We are studying the function of host extracellular matrix components in the pathogenesis of Candida albicans. Using in vitro assays to quantify adhesion of C. albicans to immobilized fibronectin and its proteolytic and recombinant fragments and to evaluate binding of soluble fibronectin to C. albicans in suspension, we found that interactions of fibronectin with this organism are not mediated by the Arg-Gly-Asp integrin recognition sequence of fibronectin. High affinity binding, observed following grown in complex medium, is primarily mediated by the collagen-binding domain of fibronectin. A 30 kDa fragment of fibronectin containing the collagen binding domain is as active as intact fibronectin for binding to C. albicans. Expression of fibronectin receptors is tightly regulated by growth conditions. C. albicans grown in defined media do not bind fibronectin. We identified hemoglobin as a highly specific activator of receptor expression, which reversible induces fibronectin binding when added to defined growth medium. This binding is of lower affinity and is mediated by the cell-binding domain of fibronectin. Hemoglobin-inducible binding was observed in all clinical isolates of C. albicans and in other members of the Candida genus. This activation may play an important role in pathogenesis, since only pathogenic strains of C. albicans express hemolytic activity. Inhibitors of this activation process may decrease the pathogenicity of C. albicans. Fibronectin (FN) receptor expression was induced by ferric (Hb+Met, Hb+CN), ferrous (HbCO, HbO2), and cobalt-protoporphyrin derivatives of Hb, whereas globin was inactive. The Hb derivatives all showed saturable, dose-dependent kinetics of FN receptor induction suggesting that Hb may be acting as a receptor ligand. Soluble Hb bound saturably to a low affinity binding site (Kd = 1.1 +/- 0.2 + 10 -6 M) on C. albicans blastospores. However, uptake kinetics of 55FeHb revealed that heme or iron transport into the cell is not requisite for induction, since internalization of 55Fe from Hb did not occur until after induction of FN binding. The serum Hb-binding protein, haptoglobin, specifically abrogated this response, indicating that protein structure rather than the heme ligand or iron is necessary for induction of this signaling pathway. These data demonstrate that C. albicans recognizes Hb through multivalent low affinity interactions, and this may be a host environmental cue that triggers extracellular matrix receptor expression at a septic site. We have identified ESTs for several genes whose expression is induced by hemoglobin. Northern analysis showed that these genes differ in their time-dependence induction by hemoglobin. Genomic clones corresponding to three of the genes were obtained and mapped. One of these encodes a gene related to YDL166c in S. cerevisiae. Disruption of this gene in C. albicans was conditional lethal for growth.

Agency
National Institute of Health (NIH)
Institute
Division of Clinical Sciences - NCI (NCI)
Type
Intramural Research (Z01)
Project #
1Z01SC009173-13
Application #
6558478
Study Section
(LP)
Project Start
Project End
Budget Start
Budget End
Support Year
13
Fiscal Year
2001
Total Cost
Indirect Cost
Name
Clinical Sciences
Department
Type
DUNS #
City
State
Country
United States
Zip Code
Navarathna, Dhammika H; Roberts, David D; Munasinghe, Jeeva et al. (2016) Imaging Candida Infections in the Host. Methods Mol Biol 1356:69-78
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Pendrak, Michael L; Roberts, David D (2007) Hemoglobin is an effective inducer of hyphal differentiation in Candida albicans. Med Mycol 45:61-71
Pendrak, Michael L; Rodrigues, Rui G; Roberts, David D (2007) Induction of a high affinity fibronectin receptor in Candida albicans by caspofungin: requirements for beta (1,6) glucans and the developmental regulator Hbr1p. Med Mycol 45:157-68
Pendrak, Michael L; Yan, S Steve; Roberts, David D (2004) Sensing the host environment: recognition of hemoglobin by the pathogenic yeast Candida albicans. Arch Biochem Biophys 426:148-56
Pendrak, Michael L; Yan, S Steve; Roberts, David D (2004) Hemoglobin regulates expression of an activator of mating-type locus alpha genes in Candida albicans. Eukaryot Cell 3:764-75
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Pendrak, M L; Krutzsch, H C; Roberts, D D (2000) Structural requirements for hemoglobin to induce fibronectin receptor expression in Candida albicans. Biochemistry 39:16110-8
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