NORE1A tumor suppressor candidate modulates p21CIP1 via p53.
NORE1A (RASSF5) is a proapoptotic Ras effector that is frequently inactivated by promoter methylation in human tumors. It is structurally related to the RASSF1A tumor suppressor and is itself implicated as a tumor suppressor. In the presence of activated Ras, NORE1A is a potent inducer of apoptosis. However, when expressed at lower levels in the absence of activated Ras, NORE1A seems to promote cell cycle arrest rather than apoptosis. The mechanisms underlying NORE1A action are poorly understood. We have used microarray analysis of an inducible NORE1A system to screen for physiologic signaling targets of NORE1A action. Using this approach, we have identified several potential signaling pathways modulated by NORE1A. In particular, we identify the cyclin-dependent kinase inhibitor p21(CIP1) as a target for NORE1A activation and show that it is a vital component of NORE1A-mediated growth inhibition. In primary human hepatocellular carcinomas (HCC), loss of NORE1A expression is frequent and correlates tightly with loss of p21(CIP1) expression. NORE1A down-regulation in HCC also correlates with poor prognosis, enhanced proliferation, survival, and angiogenic tumor characteristics. Experimental inactivation of NORE1A results in the loss of p21(CIP1) expression and promotes proliferation. The best characterized activator of p21(CIP1) is the p53 master tumor suppressor. Further experiments showed that NORE1A activates p21(CIP1) via promoting p53 nuclear localization. Thus, we define the molecular basis of NORE1A-mediated growth inhibition and implicate NORE1A as a potential component of the ill-defined connection between Ras and p53.
Institut für Pathologie, Ernst-Moritz-Arndt-Universität, Greifswald, Germany.
Diego F
DF
Calvisi
Howard
H
Donninger
Michele D
MD
Vos
Michael J
MJ
Birrer
Laura
L
Gordon
Virna
V
Leaner
Geoffrey J
GJ
Clark
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D051017:Apoptosis Regulatory Proteins; D006528:Carcinoma, Hepatocellular / Q000235:genetics; D002448:Cell Adhesion / Q000187:drug effects / Q000235:genetics; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D002478:Cells, Cultured; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D015972:Gene Expression Regulation, Neoplastic / Q000502:physiology; D016147:Genes, Tumor Suppressor / Q000502:physiology; D045325:HCT116 Cells; D006801:Humans; D008113:Liver Neoplasms / Q000235:genetics; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D041681:NIH 3T3 Cells; D034741:RNA, Small Interfering / Q000494:pharmacology; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism / Q000502:physiology*
D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; C454042:RASSF5 protein, human; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D020559:Monomeric GTP-Binding Proteins