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FBXO17 Upregulates Akt Activity and Increases Survival of Lung Epithelial Cells
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A2251 - FBXO17 Upregulates Akt Activity and Increases Survival of Lung Epithelial Cells
Author Block: T. L. Suber1, I. Nikolli1, J. Zhao1, R. K. Mallampalli2, Y. Zhao1; 1Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, United States, 2Acute Lung Injury Center of Excellence, Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh, Medical Specialty Service Line, Veterans Affairs Pittsburgh Healthcare System, Pittsburgh, PA, United States.
Rationale: The Skp1/Cullin/F-box (SCF) family of E3 ubiquitin ligases targets many substrates that mediate acute lung injury and inflammation. Prior work from our group identified FBXO17 as a novel F-box protein that targets glycogen synthase kinase-3β (GSK3β) to the proteasome and downregulates inflammatory responses in lung epithelial cells. Given the role of Akt in negative regulation of GSK3β in the mammalian target of rapamycin complex (mTORC) pathway, we examined whether increased FBXO17 expression enhanced Akt activity and cell survival.
Methods: FBXO17 was cloned into pcDNA 3.1 vector containing hemagglutinin (HA) or histidine (V5) tags. Plasmids expressing FBXO17 or empty vector were transfected into human A549 lung epithelial cells using Lipofectamine 2000. After 48h, lysates were prepared and analyzed by immunoblotting for Akt, p-Akt, p-mTOR, mTOR, survivin, and β-actin (loading control) protein expression. Knockdown experiments were conducted using scrambled small interfering RNA (siRNA) or siRNA targeting FBXO17 (Integrated DNA Technologies). RNA was isolated from cells after transfection and quantitative real-time PCR was performed using primers for AKT1, MTOR, and ACTB (control). Cell viability was analyzed using a colorimetric, tetrazolium-based assay (Promega).
Results: FBXO17 overexpression induces robust Akt and mTOR phosphorylation without influencing their mRNA transcript levels. Silencing FBXO17 gene expression reduces Akt phosphorylation. Ectopic FBXO17 expression was associated with significantly increased epithelial cell viability and metabolic activity.
Conclusions: Through negative regulation of GSK3β by FBXO17-mediated proteasomal degradation, Akt activity increases and thus leads to increased cell survival. The data suggest that FBXO17 may be implicated in remodeling and repair of lung epithelium after injury given the critical role of the PI3K/Akt/mTOR pathway in driving these mechanisms. Future translational studies will evaluate how FBXO17 may modulate the mTORC pathway in experimental models of acute lung injury.
Author Block: T. L. Suber1, I. Nikolli1, J. Zhao1, R. K. Mallampalli2, Y. Zhao1; 1Division of Pulmonary, Allergy, and Critical Care Medicine, University of Pittsburgh, Pittsburgh, PA, United States, 2Acute Lung Injury Center of Excellence, Division of Pulmonary, Allergy and Critical Care Medicine, University of Pittsburgh, Medical Specialty Service Line, Veterans Affairs Pittsburgh Healthcare System, Pittsburgh, PA, United States.
Rationale: The Skp1/Cullin/F-box (SCF) family of E3 ubiquitin ligases targets many substrates that mediate acute lung injury and inflammation. Prior work from our group identified FBXO17 as a novel F-box protein that targets glycogen synthase kinase-3β (GSK3β) to the proteasome and downregulates inflammatory responses in lung epithelial cells. Given the role of Akt in negative regulation of GSK3β in the mammalian target of rapamycin complex (mTORC) pathway, we examined whether increased FBXO17 expression enhanced Akt activity and cell survival.
Methods: FBXO17 was cloned into pcDNA 3.1 vector containing hemagglutinin (HA) or histidine (V5) tags. Plasmids expressing FBXO17 or empty vector were transfected into human A549 lung epithelial cells using Lipofectamine 2000. After 48h, lysates were prepared and analyzed by immunoblotting for Akt, p-Akt, p-mTOR, mTOR, survivin, and β-actin (loading control) protein expression. Knockdown experiments were conducted using scrambled small interfering RNA (siRNA) or siRNA targeting FBXO17 (Integrated DNA Technologies). RNA was isolated from cells after transfection and quantitative real-time PCR was performed using primers for AKT1, MTOR, and ACTB (control). Cell viability was analyzed using a colorimetric, tetrazolium-based assay (Promega).
Results: FBXO17 overexpression induces robust Akt and mTOR phosphorylation without influencing their mRNA transcript levels. Silencing FBXO17 gene expression reduces Akt phosphorylation. Ectopic FBXO17 expression was associated with significantly increased epithelial cell viability and metabolic activity.
Conclusions: Through negative regulation of GSK3β by FBXO17-mediated proteasomal degradation, Akt activity increases and thus leads to increased cell survival. The data suggest that FBXO17 may be implicated in remodeling and repair of lung epithelium after injury given the critical role of the PI3K/Akt/mTOR pathway in driving these mechanisms. Future translational studies will evaluate how FBXO17 may modulate the mTORC pathway in experimental models of acute lung injury.
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