h-89 and protein-kinase-inhibitor-peptide

cAMP-dependent protein kinase (PKA) has been implicated in the asexual stage of the Toxoplasma gondii life cycle through assaying the effect of a PKA-specific inhibitor on its growth rate. Since inhibition of the host cell PKA cannot be ruled out, a more precise evaluation of the role of PKA, as well as characterization of the kinase itself, is necessary.. The inhibitory effects of two PKA inhibitors, H89, an ATP-competitive chemical inhibitor, and PKI, a substrate-competitive mammalian natural peptide inhibitor, were estimated. In the in vitro kinase assay, the inhibitory effect of PKI on a recombinant T. gondii PKA catalytic subunit (TgPKA-C) was weaker compared to that on mammalian PKA-C. In a tachyzoite growth assay, PKI had little effect on the growth of tachyzoites, whereas H89 strongly inhibited it. Moreover, T. gondii PKA regulatory subunit (TgPKA-R)-overexpressing tachyzoites showed a significant growth defect.. Our data suggest that PKA plays an important role in the growth of tachyzoites, and the inhibitory effect of substrate-competitive inhibitor PKI on T. gondii PKA was low compared to that of the ATP competitive inhibitor H89.

Topics: Adenosine Triphosphate; Amino Acid Sequence; Binding, Competitive; Catalytic Domain; Cyclic AMP-Dependent Protein Kinases; Gene Expression Regulation, Enzymologic; Isoquinolines; Molecular Sequence Data; Peptides; Protein Kinase Inhibitors; Sulfonamides; Toxoplasma

We have examined herein whether membrane Ig (mIg) stimulates junB transcription through a protein kinase A (PKA)-dependent or PKA-independent pathway. PKA phosphotransferase activity was not increased following mIg cross-linking of Bal17 B cells. However, junB transcriptional activation was dependent upon PKA activity, as evidenced by inhibition of goat anti-mouse IgM-stimulated junB promoter-chloramphenicol acetyltransferase reporter gene activity in transfected Bal17 B cells treated with the PKA inhibitor H-89. mIg-stimulated junB promoter-chloramphenicol acetyltransferase activity was also blocked in B cells expressing a specific PKA inhibitor peptide, whereas in vivo expression of an inactive PKA inhibitor peptide variant was not inhibitory. Expression of a mutant cAMP response element binding protein (CREB) containing an inactivated kinase A phosphoacceptor site at Ser133 reduced mIg-stimulated junB transcription. Okadaic acid increased CREB1 phosphorylation at Ser133 and junB transcriptional activation, suggesting the action of protein phosphatase-1 (PP-1) or -2A (PP-2A). Extracts from unstimulated B cells exhibited phosphatase activity against an in vitro PKA-phosphorylated peptide containing the Ser133 phosphoacceptor site. The involvement of a phosphatase activity in regulating mIg-stimulated junB transcription is supported by our finding that extracts from goat anti-mouse IgM-stimulated B cells exhibited a significantly reduced level of Ser133 phosphatase activity. Hence, the level of CREB1 phosphorylation is governed by the balance between PKA and phosphatase activities. junB transcriptional activation results in part from mIg signals that negatively regulate a CREB1-targeted PP-1 or PP-2A activity.

Topics: Animals; Antibodies, Anti-Idiotypic; B-Lymphocytes; Cyclic AMP Response Element-Binding Protein; Cyclic AMP-Dependent Protein Kinases; Enzyme Activation; Genes, jun; Isoquinolines; Lymphoma, B-Cell; Mice; Peptides; Phosphoprotein Phosphatases; Phosphorylation; Protein Phosphatase 1; Proto-Oncogene Proteins c-jun; Receptors, Antigen, B-Cell; Serine; Sulfonamides; Transcription, Genetic; Transcriptional Activation; Tumor Cells, Cultured