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PubMed2002

An antisense oligonucleotide targeted to human Ku86 messenger RNA sensitizes M059K malignant glioma cells to ionizing radiation, bleomycin, and etoposide but not DNA cross-linking agents.

Ku is a heterodimer of M(r) 70,000 and M(r) 86,000 subunits. It binds with strong affinity to DNA ends and is indispensable for nonhomologous DNA end joining (NHEJ) and V(D)J recombination. In this study, we investigated whether down-regulation of the Ku86 gene, by 2'-O-methoxyethyl/uniform phosphorothioate chimeric antisense oligonucleotides (ASOs), increases the sensitivity of the DNA-protein kinase catalytic subunit (PKcs)-proficient human glioma cell line (M059K), and its isogenic DNA-PKcs-deficient counterpart (M059J), to ionizing radiation and anticancer drugs. Transfection of these cell lines with 200 nM Ku86 antisense ASOs was associated with a specific decrease in Ku86 mRNA levels (IC(50) <25 nM; n = 3) and a concomitant rapid decrease (<10% of control) in Ku86 protein expression. Moreover, transfection of M059K cells with Ku86 antisense ASOs markedly increased cell death after treatment with ionizing radiation, bleomycin, and etoposide. However, no sensitization to the DNA cross-linking agents chlorambucil and cisplatin was observed after Ku86 antisense transfection. As expected, transfection of M059J cells with Ku86 antisense ASOs did not result in any sensitization to ionizing radiation, bleomycin, or DNA cross-linking agents, but there was a 2-fold increase in sensitivity to etoposide. Thus, our results indicate that antisense ASOs targeted against Ku86 may increase the efficacy of radiotherapy and DNA-damaging agents in tumor treatment. Furthermore, Ku86 antisense ASOs may be used to create a temporal knockout in different human cell lines to further investigate the biological roles of Ku86.

Antigens, Nuclear↗
PubMed2002

Ku affects the CHK1-dependent G(2) checkpoint after ionizing radiation.

There are two major pathways for repairing DNA double strand breaks in mammalian cells: nonhomologous end joining (NHEJ) and homologous recombination repair (HRR). The nonhomologous end joining repair is deficient in cells without Ku, whereas HRR is highly efficient in such cells compared with their wild-type counterparts. The mechanism remains unclear. We reported previously that Ku80(-/-) cells show a stronger ATM-dependent S-phase checkpoint response than Ku80(+/+) cells after ionizing radiation (IR; X-Y. Zhou et al., Oncogene, 21:6377-6381, 2002). We report in this study that Ku80(-/-) cells also show a much stronger G(2) accumulation than Ku80(+/+) cells after IR. The stronger G(2) checkpoint response in Ku80(-/-) cells is ATM independent but is accompanied with a higher activity of CHK1 kinase. Treatment with Chk1 antisense oligonucleotide abolishes the stronger G(2) checkpoint response and sensitizes Ku80(-/-) cells to IR. These data indicate that the stronger G(2) checkpoint response shown in Ku80(-/-) cells is CHK1 dependent and suggest that the CHK1-dependent checkpoint response contributes to the highly efficient HRR in such cells.

Animals↗
PubMed2002

Synergistic role of Ku80 and poly(ADP-ribose) polymerase in suppressing chromosomal aberrations and liver cancer formation.

Liver cancer is one of the major human tumors in the world. Basic and epidemiological studies have proposed that the major risk factors for liver cancer include alcohol and diet as well as infection with hepatitis B and C viruses. However, the mechanistic clues for the development of this type of cancer is largely unknown. Poly(ADP-ribose) polymerase (PARP-1) and a component of nonhomologous end-joining (NHEJ) machinery, Ku80, are two major DNA end-binding molecules that play a multifunctional role in DNA damage signaling and repair, recombination as well as the maintenance of genomic stability. Here we show that the interaction of PARP-1 and Ku80 is essential for development because PARP-1/Ku80 double null mice died at embryonic day (E) 9.5. Interestingly, haplo-insufficiency of Ku80 in PARP-1-/- mice promotes the development of hepatocellular adenoma and hepatocellular carcinoma (HCC). These tumors exhibited a multistage tumor progression associated with the loss of E-cadherin expression and the mutation of beta-catenin. Cytogenetic analysis revealed that Ku80 heterozygosity elevated chromosomal instability in PARP-1-/- cells and that these liver tumors harbored a high degree of chromosomal aberrations including fragmentations, end-to-end fusions, and recurrent nonreciprocal translocations (NRT). These features are reminiscent of human HCC. Taken together, these data implicate a synergistic function of Ku80 and PARP-1 in minimized chromosome aberrations and cancer development and suggest that defects in DNA end-processing molecules may be etiological factors in human HCC formation.

