The Candida albicans histidine kinase Chk1p: Signaling and cell wall mannan

Abstract

Several published functions associated with the CHK1 histidine kinase of Candida albicans resemble those of the MAPK Cek1p and its cognate receptor Sho1p (SSU81). To explore this further, we have compared mutants lacking the proteins mentioned above and have constructed a double sho1/ chk1Δ null mutant to determine relationships among these proteins. We observed that the sensitivity to Congo red (CR), calcofluor white (CW), as well as clumping of cells, was slightly increased in the double mutant compared to the single chk1Δ or sho1Δ mutants. However, Cek1p phosphorylation via Sho1p, which occurs during log phase growth in the presence or absence of CR in Wt cells, does not require Chk1p. These data suggest that Chk1p and Sho1p are components of parallel but independent signal pathways. In addition, bulk mannan of strains was analyzed by GPC/MS and NMR. Compared to Wt and a CHK1 gene-reconstituted strain (CHK23) that contained, high, intermediate and low Mw mannan species, we found that the mannan of strains CHK21 (chk1Δ null), the cek1Δ null, and the double mutant consisted only of low Mw mannan. The sho1Δ null mutant only demonstrated a reduced intermediate type of mannan. Alcian blue binding was lower in cek1Δ, chk1Δ, and the double sho1/chk1Δ null mutant lacking high and intermediate Mw mannan than in the sho1Δ null which had a partial loss of intermediate Mw mannan only. We conclude that the Chk1p HK is part of a functionally similar but parallel pathway to the Sho1p-Cek1p pathway that confers resistance to the cell wall inhibitors CR and CW. However, a functional relationship in mannan biosynthesis of Chk1p and Cek1p exists that only partially requires Sho1p.

Two-Component Histidine Phosphotransfer Protein Ypd1 Is Not Essential for Viability in Candida albicans

“…We present data here showing that deletion of YPD1 is not a lethal event in C. albicans. Data obtained from our comprehensive analysis of the ypd1⌬/⌬ mutant and from earlier studies with the Chk1 histidine kinase (37,42,43) and the Ssk1 and Skn7 response regulators (20,27,33) support the idea of substantial rewiring of two-component signaling pathways in C. albicans compared to S. cerevisiae. At present, the molecular genetic basis for this difference in regulation is not understood, but it may be explained by the presence of a robust Sho1-mediated or alternate pathway that bypasses Ssk1 and Sln1 in C. albicans.…”

The Cek1‑mediated MAP kinase pathway regulates exposure of α‑1,2 and β‑1,2‑mannosides in the cell wall ofCandida albicansmodulating immune recognition

“…67 In fact, cek1 mutant induces higher levels of IL-10 and TNF-a during murine macrophage interaction compared to the wild type strain, which is in accordance to previously reported data. 43 The data presented here demonstrating the increased levels of a-M and b-M in cek1 mutants, together with the already published results describing an alteration of the structural integrity of cell wall mannans in these strains, 68 show that the absence of the Cek1 MAPK has a strong impact on the fungal cell wall architecture and consequent glycans exposure/expression.…”

Deletion of the Candida albicans histidine kinase gene CHK1 improves recognition by phagocytes through an increased exposure of cell wall β-1,3-glucans

“…In Dchk1, the accessibility of b-1,3-glucans is increased Earlier studies had shown that cell wall mannans of CHK1-deficient C. albicans yeasts are significantly truncated and that the glucan content is also lower than in the wild-type strain (Kruppa et al, 2003;Li et al, 2009). The inner b-glucan layer of the C. albicans cell wall is known to be shielded by these mannan chains (Netea et al, 2008;Wheeler & Fink, 2006).…”

“…A well-known example is the pathway from the histidine kinase Casln1p to the MAP kinase CaHog1p via the response regulator CaSsk1p. Recently, for Chk1p, a functional relationship with the MAP kinase Cek1p has been shown for some phenotypes, which also include mannan biosynthesis (Li et al, 2009). Moreover, it has been shown that Cek1p is also involved in b-1,3-glucan masking and correspondingly influences immune defence reactions (Galán-Diez et al, 2010).…”