Inhibiting gap junctional intercellular communication alters expression of differentiation markers in osteoblastic cells

Gap junctional intercellular communication (GJIC) may contribute to cellular differentiation. To examine this possibility in bone cells we examined markers of cellular differentiation, including alkaline phosphatase, osteocalcin, and osteopontin, in ROS17/2.8 cells (ROS), a rat osteoblastic cell line expressing phenotypic characteristics of fully differentiated osteoblasts. We utilized ROS rendered communication deficient either by stable transfection with antisense cDNA to connexin 43 (Cx43), the predominant gap junction protein in bone (RCx16 cells), or by overexpression of Cx45, a gap junction protein not normally expressed in ROS (ROS/Cx45 cells). Both RCx16 and ROS/Cx45 cells displayed reduced dye coupling and Cx43 protein expression relative to ROS, control transfectants, and ROS/Cx45tr, ROS cells expressing carboxylterminal truncated Cx45. Steady-state mRNA levels for osteocalcin as well as alkaline phosphatase activity, two markers of osteoblastic differentiation, were also reduced in poorly coupled RCx16 and ROS/Cx45 cells. On the other hand, steady-state mRNA levels for osteopontin increased slightly in RCx16 and ROS/Cx45 cells. These results suggest that GJIC at least partly contributes to the regulation of expression of markers of osteoblastic differentiation.