Sabire Karaçali

Cleavage of Atg3 protein by caspase-8 regulates autophagy during receptor-activated cell death.

Autophagy is an evolutionarily conserved mechanism contributing to cell survival under stress conditions including nutrient and growth factor deprivation. Connections and cross-talk between cell death mechanisms and autophagy is under investigation. Here, we describe Atg3, an essential regulatory component of autophagosome biogenesis, as a new substrate of caspase-8 during receptor-mediated cell death. Both, tumor necrosis factor α and tumor necrosis factor-related apoptosis inducing ligand induced cell death was accompanied by Atg3 cleavage and this event was inhibited by a pan-caspase inhibitor (zVAD) or a caspase-8-specific inhibitor (zIETD). Indeed, caspase-8 overexpression led to Atg3 degradation and this event depended on caspase-8 enzymatic activity. Mutation of the caspase-8 cleavage site on Atg3 abolished its cleavage both in vitro and in vivo, demonstrating that Atg3 was a direct target of caspase-8. Autophagy was inactive during apoptosis and blockage of caspases or overexpression of a non-cleavable Atg3 protein reestablished autophagic activity upon death receptor stimulation. In this system, autophagy was important for cell survival since inhibition of autophagy increased cell death. Therefore, Atg3 provides a novel link between apoptosis and autophagy during receptor-activated cell death.

Characterization of the Cellular Response During Apoptosis Induction in Cadmium-Treated Hep G2 Human Hepatoma Cells

Cadmium is a toxic transition heavy metal of continuing occupational and environmental concern, with a wide variety of adverse effects on regulation of gene expression and cellular signal transduction pathways. Injury to cells by cadmium leads to a complex series of events that can culminate in the death of the cell. It has been reported that cadmium induces apoptosis in many cell lines. However, the morphological characteristics leading to apoptosis or subsequent regeneration in cells exposed to cadmium have not been clarified.We evaluated whether human hepatoma cells maintained in culture undergo apoptosis when exposed to cadmium. Cytotoxic activity of cadmium on Hep G2 cells determined using 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide assay. A DNA ladder assay was performed by electrophoresis. Cell cycle analysis was quantified by flow cytometry. Nuclear morphology was studied by fluorescence microscopy after staining with propidium iodide and Hoechst 33342. Morphologic alterations in culture hepatocytes treated with CdCl2 were observed by transmission electron microscopy.We have demonstrated that apoptosis is a major mode of elimination of damaged HepG2 cells in cadmium toxicity and it precedes necrosis.

Griscelli syndrome: Report of a case and review of the literature

characterized by pigmentary dilution and variable immunodeficiency.1 The clinical symptoms consist of silver–gray hair and relatively light skin color, recurrent episodes of fever, with or without pyogenic infections, hepatosplenomegaly and lymphadenopathy.2 Central nervous system involvement has also been described in most patients.3 Clinical onset usually occurs between 4 months and 7 years of age.1–5 In the present study, we report on a 6-week-old Turkish boy with Griscelli syndrome.

Presence of sialic acid in prothoracic glands of Galleria mellonella (Lepidoptera)

The presence of sialic acid (SA) in prothoracic glands (PGs) of Galleria mellonella was determined by the methods of electron microscopy (EM), histochemistry, spectrophotometry (SP) and electronic ionization (EI)-mass spectroscopy. Histochemical observations were carried out by the cationic dye ruthenium red (RR), staining with and without neuraminidase digestion in the larval stage. Neuraminidase-sensitive SA was demonstrated by the decrease in the amount of RR-binding following neuraminidase digestion. The total amount of SA was found to be 0.09016 mg g(-1) in dry tissue by spectrophotometric determination. EI-mass spectroscopy results confirmed the EM and SP observations. The fragmentation scheme derived from EI-mass analysis exhibited the presence of the lactonized form of Neu5Gc7, 9Ac(2). On the basis of the various pieces of evidence described above, it was firmly concluded that Neu5Gc7, 9Ac(2) molecules were present in PGs of G. mellonella.

Sialic acids in developing testis of Galleria mellonella (Lepidoptera)

Summary The wide availability of sialic acids (SAs) in many organisms emphasizes their role for biological processes. The detection of SAs in insects is important for reinforcing the universal nature of SAs. In this study, the amounts and the types of SAs in testis of Galleria mellonella were investigated through gas chromatography (GC) and gas chromatography-mass (GC-MS) spectroscopy. GC analysis showed that the amount of SAs significantly decreased from young pupae to adults. The ratio of the levels of SAs in young pupa:old pupa:adult was found to be 16:5:1. Neu5Ac, Neu5Gc, Neu4,5Ac2, Neu5,9Ac2, and Neu2en5Ac were found in young pupae by GC-MS analysis. Neu5Ac, Neu5Gc Neu9Ac5Gc and Neu5,8,9Ac3 were detected in old pupae. Neu5Ac and Neu5Gc were encountered in adults. In addition to this trend of decreasing SA amounts, the variety of SA types present also decreased from young pupae to adults.

