Curcumin Targets Cell Wall Integrity via Calcineurin-Mediated Signaling in Candida albicans

Curcumin (CUR) shows antifungal activity against a range of pathogenic fungi, including Candida albicans. The reported mechanisms of action of CUR include reactive oxygen species (ROS) generation, defects in the ergosterol biosynthesis pathway, decrease in hyphal development, and modulation of multidrug efflux pumps. Reportedly, each of these pathways is independently linked to the cell wall machinery in C. albicans, but surprisingly, CUR has not been previously implicated in cell wall damage. In the present study, we performed transcriptional profiling to identify the yet-unidentified targets of CUR in C. albicans. We found that, among 348 CUR-affected genes, 51 were upregulated and 297 were downregulated. Interestingly, most of the cell wall integrity pathway genes were downregulated. The possibility of the cell wall playing a critical role in the mechanism of CUR required further validation; therefore, we performed specific experiments to establish if there was any link between the two. The fractional inhibitory concentration index values of 0.24 to 0.37 show that CUR interacts synergistically with cell wall-perturbing (CWP) agents (caspofungin, calcofluor white, Congo red, and SDS). Furthermore, we could observe cell wall damage and membrane permeabilization by CUR alone, as well as synergistically with CWP agents. We also found hypersusceptibility in calcineurin and mitogen-activated protein (MAP) kinase pathway mutants against CUR, which confirmed that CUR also targets cell wall biosynthesis in C. albicans. Together, these data provide strong evidence that CUR disrupts cell wall integrity in C. albicans. This new information on the mechanistic action of CUR could be employed in improving treatment strategies and in combinatorial drug therapy.