Elongation factor 3, EF3, associates with the calcium channel Cch1 and targets Cch1 to the plasma membrane in Cryptococcus neoformans

Assessment of the mechanism of drug resistance in Trichophyton mentagrophytes in response to various substances

BACKGROUND

Trichophyton mentagrophyte (TM), a zoonotic pathogen, has been endangering public health due to emerging drug resistance. Although increased attention is paid to this issue, there is very limited research available on drug resistance in TM. In this study, we studied the gene and proteomic changes, morphological changes, cellular fat localization, fat content changes, and biofilm of TM treated with different substances.

RESULTS

The TM growth curve showed a positive correlation with the concentration of Fenarimol (FE), genistein (GE), clotrimazole (KM), and Miconazole nitrate salt (MK). The morphology of TM cells changed in different degrees after treatment with different substances as observed by TEM and SEM. The results showed that under KM and berberine hydrochloride (BB) treatment, a total of 3305 differentially expressed genes were detected, with the highest number in the KM-treated group (578 up-regulated and 615 down-regulated). A total of 847 proteins and 1850 peptides were identified in TM proteomics. Nile red staining showed that the fat content of TM was significantly higher in the BB-, ethidium bromide- (EB), FE-, KM-, Adriamycin hydrochloride- (YA), and MK-treated group compared to the control group. Results of the biofilm thickness showed that it gradually increased under treatment with specific concentrations of KM or BB, which may be related to the up-regulation of ERG25 and CYP related gene proteins.

CONCLUSIONS

It is suggested that in order to effectively deal with dermatomycosis caused by TM, it is necessary to inhibit the expression of ERG25 and CYP related genes and fat metabolism, which can result in the inhibition of the production of biofilm by the fungus and solve the problem of fungal drug resistance in clinical settings.

The Cch1-Mid1 High-Affinity Calcium Channel Contributes to the Virulence of Cryptococcus neoformans by Mitigating Oxidative Stress

Pathogenic fungi have developed mechanisms to cope with stresses imposed by hosts. For Cryptococcus spp., this implies active defense mechanisms that attenuate and ultimately overcome the onslaught of oxidative stresses in macrophages. Among cellular pathways within Cryptococcus neoformans' arsenal is the plasma membrane high-affinity Cch1-Mid1 calcium (Ca(2+)) channel (CMC). Here we show that CMC has an unexpectedly complex and disparate role in mitigating oxidative stress. Upon inhibiting the Ccp1-mediated oxidative response pathway with antimycin, strains of C. neoformans expressing only Mid1 displayed enhanced growth, but this was significantly attenuated upon H2O2 exposure in the absence of Mid1, suggesting a regulatory role for Mid1 acting through the Ccp1-mediated oxidative stress response. This notion is further supported by the interaction detected between Mid1 and Ccp1 (cytochrome c peroxidase). In contrast, Cch1 appears to have a more general role in promoting cryptococci survival during oxidative stress. A strain lacking Cch1 displayed a growth defect in the presence of H2O2 without BAPTA [(1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, cesium salt] or additional stressors such as antimycin. Consistent with a greater contribution of Cch1 to oxidative stress tolerance, an intracellular growth defect was observed for the cch1Δ strain in the macrophage cell line J774A.1. Interestingly, while the absence of either Mid1 or Cch1 significantly compromises the ability of C. neoformans to tolerate oxidative stress, the absence of both Mid1 and Cch1 has a negligible effect on C. neoformans growth during H2O2 stress, suggesting the existence of a compensatory mechanism that becomes active in the absence of CMC.

