Inhibitors of phosphodiesterase III block stimulation of Xenopus laevis oocyte ribosomal S6 kinase activity by insulin-like growth factor-I.
Insulin-like growth factor-I (IGF-I) stimulated Xenopus laevis oocyte ribosomal S6 kinase activity 5- to 10-fold, with an apparent EC50 of 0.8 +/- 0.1 nM after 90 min of hormone treatment. IGF-I-stimulated enzyme activity was inhibited by treatment of oocytes with nonselective phosphodiesterase (PDE) inhibitors, with apparent IC50 values of 2 +/- 1 microM papaverine, 20 +/- 2 microM isobutylmethylxanthine, and 128 +/- 16 microM theophylline. Type III PDE inhibitors also inhibited IGF-I-stimulated S6 kinase activity with IC50 values of 9.7 +/- 0.3 microM Cl-930 and 84 +/- 23 microM imazodan (Cl-914). These drugs apparently affected an intracellular molecular event leading to activation of S6 kinase, since Cl-930 prevented IGF-I-stimulation of S6 kinase, but had no direct inhibitory effect when added to the S6 kinase enzyme assay mixture. While hormone-stimulated S6 kinase activity was inhibited by isobutylmethylxanthine (nonselective PDE inhibitor) and Cl-930 (PDE III inhibitor), Ro 20, 1724 and rolipram (PDE IV inhibitors) and dipyridamole (PDE V inhibitor) had no significant effect on activated enzyme levels. The time course for IGF-I stimulation of oocyte S6 kinase displayed a small early peak of activity approximately 0.15-0.4 time required for 50% of cell population to display white spots (GVBD50) and a second major increase in activity at 0.6-0.7 GVBD50 that was sustained until meiotic maturation was complete. The second wave of enzyme activation was inhibited by Cl-930, but the early increase was not.(ABSTRACT TRUNCATED AT 250 WORDS)
Sadler
S E
SE
Department of Biological Sciences, University of Denver, Colorado 80208.
D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000818:Animals; D006224:Cricetinae; D005260:Female; D007334:Insulin-Like Growth Factor I / Q000494:pharmacology*; D008540:Meiosis / Q000502:physiology; D009865:Oocytes / Q000201:enzymology* / Q000502:physiology; D009866:Oogenesis / Q000502:physiology; D010208:Papaverine / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology*; D011494:Protein Kinases / Q000378:metabolism*; D011724:Pyridazines / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D019893:Ribosomal Protein S6 Kinases; D020889:Rolipram; D013806:Theophylline / Q000494:pharmacology; D014982:Xenopus laevis
D010726:Phosphodiesterase Inhibitors; D011724:Pyridazines; D011760:Pyrrolidinones; D007334:Insulin-Like Growth Factor I; C042527:imazodan; D013806:Theophylline; D010208:Papaverine; D011494:Protein Kinases; D019893:Ribosomal Protein S6 Kinases; D020889:Rolipram; D015056:1-Methyl-3-isobutylxanthine