A dominant negative cadherin inhibits osteoblast differentiation

We have previously indicated that human osteoblasts express a repertoire of cadherins and that perturbation of cadherin-mediated cell-cell interaction reduces bone morphogenetic protein 2 (BMP-2) stimulation of alkaline phosp hatase activity. To test whether inhibition of cadherin function interferes with osteoblast function, we expressed a truncated N-cadherin mutant (NCad DeltaC) with dominant negative action in MC3T3-E1 osteoblastic cells, In s tably transfected clones, calcium-dependent cell-cell adhesion was decrease d by 50%, Analysis of matrix protein expression during a 4-week culture per iod revealed that bone sialoprotein, osteocalcin, and type I collagen were substantially inhibited with time in culture, whereas osteopontin transient ly increased. Basal alkaline phosphatase activity declined in cells express ing NCad DeltaC, relative to control cells, after 3 weeks in culture, and t heir cell proliferation rate was reduced moderately (17%), Finally, Ca-45 u ptake, an index of matrix mineralization, was decreased by 35% in NCad Delt aC-expressing cells compared with control cultures after 4 weeks in medium containing ascorbic acid and beta -glycerophosphate, Similarly, BMP-2 stimu lation of alkaline phosphatase activity and bone sialoprotein and osteopont in expression also were curtailed in NCad DeltaC cells. Therefore, expressi on of dominant negative cadherin results in decreased cell-cell adhesion as sociated with altered bone matrix protein expression and decreased matrix m ineralization, Cadherin-mediated cell-cell adhesion is involved in regulati ng the function of bone-forming cells.