Rv1675c (cmr) regulates intramacrophage and cyclic AMP-induced gene expression in Mycobacterium tuberculosis-complex mycobacteria

Cyclic AMP (cAMP) has recently been shown to be a global regulator of gene expression in Mycobacterium tuberculosis (Mtb). In this study we identified a new cAMP-associated regulon in Mtb and Mycobacterium bovis BCG, which is distinct from the previously described CRPMt regulon. Proteomic comparison of wild-type M. bovis BCG with a Rv1675c (cmr) knockout strain showed dysregulated expression of four previously identified proteins encoded by the cAMP-induced genes (cAIGs) mdh, groEL2, Rv1265 and PE_PGRS6a. Regulated expression of these four cAIGs also occurred during macrophage infection, and this regulation required cmr in both Mtb and M. bovis BCG. Purified His-Cmr bound to the DNA sequences upstream of three cAIGs (mdh, groEL2, Rv1265) in electrophoretic mobility shift assays, suggesting direct regulation of these genes by Cmr. We also found that low pH stimulated cAMP production in both Mtb and M. bovis BCG, but broadly affected cAIG regulation only in M. bovis BCG. These studies identify Cmr as a transcription factor that regulates cAIGs within macrophages, and suggest that multiple factors affect cAMP-associated gene regulation in tuberculosis-complex mycobacteria. cAMP signalling and Cmr-mediated gene regulation during Mtb infection of macrophages may have implications for TB pathogenesis.