Upregulating DAB2IP expression via EGR-1 inhibition, a new approach for overcoming fractionated-irradiation-induced cross-tolerance to ionizing radiation and mitomycin C in tumor cells.
To evaluate the effect of fractionated irradiation (FI) on tumor cells' sensitivity to ionizing radiation (IR) and antineoplastic drugs, and examine the potential of early growth response-1 (EGR-1) inhibition to sensitize tumor cells to IR.



PC3 and HepG2 cells were subjected 10 times to γ-rays at 2 Gy. The surviving cells were named PC3/R and HepG2/R, respectively. The cells' sensitivity to irradiation and chemotherapeutic drugs, including cisplatin (PT), doxorubicin (DOX), mitomycin C (MMC) and 5-fluorouracil (5-FU), were identified by colony formation assay and MMT method, respectively. Quantitative real-time polymerase chain reaction (RT-qPCR) analysis was utilized to compare the difference of gene expression between radioresistant cells and parental cells. The small interfering RNA system was implemented to inhibit endogenous EGR-1 expression in radiation-resistant cells. Western blot was employed to identify the possible mechanism by which EGR-1 regulates cells' radiosensitivity.



FI induced cross-resistant to IR and MMC in tumor cells. Along with the reduction of ovarian cancer-2/disabled homolog 2 (DOC-2/DAB2) interactive protein (DAB2IP) expression, EGR-1 gene was upregulated in FI-treated cells. On the other hand, downregulation of EGR-1 gene expression sensitized radioresistant cells to IR accompanied by DAB2IP overexpression and STAT3 inactivation. In addition, NF-κB inhibitor, BAY11-7082 enhanced resistant cells' radiosensitivity and chemosensitivity.



Conventionally FI has a higher risk of forming acquired radioresistance (ARR) in vitro. EGR-1 gene-targeted drug design could be an effective strategy to overcome DAB2IP-dysregulation-induced ARR in tumor patients.
a The Institute of Radiation Medicine , Fudan University , Shanghai , China.
Rulve
R
Chang
a The Institute of Radiation Medicine , Fudan University , Shanghai , China.
Hui
H
He
a The Institute of Radiation Medicine , Fudan University , Shanghai , China.
Guangmin
G
Mao
a The Institute of Radiation Medicine , Fudan University , Shanghai , China.
Zhaolu
Z
Kong
D002470:Cell Survival / Q000187:drug effects* / Q000528:radiation effects*; D059248:Chemoradiotherapy / Q000379:methods*; D019583:Dose Fractionation, Radiation; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D004361:Drug Tolerance; D051766:Early Growth Response Protein 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D056945:Hep G2 Cells; D006801:Humans; D016685:Mitomycin / Q000008:administration & dosage*; D011836:Radiation Tolerance / Q000187:drug effects / Q000528:radiation effects; D011839:Radiation, Ionizing; D016896:Treatment Outcome; D015854:Up-Regulation / Q000187:drug effects / Q000528:radiation effects; D020703:ras GTPase-Activating Proteins / Q000378:metabolism*
C462952:DAB2IP protein, human; C497325:EGR1 protein, human; D051766:Early Growth Response Protein 1; D020703:ras GTPase-Activating Proteins; D016685:Mitomycin
DAB2IP; EGR-1; fractionated irradiation; radioresistance