Differentiation of human fetal osteoblastic cells and gap junctional intercellular communication

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 h uman fetal osteoblastic cell line (hFOB 1.19) that when cultured at 37 degr ees C proliferates rapidly but when cultured at 39.5 degrees C proliferates slowly and displays increased alkaline phosphatase activity and osteocalci n synthesis. We found that hFOB 1.19 cells express abundant connexin 43 (Cx 43) protein and mRNA. In contrast, Cx45 mRNA was expressed to a lesser degr ee, and Cx26 and Cx32 mRNA were not detected. Culturing hFOB 1.19 cells at 39.5 degrees C, relative to 37 degrees C, inhibited proliferation, increase d Cx43 mRNA and protein expression, and increased gap junctional intercellu lar communication (GJIC). Blocking GJIC with 18 alpha-glycyrrhetinic acid p revented the increase in alkaline phosphatase activity resulting from cultu re at 39.5 degrees C but did not affect osteocalcin levels. These results s uggest that gap junction function and expression parallel. osteoblastic dif ferentiation and contribute to the expression of alkaline phosphatase activ ity, a marker for fully differentiated osteoblastic cells.