title: RLIP76 is overexpressed in human glioblastomas and is required for proliferation, tumorigenesis and suppression of apoptosis.
abstract: The guanosine triphosphatase-activating protein RLIP76 is overexpressed in many malignant tumor cells, but it is unclear if RLIP76 overexpression contributes to the high proliferative potential of glioma cells. We demonstrate that RLIP76 messenger RNA and protein expression are positively correlated with glioma grade and that higher RLIP76 expression correlates with shorter patient survival. Immunohistochemical staining revealed that RLIP76 expression was positively correlated with the expression of Ki-67, a biomarker for cell proliferation. Inhibition of RLIP76 expression in U87 and U251 glioma cell lines by stable transfection of a targeted siRNA suppressed anchorage-independent growth and enhanced apoptosis in vitro. Conversely, overexpression of RLIP76 in SW1088 and U251 cell lines enhanced proliferation and reduced apoptosis. Inhibition of RLIP76 in U251 cells also significantly suppressed tumorigenicity and induced apoptosis in an endotopic xenograft mouse model. Moreover, we demonstrate that knockdown of RLIP76 increases apoptosis in different human gliomas independently of p53 status. In addition, a constitutively active Rac1 reversed both the suppression of proliferation and the promotion of apoptosis induced by the RLIP76-targeted siRNA, indicating that RLIP76 is an upstream activator of Rac1. Rac1-mediated suppression of apoptosis and promotion of proliferation were dependent on intact c-jun N-terminal kinase (JNK) signaling. Furthermore, we demonstrate that RLIP76 promotes proliferation and suppresses glioma cell apoptosis through a mechanism independent of Rho-selective GTPase-activating protein. Instead, we found that the adenosine triphosphatase function of Rlip76 modulates Rac1 activity by regulating Rac1 protein ubiquitylation and degradation. These data demonstrate that RLIP76 may suppress apoptosis and promote the proliferation of glioma cells by direct adenosine triphosphate-dependent xenobiotic transport and by activating the Rac1-JNK signaling pathway. Inhibition of RLIP76 signaling is a potential treatment for malignant glioma.
authors.affiliation: Department of Neurosurgery, Changzheng Hospital, Second Military Medical University, 415 Fengyang Road, Shanghai, China.
authors.forename: Qi
authors.initials: Q
authors.lastname: Wang
authors.forename: Jun-Yu
authors.initials: JY
authors.lastname: Wang
authors.forename: Xiao-Ping
authors.initials: XP
authors.lastname: Zhang
authors.forename: Zhong-Wei
authors.initials: ZW
authors.lastname: Lv
authors.forename: Da
authors.initials: D
authors.lastname: Fu
authors.forename: Yi-Cheng
authors.initials: YC
authors.lastname: Lu
authors.forename: Guo-Han
authors.initials: GH
authors.lastname: Hu
authors.forename: Chun
authors.initials: C
authors.lastname: Luo
authors.forename: Ju-Xiang
authors.initials: JX
authors.lastname: Chen
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism*; D000818:Animals; D017209:Apoptosis / Q000235:genetics; D014408:Biomarkers, Tumor / Q000235:genetics; D001932:Brain Neoplasms / Q000235:genetics / Q000378:metabolism / Q000401:mortality; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D002471:Cell Transformation, Neoplastic; D020690:GTPase-Activating Proteins / Q000235:genetics / Q000378:metabolism*; D005909:Glioblastoma / Q000235:genetics / Q000378:metabolism* / Q000401:mortality / Q000473:pathology*; D057809:HEK293 Cells; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D019394:Ki-67 Antigen / Q000096:biosynthesis; D020935:MAP Kinase Signaling System; D008297:Male; D051379:Mice; D009368:Neoplasm Transplantation; D011379:Prognosis; D034622:RNA Interference; D012333:RNA, Messenger / Q000096:biosynthesis; D034741:RNA, Small Interfering; D051381:Rats; D013534:Survival; D014183:Transplantation, Heterologous; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis; D054875:Ubiquitination; D020830:rac1 GTP-Binding Protein / Q000096:biosynthesis / Q000378:metabolism
chemical_list: D018528:ATP-Binding Cassette Transporters; D014408:Biomarkers, Tumor; D020690:GTPase-Activating Proteins; D019394:Ki-67 Antigen; C095637:RALBP1 protein, human; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D048031:JNK Mitogen-Activated Protein Kinases; D020830:rac1 GTP-Binding Protein