Osteogenic protein-1 regulates L1 and neural cell adhesion molecule gene expression in neural cells

Osteogenic protein-1 (OP-1) is a member of the TGF-beta superfamily that is expressed in the nervous system. We recently showed that human recombinant osteogenic protein-1 (hOP-1) strongly promotes the aggregation of dividing neuroblastoma x glioma hybrid NG108-15 cells, in part by inducing the major isoforms of the neural cell adhesion molecule (N-CAM) (Perides, G., Safran, R. M., Rueger, D. C., and Charness, M. E. (1992) Proc. Natl. Acad. Sci. U. S. A. 89, 10326-10330). Here we show that hOP-1 induces L1 expression approximately 6-fold in NG108-15 cells without changing the levels of N-cadherin, neurofilament 200, Thy-1, tau, and G alpha s. OP-1 induction of L1 and N-CAM was unassociated with changes in cell proliferation and was not reproduced by cellular differentiation. The increased adhesiveness of hOP-1-treated NG108-15 cells could be inhibited in part by Fab fragments of an anti-L1 polyclonal antiserum. L1 and N-CAM expression first increased 12-18 h after hOP-1 treatment, reached a maximum after 2-3 days, persisted for up to 5 days, and returned to control levels 3 days after hOP-1 withdrawal. The increases in L1 and N-CAM protein levels were preceded or accompanied by large increases in the abundance of L1 and all detectable N-CAM mRNAs. Actinomycin D prevented the induction by hOP-1 of L1 and N-CAM mRNAs, suggesting that hOP-1 regulates immunoglobulin CAM gene transcription. OP-1 is the first described growth factor that regulates both N-CAM and L1 gene expression.