Animals↗
PubMed2002

Efficacy of a glutathione S-transferase pi-activated prodrug in platinum-resistant ovarian cancer cells.

Human ovarian carcinoma cells (C70 and C200) made resistant to cisplatin from A2780 cells demonstrated an approximately 20-fold resistance to the drug. These same cell lines showed no collateral resistance (as compared with the wild-type) to a novel glutathione S-transferase pi-activated prodrug [gamma-glutamyl-alpha-amino-beta[2-ethyl-N,N,N',N'-tetrakis (2-chloroethyl) phosphorodiamidate]-sulfonyl-propionyl-(R)-(-) phenylglycine; TLK286]. Previous results have shown a direct correlation between levels of GST pi expression and cytotoxicity for TLK286 (L. A. Rosario et al., Mol. Pharmacol., 58: 167-174, 2000.). However, protein levels of the isozyme were identical in wild-type C70 and C200 cell lines. In analyzing the DNA repair capacity of C70 and C200, an altered expression of the DNA-dependent protein kinase (DNA-PK) complex (catalytic subunit DNA-PKcs, and the heterodimers Ku70 and Ku80) was found. In C70 and C200 cells, DNA-PKcs was overexpressed at both the transcript and protein levels, whereas amounts of Ku70 and Ku80 were higher only at the level of protein expression. TLK286 in either its parent or activated form inhibited the catalytic kinase activity of purified DNA-PK with an IC50 value of approximately 1 microM. Coimmunoprecipitation of Ku70 after TLK286 treatment of purified DNA-PK and C70 cells showed a drug-induced destabilization of the protein-protein interaction between the catalytic subunit and the Ku heterodimer. Overall, these results implicate inhibition of DNA-PK as a component of TLK286 cytotoxicity and provide a rationale for its use in the clinical management of cisplatin-resistant ovarian cancer.

Antigens, Nuclear↗
PubMedDate not supplied

Relationship between DNA mismatch repair genes expression, Ku-genes expression and ploidy-related parameters in the progression of pigmented lesions of the skin.

Defects of DNA repair systems in cutaneous tumours are related to DNA mismatch repair genes (MLH1, MSH2, PMS1, PMS2) and Ku70/80 genes involved in double- strand repair. In this study we investigated the statistical relationship between these systems and DNA-ploidy-related parameters in 19 naevus cell naevi, 23 lentigos maligna, 76 primary melanomas and 31 melanoma metastases, applying the correlation coefficient according to Spearman. In naevi significant correlations were found between Ku70/80 gene expression and some ploidy-related parameters. In lentigos, additionally, some significant correlations between the expression of DNA mismatch repair genes were found. Similar results were demonstrated for primary melanomas. In metastases no one significant correlation between DNA mismatch repair genes and Ku-genes was present. We postulate that DNA mismatch repair genes and Ku70/80 genes are functionally independent and that some of them are able to influence ploidy-related parameters.

Adaptor Proteins, Signal Transducing↗
PubMed2003

Increased error-prone NHEJ activity in myeloid leukemias is associated with DNA damage at sites that recruit key nonhomologous end-joining proteins.

Double strand breaks (DSBs) are considered the most lethal form of DNA damage for eukaryotic cells, and misrepair of DSB can cause cell death, chromosome instability, and cancer. Nonhomologous end-joining (NHEJ) is a major mechanism for the repair of DSBs. We previously reported that the cancer predisposition Bloom's syndrome and myeloid leukemias demonstrate increased NHEJ activity and consequent misrepair. In this study, we link this increased NHEJ activity and infidelity to ongoing or induced DNA damage at sites that recruit key NHEJ proteins. We show here that in myeloid leukemia cells and normal hemopoietic cells, agents that induce DSBs produce an up to 2-fold increase in this DSB misrepair activity, whereas an alkylating agent produces little or no increases. Furthermore, NHEJ overactivity after induction of DSBs is dependent on the presence of Ku70/Ku86. We also present data to explain the constitutively activated NHEJ in myeloid leukemias. Using an immunofluorescence-based assay for DNA damage, myeloid leukemias demonstrate constitutive DNA damage in the absence of treatment with DSB-inducing agents compared with normal hemopoietic cells. Importantly, damaged foci from myeloid leukemia and normal cells colocalize with NHEJ proteins Ku70 and Ku86. These data suggest that the generation of increased constitutive DNA damage may be a common pathway for the creation of NHEJ-dependent genomic instability.

