Identification of polypeptides whose presence correlates with retention or loss of an albumin extinguisher chromosome in rat hepatoma-mouse L cell fibroblast microcell hybrids

Signalization and cytoskeleton activity through myosin IB during the early steps of phagocytosis in Entamoeba histolytica: a proteomic approach

Phagocytosis of human cells is a crucial activity for the virulence of the human parasite Entamoeba histolytica. This protozoan invades and destroys the intestine by killing and phagocytosing epithelial cells, erythrocytes and cells from the immune system. In this study, we used magnetic beads covered with proteins from human serum as a model system to study the early events involved in phagocytosis by E. histolytica. We validated the system showing that the beads uptake triggered the activation of the actin-myosin cytoskeleton and involved a PI3-kinase as previously described for erythrophagocytosis. We purified early phagosomes from wild-type (WT) amoeba and from parasites that overproduced myosin IB (MyoIB+), the unique unconventional myosin of E. histolytica. The MyoIB+ cells exhibit a slower and more synchronized uptake process than the WT strain. Proteomic analysis by liquid chromatography and tandem mass spectroscopy (LC-MS/MS) of the WT and MyoIB+ phagosomes allowed us to identify, for the first time, molecular actors involved in the early step of the uptake process. These include proteins involved in cytoskeleton activity, signalling, endocytosis, lytic activity and cell surface proteins. Interestingly, the proteins that we found specifically recruited on the phagosomes from the MyoIB+ strain were previously described in other eukarytotic cells, as involved in the regulation of cortical F-actin dynamics, such as alpha-actinin and formins. This proteomics approach allows a step further towards the understanding of the molecular mechanisms involved in phagocytosis in E. histolytica that revealed some interesting differences compared with phagocytosis in macrophages or Dictyostelium discoideum, and allowed to identify putative candidates for proteins linked to myosin IB activity during the phagocytic process.

Sex-specific and blood meal-induced proteins of Anopheles gambiae midguts: analysis by two-dimensional gel electrophoresis

BACKGROUND

Anopheles gambiae is the main vector of Plasmodium falciparum in Africa. The mosquito midgut constitutes a barrier that the parasite must cross if it is to develop and be transmitted. Despite the central role of the mosquito midgut in the host/parasite interaction, little is known about its protein composition. Characterisation of An. gambiae midgut proteins may identify the proteins that render An. gambiae receptive to the malaria parasite.

METHODS

We carried out two-dimensional gel electrophoresis of An. gambiae midgut proteins and compared protein profiles for midguts from males, sugar-fed females and females fed on human blood.

RESULTS

Very few differences were detected between male and female mosquitoes for the approximately 375 silver-stained proteins. Male midguts contained ten proteins not detected in sugar-fed or blood-fed females, which are therefore probably involved in male-specific functions; conversely, female midguts contained twenty-three proteins absent from male midguts. Eight of these proteins were specific to sugar-fed females, and another ten, to blood-fed females.

CONCLUSION

Mass spectrometry analysis of the proteins found only in blood-fed female midguts, together with data from the recent sequencing of the An. gambiae genome, should make it possible to determine the role of these proteins in blood digestion or parasite receptivity.

Interaction of Theiler's virus with intermediate filaments of infected cells

Theiler's murine encephalomyelitis virus is a neurotropic murine picornavirus which replicates permissively and causes a cytopathic effect in the BHK-21 cell line. We examined the interactions between the GDVII and DA strains of Theiler's virus and BHK-21 host cell proteins in a virus overlay assay. We observed binding of the virions to two proteins of approximately 60 kDa. These proteins were microsequenced and identified as desmin and vimentin, two main components of the intermediate filament network. The association between desmin or vimentin and virions was demonstrated by immunoprecipitation. Anti-desmin and anti-vimentin monoclonal antibodies precipitated GDVII or DA virions from extracts of infected BHK-21 cells. The intracellular distributions of virions and of the desmin and vimentin intermediate filaments of BHK-21 cells were investigated by two-color immunofluorescence confocal microscopy. Following infection, the intermediate filament network was rearranged into a shell-like structure which surrounded a viral inclusion. Finally, close contact between GDVII virus particles and 10-nm intermediate filaments was observed by electron microscopy.

Two-dimensional gel analysis of midgut proteins of Anopheles stephensi lines with different susceptibility to Plasmodium falciparum infection

Little is known about the composition of the mosquito midgut which plays a central role in the development and subsequent transmission of malaria parasites. As a first step towards the characterization of mosquito midgut molecules involved in the transmission of malaria parasites, we analysed two-dimensional gel electrophoresis patterns of the midgut proteins of sugar-fed and blood-fed Anopheles stephensi lines of different susceptibility to P. falciparum infection. Two lines fully susceptible and one line (Pb3-9A) of reduced susceptibility were used. In the refractory line ookinetes do develop but are only inefficiently transformed into oocysts (Feldmann & Ponnudurai, 1989). The protein profiles of midguts from all sugar-fed mosquito lines were similar. However, after blood feeding, the midgut of the fully susceptible lines contained proteins not found in the midgut of line Pb3-9A. Twenty-nine such proteins were detected and are candidates for involvement in the interaction between the mosquito midgut and P. falciparum.

