Hong Sang

The Gβ-like protein CpcB is required for hyphal growth, conidiophore morphology and pathogenicity in Aspergillus fumigatus

CpcB (cross pathway control B) encodes a yeast Cpc2 and mammalian RACK1 (receptor for activated protein kinase C) ortholog, which is a WD repeat protein with functional homology to the β subunit of heterotrimeric G proteins in Aspergillus fumigatus. Previous study has reported that CpcB governs growth and development in both A. fumigatus and Aspergillus nidulans. However, little is known about the functional identities of CpcB orthologs and their relationships with G protein complexes. In this study, we verified that cytoplasmic AfCpcB acts as a Gβ-like protein ortholog and plays important roles in hyphal growth, conidiophore morphology, cell wall integrity, and virulence in A. fumigatus. Furthermore, double deletion of AfcpcB and AfgpaB (Gα) causes a similar phenotype to AfgpaB mutant with abnormal multiple septa conidiophores but exhibits sparse conidiation with white and fluffy colonies. Thus, the exacerbated conidiation defect suggests that AfcpcB has its own specific function compared to the Gα subunit of AfgpaB or the G-protein complex. In addition, complementation assays using AfcpcB orthologs of A. nidulans and yeasts (Saccharomyces cerevisiae, Schizosaccharomyces pombe, Candida albicans) suggest that all tested fungal AfcpcB orthologs under the A. fumigatus native promoter can largely restore hyphal growth defects in AfcpcB deletion mutant, but only the A. nidulans cpcB ortholog completely rescues the ΔAfcpcB conidiation defect, suggesting that CpcB acts as a Gβ-like protein ortholog in the Aspergilli, but may have unique and important unexplored functions that required for conidiation, which is absent in yeast.

The Aspergillus fumigatus Damage Resistance Protein Family Coordinately Regulates Ergosterol Biosynthesis and Azole Susceptibility

ABSTRACT Ergosterol is a major and specific component of the fungal plasma membrane, and thus, the cytochrome P450 enzymes (Erg proteins) that catalyze ergosterol synthesis have been selected as valuable targets of azole antifungals. However, the opportunistic pathogen Aspergillus fumigatus has developed worldwide resistance to azoles largely through mutations in the cytochrome P450 enzyme Cyp51 (Erg11). In this study, we demonstrate that a cytochrome b5-like heme-binding damage resistance protein (Dap) family, comprised of DapA, DapB, and DapC, coordinately regulates the functionality of cytochrome P450 enzymes Erg5 and Erg11 and oppositely affects susceptibility to azoles. The expression of all three genes is induced in an azole concentration-dependent way, and the decreased susceptibility to azoles requires DapA stabilization of cytochrome P450 protein activity. In contrast, overexpression of DapB and DapC causes dysfunction of Erg5 and Erg11, resulting in abnormal accumulation of sterol intermediates and further accentuating the sensitivity of ΔdapA strains to azoles. The results of exogenous-hemin rescue and heme-binding-site mutagenesis experiments demonstrate that the heme binding of DapA contributes the decreased azole susceptibility, while DapB and -C are capable of reducing the activities of Erg5 and Erg11 through depletion of heme. In vivo data demonstrate that inactivated DapA combined with activated DapB yields an A. fumigatus mutant that is easily treatable with azoles in an immunocompromised mouse model of invasive pulmonary aspergillosis. Compared to the single Dap proteins found in Saccharomyces cerevisiae and Schizosaccharomyces pombe, we suggest that this complex Dap family regulatory system emerged during the evolution of fungi as an adaptive means to regulate ergosterol synthesis in response to environmental stimuli. IMPORTANCE Knowledge of the ergosterol biosynthesis route in fungal pathogens is useful in the design of new antifungal drugs and could aid in the study of antifungal-drug resistance mechanisms. In this study, we demonstrate that three cytochrome b5-like Dap proteins coordinately regulate the azole resistance and ergosterol biosynthesis catalyzed by cytochrome P450 proteins. Our new insights into the Dap regulatory system in fungal pathogens may have broad therapeutic ramifications beyond their usefulness for classic azole antifungals. Moreover, our elucidation of the molecular mechanism of Dap regulation of cytochrome P450 protein functionality through heme-binding activity may extend beyond the Kingdom Fungi with applicability toward Dap protein regulation of mammalian sterol synthesis. Knowledge of the ergosterol biosynthesis route in fungal pathogens is useful in the design of new antifungal drugs and could aid in the study of antifungal-drug resistance mechanisms. In this study, we demonstrate that three cytochrome b5-like Dap proteins coordinately regulate the azole resistance and ergosterol biosynthesis catalyzed by cytochrome P450 proteins. Our new insights into the Dap regulatory system in fungal pathogens may have broad therapeutic ramifications beyond their usefulness for classic azole antifungals. Moreover, our elucidation of the molecular mechanism of Dap regulation of cytochrome P450 protein functionality through heme-binding activity may extend beyond the Kingdom Fungi with applicability toward Dap protein regulation of mammalian sterol synthesis.

