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The Journal of Neuroscience, September 27, 2006, 26(39):10020-10032; doi:10.1523/JNEUROSCI.2644-06.2006

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Cellular/Molecular
Role of Megakaryoblastic Acute Leukemia-1 in ERK1/2-Dependent Stimulation of Serum Response Factor-Driven Transcription by BDNF or Increased Synaptic Activity

Katarzyna Kalita,¹ Giorgi Kharebava,¹ Jing-Juan Zheng,¹ and Michal Hetman^1,2

¹Kentucky Spinal Cord Injury Research Center and Department of Neurological Surgery and ²Department of Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky 40292

Correspondence should be addressed to Dr. Michal Hetman, Kentucky Spinal Cord Injury Research Center, University of Louisville, 511 South Floyd Street, MDR616, Louisville, KY 40292. Email: michal.hetman{at}louisville.edu

Serum response factor (SRF)-mediated transcription contributes to developmental and adult brain plasticity. Therefore, we investigated the role of a newly identified SRF coactivator, MKL1, in the regulation of SRF-driven transcription in rat forebrain neurons. MKL1 expression was found in newborn rat cortical or hippocampal neurons in culture as well as in adult rat forebrain. Immunostaining demonstrated constitutive nuclear localization of MKL1 in the CA1 region of the hippocampus, in the deep layers of the neocortex, and in cultured neurons. Overexpression of MKL1 in primary cortical neurons elevated SRF-driven transcription and enhanced its stimulation by BDNF. In addition, inhibition of endogenous MKL1 by overexpression of a dominant-negative MKL1 mutant or by small interfering RNA reduced BDNF activation of SRF-driven transcription. In neurons, endogenous MKL1 was associated with SRF-regulated chromatin regions of several endogenous genes including c-fos, JunB, Srf, and Cyr61. BDNF activation of MKL1/SRF-driven transcription was dependent on the extracellular signal-regulated kinase 1/2 (ERK1/2) pathway, which also led to MKL1 phosphorylation. Finally, synaptic activity stimulation of SRF-driven transcription was reduced by inhibition of endogenous MKL1. Conversely, synaptic activity enhanced transcription by overexpressed MKL1. MKL1 regulation by synaptic activity was mediated through the NMDA receptor-activated ERK1/2. These results suggest that neuronal MKL1 contributes to SRF-regulated gene expression induced by BDNF or synaptic activity. In addition, MKL1 appears as a novel mediator of the signaling between ERK1/2 and SRF. Moreover, MKL1 is a likely regulator of SRF-driven transcription programs that underlie neuronal plasticity.

Key words: Elk-1; MAL; MRTF-A; plasticity; MAP kinase; immediate-early genes

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Received March 16, 2006; revised Aug. 18, 2006; accepted Aug. 21, 2006.

Correspondence should be addressed to Dr. Michal Hetman, Kentucky Spinal Cord Injury Research Center, University of Louisville, 511 South Floyd Street, MDR616, Louisville, KY 40292. Email: michal.hetman{at}louisville.edu

This article has been cited by other articles:

				S. Muehlich, R. Wang, S.-M. Lee, T. C. Lewis, C. Dai, and R. Prywes Serum-Induced Phosphorylation of the Serum Response Factor Coactivator MKL1 by the Extracellular Signal-Regulated Kinase 1/2 Pathway Inhibits Its Nuclear Localization Mol. Cell. Biol., October 15, 2008; 28(20): 6302 - 6313. [Abstract] [Full Text] [PDF]

				P. Bekinschtein, M. Cammarota, I. Izquierdo, and J. H. Medina Reviews: BDNF and Memory Formation and Storage Neuroscientist, April 1, 2008; 14(2): 147 - 156. [Abstract] [PDF]

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