Gap junctional channels facilitate intercellular communication and in doing so may contribute to cellular differentiation. To test this hypothesis, we examined gap junction expression and function in a temperature-sensitive human fetal osteoblastic cell line (hFOB 1.19) that when cultured at 37°C proliferates rapidly but when cultured at 39.5°C proliferates slowly and displays increased alkaline phosphatase activity and osteocalcin synthesis. We found that hFOB 1.19 cells express abundant connexin 43 (Cx43) protein and mRNA. In contrast, Cx45 mRNA was expressed to a lesser degree, and Cx26 and Cx32 mRNA were not detected. Culturing hFOB 1.19 cells at 39.5°C, relative to 37°C, inhibited proliferation, increased Cx43 mRNA and protein expression, and increased gap junctional intercellular communication (GJIC). Blocking GJIC with 18α-glycyrrhetinic acid prevented the increase in alkaline phosphatase activity resulting from culture at 39.5°C but did not affect osteocalcin levels. These results suggest that gap junction function and expression parallel osteoblastic differentiation and contribute to the expression of alkaline phosphatase activity, a marker for fully differentiated osteoblastic cells.
Effect of glucose concentration in media on alkaline phosphatase activity and mineralization in osteoblastic cells.
