Interaction between endothelial differentiation-related factor-1 and calmodulin in vitro and in vivo

Calmodulin (CaM) is the principal Ca2+ receptor protein inside the cell. When activated by Ca2+, CaM binds and activates target proteins, thus altering the metabolism and physiology of the cell, Under basal conditions, calcium-free CaM binds to other proteins termed CaM-binding proteins, Recently, we described endothelial differentiation-related factor (EDF)-1 as a protein involved in the repression of endothelial cell differentiation (Dragoni, I., Mariotti, M., Consalez, G, G., Soria, M., and Maier, J. A. M. (1998) J, Biol, Chem. 273, 31119-31124). Here we report that (i) EDF-1 binds CaM in vitro and in vice; (ii) EDF-1 is phosphorylated in vitro and in vivo by protein kinase C; and (iii) EDF-1-CaM interaction is modulated by the concentrations of Ca2+ and by the phosphorylation of EDF-1 by protein kinase C both in vitro and in vivo,In addition, 12-O-tetradecanoylphorbol-13-acetate treatment of human umbilical vein endothelial cell stimulates the nuclear translocation of EDF-1. On the basis of the high homology of EDF-1 with multiprotein bridging factor-1, a transcriptional coactivator that binds TATA-binding protein (TBP), we also demonstrate that EDF-1 interacts with TBP in vitro and in human endothelial cells, We hypothesize that EDF-1 serves two main functions in endothelial cells as follows: (i) to bind CaM in the cytosol at physiologic concentrations of Ca2+ and (ii) to act in the nucleus as a transcriptional coactivator through its binding to TBP.