Non-canonical Raf-1/p70S6K signalling in non-small-cell lung cancer.

Zhixin Qiu,Bingwei Ye,Xin Li,Ximing Mo,Shuang Zhao,Weimin Li,Lei Li

doi:10.1111/jcmm.14636

Abstract

Lung cancer is the leading cause of cancer‐related death globally, with non–small‐cell lung cancer (NSCLC) being the predominant subtype. Overall survival remains low for NSCLC patients, and novel targets are needed to improve outcome. Raf‐1 is a key component of the Ras/Raf/MEK signalling pathway, but its role and downstream targets in NSCLC are not completely understood. Our previous study indicated a possible correlation between Raf‐1 levels and ribosomal protein S6 kinase (p70S6K) function. In this study, we aimed to investigate whether p70S6K is a downstream target of Raf‐1 in NSCLC. Raf‐1 was silenced in NSCLC cell lines by using small hairpin RNA, and Raf‐1 and p70S6K protein levels were measured via Western blot. p70S6K was then overexpressed following Raf‐1 knock‐down; then, cell proliferation, apoptosis and the cell cycle in NSCLC cell lines were examined. Tumour xenografts with NSCLC cells were then transplanted for in vivo study. Tumours were measured and weighed, and Raf‐1 and p70S6K expression, cell proliferation and apoptosis were examined in tumour tissues by Western blot, Ki‐67 staining and TUNEL staining, respectively. When Raf‐1 was silenced, p70S6K protein levels were markedly decreased in the A549 and H1299 NSCLC cell lines. A significant decrease in NSCLC cell proliferation, a profound increase in apoptosis and cell cycle arrest were observed in vitro following Raf‐1 knock‐down. Overexpression of p70S6K after Raf‐1 depletion effectively reversed these effects. Xenograft studies confirmed these results in vivo. In conclusion, Raf‐1 targets p70S6K as its downstream effector to regulate NSCLC tumorigenicity, making Raf‐1/p70S6K signalling a promising target for NSCLC treatment.

Highlights

Lung cancer is the leading cause of cancer‐related death through‐ out the world.[1]
Overexpression of p70S6K resulted in an obvious reverse of both the proliferation‐inhibiting and apoptosis‐inducing effects (Figure 5D). These results suggest that Raf‐1 signals through p70S6K to exert its pivotal role in non–small‐cell lung cancer (NSCLC) tumorigenicity, further confirming that p70S6K is a bona fide downstream target of Raf‐1
We identified a non‐canonical Raf‐1/p70S6K signalling pathway in NSCLC where Raf‐1 targets p70S6K as its downstream effector to regulate NSCLC tumour growth via sustaining prolif‐ eration, inhibiting apoptosis and promoting cell cycle progression (Figure 6)

Summary

| INTRODUCTION

Lung cancer is the leading cause of cancer‐related death through‐ out the world.[1]. The classic Raf/MEK/ERK (extracellular signal‐regulated kinase) signalling is generally accepted as responsible for the func‐ tion of Raf‐1 in cancer development, including in NSCLC. The fact that Raf‐1 is able to facilitate tumour development through mechanisms other than MEK/ERK signalling is evident by identifica‐ tion of other Raf‐1 targets.[7]. Our previous observation suggested that the function of p70S6K might be cor‐ related with Raf‐1 expression,[6] which raises the likelihood of p70S6K being a downstream target of Raf‐1 in NSCLC. To this end, this study investigated the connection between Raf‐1 and p70S6K in NSCLC

| METHODS

| DISCUSSION