Sensitization of cervical cancer cell lines to low-dose radiation by retinoic acid does not require functional p53.
OBJECTIVE
Current therapy for cervical cancer includes radiation therapy. Retinoic acid (RA) can increase the sensitivity of cervical cancer cell lines to radiation. The mechanism of this sensitization may not involve the p53 protein because the human papillomavirus (HPV) E6 protein, which is present in the majority of cervical cancers, promotes p53 degradation. The objective of this study was to determine if p53 is involved in the mechanism of RA radiosensitization.


METHODS
The effects of radiation on cervical (SiHa, CC-1, and C33a) and vulvar (SW962) cancer cell lines under various experimental conditions were evaluated using clonogenic, Coulter Counter, electrophoretic mobility shift (EMSA) and a multi-probe RNase protection assay of p53-inducible genes.


RESULTS
RA (5 microM 9-cis-RA) radiosensitized the SiHa and CC-1 cell lines that contain HPV-degraded p53, but did not radiosensitize the SW962 cell line, which is HPV negative and contains wild-type p53, nor the C33a cell line, which contains mutant p53 (R273C). Expression of mutant p53 (R273H) in SiHa cells increased the growth rate, but did not prevent RA-induced differentiation or radiosensitization at clinically relevant doses. Inhibition of p53 transactivation with pifithirin alpha did not prevent RA radiosensitization of SiHa at 5 Gy. RA repressed c-fos mRNA expression in control and irradiated SiHa cultures, but did not repress bcl-x(L), p53, GADD45, p21, bax, bcl-2, or mcl-1 mRNA expression.


CONCLUSIONS
The mechanism of RA radiosensitization does not require functional p53 and may involve c-fos in cervical cancer cell lines.
Tillmanns
Todd D
TD
Department of Obstetrics and Gynecology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73190, USA.
Kamelle
Scott A
SA
Guruswamy
Suresh
S
Gould
Natalie S
NS
Rutledge
Teresa L
TL
Benbrook
Doris M
DM
D000077556:Alitretinoin; D052160:Benzothiazoles; D002454:Cell Differentiation / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects / Q000528:radiation effects; D003131:Combined Modality Therapy; D004249:DNA Damage; D004307:Dose-Response Relationship, Radiation; D005260:Female; D016762:Genes, fos / Q000502:physiology; D006801:Humans; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D013844:Thiazoles / Q000494:pharmacology; D014050:Toluene / Q000031:analogs & derivatives* / Q000494:pharmacology; D014162:Transfection; D014212:Tretinoin / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000502:physiology*; D002583:Uterine Cervical Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy*
D052160:Benzothiazoles; D011838:Radiation-Sensitizing Agents; D013844:Thiazoles; D016159:Tumor Suppressor Protein p53; D000077556:Alitretinoin; D014050:Toluene; D014212:Tretinoin; C121565:pifithrin