p21(WAF1/CIP1) inhibits cell cycle progression but not G2/M-phase transition following methylmercury exposure.
Methylmercury (MeHg) is an environmentally prevalent organometal that is particularly toxic to the developing central nervous system (CNS). Prenatal MeHg exposure is associated with reduced brain size and weight and a reduced number of neurons, which have been associated with impaired cell proliferation. We evaluate the role of p21, a cell cycle protein involved in the G1- and G2-phase checkpoint control, in the cell cycle inhibition induced by MeHg. Primary mouse embryonic fibroblasts (MEFs) of different p21 genotypes (wild-type, heterozygous, and null) were isolated at day 14 of gestation and treated at passages 4-6 with either 0, 2, 4, or 6 microM MeHg or 50 nM colchicine for 24 h. Changes in cell cycle distribution after continuous toxicant treatment were analyzed by DNA content-based flow cytometry using DAPI. MeHg induced an increase in the proportion of cells in G2/M at 2 and 4 microM MeHg (p < or = 0.05) irrespective of p21 genotype. Effects of MeHg on cell cycle progression were subsequently evaluated using BrdU-Hoechst flow cytometric analysis. Inhibition of cell cycle progression was observed in all p21 genotypes after continuous exposure to MeHg for 24 and 48 h. p21 null (-/-) cells reached the second-round G1 at a higher fraction compared to the wild type (+/+) and heterozygous (+/-) cells (p < or = 0.05). These data support previous observations that MeHg inhibits cell cycle progression through delayed G2/M transition. Whereas the G2/M accumulation induced by MeHg was independent of p21 status, a greater proportion of p21(-/-) cells were able to complete one round of cell division in the presence of MeHg compared to p21(+/-) or p21(+/+) cells. These data suggest a role for p21 in retarding cell cycle progression, but not mitotic inhibition, following exposure to MeHg.
Mendoza
Ma Aileen C
MA
Department of Environmental Health, University of Washington, Seattle, Washington 98195, USA.
Ponce
Rafael A
RA
Ou
Ying C
YC
Faustman
Elaine M
EM
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000502:physiology*; D005347:Fibroblasts; D005434:Flow Cytometry; D016195:G2 Phase / Q000187:drug effects*; D005838:Genotype; D008767:Methylmercury Compounds / Q000633:toxicity*; D051379:Mice; D008822:Mice, Transgenic
C493957:Cdkn1a protein, mouse; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D008767:Methylmercury Compounds