Mms21: A Putative SUMO E3 Ligase in Candida albicans That Negatively Regulates Invasiveness and Filamentation, and Is Required for the Genotoxic and Cellular Stress Response

Abstract

In the life cycle of the fungal pathogen Candida albicans, the formation of filamentous cells is a differentiation process that is critically involved in host tissue invasion, and in adaptation to host cell and environmental stresses. Here, we have used the Gene Replacement And Conditional Expression library to identify genes controlling invasiveness and filamentation; conditional repression of the library revealed 69 mutants that triggered these processes. Intriguingly, the genes encoding the small ubiquitin-like modifier (SUMO) E3 ligase Mms21, and all other tested members of the sumoylation pathway, were both nonessential and capable of triggering filamentation upon repression, suggesting an important role for sumoylation in controlling filamentation in C. albicans. We have investigated Mms21 in detail. Both Mms21 nulls (mms21D/D) and SP [Siz/Pias (protein inhibitor of activated signal transducer and activator of transcription)] domain (SUMO E3 ligase domain)-deleted mutants displayed invasiveness, filamentation, and abnormal nuclear segregation; filament formation occurred even in the absence of the hyphal transcription factor Efg1. Transcriptional analysis of mms21D/D showed an increase in expression from two-to eightfold above that of the wild-type for hyphal-specific genes, including ECE1, PGA13, PGA26, HWP1, ALS1, ALS3, SOD4, SOD5, UME6, and HGC1. The Mms21-deleted mutants were unable to recover from DNA-damaging agents like methyl methane sulfonate, hydroxyurea, hydrogen peroxide, and UV radiation, suggesting that the protein is important for genotoxic stress responses. In addition, the mms21D/D mutant displayed sensitivity to cell wall and thermal stresses, and to different antifungal drugs. All these findings suggest that Mms21 plays important roles in cellular differentiation, DNA damage and cellular stress responses, and in response to antifungal drugs.

SUMOylation in Human Pathogenic Fungi: Role in Physiology and Virulence

“…In agreement with this, the smt3∆/smt3∆ cells were found to be sensitive to several stresses including thermal, oxidative, unfolded protein, cell wall and antifungal stresses, and contained high chitin in the cell wall [11]. Importantly, the C. albicans mms21∆/mms21∆ mutant also exhibited slow growth, thermal stress susceptibility, nuclear segregation defects, increased invasiveness, unregulated filamentation and diminished recovery from DNA damage [92]. This mutant also showed sensitivity to cell wall stressors, and azole and echinocandin antifungal drugs [92].…”

“…As shown in Table 2, C. albicans has a sole Smt3 SUMO protein, three Ulp domain-containing proteins CaUlp1, CaUlp2 and CaUlp3, a heterodimeric E1 activating enzyme complex of CaAos1 and CaUba2, the E2 enzyme CaUbc9, and E3 ligases CaSiz1, CaMms21, CaCst9 and CaWos1. Among these SUMOylation components, CaSmt3, CaAos1, CaUba2, CaUbc9 and CaMms21 are not essential for cell viability [92].…”

“…[90]. Over the past decade, SUMOylation has been studied in two Candida species, C. albicans and C. glabrata, and its role in Candida pathogenesis is beginning to be appreciated [11,13,91,92].…”

“…Importantly, the C. albicans mms21∆/mms21∆ mutant also exhibited slow growth, thermal stress susceptibility, nuclear segregation defects, increased invasiveness, unregulated filamentation and diminished recovery from DNA damage [92]. This mutant also showed sensitivity to cell wall stressors, and azole and echinocandin antifungal drugs [92].…”

Comparative Analysis of Virulence Factors of Homozygous and Heterozygous Strains of Candida albicans Vaginal Isolates

“…Candida albicans secretes hydrolytic enzymes, such as lipases, proteases, phospholipases, and hemolysin, which are considered to be integral to their virulence and pathogenesis. Expression of several genes, including ALS1 , ALS3 , ECE1 , and HWP1 , is required for systemic candidiasis [ 2 ]. In particular, the gene hyphal wall protein 1 ( HWP1 ) is known to encode a major C. albicans protein involved in several functions, including assemblage of cell wall, intracellular signaling, and hyphal expansion by cross-linking to the glucans of cell wall [ 3 , 4 ].…”