Effects Of ATP-sensitive Potassium Channels Activity On Glioma Cells Proliferation

Background:Human malignant gliomas are aggressive tumors that are most common malignancy in brain tumor.Many patients with gliomas respond poorly to traditional radiation and chemotherapy,and recurrence rate of human malignant gliomas is 100%.Therefore,to understand the mechanism by which glioma develops is necessary for an efficient and specific inhibition of the progression of this form of cancer.Ion channels are found in a variety of cancer cells and necessary for cell cycle and cell proliferation.The roles of K⁺ channels in the process are,however,poorly understood.It is commonly accepted that cells require K⁺ channels to proliferate.In any case,it is intuitively acceptable that K⁺ channels,as key players in controlling membrane potential,are critical in proliferation processes.In addition,K⁺ channels also control cell volume to modulate cell proliferation.Adenosine triphosphate(ATP)-sensitive potassium channel(K_ATPchannel)was first discovered by Akinori Noma in cardiac myocytes and was subsequently found to be expressed in many other cell types,e.g.in cardiac and smooth muscle, pancreatic beta cells and various brain regions.K_ATPchannels are octameric proteins consisting of two different types of subunits:members of the Kir6 inwardly rectifying potassium channel family and sulfonylurea receptor(SUR)subunits,which are members of the ATP-binding cassette transporter superfamily.In functional channels, four pore-forming Kir6 subunits are joined together with four regulatory SUR subunits.In central nervous system,K_ATPchannels are composed of Kir6.2 and SUR1 subunits.Evidence showed that expression of KATP channels is up-regulated in human uterine leiomyoma cells for estrogenmediated cell proliferation,but the effects of K_ATPchannels on glioma cells are poorly understood.Mitogen-activated protein kinases(MAPKs)are a family of serine/threonine protein kinases that regulate a wide array of cellular processes.Extracellular signal-regulated kinases(ERK)are the member of MAPKs.ERK activation is associated with cell survival and cell proliferation in response to growth factors such as platelet-derived growth factor and epidermal growth factor,which makes ERK the principal candidate in the studies of cell proliferation.The classic pathway of ERK activation is characterized by the sequential phosphorylation of upstream kinases, namely,Raf-1 and mitogen-activated kinase kinase(MEK).The aim of this study is to investigate the regulation mechanisms by which K_ATPchannels control glioma cells proliferation.Our results demonstrate that K_ATPchannels augment glioma cell proliferation via activating ERK and suggest that K_ATPchannels play a critical role in the development of human malignant gliomas.Aim:To study the mechanisms of ATP-sensitive potassium channels control glioma cells proliferation.Methods:Cell culture,Cell transfection,Immunocytochemistry,MTT assay, Western analysis,Cell cycle analysis,and Mice tumor model.Results:In the present study,we report that adenosine triphosphate (ATP)-sensitive potassium channel activity plays a critical role in the proliferation of glioma cells.The expression of K_ATPchannels in glioma tissues was greatly increased than that in normal tissues.Treatment of glioma cells with tolbutamide,K_ATP channels inhibitor,suppressed the proliferation of glioma cells and blocked glioma cell cycle in G0/G1 phase.Similarly,downregulation of K_ATPchannels by siRNA inhibited glioma cell proliferation.On the other hand,K_ATPchannels agonist diazoxide and overexpression of K_ATPchannels promoted the proliferation of glioma cells.Moreover,inhibiting K_ATPchannels slowed the formation of tumor in nude mice generated by injection of glioma cells.Whereas activating K_ATPchannels promoted development of tumor in vivo.The effect of K_ATPchannels activity on glioma cells proliferation is mediated by extracellular signal-regulated kinase(ERK) activation.We found that activating K_ATPchannel triggered ERK activation and inhibiting K_ATPchannel depressed ERK activation.U-0126,the mitogen activated kinase kinase(MEK)inhibitors blocked ERK activation and cell proliferation induced by diazoxide.Furthermore,constitutively activated MEK plasmids transfection reversed the inhibitory effects of tolbutamide on glioma proliferation,lending further support for a role of ERK in mediating this process.Conclusion:Our results suggest that K_ATPchannels control glioma cell proliferation via regulating ERK pathway.We concluded that K_ATPchannels are important in pathological cell proliferation and open a promising pathway for novel targeted therapies.