Transient tyrosine phosphorylation of p34cdc2 is an early event in radiation-induced apoptosis of prostate cancer cells.
BACKGROUND
Previous studies have demonstrated that androgen-independent human prostate cancer cells undergo radiation-induced apoptosis. The present study investigated the early events that trigger the apoptotic response of prostate cancer cells after exposure to ionizing irradiation.


METHODS
Human prostate cancer cells (PC-3) were exposed to single doses of ionizing irradiation, and the immediate protein phosphorylation events were temporally correlated with induction of apoptosis. Apoptosis among the irradiated cell populations was evaluated using the fluorescein-terminal transferase assay.


RESULTS
The kinetics of phosphorylation of a Mr 34,000 substrate followed a transient course: an initial increase was observed after 10 min postirradiation, reaching maximum levels by 60 min, and the protein subsequently underwent rapid dephosphorylation. Subsequent analysis revealed that the substrate for this tyrosine phosphorylation is the serine/ threonine p34cdc2 protein kinase, a cell cycle regulatory protein that controls cell entry into mitosis. This enhanced phosphorylation temporally preceded the radiation-induced apoptotic DNA fragmentation as detected by the terminal transferase technique. Arresting the cells in G0/G1 phase by pretreatment with suramin totally abrogated radiation-induced phosphorylation of p34cdc2 protein at the tyrosine residue, indicating that this posttranslational modification occurs in cell populations that escape G2 arrest and undergo apoptosis in response to radiation.


CONCLUSIONS
These results suggest that a rapid and transient phosphorylation of a protein that controls mitotic progression precedes and potentially triggers radiation-induced apoptosis in prostate cancer cells.
Kyprianou
N
N
Division of Urology, University of Maryland School of Medicine, Baltimore 21201, USA.
Bains
A
A
Rhee
J G
JG
D017209:Apoptosis / Q000187:drug effects / Q000502:physiology / Q000528:radiation effects*; D016203:CDC2 Protein Kinase / Q000378:metabolism* / Q000528:radiation effects; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D053938:DNA Fragmentation; D004273:DNA, Neoplasm / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D006801:Humans; D007700:Kinetics; D008297:Male; D010750:Phosphoproteins / Q000378:metabolism / Q000528:radiation effects*; D019000:Phosphotyrosine / Q000378:metabolism; D011471:Prostatic Neoplasms; D011839:Radiation, Ionizing; D013498:Suramin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D004273:DNA, Neoplasm; D010750:Phosphoproteins; D019000:Phosphotyrosine; D013498:Suramin; D016203:CDC2 Protein Kinase