Cytoskeleton reorganization and FAK phosphorylation are involved in lanthanum (III)-promoted proliferation and differentiation in rat osteoblasts

The effect of lanthanum ion (La3+) on osteoblast function and cytoskeleton is assessed in vitro. Osteoblasts were isolated from Sprague–Dawley fetal neonatal rats. Cell proliferation and gene expression levels of cbfa-1, alkaline phosphatase (ALP), osteocalcin (OC), bone sialoprotein (BSP) and osteopontin (OPN) were examined by cell counting and RT-PCR. Cytoskeleton F-actin was stained with rhodamine-conjugated phalloidin and was visualized by a confocal microscope. As the results, 10−8–10−4 M La3+-induced osteoblast proliferation on day 2. Data from the RT-PCR assay revealed that 10−6 M La3+ up-regulated the expression levels of ALP, BSP, and cbfa-1 on day 4, while it enhanced the expressions of OC and OPN on day 21. The F-actin cytoskeleton was strengthened and reorganized under the exposure of La3+. In addition, the phosphorylation of focal adhesion kinase (FAK) was significantly promoted in 24 h evaluated by Western blot analysis. These findings indicate that La3+ promotes osteoblast activity through the phosphorylation of FAK and reorganization of the cytoskeleton.