Abstract
Bone formation in response to exogenous mechanical loading is dependent on prostaglandin synthesis by the inducible isoform of cyclooxygenase, COX-2. While several transcription factors target the COX-2 gene, we examined the role of nuclear factor kappa B (NFκB) on COX-2 upregulation in osteoblasts in response to fluid shear due to its involvement in immune and inflammatory responses in other cell types. Application of 12 dyn/cm2 laminar flow to MC3T3-E1 osteoblast-like cells resulted in translocation of NFκB to the nucleus within 1 h of the onset of shear, with NFκB returning to the cytoplasm after 2 h of continuous flow. NFκB translocation in response to shear was inhibited by the protease inhibitor, Nα -p-tosyl-L-lysine chloromethylketone hydrochloride (TLCK), or a cell-permeant peptide that blocks the nuclear localization sequence (NLS) on NFκB. Block of NFκB translocation with these inhibitors blocked the shear-induced upregulation of COX-2. We found that disruption of the actin cytoskeleton with cytochalasin D or microtubules with nocodozol did not alter NFκB translocation in response to shear. However, addition of the intracellular Ca2+ chelator BAPTA completely blocked NFκB translocation. While block of Ca2+ entry with channel blockers failed to inhibit NFκB translocation, inhibition of phospholipase C (PLC)-induced intracellular Ca2+ release with the PLC inhibitor U73122 completely abrogated the NFκB response to shear. These data indicate that NFκB translocation to the nucleus is essential for the fluid shear-induced increase in COX-2. Further, these studies suggest that intracellular Ca2+ release, but not the cytoskeletal architecture, is important to NFκB translocation.
Original language | English (US) |
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Pages (from-to) | 399-410 |
Number of pages | 12 |
Journal | Bone |
Volume | 33 |
Issue number | 3 |
DOIs | |
State | Published - Sep 1 2003 |
Externally published | Yes |
Keywords
- Intracellular Ca release
- Mechanotransduction
- NFκB
- Osteoblasts
- Phospholipase C
ASJC Scopus subject areas
- Physiology
- Hematology