Activation of EPAC1/2 is essential for osteoclast formation by modulating NFKB nuclear translocation and actin cytoskeleton rearrangements.

Bisphosphonates inhibit osteoclast differentiation/function via inhibition of Rap1A isopreny-lation. As Rap1 is the effector of exchange protein directly activated by cAMP (EPAC) proteins, we determined the role of EPAC in osteoclast differentiation. We examined osteoclast differentiation as the number of primary murine/human bone-marrow precursors that differentiated into multinucleated TRAP-positive cells in the presence of EPAC-selective stimulus (8-pCTP-2=-O-Me-cAMP, 100 µM; 8-pCTP-2=-O-Me-cAMP-AM, 1 µM) or inhibitor brefeldin A (BFA), ESI-05, and ESI-09 (10 µM each). Rap1 activity was assessed, and signaling events, as well as differentiation in EPAC 1/2-knockdown RAW264.7 cells, were studied. Direct EPAC 1/2 stimulation significantly increased osteoclast differentiation, whereas EPAC1/2 inhibition diminished differentiation (113±6%, P<0.05, and 42±10%, P<0.001, of basal, respectively). Rap1 activation was maximal 15 min after RANKL stimulation (147±9% of basal, P< 0.001), whereas silencing of EPAC1/2 diminished activated Rap1 (43±13 and 20±15% of control, P< 0.001) and NFkB nuclear translocation. TRAP-stain-ing revealed no osteoclast differentiation in EPAC1/2-KO cells. Cathepsin K, NFATc1, and osteopontin mRNA expression decreased in EPAC1/2-KO cells when compared to control. RhoA, cdc42, Rac1, and FAKwere activated in an EPAC1/2-dependent manner, and there was diminished cytoskeletal assembly in EPAC1/2-KO cells. In summary, EPAC1 and EPAC2 are critical signaling intermediates in osteoclast differentiation that permit RANKL-stimulated NFkB nuclear translocation and actin rearrangements. Targeting this signaling intermediate may diminish bone destruction in inflammatory arthritis. [ABSTRACT FROM AUTHOR]

Copyright of FASEB Journal is the property of Wiley-Blackwell and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)