BMP-2 and TGF-beta stimulate expression of beta1,3-glucuronosyl transferase 1 (GlcAT-1) in nucleus pulposus cells through AP1, TonEBP, and Sp1: role of MAPKs.
The goal of the study was to investigate bone morphogenetic protein 2 (BMP-2) and transforming growth factor beta (TGF-beta) control of the expression of beta1,3-glucuronosyl transferase 1 (GlcAT-1), an important regulator of chondroitin sulfate synthesis in cells of the nucleus pulposus. Treatment with both growth factors resulted in induction of GlcAT-1 expression and promoter activity. Deletion analysis indicated that promoter constructs lacking AP1 and TonE sites were unresponsive to growth factor treatment. Experiments using dominant-negative proteins showed that these transcription factors along with Sp1 were required for induction of GlcAT-1 promoter activity. Moreover, when either AP1 or TonE binding sites were mutated, induction was suppressed. Both BMP-2 and TGF-beta increased c-Jun and TonEBP expression and phosphorylation of transactivation domains. We investigated the role of the mitogen-activated protein kinase (MAPK) signaling pathway following growth factor treatment; a robust and transient activation of ERK1/2, p38, and JNK was noted. Treatment with MAPK inhibitors blocked BMP-2- and TGF-beta-induced AP1 reporter function, GlcAT-1 expression, and GAG accumulation. We found that DN-ERK1 but not DN-ERK2 resulted in suppression of growth factor-mediated induction of GlcAT-1 promoter activity; we also showed that p38 delta was important in GlcAT-1 activation. Results of these studies demonstrate that BMP-2 and TGF-beta regulate GlcAT-1 expression in nucleus pulposus cells through a signaling network comprising MAPK, AP1, Sp1, and TonEBP. It is concluded that by controlling both GAG and aggrecan synthesis, these growth factors positively influence disk cell function.
Hiyama
Akihiko
A
Department of Orthopaedic Surgery, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Gogate
Shilpa S
SS
Gajghate
Sachin
S
Mochida
Joji
J
Shapiro
Irving M
IM
Risbud
Makarand V
MV
D000818:Animals; D055396:Bone Morphogenetic Protein 2 / Q000502:physiology*; D014453:Glucuronosyltransferase / Q000096:biosynthesis*; D006801:Humans; D007403:Intervertebral Disc / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000502:physiology*; D050778:NFATC Transcription Factors / Q000502:physiology*; D051381:Rats; D015398:Signal Transduction / Q000502:physiology; D018808:Transcription Factor AP-1 / Q000502:physiology*; D016212:Transforming Growth Factor beta / Q000235:genetics / Q000502:physiology*
D055396:Bone Morphogenetic Protein 2; D050778:NFATC Transcription Factors; D018808:Transcription Factor AP-1; D016212:Transforming Growth Factor beta; C067806:glucuronyltransferase GlcAT-1; D014453:Glucuronosyltransferase; D020928:Mitogen-Activated Protein Kinases