1,720,960 research outputs found
Identification and partial characterization of cAMP-phosphodiesterases in the ciliate Euplotes raikovi.
Get PDFIn the ciliate Euplotes raikovi, two specific isoforms of cAMP- dependent phosphodiesterases were identified, one in the soluble and the other in the particulate fraction of the cell. Their activity was shown to be stimulated by Mg2+, insensitive to Ca2+ and cGMP, and scarcely inhibited by theophylline and 3-isobutyl-1-methyl-xanthine. They appear to be related to some phosphodiesterases of class II of other unicellular organisms in their biochemical features, and their enzymatic activity is up-regulated by elevation of intracellular cAMP level similarly to PDE-4 isoforms of mammals
Cross-talk between the autocrine (mitogenic) pheromone loop of the ciliate Euplotes raikovi and the intracellular cyclic AMP concentration
Get PDFCell type-specific protein signals, called pheromones, are constitutively secreted by Euplotes raikovi and bound back in autocrine fashion, with a positive effect on the vegetative (mitotic) cell growth. In cells growing suspended with their secreted pheromone, it was found that any interruption of this autocrine signaling loop was immediately followed by an effective enhancement of the basal intracellular cyclic AMP (cAMP) level. To establish a cause-effect relationship between these pheromone-induced variations in the cytoplasmic cAMP level and cell growth, cells ready to pass from a resting stage to a new growth cycle were conditioned either to incorporate a cAMP analog resistant to phosphodiesterase degradation, or to utilize cAMP released (following cell irradiation) from incorporated “caged” cAMP. Cells responded at every induced increase in their basal cAMP level by markedly decreasing their commitment to start a new growth cycle. It was deduced that the autocrine signaling of E. raikovi pheromones involves cAMP as inhibitor of its mitogenic activity
The autocrine mitogenic loop of the ciliate Euplotes raikovi: the pheromone membrane-bound forms are the cell binding sites and potential signaling receptors of soluble pheromones
No full text
A Novel Protein Kinase from the Ciliate Euplotes raikovi with Close Structural Identity to the Mammalian Intestinal and Male-Germ Cell Kinases: Characterization and Functional Implications in the Autocrine Pheromone Signaling Loop
No full textIn the free-living ciliate Euplotes raikovi, we identified (and designated as Er-MAPK1) a protein kinase of 631 amino acids, that appears to be constantly phosphorylated in cells which are in growth stage and interact in autocrine fashion with their water-soluble signal pheromones. Er-MAPK1 is specified by a gene that requires aþ1 translational frame-shift to be expressed. Its amino-terminal region represents a canonical catalytic domain and carries an activation loop distinctive of the mitogenactivated protein kinases, with the Thr-Asp-Tyr motif deputed to be site of double phosphorylation. In contrast, the carboxy-terminal region appears to be structurally unique. It shows a strongly basic amino acid composition, is very rich in glycine repetitions, and contains a bipartite signal for translocation of Er-MAPK1 into the nucleus
The autocrine mitogenic loop of the ciliate Euplotes raikovi: the pheromone membrane-bound forms are the cell binding sites and potential signaling receptors of soluble pheromones
Get PDFHomologous proteins, denoted pheromones, promote cell mitotic proliferation and mating pair formation in the ciliate Euplotes raikovi, according to whether they bind to cells in an autocrine- or paracrine-like manner. The primary transcripts of the genes encoding these proteins undergo alternate splicing, which generates at least two distinct mRNAs. One is specific for the soluble pheromone, the other for a pheromone isoform that remains anchored to the cell surface as a type II protein, whose extracellular C-terminal region is structurally equivalent to the secreted form. The 15-kDa membrane-bound isoform of pheromone Er-1, denoted Er-1mem and synthesized by the same E. raikovi cells that secrete Er-1, has been purified from cell membranes by affinity chromatography prepared with matrix-bound Er-1, and its extracellular and cytoplasmic regions have been expressed as recombinant proteins. Using the purified material and these recombinant proteins, it has been shown that Er-1mem has the property of binding pheromones competitively through its extracellular pheromone-like domain and associating reversibly and specifically with a guanine nucleotide-binding protein through its intracellular domain. It has been concluded that the membrane-bound pheromone isoforms of E. raikovi represent the cell effective pheromone binding sites and are functionally equipped for transducing the signal generated by this binding
- …
