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Background: CIP2A may activate multiple oncogenic proteins and promote the proliferation of various cancer cells. Methods: We investigated that the role of CIP2A in radioresistant head and neck cancer (HNC) cell line with TP53 mutation and the effect of the rapamycin on the response of HN31 with TP53 mutation cells to irradiation related to CIP2A expression. Results: CIP2A expression was stimulated by p53 mutation and critical for the inhibition of senescence induction in response to radiation. The treatment with radiation alone neither induced cytotoxicity in HN31 cells nor completely suppressed the activation of CIP2A. However, the combination of radiation and rapamycin increase the radiosensitivity through the induction of senescence with downregulation of CIP2A expression both in vivo and in vitro. Conclusion: Our results suggest that CIP2A may serve as a therapeutic target of rapamycin through induction of senescence in radioresistant HNC with TP53 mutation. [ABSTRACT FROM AUTHOR]

CD47 is expressed in all human cancer cells, including head and neck cancer, and initiates a signaling cascade to inhibit macrophage phagocytosis. However, the mechanism underlying CD47 overexpression has not been elucidated in radioresistant head and neck cancer. The present study demonstrated that decreased Tristetraprolin (TTP) expression induced a sustained overexpression of CD47 using reverse transcription-quantitative PCR and western blotting, and that CD47 overexpression prevented phagocytosis using a phagocytosis assay in a radioresistant HN31R cell line. Subsequently, using TTP transfection, RNA interference, duel-luciferase assay and EMSA, it was revealed that TTP transfection enhanced phagocytosis through degradation of CD47 mRNA by directly binding to CD47 AREs within the CD47 3'UTR. Based on our previous study, methylation-specific PCR and western blotting revealed that DNMT1 was overexpressed in radioresistant HN31R cell line and TTP expression was decreased epigenetically by DMNT1 associated DNA methylation. Overall, these findings provided novel insight into the role of TTP as a biomarker of CD47-positive head and neck cancer patients. [ABSTRACT FROM AUTHOR]

EPHA3, a member of the EPH family, is overexpressed in various cancers. We demonstrated previously that EPHA3 is associated with radiation resistance in head and neck cancer via the PTEN/Akt/EMT pathway; the inhibition of EPHA3 significantly enhances the efficacy of radiotherapy in vitro and in vivo. In this study, we investigated the mechanisms of PTEN regulation through EPHA3-related signaling. Increased DNA methyltransferase 1 (DNMT1) and enhancer of zeste homolog 2 (EZH2) levels, along with increased histone H3 lysine 27 trimethylation (H3K27me3) levels, correlated with decreased levels of PTEN in radioresistant head and neck cancer cells. Furthermore, PTEN is regulated in two ways: DNMT1-mediated DNA methylation, and EZH2-mediated histone methylation through EPHA3/C-myc signaling. Our results suggest that EPHA3 could display a novel regulatory mechanism for the epigenetic regulation of PTEN in radioresistant head and neck cancer cells. [ABSTRACT FROM AUTHOR]

Radiotherapy is a well-established therapeutic modality used in the treatment of many cancers. However, radioresistance remains a serious obstacle to successful treatment. Radioresistance can cause local recurrence and distant metastases in some patients after radiation treatment. Thus, many studies have attempted to identify effective radiosensitizers. Eph receptor functions contribute to tumor development, modulating cell-cell adhesion, invasion, neo-angiogenesis, tumor growth and metastasis. However, the role of EphA3 in radioresistance remains unclear. In the current study, we established a stable radioresistant head and neck cancer cell line (AMC HN3R cell line) and found that EphA3 was expressed predominantly in the radioresistant head and neck cancer cell line through DNA microarray, real time PCR and Western blotting. Additionally, we found that EphA3 was overexpressed in recurrent laryngeal cancer specimens after radiation therapy. EphA3 mediated the tumor invasiveness and migration in radioresistant head and neck cancer cell lines and epithelial mesenchymal transition- related protein expression. Inhibition of EphA3 enhanced radiosensitivity in the AMC HN 3R cell line in vitro and in vivo study. In conclusion, our results suggest that EphA3 is overexpressed in radioresistant head and neck cancer and plays a crucial role in the development of radioresistance in head and neck cancers by regulating the epithelial mesenchymal transition pathway. [ABSTRACT FROM AUTHOR]

