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

Abstract

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 Sapl-6 under serum influence are poorly investigated. In this study, we used immunofluorescence and immunoelectron microscopy for the detection of Sapl-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. Sapl-6 expression was hardly detected in C. albicans cells cultivated in serum for 20 min. Increasing level of Sapl-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 Sapl-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 Sapl-6 were co-regulated.