A case of subcutaneous phaeohyphomycosis caused by Cladosporium cladosporioides and its treatment

Phaeohyphomycosis refers to a group of cutaneous, subcutaneous and systemic infections caused by certain dematiaceous fungi characterised by production of melanin in the mycelium. In the past decades, increasing numbers of pathogenic genera causing phaeohyphomycosis have been recognised worldwide, including mainly Exophiala, Phialophora, Cladosporium, Xylohypha, Curvularia, Dactylaria, Exserohilum, Bipolaris, Lecythophora and Alternaria. This communication reports the first case of subcutaneous phaeohyphomycosis due to Cladosporium cladosporioides in China and its pathogenic characteristics.

A rare complication of ear piercing: a case of subcutaneous phaeohyphomycosis caused by Veronaea botryosa in China

We present the third case of phaeohyphomycosis caused by Veronaea botryosa in China and the tenth case worldwide. A 16-year-old Chinese girl developed crusted, verrucous lesions, initially on the left ear and later on the left buttock, within 2-5 months of receiving an ear piercing. Histopathological examination of biopsy specimens confirmed diagnosis of subcutaneous phaeohyphomycosis. Microscopic examination of the colonies recovered in culture from a portion of the biopsy specimen resulted in the identification of Veronaea botryosa based primarily on the presence of two-celled, brownish pigmented, cylindrical conidia produced sympodially from erect conidiogenous cells. The lesions significantly improved with daily oral treatment with itraconazole 400 mg and adjuvant thermotherapy for 6 months. A maintenance therapy with low dose itraconazole was prescribed in order to achieve clinical and mycological cure. A two-year follow-up didnt reveal any recurrence of infection. Our case is the first report of V. botryosa infection associated with a cosmetic procedure, which suggests that skin piercing could precipitate V. botryosa or other dematiaceous, as well as opportunistic fungal infections.

The newly nonsporulated characterization of an Aspergillus fumigatus isolate from an immunocompetent patient and its clinic indication

Aspergillus fumigatus (A. fumigatus) commonly produces abundant and heavily melanized infectious conidia, which are the primary agents that cause invasive aspergillosis (IA) in immunocompromised patients. We isolated a white nonsporulating A. fumigatus strain (A1j) from an immunocompetent patient. It was identified by histopathological examination and morphological observation, and subsequently confirmed by DNA sequencing of internal transcribed spacer (ITS) regions and partial β-tubulin genes. Neither a long waiting time nor passage on various medium types could stimulate the formation of spores and pigment. No significant relative difference was found in sensitivity to antifungal agents or cell wall destabilizing reagents, as compared to wild-type A. fumigatus Af293. Nevertheless, A1j was hypovirulent in the immunosuppressed mice model, consistent with the good result in our patient. RNA deep-sequencing analysis (RNA-seq) revealed that hundreds of transcripts were significantly dysregulated, including those related to pigmentation and sporulation. qRT-PCR confirmed the anergic state of key regulator brlA for sporulation under the induction of conidiation conditions, but without mutation. To the best of our knowledge, this is the first report of a white, nonsporulating A. fumigatus strain infection in an immunocompetent patient. In our opinion, A1j may represent a mutant of typical A. fumigatus, providing a new clue for identification of clinical A. fumigatus isolates. Furthermore, the good prognosis of our patient and the reduced virulence in the mice model infected with A1j highlight the potential of sporulation inhibitors as a new generation of antifungal agents.

A case of a cerebral syphilitic gumma developed in a few months mimicking a brain tumor in a human immunodeficiency virus-negative patient

Abstract Cerebral syphilitic gumma is extremely rare and easily misdiagnosed. We illustrate a case of a cerebral syphilitic gumma developed in just a few months mimicking a brain tumor in a HIV-negative patient and Treponema pallidum was detected in the cerebral syphilitic gumma.

