Dual REST‐dependence of L1CAM: from gene expression to alternative splicing governed by Nova2 in neural cells

Abstract

J. Neurochem (2012) 120, 699–709. Abstract L1 cell adhesion molecule (L1CAM), an adhesion/signaling protein encoded by a gene target of the transcription repressor RE‐1‐Silencing Transcription factor (REST), is expressed in two alternatively spliced isoforms. The full‐length isoform, typical of low‐REST neural cells, plays key roles in survival/migration, outgrowth/fasciculation/regeneration of axons, synaptic plasticity; the isoform missing two mini‐exons, abundant in a few high‐REST non‐neural cells, maintains some effect on migration and proliferation. To investigate whether and how L1CAM alternative splicing depends on REST we used neural cell models expressing low or high levels of REST (PC12, SH‐SY5Y, differentiated NT2/D1 and primary neurons transduced or not with REST). The short isoform was found to rise when the low‐REST levels of neural cells were experimentally increased, while the full‐length isoform increased in high‐REST cells when the repressor tone was attenuated. These results were due to Nova2, a neural cell‐specific splicing factor shown here to be repressed by REST. REST control of L1CAM occurs therefore by two mechanisms, transcription and alternative splicing. The splicing mechanism, affecting not only L1CAM but all Nova2 targets (∼7% of brain‐specific splicing, including the mRNAs of other adhesion and synaptic proteins) is expected to be critical during development and important also for the structure and function of mature neural cells.

Neuronal SH-SY5Y cells use the C-dystrophin promoter coupled with exon 78 skipping and display multiple patterns of alternative splicing including two intronic insertion events

“…However, there have been few studies on splicing in the cancer-derived SH-SY5Y cells (Lannaccone et al 2013;Mikulak et al 2012;Saint Martin et al 2012). In this study, we revealed seven patterns of alternative splicing in the C-transcript by examining the entire length of dystrophin transcript (Fig.…”

L1CAM: Cell adhesion and more

“…The L1CAM protein exists in two splicing isoforms. In neuronal and cancer cells the splicing factor Nova2 (neurooncological ventral antigen 2) provides for the expression of full-length L1CAM [60]. In all other cells Nova2 expression is repressed by high levels of REST and due to the expression of the splicing factor Nova2 two exons are removed from L1CAM mRNA, namely E2 from the N-terminal and E27 from the C-terminal domains.…”

Plasma REST: a novel candidate biomarker of Alzheimer’s disease is modified by psychological intervention in an at-risk population

“…While this protocol has been used routinely to successfully isolate exosomes, in this context it may prove problematic, given L1-CAM gene expression and splicing is known to be regulated by REST. 5 Therefore, it is unclear how perturbed REST expression may alter the levels and forms of L1-CAM expressed on neuronal exosomes. To circumvent this, we elected to measure total peripheral REST in both membrane-bound vesicles and free forms simultaneously in patient plasma, particularly as the latter has yet to be fully explored.…”