TY - JOUR
T1 - Effects of depletion of CREB-binding protein on c-Myc regulation and cell cycle G1-S transition
AU - Rajabi, Hasan N.
AU - Baluchamy, Sudhakar
AU - Kolli, Sivanagarani
AU - Nag, Alo
AU - Srinivas, Rampalli
AU - Raychaudhuri, Pradip
AU - Thimmapaya, Bayar
PY - 2005/1/7
Y1 - 2005/1/7
N2 - We recently reported that the transcriptional coactivator and histone acetyltransferase p300 plays an important role in the G1 phase of the cell cycle by negatively regulating c-myc and thereby preventing premature G1 exit (Kolli, et al. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 4646-4651; Baluchamy, et al. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 9524-9529). Because p300 does not substitute for all CREB-binding protein (CBP) functions, we investigated whether CBP also negatively regulates c-myc and prevents premature DNA synthesis. Here, we show that antisense-mediated depletion of CBP in serum-deprived human cells leads to induction of c-myc and that such cells emerge from quiescence without growth factors at a rate comparable with that of p300-depleted cells. The CBP-depleted cells contained significantly reduced levels of the cyclin-dependent kinase inhibitor p21 and low levels of p107 and p130 (but not pRb) phosphorylation, suggesting that these factors, along with elevated levels of c-Myc, contribute to induction of DNA synthesis. Antisense c-Myc reversed the phosphorylation of p107 and p130 and the induction of S phase in CBP-depleted cells, indicating that up-regulation of c-myc is directly responsible for the induction of S phase. Furthermore, the serum-stimulated p300/CBP-depleted cells did not traverse beyond S phase, and a significant number of these cells died of apoptosis, which was not related to p53 levels. These cells also contained significantly higher levels of c-Myc compared with normal cells. When c-myc expression was blocked by antisense c-Myc, the apoptosis of the serum-stimulated CBP-depleted cells was reversed, indicating that high levels of c-Myc contribute to apoptosis. Thus, despite their high degree of structural and functional similarities, normal levels of both p300 and CBP are essential for keeping c-myc in a repressed state in G 1 and thereby preventing inappropriate entry of cells into S phase. In addition, both these proteins also provide important functions in coordinated cell cycle progression.
AB - We recently reported that the transcriptional coactivator and histone acetyltransferase p300 plays an important role in the G1 phase of the cell cycle by negatively regulating c-myc and thereby preventing premature G1 exit (Kolli, et al. (2001) Proc. Natl. Acad. Sci. U. S. A. 98, 4646-4651; Baluchamy, et al. (2003) Proc. Natl. Acad. Sci. U. S. A. 100, 9524-9529). Because p300 does not substitute for all CREB-binding protein (CBP) functions, we investigated whether CBP also negatively regulates c-myc and prevents premature DNA synthesis. Here, we show that antisense-mediated depletion of CBP in serum-deprived human cells leads to induction of c-myc and that such cells emerge from quiescence without growth factors at a rate comparable with that of p300-depleted cells. The CBP-depleted cells contained significantly reduced levels of the cyclin-dependent kinase inhibitor p21 and low levels of p107 and p130 (but not pRb) phosphorylation, suggesting that these factors, along with elevated levels of c-Myc, contribute to induction of DNA synthesis. Antisense c-Myc reversed the phosphorylation of p107 and p130 and the induction of S phase in CBP-depleted cells, indicating that up-regulation of c-myc is directly responsible for the induction of S phase. Furthermore, the serum-stimulated p300/CBP-depleted cells did not traverse beyond S phase, and a significant number of these cells died of apoptosis, which was not related to p53 levels. These cells also contained significantly higher levels of c-Myc compared with normal cells. When c-myc expression was blocked by antisense c-Myc, the apoptosis of the serum-stimulated CBP-depleted cells was reversed, indicating that high levels of c-Myc contribute to apoptosis. Thus, despite their high degree of structural and functional similarities, normal levels of both p300 and CBP are essential for keeping c-myc in a repressed state in G 1 and thereby preventing inappropriate entry of cells into S phase. In addition, both these proteins also provide important functions in coordinated cell cycle progression.
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U2 - 10.1074/jbc.M408633200
DO - 10.1074/jbc.M408633200
M3 - Article
C2 - 15522869
AN - SCOPUS:12844277305
VL - 280
SP - 361
EP - 374
JO - Journal of Biological Chemistry
JF - Journal of Biological Chemistry
SN - 0021-9258
IS - 1
ER -