Arv1 interacts with and regulates the first step of GPI biosynthesis in Candida albicans

The ubiquitous ARV1 gene shows significant functional conservation across eukaryotes. Saccharomyces cerevisiae Arv1 is implicated in several cellular processes, including lipid/sterol homeostasis, morphogenesis, and drug resistance. Human and fungal ARV1 functionally complement S. cerevisiae ARV1, and arv1Δ is rescued by the overexpression of some subunits of the GPI-N-acetylglucosaminyltransferase (GPI-GnT), which catalyzes the first GPI biosynthetic step. Human and Trypanosoma brucei Arv1 homologs co-immunoprecipitate with different GPI-GnT subunits. Based on these previous reports, we hypothesized a cross talk between Candida albicans ARV1 and the first step of GPI biosynthesis. Using super-resolution radial fluctuation (SRRF) analysis of co-localization data, co-immunoprecipitation assays, and acceptor-photobleaching FRET studies, we show that CaArv1 physically interacts with the GPI-GnT. It also regulates the expression of the GPI-GnT subunits via the epigenetic modulator, Rtt109. Overexpressing GPI19 (which encodes a GPI-GnT subunit whose expression is repressed in Caarv1Δ/Δ) rescues its cell wall phenotype, sensitivity to azoles, and GPI-GnT activity without reversing the filamentation defect. A similar rescue is observed on downregulating GPI2 (encoding another GPI-GnT subunit, whose expression is upregulated in Caarv1Δ/Δ). Thus, transcriptional control rather than physical interaction appears to be the primary mechanism by which CaArv1 controls GPI-GnT. Overexpressing RAS1 restores all phenotypes, including filamentation, without restoring GPI-GnT activity. The filamentation defect of Caarv1Δ/Δ is independent of the GPI-GnT. CaArv1 transcriptionally regulates hyphae-specific transcription factors downstream of cAMP-PKA signaling (Efg1, Flo8) and repressors (Tup1, Nrg1) to modulate filamentation. The cross talk between CaArv1 and GPI-GnT has important implications for the virulence of C. albicans.