SPECIFIC INDUCTION OF FIBRONECTIN-BINDING ACTIVITY BY HEMOGLOBIN IN CANDIDA-ALBICANS GROWN IN DEFINED MEDIA

Fibronectin (FN) is a major component of host estracellular matrix tha t may play an important role in the initiation and dissemination of Ca ndida albicans infections. Expression of FN binding requires growth of C. albicans blastoconidia in complex medium, and the regulation of FN receptor expression is poorly understood. We now demonstrate that hem oglobin is a potent and specific inducer of FN receptor expression and describe a defined medium supplemented with hemoglobin that greatly a nd stably enhances the binding activity of C. albicans for soluble FN. Enhancement of FN binding by hemoglobin in strain 44807 was concentra tion dependent and was maximal at 0.1% hemoglobin with 20- to 80-fold enhancement. The hemoglobin-induced FN binding to C. albicans was satu rable, with a K-d of 2.7 x 10(-8) M. Enhancement required growth of C. albicans in hemoglobin-containing medium, since simply exposing blast oconidia to hemoglobin in a nongrowing status did not enhance binding. Induction was reversible following removal of hemoglobin from the gro wth medium and not associated with germination. Inorganic or protein-b ound iron was not sufficient for the induction, since other iron-conta ining proteins or inorganic iron salts were inactive. Growth in the si mple medium yeast nitrogen base supplemented with hemoglobin increased cell adhesion to immobilized FN and to cultured monolayers of bovine corneal endothelial cells. These data suggest that hemoglobin may be a n important regulator of FN binding activity in C. albicans and thus m ay play a role in its pathogenesis.