Immunoproteome of Aspergillus fumigatus using sera of patients with invasive aspergillosis

Invasive aspergillosis is a life-threatening lung or systemic infection caused by the opportunistic mold Aspergillus fumigatus. The disease affects mainly immunocompromised hosts, and patients with hematological malignances or who have been submitted to stem cell transplantation are at high risk. Despite the current use of Platelia™ Aspergillus as a diagnostic test, the early diagnosis of invasive aspergillosis remains a major challenge in improving the prognosis of the disease. In this study, we used an immunoproteomic approach to identify proteins that could be putative candidates for the early diagnosis of invasive aspergillosis. Antigenic proteins expressed in the first steps of A. fumigatus germination occurring in a human host were revealed using 2-D Western immunoblots with the serum of patients who had previously been classified as probable and proven for invasive aspergillosis. Forty antigenic proteins were identified using mass spectrometry (MS/MS). A BLAST analysis revealed that two of these proteins showed low homology with proteins of either the human host or etiological agents of other invasive fungal infections. To our knowledge, this is the first report describing specific antigenic proteins of A. fumigatus germlings that are recognized by sera of patients with confirmed invasive aspergillosis who were from two separate hospital units.

Activity of the calcium channel pore Cch1 is dependent on a modulatory region of the subunit Mid1 in Cryptococcus neoformans

Calcium (Ca(2+))-mediated signaling events in fungal pathogens such as Cryptococcus neoformans are central to physiological processes, including those that mediate stress responses and promote virulence. The Cch1-Mid1 channel (CMC) represents the only high-affinity Ca(2+) channel in the plasma membrane of fungal cells; consequently, cryptococci cannot survive in low-Ca(2+) environments in the absence of CMC. Previous electrophysiological characterization revealed that Cch1, the predicted channel pore, and Mid1, a binding partner of Cch1, function as a store-operated Ca(2+)-selective channel gated by depletion of endoplasmic reticulum (ER) Ca(2+) stores. Cryptococci lacking CMC did not survive ER stress, indicating its critical role in restoring Ca(2+) homeostasis. Despite the requirement for Mid1 in promoting Ca(2+) influx via Cch1, identification of the role of Mid1 remains elusive. Here we show that the C-terminal tail of Mid1 is a modulatory region that impinges on Cch1 channel activity directly and mediates the trafficking of Mid1 to the plasma membrane. This region consists of the last 24 residues of Mid1, and the functional expression of Mid1 in a human embryonic cell line (HEK293) and in C. neoformans is dependent on this domain. Substitutions of arginine (R619A) or cysteine (C621A) in the modulatory region failed to target Mid1 to the plasma membrane and prevented CMC activity. Interestingly, loss of a predicted protein kinase C (PKC)-phosphorylated serine residue (S605A) had no effect on Mid1 trafficking but did alter the kinetics of Cch1 channel activity. Thus, establishment of Ca(2+) homeostasis in C. neoformans is dependent on a modulatory domain of Mid1.

Differential proteomic analysis of Aspergillus fumigatus morphotypes reveals putative drug targets

Aspergillus fumigatus is the main etiological agent of invasive aspergillosis, an important opportunistic infection for neutropenic patients. The main risk groups are patients with acute leukemia and bone marrow transplantation recipients. The lack of an early diagnostic test together with the limited spectrum of antifungal drugs remains a setback to the successful treatment of this disease. During invasive infection the inhaled fungal conidia enter the morphogenic cycle leading to angioinvasive hyphae. This work aimed to study differentially expressed proteins of A. fumigatus during morphogenesis. To achieve this goal, a 2D-DIGE approach was applied to study surface proteins extractable by reducing agents of two A. fumigatus morphotypes: germlings and hyphae. Sixty-three differentially expressed proteins were identified by MALDI-ToF/MS. We observed that proteins associated with biosynthetic pathways and proteins with multiple functions (miscellaneous) were over-expressed in the early stages of germination, while in hyphae, the most abundant proteins detected were related to metabolic processes or have unknown functions. Among the most interesting proteins regulated during morphogenesis, two putative drug targets were identified, the translational factor, eEF3 and the CipC-like protein. Neither of these proteins are present in mammalian cells.

