TY - JOUR
T1 - Doubly truncated FosB isoform (Delta2DeltaFosB) induces osteosclerosis in transgenic mice and modulates expression and phosphorylation of Smads in osteoblasts independent of intrinsic AP-1 activity.
AU - Sabatakos, George
AU - Rowe, Glenn C
AU - Kveiborg, Marie
AU - Wu, Meilin
AU - Neff, Lynn
AU - Chiusaroli, Riccardo
AU - Philbrick, William M
AU - Baron, Roland
N1 - Keywords: Alternative Splicing; Animals; Base Sequence; Cells, Cultured; DNA Primers; Humans; Mice; Mice, Inbred C57BL; Mice, Transgenic; Osteoclasts; Osteosclerosis; Phosphorylation; Protein Isoforms; Proto-Oncogene Proteins c-fos; RNA, Messenger; Smad1 Protein; Transcription Factor AP-1
PY - 2008
Y1 - 2008
N2 - INTRODUCTION: Activator protein (AP)-1 family members play important roles in the development and maintenance of the adult skeleton. Transgenic mice that overexpress the naturally occurring DeltaFosB splice variant of FosB develop severe osteosclerosis. Translation of Deltafosb mRNA produces both DeltaFosB and a further truncated isoform (Delta2DeltaFosB) that lacks known transactivation domains but, like DeltaFosB, induces increased expression of osteoblast marker genes. MATERIALS AND METHODS: To test Delta2DeltaFosB's ability to induce bone formation in vivo, we generated transgenic mice that overexpress only Delta2DeltaFosB using the enolase 2 (ENO2) promoter-driven bitransgenic Tet-Off system. RESULTS: Despite Delta2DeltaFosB's failure to induce transcription of an AP-1 reporter gene, the transgenic mice exhibited both the bone and the fat phenotypes seen in the ENO2-DeltaFosB mice. Both DeltaFosB and Delta2DeltaFosB activated the BMP-responsive Xvent-luc reporter gene and increased Smad1 expression. Delta2DeltaFosB enhanced BMP-induced Smad1 phosphorylation and the translocation of phospho-Smad1 (pSmad1) to the nucleus more efficiently than DeltaFosB and showed a reduced induction of inhibitory Smad6 expression. CONCLUSIONS: DeltaFosB's AP-1 transactivating function is not needed to induce increased bone formation, and Delta2DeltaFosB may act, at least in part, by increasing Smad1 expression, phosphorylation, and translocation to the nucleus.
AB - INTRODUCTION: Activator protein (AP)-1 family members play important roles in the development and maintenance of the adult skeleton. Transgenic mice that overexpress the naturally occurring DeltaFosB splice variant of FosB develop severe osteosclerosis. Translation of Deltafosb mRNA produces both DeltaFosB and a further truncated isoform (Delta2DeltaFosB) that lacks known transactivation domains but, like DeltaFosB, induces increased expression of osteoblast marker genes. MATERIALS AND METHODS: To test Delta2DeltaFosB's ability to induce bone formation in vivo, we generated transgenic mice that overexpress only Delta2DeltaFosB using the enolase 2 (ENO2) promoter-driven bitransgenic Tet-Off system. RESULTS: Despite Delta2DeltaFosB's failure to induce transcription of an AP-1 reporter gene, the transgenic mice exhibited both the bone and the fat phenotypes seen in the ENO2-DeltaFosB mice. Both DeltaFosB and Delta2DeltaFosB activated the BMP-responsive Xvent-luc reporter gene and increased Smad1 expression. Delta2DeltaFosB enhanced BMP-induced Smad1 phosphorylation and the translocation of phospho-Smad1 (pSmad1) to the nucleus more efficiently than DeltaFosB and showed a reduced induction of inhibitory Smad6 expression. CONCLUSIONS: DeltaFosB's AP-1 transactivating function is not needed to induce increased bone formation, and Delta2DeltaFosB may act, at least in part, by increasing Smad1 expression, phosphorylation, and translocation to the nucleus.
U2 - 10.1359/jbmr.080110
DO - 10.1359/jbmr.080110
M3 - Journal article
C2 - 18433296
SN - 0884-0431
VL - 23
SP - 584
EP - 595
JO - Journal of Bone and Mineral Research
JF - Journal of Bone and Mineral Research
IS - 5
ER -