Calcium-induced phosphorylation of ETS1 inhibits its specific DNA binding activity

Ets1, the founding member of the Ets gene family of transcriptional regulators, is a phosphoprotein which is highly expressed in cells of the T and B lymphoid lineages. Previous studies have shown that Ets1 becomes rapidly and transiently phosphorylated following antigen receptor (T cell (antigen) receptor (TCR) and membrane Ig) triggering a response which is absolutely dependent on ligand-induced calcium mobilization. By a combination of two-dimensional tryptic phosphopeptide and mutational analyses, the target residues of these calcium-dependent phosphorylation events are identified as 4 serine residues clustered in a domain of Ets1 adjacent to its DNA binding domain (Ets domain). From the comparison of the properties of wild type Ets1 with those of mutant proteins carrying serine-to-alanine substitution in target residues, calcium-dependent phosphorylation of Ets1 is shown to inhibit its binding to specific DNA sequences but does not affect its ability to accumulate in the nucleus, another property dependent on the Ets domain. Our data are consistent with a model in which the calcium-dependent phosphorylation of Ets1 represent the first step of a general clearance of Ets1 function during T and B cell activation.