair of heterochromatic DNA lesions, as cells knock-out for CCAR2 retain, at late time-points after genotoxic treatment, abnormal levels of DNA damage-associated nuclear foci, whose timely resolution is reinstated by HP1β depletion. Conversely, repair of DNA damages in euchromatin are not affected by CCAR2 absence.We also report that the impairment in heterochromatic DNA repair is caused by defective Chk2 activation, detectable in CCAR2 ablated cells, which finally impacts on the phosphorylation of the Chk2 substrate KAP1 that is required for the induction of heterochromatin relaxation and DNA repair.These studies further extend and confirm the role of CCAR2 in the DNA damage response and DNA repair and illustrate a new mechanism of Chk2 activity regulation. Moreover, the involvement of CCAR2 in the repair of heterochromatic DNA breaks suggests a new role for this protein in the maintenance of chromosomal stability, which is necessary to prevent cancer formation.

A novel crosstalk between CCAR2 and AKT pathway in the regulation of cancer cell proliferation

“…As these data contrast with those we previously published about normal cell cycle progression of CCAR2-KO U2OS clones, 5 we analyzed proliferation and AKT phosphorylation in these cells, but we did not find defects in AKT activation or in the rate of proliferation (Supplementary Figure 9), probably reflecting the acquired ability of CCAR2-KO clones to counteract the absence of CCAR2.…”

“…Depletion of CCAR2 induced a significant decrease in U2OS cell proliferation and colony formation (Figures 1b and c). Conversely, a similar analysis performed with a population of BJ-hTERT-KO cells 5 revealed no proliferation defects (Figure 1d). Collectively these results demonstrate that CCAR2 loss impairs the growth of U2OS, but not of BJ-hTERT cells.…”

“…3, 4 Recently, we also reported that CCAR2 itself modulates the activity of Chk2 towards KRAB-associated protein 1 (KAP1), thus influencing the repair of DNA breaks. 5 …”

ZNF326 promotes a malignant phenotype of breast cancer by interacting with DBC1

“…For example, the expression of DBC1 was found to be associated with poor prognosis in hepatitis virus‐related hepatocellular carcinoma; DBC1 also positively regulated the β‐catenin‐PROX1 signaling axis to promote colon cancer progression . Moreover, DBC1 was required for Chk2‐dependent KAP1 phosphorylation and DNA damage repair . However, contrary to the report mentioned, DBC1 could also function as a tumor suppressor by regulating p53 stability, and was associated with favorable outcomes in gastric cancer .…”

“…27 Moreover, DBC1 was required for Chk2-dependent KAP1 phosphorylation and DNA damage repair. 28 However, contrary to the report mentioned, DBC1 could also function as a tumor suppressor by regulating p53 stability, and was associated with favorable outcomes in gastric cancer. 29,30 These results suggested that DBC1 plays a different role in different types of tumors.…”