Background: The epidermal growth factor receptor (EGFR) is usually overexpressed in nasopharyngeal carcinoma (NPC) and is associated with pathogenesis of NPC. However, the downstream signaling proteins of EGFR in NPC have not yet been completely understood at the system level. The aim of this study was identify novel downstream proteins of EGFR signaling pathway in NPC cells. Results: We analyzed EGFR-regulated phosphoproteome in NPC CNE2 cells using 2D-DIGE and mass spectrometry analysis after phosphoprotein enrichment. As a result, 33 nonredundant phosphoproteins including five known EGFR-regulated proteins and twenty-eight novel EGFR-regulated proteins in CNE2 were identified, three differential phosphoproteins were selectively validated, and two differential phosphoproteins (GSTP1 and GRB2) were showed interacted with phospho-EGFR. Bioinformatics analysis showed that 32 of 33 identified proteins contain phosphorylation modification sites, and 17 identified proteins are signaling proteins. GSTP1, one of the EGFR-regulated proteins, associated with chemoresistance was analyzed. The results showed that GSTP1 could contribute to paclitaxel resistance in EGF-stimulated CNE2 cells. Furthermore, an EGFR signaling network based on the identified EGFR-regulated phosphoproteins were constructed using Pathway Studio 5.0 software, which includes canonical and novel EGFR-regulated proteins and implicates the possible biological roles for those proteins. Conclusion: The data not only can extend our knowledge of canonical EGFR signaling, but also will be useful to understand the molecular mechanisms of EGFR in NPC pathogenesis and search therapeutic targets for NPC.

Radiotherapy is the primary treatment for nasopharyngeal carcinoma (NPC), but radioresistance often remains an obstacle to successful treatment. In our previous study, it was demonstrated that Annexin A1 (ANXA1) was involved in the p53‑mediated radioresponse in NPC cells, which suggested that it may be associated with radioresistance in NPC; however, the role of ANXA1 in NPC radioresistance is unknown. In the present study, CNE2 cells were stably transfected with pLKO.1‑ANXA1‑small hairpin (sh)RNAs to investigate the effects of ANXA1 on the radiosensitivity of NPC. CNE2 cells transfected with pLKO.1 were used as the control. The radiosensitivities of the cells in vitro were analyzed using the clonogenic survival assay, cell growth analysis, flow cytometry and Hoechst 33258 staining. ANXA1 downregulation significantly enhanced clonogenic survival and cell growth following treatment of CNE2 cells with ionizing radiation (IR), increased the number of cells in the S phase and decreased IR‑induced apoptosis. These results suggested that the radiosensitivity of CNE2 cells transfected with ANXA1‑specific shRNA was significantly lower compared with the control cells. Therefore, ANXA1 downregulation may be involved in the radioresistance of NPC, and ANXA1 may be considered a novel biomarker for predicting NPC response to radiotherapy.

We found that selenium-binding protein 1 (SBP1) was progressively decreased in the human bronchial epithelial carcinogenic processes. Knockdown of SBP1 in immortalized human bronchial epithelial cell line 16HBE cells significantly increased the efficiency of B[a]P-induced cell transformation. However, the relationship between SBP1 expression and clinicopathological factors of patients has not been defined completely. The specific role of SBP1 in prognosis of lung squamous cell carcinoma (LSCC) is still unknown. Tissue samples from 82 patients treated by pulmonary lobectomy for LSCC were used. Immunohistochemistry and western blotting were used to detect the expressions of SBP1 protein. The relationships between the expression level of SBP1 and the clinicopathological features of patients were analyzed. Cox proportional hazard regression analysis and Kaplan–Meier method were used to perform survival analysis. Expressions of SBP1 proteins were significantly lower in LSCC tissues than that in the corresponding normal bronchial epithelium (NBE) tissues (P = 0.000). In LSCC, The expression levels of SBP1 had not correlated with patients’ age, gender, smoking state, primary tumor stages (T), TNM clinical stages, and distant metastasis (M) (P > 0.05). However, downregulation of SBP1 was significantly associated with higher lymph node metastasis and lower overall survival rate (P < 0.05). Cox regression analysis indicated low expressions of SBP1 can be an independent prognostic factor for poor overall survival in LSCC patients (P = 0.002). Downregulation of SBP1 may play a key role in the tumorigenic process of LSCC. SBP1 may be a novel potential prognostic factor of LSCC.

Radiotherapy is the primary treatment for nasopharyngeal carcinoma while radioresistance can hinder efficient treatment. To explore the role of annexin A1 and its potential mechanisms in radioresistance of nasopharyngeal carcinoma, human nasopharyngeal carcinoma cell line CNE2-sh annexin A1 (knockdown of annexin A1) and the control cell line CNE2-pLKO.1 were constituted and CNE2-sh annexin A1 xenograft mouse model was generated. The effect of annexin A1 knockdown on the growth of xenograft tumor after irradiation and radiation-induced DNA damage and repair was analyzed. The results of immunohistochemistry assays and Western blotting showed that the level of annexin A1 was significantly downregulated in the radioresistant nasopharyngeal carcinoma tissues or cell line compared to the radiosensitive nasopharyngeal carcinoma tissues or cell line. Knockdown of annexin A1 significantly promoted CNE2-sh annexin A1 xenograft tumor growth compared to the control groups after irradiation. Moreover, the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assays revealed that knockdown of annexin A1 significantly inhibited apoptosis in vivo compared to the control groups. We assessed the intracellular reactive oxygen species levels and the extent of radiation-induced DNA damage and repair using reactive oxygen species assay, comet assays, and immunohistochemistry assay. The results showed that knockdown of annexin A1 remarkedly reduced the intracellular reactive oxygen species levels, level of DNA double-strand breaks, and the phosphorylation level of H2AX and increased the accumulation of DNA-dependent protein kinase in nasopharyngeal carcinoma cells after irradiation. The findings suggest that knockdown of annexin A1 inhibits DNA damage via decreasing the generation of intracellular reactive oxygen species and the formation of γ-H2AX and promotes DNA repair via increasing DNA-dependent protein kinase activity and therefore improves the radioresistance in nasopharyngeal carcinoma cells. Together, our findings suggest that knockdown of annexin A1 promotes radioresistance in nasopharyngeal carcinoma and provides insights into therapeutic targets for nasopharyngeal carcinoma radiotherapy.