title: Polyamine depletion arrests growth of IEC-6 and Caco-2 cells by different mechanisms.
abstract: The polyamines spermidine and spermine and their precursor, putrescine, are required for the growth and proliferation of eukaryotic cells. This study compares and contrasts growth arrest caused by polyamine depletion in the untransformed IEC-6 cell line with that in the p53-mutated colon cancer Caco-2 cell line. Cells were grown in the presence or absence of alpha-difluoromethylornithine (DFMO), a specific inhibitor of ornithine decarboxylase, the first rate-limiting enzyme in the synthesis of polyamines. Depletion of polyamines inhibited the growth of both cell lines equally and over the same time frame. However, whereas IEC-6 cells were arrested in the G(1) phase of the cell cycle, there was no accumulation of Caco-2 cells in any particular phase. In IEC-6 cells, growth arrest was accompanied by elevated levels of p53 and p21(Waf1/Cip1) (p21). There were no changes in p53 levels in Caco-2 cells. Levels of p21 increased in Caco-2 cells on day 2 without any effect on cell cycle progression. The amount of cyclin-dependent kinase (Cdk)2 protein was unchanged by polyamine depletion in both cell lines. However, the activity of Cdk2 was significantly inhibited by DFMO in IEC-6 cells. These data suggest that in the untransformed IEC-6 cells the regulation of Cdk2 activity and progression through the cell cycle are p53- and p21 dependent. Growth arrest in the p53-mutated Caco-2 line after polyamine depletion occurs by a different, yet unknown, mechanism.
authors.affiliation: Department of Physiology, College of Medicine, The University of Tennessee Health Science Center, Memphis, Tennessee 38163, USA.
authors.forename: R M
authors.initials: RM
authors.lastname: Ray
authors.forename: S A
authors.initials: SA
authors.lastname: McCormack
authors.forename: L R
authors.initials: LR
authors.lastname: Johnson
mesh_terms: D042846:CDC2-CDC28 Kinases; D018938:Caco-2 Cells; D002455:Cell Division / Q000502:physiology; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018844:Cyclin-Dependent Kinases / Q000378:metabolism; D016213:Cyclins / Q000378:metabolism; D000518:Eflornithine / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007413:Intestinal Mucosa / Q000166:cytology* / Q000201:enzymology*; D009955:Ornithine Decarboxylase / Q000378:metabolism; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D011700:Putrescine / Q000378:metabolism; D013096:Spermine / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
chemical_list: C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D004791:Enzyme Inhibitors; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines; D011518:Proto-Oncogene Proteins; D016159:Tumor Suppressor Protein p53; D013096:Spermine; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495894:CDK2 protein, human; C495900:CDK4 protein, human; D051357:Cyclin-Dependent Kinase 2; D051358:Cyclin-Dependent Kinase 4; D018844:Cyclin-Dependent Kinases; D009955:Ornithine Decarboxylase; D011700:Putrescine; D000518:Eflornithine