Attenuation of G2 checkpoint function precedes human cell immortalization
Kaufmann, W.K.; Levedakou, E.N.; Grady, H.L.; Paules, R.S.; Stein, G.H.
Cancer Research 55(1): 7-11
1995
ISSN/ISBN: 0008-5472 PMID: 7805043 Document Number: 445471
We have investigated the hypothesis that attenuation of the G-2 checkpoint, which delays entry into mitosis in response to damage to DNA and protects against clastogenesis, may contribute to the genetic instability of immortal human cell lines. IMR-90 normal human fibroblasts displayed stringent G-2 checkpoint response to gamma-radiation-induced DNA damage. Irradiation with 1.5 Gy induced 98% inhibition of mitosis and 79% inhibition of cyclin B1/p34-CDC2 kinase activity within 2 h. SV40-transformed IMR-90 cells with extended in vitro proliferative lifespan and immortal derivative cells displayed significantly less radiation-induced G-2 delay (60-70%) and less inhibition of cyclin B1/p34-CDC2 protein kinase activity (43-46%) than was seen in normal cells. Two other SV40-transformed lines and a ribrosarcoma line displayed a similar attenuation of G-2 checkpoint function. The attenuation of G-2 checkpoint function in SV40 transformed IMR-90 cells was associated with elevated levels of expression of cyclin B1 (8-fold greater) and p34-CDC2 (2.5-fold greater). By allowing cells with damaged chromatids to enter mitosis, an attenuation of G-2 checkpoint function in finite lifespan cells may promote the genetic alterations necessary for the conversion to immortality.