Misexpression of the opaque-phase-specific gene PEP1 (SAP1) in the white phase of Candida albicans confers increased virulence in a mouse model of cutaneous infection.

Candida albicans WO-1 switches reversibly and at high frequency between a white and an opaque colony-forming phenotype that includes dramatic changes in cell morphology and physiology. A misexpression strategy has been used to investigate the role of the opaque-phase-specific gene PEP1 (SAP1), which encodes a secreted aspartyl proteinase, in the expression of the unique opaque-phase phenotype and phase-specific virulence in two animal models. The PEP1 (SAP1) open reading frame was inserted downstream of the promoter of the white-phase-specific gene WH11 in the transforming vector pCPW7, and the resulting transformants were demonstrated to misexpress PEP1 (SAP1) in the white phase. Misexpression did not confer any of the unique morphological characteristics of the opaque phase to cells in the white phase and had no effect on the switching process. However, misexpression conferred upon white-phase cells the increased capacity of opaque-phase cells to grow in medium in which protein was the sole nitrogen source. Misexpression of PEP1 (SAP1) had no effect on the virulence of white-phase cells in a systemic mouse model, in which white-phase cells were already more virulent than opaque-phase cells. Misexpression did, however, confer upon white-phase cells the dramatic increase in colonization of skin in a cutaneous mouse model that was exhibited by opaque-phase cells. Misexpression of PEP1 (SAP1) conferred upon white-phase cells two dissociable opaque-phase characteristics: increased adhesion and the capacity to cavitate skin. The addition of pepstatin A to the cutaneous model inhibited the latter, but not the former, suggesting that the latter is effected by released enzyme, while the former is effected by cell-associated enzyme.