cAMP levels withinMycobacterium tuberculosisandMycobacterium bovisBCG increase upon infection of macrophages

Abstract

Adenosine 3',5'-cyclic monophosphate (cAMP)-mediated signal transduction is common in both prokaryotes and eukaryotes, and several bacterial pathogens modulate cAMP signaling pathways with their mammalian hosts during infection. In this study, cAMP levels associated with M. tuberculosis and M. bovis BCG were measured during macrophage infection. cAMP levels within both bacteria increased approximately 50-fold during infection of J774.16 macrophages, relative to the cAMP levels within bacteria incubated in tissue culture media alone. cAMP levels also increased within the macrophage cytoplasm upon uptake of live, but not dead, mycobacteria. The presence of albumin in the absence of oleic acid significantly decreased cAMP secretion and production by both M. tuberculosis and M. bovis BCG. These results suggest that cAMP signaling plays a role in the interaction of TB-complex mycobacteria with macrophages during infection, and that albumin may be a physiological indicator differentiating host environments during infection.

A Universal Stress Protein (USP) in Mycobacteria Binds cAMP

“…Cytosolic as well as extracellular cAMP levels in mycobacteria can reach 100 M, as measured by radioimmunoassay and ELISA procedures (19,22). Such measurements incorporate procedures that dissociate cAMP bound to proteins, therefore estimating concentrations of cAMP that reflect the total amount present in the cellular fraction.…”

“…Indeed, intracellular levels of cAMP can reach hundreds of micromolars (19,20). Cyclic AMP is also effectively secreted by mycobacteria (19,21,22), perhaps modulating host macrophage function during disease establishment and the formation of the caseous granulomacontaining dormant mycobacteria. In concert with the high levels of cAMP, the genome of M. tuberculosis H37Rv encodes 10 proteins that harbor the CNB domain, and two proteins containing the GAF domain (5 similar to the bacterial transcription factor, CRP, or cAMP receptor protein (4,23,24).…”

Acylation of Biomolecules in Prokaryotes: a Widespread Strategy for the Control of Biological Function and Metabolic Stress

“…While cAMP concentrations do not fluctuate with the addition of glucose to the medium, cAMP availability increases ϳ50-fold during macrophage infection (237). The entry of M. tuberculosis into a nonreplicating persister or "quiescent" state during chronic infection requires a significant downshift in metabolism, which is thought to be achieved by diverting acetyl-CoA away from the TCA cycle toward the synthesis of triacylglycerides (243).…”

“…The global transcriptional regulator Crp mediates this cAMP-dependent response (236). In mycobacteria, cAMP not only plays a role in basic physiology but also acts as a secondary messenger and is involved in the rerouting of host signaling during infection (237). Notably, M. tuberculosis has 15 adenylate cyclase enzymes for the production of cAMP, whereas E. coli has only 1 (CyaA) (reviewed in reference 238).…”

Novel regulatory roles of cAMP receptor proteins in fast-growing environmental mycobacteria

“…Consequently, intracellular cAMP concentrations in mycobacterial cells are considered to be~100-fold higher than those of other bacteria (Dass et al, 2008;Padh & Venkitasubramanian, 1976, 1980, but the significance of this is not known. Secretion of cAMP directly into host macrophages after infection has been reported and is thought to be important in tuberculosis pathogenesis (Agarwal et al, 2009;Bai et al, 2009;Lowrie et al, 1975). M. tuberculosis H37Rv contains a single CRP-FNR homologue encoded by the gene Rv3676 (Cole et al, 1998), which is 32 % identical to the E. coli CRP over 189 amino acid residues.…”