Azole resistance in a Candida albicans mutant lacking the ABC transporter CDR6/ROA1 depends on TOR signaling.

Abstract

ATP-binding cassette (ABC) transporters help export various substrates across the cell membrane and significantly contribute to drug resistance. However, a recent study reported an unusual case in which the loss of an ABC transporter in Candida albicans, orf19.4531 (previously named ROA1), increases resistance against antifungal azoles, which was attributed to an altered membrane potential in the mutant strain. To obtain further mechanistic insights into this phenomenon, here we confirmed that the plasma membrane-localized transporter (renamed CDR6/ROA1 for consistency with C. albicans nomenclature) could efflux xenobiotics such as berberine, rhodamine 123, and paraquat. Moreover, a CDR6/ROA1 null mutant, NKKY101, displayed increased susceptibility to these xenobiotics. Interestingly, fluorescence recovery after photobleaching (FRAP) results indicated that NKKY101 mutant cells exhibited increased plasma membrane rigidity, resulting in reduced azole accumulation and contributing to azole resistance. Transcriptional profiling revealed that ribosome biogenesis genes were significantly up-regulated in the NKKY101 mutant. As ribosome biogenesis is a well-known downstream phenomenon of target of rapamycin (TOR1) signaling, we suspected a link between ribosome biogenesis and TOR1 signaling in NKKY101. Therefore, we grew NKKY101 cells on rapamycin and observed TOR1 hyperactivation, which leads to Hsp90-dependent calcineurin stabilization and thereby increased azole resistance. This in vitro finding was supported by in vivo data from a mouse model of systemic infection in which NKKY101 cells led to higher fungal load after fluconazole challenge than wild-type cells. Taken together, our study uncovers a mechanism of azole resistance in C. albicans, involving increased membrane rigidity and TOR signaling.

• Authors: Nitesh Kumar Khandelwal, Neeraj Chauhan, Parijat Sarkar, Brooke D Esquivel, Paola Coccetti, Ashutosh Singh, Alix T Coste, Meghna Gupta, Dominique Sanglard, Theodore C White, Murielle Chauvel, Christophe d'Enfert, Amitabha Chattopadhyay, Naseem A Gaur, Alok Kumar Mondal, Rajendra Prasad
• Journal: The Journal of biological chemistry (J Biol Chem) Vol. 293 Issue 2 Pg. 412-432 (01 12 2018) ISSN: 1083-351X [Electronic] United States
• PMID: 29158264 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: © 2018 by The American Society for Biochemistry and Molecular Biology, Inc.

Chemical References

• ATP-Binding Cassette Transporters
• Antifungal Agents
• Azoles
• Fungal Proteins
• Membrane Transport Proteins
• Fluconazole
• TOR Serine-Threonine Kinases

Topics

• ATP-Binding Cassette Transporters (genetics, metabolism)
• Antifungal Agents (pharmacology)
• Azoles (pharmacology)
• Biological Transport (drug effects, genetics)
• Candida albicans (drug effects, genetics, metabolism)
• Drug Resistance, Fungal (drug effects, genetics)
• Fluconazole (pharmacology)
• Fluorescence Recovery After Photobleaching
• Fungal Proteins (genetics, metabolism)
• Membrane Transport Proteins (genetics, metabolism)
• Microbial Sensitivity Tests
• TOR Serine-Threonine Kinases (genetics, metabolism)