RNA Polymerase 1-driven Transcription as a Mediator of BDNF-induced Neurite Outgrowth

Cynthia Gomes,Scott C Smith,Mark N Youssef,Jing-Juan Zheng,Theo Hagg,Michal Hetman

doi:10.1074/jbc.m110.170134

Cynthia Gomes, Scott C Smith + Show 4 more

Open Access

https://doi.org/10.1074/jbc.m110.170134

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Abstract

Neurite outgrowth is essential for development of the nervous system. Neurotrophins including BDNF are among extracellular signals that regulate neurite outgrowth. The ERK1/2 pathway contributes to intracellular signaling networks transducing the pro-neuritic effects of BDNF. In the nucleolus, RNA polymerase-1 (Pol1)-mediated transcription regulates ribosomal biogenesis, enabling cellular protein synthesis and growth. Hence, we tested the possibility that Pol1 is an effector for pro-neuritic signals such as BDNF. We report that Pol1-mediated nucleolar transcription was increased by BDNF in an ERK1/2-dependent manner in rat forebrain neurons. Conversely, in cultured hippocampal neurons, knockdown of a Pol1 coactivator, transcription initiation factor 1A (TIF1A), attenuated BDNF- or ERK1/2-induced neurite outgrowth. Also, upon overexpression, a constitutively active mutant of TIF1A strongly promoted neurite outgrowth, including increases in total neurite length and branching. Finally, overexpression of wild-type TIF1A enhanced the pro-neuritic effects of ERK1/2 activation. These observations indicate that the Pol1-mediated nucleolar transcription regulates neurite outgrowth and serves as a major pro-neuritic effector of the BDNF-activated ERK1/2 pathway. Thus, development of the nervous system appears critically dependent on the nucleolus.

Highlights

We determined whether BDNF stimulates nucleolar transcription in developing forebrain neurons
The shRNA against TIF1A (shTIF1A) markedly reduced the morphogenic effects of BDNF (Fig. 2), indicating that nucleolar transcription is required for somatoneuritic growth and neurite branching in response to neurotrophic stimulation
As the ERK1/2 pathway is the major mediator of both neurotrophin-induced neuritic morphogenesis and Pol1 activation by growth factors [2, 9], we evaluated its contribution to BDNF effects on nucleolar transcription

Summary

Introduction

We investigated whether nucleolar transcription in developing rat forebrain contributes to BDNF-mediated neurite outgrowth. Using a construct consisting of a luciferase reporter gene under the control of the rDNA promoter, we observed increased activity of the latter upon cortical neuron exposure to BDNF (Fig. 1D). The glial origin of the BDNF effects on the overexpressed rDNA-reporter construct is unlikely, as in rat cortical cultures, virtually all successfully transfected cells were identified as MAP2-positive neurons (data not shown).

Results

Conclusion