Sirtuin 3 (SIRT3) regulates mitochondrial function as a mitochondrial deacetylase during oxidative stress. However, the specific regulatory mechanism and function of SIRT3 in radioresistant cancer cells are unclear. In this study, we aim to investigate how SIRT3 determines the susceptibility to glucose deprivation and its regulation in p53-based radioresistant head and neck cancer cells. We observed mitochondrial function using two established isogenic radioresistant subclones (HN3R-A [p53 null] and HN3R-B [p53 R282W]) with intratumoral p53 heterogeneity. Cell counting analysis was performed to evaluate cell proliferation and cell death. The correlation between the regulation of SIRT3 and enhancer of zeste homolog 2 (EZH2) was confirmed by immunoblotting and chromatin immunoprecipitation assay. p53-deficient radioresistant cells (HN3R-A) expression reduced SIRT3 levels and increased sensitivity to glucose deprivation due to mitochondrial dysfunction compared to other cells. In these cells, activation of SIRT3 significantly prevented glucose deprivation-induced cell death, whereas the loss of SIRT3 increased the susceptibility to glucose deficiency. We discovered that radiation-induced EZH2 directly binds to the SIRT3 promoter and represses the expression. Conversely, inhibiting EZH2 increased the expression of SIRT3 through epigenetic changes. Our findings indicate that p53-deficient radioresistant cells with enhanced EZH2 exhibit increased sensitivity to glucose deprivation due to SIRT3 suppression. The regulation of SIRT3 by EZH2 plays a critical role in determining the cell response to glucose deficiency in radioresistant cancer cells. Therefore, EZH2-dependent SIRT3 could be used as a predictive biomarker to select treatment options for patients with radiation-resistance. • p53-deficient radioresistant cells are sensitive to glucose starvation. • SIRT3 is a pivotal regulator of glucose deprivation-induced cell death. • EZH2 directly binds to the SIRT3 promoter and represses the expression of SIRT3. • EZH2-dependent SIRT3: a predictive biomarker for radiation-resistant patients. [ABSTRACT FROM AUTHOR]

Objectives: PI3K/Akt/mTOR pathway is commonly activated in most cancers and is correlated with resistance to anticancer therapies such as radiotherapy. Therefore, PI3K is an attractive target for treating PI3K-associated cancers.Material and Methods: We investigated the basal expression and the expression after treatment of PI3K inhibitor or Src inhibitor of PI3K/Akt pathway-related proteins in AMC-HN3, AMC-HN3R, HN30 and HN31 cells by performing immunoblotting analysis. The sensitivity to PI3K inhibitors or Src inhibitor was analyzed by MTT assay and clonogenic assay. To determine the antitumoral activity of combination treatment with PI3K inhibitor and Src inhibitor, we used using xenograft mouse model.Results: We found that PI3K regulatory subunit p85 was predominantly phosphorylated in radioresistant head and neck cancer cell line (HN31), which showed resistance to PI3K inhibitors. Next, we investigated mechanism through which PI3K p85 phosphorylation modulated response to PI3K inhibitors. Of note, constitutive activation of Src was found in HN31 cells and upon PI3K inhibitor treatment, restoration of p-Src was occurred. Src inhibitor improved the efficacy of PI3K inhibitor treatment and suppressed the reactivation of both Src and PI3K p85 in HN31 cells. Furthermore, downregulation of PI3K p85 expression by using a specific siRNA suppressed Src phosphorylation.Conclusions: Together, our results imply the novel role of the PI3K regulatory subunit p85 in the development of resistance to PI3K inhibitors and suggest the presence of a regulatory loop between PI3K p85 and Src in radioresistant head and neck cancers with constitutively active PI3K/Akt pathway. [ABSTRACT FROM AUTHOR]