title: The phosphodiesterase inhibitor SQ 20006 selectively blocks mitogen activation of p70S6k and transition to S phase of the cell division cycle without affecting the steady state phosphorylation of eIF-4E.
abstract: In quiescent cells high levels of protein synthesis are required in order to re-enter the cell cycle upon stimulation. Initiation of polypeptide synthesis is the step most often subject to regulation, controlled in part by phosphorylation of 40 S ribosomal protein S6 and a number of initiation factors. The kinase responsible for S6 phosphorylation is p70S6k. We now show that the p70S6k pathway can be selectively blocked by the aminopurine analogue, SQ 20006. This agent is known to raise cAMP levels, resulting in activation of protein kinase A. We present evidence that the increase in cAMP is not responsible for the inhibitory effect observed. We also show that SQ 20006 can prevent the activation of p70S6k in a rapid and reversible manner. The compound does not exert its inhibitory activity on p70S6k but can inhibit in vitro two protein kinase C isozymes (alpha and gamma). In a B lymphoblastoid cell line, treatment with SQ 20006 results in inhibition of protein synthesis at the initiation stage. In contrast, when tested directly upon the translational machinery in the reticulocyte lysate, inhibition is manifest at both the level of initiation and elongation. The role of protein kinase A in the modulation of p70S6k and the rate of translation is discussed.
authors.affiliation: Department of Biochemistry, School of Biological Sciences, University of Sussex, Falmer, Brighton, United Kingdom.
authors.forename: V
authors.initials: V
authors.lastname: Frost
authors.forename: S J
authors.initials: SJ
authors.lastname: Morley
authors.forename: L
authors.initials: L
authors.lastname: Mercep
authors.forename: T
authors.initials: T
authors.lastname: Meyer
authors.forename: D
authors.initials: D
authors.lastname: Fabbro
authors.forename: S
authors.initials: S
authors.lastname: Ferrari
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D016475:3T3 Cells; D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002453:Cell Cycle / Q000187:drug effects*; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D004640:Emetine / Q000494:pharmacology; D004789:Enzyme Activation; D039561:Eukaryotic Initiation Factor-4E; D006801:Humans; D006918:Hydroxyurea / Q000494:pharmacology; D007166:Immunosuppressive Agents / Q000494:pharmacology; D007700:Kinetics; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1; D008934:Mitogens / Q000037:antagonists & inhibitors / Q000494:pharmacology*; D009539:Nicotinic Acids / Q000494:pharmacology*; D010448:Peptide Initiation Factors / Q000378:metabolism*; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D010766:Phosphorylation; D011090:Polyenes / Q000494:pharmacology; D011132:Polyribosomes / Q000378:metabolism; D014176:Protein Biosynthesis / Q000187:drug effects; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D012156:Reticulocytes / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases; D016196:S Phase / Q000187:drug effects; D020123:Sirolimus
chemical_list: D039561:Eukaryotic Initiation Factor-4E; D007166:Immunosuppressive Agents; D008934:Mitogens; D009539:Nicotinic Acids; D010448:Peptide Initiation Factors; D010726:Phosphodiesterase Inhibitors; D011090:Polyenes; D047428:Protein Kinase Inhibitors; D015124:8-Bromo Cyclic Adenosine Monophosphate; C011610:SQ 20006; D000242:Cyclic AMP; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D015056:1-Methyl-3-isobutylxanthine; D020123:Sirolimus; D006918:Hydroxyurea; D004640:Emetine