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Candida albicans expresses at least two biochemically distinct fibronectin receptors. Hemoglobin induces expression of a low affinity receptor recognizing the fibronectin cell-binding domain, whereas growth in complex media induces a high affinity receptor recognizing the collagen-binding domain. We now show that sub-inhibitory concentrations of caspofungin and nikkomycin Z, but not fluconazole, induce the high affinity fibronectin receptor in a dose-dependent manner. Macromolecular complexes mechanically sheared from caspofungin-treated cells retained high affinity fibronectin binding that was sensitive to protease, disulfide reduction, and beta (1,3) glucanase digestion. The high affinity fibronectin receptor was not inducible in a Kre9 mutant strain of C. albicans deficient in beta (1,6) glucans. Conversely, a mutant strain lacking the fibronectin binding protein Als5p showed no defects in induction of high or low affinity fibronectin receptors. Heterozygous mutants of a regulator of white-opaque phenotypic switching, HBR1, lacked any detectable high affinity fibronectin receptor expression in response to caspofungin, and re-introduction of the gene restored activity. Therefore, sub-inhibitory dosages of caspofungin induce a high affinity fibronectin receptor that is distinct from the known receptor Als5p and is dependent on beta (1,6) glucans and HBR1.

The recognition of extracellular matrix components can be regulated by conformational changes that alter the activity of cell surface integrins. We now demonstrate that conformational regulation of the matrix glycoprotein thrombospondin-1 (TSP1) can also modulate its binding to an integrin receptor. F18 1G8 is a conformation-sensitive TSP1 antibody that binds weakly to soluble TSP1 in the presence of divalent cations. However, binding of the antibody to melanoma cells was strongly stimulated by adding exogenous TSP1 in the presence of calcium, suggesting that TSP1 undergoes a conformational change following its binding to the cell surface. This conformation was not induced by known cell surface TSP1 receptors, whereas binding of F18 was stimulated when TSP1 bound to fibronectin but not to heparin or fibrinogen. Conversely, binding of F18 to TSP1 enhanced TSP1 binding to fibronectin. Exogenous fibronectin also stimulated TSP1-dependent binding of F18 to melanoma cells. Binding of the fibronectin-TSP1 complex to melanoma cells was mediated by alpha4beta1 and alpha5beta1 integrins. Furthermore, binding to F18 or fibronectin strongly enhanced the adhesive activity of immobilized TSP1 for some cell types. This enhancement of adhesion was mediated by alpha3beta1 integrin and required that the alpha3beta1 integrin be in an active state. Fibronectin also enhanced TSP1 binding to purified alpha3beta1 integrin. Therefore, both fibronectin and the F18 antibody induce conformational changes in TSP1 that enhance the ability of TSP1 to be recognized by alpha3beta1 integrin. The conformational and functional regulation of TSP1 activity by fibronectin represents a novel mechanism for extracellular signal transduction.

Candida albicans is one of the most common human opportunistic pathogens and causes a variety of diseases, from superficial candidiasis to systemic infections in immunocompromised hosts (7). The adhesion of C. albicans to host tissues, mediated through binding to various extracellular matrix proteins such as fibronectin (FN) and laminin, is correlated with pathogenicity (4, 6, 12, 14, 19). FN is a major component of the host extracellular matrix that may play an important role in the initiation and dissemination of C. albicans infections (6, 14, 18). As has been found for mammalian cells (23) and some pathogenic bacteria (5, 20), several domains of FN are recognized by C. albicans. Klotz and Smith (13) suggested that the cell-binding domain of FN mediated its binding to C. albicans. Further evidence indicated that peptides containing the RGD sequence from this domain inhibit the binding of C. albicans to FN both in solution and in adhesion assays (19). Additional domains of FN, however, have been found to interact with C. albicans (18). Four domains of FN can interact with C. albicans grown in Sabouraud dextrose medium (18). Among them, a proteolytic fragment from the gelatin- and collagen-binding domain of FN exhibited the highest affinity, i.e., it was as potent as intact FN. However, all of these interactions of C. albicans with FN were studied by using cultures grown in complex media. We have previously reported that hemoglobin induces a specific enhancement of FN-binding activity in C. albicans grown in defined medium (24). This induction is reversible and is not due to a bridge effect of hemoglobin between a receptor on the organism and FN. In addition, adhesion to immobilized FN was significantly increased for C. albicans grown in hemoglobin-containing medium. Because cells must be growing in the presence of hemoglobin for several hours to induce binding, expression of a specific FN receptor may be induced by hemoglobin. We have now used these defined growth conditions to determine which domain of FN is recognized by the receptors induced by hemoglobin. We report here that binding and adhesion to the cell-binding domain are specifically induced by hemoglobin. This binding was localized to the 9th through 13th type III repeats of the cell-binding domain of FN but does not require the RGD sequence in the 10th type III repeat. Therefore, hemoglobin in defined medium specifically induces a class of receptors in C. albicans with a specificity different from those previously reported for this organism.

