ELAV tumor antigen, Hel-N1, increases translation of neurofilament M mRNA and induces formation of neurites in human teratocarcinoma cells

Abstract

Human ELAV proteins are implicated in cell growth and differentiation via regulation of mRNA expression in the cytoplasm. In human embryonic teratocarcinoma (hNT2) cells transfected with the human neuronal ELAV-like protein, Hel-N1, neurites formed, yet cells were not terminally differentiated. Cells in which neurite formation was associated with Hel-N1 overexpression, also expressed increased levels of endogenous neurofilament M (NF-M) protein, which distributed along the neurites. However, steady-state levels of NF-M mRNA remained similar whether or not hNT2 cells were transfected with Hel-N1. These findings suggest that turnover of NF-M mRNA was not affected by Hel-N1 expression, despite the fact that Hel-N1 can bind to the 3 UTR of NF-M mRNA and was found directly associated with NF-M mRNA in transfected cells. Analysis of the association of NF-M mRNA with the translational apparatus in Hel-N1 transfectants showed nearly complete recruitment to heavy polysomes, indicating that Hel-N1 caused an increase in translational initiation. Our results suggest that the stability and/or translation of ARE-containing mRNAs can be regulated independently by the ELAV protein, Hel-N1, depending upon sequence elements in the 3 UTRs and upon the inherent turnover rates of the mRNAs that are bound to Hel-N1 in vivo.

Cytoplasmic localization is required for the mammalian ELAV‐like protein HuD to induce neuronal differentiation

“…2B), although whether HuD binds to the NF-H mRNA has yet to be determined. Thus, as was suggested recently, neurone-speci®c Hu proteins are likely to be involved in the translational up-regulation of speci®c AREcontaining mRNAs, which encode proteins that are critical for neuronal differentiation (Antic et al 1999). Moreover, our data also suggest the involvement of mRNA export from the nucleus to the cytoplasm in the function of neurone-speci®c Hu proteins.…”

“…7). Consistent with this, the repression of human HuB expression by HuB antisense RNA has been shown to result in the inhibition of retinoic acidinduced neuronal differentiation of hNT-2 cells (Antic et al 1999). In addition, it has recently been shown that the inhibition of HuD expression by the HuD antisense oligonucleotides severely inhibits NGF-induced neurite outgrowth in PC12 cells (Dobashi et al 1998;ArandaAbreu et al 1999).…”

“…1B), and because it has recently been reported that the stable transfection of human embryonal carcinoma hNT-2 cells with human HuB/Hel-N1 resulted in the induction of neurite-like processes in the absence of retinoic acid stimulation (Antic et al 1999). It is known that 10,20% of the population of P19 cells usually differentiate into neurones and exhibit neurites in response to retinoic acid (Jones-Villeneuve et al Fig.…”

“…As presumed from the difference in subcellular localization and in neurite-inducing activity, neurone-speci®c Hu proteins may have a physiological function(s) that is different from that of HuR, although we can not exclude the possibility that these proteins have a similar RNA stabilization function. In this respect, human HuB/Hel-N1 has been implicated in translational up-regulation but not in the stabilization of the NF-M mRNA: HuB binds to the ARE of the NF-M mRNA and then recruits it to the translational apparatus in the cytoplasm (Antic et al 1999). This is consistent with our ®nding that, even after retinoic acid treatment, NF-M protein was not produced in P19 cells in which the function of the endogenous neurone-speci®c Hu proteins had been inhibited by the dominant negative HuD mutants (Fig.…”

RNA-binding proteins in neurological diseases

“…Approximately 5%8% of human protein-coding genes contain AREs, suggesting the overall importance of Hu proteins in regulating mRNA stability [54,59]. In addition to mRNA stability, Hu proteins also regulate translation by acting as either enhancers or repressors of translation of their target genes, including neurofilament M, hypoxia inducible factor 1a and CD83 [56,60,61]. In the nucleus, Hu proteins serve as regulators of polyadenylation and alternative splicing [62].…”