Functional Characterization of the Small Heat Shock Protein Hsp12p from Candida albicans

Abstract

Hsp12p is considered to be a small heat shock protein and conserved among fungal species. To investigate the expression of this heat shock protein in the fungal pathogen Candida albicans we developed an anti-CaHsp12p antibody. We show that this protein is induced during stationary phase growth and under stress conditions including heat shock, osmotic, oxidative and heavy metal stress. Furthermore, we find that CaHsp12p expression is influenced by the quorum sensing molecule farnesol, the change of CO2 concentration and pH. Notably we show that the key transcription factor Efg1p acts as a positive regulator of CaHsp12p in response to heat shock and oxidative stress and demonstrate that CaHsp12p expression is additionally modulated by Hog1p and the cAMP-PKA signaling pathway. To study the function of Hsp12p in C. albicans we generated a null mutant, in which all four CaHSP12 genes have been deleted. Phenotypic analysis of the strain shows that CaHSP12 is not essential for stress resistance, morphogenesis or virulence when tested in a Drosophila model of infection. However, when overexpressed, CaHSP12 significantly enhanced cell-cell adhesion, germ tube formation and susceptibility to azole antifungal agents whilst desensitizing C. albicans to the quorum sensing molecule farnesol.

Heat shock protein 9 mRNA expression increases during fruiting body differentiation in Grifola frondosa and other edible mushrooms

“…Possibly, HSP9 is required for cell-to-cell adhesion in a large structure like a mushroom. This function was suggested by the fact that overexpression of HSP12 in C. albicans significantly enhanced aggregation of cells (Fu et al 2012). We predict that a DHSP9 mutant of Grifola frondosa will display fruiting body hypoplasia.…”

“…However, expression of S. cerevisiae HSP12 and S. pombe HSP9 was induced after heat shock of 40 min or 60 min at 37 C (Praekelt and Meacock 1990;Orlandi I et al 1996). Expression of C. albicans HSP12 could be induced after a heat shock of 10 min at 45 C (Fu et al 2012). Analysis of the G. frondosa promoter sequence and gene expression pattern suggested that Gf.HSP9 might not be induced by heat shock alone.…”

“…Analysis of the G. frondosa promoter sequence and gene expression pattern suggested that Gf.HSP9 might not be induced by heat shock alone. In C. albicans, HSP12 is co-regulated by physiological CO 2 and pH (Fu et al 2012); however, S. cerevisiae HSP12 was unaffected by the growth medium's pH (Sheth et al 2008). Therefore, how HSP9/12 responds to different types of stress maybe species-dependent.…”

“…Analysis of a deletion mutant of DHSP12 suggested the HSP12 gene is important for the survival of S. cerevisiae against heat shock, oxidative stress, osmotic stress, and cellular aging (Welker et al 2010). HSP9/12, a homolog of S. cerevisiae HSP12 in Schizosaccharomyces pombe and Candida albicans, undergoes the same elevation in expression at HSP12 upon entry into the stationary phase and in response to stress (Orlandi et al 1996;Ahn et al 2011;Fu et al 2012). Thus, fungal HSP9/12 likely also plays an important role in stress adaptation.…”

Candida Survival Strategies

“…In addition, six small heat shock proteins (sHsps), that have to form multimeres to bind their client proteins, have been predicted in C. albicans (Mayer et al, 2013a). These include Hsp12 and Hsp21, which are both upregulated under a variety of stress conditions (Fu, De Sordi, & Muhlschlegel, 2012;Mayer, Wilson, & Hube, 2013b;Mayer, Wilson, Jacobsen, Miramon, Slesiona, et al, 2012). In addition, thermal and oxidative stress lead to the intracellular accumulation of trehalose, which can function as a "chemical chaperone" by stabilizing protein folding (Brown, Budge, et al, 2014).…”