Downregulation of protein kinase C-alpha enhances intracellular survival of Mycobacteria: role of PknG

Abstract

BackgroundIntracellular trafficking of mycobacteria is comprehensively dependent on the unusual regulation of host proteins. Recently, we have reported that infection of macrophages by Mycobacterium tuberculosis H37Rv (Rv) selectively downregulates the expression of PKCα while infection by Mycobacterium smegmatis (MS) does not.ResultsBased on our earlier study, we have extrapolated for the first time that knockdown of PKCα, impairs phagocytosis of mycobacteria by macrophages while their intracellular survival is drastically increased. Mycobacterium bovis BCG (BCG) and Mycobacterium tuberculosis H37Ra (Ra) have also been shown to downregulate the expression of PKCα during the infection. Since PknG is uniquely expressed in BCG, Ra, Rv but not in MS and has been reported to promote intracellular survival of mycobacteria, led us to believe that PknG may be involved in such downregulation of PKCα. THP-1 cells infected with recombinant MS expressing PknG (MS-G), showed significant reduction in PKCα expression. In normal THP-1 cells survival of MS-G was enhanced as compared to MS, while their behavior in PKCα deficient cells could not be distinguished. The results strongly demonstrate that pathogenic mycobacteria recognize and then inhibit PKCα to circumvent phagocytosis and the hostile environment of macrophages. We emphasize that, this inhibition is controlled by PknG.ConclusionsAll together, our data reveal a mechanism that shows substantial interdependence of PKCα with PknG, in sustaining mycobacterial infection.

Phospholipase C‐γ2 promotes intracellular survival of mycobacteria

“…These interactions further decide the intracellular fate of pathogen as well as pathogenesis in TB. 7,23 Listeria monocytogenes, an intracellular pathogen, interferes with Ca 2+ signalling in J774A.1 cells. 21 Some previous studies have implicated the role of PLC isoforms during pathogenic infection, but their roles in regulating phagocytosis and intracellular survival of mycobacteria in macrophages have not been studied.…”

“…7,18 Mycobacterial cultures (Mycobacterium smegmatis MC 2 155 (MS) and Mtb-Ra; ATCC 25177, originally acquired from the American Type Culture Collection, Manassas, VA) were obtained from CSIR-CDRI (Lucknow, India). 7,18 Mycobacterial cultures (Mycobacterium smegmatis MC 2 155 (MS) and Mtb-Ra; ATCC 25177, originally acquired from the American Type Culture Collection, Manassas, VA) were obtained from CSIR-CDRI (Lucknow, India).…”

“…7,18 In brief, mycobacteria grown up to mid-log phase (OD 650 = 0.6-0.9) were used for infections. 7,18 In brief, mycobacteria grown up to mid-log phase (OD 650 = 0.6-0.9) were used for infections.…”

“…Recognition of the antigen-MHC complexes exposed on macrophage surface by T-cell receptors directs the activation and secretion of various cytokines by T cells that ultimately culminates in the generation of an effective immune response. 7 Phospholipase C (PLC) is a family of diverse enzymes that execute their biological functions through inositol trisphosphate (IP3) and diacylglycerol (DAG), which are produced after cleavage of phospholipids, but each isoform also contributes to some of their unique cellular functions. Upon infection, macrophages mount several bactericidal strategies to kill the invading pathogen while Mtb uses various defensive mechanisms to avoid destruction by these cells.…”

Protein kinase C-delta (PKCδ), a marker of inflammation and tuberculosis disease progression in humans, is important for optimal macrophage killing effector functions and survival in mice

“…45 The PKC isoforms, including b 27 and a, 28 were reported to be important for maturation of Mtb-containing phagosomes. In contrast to PKCb and PKCa, our findings indicated that PKCd is dispensable for phagosome maturation and autophagy in Mtb-infected macrophages.…”