HIV-1 Tat depresses DNA-PK(CS) expression and DNA repair, and sensitizes cells to ionizing radiation.
OBJECTIVE
There is accumulating evidence that cancer patients with human immmunodeficiency virus-1/acquired immunodeficency syndrome (HIV-1/AIDS) have more severe tissue reactions and often develop cutaneous toxic effects when subjected to radiotherapy. Here we explored the effects of the HIV-1 Tat protein on cellular responses to ionizing radiation.


METHODS
Two Tat-expressing cell lines, TT2 and TE671-Tat, were derived from human rhabdomyosarcoma cells by transfecting with the HIV-1 tat gene. Radiosensitivity was determined using colony-forming ability. Gene expression was assessed by cDNA microarray and immunohybridization. The Comet assay and gamma-H2AX foci were use to detect DNA double-strand breaks (DSBs) and repair. Radiation-induced cell cycle changes were detected by flow cytometry.


RESULTS
The radiosensitivity of TT2 and TE671-Tat cells was significantly increased as compared with parental TE671 cells or the control TE671-pCI cells. Tat also increased proliferation activity. The comet assay and gammaH2AX foci detection revealed a decreased capacity to repair radiation-induced DNA DSBs in Tat-expressing cells. Microarray assay demonstrated that the DNA repair gene DNA-PKcs, and cell cycle-related genes Cdc20, Cdc25C, KIF2C and CTS1 were downregulated in Tat-expressing cells. Depression of DNA-PKcs in Tat-expressing cells was further confirmed by RT-PCR and immuno-hybridization analysis. Tat-expressing cells exhibited a prolonged S phase arrest after 4 Gy gamma-irradiation, and a noticeable delay in the initiation and elimination of radiation-induced G(2)/M arrest as compared with parental cells. In addition, the G(2)/M arrest was incomplete in TT2 cells. Moreover, HIV-1 Tat resulted in a constitutive overexpression of cyclin B1 protein.


CONCLUSIONS
HIV-1 Tat protein sensitizes cells to ionizing radiation via depressing DNA repair and dysregulating cell cycle checkpoints. These observations provide new insight into the increased tissue reactions of AIDS cancer patients to radiotherapy.
Sun
Yi
Y
Department of Radiation Toxicology and Oncology, Beijing Institute of Radiation Medicine, Beijing, People's Republic of China.
Huang
Yue-Chen
YC
Xu
Qin-Zhi
QZ
Wang
Hui-Ping
HP
Bai
Bei
B
Sui
Jian-Li
JL
Zhou
Ping-Kun
PK
D000163:Acquired Immunodeficiency Syndrome / Q000150:complications*; D002460:Cell Line / Q000528:radiation effects; D049109:Cell Proliferation / Q000528:radiation effects; D020552:Comet Assay; D004249:DNA Damage / Q000235:genetics; D004260:DNA Repair / Q000502:physiology*; D051747:DNA-Activated Protein Kinase / Q000378:metabolism*; D016195:G2 Phase / Q000235:genetics / Q000528:radiation effects; D015870:Gene Expression; D015696:Gene Products, tat / Q000502:physiology*; D015497:HIV-1; D006801:Humans; D020411:Oligonucleotide Array Sequence Analysis / Q000379:methods; D011836:Radiation Tolerance / Q000235:genetics; D054322:tat Gene Products, Human Immunodeficiency Virus
D015696:Gene Products, tat; D054322:tat Gene Products, Human Immunodeficiency Virus; D051747:DNA-Activated Protein Kinase