Mycobacterium tuberculosis SigF Regulates Genes Encoding Cell Wall-Associated Proteins and Directly Regulates the Transcriptional Regulatory Gene phoY1

Abstract

Mycobacterium tuberculosisSigF is homologous to stress response and sporulation sigma factors in many bacteria. Consistent with a possible role in mycobacterial survival under stress conditions, M. tuberculosis sigF is strongly induced within cultured human macrophages and upon nutrient starvation, and SigF has been implicated in M. tuberculosis entry into stationary phase. On the other hand, SigF appears to contribute to the immune pathology of tuberculosis (TB), and a sigF-deficient mutant has altered cell membrane properties. Using an M. tuberculosis sigF deletion mutant, we show here that sigF is not required for bacillary survival under nutrient starvation conditions and within activated murine macrophages or for extracellular persistence in an in vivo granuloma model of latent TB infection. Using a chemically inducible recombinant strain to conditionally overexpress sigF, we did not observe arrest or retardation of growth in exponentially growing cultures or reduced susceptibility to rifampin and isoniazid. Consistent with our hypothesis that SigF may mediate TB immunopathogenesis by altering cell membrane properties, we found that overexpression of sigF resulted in the differential regulation of many cell wall-associated proteins, including members of the MmpL, PE, and PPE families, several of which have been shown to influence host-pathogen interactions. The most highly upregulated gene by quantitative reverse transcription-PCR at all time points following sigF induction was Rv3301c (phoY1), which encodes a probable transcriptional regulatory protein homologous to PhoU proteins involved in regulation of phosphate uptake. Using in vitro transcription analysis, we show that SigF directly regulates phoY1, whose proposed promoter sequence is GGATTG-N 16 -GGGTAT.

A comparative study of host response to three Mycobacterium tuberculosis PE_PGRS proteins

“…In contrast to our previous findings (Dheenadhayalan et al, 2006b), Williams et al (2007) have shown that expression of M. tuberculosis PE_PGRS 26 is significantly upregulated following induction of sigma factor F, which may help mycobacteria survive under stressful environmental conditions. The differences in host cell responses observed in the present studies using PE_PGRS 16 compared to PE_PGRS 33 and PE_PGRS 26 suggest that regulated expression of different PE_PGRS proteins by M. tuberculosis could affect the fate of the mycobacterial pathogen as well as the response by the host to infection.…”

The alternative sigma factor SigF of Mycobacterium smegmatis is required for survival of heat shock, acidic pH and oxidative stress

“…SigF did not appear to be required for survival of stress conditions such as heat and cold shock or long-term stationary-phase survival (Chen et al, 2000). In fact, a recent study using both deletion as well as overexpression of sigF in M. tuberculosis suggested that SigF has a role in the regulation of the structure and function of the mycobacterial cell wall, rather than being a general stressresponse sigma factor (Williams et al, 2007).…”

“…No induction compared to unexposed control cells was observed under these conditions (data not shown), confirming that the observed induction of rsbW-lacZ was indeed due to exposure to D-cycloserine. In M. tuberculosis, SigF appears to have a role in the regulation of genes involved in cell envelope biosynthesis (Geiman et al, 2004;Williams et al, 2007). It may therefore be that cell wall stress, e.g.…”

The SigF Regulon in Mycobacterium smegmatis Reveals Roles in Adaptation to Stationary Phase, Heat, and Oxidative Stress

“…However, it has since become clear that SigF is well conserved among mycobacteria (30,31) and regulates more than just virulence. While SigF is related to stress response and sporulation sigma factors in other bacteria (8), its role as a stress and stationary-phase sigma factor in M. tuberculosis is under debate (40).…”

“…Loss of the alternative sigma factor SigF decreased the virulence of M. tuberculosis in mice (5) and disease-associated tissue damage in mice (13) as well as guinea pigs (20). Loss of SigF also leads to an altered cell wall composition due to a lack of virulence-related sulfolipids (13), and overexpression of sigF has been shown to affect the regulation of other cell wall-associated proteins involved in host-pathogen interaction (40).…”