Comparative proteomic analysis of Gib2 validating its adaptor function in Cryptococcus neoformans

PLoS One. 2017 Jul 7;12(7):e0180243. doi: 10.1371/journal.pone.0180243. eCollection 2017.

Abstract

Cryptococcus neoformans causes often-fatal fungal meningoencephalitis in immunocompromised individuals. While the exact disease mechanisms remain elusive, signal transduction pathways mediated by key elements such as G-protein α subunit Gpa1, small GTPase Ras1, and atypical Gβ-like/RACK1 protein Gib2 are known to play important roles in C. neoformans virulence. Gib2 is important for normal growth, differentiation, and pathogenicity, and it also positively regulates cAMP levels in conjunction with Gpa1. Interestingly, Gib2 displays a scaffold protein property by interacting with a wide variety of cellular proteins. To explore Gib2 global regulatory functions, we performed two-dimensional differential gel electrophoresis (DIGE) analysis and found that GIB2 disruption results in an increased expression of 304 protein spots (43.4%) and a decreased expression of 396 protein spots (56.6%). Analysis of 96 proteins whose expression changes were deemed significant (≥ +/- 1.5- fold) revealed that 75 proteins belong to at least 12 functional protein groups. Among them, eight groups have the statistical stringency of p ≤ 0.05, and four groups, including Hsp70/71 heat shock protein homologs and ribosomal proteins, survived the Bonferroni correction. This finding is consistent with earlier established roles for the human Gβ-like/RACK1 and the budding yeast Saccharomyces cerevisiae Asc1. It suggests that Gib2 could also be part of the complex affecting ribosomal biogenesis and protein translation in C. neoformans. Since eukaryotic Hsp70/71 proteins are involved in the facilitation of nascent protein folding, processing, and protection of cells against stress, we also propose that Gib2-regulated stress responses are linked to fungal virulence. Collectively, our study supports a conserved role of Gβ-like/RACK/Gib2 proteins in the essential cellular process of ribosomal biogenesis and protein translation. Our study also highlights a multifaceted regulatory role of Gib2 in the growth and pathogenicity of C. neoformans.

Publication types

  • Comparative Study

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism
  • Cryptococcus neoformans / genetics*
  • Cryptococcus neoformans / metabolism
  • Cryptococcus neoformans / pathogenicity*
  • Cyclic AMP / metabolism
  • Electrophoresis, Gel, Two-Dimensional
  • Fungal Proteins / genetics*
  • Fungal Proteins / metabolism
  • GTP-Binding Proteins / genetics*
  • GTP-Binding Proteins / metabolism
  • Gene Expression Regulation, Fungal*
  • HSP70 Heat-Shock Proteins / genetics
  • HSP70 Heat-Shock Proteins / metabolism
  • Molecular Sequence Annotation
  • Organelle Biogenesis
  • Protein Binding
  • Protein Biosynthesis
  • Ribosomal Proteins / genetics
  • Ribosomal Proteins / metabolism
  • Ribosomes / genetics
  • Ribosomes / metabolism
  • Saccharomyces cerevisiae Proteins / genetics
  • Saccharomyces cerevisiae Proteins / metabolism
  • Sequence Homology, Amino Acid
  • Signal Transduction
  • Virulence Factors / genetics*
  • Virulence Factors / metabolism

Substances

  • ASC1 protein, S cerevisiae
  • Adaptor Proteins, Signal Transducing
  • Fungal Proteins
  • HSP70 Heat-Shock Proteins
  • Ribosomal Proteins
  • Saccharomyces cerevisiae Proteins
  • Virulence Factors
  • Cyclic AMP
  • GTP-Binding Proteins