HacA Governs Virulence Traits and Adaptive Stress Responses in Trichophyton rubrum

Abstract

The ability of fungi to sense environmental stressors and appropriately respond is linked to secretory system functions. The dermatophyte infection process depends on an orchestrated signaling regulation that triggers the transcription of genes responsible for adherence and penetration of the pathogen into host-tissue. A high secretion system is activated to support the host-pathogen interaction and assures maintenance of the dermatophyte infection. The gateway of secretion machinery is the endoplasmic reticulum (ER), which is the primary site for protein folding and transport. Current studies have shown that ER stress that affects adaptive responses is primarily regulated by UPR and supports fungal pathogenicity; this has been assessed for yeasts and Aspergillus fumigatus, in regard to how these fungi cope with host environmental stressors. Fungal UPR consists of a transmembrane kinase sensor (Ire1/IreA) and a downstream target Hac1/HacA. The active form of Hac is achieved via non-spliceosomal intron removal promoted by endonuclease activity of Ire1/IreA. Here, we assessed features of HacA and its involvement in virulence and susceptibility in Trichophyton rubrum. Our results showed that exposure to antifungals and ER-stressing agents initiated the activation of HacA from T. rubrum. Interestingly, the activation occurs when a 20 nt fragment is removed from part of the exon-2 and part of intron-2, which in turn promotes the arisen of the DNA binding site motif and a dimer interface domain. Further, we found changes in the cell wall and cellular membrane composition in the hacA mutant as well as an increase in susceptibility toward azole and cell wall disturbing agents. Moreover, the hacA mutant presented significant defects in important virulence traits like thermotolerance and growth on keratin substrates. For instance, the development of the hacA mutant was impaired in co-culture with keratinocytes or human nail fragments. Changes in the pro-inflammatory cytokine release were verified for the hacA mutant during the co-culture assay, which might be related to differences in pathogen-associated molecular patterns (PAMPs) in the cell wall. Together, these results suggested that HacA is an integral part of T. rubrum physiology and virulence, implying that it is an important molecular target for antidermatophytic therapy.

Comprehensive genome and transcriptome analysis of the dermatophyte Trichophyton schoenleinii reveals the candidate pathogenic genes

“…The transcription factor HacA regulates gene expression in response to various forms of secretion stress and as part of secretory cell differentiation. The ΔhacA mutant of T. rubrum showed decreased growth on keratin substrates and increased susceptibility toward antifungal agents, suggesting its involvement in virulence and susceptibility in T. rubrum 36 . Another transcription factor gene stuA was activated in T. schoenleinii grown in soy medium.…”

“…and increased susceptibility toward antifungal agents, suggesting its involvement in virulence and susceptibility in T. rubrum. 36 Another transcription factor gene stuA was activated in T. schoenleinii grown in soy medium. StuA has been shown to control development, adaptation, stress tolerance and virulence of the T. rubrum.…”

State-of-the-Art Dermatophyte Infections: Epidemiology Aspects, Pathophysiology, and Resistance Mechanisms

“…Indeed, the search for putative HacA target genes showed that HacA may regulate approximately 25% of the T. rubrum genome. Among the UPR target genes are the genes that encode mannosyltransferase enzymes, heat shock proteins (Hsps), fatty acid biosynthetic enzymes, cell wall enzymes, and proteases [ 22 ].…”

“…As mentioned above, PacC and HacA are involved in mannosyltransferase regulation, and both transcription factors are also related to Hsp regulation [ 22 , 24 ]. Hsps are conserved chaperones with multiple roles in the cell, such as aiding the folding and transport of proteins, protection under stressful conditions, and fungal pathogenicity.…”

“…Several factors have been described in the pathogenesis of dermatophytosis, such as the secreted enzymes that enable keratin degradation, metabolic changes to use nutrients from the host tissue, adaptation to skin pH, transcription factors that regulate fungal adaptation to stress, and extracellular vesicles that modulate the host immune response [ 21 , 22 , 23 , 24 , 25 , 26 ]. During infection, dermatophytes trigger the release of cytokines and chemokines that contribute to the inflammatory response in the skin.…”