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 a2 and b1 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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