Candida albicans CHK1 gene regulates its cross-kingdom interactions with Streptococcus mutans to promote caries

The cross-kingdom interactions between Candida albicans and Streptococcus mutans have played important roles in early childhood caries (ECC). However, the key pathways of C. albicans promoting the cariogenicity of S. mutans are still unclear. Here, we found that C. albicans CHK1 gene was highly upregulated in their dual-species biofilms. C. albicans chk1Δ/Δ significantly reduced the synergistical growth promotion, biofilm formation, and exopolysaccharides (EPS) production of S. mutans, the key cariogenic agent, compared to C. albicans wild type (WT) and CHK1 complementary strains. C. albicans WT upregulated the expressions of S. mutans EPS biosynthesis genes gtfB, gtfC, and gtfD, and their regulatory genes vicR and vicK, but chk1Δ/Δ had no effects. Both C. albicans WT and chk1Δ/Δ failed to promote the biofilm formation and EPS production of S. mutans ΔvicK and antisense-vicR strains, indicating that C. albicans CHK1 upregulated S. mutans vicR and vicK to increase the EPS biosynthesis gene expression, then enhanced the EPS production and biofilm formation to promote the cariogenicity. In rat caries model, the coinfection with chk1Δ/Δ and S. mutans decreased the colonization of S. mutans and developed less caries especially the severe caries compared to that from the combinations of S. mutans with C. albicans WT, indicating the essential role of C. albicans CHK1 gene in the development of dental caries. Our study for the first time demonstrated the key roles of C. albicans CHK1 gene in dental caries and suggested that it may be a practical target to reduce or treat ECC. KEY POINTS: • C. albicans CHK1 gene is important for its interaction with S. mutans. • CHK1 regulates S. mutans two-component system to promote its cariogenicity. • CHK1 gene regulates the cariogenicity of S. mutans in rat dental caries.

Candida albicans CHK1 gene from two-component system is essential for its pathogenicity in oral candidiasis

The roles of Candida albicans CHK1, a key gene from two-component system, in oral mucosal infection are not clear. This study evaluated the key roles of CHK1 gene in vitro and in vivo. The expression of CHK1 and its regulated virulence factors were tested during the oral epithelial cell infection. The production of lactate dehydrogenase, ROS, and IL-1α combined with the confocal and scanning electron microscope observation was employed to identify the capability of CHK1 in damaging the epithelial cells. Both immunocompetent and immunodeficient mice oropharyngeal infection models were involved to confirm the roles of CHK1 gene in vivo. The expression of CHK1 gene was significantly increased during the oral epithelial cell infection. The chk1Δ/Δ mutant failed to damage the epithelial cells or induce IL-α and ROS production. Interestingly, chk1Δ/Δ can also form the similar hyphae with WT and complementary strains. Accordingly, chk1Δ/Δ did not affect the adhesion and invasion rates of C. albicans to oral epithelial cells. However, chk1Δ/Δ significantly decreased the expression levels of the virulence factors, including ALS2, SAP6, and YWP1. The chk1Δ/Δ also failed to cause oral candidiasis in both immunocompetent and immunodeficient mice indicating that CHK1 gene from the two-component system is essential for the pathogenicity of C. albicans. KEY POINTS: • CHK1gene is essential for C. albicans in oral candidiasis • C. albicans without CHK1 gene can form "non-pathogenic" hyphae. • CHK1 gene regulates the virulence of C. albicans.