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. Wh en activated by Ca2+, CaM binds and activates target proteins, thus alterin g the metabolism and physiology of the cell, Under basal conditions, calciu m-free CaM binds to other proteins termed CaM-binding proteins, Recently, w e 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 v itro and in vice; (ii) EDF-1 is phosphorylated in vitro and in vivo by prot ein kinase C; and (iii) EDF-1-CaM interaction is modulated by the concentra tions 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 trea tment of human umbilical vein endothelial cell stimulates the nuclear trans location of EDF-1. On the basis of the high homology of EDF-1 with multipro tein bridging factor-1, a transcriptional coactivator that binds TATA-bindi ng protein (TBP), we also demonstrate that EDF-1 interacts with TBP in vitr o 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 t ranscriptional coactivator through its binding to TBP.