Characterization of a Novel Heat Shock Protein (Hsp22.5) Involved in the Pathogenesis of Mycobacterium tuberculosis

Abstract

Tuberculosis is a worldwide health problem, given that one-third of the world's population is currently infected with Mycobacterium tuberculosis. Understanding the regulation of virulence on the molecular level will provide a better understanding of how M. tuberculosis can establish chronic infection. Using in vivo microarray analysis (IVMA), we previously identified a group of genes that are activated in BALB/c mouse lungs compared to in vitro cultures, including the rv0990c gene. Our analysis indicated that this gene is a member of the heat shock regulon and was activated under other stress conditions, including survival in macrophages or during the late phase of chronic tuberculosis in the murine lungs. Deletion of rv0990c from the genome of M. tuberculosis strain H37Rv affected the transcriptional profiles of many genes (n ‫؍‬ 382) and operons involved in mycobacterial survival, including the dormancy regulon, ATP synthesis, respiration, protein synthesis, and lipid metabolism. Comparison of the proteomes of the mutant to those of the wild-type strain further confirmed the differential expression of 15 proteins, especially those involved in the heat shock response (e.g., DnaK and GrpE). Finally, the rv0990c mutant strain showed survival equivalent to that of the isogenic wild-type strain during active tuberculosis in guinea pigs, despite showing significant attenuation in BALB/c mice during the chronic phase of the disease. Overall, we suggest that rv0990c encodes a heat shock protein that plays an important role in mycobacterial virulence. Hence, we renamed rv0990c heat shock protein 22.5 (hsp22.5), reflecting its molecular mass.Tuberculosis is a devastating disease that threatens onethird of the world's population, with 1.8 million deaths each year from infection with Mycobacterium tuberculosis (11). Following aerosol infection, M. tuberculosis can persist inside the host macrophages for long periods, leading to chronic infection. Under certain circumstances, chronically infected patients can develop an active progressive infection that could lead to death (6). Unfortunately, several aspects of the chronic phase of tuberculosis are not completely understood. For example, the molecular basis responsible for the persistence of M. tuberculosis inside the host remains largely unknown. Also, the triggers for M. tuberculosis reactivation are not well characterized. Several in vitro and in vivo models have been developed in order to elucidate the mechanisms employed by the pathogen to survive and persist inside the host (5, 12, 25, 30-33). Such studies have identified genes activated during M. tuberculosis survival inside macrophages or under hostile stress conditions, including transcriptional regulators which control the expression of a large number of genes (1,22). One such gene is rv0990c, which was preferentially activated in murine lungs among a group of 32 genes sharing the same genomic locus, termed the in vivo-expressed genomic island, iVEGI (31). The iVEGI includes several genes and operons that are inv...

Virulence factors of theMycobacterium tuberculosiscomplex

“…In addition, the survival of mice infected with the mutant strains is longer than that of the wild type. The introduction of a wild-type copy of Rv0990c in the mutant strain partially complements the lethal phenotype of M. tuberculosis 476 . These results, together with the findings that the mutation of hspX and acr2 genes results in alteration of the M. tuberculosis virulence, highlight the role of heat shock proteins during the infection of pathogenic mycobacteria.…”

Mycobacterium tuberculosisRv0991c is a redox-regulated molecular chaperone

“…Supporting the hypothesis that Ruc contributes to M. tuberculosis pathogenesis, a previous screen to identify genes required for M. tuberculosis virulence in mice found that bacteria with transposon insertions in ruc are defective for in vivo growth during mixed infections (51). In another study, mice infected with an M. tuberculosis strain containing a deletion-disruption of Rv0990c (encoding Hsp22.5), the gene directly downstream of ruc , had a lower bacterial burden during the later stages of infection and increased time to death compared to mice infected with a WT strain; however, the phenotypes in this study could not be fully complemented (52). Conceivably, the Rv0990c mutation could have affected Ruc production, which might explain the incomplete complementation of the Rv0990c mutation to fully restore virulence.…”

Mycobacterium tuberculosis Rv0991c Is a Redox-Regulated Molecular Chaperone

“…Notably, a previous screen to identify genes required for M. tuberculosis virulence in mice during mixed infections found that bacteria with transposon insertions in ruc exhibited approximately 2-fold less growth in vivo than growth in vitro ( 56 ), possibly mirroring the subtle phenotype we observed in our mouse infections. In another study, mice of a different genetic background (BALB/c) that were infected with an M. tuberculosis strain containing a deletion and disruption mutation of Rv0990c (encoding Hsp22.5), the gene directly downstream of ruc , had a lower bacterial burden during the later stages of infection and increased time to death than mice infected with a WT strain; however, the phenotypes in this study could not be fully complemented ( 57 ). Conceivably, the Rv0990c mutation could have affected Ruc production, which might explain the incomplete complementation of the Rv0990c mutation to fully restore virulence.…”