Opposing roles of Elk-1 and its brain-specific isoform, short Elk-1, in nerve growth factor-induced PC12 differentiation.
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.
Vanhoutte
P
P
Laboratoire de Neurochimie-Anatomie, Institut des Neurosciences, CNRS-UMR 7624, Université Pierre et Marie Curie, 75005 Paris, France.
Nissen
J L
JL
Brugg
B
B
Gaspera
B D
BD
Besson
M J
MJ
Hipskind
R A
RA
Caboche
J
J
D021581:Active Transport, Cell Nucleus; D000818:Animals; D000906:Antibodies / Q000276:immunology; D001921:Brain / Q000378:metabolism*; D002454:Cell Differentiation; D002467:Cell Nucleus / Q000378:metabolism; D018387:Codon, Initiator; D004268:DNA-Binding Proteins / Q000235:genetics / Q000276:immunology / Q000502:physiology; D008297:Male; D020932:Nerve Growth Factor / Q000494:pharmacology*; D009474:Neurons / Q000166:cytology* / Q000378:metabolism; D016716:PC12 Cells; D010641:Phenotype; D020033:Protein Isoforms / Q000235:genetics / Q000276:immunology / Q000502:physiology; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000276:immunology / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D014157:Transcription Factors / Q000235:genetics / Q000276:immunology / Q000502:physiology; D015533:Transcriptional Activation; D050807:ets-Domain Protein Elk-1
D000906:Antibodies; D018387:Codon, Initiator; D004268:DNA-Binding Proteins; C494114:Elk1 protein, rat; D020033:Protein Isoforms; D011518:Proto-Oncogene Proteins; D014157:Transcription Factors; D050807:ets-Domain Protein Elk-1; D020932:Nerve Growth Factor