Fluid shear stress induces beta-catenin signaling in osteoblasts.
beta-Catenin plays a dual role in cells: one at cell-cell junctions and one regulating gene transcription together with TCF (T-cell Factor) in the nucleus. Recently, a role for beta-catenin in osteoblast differentiation and gene expression has begun to be elucidated. Herein we investigated the effects of fluid shear stress (FSS) on beta-catenin signaling. FSS is a well-characterized anabolic stimulus for osteoblasts; however, the molecular mechanisms for the effects of this stimulation remain largely unknown. We found that 1 hour of laminar FSS (10 dynes/cm(2)) induced translocation of beta-catenin to the nucleus and activated a TCF-reporter gene. Analysis of upstream signals that may regulate beta-catenin signaling activity revealed two potential mechanisms for increased beta-catenin signaling. First, FSS induced a transient, but significant, increase in the phosphorylation of both glycogen synthase kinase 3beta (GSK-3beta) and Akt. Second, FSS reduced the levels of beta-catenin associated with N-cadherin, suggesting that less sequestration of beta-catenin by cadherins occurs in osteoblasts subjected to FSS. Functional analysts of potential genes regulated by beta-catenin signaling in osteoblasts revealed two novel observations. First, endogenous, nuclear beta-catenin purified from osteoblasts formed a complex with a TCF -binding element in the cyclooxygenase-2 promoter, and, second, overexpression of either a constitutively active beta-catenin molecule or inhibition of GSK-3beta activity increased basal cyclooxygenase-2 levels. Together, these data demonstrate for the first time that FSS modulates the activity of both GSK-3beta and beta-catenin and that these signaling molecules regulate cyclooxygenase-2 expression in osteoblasts.
Norvell
S M
SM
Department of Cellular and Integrative Physiology, Indiana University School of Medicine, Indianapolis, IN 46202, USA. snorvell@iupui.edu
Alvarez
M
M
Bidwell
J P
JP
Pavalko
F M
FM
D016475:3T3 Cells; D000818:Animals; D000831:Animals, Newborn; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D024202:Electrophoretic Mobility Shift Assay; D019084:Fluorescent Antibody Technique, Indirect; D017930:Genes, Reporter; D038341:Glycogen Synthase Kinases / Q000378:metabolism; D015151:Immunoblotting; D051379:Mice; D009154:Mutation; D010006:Osteoblasts / Q000502:physiology*; D010766:Phosphorylation; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D051381:Rats; D015398:Signal Transduction; D012886:Skull / Q000166:cytology; D013314:Stress, Mechanical; D013997:Time Factors; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin
C495267:CTNNB1 protein, mouse; C495268:Ctnnb1 protein, rat; D003598:Cytoskeletal Proteins; D011518:Proto-Oncogene Proteins; D015534:Trans-Activators; D051176:beta Catenin; D038341:Glycogen Synthase Kinases; C494920:Akt1 protein, rat; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt