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Two- and Three-Dimensional Live Cell Imaging of DNA Damage Response Proteins
Published on: September 28, 2012
MG132 selectively upregulates MICB through the DNA damage response pathway in A549 cells
Dan Luo1, Xi-Wen Dong2, Bing Yan3
1College of Life Science and Bioengineering, School of Science, Beijing Jiaotong University, Beijing 100044, P.R. China.
Abstract:
Natural killer (NK) cells recognize stress‑activated NK group 2, member D (NKG2D) ligands in tumors. In the present study, the expression levels of NKG2D ligands were examined in four lung cancer cell lines (A549, PLA801D, NCI‑H157 and NCI‑H520). In the A549 cells, the expression of MHC class I polypeptiderelated sequence (MIC)A/B and UL16 binding protein (ULBP)1 was weak, the expression of ULBP2 was typical, and neither ULBP3 nor ULBP4 were expressed. The mechanism underlying the regulatory effect of a cancer treatment agent on the expression of NKG2D ligands was investigated using the proteasome inhibitor MG132. Following treatment for 8 h with MG132, the transcription levels of MICB and ULBP1 were upregulated 10.62‑ and 11.09‑fold, respectively, and the expression levels of MICB and ULBP1 were increased by 68.18 and 23.65%, respectively. Notably, MICB exhibited significant time‑dependent change. MG132 increased the transcription of MICB by acting at a site in the 480‑bp MICB upstream promoter. The activity of the MICB promoter was upregulated 1.77‑fold following treatment with MG132. MG132 treatment improved the cytotoxicity of NK cells, which was partially blocked by an antibody targeting NKG2D, and more specifically the MICB molecule. The expression of MICB induced by MG132 was inhibited by KU‑55933 [ataxia telangiectasia mutated (ATM) kinase inhibitor], wortmannin (phosphoinositide 3 kinase inhibitor) and caffeine (ATM/ATM‑Rad3‑related inhibitor). The phosphorylation of checkpoint kinase 2 (Chk2), an event associated with DNA damage, was observed following treatment with MG132. These results indicated that MG132 selectively upregulates the expression of MICB in A549 cells, and increases the NKG2D‑mediated cytotoxicity of NK cells. The regulatory effect of MG132 may be associated with the activation of Chk2, an event associated with DNA damage. The combination of MG132 with NK cell immunotherapy may have a synergistic effect that improves the therapeutic effect of lung cancer treatment.
Insights
The proteasome inhibitor MG132 upregulates NKG2D ligands, enhancing natural killer (NK) cell cytotoxicity against lung cancer. This suggests a potential synergistic effect when combining MG132 with NK cell immunotherapy for improved lung cancer treatment.
Area of Science:
- Immunology
- Cancer Biology
- Molecular Biology
Background:
- Natural killer (NK) cells are crucial for tumor surveillance, recognizing stress-induced NKG2D ligands on cancer cells.
- Understanding the regulation of NKG2D ligands is vital for developing effective immunotherapies.
Purpose of the Study:
- To investigate the effect of the proteasome inhibitor MG132 on NKG2D ligand expression in lung cancer cells.
- To elucidate the mechanism underlying MG132-induced changes in NKG2D ligand expression and its impact on NK cell cytotoxicity.
Main Methods:
- Examined NKG2D ligand expression (MICA/B, ULBP1-4) in lung cancer cell lines (A549, PLA801D, NCI-H157, NCI-H520).
- Treated A549 cells with MG132 and assessed changes in MICB and ULBP1 transcription and protein levels.
- Investigated MG132's effect on MICB promoter activity and NK cell-mediated cytotoxicity.
- Utilized kinase inhibitors (KU-55933, wortmannin, caffeine) and assessed Chk2 phosphorylation to explore signaling pathways.
Main Results:
- MG132 treatment significantly upregulated MICB and ULBP1 transcription and expression in A549 cells, with MICB showing time-dependent changes.
- MG132 enhanced MICB promoter activity and increased NK cell cytotoxicity, partially mediated by NKG2D and MICB.
- MG132-induced MICB expression was inhibited by ATM/PI3K pathway inhibitors and associated with Chk2 phosphorylation, indicating DNA damage signaling.
Conclusions:
- MG132 selectively upregulates MICB expression in A549 lung cancer cells, enhancing NKG2D-mediated NK cell cytotoxicity.
- The mechanism involves DNA damage response pathways, including Chk2 activation.
- Combining MG132 with NK cell immunotherapy may offer synergistic benefits for lung cancer treatment.
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