Adhesion of hemocytes to desialylated prothoracic glands of Galleria mellonella (Lepidoptera) in the larval stage.

Summary Earlier work showed the existence of sialic acid (SA) in the prothoracic glands (PGs) of Galleria mellonella (Karaçali et al., 1997). In this paper we investigated the role of SA during the degeneration process of PGs. Neuraminidase-digested larval PGs were incubated within the hemolymph collected from same age larvae. Light and electron microscopic observations showed incomplete capsule formation by the accumulation of hemocytes around desialylated gland cells, but not in the control group. Desialylated larval PG cells were recognized as a foreign structure or non-self by hemocytes. The result indicates that SA acts as a mask for hemocytic receptors during the larval period under normal conditions. However, in the absence of SA, the glands start to degenerate. We provide an explanation for the role of SA in the recognition process of hemocytes that initiates the degeneration of PGs in pupal cells and show the functionality of SA in insects, confirming that SA is a universal molecule.

Biochemical and morphological characteristics of selenite-induced apoptosis in human hepatoma hep G2 cells

Selenium is a cellular growth inhibitor in many mammary tumor cells. To comprehend the mechanism for the selenium-induced cell death, we examined the effects of sodium selenite, which has been one of the most extensively investigated selenium compounds, in human hepatoma Hep G2 cells.Cell viability gradually decreased after treatment with sodium selenite within the concentration range of 10–50 µM. Low (10 µM) selenite has shown a high-percentage laddering pattern compared to the high (25 µM) cytotoxic selenium concentration in agarose gel electrophoresis. G2M-phase enrichment was also concentration dependent. The most consistent transmission electron microscopic finding was the existence of large lysosomes.Based on these data, we hypothesize that sodium selenite predominantly shows its apoptotic effect over hydrogen selenite accumulation.

Genetic Characterization of Toxoplasma gondii Isolates and Toxoplasmosis Seroprevalence in Stray Cats of İzmir, Turkey

Currently, some Toxoplasma gondii genotypes are being associated with serious clinical presentations. A recent report showing the Africa 1 genotype in two local congenital toxoplasmosis cases acquired in Turkey formed the basis of this study because atypical Africa 1 genotype is most frequently detected in animals and patients from sub-Saharan Africa. Since stray cats are considered as the linkage between wild life and urban life in T. gondii transmission, the present study aimed to isolate and characterize T. gondii strains circulating in stray cats of İzmir (Western Turkey). A secondary objective was to determine toxoplasmosis seroprevalence in this cat population. Tissues obtained from 100 deceased stray cats were bioassayed and isolated strains were genotyped using 15 microsatellite markers. In addition, toxoplasmosis seroprevalence was analyzed in 1121 cat sera collected from several large veterinary clinics in İzmir. Among the 22 isolates, 19 were Type II (86.3%), two were Type III (9%) and one was Africa 1 genotype (4.5%). The overall seropositivity rates in cats were 42–48% and 33.4–34.4% according to IFA and ELISA, respectively. Seroprevalence in deceased cats was significantly higher than in healthy cats (Pu200a=u200a0.0033). Finding both the major clonal Type II lineage together with the Type III lineage also found in Middle East, and an atypical genotype, Africa 1 appears consistent with the specific geographic location of Turkey between three continents and raises the possibility of transportation of these strains between continents through trade routes or long distance migratory birds. In addition, the first large study of toxoplasma seroprevalence in a stray cat population was also reported. The relatively high seropositivity rates and the variety of T. gondii genotypes confirm the local stray cat population as a risk factor for human toxoplasmosis in İzmir.

Rhabdome-bearing cells within the corpus cardiacum of Melanogryllus desertus (orthoptera, gryllidae).

Cells with rhabdomeric structures characteristic of photoreceptor cells occur within the corpus cardiacum of Melanogryllus desertus. These cells are few in number and are larger than intrinsic secretory cells. Each has numerous rhabdomeric microvilli forming a rhabdome within the cell. The arrangement of large mitochondria under the rhabdomeric microvilli around the dilated endoplasmic reticulum membranes and multivesiculated bodies is distinctive. Rhabdome cells have synaptic contacts with the numerous neurosecretory axons that surround them. Other neurosecretory axons come in close contact with the membranes of microvilli.

The neurosecretory system of the adult Melanogryllus desertus Pall. (Orthoptera, Gryllidae)

SummaryBased on the nature of their granules, eight principal types of neurons, six of which are thought to be neurosecretory, are recognized in the median neurosecretory cell group of the brain of Melanogryllus desertus. Most of the neurosecretory cells contain granules with diameters of 200–300 nm. In a few the granules are smaller with diameters varying from 60–100 nm. Most of the cells have well developed Golgi areas and dense bodies of different sizes. Dense bodies are closely associated with neurosecretory granules. Accumulations of electron-dense granular material occur in expanded cisterns of endoplasmic reticulum, particularly in type-I cells.