Stimulation of Chitin Synthesis Rescues Candida albicans from Echinocandins

Abstract

Echinocandins are a new generation of novel antifungal agent that inhibit cell wall β(1,3)-glucan synthesis and are normally cidal for the human pathogen Candida albicans. Treatment of C. albicans with low levels of echinocandins stimulated chitin synthase (CHS) gene expression, increased Chs activity, elevated chitin content and reduced efficacy of these drugs. Elevation of chitin synthesis was mediated via the PKC, HOG, and Ca2+-calcineurin signalling pathways. Stimulation of Chs2p and Chs8p by activators of these pathways enabled cells to survive otherwise lethal concentrations of echinocandins, even in the absence of Chs3p and the normally essential Chs1p, which synthesize the chitinous septal ring and primary septum of the fungus. Under such conditions, a novel proximally offset septum was synthesized that restored the capacity for cell division, sustained the viability of the cell, and abrogated morphological and growth defects associated with echinocandin treatment and the chs mutations. These findings anticipate potential resistance mechanisms to echinocandins. However, echinocandins and chitin synthase inhibitors synergized strongly, highlighting the potential for combination therapies with greatly enhanced cidal activity.

Comparative genomics of MAP kinase and calcium–calcineurin signalling components in plant and human pathogenic fungi

“…Calcium signalling through the Ca 2+ -binding protein calmodulin and the Ca 2+ -calmodulin-dependent phosphatase calcineurin has been implicated in a multitude of processes, including stress response, mating, budding, and actin-based processes (Cyert, 2001) as well as in determining tolerance to antifungal drugs (Cruz et al, 2002;Del Poeta et al, 2000;Kontoyiannis et al, 2003;Sanglard et al, 2003;Steinbach et al, 2007;Walker et al, 2008). Cellular calcium levels in S. cerevisiae are regulated by multiple channels and transporters, including the voltage-gated high-affinity calcium channel Cch1 which functions together with the stretch-activated cation channel Mid1 (Locke et al, 2000).…”

Paradoxical Effect of Caspofungin against Candida Bloodstream Isolates Is Mediated by Multiple Pathways but Eliminated in Human Serum

“…Contribution of the Inp51-Irs4 PI(4,5)P2 regulatory complex and the Cek1-MAPK and Ras-cAMP hyphal regulatory pathways to paradoxical growth. Activation of the PKC-Mkc1 cell wall integrity signaling pathway also has been shown to contribute to paradoxical growth (17,27,28), at least in part by coordinately regulating chitin synthesis in conjunction with the calcineurin pathway. In previous studies, we demonstrated that independent disruptions of the PI(4,5)P2 5Ј-phosphatase Inp51 and its interacting EH-domain protein Irs4p resulted in elevated PI(4,5)P2 levels, overactivation of the PKC-Mkc1 pathway in response to cell wall stress, and hypersusceptibility to caspofungin (1,2).…”

Echinocandin resistance due to simultaneous FKS mutation and increased cell wall chitin in a Candida albicans bloodstream isolate following brief exposure to caspofungin

“…In the case described by Costa-de-Oliveira et al (2011), the C. glabrata strain had a mutation in the FKS region but the chitin content was unspecified. Understanding the mechanisms of resistance will help promote further research into chitin synthase inhibitors which are known to act synergistically with the echinocandins (Walker et al, 2008). To our knowledge, this is the first report of a Candida isolated from bloodstream with both FKS mutation and altered cell wall chitin content.…”

“…Mutations in the FKS2 gene have also been reported in Candida glabrata and Candida guilliermondii. In contrast to the FKS1 mutations, the compensatory rise in chitin synthesis is related to the cell wall salvage pathway involving protein kinase C (PKC) signalling (Walker et al, 2008). The compensatory mechanism of the chitin-rescue phenomenon is not yet fully understood.…”

“…Mean±SEM (n52). (Walker et al, 2008), but has been less well studied in clinical isolates. In an experimental murine model, infection with C. albicans with elevated chitin levels was associated with reduced survival following treatment with caspofungin (Lee et al, 2012).…”