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.
Xia
Xuechun
X
Department of Biochemistry, University of Texas Health Science Center, 7703 Floyd Curl Drive, San Antonio, TX 78229-3900, USA.
Batra
Nidhi
N
Shi
Qian
Q
Bonewald
Lynda F
LF
Sprague
Eugene
E
Jiang
Jean X
JX
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