The Candida albicans stress response gene Stomatin-Like Protein 3 is implicated in ROS-induced apoptotic-like death of yeast phase cells

Abstract

The ubiquitous presence of SPFH (Stomatin, Prohibitin, Flotillin, HflK/HflC) proteins in all domains of life suggests that their function would be conserved. However, SPFH functions are diverse with organism-specific attributes. SPFH proteins play critical roles in physiological processes such as mechanosensation and respiration. Here, we characterize the stomatin ORF19.7296/SLP3 in the opportunistic human pathogen Candida albicans. Consistent with the localization of stomatin proteins, a Slp3p-Yfp fusion protein formed visible puncta along the plasma membrane. We also visualized Slp3p within the vacuolar lumen. Slp3p primary sequence analyses identified four putative S-palmitoylation sites, which may facilitate membrane localization and are conserved features of stomatins. Plasma membrane insertion sequences are present in mammalian and nematode SPFH proteins, but are absent in Slp3p. Strikingly, Slp3p was present in yeast cells, but was absent in hyphal cells, thus categorizing it as a yeast-phase specific protein. Slp3p membrane fluorescence significantly increased in response to cellular stress caused by plasma membrane, cell wall, oxidative, or osmotic perturbants, implicating SLP3 as a general stress-response gene. A slp3Δ/Δ homozygous null mutant had no detected phenotype when slp3Δ/Δ mutants were grown in the presence of a variety of stress agents. Also, we did not observe a defect in ion accumulation, filamentation, endocytosis, vacuolar structure and function, cell wall structure, or cytoskeletal structure. However, SLP3 over-expression triggered apoptotic-like death following prolonged exposure to oxidative stress or when cells were induced to form hyphae. Our findings reveal the cellular localization of Slp3p, and for the first time associate Slp3p function with the oxidative stress response.

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

“…Growth assays on solid and liquid nutrient growth medium were performed as previously described [70]. Briefly, C. albicans overnight cultures were diluted to a starting OD 600nm of 3.0.…”

Fungal plasma membrane domains

“…Very few fungal members of the family have been studied to date, including the prohibitins Phb1 and Phb2 of S. cerevisiae, and the Stomatin StoB of A. nidulans, which localize at the inner mitochondrial membrane (Osman et al 2006;Takeshita, Diallinas and Fischer 2012). The only plasma membrane-bound fungal SPFH members studied are the Flotillin FloA and the Stomatin StoA of A. nidulans (Takeshita, Diallinas and Fischer 2012), as well as the Stomatin-like protein Slp3 of C. albicans (Conrad et al 2018). FloA or StoA have no obvious orthologues in S. cerevisiae.…”

“…StoA alone did not significantly affect the formation of SRDs, however the floAΔ stoAΔ double mutant showed severely abnormal hyphae due to defects in the formation of SRDs. Intriguingly, the sole stomatin studied in C. albicans, Slp3, is a single cell-phase specific protein that is not expressed in the hyphae of this yeast (Conrad et al 2018). Its expression is altered in response to several stress conditions, while it is induced in the late stationary phase of growth.…”

SUMOylation in Human Pathogenic Fungi: Role in Physiology and Virulence

“…Of note, CaWOS1 loss had no effect on the virulence of C. albicans in mice, however, its overexpression led to attenuated virulence [91]. Consistent with the central role of SUMOylation in modulation of the virulence traits of C. albicans, a potential SUMOylation site in the yeast phase-specific protein CaSlp3 (Stomatin Like Protein 3), that may be involved in its targeting to the plasma membrane and the vacuole, has recently been identified [96]. Of note, Slp3 in C. albicans has also been shown to be an oxidative stress response protein, whose overproduction resulted in mitochondrial depolarization and apoptotic-like cell death upon prolonged oxidative stress [96].…”