Candidalysin

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Candidalysin is a cytolytic 31-amino acid α-helical amphipathic peptide toxin found in the opportunistic pathogen Candida albicans that activates epithelial cells. As such, Candidalysin is a rare fungal example of a classical virulence factor. Hyphal morphogenesis in C. albicans is associated with damage to host epithelial cells; during this process Candidalysin is released.[1] Candidalysin promotes damage of oral epithelial cells by inducing lactate dehydrogenase release and calcium ion influx. It is unique in the fact that it is the first peptide toxin to be identified in any human fungal pathogen.[2]

C. albicans produces the protein Ece1 (extent of cell elongation 1) during the formation of hyphae.[3] Cleavage of Ece1 at arginine/lysine residues by Kex2 and Kex1 releases several peptides, including the toxin Candidalysin. Consequently, Candidalysin is also known as Ece1-III62–92K. C. albicans strains missing Candidalysin do not damage epithelial cells and are said to be avirulent with respect to mucosal infections. The toxin is also responsible for the activation and propagation of a cellular immune response.[4]

Epithelial Damage[edit]

As Ece1-III62–92K levels accumulate, it evokes direct tissue damage.[4] Candidalysin promotes damage of oral epithelial cells by inducing the release of lactate dehydrogenase and calcium ion influx which are characteristics of membrane destabilization and cell damage.[2] Candidalysin is able to cause epithelial damage through permeabilization, pore formation, and membrane intercalation. It can cause IL-1β production and is a driver of inflammasome activation in macrophages.[5]

Immune response[edit]

Epithelial immunity can recognize Ece1-III62–92K without harming cells. Epithelial cells have evolved to particularly recognize the peptide, which indicates that during mucosal infection the fungus secretes this toxin.[4] Immune cells can either be exposed extracellularly or intracellularly and this is due to the fact that phagocytes can be exposed to the fungal hyphae pre-phagocytosis or post-phagocytosis.[5] Epithelial immunity is achieved predominantly through mitogen-activated protein kinase (MAPK) signaling, more specifically the p38 pathway. The p38 pathway leads to the activation of AP-1 transcription factor c-Fos and the ERK1/2 pathway. The ERK1/2 pathway then leads to the activation of the enzyme MAPK phosphatase 1 which regulates the immune response.[2]

p38 MAPK Pathway[edit]

The p38 mitogen activated protein kinase (MAPK) pathway is similar to the JNK pathway but differs from the ERK pathway. The p38 MAP kinase, JNK MAP kinase, and ERK MAP kinase are all types of mammalian MAP kinases.[6] The p38 MAP kinase is activated by two other MAP kinases known as MKK3 and MKK4. MKK4 is also known to activate the JNK MAP kinase, however, MKK3 is unique to the p38 MAP kinase. The p38 MAPK pathway is required to be activated by dual phosphorylation of the amino acids: tyrosine and threonine and also environmental stress and pro-inflammatory cytokines. Examples of environmental stress than can activate the p38 MAP Kinase include UV radiation and osmotic stress. Examples of pro-inflammatory cytokines that can activate the p38 MAP Kinase include tumor necrosis factor, Interleukin-1, and lipopolysaccharide (LPS).[7] The p38 MAP kinase plays an important role in regulating Interleukin-10 synthesis and toll-like receptor signaling.[8]

MAPK Phosphatase MKP1[edit]

MAPK Phosphatase 1 negatively regulates the activity of mitogen activate protein kinase (MAPK) activity. A deficiency of this phosphatase leads to a prolonged and continual activation of the p38 MAP kinase and JNK MAP kinase. MAPK phosphatase 1 is the founding member of the family of MAPK phosphatases which is a group of 11 phosphatases. The N-terminus of MAPK phosphatase 1 is responsible for the localization of the nucleus. The p38 MAPK and JNK pathways are preferred to be dephosphorylated over the ERK pathway.[8]

References[edit]

  1. ^ Wilson, Duncan; Naglik, Julian R.; Bernhard Hube (2016). "The Missing Link between Candida albicans Hyphal Morphogenesis and Host Cell Damage". PLOS Pathogens. 12 (10): e1005867. doi:10.1371/journal.ppat.1005867. PMC 5072684. PMID 27764260.
  2. ^ a b c Naglik, Julian R; König, Annika; Hube, Bernhard; Gaffen, Sarah L (2017-12-01). "Candida albicans–epithelial interactions and induction of mucosal innate immunity". Current Opinion in Microbiology. Host-microbe interactions: fungi * Host-microbe interactions: parasites. 40: 104–112. doi:10.1016/j.mib.2017.10.030. ISSN 1369-5274. PMC 5733685. PMID 29156234.
  3. ^ Birse CE, Irwin MY, Fonzi WA, Sypherd PS (1993). "Cloning and characterization of ECE1, a gene expressed in association with cell elongation of the dimorphic pathogen Candida albicans". Infect. Immun. 61 (3648–3655): 3648–55. PMC 281060. PMID 8359888.
  4. ^ a b c Moyes, David L.; Wilson, Duncan; Richardson, Jonathan P.; et al. (April 2016). "Candidalysin is a fungal peptide toxin critical for mucosal infection". Nature. 532 (7597): 64–68. doi:10.1038/nature17625. PMC 4851236. PMID 27027296.
  5. ^ a b Kasper, Lydia; König, Annika; Koenig, Paul-Albert; Gresnigt, Mark S.; Westman, Johannes; Drummond, Rebecca A.; Lionakis, Michail S.; Groß, Olaf; Ruland, Jürgen; Naglik, Julian R.; Hube, Bernhard (2018-10-15). "The fungal peptide toxin Candidalysin activates the NLRP3 inflammasome and causes cytolysis in mononuclear phagocytes". Nature Communications. 9 (1): 4260. doi:10.1038/s41467-018-06607-1. ISSN 2041-1723. PMC 6189146. PMID 30323213.
  6. ^ Chang, Lufen; Karin, Michael (March 2001). "Mammalian MAP kinase signalling cascades". Nature. 410 (6824): 37–40. doi:10.1038/35065000. ISSN 1476-4687. PMID 11242034.
  7. ^ Raingeaud, Joël; Gupta, Shashi; Rogers, Jeffrey S.; Dickens, Martin; Han, Jiahuai; Ulevitch, Richard J.; Davis, Roger J. (1995-03-31). "Pro-inflammatory Cytokines and Environmental Stress Cause p38 Mitogen-activated Protein Kinase Activation by Dual Phosphorylation on Tyrosine and Threonine". Journal of Biological Chemistry. 270 (13): 7420–7426. doi:10.1074/jbc.270.13.7420. ISSN 0021-9258. PMID 7535770.
  8. ^ a b Chi, Hongbo; Barry, Sean P.; Roth, Rachel J.; Wu, J. Julie; Jones, Elizabeth A.; Bennett, Anton M.; Flavell, Richard A. (2006-02-14). "Dynamic regulation of pro- and anti-inflammatory cytokines by MAPK phosphatase 1 (MKP-1) in innate immune responses". Proceedings of the National Academy of Sciences. 103 (7): 2274–2279. doi:10.1073/pnas.0510965103. ISSN 0027-8424. PMC 1413743. PMID 16461893.