Decreased Expression Level and DNA-binding Activity of Specificity Protein 1 Via Cyclooxygenase-2 Inhibition Antagonizes Radiation Resistance, Cell Migration and Invasion in Radiation-resistant Lung Cancer Cells

Radiation is able to inhibit tumor growth, promote tumor cell apoptosis and prolong patient survival. However, radiation resistance remains a major impediment to radiotherapy. Local and metastatic recurrences following radiation are still large impediments to overall survival. Although cyclooxygenase-2 (COX-2) inhibitors may induce radiation sensitivity in cancer cells, the underlying mechanisms are not fully understood. The present study demonstrated high potential for cell proliferation, migration and invasion in radiation-resistant lung cancer cell lines. The present study observed the overexpression of specificity protein 1 (Sp1) in these cells, and the overexpression of Sp1 induced upregulation of matrix metalloproteinase (MMP)-2, MMP-9, B cell lymphoma-2, in addition to a high potential for radiation resistance, migration and invasion in these cells. The present study revealed that the COX-2 selective inhibitor, celecoxib, enhanced radiation sensitivity and inhibited migration and invasion in these cells by inhibiting the expression and DNA-binding activity of Sp1. Furthermore, celecoxib downregulated Sp1 by inhibiting c-Jun N-terminal kinase (JNK). Taken together, the present study demonstrated that Sp1 overexpression in radiation-resistant cancer cells and COX-2 inhibitors enhanced radiation sensitivity and inhibited the migration and invasion of cancer cells, at least partially, via inactivation of the JNK/Sp1 signaling pathway and a decrease in Sp1 DNA-binding activity.