The osteoclast (OCL) is the primary bone resorbing cell. OCL formation and activity is regulated by local factors produced in the bone microenvironment. We recently identified OCL inhibitory peptide-1 (OIP-1/ hSca) as a novel inhibitor of OCL formation and bone resorption that is produced by OCLs. OIP-1 is a glycosylphosphatidyl-inositol (GPI)-linked membrane protein (16 kDa) related to the mouse Ly-6 family of hematopoietic proteins. OIP-1 mRNA is expressed in human OCL precursors, granulocyte-macrophage colony-forming unit (GM-CFU), bone marrow cells, and osteoblast cells. We used cycle-dependent reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, which further demonstrated that interferon-γ (IFN-γ) strongly enhanced OIP-1/hSca mRNA expression in bone marrow cells and GM-CFU. Similarly, interleukin (IL)-1β also enhanced OIP-1 mRNA expression in GM-CFU. To determine the participation of OIP-1 in IFN-γ inhibition of OCL formation, we tested the capacity of a neutralizing antibody specific to OIP-1 c-peptide to inhibit IFN-γ's effects on OCL-like cell differentiation of mouse macrophages, RAW 264.7 cells. Anti-OIP-1 c-peptide specific antibody partially neutralized IFN-γ inhibition of OCL differentiation. Furthermore, OIP-1 inhibited phospho-c-Jun (p-c-Jun) kinase activity in RAW 264.7 cells. However, OIP-1/ hSca did not affect NF-κB activation in these cells. Western blot analysis further demonstrated that OIP-1 significantly decreased TNF receptor associated factor 2 (TRAF-2) expression in RAW 264.7 cells. However, OIP-1 had no effect on TRAF-6 expression in these cells. These data show that IFN-γ enhances OIP-1/hSca expression in OCL precursors, GM-CFU, and that OIP-1 inhibits OCL formation through suppression of TRAF-2 and p-c-Jun kinase activity.
All Science Journal Classification (ASJC) codes
- Endocrinology, Diabetes and Metabolism
- Orthopedics and Sports Medicine