Unique and redundant roles of Smad3 in TGF-beta-mediated regulation of long bone development in organ culture.
The most well-characterized intracellular signaling molecules for transforming growth factor-beta (TGF-beta) are the Smads. R-Smads interact with and are phosphorylated directly by the TGF-beta type I receptor. Phosphorylated R-Smads can then associate with Smad4, translocate to the nucleus and regulate transcription. Specific R-Smads transduce distinct signals for members of the TGF-beta superfamily. Smad2 and -3 mediate signaling by TGF-beta/activin, whereas Smad1, -5, and -8 mediate bone morphogenetic protein signaling. TGF-beta inhibits proliferation and hypertrophic differentiation in metatarsal organ cultures by a perichondrium-dependent mechanism. To determine the mechanism of TGF-beta signaling in the perichondrium, we tested the hypothesis that TGF-beta-restricted Smad2 and Smad3 regulate chondrocyte proliferation and differentiation in embryonic metatarsal organ cultures. Perichondrium was infected with adenoviruses containing dominant-negative forms of Smad2 (Ad-Smad2-3SA) and Smad3 (Ad-Smad3 Delta C). Proliferation and differentiation were measured in response to treatment with TGF-beta 1. Results were compared with control bones infected with a beta-galactosidase reporter virus (Ad-beta-gal). Infection with Ad-Smad2-3SA completely blocked the effects of TGF-beta 1 on metatarsal development while Ad-Smad3 Delta C only partially blocked TGF-beta 1 effects. To further characterize the role of Smad3 in long bone development, TGF-beta 1 responsiveness in cultures from Smad3(+/+) and Smad3(ex8/ex8) mice were compared. Loss of Smad3 only partially blocked the effects of TGF-beta1 on differentiation. In contrast, the effects of TGF-beta 1 on chondrocyte proliferation were blocked completely. We conclude that Smad2 signaling in the perichondrium can compensate for the loss of Smad3 to regulate inhibition of hypertrophic differentiation; however, Smad3 is required for TGF-beta 1-mediated effects on proliferation.
Alvarez
Jesus
J
Department of Cell Biology, University of Alabama at Birmingham, 35294, USA.
Serra
Rosa
R
D021581:Active Transport, Cell Nucleus; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D001842:Bone and Bones; D001973:Bromodeoxyuridine / Q000494:pharmacology; D002356:Cartilage / Q000166:cytology; D002454:Cell Differentiation; D049109:Cell Proliferation; D019902:Chondrocytes / Q000166:cytology / Q000378:metabolism; D004247:DNA / Q000737:chemistry; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005799:Genes, Dominant; D017930:Genes, Reporter; D005838:Genotype; D006614:Hindlimb / Q000196:embryology*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008682:Metatarsal Bones / Q000196:embryology* / Q000378:metabolism; D051379:Mice; D008813:Mice, Inbred ICR; D008856:Microscopy, Fluorescence; D009924:Organ Culture Techniques; D010766:Phosphorylation; D015398:Signal Transduction; D051899:Smad2 Protein; D051900:Smad3 Protein; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism / Q000502:physiology*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism*; D019076:Transgenes; D001616:beta-Galactosidase / Q000378:metabolism
D004268:DNA-Binding Proteins; D051899:Smad2 Protein; C497783:Smad2 protein, mouse; D051900:Smad3 Protein; C497791:Smad3 protein, mouse; D015534:Trans-Activators; D016212:Transforming Growth Factor beta; D004247:DNA; D001616:beta-Galactosidase; D001973:Bromodeoxyuridine