title: cAMP-mediated inhibition of DNA replication and S phase progression: involvement of Rb, p21Cip1, and PCNA.
abstract: cAMP exerts an antiproliferative effect on a number of cell types including lymphocytes. This effect of cAMP is proposed to be mediated by its ability to inhibit G1/S transition. In this report, we provide evidence for a new mechanism whereby cAMP might inhibit cellular proliferation. We show that elevation of intracellular levels of cAMP inhibits DNA replication and arrests the cells in S phase. The cAMP-induced inhibition of DNA synthesis was associated with the increased binding of p21Cip1 to Cdk2-cyclin complexes, inhibition of Cdk2 kinase activity, dephosphorylation of Rb, and dissociation of PCNA from chromatin in S phase cells. The ability of cAMP to inhibit DNA replication and trigger release of PCNA from chromatin required Rb and p21Cip1 proteins, since both processes were only marginally affected by increased levels of cAMP in Rb-/- and p21Cip1-/- 3T3 fibroblasts. Importantly, the implications of cAMP-induced inhibition of DNA synthesis in cancer treatment was demonstrated by the ability of cAMP to reduce apoptosis induced by S phase-specific cytotoxic drugs. Taken together, these results demonstrate a novel role for cAMP in regulation of DNA synthesis and support a model in which activation of cAMP-dependent signaling protects cells from the effect of S phase-specific antitumor agents.
authors.affiliation: Institute of Basic Medical Sciences, Department of Biochemistry, University of Oslo, Oslo N-0317, Norway. soheil.naderi@basalmed.uio.no
authors.forename: Soheil
authors.initials: S
authors.lastname: Naderi
authors.forename: Jean Y J
authors.initials: JY
authors.lastname: Wang
authors.forename: Tung-Ti
authors.initials: TT
authors.lastname: Chen
authors.forename: Kristine B
authors.initials: KB
authors.lastname: Gutzkow
authors.forename: Heidi K
authors.initials: HK
authors.lastname: Blomhoff
mesh_terms: D000818:Animals; D017209:Apoptosis; D015152:Blotting, Northern; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002467:Cell Nucleus / Q000378:metabolism; D049109:Cell Proliferation; D002843:Chromatin / Q000378:metabolism; D003001:Cloning, Molecular; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D050759:Cyclin-Dependent Kinase Inhibitor p21; D004247:DNA / Q000378:metabolism*; D004261:DNA Replication; D004305:Dose-Response Relationship, Drug; D005434:Flow Cytometry; D016193:G1 Phase; D006801:Humans; D015151:Immunoblotting; D008214:Lymphocytes / Q000378:metabolism; D051379:Mice; D008856:Microscopy, Fluorescence; D008954:Models, Biological; D041681:NIH 3T3 Cells; D010766:Phosphorylation; D018809:Proliferating Cell Nuclear Antigen / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000378:metabolism*; D016196:S Phase; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors
chemical_list: C493956:CDKN1A protein, human; C493957:Cdkn1a protein, mouse; D018797:Cell Cycle Proteins; D002843:Chromatin; D050759:Cyclin-Dependent Kinase Inhibitor p21; D018809:Proliferating Cell Nuclear Antigen; D016160:Retinoblastoma Protein; D005576:Colforsin; D004247:DNA; D000242:Cyclic AMP