Ependymin (EPN) is a goldfish brain
neurotrophic factor previously shown to function in a variety of cellular events related to long-term memory formation and neuronal regeneration.
CMX-8933, an 8-amino-acid synthetic
peptide fragment of EPN, was designed for aiding an investigation of the
biological properties of this
glycoprotein. We reported from previous studies that treatment of mouse
neuroblastoma (NB2a) cultures with
CMX-8933 promotes activation of
transcription factor AP-1, a characteristic previously associated with the following full-length
neurotrophic factors:
nerve growth factor, neurotropin-3, and
brain-derived neurotrophic factor. The CMX-8933-activated
AP-1 specifically bound an
AP-1 consensus probe and appeared to contain c-Jun and
c-Fos protein components in antibody supershift experiments. Because
AP-1 influences a variety of positive and negative cellular processes, determined in part by its exact
protein composition and mechanism of activation, we extended these initial
AP-1 observations in the current study to confirm the identity of the CMX-8933-activated c-Jun and c-Fos components.
CMX-8933 increases the enzymatic activity of
c-Jun N-terminal kinase (JNK), increases the phosphorylation of JNK and
c-Jun proteins, and increases the cellular titers of c-Jun and c-Fos mRNAs. Furthermore, the
AP-1 activated by
CMX-8933 is functional, insofar as it transactivates both synthetic and natural AP-1-dependent reporter plasmids. Inhibition studies indicate that activation of the 8933-induced
AP-1 occurs via the
mitogen-activated protein kinase pathway. These data are in agreement with the recently proposed model for the conversion of short- to long-term synaptic plasticity and memory, in which a JNK-activated
transcription factor AP-1, containing c-Jun and c-Fos components, functions at the top of a hierarchy of
transcription factors known to regulate long-term neural plasticity.