Prostaglandin promotion of osteocyte gap junction function through transcriptional regulation of connexin 43 by glycogen synthase kinase 3/beta-catenin signaling.
Gap junction intercellular communication in osteocytes plays an important role in bone remodeling in response to mechanical loading; however, the responsible molecular mechanisms remain largely unknown. Here, we show that phosphoinositide-3 kinase (PI3K)/Akt signaling activated by fluid flow shear stress and prostaglandin E(2) (PGE(2)) had a stimulatory effect on both connexin 43 (Cx43) mRNA and protein expression. PGE(2) inactivated glycogen synthase kinase 3 (GSK-3) and promoted nuclear localization and accumulation of beta-catenin. Knockdown of beta-catenin expression resulted in a reduction in Cx43 protein. Furthermore, the chromatin immunoprecipitation (ChIP) assay demonstrated an association of beta-catenin with the Cx43 promoter, suggesting that beta-catenin could regulate Cx43 expression at the level of gene transcription. We have previously reported that PGE(2) activates cyclic AMP (cAMP)-protein kinase A (PKA) signaling and increases Cx43 and gap junctions. Interestingly, the activation of PI3K/Akt appeared to be independent of the activation of PKA, whereas both PI3K/Akt and PKA signaling inactivated GSK-3 and increased beta-catenin translocation. Together, these results suggest that shear stress, through PGE(2) release, activates both PI3K/Akt and cAMP-PKA signaling, which converge through the inactivation of GSK-3, leading to the increase in nuclear accumulation of beta-catenin. beta-Catenin binds to the Cx43 promoter, stimulating Cx43 expression and functional gap junctions between osteocytes.
Department of Biochemistry, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
Xuechun
X
Xia
Nidhi
N
Batra
Qian
Q
Shi
Lynda F
LF
Bonewald
Eugene
E
Sprague
Jean X
JX
Jiang
D021581:Active Transport, Cell Nucleus; D000818:Animals; D002460:Cell Line; D002467:Cell Nucleus / Q000378:metabolism; D018031:Connexin 43 / Q000235:genetics / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D015232:Dinoprostone / Q000502:physiology*; D017629:Gap Junctions / Q000502:physiology*; D038362:Glycogen Synthase Kinase 3 / Q000502:physiology*; D051379:Mice; D010011:Osteocytes / Q000502:physiology*; D019869:Phosphatidylinositol 3-Kinases / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology; D015398:Signal Transduction; D014158:Transcription, Genetic; D051176:beta Catenin / Q000096:biosynthesis / Q000502:physiology*
C495267:CTNNB1 protein, mouse; D018031:Connexin 43; C543076:GJA1 protein, mouse; D051176:beta Catenin; D000242:Cyclic AMP; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D017868:Cyclic AMP-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3; D015232:Dinoprostone