Molecular Characterization of Gβ-Like Protein CpcB Involved in Antifungal Drug Susceptibility and Virulence in A. fumigatus

Aspergillus fumigatus is an airborne human fungal pathogen that can survive in a wide range of environmental condition. G protein complex transduces external signals from a variety of stimuli outside a cell to its interior effectors in all eukaryotes. Gβ-like CpcB (cross pathway control B) belongs to a WD40 repeat protein family with the conserved G–H and W–D residues. Previous studies have demonstrated that Gβ-like proteins cooperate with related signal transduction proteins to function during many important developmental processes in A. fumigatus. However, the molecular characteristics of Gβ-like CpcB have not yet been identified. In this study, we demonstrated that the G–H residues in WD repeat 1, 2, 3, and the W–D residue in WD repeat 2 of CpcB are required not only to control normal hyphal growth and conidiation but also to affect antifungal drug susceptibility. The enhanced drug resistance might be due to reduced intracellular drug accumulation and altered ergosterol component. Moreover, we find that the first G–H residue of CpcB plays an important role in the virulence of A. fumigatus. To our knowledge, this is the first report for finding the importance of the conserved G–H and W–D residues for a Gβ-like protein in understanding of G protein functions.

Combined acute interstitial pneumonitis and pancytopenia induced by low-dose methotrexate in a hemodialysis patient treated for bullous pemphigoid.

Methotrexate has been widely used for many years in the treatment of a variety of diseases. Acute pneumonitis and bone marrow suppression are very serious side effects in methotrexate treatment. A 48-year-old man with end-stage renal disease undergoing chronic hemodialysis developed combined acute pneumonitis and pancytopenia after a cumulative dose of 20 mg methotrexate for bullous pemphigoid. Continuous renal replacement therapy (CRRT) can effi ciently decrease serum methotrexate concentration. A rapid improvement of clinical symptoms and resolution of pulmonary opacifi cation were found after CRRT. Blood cell counts returned to normal after component blood transfusion and cytokine supportive therapy. Patients with impaired renal function are at high risk of methotrexate toxicity, and low-dose methotrexate should be prescribed with great caution.

Erg4A and Erg4B are required for conidiation and azole resistance via regulation of ergosterol biosynthesis in Aspergillus fumigatus.

ABSTRACT Ergosterol, a fungus-specific sterol enriched in cell plasma membranes, is an effective antifungal drug target. However, current knowledge of the ergosterol biosynthesis process in the saprophytic human fungal pathogen Aspergillus fumigatus remains limited. In this study, we found that two endoplasmic reticulum-localized sterol C-24 reductases encoded by both erg4A and erg4B homologs are required to catalyze the reaction during the final step of ergosterol biosynthesis. Loss of one homolog of Erg4 induces the overexpression of the other one, accompanied by almost normal ergosterol synthesis and wild-type colony growth. However, double deletions of erg4A and erg4B completely block the last step of ergosterol synthesis, resulting in the accumulation of ergosta-5,7,22,24(28)-tetraenol, a precursor compound of ergosterol. Further studies indicate that erg4A and erg4B are required for conidiation but not for hyphal growth. Importantly, the Δerg4A Δerg4B mutant still demonstrates wild-type virulence in a compromised mouse model but displays remarkable increased susceptibility to antifungal azoles. Our data suggest that inhibitors of Erg4A and Erg4B may serve as effective candidates for adjunct antifungal agents with azoles. IMPORTANCE Knowledge of the ergosterol biosynthesis pathway in the human opportunistic pathogen A. fumigatus is useful for designing and finding new antifungal drugs. In this study, we demonstrated that the endoplasmic reticulum-localized sterol C-24 reductases Erg4A and Erg4B are required for conidiation via regulation of ergosterol biosynthesis. Moreover, inactivation of both Erg4A and Erg4B results in hypersensitivity to the clinical guideline-recommended antifungal drugs itraconazole and voriconazole. Therefore, our finding indicates that inhibition of Erg4A and Erg4B might be an effective approach for alleviating A. fumigatus infection.

Drug eruptions induced by allopurinol associated with HLA-B*5801.

Allopurinol, a drug commonly used for treating gout and hyperuricemia, is a frequent cause of drug eruptions. Recent investigations suggest that HLA-BFNx015801 allele is a very strong marker for allopurinol-induced cutaneous adverse drug reactions (cADRs). In this article we report two cases of allopurinol-induced drug eruptions in patients carrying the HLA-BFNx015801 allele and review the literature on the association between HLA-BFNx015801 and allopurinol-induced cADRs based on a MEDLINE and PubMed search.