A tag-based approach for high-throughput analysis of CCWGG methylation

Molecular characterization of an rsmD-like rRNA methyltransferase from the Wolbachia endosymbiont of Brugia malayi and antifilarial activity of specific inhibitors of the enzyme

The endosymbiotic organism Wolbachia is an attractive antifilarial drug target. Here we report on the cloning and expression of an rsmD-like rRNA methyltransferase from the Wolbachia endosymbiont of Brugia malayi, its molecular properties, and assays for specific inhibitors. The gene was found to be expressed in all the major life stages of B. malayi. The purified enzyme expressed in Escherichia coli was found to be in monomer form in its native state. The activities of the specific inhibitors (heteroaryl compounds) against the enzyme were tested with B. malayi adult and microfilariae for 7 days in vitro at various concentrations, and NSC-659390 proved to be the most potent compound (50% inhibitory concentration [IC50], 0.32 μM), followed by NSC-658343 (IC50, 4.13 μM) and NSC-657589 (IC50, 7.5 μM). On intraperitoneal administration at 5 mg/kg of body weight for 7 days to adult jirds into which B. malayi had been transplanted intraperitoneally, all the compounds killed a significant proportion of the implanted worms. A very similar result was observed in infected mastomys when inhibitors were administered. Docking studies of enzyme and inhibitors and an in vitro tryptophan quenching experiment were also performed to understand the binding mode and affinity. The specific inhibitors of the enzyme showed a higher affinity for the catalytic site of the enzyme than the nonspecific inhibitors and were found to be potent enough to kill the worm (both adults and microfilariae) in vitro as well as in vivo in a matter of days at micromolar concentrations. The findings suggest that these compounds be evaluated against other pathogens possessing a methyltransferase with a DPPY motif and warrant the design and synthesis of more such inhibitors.

The stem cell signature of CHH/CHG methylation is not present in 271 cancer associated 5'UTR gene regions

Non-CpG methylation is frequently present in stem cell DNA. We investigated the value of this epigenetic modification in cancerous DNA in order to establish the implications of CHH/CHG methylation for biomarker development. Therefore we used the restriction enzymes BstNI and PspGI within a combined multiplex PCR and targeted microarray approach for the elucidation of non-CpG (CCWGG) methylation. Targeting 544 CCWGG sites in 271 5' gene regions, the CHH/CHG methylation status of the MCF7 breast cancer cell line and blood from healthy volunteers and childhood ALL was analyzed. Statistical analysis of microarray data and subsequent SYBR green based qPCR on DNA digests was applied to confirm the results from the microarray screen.

RESULT/CONCLUSION

The microarray experiments identified for the MCF7 cell line the genes MSH2 (p < 0.001), EREG (p < 0.001) and HSPA2 (p = 0.029) with CHH/CHG methylation, and in childhood ALL the genes HIST1H2AG (p = 0.003), PGF (p = 0.02), CPEB4 (p = 0.039) and TJP2 (p = 0.04). Validation using qPCR upon restriction digestion did not confirm the presence of CHH/CHG methylation in MCF7 DNA. In ALL samples only TJP2 was found harboring CHH/CHG methylation (p = 0.02). However, applying Bonferroni-correction for multiple testing that qPCR-result was not rated as statistically significant anymore. We concluded that non-CpG methylation in 544 CCWGG sites analyzed did not change in tumor cells. Thus any change of the CHH/CHG methylation pattern is a minor event in tumorigenesis, even if the stem cell markers OCT4, NANOG, STELLAR and GDF3 are expressed like in the MCF7 breast cancer cell line.