Activation of STAT5-dependent transcription by the neurotrophin receptor Trk

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Abstract
Neurotrophins exert many of their biological effects via the Trk receptor tyrosine kinases and require the regulated activation of distinct transcriptional and post‐translational cellular events. Here we provide evidence for a novel signaling cascade from activated Trks to the transcription factor STAT5. Utilizing the STAT5 responsive element derived from the p21WAF1/Cip1 promoter to modulate luciferase expression, neurotrophin‐dependent activation of Trk A, B, and C was found to induce STAT5‐mediated transcriptional response. Structure‐function analysis using Trk A mutants in heterologous cells further revealed that the kinase activity and an intact phospholipase C‐gamma binding site are required for STAT5 activation. In most cytokine responsive cell systems, STAT5 function is modulated by JAK2‐dependent tyrosine phosphorylation. However, reconstitution studies using a JAK2 deficient cell line indicate that neurotrophin‐induced STAT5 activation does not require the cognate upstream kinase JAK2. In contrast, the Src kinase inhibitor PP1 significantly abolishes STAT5‐dependent transcription in Trk A expressing 293T cells and in BDNF‐treated primary cortical neurons. Together these results suggest that neurotrophins may regulate neuronal gene expression via STAT5 in a JAK2 independent manner. © 2005 Wiley Periodicals, Inc. J Neurobiol, 2005