An expanded cell wall damage signaling network is comprised of the transcription factors Rlm1 and Sko1 in Candida albicans

PLoS Genet. 2020 Jul 8;16(7):e1008908. doi: 10.1371/journal.pgen.1008908. eCollection 2020 Jul.

Abstract

The human fungal pathogen Candida albicans is constantly exposed to environmental challenges impacting the cell wall. Signaling pathways coordinate stress adaptation and are essential for commensalism and virulence. The transcription factors Sko1, Cas5, and Rlm1 control the response to cell wall stress caused by the antifungal drug caspofungin. Here, we expand the Sko1 and Rlm1 transcriptional circuit and demonstrate that Rlm1 activates Sko1 cell wall stress signaling. Caspofungin-induced transcription of SKO1 and several Sko1-dependent cell wall integrity genes are attenuated in an rlm1Δ/Δ mutant strain when compared to the treated wild-type strain but not in a cas5Δ/Δ mutant strain. Genome-wide chromatin immunoprecipitation (ChIP-seq) results revealed numerous Sko1 and Rlm1 directly bound target genes in the presence of caspofungin that were undetected in previous gene expression studies. Notable targets include genes involved in cell wall integrity, osmolarity, and cellular aggregation, as well as several uncharacterized genes. Interestingly, we found that Rlm1 does not bind to the upstream intergenic region of SKO1 in the presence of caspofungin, indicating that Rlm1 indirectly controls caspofungin-induced SKO1 transcription. In addition, we discovered that caspofungin-induced SKO1 transcription occurs through self-activation. Based on our ChIP-seq data, we also discovered an Rlm1 consensus motif unique to C. albicans. For Sko1, we found a consensus motif similar to the known Sko1 motif for Saccharomyces cerevisiae. Growth assays showed that SKO1 overexpression suppressed caspofungin hypersensitivity in an rlm1Δ/Δ mutant strain. In addition, overexpression of the glycerol phosphatase, RHR2, suppressed caspofungin hypersensitivity specifically in a sko1Δ/Δ mutant strain. Our findings link the Sko1 and Rlm1 signaling pathways, identify new biological roles for Sko1 and Rlm1, and highlight the complex dynamics underlying cell wall signaling.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antifungal Agents / pharmacology
  • Basic-Leucine Zipper Transcription Factors / genetics*
  • Candida albicans / drug effects*
  • Candida albicans / genetics
  • Candida albicans / pathogenicity
  • Caspofungin / pharmacology*
  • Cell Wall / drug effects
  • Cell Wall / genetics
  • Fungal Proteins / genetics
  • Gene Expression Regulation, Fungal
  • Humans
  • MADS Domain Proteins / genetics*
  • Phosphorylation / drug effects
  • Repressor Proteins / genetics*
  • Saccharomyces cerevisiae / genetics
  • Saccharomyces cerevisiae Proteins / genetics*
  • Signal Transduction / drug effects
  • Transcription Factors / genetics

Substances

  • Antifungal Agents
  • Basic-Leucine Zipper Transcription Factors
  • Fungal Proteins
  • MADS Domain Proteins
  • RLM1 protein, S cerevisiae
  • Repressor Proteins
  • SKO1 protein, S cerevisiae
  • Saccharomyces cerevisiae Proteins
  • Transcription Factors
  • Caspofungin