In vitro study of secreted aspartyl proteinases Sap1 to Sap3 and Sap4 to Sap6 expression in Candida albicans pleomorphic forms.

Transition from round budding cells to long hyphal forms and production of secreted aspartic proteases (Saps) are considered virulence-associated factors of Candida albicans. Although plenty of data dealing with Saps involvement in the infection process have been published, Saps expression by the different pleomorphic forms as well as the capacity of C. albicans filaments to express Sap1-6 under serum influence are poorly investigated. In this study, we used immunofluorescence and immunoelectron microscopy for the detection of Sap1-6 isoenzymes in C. albicans pleomorphic cells (blastoconidia, germ tubes, pseudohyphae, true hyphae) grown in Sap-inductive human serum and Sap non-inductive medium - yeast extract-peptone-glucose (YEPD). Isoenzymes were below the detection level in all blastoconidial cells grown in YEPD for 18 h. Sap1-6 expression was hardly detected in C. albicans cells cultivated in serum for 20 min. Increasing level of Sap1-6 expression was observed when C. albicans was incubated for 2, 6 and 18 h in serum corresponding to the development of germ tubes, pseudohyphae and true hyphae. The expression of Sap1-3 in pseudohyphae and true hyphae was more intensive compared to Sap4-6. Thus, we could show that human serum induced hyphae formation and the expression of Sap1-6 were co-regulated.