title: c-Src-mediated phosphorylation of thyroid hormone receptor-interacting protein 6 (TRIP6) promotes osteoclast sealing zone formation.
abstract: Osteoclasts resorb bone through the formation of a unique attachment structure called the sealing zone. In this study, a role for thyroid hormone receptor-interacting protein 6 (TRIP6) in sealing zone formation and osteoclast activity was examined. TRIP6 was shown to reside in the sealing zone through its association with tropomyosin 4, an actin-binding protein that regulates sealing dimensions and bone resorptive capacity. Suppression of TRIP6 in mature osteoclasts by RNA interference altered sealing zone dimensions and inhibited bone resorption, whereas overexpression of TRIP6 increased the sealing zone perimeter and enhanced bone resorption. Treatment of osteoclasts with lysophosphatidic acid (LPA), which phosphorylates TRIP6 at tyrosine 55 through a c-Src-dependent mechanism, caused increased association of TRIP6 with the sealing zone, as did overexpression of a TRIP6 cDNA bearing a phosphomimetic mutation at tyrosine 55. Further, LPA treatment caused increases in osteoclast fusion, sealing zone perimeter, and bone resorptive capacity. In contrast, overexpression of TRIP6 containing a nonphosphorylatable amino acid residue at position 55 severely diminished sealing zone formation and bone resorption and suppressed the effects of LPA on the cytoskeleton. LPA effects were mediated through its receptor isoform LPA(2), as indicated by treatments with receptor-specific agonists and antagonists. Thus, these studies suggest that TRIP6 is a critical downstream regulator of c-Src signaling and that its phosphorylation is permissive for its presence in the sealing zone where it plays a positive role in osteoclast bone resorptive capacity.
authors.affiliation: Department of Physiology and Cell Biology, The Ohio State University College of Medicine, Columbus, Ohio 43210, USA.
authors.forename: Brooke K
authors.initials: BK
authors.lastname: McMichael
authors.forename: Stephanie M
authors.initials: SM
authors.lastname: Meyer
authors.forename: Beth S
authors.initials: BS
authors.lastname: Lee
mesh_terms: D000074183:ATPases Associated with Diverse Cellular Activities; D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D000818:Animals; D001862:Bone Resorption / Q000378:metabolism*; D000081247:CSK Tyrosine-Protein Kinase; D002459:Cell Fusion; D060588:LIM Domain Proteins; D008246:Lysophospholipids / Q000494:pharmacology; D051379:Mice; D010010:Osteoclasts / Q000502:physiology*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D019061:src-Family Kinases
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D060588:LIM Domain Proteins; D008246:Lysophospholipids; C092282:PSMC5 protein, human; D014157:Transcription Factors; D011505:Protein-Tyrosine Kinases; D000081247:CSK Tyrosine-Protein Kinase; D019061:src-Family Kinases; C000631346:CSK protein, human; D046988:Proteasome Endopeptidase Complex; D000074183:ATPases Associated with Diverse Cellular Activities; C032881:lysophosphatidic acid