Antibodies↗
PubMed2003

Breast cancer risk associated with genotypic polymorphism of the nonhomologous end-joining genes: a multigenic study on cancer susceptibility.

The role of the familial breast cancer susceptibility genes, BRCA1 and BRCA2, in the homologous recombination pathway for DNA double-strand break (DSB) repair suggests that the mechanisms involved in DNA DSB repair are of particular etiological importance during breast tumorigenesis. However, there is currently no evidence for an association between breast cancer and the other DSB repair pathway, the nonhomologous end-joining (NHEJ) pathway. It is possible that, because this DNA repair pathway is so crucial for mammalian cells to maintain genomic stability, any severe defects in it would result in serious outcomes, such as genomic instability and cell death, and block subsequent cell outgrowth and tumor formation. Thus, only subtle defects arising from low-penetrance alleles would escape lethality accumulating essential genetic changes and be associated with cancer formation, and the tumorigenic contribution of these alleles would become more obvious if individual putative high-risk genotypes of each NHEJ gene act jointly. Furthermore, this joint effect might be modified by specific environmental factors, and we hypothesized that estrogen exposure might be one such factor because estrogen is suggested to cause DNA DSBs, triggering breast tumorigenesis. Because single nucleotide polymorphisms (SNPs) are the most subtle genetic variation in the genome, to examine these hypotheses, we have genotyped 30 SNPs in all five NHEJ genes (Ku70, Ku80, DNA-PKcs, Ligase IV, and XRCC4) in 254 primary breast cancer patients and 379 healthy controls. Support for these hypotheses came from the observations that (a) two SNPs in Ku70 and XRCC4 were associated with breast cancer risk (P < 0.05); (b) a trend toward increased risk of developing breast cancer was found in women harboring a greater number of putative high-risk genotypes of NHEJ genes (an adjusted odds ratio of 1.46 for having one additional putative high-risk genotype; 95% confidence interval, 1.19-1.80); (c) this association between risk and the number of putative high-risk genotypes was stronger and more significant in women thought to be more susceptible to estrogen, i.e., those with no history of full-term pregnancy; and (d) the protective effect conferred by a history of full-term pregnancy was only significant in women with a lower number of putative high-risk genotypes of NHEJ genes. Based on comprehensive NHEJ gene profiles, this study provides new insights to suggest the role of the NHEJ pathway in breast cancer development and supports the possibility that breast cancer is initiated by estrogen exposure, which causes DNA DSBs.

Antigens, Nuclear↗
PubMed2003

Enhancement of radiation response by roscovitine in human breast carcinoma in vitro and in vivo.

Frequent deregulation of cyclin-dependent kinase (CDK) activation associated with loss of cell cycle control was found in most of human cancers. A recent development of a new class of antineoplasic agents targeting the cell cycle emerged as a small molecule CDK inhibitor, roscovitine, which presents potential antiproliferative and antitumoral effects in human tumors. Additional studies reported that roscovitine combined with cytotoxic agents can cooperate with DNA damage to activate p53 protein. However, little is known about the biological effect of roscovitine combined with ionizing radiation (IR) in human carcinoma, and no studies were reported thus far in p53 mutated carcinoma. In the breast cancer cell line MDA-MB 231, which lacks a functional p53 protein, we found a strong radiosensitization effect of roscovitine in vitro by clonogenic survival assay and in vivo in MDA-MB 231 xenograft model. Using Pulse Field Gel Electrophoresis, a strong impairment in DNA-double-strand break rejoining was observed after roscovitine and IR treatment as compared with IR alone. Cell cycle analysis showed a G(2) delay and no increase in radiation-induced apoptosis in the cells treated with IR or roscovitine and IR. On the other hand, we found a significant induction in micronuclei frequency after roscovitine and IR treatment as compared with IR alone. This effect was also observed in BALB murine cells in contrast to SCID murine cells, which are deficient in DNA-PKcs, suggesting a possible DNA-double-strand break repair defect in the nonhomologous end joining pathways. In MDA-MB 231 cells, the radiosensitization effect of roscovitine was associated with an inhibition of the DNA-dependent protein kinase activity caused by a marked decrease in Ku-DNA binding by using the electrophoretic mobility shift assay. In conclusion, we found a novel effect on DNA repair of the CDK inhibitor roscovitine, which acts as a radiosensitizer in vitro and in vivo in breast cancer cells lacking a functional p53.

