Effect of dibutyryl cyclic AMP on the cyclin-dependent kinase inhibitor p27Kip1 in the human hepatoma cells PLC/PRF/5.
The cyclin-dependent kinase (cdk) inhibitor p27Kip1 is known to play a role in cell-cycle regulation at G1 and G1/S phase. We investigated the effect of the putative growth-inhibiting agent dibutyryl cyclic AMP (DBcAMP) on the serial changes of p27Kip1 expression in the human hepatoma cells PLC/PRF/5 in culture. The p27Kip1 protein level increased at an early stage of G1 phase (2 hours) after a release from serum-starvation and subsequently maintained the level until the entry to S phase, whereas an addition of DBcAMP at 1mM increased the p27Kip1 protein level during G1 phase. In contrast, the relative expression levels of p27Kip1 mRNA at 2 hours, 4 hours and 6 hours were lower in DBcAMP-added cells. The effects of DBcAMP on cell growth were, reduction of S-phase cells, inhibition of DNA synthesis, and accumulation of G2-phase cells. In the presence of the antisense oligodeoxynucleotides against p27Kip1 mRNA, DBcAMP-induced growth inhibition was partially abolished. These findings suggest that DBcAMP elevates p27Kip1 protein expression during G1 phase, which could be associated with growth inhibition. DBcAMP may inhibit the degradation of p27Kip1 protein.
Kikukawa
M
M
Third Department of Internal Medicine, Nara Medical University, Japan.
Okamoto
Y
Y
Fukui
H
H
Nakano
H
H
D003994:Bucladesine / Q000494:pharmacology*; D006528:Carcinoma, Hepatocellular / Q000201:enzymology; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D004273:DNA, Neoplasm / Q000096:biosynthesis; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006131:Growth Inhibitors / Q000494:pharmacology; D006801:Humans; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D018797:Cell Cycle Proteins; D004273:DNA, Neoplasm; D006131:Growth Inhibitors; D008869:Microtubule-Associated Proteins; D025521:Tumor Suppressor Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; D003994:Bucladesine