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Centre for Science and Technology in Medicine, School of Postgraduate Medicine, Keele University, North Staffordshire Hospital, Stoke on Trent ST4 7QB, United Kingdom
The regulatory pathways involved in the rapid response of the AP-1
transcription factor, c-fos, to mechanical load in human primary osteoblast-like (HOB) cells and the human MG-63 bone cell line
were investigated using a four-point bending model. HOB and MG-63 cells
showed upregulation of c-fos expression on fibronectin and
collagen type I substrates; however, MG-63 cells did not
respond on laminin YIGSR substrates. Addition of cytochalasin D and
Arg-Gly-Asp peptides during loading did not inhibit the response,
whereas addition of
1-integrin antibodies inhibited the
load response. The role of Ca2+ signaling has been
demonstrated by blocking upregulation with addition of 2 mM EGTA, which
chelates extracellular Ca2+, and gadolinium (10 µM),
which inhibits stretch-activated channels. Addition of the
Ca2+ ionophore A-23187 induced upregulation without
loading; however, addition of nifedipine (10 µM), the L-type channel
blocker, failed to prevent the load response. Inhibitors of downstream
pathways indicated the involvement of protein kinase C. Our results
demonstrate a key involvement of Ca2+ signaling pathways
and integrin binding in the c-fos response to mechanical strain.
secondary messenger; mechanical loading; gene regulation; calcium channels; integrins
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