Overexpressed p-S6 associates with lymph node metastasis and predicts poor prognosis in non-small cell lung cancer

Background Ribosomal protein S6 (S6), a downstream effect media of the AKT/mTOR pathway, not only is a part of 40S small subunit of eukaryotic ribosome, but also involves in protein synthesis and cell proliferation during cancer development. Methods In present study, we explore the association between phosphorylated S6 (p-S6) protein expression and clinicopathological features as well as prognostic implications in NSCLC. P-S6 was detected in tissue microarrays (TMAs) containing 350 NSCLC, 53 non-cancerous lung tissues (Non-CLT), and 88 cases of matched metastatic lymph node lesions via immunohistochemistry (IHC). Transwell assays and wound healing assay were used to assess the effects of p-S6 inhibition on NSCLC cell metastasis. Results The p-S6 expression in NSCLC was more evident than that in Non-CLT (p < 0.05). Compared to NSCLC patients who have no lymph node metastasis (LNM), those with LNM had higher p-S6 expression (p = 0.001). Regardless of lung squamous cell carcinoma (SCC) or adenocarcinoma (ADC), p-S6 was increased obviously in metastatic lymph nodes compared with matched primary cancers (p = 0.001, p = 0.022, respectively). Inhibition of p-S6 decreased the metastasis ability of NSCLC cells. In addition, p-S6 was an independent predicted marker for LNM in patients with NSCLC (p < 0.001). According to survival analysis, patients with highly expressed p-S6 had a lower survival rate compared with that with lower expression (p = 0.013). P-S6 is an unfavorable independent prognostic factor for NSCLC patients (p = 0.011). Conclusion Increased expression of p-S6 is not only a novel predictive biomarker of LNM but also poor prognosis in NSCLC.