OBJECTIVES: The molecular mechanisms that regulate cardiomyocyte cell cycle and terminal differentiation in humans remain largely unknown. To determine which cyclins, cyclin dependent kinases (CDKs) and cyclin kinase inhibitors (CKIs) are important for cardiomyocyte proliferation, we have examined protein levels of cyclins, CDKs and CKIs during normal atrial development in humans. METHODS: Atrial tissues were obtained in the fetus from inevitable abortion and in the adult during surgery. Cyclin and CDK proteins were determined by Western blot analysis. CDK activities were determined by phosphorylation amount using specific substrate. RESULTS: Most cyclins and CDKs were high during the fetal period and their levels decreased at different rates during the adult period. While the protein levels of cyclin D1, cyclin D3, CDK4, CDK6 and CDK2 were still detectable in adult atria, the protein levels of cyclin E, cyclin A, cyclin B, cdc2 and PCNA were not detectable. Interestingly, p27KIP1 protein increased markedly in the adult period, while p21CIP1 protein in atria was detectable only in the fetal period. While the activities of CDK6, CDK2 and cdc2 decreased markedly, the activity of CDK4 did not change from the fetal period to the adult period. CONCLUSION: These findings indicate that marked reduction of protein levels and activities of cyclins and CDKs, and marked induction of p27KIP1 in atria, are associated with the withdrawal of cardiac cell cycle in adult humans.
Adult ; Age Factors ; Animal ; Blotting, Western ; Cell Cycle ; Cells, Cultured ; Comparative Study ; Cyclin A/analysis ; Cyclin B/analysis ; Cyclin D1/analysis ; Cyclin E/analysis ; Cyclin-Dependent Kinases/analysis* ; Cyclins/analysis* ; Female ; Fetal Development ; Heart Atrium/growth & development* ; Heart Atrium/embryology ; Heart Atrium/cytology* ; Heart Atrium/chemistry ; Human ; Male ; Middle Age ; Myocardium/chemistry* ; Rats ; Rats, Sprague-Dawley ; Substances: Cyclin D1 ; Substances: Cyclins ; Substances: Cyclin-Dependent Kinases ; Substances: Cyclin E ; Substances: Cyclin B ; Substances: Cyclin A

A C6 beta-chemokine, CKbeta8-1, suppressed the colony formation of CD34 + cells of human cord blood (CB). Molecular mechanisms involved in CKbeta8-1-medicated suppression of colony formation of CD34 + cells are not known. To address this issue, the level of various G1/S cell cycle regulating proteins in CKbeta8-1-treated CD34 + cells were compared with those in untreated CD34 + cells. CKbeta8-1 did not significantly alter the expression of the G1/S cycle regulation proteins (cyclin D1, D3, and E), CDK inhibitor (p27and Rb), and other cell proliferation regulation protein (p53) in CB CD34 + cells. Here we describe an in vitro system in which CB CD34 + cells were committed to a multipotent progenitor lineage of colony forming units-granulocyte/macrophage (CFU-GM) by a simple combination of recombinant human (rh) GM-CSF and rhIL-3. In this culture system, we found that cyclin E protein appeared later and disappeared faster in the CKbeta8-1-treated cells than in the control cells during CFU-GM lineage development. These findings suggested that cyclin E may play a role in suppressing the colony formation of CFU-GM by CKbeta8-1.
Antigens, CD34/metabolism ; Cell Cycle Proteins/metabolism ; Cell Lineage ; Cells, Cultured ; Chemokines, CC/*pharmacology ; Cyclin E/*metabolism ; Fetal Blood/*cytology ; G1 Phase/drug effects ; Gene Expression Regulation/*drug effects ; Granulocytes/cytology/*drug effects/metabolism ; Growth Substances/pharmacology ; Humans ; Macrophages/cytology/*drug effects/metabolism ; Research Support, Non-U.S. Gov't ; Stem Cells/cytology/*drug effects/metabolism