Ku80 functions as a tumor suppressor in hepatocellular carcinoma by inducing S-phase arrest through a p53-dependent pathway

Research Laboratory and Hepatic Surgical Center, Department of Surgery, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, 1095 Jie Fang Da Dao, Wuhan, China.
Carcinogenesis (Impact Factor: 5.33). 03/2012; 33(3):538-47. DOI: 10.1093/carcin/bgr319
Source: PubMed


Ku80 is a component of the protein complex called DNA-dependent protein kinase, which is involved in DNA double-strand break
repair and multiple other functions. Previous studies revealed that Ku80 haplo-insufficient and poly (adenosine diphosphate-ribose)
polymerase-null transgenic mice developed hepatocellular carcinoma (HCC) at a high frequency. The role of Ku80 has never been
investigated in human HCC. Ku80 expressions in HCC and adjacent liver tissue were investigated by using immunohistochemical
staining and western blot. Ku80 was transfected into a Ku80-deficient HCC cell line SMMC7721 cells, and the growth features
of the Ku80-expressing cells and vector-transfected cells were studied both in vitro and in vivo. Cell cycle analysis and RNA interference were employed to investigate the mechanisms underlying the growth regulation associated
with Ku80 expression. Ku80 was found frequently downregulated in HCC compared with adjacent liver tissue. Ku80 downregulation
was significantly correlated with elevated hepatitis B virus-DNA load and severity of liver cirrhosis. Overexpression of Ku80
in SMMC7721 cells significantly suppressed cell proliferation in vitro and in vivo. Ku80 overexpression caused S-phase cell cycle arrest and was associated with upregulation of p53 and p21CIP1/WAF1, and the inhibition of p53 or p21CIP1/WAF1 expression by RNA interference overcame the growth suppression and S-phase arrest in the Ku80-expressing cells. A novel mechanism
was revealed that Ku80 functions as a tumor suppressor in HCC by inducing S-phase arrest through a p53-dependent pathway.

