Cyclic AMP secretion mechanisms in M. tuberculosis

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Abstract Control of the current tuberculosis (TB) epidemic will require better understanding of the biological mechanisms used by Mycobacterium tuberculosis (Mtb) to sense, respond to and manipulate its host environment during infection. Cyclic AMP (cAMP) is a universal signal molecule used by both microbial pathogens and their mammalian hosts to sense and respond to environmental cues. cAMP plays a central role in virulence gene regulation in several important bacterial pathogens, and regulates many aspects of mammalian host biology, including the immune response. Many bacteria, including Mtb, exploit this common signaling molecule by elevating cAMP levels in their host cells as a pathogenic strategy. Levels of cAMP within Mtb bacteria increase dramatically upon bacterial entry into macrophages, and some of this cAMP is secreted into host macrophages to alter the course of infection. The scientific premise for this proposal is that the cAMP export from Mtb bacteria into macrophages contributes to TB pathogenesis, but the mechanisms underlying cAMP secretion and its specific activities within the host cell are not known. We hypothesize that cyclic AMP secretion from the bacterium is regulated in response to environmental conditions, and that Mtb actively facilitates access of secreted cAMP to the cytoplasm of infected host macrophages to manipulate the host response to infection. Major goals of this proposal are to identify bacterial factors that i) control secretion of cAMP from Mtb bacteria, and ii) affect cytoplasmic access of this Mtb-secreted cAMP during macrophage infection. Knowledge of these factors will provide a critical basis for understanding the mechanisms underlying both cAMP export processes and their specific roles in Mtb pathogenesis, with the long term potential for identification of new TB interventions and/or biomarkers of disease progression.