Exploring Drug Action on Mycobacterium Tuberculosis Using Affymetrix Oligonucleotide Genechips

DNA microarrays have rapidly emerged as an important tool for Mycobacterium tuberculosis research. While the microarray approach has generated valuable information, a recent survey has found a lack of correlation among the microarray data produced by different laboratories on related issues, raising a concern about the credibility of research findings. The Affymetrix oligonucleotide array has been shown to be more reliable for interrogating changes in gene expression than other platforms. However, this type of array system has not been applied to the pharmacogenomic study of M. tuberculosis. The goal here was to explore the strength of the Affymetrix array system for monitoring drug-induced gene expression in M. tuberculosis, compare with other related studies, and conduct cross-platform analysis. The genome-wide gene expression profiles of M. tuberculosis in response to drug treatments including INH (isoniazid) and ethionamide were obtained using the Affymetrix array system. Up-regulated or down-regulated genes were identified through bioinformatic analysis of the microarray data derived from the hybridization of RNA samples and gene probes. Based on the Affymetrix system, our method identified all drug-induced genes reported in the original reference work as well as some other genes that have not been recognized previously under the same drug treatment. For instance, the Affymetrix system revealed that Rv2524c (fas) was induced by both INH and ethionamide under the given levels of concentration, as suggested by most of the probe sets implementing this gene sequence. This finding is contradictory to previous observations that the expression of fas is not changed by INH treatment. This example illustrates that the determination of expression change for certain genes is probe-dependent, and the appropriate use of multiple probe-set representation is an advantage with the Affymetrix system. Our data also suggest that whereas the up-regulated gene expression pattern reflects the drug's mode of action, the down-regulated pattern is largely non-specific. According to our analysis, the Affymetrix array system is a reliable tool for studying the pharmacogenomics of M. tuberculosis and lends itself well in the research and development of anti-TB drugs.