title: SUMO-1/Ubc9 promotes nuclear accumulation and metabolic stability of tumor suppressor Smad4.
abstract: Tumor suppressor Smad4/DPC4 is a central intracellular signal transducer for transforming growth factor-beta (TGF-beta) signaling. We recently reported that transcriptional potential of Smad4 was regulated by SUMOylation in transfected HeLa cells (1), but the precise mechanism and function of Smad4 SUMOylation in TGF-beta signaling remain to be elucidated. Here, we describe the regulation of TGF-beta signaling by SUMOylation through the control of Smad4 metabolic stability and subcellular localization. We found that SUMO-1 overexpression strongly increases Smad4 levels, while inhibition of SUMOylation by small interfering RNA (siRNA)-mediated knockdown of the E2 enzyme Ubc9 reduces endogenous Smad4 levels. Concomitantly, SUMO-1 overexpression enhances and Ubc9 knockdown reduces levels of intranuclear Smad4, growth inhibitory response, as well as transcriptional responses to TGF-beta. Comparison of wild type and mutant forms of Smad4 for SUMOylation, ubiquitination, and half-life allows the conclusion that SUMO-1 modification serves to protect Smad4 from ubiquitin-dependent degradation and consequently enhances the growth inhibitory and transcriptional responses of Smad4.
authors.affiliation: Michael E. DeBakey Department of Surgery, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Xia
authors.initials: X
authors.lastname: Lin
authors.forename: Min
authors.initials: M
authors.lastname: Liang
authors.forename: Yao-Yun
authors.initials: YY
authors.lastname: Liang
authors.forename: F Charles
authors.initials: FC
authors.lastname: Brunicardi
authors.forename: Xin-Hua
authors.initials: XH
authors.lastname: Feng
mesh_terms: D002455:Cell Division / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D009154:Mutation; D017395:Plasminogen Activator Inhibitor 1 / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering; D025842:SUMO-1 Protein / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology; D051901:Smad4 Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000378:metabolism; D025521:Tumor Suppressor Proteins / Q000235:genetics / Q000378:metabolism*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D004268:DNA-Binding Proteins; D017395:Plasminogen Activator Inhibitor 1; D034741:RNA, Small Interfering; C497796:SMAD4 protein, human; D025842:SUMO-1 Protein; D051901:Smad4 Protein; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D025521:Tumor Suppressor Proteins; D025801:Ubiquitin