DNA repair protein: endo-exonuclease as a new frontier in cancer therapy

Substitutions of short heterologous DNA segments of intragenomic or extragenomic origins produce clustered genomic polymorphisms

In a screen for unexplained mutation events we identified a previously unrecognized mechanism generating clustered DNA polymorphisms such as microindels and cumulative SNPs. The mechanism, short-patch double illegitimate recombination (SPDIR), facilitates short single-stranded DNA molecules to invade and replace genomic DNA through two joint illegitimate recombination events. SPDIR is controlled by key components of the cellular genome maintenance machinery in the gram-negative bacterium Acinetobacter baylyi. The source DNA is primarily intragenomic but can also be acquired through horizontal gene transfer. The DNA replacements are nonreciprocal and locus independent. Bioinformatic approaches reveal occurrence of SPDIR events in the gram-positive human pathogen Streptococcus pneumoniae and in the human genome.

A novel ruthenium(II)-polypyridyl complex inhibits cell proliferation and induces cell apoptosis by impairing DNA damage repair

Ruthenium complexes are widely recognized as one of the most promising DNA damaging chemotherapeutic drugs. The main goal of this study was to explore the anticancer activity and underlying mechanisms of [Ru(phen)(2)(p-BrPIP)](ClO(4))(2), a novel chemically synthesized ruthenium (Ru) complex. To this end, we employed MTT assays to determine the anticancer activity of the complex, and performed single-cell gel electrophoresis (SCGE) and Western blotting to evaluate DNA damage. Our results showed that the Ru(II)-poly complex caused severe DNA damage, possibly by downregulating key factors involved in DNA repair pathways, such as proliferating cell nuclear antigen (PCNA) and ring finger protein 8 (RNF8). In addition, this complex induced cell apoptosis by upregulating both p21 and p53. Taken together, our findings demonstrate that the Ru(II)-poly complex exhibits antitumour activity by inducing cell apoptosis, which results from the accumulation of large amounts of unrepaired DNA damage.

Intracellular clusterin negatively regulates ovarian chemoresistance: compromised expression sensitizes ovarian cancer cells to paclitaxel

Understanding the molecular events that lead to paclitaxel (TX) resistance is necessary to identify effective means to prevent chemoresistance. Previously, results from our lab revealed that secretory clusterin (CLU) form positively mediates TX response in ovarian cancer cells. Thus, we had interest to study the role of another non-secreted form (intracellular clusterin (i-CLU)) in chemo-response. Here, we provide evidences that i-CLU form localizes mainly in the nucleus and differentially expressed in the TX-responsive KF cells, versus TX-resistant, KF-TX, ovarian cancer cells and negatively regulate cellular chemo-response. I-CLU was cloned, by deleting the secretion-leading signaling peptide from full-length CLU cDNA, and transiently over-expressed in OVK-18 cells. Forced expression of truncated i-CLU was mainly detectable in the nuclei and significantly reduced cellular growth, accumulating cells in G1 phase which finally died through apoptosis. Importantly, compromised expression of i-CLU under an inducible promoter was tolerated and did not induce apoptosis but sensitized ovarian cancer cells to TX. We then demonstrated that this sensitization mechanism was cell cycle independent and relied on i-CLU/Ku70 binding probably due to controlling the free amount of Ku70 available for DNA repair in the nucleus. Results from CLU immunohistochemistry in ovarian tumor tissues verified the retardation of nuclear CLU staining in the recurrent tumor even though their primary counterparts showed nuclear CLU staining. Thus, the controversial data on CLU function in chemo-response/resistance may be explained by a shift in the pattern of CLU expression and intracellular localization as well when tumor acquires chemoresistance.

Clusterin and DNA repair: a new function in cancer for a key player in apoptosis and cell cycle control

The glycoprotein clusterin (CLU), has two known isoforms generated in human cells. A nuclear form of CLU protein (nCLU) is pro-apoptotic, while a secretory form (sCLU) is pro-survival. Both forms are implicated in various cell functions, including DNA repair, cell cycle regulation, and apoptotic cell death. CLU expression has been associated with tumorigenesis and the progression of various malignancies. In response to DNA damage, cell survival can be enhanced by activation of DNA repair mechanisms, while simultaneously stimulating energy-expensive cell cycle checkpoints that delay the cell cycle progression to allow more time for DNA repair. This review summarizes our current understanding of the role of clusterin in DNA repair, apoptosis, and cell cycle control and the relevance.