Inhibition of Transforming Growth Factor-β Signaling in Normal Lung Epithelial Cells Confers Resistance to Ionizing Radiation

Abstract

Purpose-To address the functional role of radiation-induced TGF-β signaling in normal epithelial background, we selected spontaneously immortalized lung epithelial cell line derived from the normal lung tissue of dominant-negative mutant of TGF-β RII (ΔRII) transgenic mouse that expressed conditionally ΔRII under the control of metallothionein promoter (MT-1) and assessed it's impact on radio-sensitivity.Method and Materials-Spontaneously immortalized lung epithelial cell culture (SILECC) was established and all analyses were performed within 50 passages. Colony-forming and TUNEL assays were used to assess the clonogenic inhibition and apoptosis respectively. Western blot analysis was performed to assess the kinetics of p21, bax and RII proteins. TGF-β responsive promoter activity was measured using dual-luciferase reporter assay.Results-Exposure to ZnSO 4 inhibited TGF-β signaling induced either by recombinant TGF-β1 or ionizing radiation. SILECC treated either with ZnSO 4 or neutralizing antibody against TGF-β showed a significant increase in radio-resistance when compared to untreated cells. Furthermore, the expression of the ΔRII inhibited the radiation-induced up-regulation of the TGF-β effector gene p21 waf1/cip1. . Conclusions-Our findings imply that inhibition of radiation-induced TGF-β signaling via abrogation of RII function enhances radio-resistance of the normal lung epithelial cells, and this can be directly attributed to the loss of TGF-β signaling function.

Na,K-ATPase Subunits as Markers for Epithelial-Mesenchymal Transition in Cancer and Fibrosis

“…Luciferase activity was measured after 24 hours of TGF-β 1 treatment using the Dual-Luciferase Reporter Assay System (Promega) as described (32). The firefly luciferase activity was normalized to the activity of the internal control (Renilla luciferase, pRL vector) that was co-transfected along with the reporter vector.…”

Role of Radiation-induced TGF-beta Signaling in Cancer Therapy

“…The absence or low level of expression of RII or Smad4 is thought to be reason for resistance to chemo- or radiotherapy in lung cancer. We showed that restoration of RII receptor in normal lung cells that specifically harbored defective TGF-β signaling pathway increased sensitivity to radiation and will decrease malignant potential by increasing apoptosis (87). The wild-type p53 protein is reported to affect radiation responsiveness in several types of cancers, with radiation causing an accumulation of p53 protein that initiates apoptosis.…”

“…Based on previous studies on eight human colorectal cancers, it was postulated that radiation-induced sensitization to TGF-β require functional p53, but our study demonstrated that MIA PaCa-2/RII cells with restored TGF-β signaling are sensitive to radiation despite the fact that these cells harbor a mutated p53 gene (47). Importantly, radiation failed to induce p21 protein expression in parental MIA PaCa cells, since both the p53 and TGF-β pathways are not functional in these cells, but after restoration of functional RII, radiation exposure resulted in p21 protein elevation (87). …”

Inhibiting TGFβ1 has a protective effect on mouse bone marrow suppression following ionizing radiation exposure in vitro

“…Many studies suggest inhibiting TGFβ1 could protect lungs, kidneys, blood vessels, liver, skin, etc. from radiotherapy-induced injury [30–33]. In addition, TGF-β1 inhibitor can attenuate tumor cell migration [34] and enhance sensitivity to radiation therapy in pancreatic cancer, glioblastoma and breast cancer [35–37].…”