Inhibition Of BMK1 Pathway Suppresses Cancer Stem Cells Through BNIP3 And BNIP3L

Objective: As is known to all,mitogen-activated protein kinases(MAPKs),signaling pathway plays an important role on cell survival,proliferation and death.It is a three-level cascade enzymatic reaction: MAPKKK?MAPKK?MAPK.In mammals,there are four types of MAPK signaling pathways,namely,extracellular signal regulating kinase1/2,(ERK1/2),BMK1(also called MAPK7 or ERK5),p38 and JNKs,respectively.Generally,ERK1/2 and BMK1 are activated by oncogenic signals and involved in promoting cell proliferation and survival;while JNK and p38 are supposed to regulate cell death and proliferation.Although BMK1 and ERK1/2 are closely correlated,ERK1/2 and BMK1 signaling pathways in the stem cells and progenitor cells play an opposite effect.Meanwhile,our previous studies have found that BMK1 knock down resulted in embryonic death.It also show that BMK1 may play an important role in cells totipotency.In addition,BMK1 signaling pathways are closely related to the many characteristics of malignant tumor,such as drug resistance,proliferation,metastasis and tumorigenicity of the tumor.Cancer stem cells(CSCs)possess many characteristics associated with stem cells and are believed to drive tumor initiation.Cancer stem cells mainly has four important features: the ability of self-renewal,value-added capacity and multiple differentiation potential,resistance.As for malignant tumor,cancer cells can be killed using chemotherapy,radiotherapy and biological immunotherapy,but not radically cure tumor.Traditional cancer treatments tend to eradicate the common tumor cells,but cancer stem cells remain in the tumor tissue,which will lead to tumor recurrence.So,determining the key pathways of the tumor stem cells are very important for targeted therapy of cancer stem cell.Method: Although targeting of CSCs offers great promise for the new generation of therapeutics,lack of the effective drug target and appropriate pharmacological reagents significantly impedes the development of chemotherapies.Here,we show that the phosphorylation of BMK1 was significantly correlated with not only embryonic and induced pluripotent stem(iPS)cells,but also the CSCs.It was showed that activation of BMK1 by the expression of MEK5 D enhanced the self-renew(sphere formation),proliferation(clone formation)and tumorigenic capacity of CSCs.While BMK1 inhibitor,XMD8-92,suppressed these capacities.RNA-seq and microarray analysis revealed that inhibition of BMK1 significantly enhanced the expression of BNIP3 and BNIP3 L,which play important roles in cell death.Further study indicated that shRNA-mediated knock down of BNIP3 and BNIP3 L impairs the BMK1 inhibitor,XMD8-92-induced suppression of sphere formation and clone formation of CSC.Result: 1.Phospho-BMK1 was correlated with iPS,embryonic and cancer stem cells;2.Inhibition of BMK1 effectively suppressed the self-renew and proliferation of cancer stem cells;3.Phosphorylation of BMK1 promoted the proliferation,selfrenewal,and tumorigenicity of cancer stem cells;4.Inhibition of BMK1 pathway suppressed the stemness of cancer stem cells through BNIP3 and BNIP3 L.Conclusion: Collectively,these results not only indicate that BMK1 plays an important role in maintaining “stemness” of CSCs,but also implicate that BMK1 might be a potential drug target for CSCs.