Abstract
Replicative senescence may be an important tumor suppressive mechanism for human cells. We investigated the mechanism of cell cycle arrest at senescence in human mammary epithelial cells (HMECs) that have undergone a period of 'self-selection', and as a consequence exhibit diminished p16(INK4A) levels. As HMECs approached senescence, the proportion of cells with a 2N DNA content increased and that in S phase decreased progressively. Cyclin D1-cdk4, cyclin E-cdk2 and cyclin A-cdk2 activities were not abruptly inhibited, but rather diminished steadily with increasing population age. In contrast to observations in fibroblast, p21(Cip1) was not increased at senescence in HMECs. There was no increase in p27(Kip1) levels nor in KIP association with targets cdks. While p15(INK4B) and its binding to both cdk4 and cdk6 increased with increasing passage, some cyclin D1-bound cdk4 and cdk6 persisted in senescent cells, whose inhibition could not be attributed to p15(INK4B). The inhibition of cyclin E-cdk2 in senescent HMECs was accompanied by increased inhibitory phosphorylation of cdk2, in association with a progressive loss of Cdc25A. Recombinant Cdc25A strongly reactivated cyclin E-cdk2 from senescent HMECs suggesting that reduction of Cdc25A contributes to cyclin E-cdk2 inhibition and G1 arrest at senescence. Although ectopic expression of Cdc25A failed to extend the lifespan of HMECs, the exogenous Cdc25A appeared to lack activity in these cells, since it neither shortened the G1-to-S phase interval nor activated cyclin E-cdk2. In contrast, in the breast cancer-derived MCF-7 line, Cdc25A overexpression increased both cyclin E-cdk2 activity and the S phase fraction. Thus, mechanisms leading to HMEC immortalization may involve not only the re-induction of Cdc25A expression, but also activation of this phosphatase.
| Original language | English |
|---|---|
| Pages (from-to) | 5314-5323 |
| Number of pages | 10 |
| Journal | Oncogene |
| Volume | 19 |
| Issue number | 47 |
| State | Published - Nov 9 2000 |
| Externally published | Yes |
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Keywords
- Cdc25A
- Cell cycle
- Cyclin E-cdk2
- HMEC
- P15(INK4B)
- Senescence
ASJC Scopus subject areas
- Molecular Biology
- Cancer Research
- Genetics
Cite this
Reduction of Cdc25A contributes to cyclin E1-Cdk2 inhibition at senescence in human mammary epithelial cells. / Sandhu, Charanjit; Donovan, Jeffrey; Bhattacharya, Nandita; Stampfer, Martha; Worland, Peter; Slingerland, Joyce M.
In: Oncogene, Vol. 19, No. 47, 09.11.2000, p. 5314-5323.Research output: Contribution to journal › Article
}
TY - JOUR
T1 - Reduction of Cdc25A contributes to cyclin E1-Cdk2 inhibition at senescence in human mammary epithelial cells
AU - Sandhu, Charanjit
AU - Donovan, Jeffrey
AU - Bhattacharya, Nandita
AU - Stampfer, Martha
AU - Worland, Peter
AU - Slingerland, Joyce M
PY - 2000/11/9
Y1 - 2000/11/9
N2 - Replicative senescence may be an important tumor suppressive mechanism for human cells. We investigated the mechanism of cell cycle arrest at senescence in human mammary epithelial cells (HMECs) that have undergone a period of 'self-selection', and as a consequence exhibit diminished p16(INK4A) levels. As HMECs approached senescence, the proportion of cells with a 2N DNA content increased and that in S phase decreased progressively. Cyclin D1-cdk4, cyclin E-cdk2 and cyclin A-cdk2 activities were not abruptly inhibited, but rather diminished steadily with increasing population age. In contrast to observations in fibroblast, p21(Cip1) was not increased at senescence in HMECs. There was no increase in p27(Kip1) levels nor in KIP association with targets cdks. While p15(INK4B) and its binding to both cdk4 and cdk6 increased with increasing passage, some cyclin D1-bound cdk4 and cdk6 persisted in senescent cells, whose inhibition could not be attributed to p15(INK4B). The inhibition of cyclin E-cdk2 in senescent HMECs was accompanied by increased inhibitory phosphorylation of cdk2, in association with a progressive loss of Cdc25A. Recombinant Cdc25A strongly reactivated cyclin E-cdk2 from senescent HMECs suggesting that reduction of Cdc25A contributes to cyclin E-cdk2 inhibition and G1 arrest at senescence. Although ectopic expression of Cdc25A failed to extend the lifespan of HMECs, the exogenous Cdc25A appeared to lack activity in these cells, since it neither shortened the G1-to-S phase interval nor activated cyclin E-cdk2. In contrast, in the breast cancer-derived MCF-7 line, Cdc25A overexpression increased both cyclin E-cdk2 activity and the S phase fraction. Thus, mechanisms leading to HMEC immortalization may involve not only the re-induction of Cdc25A expression, but also activation of this phosphatase.
AB - Replicative senescence may be an important tumor suppressive mechanism for human cells. We investigated the mechanism of cell cycle arrest at senescence in human mammary epithelial cells (HMECs) that have undergone a period of 'self-selection', and as a consequence exhibit diminished p16(INK4A) levels. As HMECs approached senescence, the proportion of cells with a 2N DNA content increased and that in S phase decreased progressively. Cyclin D1-cdk4, cyclin E-cdk2 and cyclin A-cdk2 activities were not abruptly inhibited, but rather diminished steadily with increasing population age. In contrast to observations in fibroblast, p21(Cip1) was not increased at senescence in HMECs. There was no increase in p27(Kip1) levels nor in KIP association with targets cdks. While p15(INK4B) and its binding to both cdk4 and cdk6 increased with increasing passage, some cyclin D1-bound cdk4 and cdk6 persisted in senescent cells, whose inhibition could not be attributed to p15(INK4B). The inhibition of cyclin E-cdk2 in senescent HMECs was accompanied by increased inhibitory phosphorylation of cdk2, in association with a progressive loss of Cdc25A. Recombinant Cdc25A strongly reactivated cyclin E-cdk2 from senescent HMECs suggesting that reduction of Cdc25A contributes to cyclin E-cdk2 inhibition and G1 arrest at senescence. Although ectopic expression of Cdc25A failed to extend the lifespan of HMECs, the exogenous Cdc25A appeared to lack activity in these cells, since it neither shortened the G1-to-S phase interval nor activated cyclin E-cdk2. In contrast, in the breast cancer-derived MCF-7 line, Cdc25A overexpression increased both cyclin E-cdk2 activity and the S phase fraction. Thus, mechanisms leading to HMEC immortalization may involve not only the re-induction of Cdc25A expression, but also activation of this phosphatase.
KW - Cdc25A
KW - Cell cycle
KW - Cyclin E-cdk2
KW - HMEC
KW - P15(INK4B)
KW - Senescence
UR - http://www.scopus.com/inward/record.url?scp=0034626721&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=0034626721&partnerID=8YFLogxK
M3 - Article
VL - 19
SP - 5314
EP - 5323
JO - Oncogene
JF - Oncogene
SN - 0950-9232
IS - 47
ER -