title: A Ric8/synembryn homolog promotes Gpa1 and Gpa2 activation to respectively regulate cyclic AMP and pheromone signaling in Cryptococcus neoformans.
abstract: The G protein α subunits Gpa1, Gpa2, and Gpa3 mediate signal transduction and are important in the growth and virulence of Cryptococcus neoformans. To understand how Gpa1 functions without a conventional Gβ subunit, we characterized a resistance to inhibitors of cholinesterase 8 (Ric8) homolog from C. neoformans, which shares amino acid sequence homology with other Ric8 proteins that exhibit guanine nucleotide exchange factor (GEF) activity toward Gα. We found that the ric8 mutant was reduced in capsule size and melanin formation, which could be suppressed by cyclic AMP (cAMP) supplementation or by introducing the activated GPA1(Q284L) allele. Consistent with the fact that Ric8 participates in cAMP signaling to regulate virulence, the ric8 mutant was attenuated in virulence toward mice. Interestingly, disruption of RIC8 also resulted in opposing effects on pheromone signaling, as the ric8 mutant showed reduced mating but an enhanced ability to induce the pheromone response in the mating partner. To identify Ric8 functional mechanisms, we examined the interactions between Ric8 and the three Gα proteins. Ric8 interacted with Gpa1 and Gpa2, but not Gpa3. The presence of Gpa1(Q284L) negatively affected its interaction with Ric8, whereas the activated Gpa2(Q203L) allele abolished the interaction. Collectively, these findings suggest that Ric8 functions as a GEF to facilitate the activation of Gpa1-cAMP signaling and to promote Gpa2, affecting mating efficiency. Our study highlights the distinct and conserved characteristics associated with G protein signaling and contributes to our overall understanding of how G protein α subunits function with or without a canonical Gβ partner in C. neoformans.
authors.affiliation: Research Institute for Children, Children's Hospital, New Orleans, Louisiana, USA.
authors.forename: Jinjun
authors.initials: J
authors.lastname: Gong
authors.affiliation: School of Liberal Arts, Tulane University, New Orleans, Louisiana, USA.
authors.forename: Jacob D
authors.initials: JD
authors.lastname: Grodsky
authors.affiliation: Department of Plant Pathology, Nanjing Agricultural University, Nanjing, China.
authors.forename: Zhengguang
authors.initials: Z
authors.lastname: Zhang
authors.affiliation: Research Institute for Children, Children's Hospital, New Orleans, Louisiana, USA Department of Microbiology, Immunology, and Parasitology, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA Department of Pediatrics, Louisiana State University Health Sciences Center, New Orleans, Louisiana, USA pwang@lsuhsc.edu.
authors.forename: Ping
authors.initials: P
authors.lastname: Wang
mesh_terms: D000818:Animals; D002800:Cholinesterase Inhibitors / Q000494:pharmacology; D002802:Cholinesterases / Q000235:genetics* / Q000378:metabolism; D003455:Cryptococcus neoformans / Q000235:genetics*; D000242:Cyclic AMP / Q000235:genetics / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics*; D044385:GTP-Binding Protein alpha Subunits / Q000235:genetics* / Q000378:metabolism; D051379:Mice; D010675:Pheromones / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics
chemical_list: D002800:Cholinesterase Inhibitors; D005656:Fungal Proteins; D044385:GTP-Binding Protein alpha Subunits; D010675:Pheromones; D000242:Cyclic AMP; D002802:Cholinesterases
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