ARHGEF39 Promotes Tumor Progression Via Activating Rac1/P38 MAPK/ATF2 Signaling And Predicts Poor Prognosis Of Non-small Cell Lung Cancer Patients

Objective: Rho guanine nucleotide exchange factor 39(ARHGEF39),also called C9orf100,is a new member of Dbl-family guanine nucleotide exchange factors.Although ARHGEF39 have been proven to regulate tumor progression in hepatocellular carcinoma,the downstream signaling pathway of ARHGEF39 and its clinical associations in non-small cell lung cancer(NSCLC)are unknown to date.Methods: The Western blotting was performed to investigate the expression ARHGEF39 in 8 NSCLC cell lines and 16 tissue samples.Stable transfection of ARHGEF39 and transient knockdown were used to investigate the biological role,which were further verified by rescue experiments using P38 inhibitor.MTT assay,colony formation assay,cell cycle analysis,wound healing assay and transwell assay in A549 and H460 cells were carried out to evaluate the effects of ARHGEF39 on NSCLC in vitro.Xenograft model were performed to identify the effect of ARHGEF39 in vivo.immunofluorescence and immunohistochemistry were used to evaluate the expression pattern of ARHGEF39 in 3 cells and 109 tissue samples,as well as in nude mice xenografts.Results: In the present study,we found that ARHGEF39 promoted tumor development and upregulated the expression of Cyclin A2,Cyclin D1,and MMP2 through activating Rac1,which thereby elevated the phosphorylation of P38 and ATF2.Incorporation of P38 inhibitor counteracted the effect of ARHGEF39 overexpression on increasing Cyclin A2,Cyclin D1,and MMP2 expression.Moreover,the elevating levels of p-P38 and p-ATF2 caused by ARHGEF39 overexpression can be inhibited by expression of dominant negative Rac1 plasmid(T17N);and the inhibition of the expression of p-P38 and p-ATF2 by ARHGEF39 RNAi can be restored by expression of constitutively active Rac1(Q61L).Using immunohistochemistry,ARHGEF39 expression positively correlated with larger tumor size(P=0.008).The Kaplan-Meier test revealed that the ARHGEF39 expression significantly affected the overall survival of NSCLC patients(52.55 ± 6.40 months vs 64.30 ± 5.40 months,P=0.017).Conclusion: we identified ARHGEF39 promoted tumor growth and invasion through activating Rac1-P38-ATF2 signaling pathway,as well as facilitated the expression of Cyclin A2,Cyclin D1 and MMP2 in NSCLC cells.ARHGEF39 may be a useful marker to predict poor prognosis of NSCLC patients.