The Alternative Sigma Factor SigH Regulates Major Components of Oxidative and Heat Stress Responses inMycobacterium tuberculosis

Abstract

Mycobacterium tuberculosis is a specialized intracellular pathogen that must regulate gene expression to overcome stresses produced by host defenses during infection. SigH is an alternative sigma factor that we have previously shown plays a role in the response to stress of the saprophyte Mycobacterium smegmatis. In this work we investigated the role of sigH in the M. tuberculosis response to heat and oxidative stress. We determined that a M. tuberculosis sigH mutant is more susceptible to oxidative stresses and that the inducible expression of the thioredoxin reductase/thioredoxin genes trxB2/trxC and a gene of unknown function, Rv2466c, is regulated by sigH via expression from promoters directly recognized by SigH. We also determined that the sigH mutant is more susceptible to heat stress and that inducible expression of the heat shock genes dnaK and clpB is positively regulated by sigH. The induction of these heat shock gene promoters but not of other SigH-dependent promoters was markedly greater in response to heat versus oxidative stress, consistent with their additional regulation by a heat-labile repressor. To further understand the role of sigH in the M. tuberculosis stress response, we investigated the regulation of the stress-responsive sigma factor genes sigE and sigB. We determined that inducible expression of sigE is regulated by sigH and that basal and inducible expression of sigB is dependent on sigE and sigH. These data indicate that sigH plays a central role in a network that regulates heat and oxidative-stress responses that are likely to be important in M. tuberculosis pathogenesis.Tuberculosis remains a major cause of human suffering, exacting an enormous toll of morbidity and mortality in much of the world (11). The cause of tuberculosis, the obligate pathogen Mycobacterium tuberculosis, is highly adapted for survival in the host organism. Following infection M. tuberculosis is ingested by macrophages and must persist in this environment in order to survive, either in a quiescent state or through active replication that results in tissue destruction and the disease of tuberculosis. In adapting to this intracellular environment, this bacterium must regulate its physiology to survive a variety of stresses produced by the macrophage, including reactive oxygen and reactive nitrogen species produced by these cells (1, 4, 28). In addition M. tuberculosis has been shown to alter the physiology of the macrophage to modulate host defenses (51). Although the sequencing of the M. tuberculosis genome and recent insights are beginning to shed light on pathogenic mechanisms of this organism (7,8,27,30), the means by which M. tuberculosis adapts to survive and replicate in the host remain poorly understood.Data from a number of laboratories have implicated several alternative sigma factors of mycobacteria, including SigB, SigE, SigF, and SigH, in the adaptation of the pathogen M. tuberculosis and the saprophyte Mycobacterium smegmatis to several stresses (5,9,12,20,29,53). M. smegmatis SigH has been shown ...

Evidence for complex interactions of stress-associated regulons in an mprAB deletion mutant of Mycobacterium tuberculosis

“…We identified an additional start site, TSP4, which is coincident with the putative start codon of sigE, and upstream of TSP3 (Fig. 3a, b, g), supporting reports that sigE is smaller than predicted (Raman et al, 2001;Wu et al, 1997). TSP4 is activated by SDS stress in H37Rv, in an MprA-dependent manner, as indicated by the reduced intensity of bands for Rv-D981 (Fig.…”

“…The sequence GGCCA near the end of this site (Fig. 2b) has some similarity to the consensus sequences for SigE-and SigH-dependent promoters (Manganelli et al, 2001(Manganelli et al, , 2002Raman et al, 2001), consistent with the regulation of mprA by SigE (Manganelli et al, 2001). It is likely, however, that, when MprA is bound, sigma factors do not interact directly with this 235 region.…”

“…3g). Sequences beginning at 233 (TGGCCCA) and 211 (CGGTA) each share four bases, respectively, with the 235 and 210 regions of SigH-dependent promoters (Manganelli et al, 2002;Raman et al, 2001). However, as some of the invariant residues reported for SigH-dependent promoters are missing (Manganelli et al, 2002;Raman et al, 2001), it is likely that another sigma factor regulates sigE from this promoter.…”

“…However, as some of the invariant residues reported for SigH-dependent promoters are missing (Manganelli et al, 2002;Raman et al, 2001), it is likely that another sigma factor regulates sigE from this promoter.…”

“…SigE is a major stress-responsive sigma factor of M. tuberculosis (Jensen-Cain & Quinn, 2001;Manganelli et al, 1999Manganelli et al, , 2001Raman et al, 2001), and often functions within a regulatory cascade (Manganelli et al, 2002;Raman et al, 2001). SDS exposure upregulates SigE, which then activates 23 genes, including sigB, mprA, mprB and four other transcription factor genes (Manganelli et al, 2001).…”