Regulation of IkappaBbeta degradation. Similarities to and differences from IkappaBalpha

The transcription factor NF-kappaB (nuclear factor-kappaB) is neutralized in nonstimulated cells through cytoplasmic retention by IkappaB inhibitors. In mammalian cells, two major forms of IkappaB proteins, IkappaBalpha and IkappaBbeta, have been identified. Upon treatment with a large variety of inducers, IkappaBalpha and IkappaBbeta are proteolytically degraded, resulting in NF-kappaB translocation into the nucleus. Recent observations suggest that phosphorylation of serines 32 and 36 and subsequent ubiquitination of lysines 21 and 22 of IkappaBalpha control its signal-induced degradation. In this study we provide evidence that critical residues in the NH2-terminal region of IkappaBbeta (serines 19 and 23) as well as its COOH-terminal PEST region control IkappaBbeta proteolysis. However Lys-9, the unique lysine residue in the NH2-terminal region of IkappaBbeta, is not absolutely required for its degradation. We also demonstrate that following stimulation, an underphosphorylated nondegradable form of IkappaBbeta accumulates. Surprisingly, our data suggest that unlike IkappaBalpha, IkappaBbeta is constitutively phosphorylated on one or two of the critical NH2-terminal serine residues. Thus, phosphorylation of these sites is necessary for degradation but does not necessarily constitute the signal-induced event that targets the molecule for proteolysis.

Characterization of somatic cell hybrids exhibiting extinction of AFP, albumin and an AFP-HPRT transgene

We utilized an AFP-HPRT transgene, i.e. the HPRT coding sequences under the regulation of AFP enhancer and promoter sequences, to localize the AFP extinguisher locus in intertypic somatic cell hybrids (hepatoma X fibroblast). This hybrid gene construct, which directly links AFP regulation to a reversibly selective gene, enabled the selection of stably transfected cells which express AFP, as well as cells showing extinction of AFP. Mouse hepatoma cells stably transfected with and expressing the transgene were fused to human fibroblasts, and the resulting somatic cell hybrids were characterized using Southern, Northern and karyotypic analyses. That several hybrids exhibited the proper extinction of AFP, AFP-HPRT and albumin suggests coregulation of these genes by an extinguisher. Segregant lines derived from these hybrids were selected for the loss of extinguisher activity and for reexpression of the transgene. Karyotypic analysis of hybrid and segregant lines, exhibiting proper AFP, albumin and AFP-HPRT phenotypes, revealed that the presence of human chromosome 7 was most closely associated with the AFP-extinguished state. The hybrids generated in these studies now make it possible to isolate the sequences responsible for AFP and albumin extinction.

N- and C-terminal sequences control degradation of MAD3/I kappa B alpha in response to inducers of NF-kappa B activity

The proteolytic degradation of the inhibitory protein MAD3/I kappa B alpha in response to extracellular stimulation is a prerequisite step in the activation of the transcription factor NF-kappa B. Analysis of the expression of human I kappa B alpha protein in stable transfectants of mouse 70Z/3 cells shows that, as for the endogenous murine protein, exogenous I kappa B alpha is degraded in response to inducers of NF-kappa B activity, such as phorbol myristate acetate or lipopolysaccharide. In addition, pretreatment of the cells with the proteasome inhibitor N-Ac-Leu-Leu-norleucinal inhibits this ligand-induced degradation and, in agreement with previous studies, stabilizes a hyperphosphorylated form of the human I kappa B alpha protein. By expressing mutant forms of the human protein in this cell line, we have been able to delineate the sequences responsible for both the ligand-induced phosphorylation and the degradation of I kappa B alpha. Our results show that deletion of the C terminus of the I kappa B alpha molecule up to amino acid 279 abolishes constitutive but not ligand-inducible phosphorylation and inhibits ligand-inducible degradation. Further analysis reveals that the inducible phosphorylation of I kappa B alpha maps to two serines in the N terminus of the protein (residues 32 and 36) and that the mutation of either residue is sufficient to abolish ligand-induced degradation, whereas both residues must be mutated to abolish inducible phosphorylation of the protein. We propose that treatment of 70Z/3 cells with either phorbol myristate acetate or lipopolysaccharide induces a kinase activity which phosphorylates serines 32 and that these phosphorylations target the protein for rapid proteolytic degradation, possibly by the ubiquitin-26S proteasome pathway, thus allowing NF-kappa B to translocate to the nucleus and to activate gene expression.