Hypoxia-induced irreversible S-phase arrest involves down-regulation of cyclin A.
We have studied hypoxia-induced cell cycle arrest in human cells where the retinoblastoma tumour suppressor protein (pRB) is either functional (T-47D cells) or abrogated by expression of the HPV18 E7 oncoprotein (NHIK 3025 cells). All cells in S phase are immediately arrested upon exposure to extreme hypoxia. During an 18-h extreme hypoxia regime, the cyclin A protein level is down-regulated in cells of both types when in S-phase, and, as we have previously shown, pRB re-binds in the nuclei of all T-47D cells (Amellem et al. 1996). Hence, pRB is not necessary for the down-regulation of cyclin A during hypoxia. However, our findings indicate that re-oxygenation cannot release pRB from its nuclear binding following this prolonged exposure. The result is permanent S-phase arrest even after re-oxygenation, and this is correlated with a complete and permanent down-regulation of cyclin A in the pRB functional T-47D cells. In contrast, both cell cycle arrest and cyclin A down-regulation in S phase are reversed upon re-oxygenation in non-pRB-functional NHIK 3025 cells after prolonged exposure to extreme hypoxia. Our results indicate that pRB is involved in permanent S-phase arrest and down-regulation of cyclin A after extreme hypoxia.
Seim
J
J
Department of Physics, the Biophysic group, University of Oslo, Oslo, Norway.
Graff
P
P
Amellem
O
O
Landsverk
K S
KS
Stokke
T
T
Pettersen
E O
EO
D015687:Cell Hypoxia / Q000502:physiology*; D002467:Cell Nucleus / Q000378:metabolism; D019925:Cyclin A / Q000378:metabolism*; D019927:Cyclin E / Q000378:metabolism; D015536:Down-Regulation; D006801:Humans; D010100:Oxygen / Q000378:metabolism; D016160:Retinoblastoma Protein / Q000378:metabolism*; D016196:S Phase / Q000502:physiology*; D014407:Tumor Cells, Cultured
D019925:Cyclin A; D019927:Cyclin E; D016160:Retinoblastoma Protein; D010100:Oxygen