title: Hrk1 plays both Hog1-dependent and -independent roles in controlling stress response and antifungal drug resistance in Cryptococcus neoformans.
abstract: The HOG (High Osmolarity Glycerol response) pathway plays a central role in controlling stress response, ergosterol biosynthesis, virulence factor production, and differentiation of Cryptococcus neoformans, which causes fatal fungal meningoencephalitis. Recent transcriptome analysis of the HOG pathway discovered a Hog1-regulated gene (CNAG_00130.2), encoding a putative protein kinase orthologous to Rck1/2 in Saccharomyces cerevisiae and Srk1 in Schizosaccharomyces pombe. Its function is not known in C. neoformans. The present study functionally characterized the role of Hrk1 in C. neoformans. Northern blot analysis confirmed that HRK1 expression depends on the Hog1 MAPK. Similar to the hog1Δ mutant, the hrk1Δ mutant exhibited almost complete resistance to fludioxonil, which triggers glycerol biosynthesis via the HOG pathway. Supporting this, the hrk1Δ mutant showed reduced intracellular glycerol accumulation and swollen cell morphology in response to fludioxonil, further suggesting that Hrk1 works downstream of the HOG pathway. However, Hrk1 also appeared to have Hog1-independent functions. Mutation of HRK1 not only further increased osmosensitivity of the hog1Δ mutant, but also suppressed increased azole-resistance of the hog1Δ mutant in an Erg11-independent manner. Furthermore, unlike the hog1Δ mutant, Hrk1 was not involved in capsule biosynthesis. Hrk1 was slightly involved in melanin production but dispensable for virulence of C. neoformans. These findings suggest that Hrk1 plays both Hog1-dependent and -independent roles in stress and antifungal drug susceptibility and virulence factor production in C. neoformans. Particularly, the finding that inhibition of Hrk1 substantially increases azole drug susceptibility provides a novel strategy for combination antifungal therapy.
authors.affiliation: Department of Biotechnology, College of Life Science and Biotechnology, Center for Fungal Pathogenesis, Yonsei University, Seoul, Korea.
authors.forename: Seo-Young
authors.initials: SY
authors.lastname: Kim
authors.forename: Young-Joon
authors.initials: YJ
authors.lastname: Ko
authors.forename: Kwang-Woo
authors.initials: KW
authors.lastname: Jung
authors.forename: Anna
authors.initials: A
authors.lastname: Strain
authors.forename: Kirsten
authors.initials: K
authors.lastname: Nielsen
authors.forename: Yong-Sun
authors.initials: YS
authors.lastname: Bahn
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000935:Antifungal Agents / Q000494:pharmacology*; D029742:Caenorhabditis elegans Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D003455:Cryptococcus neoformans / Q000187:drug effects* / Q000502:physiology; D004352:Drug Resistance, Microbial; D005786:Gene Expression Regulation; D005990:Glycerol / Q000378:metabolism; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D008969:Molecular Sequence Data; D009997:Osmotic Pressure; D018384:Oxidative Stress; D017386:Sequence Homology, Amino Acid; D014774:Virulence
chemical_list: D000935:Antifungal Agents; D029742:Caenorhabditis elegans Proteins; D020928:Mitogen-Activated Protein Kinases; D005990:Glycerol