guanosine-triphosphate and sotrastaurin

Mycophenolic acid (MPA) is the active metabolite of mycophenolate mofetil, an effective immunosuppressive drug. Both MPA and mycophenolate mofetil are highly specific inhibitors of guanine nucleotide synthesis and of T-cell activation. However, the mechanism by which guanine nucleotide depletion suppresses T-cell activation is unknown. Depletion of GTP inhibits ribosomal RNA synthesis in T cells by inhibiting transcription initiation factor I (TIF-IA), a GTP-binding protein that recruits RNA polymerase I to the ribosomal DNA promoter. TIF-IA-GTP binds the ErbB3-binding protein 1, and together they enhance the transcription of proliferating cell nuclear antigen (PCNA). GTP binding by TIF-IA and ErbB3-binding protein 1 phosphorylation by protein kinase C δ are both required for optimal PCNA expression. The protein kinase C inhibitor sotrastaurin markedly potentiates the inhibition of ribosomal RNA synthesis, PCNA expression, and T-cell activation induced by MPA, suggesting that the combination of the two agents are more highly effective than either alone in inducing immunosuppression.

Topics: Adaptor Proteins, Signal Transducing; Blotting, Western; Cell Proliferation; Cells, Cultured; DNA, Ribosomal; Gene Expression; Guanosine Triphosphate; HEK293 Cells; Humans; Jurkat Cells; Keratin-20; Lymphocyte Activation; Mutation; Mycophenolic Acid; Phosphorylation; Pol1 Transcription Initiation Complex Proteins; Proliferating Cell Nuclear Antigen; Promoter Regions, Genetic; Protein Binding; Protein Kinase C-delta; Pyrroles; Quinazolines; RNA Interference; RNA Polymerase I; RNA-Binding Proteins; RNA, Ribosomal; T-Lymphocytes