KU70 Inhibition Impairs Both Non-Homologous End Joining and Homologous Recombination DNA Damage Repair Through SHP-1 Induced Dephosphorylation of SIRT1 in Adult T-Cell Leukemia-Lymphoma Cells

Abstract

Background/Aims: Adult T-cell leukemia-lymphoma (ATL) is an aggressive disease which is highly resistant to chemotherapy. Studies show that enhanced ability of DNA damage repair (DDR) in cancer cells plays a key role in chemotherapy resistance. Here, we suggest that defect in DDR related genes might be a promising target to destroy the genome stability of tumor cells. Methods: Since KU70 is highly expressed in Jurkat cells, one of the most representative cell lines of ATL, we knocked down KU70 by shRNA and analyzed the impact of KU70 deficiency in Jurkat cells as well as in NOD-SCID animal models by western blot, immunofluorescence, flow cytometry and measuring DNA repair efficiency. Results: It is observed that silencing of KU70 resulted in accumulated DNA damage and impaired DDR in Jurkat cells, resulting in more apoptosis, decreased cell proliferation and cell cycle arrest. DNA damage leads to DNA double-strand breaks (DSBs), which are processed by either non-homologous end joining(NHEJ) or homologous recombination(HR). In our study, both NHEJ and HR are impaired because of KU70 defect, accompanied with increased protein level of SHP-1, a dephosphorylation enzyme. In turn, SHP-1 led to dephosphorylation of SIRT1, which further impaired HR repair efficiency. Moreover, KU70 deficiency prolonged survival of Jurkat-xenografted mice. Conclusion: These findings suggest that targeting KU70 is a promising target for ATL and might overcome the existing difficulties in chemotherapy.

NAD+ metabolism: pathophysiologic mechanisms and therapeutic potential

“…[164][165][166][167] Similarly, DNA damage induces the relocalization of NAD + -dependent deacetylase SIRT1 to DNA breaks, which promotes DNA repair via opening the chromatin and recruiting the main DNA repair factors including KU70, NBS1, WRN, KAP1, XPA and APEX1. [168][169][170][171][172][173][174][175][176][177] Additionally, PARPs and sirtuins also simulate genomic damage-signaling kinases, including ATM, p53, DNA-PK, CIRBP and FOXOs, to accelerate DNA repair. [178][179][180][181][182] Given that DNA damage-activated PARPs account for up to 90% of cellular NAD + consumption, the DNA repair activity is highly dependent on the cellular NAD + concentration.…”

The Role of SIRT1 on DNA Damage Response and Epigenetic Alterations in Cancer

“…On the other hand, when the LSD1–KU70 interaction is favored, there is less chromatin opening and the repair is then decreased, resulting in increased DNA damage and cell death [72]. More recently, Yu and collaborators [92] showed that KU70 also controls SIRT1 activity through SHP-1, a dephosphorylating enzyme member of the protein tyrosine phosphatase (PTP) family. Thus, KU70 inhibition was shown to reduce DNA repair efficiency by both NHEJ and HR pathways in adult T-cell leukemia-lymphoma (ATL) cells and the tumorigenesis ability was impaired in Jurkat-xenografted mice after KU70 silencing [92].…”

The Critical Role of SIRT1 in Parkinson’s Disease: Mechanism and Therapeutic Considerations

“…Studies by other investigators have shown that during cell stress, SIRT1 deacetylates the C-terminal residues of the main site of p53 ubiquitination, which helps block protein degradation and stabilize p53 [72]. SIRT1 can also deacetylate Ku70 in tumor [73,74] and retinal cells [75] to enhance DNA repair activity and chelate Bcl-2-associated X protein (Bax) in the cytoplasm to prevent apoptosis and extend cell lifespan. However, the role of the SIRT1/Ku70 pathway in the nervous system requires further elucidation.…”