Roles of Cch1 and Mid1 in morphogenesis, oxidative stress response and virulence in Candida albicans

Ca(2+) channel Cch1, and its subunit Mid1, has been suggested as the protein complex responsible for mediating Ca(2+) influx, which is often employed by fungal cells to maintain cell survival. The abilities of morphological switch and response to stress conditions are closely related to pathogenicity in Candida albicans. Cch1 and Mid1 activity are required for virulence of Cryptococcus neoformans and Claviceps purpurea, respectively. To investigate whether Cch1 and Mid1 also play a role in the virulence of C. albicans, we constructed cch1Δ/Δ and mid1Δ/Δ mutant strains for functional analysis of CCH1 and MID1. Although both of the mutants displayed the ability of yeast-to-hypha transition, they were defective in hyphae maintenance and invasive growth. Interestingly, deletion of CCH1 or MID1 in C. albicans led to an obvious defect phenotype in oxidative stress response. Moreover, the virulence of the mutants was reduced in a mouse model. Our results demonstrated that Cch1 and Mid1 activity are related to the virulence of C. albicans and may provide a new antifungal target.

Cch1 restores intracellular Ca2+ in fungal cells during endoplasmic reticulum stress

Pathogens endure and proliferate during infection by exquisitely coping with the many stresses imposed by the host to prevent pathogen survival. Recent evidence has shown that fungal pathogens and yeast respond to insults to the endoplasmic reticulum (ER) by initiating Ca(2+) influx across their plasma membrane. Although the high affinity Ca(2+) channel, Cch1, and its subunit Mid1, have been suggested as the protein complex responsible for mediating Ca(2+) influx, a direct demonstration of the gating mechanism of the Cch1 channel remains elusive. In this first mechanistic study of Cch1 channel activity we show that the Cch1 channel from the model human fungal pathogen, Cryptococcus neoformans, is directly activated by the depletion of intracellular Ca(2+) stores. Electrophysiological analysis revealed that agents that enable ER Ca(2+) store depletion promote the development of whole cell inward Ca(2+) currents through Cch1 that are effectively blocked by La(3+) and dependent on the presence of Mid1. Cch1 is permeable to both Ca(2+) and Ba(2+); however, unexpectedly, in contrast to Ca(2+) currents, Ba(2+) currents are steeply voltage-dependent. Cch1 maintains a strong Ca(2+) selectivity even in the presence of high concentrations of monovalent ions. Single channel analysis indicated that Cch1 channel conductance is small, similar to that reported for the Ca(2+) current I(CRAC). This study demonstrates that Cch1 functions as a store-operated Ca(2+)-selective channel that is gated by intracellular Ca(2+) depletion. The inability of cryptococcal cells that lacked the Cch1-Mid1 channel to survive ER stress suggests that Cch1 and its co-regulator, Mid1, are critical players in the restoration of Ca(2+) homeostasis.

The functional expression of toxic genes: lessons learned from molecular cloning of CCH1, a high-affinity Ca2+ channel

Some genes cannot be cloned by conventional methods because in most cases the genes or gene products are toxic to Escherichia coli. CCH1 is a high-affinity Ca(2+) channel present in the plasma membrane of Cryptococcus neoformans and other fungi. Like many toxic genes, the molecular cloning of CCH1 has been a major challenge; consequently, direct studies of CCH1 channel activity in heterologous expression systems have been impossible. We have devised a straightforward approach that resulted in the molecular cloning and functional expression of CCH1 by exploiting homologous recombination both in vitro and in vivo. This approach precluded the standard enzyme digestion-mediated ligation reactions and the subsequent isolation of plasmids from E. coli. The shuttle plasmid carrying CCH1-GFP, which was prepared in vitro and propagated in yeast, was successfully expressed in the mammalian cell line HEK293 (human embryonic kidney 293). CCH1 transcripts were detected only in HEK293 cells transfected with the plasmid DNA. Fluorescence microscopy studies revealed the expression of CCH1-GFP fusion protein on the cell surface of HEK293 cells, similar to the localization pattern of a well-characterized plasma membrane-associated K(+) channel. This approach will be particularly useful for genes that encode ion channels and transporters that cannot be cloned by conventional techniques requiring E. coli.