Inhibition of c-Jun N-Terminal Kinase Activity Enhances Vestibular Schwannoma Cell Sensitivity to Gamma Irradiation

Abstract

Background Radiosurgery is increasingly used to treat vestibular schwannomas (VSs). Increasing the sensitivity of VS cells to irradiation (IR) could allow for lower and/or more effective doses of IR, improving safety and efficacy. Persistent JNK activity in VS cells reduces cell death by suppressing accumulation of reactive oxygen species (ROS) raising the possibility that JNK activity protects against IR-induced VS cell death, which is mediated by ROS. Objective Determine the extent to which JNK signaling contributes to VS cell radiosensitivity. Methods Primary human VS cultures, derived from acutely resected tumors, received single doses (5–40 Gy) of γ-irradiation. Histone 2AX phosphorylation, a marker of IR-induced DNA damage, was assayed by western blot and immunostaining. ROS levels were quantified by measuring 2',7'-dichlorodihydrofluorescein diacetate (CM-H2DCFDA) fluorescence. Cell apoptosis was determined by terminal deoxynucleotidyl transferase dUTP nick end labeling. Results The JNK inhibitors, SP6000125 and I-JIP, reduced H2AX phosphorylation following IR. They also increased H2DCFDA fluorescence in non-irradiated cultures and significantly increased IR-induced (5–10 Gy) H2DCFDA fluorescence 72 hours, but not 2 hours, after IR. Finally, I-JIP (50 µM) significantly increased VS cell apoptosis in cultures treated with 20–40 Gy. I-JIP (20 µM), SP600125 (20 µM), and JNK1/2 siRNA knock-down each increased VS cell apoptosis in cultures treated with 30–40 Gy, but not lower doses, of IR. Conclusions Inhibition of JNK signaling decreases H2AX phosphorylation and increases ROS and apoptosis in VS cells following γ-irradiation. These results raise the possibility of using JNK inhibitors to increase the effectiveness of radiosurgery for treatment of VSs.

Enhancement of radiosensitivity by inhibition of c-Jun N-terminal kinase activity in a Lewis lung carcinoma-bearing subcutaneous tumor mouse model

“…JNK is involved in cellular differentiation and proliferation, neurodegeneration, inflammatory conditions and apoptosis mediated by activation protein-1 (AP-1), RANTES, IL-8 and gm-CSF (23). Yue et al reported that inhibition of JNK activity can enhance the radiosensitivity of vestibular schwannoma cells (5).…”

“…JNK also participates in the phosphorylation of H2AX after radiation (4). Based on this finding, Yue et al reported that inhibition of JNK activity enhanced radiosensitivity and apoptosis in vestibular schwannoma (5). Accumulating evidence has demonstrated the important role of JNK in the process of DNA repair after radiation.…”

Tanshinone sensitized the antitumor effects of irradiation on laryngeal cancer via JNK pathway

“…The results showed that, although all three signaling molecules were activated under irradiation, only JNK became more active after the addition of Tanshinone IIA (Figure A), suggesting that Tanshinone IIA enhanced the irradiation sensitivity via the JNK pathway. SP600125 (1,9‐pyrazoloanthrone anthrapyrazolone) was reported to be a specific inhibitor of JNK . Therefore, we next examined the survival and proliferation of laryngeal cancer cell AMC‐HN‐8 treated with irradiation, Tanshinone IIA, and SP600125 by clonogenic assay kit.…”

“…SP600125 (1,9-pyrazoloanthrone anthrapyrazolone) was reported to be a specific inhibitor of JNK. 1,[14][15][16] Therefore, we next examined the survival and proliferation of laryngeal cancer cell AMC-HN-8 treated with irradiation, Tanshinone IIA, and SP600125 by clonogenic assay kit. SP600125 treatment antagonized radiation sensitization induced by Tanshinone IIA (Figure 5B), confirming that Tanshinone IIA radiation sensitization was mediated by the JNK signaling pathway.…”

Proteomic Analysis of Vestibular Schwannoma

“…There are many reports that merlin inhibits several intracellular signals implicated in cell proliferation and tumor formation (1Y4). It was also reported that c-JUN N-terminal kinase activity could either promote tumor cell proliferation in VS or increase apoptosis in normal Schwann cells (17,18).…”