Animals↗
PubMed2003

Flavopiridol, a cyclin-dependent kinase inhibitor, enhances radiosensitivity of ovarian carcinoma cells.

Flavopiridol, a cyclin-dependent kinase (cdk) inhibitor, can cause cell cycle arrest, induce apoptosis in cancer cells, and inhibit tumor cell growth in vivo. The present study investigated the in vitro radiosensitizing effect of flavopiridol and the underlying molecular mechanisms in a murine ovarian cancer cell line, OCA-I. Flavopiridol inhibited cell growth in a dose-dependent manner and enhanced cell radiosensitivity assessed by the clonogenic cell survival assay. A flavopiridol dose of 300 nM, given for 1 day, enhanced radiosensitivity by a factor of 2.1. Clonogenic cell survival after split-dose radiation showed that flavopiridol inhibited repair from radiation damage. In addition, flavopiridol treatment (300 nM, 1 day) resulted in decreased levels of Ku70 and Ku86 proteins that play a role in DNA repair processes, suggesting that DNA repair processes may have been disrupted by this agent. Flow cytometry analysis showed that flavopiridol (300 nM, 1 day) accumulated the cells in G(1) and G(2) phases, with a significant reduction in the S phase component. This cell cycle redistribution is likely another mechanism underlying flavopiridol-induced cell radiosensitivity. Flavopiridol down-regulated cyclin D1 and cyclin E protein levels and also inhibited phosphorylation of retinoblastoma protein, which is inconsistent with the observed cell cycle arrest. Among the cdks tested, cdk-9, the catalytic subunit of positive transcription elongation factor b, was significantly down-regulated by flavopiridol, suggesting that flavopiridol may modulate cellular transcription processes. Furthermore, flavopiridol on its own induced apoptosis in the OCA-I cells, whereas in combination with radiation, exerted no additional increase in apoptosis. Taken together, our data show that flavopiridol strongly augmented the response of ovarian carcinoma cells to radiation and that the underlying mechanisms included inhibition of sublethal DNA damage repair and cell cycle redistribution. At the molecular level, transcriptional regulation by flavopiridol may have been involved.

Animals↗
PubMed2003

Adenovirus-mediated heat-activated antisense Ku70 expression radiosensitizes tumor cells in vitro and in vivo.

Ku70 is one component of a protein complex, Ku70 and Ku80, that functions as a heterodimer to bind DNA double-strand breaks and activates DNA-dependent protein kinase. Our previous study with Ku70-/- and Ku80-/- mice, and cell lines has shown that Ku70- and Ku80-deficiency compromises the ability of cells to repair DNA double-strand breaks, increases radiosensitivity of cells, and enhances radiation-induced apoptosis. In this study, we examined the feasibility of using adenovirus-mediated, heat-activated expression of antisense Ku70 RNA as a gene therapy paradigm to sensitize cells and tumors to ionizing radiation. First, we performed experiments to test the heat inducibility of heat shock protein (hsp) 70 promoter and the efficiency of adenovirus-mediated gene transfer in rodent and human cells. Replication-defective adenovirus vectors were used to introduce a recombinant DNA construct, containing the enhanced green fluorescent protein (EGFP) under the control of an inducible hsp70 promoter, into exponentially growing cells. At 24 h after infection, cells were exposed to heat treatment, and heat-induced EGFP expression at different times was determined by flow cytometry. Our data clearly show that heat shock at 42 degrees C, 43 degrees C, or 44 degrees C appears to be equally effective in activating the hsp70 promoter-driven EGFP expression (>300-fold) in various tumor cells. Second, we have generated adenovirus vectors containing antisense Ku70 under the control of an inducible hsp70 promoter. Exponentially growing cells were infected with the adenovirus vector, heat shocked 24 h later, and the radiosensitivity determined 12 h after heat shock. Our data show that heat shock induces antisense Ku70 RNA, reduces the endogenous Ku70 level, and significantly increases the radiosensitivity of the cells. Third, we have performed studies to test whether Ku70 protein level can be down-regulated in a solid mouse tumor (FSa-II), and whether this results in enhanced radiosensitivity in vivo, as assessed by in vivo/in vitro colony formation and by the tumor growth delay. Our data demonstrate that heat-shock-induced expression of antisense Ku70 RNA attenuates Ku70 protein expression in FSa-II tumors, and significantly sensitizes the FSa-II tumors to ionizing radiation. Taken together, our results suggest that adenovirus-mediated, heat-activated antisense Ku70 expression may provide a novel approach to radiosensitize human tumors.

