HDJ-2 as a target for radiosensitization of glioblastoma multiforme cells by the farnesyltransferase inhibitor R115777 and the role of the p53/p21 pathway.
Resistance of glioblastoma multiforme to radiotherapy poses a major clinical challenge. Farnesyltransferase inhibitors (FTI), such as R115777, have potential to increase radiotherapeutic benefit in this disease, although their mechanism of action is unclear. In our study with eight glioblastoma multiforme cell lines, the most sensitive ones underwent cell cycle arrest in response to FTI treatment. Radiosensitization by FTIs, however, seemed to involve other pathways. If R115777 treatment was initiated < 6 hours before irradiation, all eight glioblastoma multiforme lines were radiosensitized. However, if the time between drug and radiation was extended to 24 hours, cells harboring wild type but not mutated p53 were able to counteract drug-induced radiosensitization. The involvement of the p53/p21 pathway in the development of resistance was confirmed by showing that U87 cells transfected with human papillomavirus E6 to block p53 or interfering RNA to inhibit p21 stayed radiosensitive for 24 hours after drug treatment. The time dependency of R115777-induced radiosensitization suggested that the initial FTI target for early radiosensitization was short-lived, and that a p21-directed pathway restored resistance. Consideration of prenylated molecules that could potentially be involved led us to consider HDJ-2, a co-chaperone of heat shock protein 70. This hypothesis was strengthened by finding that cellular radiosensitivity was increased by genetic inhibition of HDJ-2, whereas overexpression conferred radioresistance. Importantly, irradiation of cells caused HDJ-2 to migrate from the cytoplasm to the nucleus, and this migration was inhibited by prior FTI treatment. These results have clinical relevance in that they help explain the variability in responses to FTIs that occurs following radiotherapy and elucidate some of the reasons for the complexity underlying FTI-induced radiosensitization.
Wang
Chun-Chieh
CC
Departments of Radiation Oncology and Pathology and Laboratory Medicine, University of California at Los Angeles School of Medicine, 10833 Le Conte Avenue, Los Angeles, CA 90095, USA.
Liao
Yu-Pei
YP
Mischel
Paul S
PS
Iwamoto
Keisuke S
KS
Cacalano
Nicholas A
NA
McBride
William H
WH
D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D045744:Cell Line, Tumor; D003131:Combined Modality Therapy; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D051231:Farnesyltranstransferase / Q000037:antagonists & inhibitors*; D005909:Glioblastoma / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology / Q000532:radiotherapy*; D050956:HSP40 Heat-Shock Proteins / Q000378:metabolism / Q000502:physiology*; D006801:Humans; D015363:Quinolones / Q000494:pharmacology*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C107481:DNAJA1 protein, human; D004791:Enzyme Inhibitors; D050956:HSP40 Heat-Shock Proteins; D015363:Quinolones; D011838:Radiation-Sensitizing Agents; C495901:TP53 protein, human; D016159:Tumor Suppressor Protein p53; D051231:Farnesyltranstransferase; C402769:tipifarnib