BackgroundSporothrix schenckii is a pathogenic dimorphic fungus, the etiological agent of sporotrichosis, a lymphocutaneous disease that can remain localized or can disseminate, involving joints, lungs, and the central nervous system. Pathogenic fungi use signal transduction pathways to rapidly adapt to changing environmental conditions and S. schenckii is no exception. S. schenckii yeast cells, either proliferate (yeast cell cycle) or engage in a developmental program that includes proliferation accompanied by morphogenesis (yeast to mycelium transition) depending on the environmental conditions. The principal intracellular receptors of environmental signals are the heterotrimeric G proteins, suggesting their involvement in fungal dimorphism and pathogenicity. Identifying these G proteins in fungi and their involvement in protein-protein interactions will help determine their role in signal transduction pathways.ResultsIn this work we describe a new G protein α subunit gene in S. schenckii, ssg-2. The cDNA sequence of ssg-2 revealed a predicted open reading frame of 1,065 nucleotides encoding a 355 amino acids protein with a molecular weight of 40.9 kDa. When used as bait in a yeast two-hybrid assay, a cytoplasmic phospholipase A2 catalytic subunit was identified as interacting with SSG-2. The sspla2 gene, revealed an open reading frame of 2538 bp and encoded an 846 amino acid protein with a calculated molecular weight of 92.62 kDa. The principal features that characterize cPLA2 were identified in this enzyme such as a phospholipase catalytic domain and the characteristic invariable arginine and serine residues. A role for SSPLA2 in the control of dimorphism in S. schenckii is suggested by observing the effects of inhibitors of the enzyme on the yeast cell cycle and the yeast to mycelium transition in this fungus. Phospholipase A2 inhibitors such as AACOCF3 (an analogue of archidonic acid) and isotetrandrine (an inhibitor of G protein PLA2 interactions) were found to inhibit budding by yeasts induced to re-enter the yeast cell cycle and to stimulate the yeast to mycelium transition showing that this enzyme is necessary for the yeast cell cycle.ConclusionA new G protein α subunit gene was characterized in S. schenckii and protein-protein interactions studies revealed this G protein alpha subunit interacts with a cPLA2 homologue. The PLA2 homologue reported here is the first phospholipase identified in S. schenckii and the first time a PLA2 homologue is identified as interacting with a G protein α subunit in a pathogenic dimorphic fungus, establishing a relationship between these G proteins and the pathogenic potential of fungi. This cPLA2 homologue is known to play a role in signal transduction and fungal pathogenesis. Using cPLA2 inhibitors, this enzyme was found to affect dimorphism in S. schenckii and was found to be necessary for the development of the yeast or pathogenic form of the fungus.

Background: Sporothrix schenckii is a pathogenic, dimorphic fungus, the etiological agent of sporotrichosis, a subcutaneous lymphatic mycosis. Dimorphism in S. schenckii responds to second messengers such as cAMP and calcium, suggesting the possible involvement of a calcium/calmodulin kinase in its regulation. In this study we describe a novel calcium/calmodulin-dependent protein kinase gene in S. schenckii, sscmk1, and the effects of inhibitors of calmodulin and calcium/calmodulin kinases on the yeast to mycelium transition and the yeast cell cycle.