Host infection by the pathogenic fungusCandida albicans is initiated by adhesion and mediated by binding to several host extracellular matrix proteins. Previously, we demonstrated that hemoglobin supplemented into a chemically defined medium significantly and specifically induced fibronectin binding toC. albicans. We now report that hemoglobin also induces binding of laminin, fibrinogen, and type IV collagen but not of thrombospondin-1 or type I collagen. The binding of each protein was inhibited by the respective unlabeled ligand in a concentration-dependent manner. Fibrinogen inhibited the binding of radiolabeled fibronectin, laminin, and fibrinogen with similar IC50 values, suggesting that a single promiscuous receptor recognizes these three proteins. Competitive binding studies indicated that a second class of receptor binds specifically to laminin. Growth of C. albicans in the presence of hemoglobin also increased cell adhesion to immobilized fibronectin, laminin, fibrinogen, and type IV collagen but not to thrombospondin-1 or type I collagen. Exposure to hemoglobin induced increased orde novo expression of several surface proteins on C. albicans. One of these proteins with a molecular weight of 55,000 recognized fibronectin, based on ligand protection and affinity chromatography on immobilized fibronectin. Thus, hemoglobin induces both promiscuous and specific receptors for extracellular matrix proteins and, therefore, may regulate matrix adhesion during dissemination of C. albicans infections.

We describe the findings of anhidrotic/hypohidrotic ectodermal dysplasia in three successive generations of a family. All three women had variable alopecia, anhidrosis, hypodontia and malar hypoplasia. Chromosomal studies revealed a defect of the 2q12 region in all three patients. Previous studies have reported rare cases of autosomal dominant ectodermal dysplasia associated with defects in the 2q11-13 region1. These rare disorders are characterized by common anomalies of at least two elements of the ectoderm and its appendages--namely, the skin, teeth, hair, nails and sweat glands. These patients also frequently have chronic dental problems with early loss of teeth and recurrent lung, ear and nose infections secondary to a defect in mucous membrane function. The majority of reported cases of ectodermal dysplasias have historically been X-linked recessive, but our findings indicate that an autosomal version may be more prevalent than previously thought.

BACKGROUND: There has been great debate surrounding the appropriate treatment regimens in children who present with acute asthma exacerbations secondary to upper respiratory tract infections. OBJECTIVE: To determine whether treatment with corticosteroids alone or in combination with antibiotics will decrease respiratory symptoms in children who develop asthma exacerbations secondary to upper respiratory tract infections. METHODS: A retrospective cohort control study involving 86 African-American children, ages 5-16, with mild intermittent asthma. The patients were treated with an albuterol inhaler (control group), inhaler plus five days of Prednisone; or inhaler, Prednisone, and 10 days of Amoxicillin. All patients were assessed regarding peak flows, albuterol inhaler usage, and symptomatology. RESULTS: On follow up five- to seven days after presentation, the corticosteroids group demonstrated a marked improvement in peak flows (88% versus 77%) and a significantly lower albuterol inhaler usage rate (2.2 versus 3.7 times a day) relative to the control group. The corticosteroids plus antibiotics group demonstrated peak flows (86% versus 88%) and inhaler usage (2.4 versus 2.2) nearly identical to corticosteroids alone, but the severity of underlying respiratory symptoms was significantly less. CONCLUSION: A five-day course of oral corticosteroids will significantly improve lung function and lessen severity of asthma symptoms. The addition of antibiotics to the treatment regimen has no additive effect on the reactive airway symptoms.

Thrombospondin-1 (TSP1) is a matricellular protein that displays both pro- and anti-adhesive activities. Binding to sulfated glycoconjugates mediates most high affinity binding of soluble TSP1 to MDA-MB-435 cells, but attachment and spreading of these cells on immobilized TSP1 is primarily beta1 integrin-dependent. The integrin alpha3beta1 is the major mediator of breast carcinoma cell adhesion and chemotaxis to TSP1. This integrin is partially active in MDA-MB-435 cells but is mostly inactive in MDA-MB-231 and MCF-7 cells, which require beta1 integrin activation to induce spreading on TSP1. Integrin-mediated cell spreading on TSP1 is accompanied by extension of filopodia containing beta1 integrins. TSP1 binding activity of the alpha3beta1 integrin is not stimulated by CD47-binding peptides from TSP1 or by protein kinase C activation, which activate alphavbeta3 integrin function in the same cells. In MDA-MB-231 but not MDA-MB-435 cells, this integrin is activated by pertussis toxin, whereas serum, insulin, insulin-like growth factor-1, and ligation of CD98 increase activity of this integrin in both cell lines. Serum stimulation is accompanied by increased surface expression of CD98, whereas insulin-like growth factor-1 does not increase CD98 expression. Thus, the pro-adhesive activity of TSP1 for breast carcinoma cells is controlled by several signals that regulate activity of the alpha3beta1 integrin.

Fibronectin (FN) is an abundant host protein that is specifically recognized by several pathogenic yeasts. Binding of FN in solution to Candida, Trichosporon, and Saccharomyces species is increased 20- to 110-fold by growth in medium containing hemoglobin, but specific adhesion to immobilized FN is increased only in Candida albicans, Candida tropicalis, Candida krusei, and Candida glabrata. Hemoglobin induces both specific and nonspecific binding of soluble FN. Nonspecific binding accounts for all of the enhancement in Trichosporon beigelii and Saccharomyces cerevisiae, but the Candida species possess a saturable, high-affinity binding site for FN that is induced by hemoglobin. Induction of displaceable soluble FN binding correlates with the ability of hemoglobin to regulate adhesion to immobilized FN, since hemoglobin does not induce adhesion of S. cerevisiae or T. beigelii to immobilized FN. Regulation by hemoglobin of FN binding to Candida species may therefore be an important factor in the pathogenesis in these yeast infections.