Dickkopf homolog 1 mediates endothelin-1-stimulated new bone formation.
Tumor-produced endothelin-1 (ET-1) stimulates osteoblasts to form new bone and is an important mediator of osteoblastic bone metastasis. The anabolic actions of ET-1 in osteoblasts were investigated by gene microarray analyses of murine neonatal calvarial organ cultures. Targets of ET-1 action were validated by real-time RT-PCR in murine primary osteoblast cultures. IL-6, IL-11, the CCN (CYR61, CTGF, NOV) family members cysteine-rich protein 61 and connective tissue growth factor, inhibin beta-A, serum/glucocorticoid regulated kinase, receptor activator of nuclear factor kappaB ligand, snail homolog 1, tissue inhibitor of metalloproteinase 3, and TG-interacting factor transcripts were increased by ET-1. ET-1 decreased the transcript for the Wnt signaling pathway inhibitor, dickkopf homolog 1 (Dkk1). Calvarial organ cultures treated with ET-1 had lower concentrations of DKK1 protein in conditioned media than control cultures. High DKK1 concentrations in bone marrow suppress bone formation in multiple myeloma. We hypothesized that the converse occurs in osteoblastic bone metastasis, where ET-1 stimulates osteoblast activity by reducing autocrine production of DKK1. Recombinant DKK1 blocked ET-1-mediated osteoblast proliferation and new bone formation in calvarial organ cultures, whereas a DKK1-neutralizing antibody increased osteoblast numbers and new bone formation. ET-1 directed nuclear translocation of beta-catenin in osteoblasts, indicating activation of the Wnt signaling pathway. The data suggest that ET-1 increases osteoblast proliferation and new bone formation by activating the Wnt signaling pathway through suppression of the Wnt pathway inhibitor DKK1.
Clines
Gregory A
GA
Department of Internal Medicine, Division of Endocrinology and Metabolism, Aurbach Laboratory, The University of Virginia, P.O. Box 801419, Charlottesville, Virginia 22908-1419, USA.
Mohammad
Khalid S
KS
Bao
Yongde
Y
Stephens
Owen W
OW
Suva
Larry J
LJ
Shaughnessy
John D
JD
Fox
Jay W
JW
Chirgwin
John M
JM
Guise
Theresa A
TA
D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D019332:Endothelin-1 / Q000502:physiology*; D005260:Female; D005786:Gene Expression Regulation; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis / Q000502:physiology*; D015850:Interleukin-6 / Q000096:biosynthesis; D051379:Mice; D020411:Oligonucleotide Array Sequence Analysis; D009924:Organ Culture Techniques; D010006:Osteoblasts / Q000166:cytology / Q000502:physiology*; D010012:Osteogenesis / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012886:Skull / Q000166:cytology; D051153:Wnt Proteins / Q000502:physiology
C501127:Dkk1 protein, mouse; D019332:Endothelin-1; D036341:Intercellular Signaling Peptides and Proteins; D015850:Interleukin-6; D051153:Wnt Proteins