Adenocarcinoma↗
PubMed2003

Prediction of tumor radiosensitivity in rectal carcinoma based on p53 and Ku70 expression.

The identification of predictive indicators of radiosensitivity is extremely useful in selecting patients suited for preoperative radiotherapy and avoiding unnecessary preoperative treatment. In this study, we evaluated the possible role of the immunohistochemical expression pattern of p53 and Ku70 protein in determining tumor radiosensitivity in rectal cancer before preoperative irradiation. We examined pretreatment biopsy materials from 111 patients by immunohistochemistry. The expression pattern of p53 and Ku70 was evaluated for association with tumor radiosensitivity, which was defined according to the criteria of the Japanese Research Society for Cancer of the Colon and Rectum. There was a significant correlation between the expression pattern of p53 and tumor radiosensitivity (P = 0.045); Ku70 and tumor radiosensitivity (P < 0.001); and the combination of p53 and Ku70, and tumor radiosensitivity (P < 0.001). The sensitivity, specificity, positive predictive value, negative predictive value, and accuracy in both p53 and Ku70-positive cases for radioresistance were all superior to those of the group positive for p53 alone. In conclusion the examination of the combination of p53 and Ku70 may predict the radiosensitivity of rectal cancer before preoperative irradiation.

Adult↗
PubMed2003

Coordinated regulation of the promoter and enhancer regions of human CD23 gene by signal through IL-4R and CD40, and the role of Ku70/80 in the enhancer activity.

CD23 has roles in proliferation, antigen uptake and presentation, and the generation of IgE. Signals through IL-4R and CD40 stimulate transcription of CD23 in B cells and are necessary for immunoglobulin class switch (IgCS). The same signals induce nuclear translocation of Ku, which is also required for IgCS, in human resting B cells, suggesting that these signaling pathways are connected. We examined the regulation of CD23 gene, and located the minimal promoter at -132+80 region. A pair of 188bp inverted repeats inhibited its activity. The intronic region including EBV responsive element (EBVRE) and the surrounding sequence, required the gene specific promoter to enhance the reporter gene activity. Western blotting and FACS analysis using subclones of DND39 B cells infected with recombinant EBV, revealed that CD23 upregulation did not necessarily correlate with EBNA 2 and LMP 1 expression. Although the specific binding of Ku to EBVRE was not demonstrated, dominant negative Ku80 suppressed IL-4 + anti-CD40-driven CD23 expression. These results suggest that Ku is involved in gene regulation as a signal transducer and gene enhance. Detailed analysis of CD23 gene regulation would lead to a better understanding of disorders such as allergy and lymphoproliferation.

Antigens, Nuclear↗
PubMed2004

Radiosensitizer effect of wortmannin in radioresistant bladder tumoral cell lines.

This work analyzes the effectiveness of wortmannin in boosting the lethality induced by different doses of X-rays, using the colorimetric assay of MTT. Bladder tumoral cell lines differing in radiosensitivity and p53 status were used. Since wortmannin is able to inhibit DNA-dependent protein kinase (DNA-PK) and rejoining of double-strand breaks (DSBs), we have analyzed the constitutive contents and expression after irradiation of the catalytic subunit of DNA-PK (DNA-PKcs) in our cell lines with the aim of explaining the differential effect of wortmannin as radiosensitizer. Considering that DNA-PK is the main protein complex involved in DNA DSB repair, the ability to remove DSBs after irradiation (with or without wortmannin) was evaluated in the different cell lines by the use of pulse-field gel electrophoresis. Our results indicate a higher radiosensitization in the radio-resistant cell line that shows both high constitutive contents of DNA-PKcs and a high rate of DNA repair by the fast component. In contrast, no radiosensitizer effect of wortmannin was observed in the radiosensitive cell line, previously characterized as defective in DSB repair by a low repair fidelity, and - as our results show - with low constitutive contents and later post-irradiation expression of DNA-PKcs. No clear effect related to p53 status of the cell line was observed. These results suggest that high constitutive contents of DNA-PKcs are indicative of radio-resistant phenotypes, and analysis of the expression of this protein could be helpful in the optimal establishment of wortmannin as radiosensitizer in bladder tumoral cell lines.

