Uptake and cellular actions of mycolactone, a virulence determinant for Mycobacterium ulcerans

• Published in: Microbial pathogenesis Vol. 34; no. 2; pp. 91 - 101
• Main Authors: Snyder, D.Scott, Small, P.L.C
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier India Pvt Ltd 01.02.2003; Elsevier
• Subjects: Bacterial Toxins - classification; Bacterial Toxins - metabolism; Bacterial Toxins - toxicity; Bacteriology; Biological and medical sciences; Calcium; Calcium - metabolism; Caspases - analysis; Caspases - metabolism; Cells, Cultured; Confocal microscopy; Fibroblasts - enzymology; Fibroblasts - metabolism; Fundamental and applied biological sciences. Psychology; Macrolide; Macrolides; Microbiology; Mitochondria - metabolism; Molecular Structure; Mycobacterium Infections, Nontuberculous - microbiology; Mycobacterium ulcerans - pathogenicity; Mycolactone; Pathogenicity, virulence, toxins, bacteriocins, pyrogens, host-bacteria relations, miscellaneous strains; Signal transduction; Tropical medicine; Virulence Factors - metabolism; Signal transduction; Mycolactone; Calcium; DMEM, Dulbecco's modified Eagle's medium; BAPTA-AM, 1,2 bis( o-aminophenoxy)ethane N, N, N′, N′-tetraacetic acid tetra(acetoxymethyl) ester; FBS, fetal bovine serum; Confocal microscopy; Macrolide; Virulence; Lactone; Mycobacterial infection; In vitro; Biological activity; Uptake; Infection; Mycobacterium ulcerans; Mycobacteriales; Buruli ulcer; Bacteriosis; Mycobacteriaceae; Bacteria; Actinomycetes; Property structure relationship
• ISSN: 0882-4010; 1096-1208
• DOI: 10.1016/S0882-4010(02)00210-3

Mycolactone is a macrolide secreted by Mycobacterium ulcerans. Experimental evidence suggests that mycolactone plays a prominent role in the pathogenesis of Buruli ulcer by causing both tissue destruction and immunosuppression. To understand the cell biology of mycolactone activity, we have synthesized the fluorescent mycolactone derivativebodipymycolactone. Although derivatization resulted in a modest decrease in cytopathic activity, the derivatized and native molecules produce identical phenotypes in cultured cells. Confocal microscopy of bodipymycolactone added to cultured fibroblasts, shows that it is localized to the cytosol. Bodipymycolactone fails to bind to the cell membrane and is excluded from the nucleus. Uptake is both nonsaturable and noncompetitive with excess mycolactone, consistent with passive diffusion of this toxin through the cell membrane. These facts, combined with the inability of signal transduction inhibitors to inhibit mycolactone cytopathicity point towards the presence of an cytosolic target for mycolactone. A dose dependent increase in intracellular calcium levels at occurs upon mycolactone exposure, but chelation of intracellular calcium alters neither the cytopathicity nor the caspase induction profile of treated cells. Mitochondrial polarization is maintained in treated cells for up to 3 days arguing that the rise in intracellular calcium levels may be a result of cytoskeletal remodeling.