Post-transcriptional regulation of neuro-oncological ventral antigen 1 by the neuronal RNA-binding proteins ELAV

Alternative splicing of pre-mRNAs plays an important role in
generating biological and functional diversity. Neuro-oncological
ventral antigen 1 (Nova1) is a neuron-specific splicing factor
that controls the alternative processing of a wide array of
mRNAs important for synaptic activity. It is essential for the
proper development of the mammalian motor system and for
the survival of motoneurons. Because Nova1 gene contains
putative regulatory AU-rich elements (ARE) in its highly conserved
3-untranslated region, we investigated whether its
expression is regulated by post-transcriptional mechanisms
mediated by ARE-binding proteins. Among these, the neuronal
ELAV (nELAV) factors are interesting candidates, because their
RNA binding activity is necessary for neuronal differentiation
and maintenance. By analysis of ribonucleoprotein complexes
in vivo and in vitro we demonstrated that the Nova1 mRNA is a
novel target of the nELAV proteins. We defined the nELAV
binding site by functional experiments with luciferase reporter
gene and Nova1 3-untranslated region deletion sequences.
Gene silencing and overexpression of the nELAV member HuD
in motoneuronal NSC34 cells indicate that Nova1mRNAstability
and translation are positively and strongly controlled by the
nELAVproteins. In addition,nELAVphosphorylation by aPKCdependent
pathway induces the recruitment of Nova1mRNAto
polysomes. Noteworthy, we found that nELAV proteins are also
able to modulate Nova1 splicing activity on its target genes. Our
data indicate nELAV proteins as the first factors affecting the
expression and activity of the neuronal splicing regulator Nova1
and, consequently, as major candidates for the physiological
modulation of Nova1-dependent processing of pre-mRNAs in
neurons.