Androstadienes↗
PubMed2003

[Construction of double-strand break repair protein hKu70 deficient cell strain and its biologic characters].

OBJECTIVE: To construct DNA double-strand break (DSB) repair protein hKu70 deficient cell strain and to observe its biological characters for studying the functions of hKu70 gene and the effects of occupational harmfulness factors on DSB repair. METHODS: Human lung fibroblasts (HLF) were transfected with the eukaryotic expression plasmids of hKu70 gene antisense RNA (pEGFP-C1-K) to construct hKu70 protein deficient cells (named as "HLFK"). The protein expression levels of hKu70 gene in HLFC and HLFK were detected by the Western blotting to estimate the effects of antisense inhibition. Morphology, growth character and growth status in soft agar of transfected HLFK were observed. RESULTS: pEGFP-C1-K vector was successfully expressed in HLF. The protein expression level of hKu70 gene in HLFK was decreased by 42% as compared with that in HLFC. No obvious changes of the biologic characters were observed in HLFK. CONCLUSION: The hKu70 protein deficient cell strain was successfully constructed. The hKu70 protein deficiency alone didn't induce obvious changes of the biological characters in HLFK.

Antigens, Nuclear↗
PubMed2004

Up-regulation of DNA-dependent protein kinase activity and Sp1 in colorectal cancer.

Tumor tissues and adjacent normal tissues in 12 colorectal cancers were examined for quantitative differences in: i) activity of DNA-dependent protein kinase (DNA-PK), which functions in DNA double-strand breads repair, and ii) protein and mRNA levels of Ku70, Ku80, DNA-PKcs and transcriptional factor Sp1. DNA-PK activity and protein/mRNA levels of Ku70, Ku80, DNA-PKcs and Sp1 were significantly higher in the tumor tissues compared with the normal tissues. Significant correlations between DNA-PK activity and protein/mRNA levels of Ku70, Ku80, DNA-PKcs and Sp1 were observed. Because Ku80 and DNA-PKcs have consensus Sp1 recognition elements in their promoter region, the DNA sequence of Ku70 promoter region was analyzed. Analysis of Ku70 promoter region reveled that Ku70 gene has consensus Sp1 recognition elements in its promoter region. mRNA levels of Ku70, Ku80 and DNA-PKcs were correlated with one another, and significant correlations between Sp1 protein level and mRNA levels of Ku70 and Ku80 were observed. These results suggest that DNA-PK activity and protein- and mRNA-levels of Ku70, Ku80 and DNA-PKcs were elevated in tumor tissues in patients with colorectal cancer because of elevated Sp1 protein levels in tumor tissues.

Adenocarcinoma↗
PubMed2004

Targeting Ku protein for sensitizing of breast cancer cells to DNA-damage.

Targeting molecular components that are critically involved in the maintenance of genome stability is a promising approach for overcoming intrinsic tumor cell resistance to DNA-damaging treatments. In mammalian cells, the Ku-dependent non-homologous end-joining repair pathway is the predominant process for the repair of double-strand breaks (DSBs) in DNA. Previously, RNA aptamers were selected to efficiently block DNA-binding activity of the Ku protein in vitro. In the present study, we have tested the efficacy of RNA aptamers against the Ku protein as molecular sensitizer of MCF-7 breast carcinoma cells to DNA-damage. Toward this end, we established MCF-7 cell sublines stably expressing SC4 aptamer RNAs under the control of the human 7SL small nuclear RNA gene promoter. Vector-transfected (MCF/7SL) cells and cells stably expressing SC4 aptamers (MCF/SC4) were exposed to the anticancer drug etoposide and cellular responses to DNA-damage were evaluated. We found that the presence of RNA aptamers against Ku protein enhanced etoposide-induced growth inhibition of MCF-7 breast cancer. The SC4 aptamer-mediated sensitization of MCF-7 cells to the anticancer drug is attributable to an increased susceptibility of these cells to apoptosis. The observed effects cannot be accounted for by the differential expression levels of Ku protein in control and SC4 aptamer-expressing cells, but are rather due to augmented DNA binding-capacity of Ku protein, as demonstrated in in vitro studies. Thus, RNA aptamers against Ku protein show potential to sensitize MCF-7 breast carcinoma cells to DNA-damaging agents.

Antigens, Nuclear↗