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    • "We speculate that the level of Ku is regulated in Ku80+/− HCT 116 cells by a mechanism that either controls protein levels or negatively affects the survival/proliferation of cells expressing excessive amounts of Ku. In agreement with this hypothesis, the overexpression of Ku80 is reported to induce the activation of apoptosis in human hepatocellular carcinoma [58]. Intriguingly, p53 seems to contribute to this hypothetical process. "
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    ABSTRACT: Ku, a cellular complex required for human cell survival and involved in double strand break DNA repair and multiple other cellular processes, may modulate retroviral multiplication, although the precise mechanism through which it acts is still controversial. Recently, Ku was identified as a possible anti-human immunodeficiency virus type 1 (HIV-1) target in human cells, in two global approaches. Here we investigated the role of Ku on the HIV-1 replication cycle by analyzing the expression level of a panel of non-replicative lentiviral vectors expressing the green fluorescent protein in human colorectal carcinoma HCT 116 cells, stably or transiently depleted of Ku. We found that in this cellular model the depletion of Ku did not affect the efficiency of (pre-)integrative steps but decreased the early HIV-1 expression by acting at the transcriptional level. This negative effect was specific of the HIV-1 promoter, required the obligatory step of viral DNA integration and was reversed by transient depletion of p53. We also provided evidence on a direct binding of Ku to HIV-1 LTR in transduced cells. Ku not only promotes the early transcription from the HIV-1 promoter, but also limits the constitution of viral latency. Moreover, in the presence of a normal level of Ku, HIV-1 expression was gradually lost over time, likely due to the counter-selection of HIV-1-expressing cells. On the contrary, the reactivation of transgene expression from HIV-1 by means of trichostatin A- or tumor necrosis factor α-administration was enhanced under condition of Ku haplodepletion, suggesting a phenomenon of provirus latency. These observations plead in favor of the hypothesis that Ku has an impact on HIV-1 expression and latency at early- and mid-time after integration.
    Full-text · Article · Jul 2013 · PLoS ONE
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    • "Furthermore, DNA-PK depended phosphorylation of S473 of AKT in response to platinum based chemotherapy has been shown to inhibit apoptotic response limiting drug efficacy (Stronack et al., 2011). There is also in vitro evidence that DNA-PK interacts with or influences p53 and p21 activities leading to cellular senescence and apoptosis (Azad et al., 2011; Rudolf et al., 2011; Stronack et al., 2011; Wei et al., 2012). Even so, only a few in vivo DNA-PK substrates are known, these include DNA-PKcs autophosphorylation and histone variant H2AX. "
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    ABSTRACT: Many current chemotherapies function by damaging genomic DNA in rapidly dividing cells ultimately leading to cell death. This therapeutic approach differentially targets cancer cells that generally display rapid cell division compared to normal tissue cells. However, although these treatments are initially effective in arresting tumor growth and reducing tumor burden, resistance and disease progression eventually occur. A major mechanism underlying this resistance is increased levels of cellular DNA repair. Most cells have complex mechanisms in place to repair DNA damage that occurs due to environmental exposures or normal metabolic processes. These systems, initially overwhelmed when faced with chemotherapy induced DNA damage, become more efficient under constant selective pressure and as a result chemotherapies become less effective. Thus, inhibiting DNA repair pathways using target specific small molecule inhibitors may overcome cellular resistance to DNA damaging chemotherapies. Non-homologous end joining (NHEJ) a major mechanism for the repair of double strand breaks (DSB) in DNA is regulated in part by the serine/threonine kinase, DNA dependent protein kinase (DNA-PK). The DNA-PK holoenzyme acts as a scaffold protein tethering broken DNA ends and recruiting other repair molecules. It also has enzymatic activity that may be involved in DNA damage signaling. Because of its’ central role in repair of DSBs, DNA-PK has been the focus of a number of small molecule studies. In these studies specific DNA-PK inhibitors have shown efficacy in synergizing chemotherapies in vitro. However, compounds currently known to specifically inhibit DNA-PK are limited by poor pharmacokinetics: these compounds have poor solubility and have high metabolic lability in vivo leading to short serum half-lives. Future improvement in DNA-PK inhibition will likely be achieved by designing new molecules based on the recently reported crystallographic structure of DNA-PK. Computer based drug
    Full-text · Article · Jan 2013 · Frontiers in Pharmacology
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    ABSTRACT: Unlabelled: Hepatocellular carcinoma (HCC) is a devastating consequence of chronic inflammatory liver diseases. The goal of this study was to investigate whether Toll-like receptor 4 (TLR4) activity contributes to HCC initiation and progression in mice. A mouse model of diethylnitrosamine (DEN)-induced HCC was generated with wild-type and TLR4 mutant mice, and the development and progression of HCC and senescent responses were assessed using morphologic, immunological, and biochemical criteria. We found that genetic or pharmacologic blocking of TLR4 increased susceptibility to DEN-induced HCC carcinogenesis and progression, which was indicated by increases in number of tumor nodules, tumor volume, and animal death. The enhanced HCC was associated with a broad-spectrum reduction of immune response to DEN liver injury, as indicated by decreases in the liver-infiltrating F4/80+ macrophages, the apoptosis signal-regulating kinase 1/p38 mitogen-activated protein kinase/NF-κB and IRF3 signaling activities, and the expression of inflammatory cytokines. Suppressed immune networks resulted in a halt of cellular senescence induction in TLR4 mutant liver tissue, which promoted proliferation and suppressed programmed cell death. Moreover, TLR4 mutation resulted in a suppressed capacity of DNA repair due to a decrease in TLR4-medicated expression of DNA repair proteins Ku70/80 in liver tissue and cells. Isotopic expression of Ku70 in TLR4 mutant mice restored senescence and interrupted the positive feedback loop of DNA damage and oxidative stress, which reversed TLR4 mutation-deteriorated HCC carcinogenesis and progression. Conclusion: TLR4 plays an integrated defense role against HCC carcinogenesis by enhancing the expression and function of DNA repair protein Ku70. Our studies provide novel insight into TLR4 activity in the regulation of HCC tumorigenesis, which may be useful for the prevention of HCC development.
    Full-text · Article · May 2013 · Hepatology
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