Candida albicans Sfp1 Is Involved in the Cell Wall and Endoplasmic Reticulum Stress Responses Induced by Human Antimicrobial Peptide LL-37

Abstract

Candida albicans is a commensal fungus of humans but can cause infections, particularly in immunocompromised individuals, ranging from superficial to life-threatening systemic infections. The cell wall is the outermost layer of C. albicans that interacts with the host environment. Moreover, antimicrobial peptides (AMPs) are important components in innate immunity and play crucial roles in host defense. Our previous studies showed that the human AMP LL-37 binds to the cell wall of C. albicans, alters the cell wall integrity (CWI) and affects cell adhesion of this pathogen. In this study, we aimed to further investigate the molecular mechanisms underlying the C. albicans response to LL-37. We found that LL-37 causes cell wall stress, activates unfolded protein response (UPR) signaling related to the endoplasmic reticulum (ER), induces ER-derived reactive oxygen species and affects protein secretion. Interestingly, the deletion of the SFP1 gene encoding a transcription factor reduced C. albicans susceptibility to LL-37, which is cell wall-associated. Moreover, in the presence of LL-37, deletion of SFP1 attenuated the UPR pathway, upregulated oxidative stress responsive (OSR) genes and affected bovine serum albumin (BSA) degradation by secreted proteases. Therefore, these findings suggested that Sfp1 positively regulates cell wall integrity and ER homeostasis upon treatment with LL-37 and shed light on pathogen-host interactions.

Associations of Rap1 with Cell Wall Integrity, Biofilm Formation, and Virulence in Candida albicans

“…Baker], 1% Triton X-100 [United States Biological, Salem, MA, USA], 4 μM leupeptin, 0.2 mM phenylmethylsulfonyl fluoride [PMSF], 1 mM Na 3 VO 4 , 1 mM NaF [Fluka], 1 μM pepstatin A, and 1 μg/mL aprotinin). Cells were disrupted by vortexing with acid-washed glass beads, and total proteins were extracted as previously described ( 86 ). The total protein concentration was determined using a Bradford protein assay kit (Bio-Rad).…”

“…To detect activation of the Mkc1, Cek1, and Hog1 MAP kinases, proteins were resolved using 10% sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE) as previously described ( 86 ). For Western blotting, anti-phospho-p44/42 MAPK antibody (catalog no.…”

The Tricalbin-Family Endoplasmic Reticulum-Plasma Membrane Tethering Proteins Attenuate ROS-Involved Caspofungin Sensitivity in Candida albicans

“…Ero1 is a conserved oxidoreductase in the ER that is critical for protein disulfide bond formation ( 30 ), which constitutes the main source of ER-derived ROS ( 31 ). We previously found that cell wall stress agents (e.g., CFW, caspofungin) enhanced Ero1 oxidation in the ER, leading to ROS accumulation and fungal cell death ( 25 ).…”

Antimicrobial Peptides with Anti-Candida Activity

“…According to these results, LL-37 alters and even fractures the membrane morphology of the fungus, as was observed by freeze-fracture electron microscopy [ 67 ]. Apart from that, LL-37 also causes cell wall and endoplasmic reticulum stresses in C. albicans [ 74 ].…”