Catalytic activities of hammerhead ribozymes with a triterpenoid linker instead of stem/loop II

Maxizyme against mtp53 transfected by adenovirus enhanced transferrin receptor-mediated gene delivery systeminduced apoptosis of hepatoma cells

AIM: To evaluate the influence of introduction of maxizyme against mtp53 by adenovirus enhanced transferrin receptor-mediated gene delivery system on MHCC97 cells.

METHODS: Hepatoma cell line MHCC97 containing mutated p53 gene was served as a model. The maxizyme against mtp53 was transfected to the cells by adenovirus enhanced transferrin receptor-mediated gene delivery system. The level of mtp53-mRNA was detected by means of semi-quantitative reverse transcription polymerase chain reaction (RT-PCR). The apoptosis of the hepatoma cells was measured by DNA ladder assay and FCM.

RESULTS: After 48 hours of transfection by AVET system, RT-PCR results indicated the expression of mtp53 mRNA in pEGFP-Maxizyme group was significantly lower than that in control group. And DNA "ladder" with agarose gel electrophoresis was observed in pEGFP-maxizyme group. The result of flow cytometry exhibited apoptotic index in pEGFP-maxizyme group was 22.95%, which was higher than those in blank control group and pEGFP group.

CONCLUSION: The recombinant ribozyme cDNA eukaryotic expression vector pEGFP-maxizyme can be efficiently transfected into MHCC97 cell by adenovirus enhanced transferrin receptor-mediated gene delivery system and the expression of maxizyme may inhibit the mtp53 gene expression and promote apoptosis of MHCC97 cells. The AVET system may be a useful tool in gene delivery for gene therapy of human HCC.

A simple assay system for examination of the inhibitory potential in vivo of decoy RNAs, ribozymes and other drugs by measuring the Tat-mediated transcription of a fusion gene composed of the long terminal repeat of HIV-1 and a gene for luciferase

Nucleic acid-based drugs, including antisense RNA and DNA, ribozymes and decoys appear to have potential for the suppression of the expression of specific genes. To allow the examination of the potential of such agents in vivo as anti-HIV drugs in standard laboratories, where facilities for handling live virions are not available, we constructed a simple assay system (HIV-1 model) that allows measurement of the extent of inhibition of Tat-mediated transcription of HIV-1 by nucleic acid-based drugs and other agents. In cells that harbor a stable chimeric long terminal repeat (LTR)-Luc construct (a fusion gene consisting of the LTR of HIV-1 and the gene for luciferase), total luciferase activity in an aliquot of cell lysate is dose- and promoter-dependent on transfection with a Tat expression plasmid, reflecting the character of the LTR promoter of HIV. When HeLa cells were co-transfected with the Tat expression plasmid and another plasmid that encoded the U6 promoter or the promoter of the gene for tRNA(Val) linked to the trans-activating response (TAR) sequence, total luciferase activity was inhibited by 60 or 40%, respectively. The inhibition was also dependent on the dose of the TAR expression plasmid. These results demonstrate the usefulness of this simple assay system for detection of the efficacy of a decoy RNA or a ribozyme in vivo, without a requirement for HIV-infected cells, by measurement of luciferase activity in vitro.

Comparison of the specificities and catalytic activities of hammerhead ribozymes and DNA enzymes with respect to the cleavage of BCR-ABL chimeric L6 (b2a2) mRNA

With the eventual goal of developing a treatment for chronic myelogenous leukemia (CML), attempts have been made to design hammerhead ribozymes that can specifically cleave BCR-ABL fusion mRNA. In the case of L6 BCR-ABL fusion mRNA (b2a2 type; BCR exon 2 is fused to ABL exon 2), which has no effective cleavage sites for conventional hammerhead ribozymes near the BCR-ABL junction, it has proved very difficult to cleave the chimeric mRNA specifically. Several hammerhead ribozymes with relatively long junction-recognition sequences have poor substrate-specificity. Therefore, we explored the possibility of using newly selected DNA enzymes that can cleave RNA molecules with high activity to cleave L6 BCR-ABL fusion (b2a2) mRNA. In contrast to the results with the conventional ribozymes, the newly designed DNA enzymes, having higher flexibility for selection of cleavage sites, were able to cleave this chimeric RNA molecule specifically at sites close to the junction. Cleavage occurred only within the abnormal BCR-ABL mRNA, without any cleavage of the normal ABL or BCR mRNA. Thus, these chemically synthesized DNA enzymes seem to be potentially useful for application in vivo , especially for the treatment of CML, if we can develop exogenous delivery strategies.