Cross talk between the cell wall integrity and cyclic AMP/protein kinase A pathways in Cryptococcus neoformans.
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2014-08
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Cryptococcus neoformans is a fungal pathogen of immunocompromised people that causes fatal meningitis. The fungal cell wall is essential to viability and pathogenesis of C. neoformans, and biosynthesis and repair of the wall is primarily controlled by the cell wall integrity (CWI) signaling pathway. Previous work has shown that deletion of genes encoding the four major kinases in the CWI signaling pathway, namely, PKC1, BCK1, MKK2, and MPK1 results in severe cell wall phenotypes, sensitivity to a variety of cell wall stressors, and for Mpk1, reduced virulence in a mouse model. Here, we examined the global transcriptional responses to gene deletions of BCK1, MKK2, and MPK1 compared to wild-type cells. We found that over 1,000 genes were differentially expressed in one or more of the deletion strains, with 115 genes differentially expressed in all three strains, many of which have been identified as genes regulated by the cyclic AMP (cAMP)/protein kinase A (PKA) pathway. Biochemical measurements of cAMP levels in the kinase deletion strains revealed significantly less cAMP in all of the deletion strains compared to the wild-type strain. The deletion strains also produced significantly smaller capsules than the wild-type KN99 strain did under capsule-inducing conditions, although the levels of capsule they shed were similar to those shed by the wild type. Finally, addition of exogenous cAMP led to reduced sensitivity to cell wall stress and restored surface capsule to levels near those of wild type. Thus, we have direct evidence of cross talk between the CWI and cAMP/PKA pathways that may have important implications for regulation of cell wall and capsule homeostasis.Importance
Cryptococcus neoformans is a fungal pathogen of immunocompromised people that causes fatal meningitis. The fungal cell wall is essential to viability and pathogenesis of C. neoformans, and biosynthesis and repair of the wall are primarily controlled by the cell wall integrity (CWI) signaling pathway. In this study, we demonstrate that deletion of any of three core kinases in the CWI pathway impacts not only the cell wall but also the amount of surface capsule. Deletion of any of the kinases results in significantly reduced cellular cyclic AMP (cAMP) levels, and addition of exogenous cAMP rescues the capsule defect and some cell wall defects, supporting a direct role for the CWI pathway in regulation of capsule in conjunction with the cAMP/protein kinase A pathway.Type
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Donlin, Maureen J, Rajendra Upadhya, Kimberly J Gerik, Woei Lam, Laura G VanArendonk, Charles A Specht, Neil K Sharma, Jennifer K Lodge, et al. (2014). Cross talk between the cell wall integrity and cyclic AMP/protein kinase A pathways in Cryptococcus neoformans. mBio, 5(4). pp. e01573–e01514. 10.1128/mbio.01573-14 Retrieved from https://hdl.handle.net/10161/34741.
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Rajendra Upadhya
My research focuses on fungal disease and virulence pathways in the model yeast Cryptococcus neoformans. During my initial training in Dr. Ian Willis' lab at the Albert Einstein College of Medicine, NY, I discovered a novel yeast protein that is a major regulator of RNA polymerase III transcription and consequently affects cell growth and proliferation. Later, I used this expertise to functionally characterize the genome of Toxoplasma gondii, where I created a number of genome-based methodologies to define the Toxoplasma genomeWe are primarily interested in the characterization of fungal cell walls and how they influence fungal virulence and disease. Fungal cell wall biosynthesis and architecture are good targets for creating new antifungals since the cell wall is important for the yeast but missing in the host. We revealed that cell wall chitosan is necessary for maintaining cell wall integrity in Cryptococcus and is also important for fungal virulence by applying several genomic, molecular biology, and cell biology approaches to the Cryptococcus genome. Chitosan deficient mutants are avirulent in mice due to their good clearance from the host. This efficient clearance from the host is accompanied by the activation of a protective immunological response, which protects the mice from infection with a virulent wild-type strain later on. As a result, one of our primary goals is to better understand the biogenesis of chitosan in C. neoformans and C. gattii. We discovered that C. neoformans and C. gattii have different mechanisms for controlling chitosan synthesis. Cda1 and Cda2 are both engaged in fugal pathogenesis in C. neoformans, however Cda3 is the sole one implicated in C. gattii virulence. We have observed that different growth circumstances influence the amount of chitosan in the cell wall. In mice, these chitosan-deficient wild-type strains induced protective immunity against C. neoformans infection. Interestingly, the nature of the host immune response varied considerably between chitosan deficient mutants and wild-type that have been grown under different conditions to alter their chitosan levels. These mutants and wild-type strains with varied levels of chitosan allow us to explore the mechanisms of protective immunity evoked by C. neoformans cda1Δ2Δ3Δ.
Jennifer Lodge
Jennifer Lodge, Ph.D., a professor of molecular genetics and microbiology, is Duke’s vice president for Research & Innovation.
As the university’s chief research and innovation officer, Lodge leads oversight of Duke’s $1.2 billion annual research portfolio, including grants administration, ethical practices and commercialization. Lodge works with campus and medical center research staff, faculty and trainees, and is a key figure in Duke’s connection with external partners.
Before coming to Duke in January 2022, Lodge served as vice chancellor for research and senior associate dean for research for the School of Medicine at Washington University in St. Louis (WUSTL). There, she was responsible for WUSTL’s research development, ethics, education, compliance and research administration systems, and earned a reputation for encouraging innovation and entrepreneurship.
Lodge’s own research is on the human pathogenic fungus Cryptococcus neoformans. Her lab has been funded continuously by NIH for more than two decades, with as many as three prestigious R01 grants at one time. Her lab in the Duke University School of Medicine continues to explore the biochemical processes by which this fungus builds its cell walls. Such knowledge could lead to new antifungal therapies and vaccines.
Lodge is a fellow of the American Academy of Microbiology, the American Association for the Advancement of Science (AAAS) and the National Academy of Inventors. She is also the former chair of the Group on Research at the American Association of Medical Colleges (AAMC).
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