Different patterns of cyclin D1/CDK4-E2F-1/4 pathways in human embryo lung fibroblasts treated by benzo[a]pyrene at different doses.
OBJECTIVE
To investigate the roles of the cyclin D1/CDK4 and E2F-1/4 pathways and compare their work patterns in cell cycle changes induced by different doses of B[a]P.


METHODS
Human embryo lung fibroblasts (HELFs) were treated with 2 micromol/L or 100 micromol/L B[a]P which were provided with some characteristics of transformed cells (T-HELFs). Cyclin D1, CDK4 and E2F-1/4 expressions were determined by Western blotting. Flow cytometry was used to detect the distribution of cell cycle.


RESULTS
After B[a]P treatment, the proportion of the first gap (G1) phase cells decreased. CDK4 and E2F-4 expression did not change significantly. In 2 micromol/L treated cells, a marked overexpression of cyclin D1 and E2F-1 was observed. However, in T-HELFs overexpression was limited to cyclin D1 only, and no overexpression of E2F-1 was observed. The decreases of G1 phase in response to B[a]P treatment were blocked in antisense cyclin D1 and antisense CDK4 transfected HELFs (A-D1 and A-K4) and T-HELFs (T-A-D1 and T-A-K4). After 2 micromol/L B[a]P treatment, overexpression of E2F-1 was attenuated in A-D1, and E2F-4 expression was decreased significantly in A-K4. In T-A-D1 and T-A-K4, E2F-4 expression was increased significantly, compared with T-HELFs. The E2F-1 expression remained unchanged in T-A-D1 and T-A-K4.


CONCLUSIONS
Cyclin D1/CDK4-E2F-1/4 pathways work in different patterns in response to low dose and high dose B[a]P treatment. In HELFs treated with 2 micromol/L B[a]P, cyclin D1 positively regulates the E2F-1 expression while CDK4 negatively regulates the E2F-4 expression; however, in HELFs treated with 100 micromol/L B[a]P, both cyclin D1 and CDK4 negatively regulate the E2F-4 expression.
Ye
Meng
M
National Institute of Occupational Health and Poison Control, Chinese Center for Disease Control and Prevention, 29 Nanwei Road, Beijing 100050, China.
Liu
Bing-Ci
BC
Shi
Xiang-Lin
XL
You
Bao-Rong
BR
Du
Hong-Ju
HJ
Jia
Xiao-Wei
XW
Shen
Fu-Hai
FH
D001564:Benzo(a)pyrene / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D019938:Cyclin D1 / Q000378:metabolism*; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D050704:E2F4 Transcription Factor / Q000378:metabolism*; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D006801:Humans; D008168:Lung / Q000166:cytology / Q000187:drug effects* / Q000196:embryology / Q000201:enzymology / Q000378:metabolism
D050704:E2F4 Transcription Factor; D019938:Cyclin D1; D001564:Benzo(a)pyrene; D051358:Cyclin-Dependent Kinase 4