Changes of apoptosis, p53, and bcl-2 by irradiation in poorly differentiated thyroid carcinoma cell lines: a prognostic marker for the prospect of therapeutic success?
BACKGROUND
Poorly differentiated thyroid carcinoma (PDTC) has an unfavorable prognosis. Surgical management is the principal treatment approach. In addition, radioiodine treatment and external beam radiotherapy (EBRT) are given to reduce the risk of local relapse. Despite aggressive therapy, the response to treatment tends to become increasingly poorer over time. The objective of this study was to investigate the induction of apoptosis by EBRT as a function of p53 and bcl-2 protein levels in PDTC. The predictive value of these molecules with respect to treatment efficacy was evaluated.


METHODS
Two different cell lines of PDTC (FTC-133 and ML-1) were irradiated with a dose of 30 Gy. Apoptotic cells were quantified using terminal deoxynucleotidyltransferase-dUTP nick-end labeling staining without irradiation, 48 and 96 hours after irradiation. The protein levels of p53 and bcl-2 were measured simultaneously using flow cytometry and western blotting. The cell cycle distribution was determined.


RESULTS
Untreated FTC-133 cells showed a high rate of apoptosis, a high protein level of p53, and a low bcl-2 protein level. Forty-eight hours after irradiation, a slight reduction in apoptotic cells was observed in conjunction with an increase in bcl-2 and p53 protein levels. The slightly reduced fraction of apoptotic cells remained at the same level up to 96 hours after irradiation, whereas the p53 protein level was further downregulated. The cell cycle distribution showed a significant G2/M arrest after 48 hours and recovery 96 hours after irradiation. ML-1 cells did not show any detectable p53 levels and revealed a low rate of apoptosis which significantly increased 48 hours after irradiation. Ninety-six hours after irradiation, a decrease in apoptosis was detectable. The protein level of bcl-2 increased significantly within 48 hours and decreased 96 hours after irradiation. The cell cycle distribution showed a G2/M arrest after 48 hours without a recovery 96 hours after irradiation.


CONCLUSIONS
The p53 and bcl-2 expression profiles and the observed apoptotic rates of FTC-133 and ML-1 under irradiation are consistent with a more aggressive FTC-133 phenotype. Alterations in p53- and bcl-2 protein levels yield predictive information for EBRT efficacy.
Department of Radio-Oncology, University of Regensburg, Regensburg, Germany. fabian.pohl@klinik.uni-regensburg.de
Fabian
F
Pohl
Jirka
J
Grosse
Daniela
D
Grimm
Gero
G
Brockhoff
Kriss
K
Westphal
Jutta
J
Moosbauer
Oliver
O
Koelbl
Manfred
M
Infanger
Christoph
C
Eilles
Johann
J
Schoenberger
D017209:Apoptosis / Q000528:radiation effects*; D002453:Cell Cycle / Q000528:radiation effects; D045744:Cell Line, Tumor; D006801:Humans; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism / Q000528:radiation effects*; D013964:Thyroid Neoplasms / Q000235:genetics / Q000532:radiotherapy*; D016159:Tumor Suppressor Protein p53 / Q000502:physiology / Q000528:radiation effects*
D019253:Proto-Oncogene Proteins c-bcl-2; D016159:Tumor Suppressor Protein p53