Inhibition of G1 cyclin expression in normal rat kidney cells by inostamycin, a phosphatidylinositol synthesis inhibitor.
We previously reported that inostamycin, an inhibitor of CDP-DG: inositol transferase, inhibited cell proliferation in normal rat kidney (NRK) cells by blocking cell cycle progression at the G1 phase. In the present paper, we report the effect of inostamycin on the serum-induced activation of Ser/Thr protein kinases that are involved in G1 progression. In quiescent NRK cells mitogen-activated protein kinase (MAP kinase) and casein kinase II were activated within 15 min after serum addition. Neither activation was affected by the treatment with inostamycin. However, in the inostamycin-treated cell, cyclin-dependent kinase 2 (CDK2) failed to be activated after serum stimulation. Since serum-induced expression of cyclin E was also suppressed by inostamycin, this inhibitor would appear to block CDK2 activation by inhibiting cyclin E expression. Furthermore, inostamycin also inhibited cyclin D1 expression induced by serum; and consequently, hyperphosphorylation of retinoblastoma protein (pRB) by RB-kinases such as CDK4 and CDK2 was abolished, which would result in elimination of functional inactivation of pRB. Thus, early G1 arrest in NRK cells by inostamycin is due to the inhibition of cyclin D1 and E expressions.
Deguchi
A
A
Department of Applied Chemistry, Faculty of Science and Technology, Keio University, Yokohama.
Imoto
M
M
Umezawa
K
K
D000818:Animals; D015153:Blotting, Western; D042846:CDC2-CDC28 Kinases; D051607:CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D047390:Casein Kinase II; D019938:Cyclin D1; D056746:Cyclin G; D056766:Cyclin G1; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000096:biosynthesis*; D004789:Enzyme Activation; D005663:Furans / Q000494:pharmacology; D007668:Kidney / Q000378:metabolism*; D008565:Membrane Proteins; D015513:Oncogene Proteins / Q000096:biosynthesis; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017855:Transferases (Other Substituted Phosphate Groups) / Q000037:antagonists & inhibitors*
C534704:Ccng1 protein, rat; D056746:Cyclin G; D056766:Cyclin G1; D016213:Cyclins; D005663:Furans; D008565:Membrane Proteins; D015513:Oncogene Proteins; C071861:inostamycin; D019938:Cyclin D1; D047390:Casein Kinase II; D017346:Protein Serine-Threonine Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D042846:CDC2-CDC28 Kinases; C495892:Cdk2 protein, rat; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases; D017855:Transferases (Other Substituted Phosphate Groups); D051607:CDP-Diacylglycerol-Inositol 3-Phosphatidyltransferase; C496767:Cdipt protein, rat