Noriko Fujii

Osteopontin involvement in integrin-mediated cell signaling and regulation of expression of alkaline phosphatase during early differentiation of UMR cells.

To clarify the function of osteopontin in osteoblast differentiation, we have examined the signal transduction pathway in an osteoblastic cell line (UMR106‐6) bound to osteopontin, fibronectin, vitronectin and collagen type I surfaces. This was done by investigating the production and autophosphorylation of focal adhesion kinase (FAK) and the expression of alkaline phosphatase (ALP) at the transcription level. Results suggest that osteopontin was not only responsible for the autophosphorylation of FAK but regulated the expression of ALP, which was strongly correlated with FAK activity. These results suggest that osteopontin might act as a trigger in the early differentiation of osteoblasts.

The mechanisms of simultaneous stereoinversion, racemization, and isomerization at specific aspartyl residues of aged lens proteins

Proteins have been considered to consist exclusively of L-amino acids in living tissues. However, we found biologically uncommon D-aspartyl (Asp) residues at specific sites in alphaA- and alphaB-crystallin from the aged human lens (mean age: 80 years). In alphaB-crystallin, the Asp-36 and Asp-62 residues are highly racemized (D/L ratios: 0.92 for Asp-36; 0.54 for Asp-62). More interestingly, the configuration of the Asp-58 and Asp-151 residues in alphaA-crystallin is inverted to the D-isomer (D/L ratio: 3.1 for Asp-58, 5.7 for Asp-151). A D/L ratio > 1.0 is not considered to be due to racemization, but rather is thought to result from stereoconfiguration inversion. Our report was the first observation that inversion occurred in the configuration of amino acids in vivo during the natural aging process. We also found that these enantiomers were simultaneously isomerized to form beta-Asp residues. We propose that the mechanism of D- and beta-Asp formation in the protein depends on the primary structure and the presence of a chiral reaction field, which induces formation of D-Asp.