2114 Disordered K+ efflux and osmotically induced water loss leads to red blood cell (RBC) dehydration and plays a role in the pathophysiology of Sickle Cell Disease. We previously reported that activation of endothelin-1 (ET-1) receptors in sickle erythrocyte was partially responsible for dense sickle cell formation. However, the mechanism by which ET-1 regulates RBC volume remains unclear. Serine/threonine kinases have been shown to regulate K+ transport in RBC. Casein Kinase II (CK2), a serine/threonine kinase, phosphorylates acidic proteins, regulates calmodulin activity and cytoskeletal proteins and is present in RBC. CK2 activity is blocked by apigenin, emodin, heparin, and ornithine decarboxylase. Previous reports have shown a role for flavonoids such as apigenin as substrates for erythrocyte plasma membrane oxidoreductases. We recently observed a role for Protein Disulfide Isomerase (PDI) in regulating cellular hydration and K+ efflux in human RBC. PDI catalyzes disulfide interchange reactions in the plasma membrane, mediates redox modifications and is up-regulated under hypoxic conditions. However the relationship between CK2 and PDI in the setting of cellular hydration status is un-explored. Our results indicate that erythrocyte membrane CK2 activity increases when sickle cells are incubated with 500 nM ET-1 for 30 min (2.8 ± 0.1 to 4.9 ± 0.01 nmol/min/mL * 106 cell) an event that is blunted by pre-incubation with the ET-1 B receptor blocker, BQ788 (2.5 ± 0.1 nmol/min/mL * 106 cell, n=3, p<0.04) and 20 μM apigenin (2.7 ± 0.4 nmol/min/mL * 106 cell, n=3, p<0.04). We examined the role of CK2 activation on cellular dehydration. We incubated sickle erythrocytes for 3 hours in deoxygenation-oxygenation cycles in the presence or absence of 20μM apigenin or 2μM 4,5,6,7-tetrabromobenzotriazole (TBB), a specific CK2 inhibitor, and measured the changes in erythrocyte density by phthalate oil density analysis. We observed that inhibition of CK2 led to reduced deoxygenation-stimulated cellular dehydration in sickle erythrocytes by apigenin (D50= 1.106 to 1.100 g/mL) or TBB (D50 =1.097 g/mL). We then studied the role of CK2 inhibitors on PDI activity by Insulin Turbidity Assay and observed that apigenin and TBB led to significant reductions in PDI activity in vitro (64% and 42% respectively). We also studied the effects of the flavonoids: naringenin, naringin, apigenin and rutin on PDI activity and observed reductions in PDI activity that were greater with apigenin>rutin>TBB>naringin>naringenin (n=2, P<0.05). Furthermore, we observed that K+ flux via Gardos channel activation is correlated with PDI activity in vitro in sickle erythrocytes. Taken together our results implicate CK2 and PDI as intermediate regulators of ET-1 stimulated cellular volume systems in red blood cells. Supported by NIH R01-HL09632 to AR. Disclosures: No relevant conflicts of interest to declare.

Background Disordered endothelial cell activation plays an important role in the pathophysiology of atherosclerosis, cancer, sepsis, viral infections, and inflammatory responses. There is interest in developing novel therapeutics to regulate endothelial cell function in atherothrombotic, metabolic, vascular, and hematological diseases. Extracts from leaves of the Syzygium jambos (L.) Alston (S. jambos) trees have been proposed to treat cardiovascular diseases and diabetes through unclear mechanisms. We investigated the effects of the S. jambos extract on biomarkers of endothelial dysfunction and immune responses in the human endothelial cell line, EA.hy926. Methods Leaves of S. jambos were collected, concocted and lyophilized. To study the effects of S. jambos on endothelial cell activation, we used the human endothelial cell line. IL-6 levels were measured using qPCR and ELISA. PDI activity was measured using Insulin Turbidity and Di-E-GSSG assays. CM-H2DCFDA was used to study ROS levels. Migration assay was used to study S. jambos effect on ex vivo human polymorphonuclear and human mononuclear cells. Results Our results show that incubation of EA.hy926 cells with ET-1 led to a 6.5 ± 1.6 fold increase in IL-6 expression by qPCR, an event that was blocked by S. jambos. Also, we observed that ET-1 increased extracellular protein disulfide isomerase (PDI) activity that was likewise dose-dependently blocked by S. jambos (IC50 = 14 μg/mL). Consistent with these observations, ET-1 stimulated ex vivo human polymorphonuclear and mononuclear cell migration that also was dose-dependently blocked by S. jambos. In addition, ET-1 stimulation led to significant increases in ROS production that were sensitive to S. jambos. Conclusion Our results suggest that the S. jambos extract represents a novel cardiovascular protective pharmacological approach to regulate endothelial cell activation, IL-6 expression, and immune-cell responses.