Opposing Roles of Elk-1 and Its Brain-specific Isoform, Short Elk-1, in Nerve Growth Factor-induced PC12 Differentiation

• Published in: The Journal of biological chemistry Vol. 276; no. 7; pp. 5189 - 5196
• Main Authors: Vanhoutte, Peter, Nissen, Johan L., Brugg, Bernard, Gaspera, Bruno Della, Besson, Marie-Jo, Hipskind, Robert A., Caboche, Jocelyne
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 16.02.2001; American Society for Biochemistry and Molecular Biology
• Subjects: Active Transport, Cell Nucleus; Animals; Antibodies - immunology; Brain - metabolism; Cell Differentiation; Cell Nucleus - metabolism; Codon, Initiator; DNA-Binding Proteins - genetics; DNA-Binding Proteins - immunology; DNA-Binding Proteins - physiology; ets-Domain Protein Elk-1; Life Sciences; Male; Nerve Growth Factor - pharmacology; Neurons - cytology; Neurons - metabolism; Neurons and Cognition; PC12 Cells; Phenotype; Protein Isoforms - genetics; Protein Isoforms - immunology; Protein Isoforms - physiology; Proto-Oncogene Proteins - genetics; Proto-Oncogene Proteins - immunology; Proto-Oncogene Proteins - physiology; Rats; Rats, Sprague-Dawley; Transcription Factors - genetics; Transcription Factors - immunology; Transcription Factors - physiology; Transcriptional Activation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M006678200

The ternary complex factor Elk-1, a major nuclear target of extracellular signal-regulated kinases, is a strong transactivator of serum-responsive element (SRE) driven gene expression. We report here that mature brain neurons and nerve growth factor (NGF)-differentiated PC12 cells also express a second, smaller isoform of Elk-1, short Elk-1 (sElk-1). sElk-1 arises from an internal translation start site in the Elk-1 sequence, which generates a protein lacking the first 54 amino acids of the DNA-binding domain. This deletion severely compromises the ability of sElk-1 to form complexes with serum response factor on the SRE in vitro and to activate SRE reporter genes in the presence of activated Ras. Instead, sElk, but not a mutant that cannot be phosphorylated, inhibits transactivation driven by Elk-1. More pertinent to the neuronal-specific expression of sElk-1, we show it plays an opposite role to Elk-1 in potentiating NGF-driven PC12 neuronal differentiation. Overexpression of sElk-1 but not Elk-1 increases neurite extension, an effect critically linked to its phosphorylation. Interestingly, in the presence of sElk-1, Elk-1 loses its strictly nuclear localization to resemble the nuclear/cytoplasm pattern observed in the mature brain. This is blocked by mutating a normally cryptic nuclear export signal in Elk-1. These data provide new insights into molecular events underlying neuronal differentiation of PC12 cells mediated by the NGF-ERK signaling cascade.