ALS3 and ALS8 represent a single locus that encodes a Candida albicans adhesin; functional comparisons between Als3p and Als1p

Abstract

The ALS (agglutinin-likesequence) gene family ofCandida albicansencodes eight cell-surface glycoproteins, some of which are involved in adherence to host surfaces. A mutational analysis of each ALS gene is currently being performed to deduce the functions of the encoded proteins and to better understand the role of these proteins inC. albicansbiology and pathogenesis. This paper describes construction of anals3/als3mutant and comparison of its phenotype to anals1/als1strain. Efforts to disruptALS3indicated that the gene could be deleted in two transformation steps, suggesting that the gene is encoded by a single locus and that theALS3-like locus,ALS8, does not exist. Strains lackingALS3orALS1did not exhibit a defect in germ tube formation when grown in RPMI 1640 medium, but theals1/als1mutant formed significantly fewer germ tubes in Lee medium. Analysis ofALS3andALS1promoter activity using green fluorescent protein (GFP) reporter strains and flow cytometry showed that when cells are placed into medium that promotes germ tube formation,ALS1is transcribed prior toALS3. Comparison of the mutant strains in adhesion assays showed that theals3/als3strain was defective in adhesion to both human umbilical vein endothelial cells (HUVEC) and buccal epithelial cells (BEC), but not to fibronectin-coated plastic plates. In contrast, theals1/als1strain showed decreased adherence to HUVEC, but adherence to BEC and fibronectin were the same as wild-type controls. Inoculation of the buccal reconstituted human epithelium (RHE) model of oral candidiasis with the mutant strains showed nearly a total lack of adhesion and epithelial destruction by theals3/als3mutant while theals1/als1strain showed only a slightly reduced degree of epithelial destruction compared to the wild-type control. Adhesion data presented here suggest that, in the assays performed, loss of Als3p affectsC. albicansadhesion more than loss of Als1p. Collectively, these results demonstrate functional similarities and differences between Als1p and Als3p, and suggest the potential for more complex interrelationships between the ALS genes and their encoded proteins.