ASGSB 2003 Annual Meeting Abstracts
RELATIONSHIP BETWEEN CELL SURFACE INTEGRIN AND CONTINUOUS ERK ACTIVATION
DURING OSTEOBLAST DIFFERENTIATION.
D. Shiba1, J-I. Gyotoku2 and M. Takaoki2.
1Space Utilization Research Program, and 2Space
Utilization Research Center, NASDA, Japan.
Mechanical stimuli brought about by altered gravitational environment play key
roles in osteoblast functions. Adhesion receptors like integrins are among
candidates for transducers of mechanical stimuli. As a mediator of mechanical
stimuli via integrins, ERK (extracellular signal-regulated kinase)
which has an essential role in osteoblast proliferation and differentiation is
focused attention on. However, it has not been fully understood how ERK
activation relates to either osteoblast differentiation or mechanical stimulus
perception. We investigated the transitions in ERK activation and cell surface
integrin expression during in vitro differentiation of osteoblast-like
MC3T3-E1 cells. Alkaline phosphatase (ALP) activity, an osteoblastic marker,
increased after confluence. The increase in ALP activity was suppressed by
treating with DGEA peptide, which interferes collagen-a2b1
integrin interaction. Phosphorylation of ERK detected by western blot analysis
was observed throughout 15 days culture. The degree of ERK activation in
15-day culture was about 40 % of that in 3-day culture. U0126, an inhibitor of
ERK activation, suppressed both ERK activation and ALP increase. Cell surface
expressions of integrin
decreased as culture days extended. These findings suggest that continuous ERK
activation is essential and more important in earlier stages of osteoblast
differentiation, and may be regulated by signals from cell surface integrins.
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