The age-dependent binding of CBP/tk, a CCAAT binding protein, is deregulated in transformed and immortalized mammalian cells but absent in premature aging cells.
CBP/tk, CCAAT Binding Protein for thymidine kinase, has been shown to bind to the distal and proximal CCAAT elements in human TK gene at G1/S boundary in normal human IMR-90 cells after serum stimulation (Pang and Chen, 1993). We now show that the serum-induced binding activity of CBP/tk was inversely related to the population doubling level (PDL) of the normal IMR-90 cells. However, little or almost no CBP/tk binding activity was observed in cells derived from patients with premature aging syndromes (e.g., Werner, Hutchinson-Gilford, and Cockayne syndrome). In contrast, CBP/tk binding activity in SV-40 virus-transformed human cells and in HeLa cells was overexpressed at levels 5- to 15-fold higher than that in normal cells and appeared to be deregulated. The half-life of CBP/tk binding activity in SV-40 transformed cells was at least 10 times longer than that in normal IMR-90 cells, suggesting that posttranslational control may contribute to the deregulation. CBP/tk binding activity detected in other mammalian cells such as murine NIH3T3, an immortal cell line, did not reveal any cell cycle dependence either. Further characterization of CBP/tk binding complex indicates that the binding complex may contain NF-YA and NF-YB and that the binding activity was sensitive to oxidizing reagents. Taken together, our data showed that the age- and cell cycle-dependent nature of CBP/tk is a function of cell types and that CBP/tk binding activity may be subjected to posttranslational and redox regulation.
Pang
J H
JH
Department of Chemistry, Rutgers-The State University of New Jersey, Piscataway 08855-0939, USA.
Good
L F
LF
Chen
K Y
KY
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D022762:CCAAT-Enhancer-Binding Proteins; D002453:Cell Cycle; D002461:Cell Line, Transformed; D002478:Cells, Cultured; D016922:Cellular Senescence; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D013937:Thymidine Kinase / Q000235:genetics
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D013937:Thymidine Kinase