Leukemia-Related Transcription Factor TEL Is Negatively Regulated through Extracellular Signal-Regulated Kinase-Induced Phosphorylation

Abstract

TEL is an ETS family transcription factor that possesses multiple putative mitogen-activated protein kinase phosphorylation sites. We here describe the functional regulation of TEL via ERK pathways. Overexpressed TEL becomes phosphorylated in vivo by activated ERK. TEL is also directly phosphorylated in vitro by ERK. The inducible phosphorylation sites are Ser²¹³ and Ser²⁵⁷. TEL binds to a common docking domain in ERK. In vivo ERK-dependent phosphorylation reduces trans-repressional and DNA-binding abilities of TEL for ETS-binding sites. A mutant carrying substituted glutamates on both Ser²¹³ and Ser²⁵⁷ functionally mimics hyperphosphorylated TEL and also shows a dominant-negative effect on TEL-induced transcriptional suppression. Losing DNA-binding affinity through phosphorylation but heterodimerizing with unmodified TEL could be an underlying mechanism. Moreover, the glutamate mutant dominantly interferes with TEL-induced erythroid differentiation in MEL cells and growth suppression in NIH 3T3 cells. Finally, endogenous TEL is dephosphorylated in parallel with ERK inactivation in differentiating MEL cells and is phosphorylated through ERK activation in Ras-transformed NIH 3T3 cells. These data indicate that TEL is a constituent downstream of ERK in signal transduction systems and is physiologically regulated by ERK in molecular and biological features.

TEL10/pCDNA3, pGL2-754TR, and pCMVMK were generous gifts from T. R. Golub (Dana-Farber Cancer Institute, Boston, Mass.), L. M. Matrisian (Vanderbilt Cancer Center, Nashville, Tenn.), and T. Kadowaki (University of Tokyo, Tokyo, Japan), respectively. pCXN2 and pCAGIPuro were kindly provided by J. Miyazaki (University of Osaka, Osaka, Japan). We thank Y. Furuta for special technical assistance.

This work was financially supported in part by grants-in-aid from the Japan Ministries of both Education, Culture, Sports, Science and Technology and Health, Labor and Welfare and from the Japanese Society for the Promotion of Science. This work was also supported by the Uehara Memorial Foundation and the Japan Intractable Diseases Research Foundation.