PPE38 Modulates the Innate Immune Response and Is Required for Mycobacterium marinum Virulence

Abstract

The proline-glutamic acid (PE) and proline-proline-glutamic acid (PPE) family proteins are prevalent in pathogenic mycobacteria and play a diverse role in mycobacterial pathogenesis. While some members have been studied, the function of most PE/PPE proteins remains unknown. In this study, we isolated a transposon-inactivated PPE38 mutant of Mycobacterium marinum and characterized its phenotype. We found that the PPE38 protein is associated with the cell wall and exposed on the cell surface. The inactivation of PPE38 altered the bacterial cell surface properties and led to deficiencies in cord formation, sliding motility, and biofilm formation. The PPE38 mutant was defective in phagocytosis by macrophages and exhibited reduced virulence in adult zebrafish. We also found that PPE38 is involved in the induction of proinflammatory cytokines in infected macrophages. Together, our results indicate that PPE38, a previously uncharacterized protein, plays a role in mycobacterial virulence, presumably by modulating the host innate immune response. Mycobacterium tuberculosis is a highly successful human pathogen that latently infects one-third of the world's population, causing 10 million new infections and 2 million deaths annually. One reason for the success of M. tuberculosis lies in its ability to evade host immune defense mechanisms and to create a niche within host cells, enabling the bacterium to persist for long periods. M. tuberculosis infects and survives within macrophages by evading macrophage killing mechanisms through a variety of strategies (reviewed in references 51 and 56). During persistent infection, M. tuberculosis is thought to reside within a granuloma, a cellular accumulation around the bacilli that is comprised mainly of macrophages, dendritic cells, T cells, B cells, and fibroblasts (reviewed in reference 31). Granulomas are generally thought to contain the infection by limiting bacterial growth and spread (21, 61). However, recent studies by Ramakrishnan and coworkers using zebrafish embryos demonstrated that the granuloma is a dynamic structure and that Mycobacterium marinum, an aquatic mycobacterium closely related to M. tuberculosis, uses the granuloma as a niche to recruit uninfected macrophages, raising the possibility that granulomas are exploited by the pathogen for expansion and dissemination in early infection (23,25,26).PE and PPE family proteins, named for the conserved N-terminal-domain-containing proline-glutamic acid (PE) motif or proline-proline-glutamine (PPE) motif, are unique to mycobacteria and particularly prevalent in pathogenic mycobacteria (35). They account for a significant fraction (ϳ10%) of the coding capacity of pathogenic mycobacteria. There are 168 PE/PPE proteins in M. tuberculosis (22) and 281 in M. marinum (64). The relatively conserved N termini are approximately 110 and 180 amino acids in the PE and PPE families, respectively. The C-terminal domains of both the PE and PPE protein families are highly variable in both size and sequence and often contain repetitive ...

Cyclopropanation of α-mycolic acids is not required for cording in Mycobacterium brumae and Mycobacterium fallax

“…Alterations in biosynthesis, chain length and functional groups of mycolic acids in mutants of M. bovis BCG, M. tuberculosis and M. marinum caused the loss of the cording phenotype (Dong et al, 2012;Glickman et al, 2000). The need for the presence of a cyclopropane ring in the proximal position of a-mycolic acids for cording was established in one of these studies (Glickman et al, 2000).…”

“…These authors compared the virulent H37Rv and avirulent H37Ra M. tuberculosis strains and found that the formation of cords only occurred in the virulent strain. Later, other researchers working with natural or constructed mutants of M. tuberculosis, M. bovis, M. marinum and M. abscessus reported a decrease in the virulence of mutants that lost cording (Bhatt et al, 2007;Dong et al, 2012;Gao et al, 2003Gao et al, , 2004Glickman et al, 2000;Howard et al, 2006;Makinoshima & Glickman, 2005). In addition, we have demonstrated an increase in the virulence of natural mutants of M. vaccae, M. chubuense, M. gilvum, M. obuense and M. parafortuitum that had acquired the capacity to form microscopic cords (Julián et al, 2010).…”

CpsA, a LytR-CpsA-Psr Family Protein in Mycobacterium marinum, Is Required for Cell Wall Integrity and Virulence

“…Adult zebrafish were infected with M. marinum as described previously (27). Briefly, after being anesthetized with 0.1% 3-aminobenzoic acid ethyl ester (tricaine), adult zebrafish were infected by intraperitoneal injection with 10 l of single-cell bacterial suspensions at a dosage of 10 individual strains for each experiment.…”

Mycobacterium TuberculosisPPE Family Protein Rv1808 Manipulates Cytokines Profile via Co-Activation of MAPK and NF-κB Signaling Pathways

“…PPE family protein PPE34 [11], PPE41 [7] and PPE38 [15] were experimentally demonstrated to be cell surface exposed. PPE38 can modulate the host innate immune response via manipulating the production of TNF-α and IL-6 [15]. PPE-SVP subfamily protein Rv1808 has 49% similarity with Mycobacterium avium subsp.…”