Biology subjects

Pianalto, K. M.

Publications and source records attributed to Pianalto, K. M..

3 recordsLinked to original sources

bioRxiv2024

Malassezia responds to environmental pH signals through the conserved Rim/Pal pathway

During mammalian colonization and infection, microorganisms must be able to rapidly sense and adapt to changing environmental conditions including alterations in extracellular pH. The fungus-specific Rim/Pal signaling pathway is one process that supports microbial adaptation to alkaline pH. This cascading series of interacting proteins terminates in the proteolytic activation of the highly conserved Rim101/PacC protein, a transcription factor that mediates microbial responses that favor survival in neutral/alkaline pH growth conditions, including many mammalian tissues. We identified the putative Rim pathway proteins Rim101 and Rra1 in the human skin colonizing fungus Malassezia sympodialis. Gene deletion by transconjugation and homologous recombination revealed that Rim101 and Rra1 are required for M. sympodialis growth at higher pH. Additionally, comparative transcriptional analysis of the mutant strains compared to wild-type suggested mechanisms for fungal adaptation to alkaline conditions. These pH-sensing signaling proteins are required for optimal growth in a murine model of atopic dermatitis, a pathological condition associated with increased skin pH. Together these data elucidate both conserved and phylum-specific features of microbial adaptation to extracellular stresses. ImportanceThe ability to adapt to host pH has been previously associated with microbial virulence in several pathogenic fungal species. Here we demonstrate that a fungal-specific alkaline response pathway is conserved in the human skin commensal fungus Malassezia sympodialis (Ms). This pathway is characterized by the pH-dependent activation of the Rim101/PacC transcription factor that controls cell surface adaptations to changing environmental conditions. By disrupting genes encoding two predicted components of this pathway, we demonstrated that the Rim/Pal pathway is conserved in this fungal species as a facilitator of alkaline pH growth. Moreover, targeted gene mutation and comparative transcriptional analysis supports the role of the Ms Rra1 protein as a cell surface pH sensor conserved within the basidiomycete fungi, a group including plant and human pathogens. Using an animal model of atopic dermatitis, we demonstrate the importance of Ms Rim/Pal signaling in this common inflammatory condition characterized by increased skin pH.

microbiology↗

bioRxiv2020

Internalization of the host alkaline pH signal in a fungal pathogen

The ability for cells to internalize extracellular cues allows them to adapt to novel and stressful environments. This adaptability is especially important for microbial pathogens that must sense and respond to drastic changes when encountering the human host. Cryptococcus neoformans is an environmental fungus and opportunistic pathogen that naturally lives in slightly acidic reservoirs, but must adapt to the relative increase in alkalinity in the human host in order to effectively cause disease. The fungal-specific Rim alkaline response signaling pathway effectively converts this extracellular signal into an adaptive cellular response allowing the pathogen to survive in its new environment. The newly identified Rra1 protein, the most upstream component of the C. neoformans Rim pathway, is an essential component of this alkaline response. Previous work connected Rra1-mediated signaling to the dynamics of the plasma membrane. Here we identify the specific mechanisms of Rim pathway signaling through detailed studies of the activation of the Rra1 protein. Specifically, we observe that the Rra1 protein is internalized and recycled in a pH-dependent manner, and that this dynamic pattern of localization further depends on specific residues in its C-terminal tail, clathrin-mediated endocytosis, and the integrity of the plasma membrane. The data presented here continue to unravel the complex and intricate processes of pH-sensing in a relevant human fungal pathogen. These studies will further elucidate general mechanisms by which cells respond to and internalize extracellular stress signals. Author SummaryThe work described here explores the genetics and mechanics of a cellular signaling pathway in a relevant human fungal pathogen, Cryptococcus neoformans. The findings presented in this manuscript untangle the complex interactions involved in the activation of a fungal-specific alkaline response pathway, the Rim pathway. Specifically, we find that C. neoformans is able to sense an increase in pH within the human host, internalize a membrane-bound pH-sensor, and activate a downstream signaling pathway enabling this pathogen to adapt to a novel host environment and effectively cause disease. Revealing the mechanisms of Rim pathway activation within the larger context of the fungal cell allows us to understand how and when this microorganism interprets relevant host signals. Furthermore, understanding how this pathogenic organism converts extracellular stress signals into an adaptive cellular response will elucidate more general mechanisms of microbial environmental sensing and stress response.

cell biology↗

bioRxiv2018

Roles for stress response and cell wall biosynthesis pathways in caspofungin tolerance in Cryptococcus neoformans

Limited antifungal diversity and availability are growing problems for the treatment of fungal infections in the face of increasing drug resistance. The echinocandins, one of the newest classes of antifungal drugs, inhibit production of a crucial cell wall component. However, these compounds do not effectively inhibit the growth of the opportunistic fungal pathogen Cryptococcus neoformans, despite potent inhibition of the target enzyme. We therefore performed a forward genetic screen to identify cellular processes that mediate the relative tolerance of this organism to the echinocandin drug, caspofungin. Through these studies, we identified 14 genetic mutants that enhance caspofungin antifungal activity. Rather than directly affecting caspofungin antifungal activity, these mutations seem to prevent the activation of various stress-induced compensatory cellular processes. For example, the pfa4{Delta} mutant has defects in the palmitoylation and localization of many of its target proteins, including the Ras GTPase and the Chs3 chitin synthase which are both required for caspofungin tolerance. Similarly, we have confirmed the link between caspofungin treatment and calcineurin signaling in this organism, but we suggest a deeper mechanism in which caspofungin tolerance is mediated by multiple pathways downstream of calcineurin function. Additionally, a partial loss-of-function mutant of a COP9 signalosome component results in a highly caspofungin-susceptible strain of C. neoformans. In summary, we describe here several pathways in C. neoformans that contribute to the complex caspofungin tolerance phenotype in this organism.

genetics↗