Effects of cetyltrimethylammonium bromide on reactions catalyzed by maxizymes, a novel class of metalloenzymes

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.

Maxizyme-mediated specific inhibition on mutant-type p53 in vitro

AIM

To evaluate the specific inhibition of maxizyme directing against mutant-type p53 gene (mtp53) at codon 249 in exon 7 (AGG-AGT) in vitro.

METHODS

Two different monomers of anti-mtp53 maxizyme (maxizyme right MzR, maxizyme left MzL) and control mutant maxizyme (G(5)-A(5)) were designed by computer and cloned into vector pBSKU6 (pBSKU6MzR, pBSKU6MzL). After being sequenced, the restrictive endonuclease site in pBSKU6MzR was changed by PCR and then U6MzR was inserted into pBSKU6MzL, the recombinant vector was named pU6Mz and pU6asMz (mutant maxizyme). Mtp53 and wild-type p53 (wtp53) gene fragments were cloned into pGEM-T vector under the T7 promoter control. The (32)p-labeled mtp53 transcript was the target mRNA. Cold maxizyme transcripts were incubated with (32)p-labeled target RNA in vitro and radioautographed after denaturing polyacrylamide gel electrophoresis.

RESULTS

In cell-free systems, pU6Mz showed a specific cleavage activity against target mRNA at 37 degrees and 25 mM MgCL(2). The cleavage efficiency of pU6Mz was 42 %, while pU6asMz had no inhibitory effect. Wtp53 was not cleaved by pU6Mz either.

CONCLUSION

pU6Mz had a specific catalytic activity against mtp53 in cell-free system. These lay a good foundation for studying the effects of anti-mtp53 maxizyme in HCC cell lines. The results suggest that maxizyme may be a promising alternative approach for treating hepatocellular carcinoma containing mtp53.

Allosterically controlled single-chained maxizymes with extremely high and specific activity

For the treatment of chronic myelogenous leukemia (CML), attempts have been made to design various ribozyme motifs that can specifically recognize and cleave BCR-ABL fusion mRNAs. In the case of L6 BCR-ABL b2a2 mRNA, it is difficult to cleave the abnormal mRNA specifically because the mRNA includes no sequences that can be cleaved efficiently by conventional hammerhead ribozymes near the BCR-ABL junction. We recently succeeded in designing a novel maxizyme, which specifically cleaves BCR-ABL fusion mRNA, as a result of the formation of a dimeric structure [Kuwabara, T.; et al. Mol. Cell 1998, 2, 617-627; Tanabe, T.; et al. Nature 2000, 406, 473-474]. Specifically, we tailored the maxizyme with molecular switching function: the maxizyme splices a cleavable GUC site, but only when it appears within a strand of mRNA that possesses the abnormal splice junction. We demonstrated that this approach is generalizable [Tanabe, T.; et al. Biomacromolecules 2000, 1, 108-117]. All the maxizymes designed in the past functioned as a result of the formation of a dimeric structure. Questions have been asked whether a similar molecular switching might be possible within a single molecule when two monomer units of the maxizyme were connected via a linker sequence. We found that an analogous conformational change could not be induced within a single molecule when two maxizyme units were simply connected via a nonregulatable linker sequence. However, an active conformation was achieved by the introduction of an antisense modulator within the linker sequence that adjusted the overall structure to the correct form. Results of studies in cultured cells suggested that the desired conformational change could indeed be induced within the modified single-chained maxizyme and such a construct caused apoptosis only in leukemic cells with the Philadelphia chromosome.