Change in Expression of Genes Involved in the G-Protein Signaling Pathway (GP-SP) is Associated with Voriconazole-Resistance (VCZ-R) in Aspergillus Species
Suganthini Krishnan Natesan *
Department of Medicine, Division of Infectious Diseases, John D. Dingell VA Medical Center, Detroit, MI, USA and Department of Medicine, Division of Infectious Diseases, Wayne State University, Detroit, MI, USA.
Lulu Farhana
Department of Medicine, Division of Infectious Diseases, John D. Dingell VA Medical Center, Detroit, MI, USA.
Wenjuan Wu
Department of Medicine, Division of Infectious Diseases, Wayne State University, Detroit, MI, USA.
*Author to whom correspondence should be addressed.
Abstract
Background: Invasive infections due to Aspergillus species continue to be associated with a significant morbidity in immuno-compromised patients. Despite the availability of several azoles [isavuconazole (ISZ), posaconazole (POS), voriconazole (VCZ) and itraconazole (ITZ)], mortality remains high. Studies from various cancer and transplant centers around the world have reported the emergence of azole-resistance in clinical and environmental isolates of Aspergillus fumigatus and Aspergillus flavus. The major mechanism of high-level azole- resistance in Aspergillus species reported so far is mutation and/or overexpression of target site namely cyp51A, that encodes lanosterol demethylase of the fungal cell wall. However, some azole-resistant isolates have not exhibited either of these mechanisms, suggesting other novel non-cyp51 related mechanisms of triazole- resistance.
Aim: To evaluate the possible role of G-protein signaling pathway genes in VCZ-R in Aspergillus species.
Materials and Methods: CLSI based susceptibility, and cyp51 gene-specific PCR experiments were performed on wild type and specific mutant strains of Aspergillus species to analyse the phenotypic alterations and changes in triazole-susceptibility pattern in Aspergillus species.
Results: Voriconazole inhibits conidiation in A. flavus, possibly through its effect on several genes involved in the GP-SP. Mutations or changes in expression of these genes contribute to VCZ-R in A. flavus. Loss of conidiation and pigmentation with switch to pure vegetative growth, exclusively by hyphal elongation, is associated with VCZ-R in A. flavus.
Conclusion: Our results suggest that VCZ inhibits conidiation by targeting one of the critical genes in the G-protein pathway and specific alterations in these genes likely lead to loss of conidiation and VCZ-R in A. flavus. Cross resistance to other triazoles including POS and ISZ need to be tested as well. Based on our data we propose to continue our studies on G-protein pathway genes involved in antifungal drug resistance in Aspergillus species. This pathway needs to be further explored not only for its possible contribution to VCZ-R but also to delineate its role in pathogenesis and also as a potential antifungal drug target
Keywords: Aspergillus, antifungal drug resistance, voriconazole, posaconazole, G- protein signaling pathway, brlA, fluG, pkaC, flbA, fadA, mutation, overexpression, VCZ-resistance, triazole resistance