MEK1/2 Induces STAT5-Mediated Germline Transcription of the TCRγ Locus in Response to IL-7R Signaling

Abstract

The IL-7R plays an essential role in γδ T cell development by inducing V-J recombination of the TCRγ locus through STAT5. Although tyrosine residues in the intracellular domain of the mouse IL-7R α-chain (IL-7Rα) have been implicated in STAT5 activation, it is still unknown whether they are essential for γδ T cell development. In this study, we showed that those IL-7Rα tyrosine residues are not essential for γδ T cell development, because phenylalanine replacement of four intracellular tyrosine residues (IL-7R-FFFF) partially rescued γδ T cell development of IL-7Rα−/− progenitors. To examine signaling pathways activated by IL-7R-FFFF, we introduced a chimeric receptor consisting of the human IL-4R α-chain and mouse IL-7R-FFFF (4R/7R-FFFF) into an IL-7-dependent pre-B cell line and found that 4R/7R-FFFF induced TCRγ germline transcription and STAT5 activation. Treatment of cells with MEK1/2 inhibitors significantly decreased levels of TCRγ germline transcription and STAT5 tyrosine phosphorylation mediated by 4R/7R-FFFF, suggesting that MEK1/2 plays an alternative role in STAT5 activation by IL-7R. MEK1/2 associated with STAT5 and induced STAT5 tyrosine phosphorylation and DNA binding activity. Furthermore, MEK1 directly phosphorylated a STAT5 tyrosine residue in vitro. Finally, active MEK1 partially rescued TCRγ germline transcription by IL-7R in a pre-T cell line. These results demonstrate that MEK1/2 induces TCRγ germline transcription by phosphorylating STAT5 through IL-7R-FFFF and suggest a potential role for MAPK in IL-7R tyrosine-independent activation of STAT5.

The TNF-Family Ligand TL1A and Its Receptor DR3 Promote T Cell–Mediated Allergic Immunopathology by Enhancing Differentiation and Pathogenicity of IL-9–Producing T Cells

“…TL1A signaling through DR3 is unlikely to directly induce STAT5 activation, but may enhance STAT5 activity indirectly. MEK and ERK kinases have been found to phosphorylate STAT5 (68, 69), and NF-kB and STAT proteins can bind coordinately to the promoters of a number of genes, including TLR2 (70), FcɛRII (71), and NOS2 (72). The IL-9 promoter contains binding sites for NF-κB and STAT5 making such transcriptional coordination possible (17, 73).…”

Mitogen-activated Protein Kinase Kinase 1 (MEK1) Stabilizes MyoD through Direct Phosphorylation at Tyrosine 156 During Myogenic Differentiation

“…In addition, it is reported that dual-specificity kinases phosphorylate various target proteins, including transcription factors in addition to downstream kinases (39). A recent study reported that MEK1 associates with STAT5 and induces its tyrosine phosphorylation and DNA binding activity (40). The fact that activated nuclear MEK1 reduces the transcriptional activity of PPAR␥ by associating with it, followed by a rapid nuclear export of the complex also supports the unexpected function of MEK1 for MyoD phophorylation in the nucleus (41).…”

Mechanisms of STAT Protein Activation by Oncogenic KIT Mutants in Neoplastic Mast Cells

“…Ali and Sayeski (23)); pGEX-STAT3 (a gift from Drs. Cao and Cheh Peng (24)); and pGEX-STAT5A (amino acids 494 -793) (a gift from Dr. Ikuta (25)). pGEX-STAT5A-Y694F was obtained by sitedirected mutagenesis using the QuikChange kit (Stratagene) according to the manufacturer's instructions.…”