The role of RHD1, a putative essential transmembrane protein, in filamentation, virulence and drug susceptibility. (c2008)

Abstract

Candida albicans is one of the pathogenic fungal organisms that cause mucosal and systemic infections leading to death in immunocompromised individuals. Its pathogenicity can be ascribed to its ability to exist in different morphological states. Many transmembrane proteins have been implicated in morphological switching from yeast to hyphal form. Such is Rhdl (Repressed under Hyphal Development), a putative transmembrane protein that was found to be repressed five fold under yeast to hyphal transition. The aim of the present study is to investigate and characterize the role of Rhdl in in vitro filamentation and in vivo virulence in a mouse model through generating a homozygous null mutant strain. Moreover, this study aims to assess the antifungal drug susceptibility of mutant strain against azoles, caspofungin and anlphotericin B, using E-test method as well as oxidative stress response to a lethal dose of hydrogen peroxide and white opaque switching. Interestingly, RHDI appears to be an essential gene since only a heterozygote strain was generated. However, no haploinsufficiency was observed as both wild type and mutant showed similar behavior on different solid and liquid hyphal inducing and non inducing media. In vivo, the mice survival rate was 0% after 16 days of post injection with the heterozygote strain compared to 0% survival at 19 days with parental strain. Moreover, Rhd 1 does not appear to play a ro le in drug resistance, white opaque switching and oxidative stress. Finally, a BLASTP of the Rhdl ORF against the entire C albicans genome revealed homology to orf.l9.l464 a yet uncharacterized protein. This homology did not span the N terminal signal peptide (1 -11) or the transmembrane region (38-58).