V. Patel et al., Induction of apoptosis in head-and-neck squamous carcinoma cells by gamma-irradiation and bleomycin is p53-independent, INT J CANC, 88(5), 2000, pp. 737-743
We have examined the ability of w gamma -irradiation and bleomycin to induc
e apoptosis in a model system consisting of cell lines derived from natural
ly occurring human head-and-neck squamous-cell carcinomas with contrasting
p53 status and expression levels of pro- and anti-apoptotic molecules. Foll
owing exposure to gamma -irradiation (20 Gy) or bleomycin (3.5 muM) for 0 t
o 96 hr, cells expressing either transcriptionally inactive mutant p53 (HN6
) or a truncated p53 molecule (HN 19) underwent apoptosis, as assessed by f
luorescence-activated cell sorting and terminal deoxynucleotidyl transferas
e-mediated dUTP nick end-labeling, in contrast to cells that express wild-t
ype p53 (HN30), suggesting that apoptosis induced by these agents occurs by
p53-independent mechanisms. Apoptosis in HN6 and HN19 cells was preceded b
y a G(2)/M cell-cycle block, as analyzed by DNA content and BrdU staining.
In contrast, HN30 cells remained blocked in both G(1) and G(2)/M and failed
to re enter the cell cycle. Levels of Bcl-2 were elevated in 3 of 10 cell
lines, and only marginal differences were observed for Bcl-x(L). Pro-apopto
tic proteins bar and Bcl-x(S) were detectable in normal keratinocytes and 4
tumor cell lines. Bar-delta (16 kDa) was highly represented in normal kera
tinocytes, and levels of bak were variable between cell lines. Elevated exp
ression of Bcl-2 failed to protect HN19 cells from either gamma -irradiatio
n or bleomycin-induced apoptosis. Our data support the existence of p53- an
d Bcl-2-independent pathways regulating apoptosis in keratinocytes and sugg
est that efficacy of either radiotherapy or bleomycin treatment for oral sq
uamous-cell neoplasms may not, therefore, be influenced solely by endogenou
s p53 status. Published 2000 Wiley-Liss, Inc.(dagger).