Nuclear fragments of the neural cell adhesion molecule NCAM with or without polysialic acid differentially regulate gene expression

Nina Westphal,Ralf Kleene,Gabriele Loers,Thomas Theis,Melitta Schachner

doi:10.1038/s41598-017-14056-x

Abstract

The neural cell adhesion molecule (NCAM) is the major carrier of polysialic acid (PSA) which modulates NCAM functions of neural cells at the cell surface. In previous studies, we have shown that stimulation of cultured neurons with surrogate NCAM ligands leads to the generation and nuclear import of PSA-lacking and -carrying NCAM fragments. Here, we show that the nuclear import of the PSA-carrying NCAM fragment is mediated by positive cofactor 4 and cofilin, which we identified as novel PSA-binding proteins. In the nucleus, the PSA-carrying NCAM fragment interacts via PSA with PC4 and cofilin, which are involved in RNA polymerase II-dependent transcription. Microarray analysis revealed that the nuclear PSA-carrying and -lacking NCAM fragments affect expression of different genes. By qPCR and immunoblot analysis we verified that the nuclear PSA-carrying NCAM fragment increases mRNA and protein expression of nuclear receptor subfamily 2 group F member 6, whereas the PSA-lacking NCAM fragment increases mRNA and protein expression of low density lipoprotein receptor-related protein 2 and α-synuclein. Differential gene expression evoked by nuclear NCAM fragments without and with PSA indicates that PSA-carrying and -lacking NCAM play different functional roles in the nervous system.

Highlights

neural cell adhesion molecule (NCAM) plays important roles in neural cell migration, neurite outgrowth and fasciculation, synaptogenesis and synaptic plasticity, and it is associated with certain forms of emotional behaviour[1,2,3,4]
Since nuclear cofilin plays a role in the elongation phase of RNA polymerase II-dependent transcription[30] and since positive cofactor 4 (PC4) activates RNA polymerase II-dependent transcription[37], it is conceivable that the interactions of polysialic acid (PSA) with PC4 and cofilin in the nucleus stimulate RNA polymerase II-mediated transcription
Since stimulation of cerebellar neurons with function-triggering NCAM antibody enhances the levels of acetylated histone H3 at position Lys[9], being associated with enhanced transcription levels, we proposed that the generation and nuclear import of PSA-carrying and PSA-lacking NCAM fragments regulate transcription in distinct manners

Summary

Introduction

NCAM plays important roles in neural cell migration, neurite outgrowth and fasciculation, synaptogenesis and synaptic plasticity, and it is associated with certain forms of emotional behaviour[1,2,3,4]. We have found that PSA-lacking and -carrying proteolytic NCAM fragments comprising the intracellular and transmembrane domains as well as part of the extracellular domain enter the cell nucleus after their generation at the plasma membrane[25,26]. Calmodulin mediates the nuclear import of the PSA-lacking fragment and associates with this NCAM fragment in the nucleus[25]. We provide evidence that PC4 and cofilin mediate the import of the PSA-carrying NCAM fragment and interact with the PSA-carrying NCAM www.nature.com/scientificreports/. PC431,32, a non-histone component of chromatin, plays important roles in chromatin organization, DNA replication, DNA repair, and activation of RNA polymerase II-dependent transcription[31,32,33,34,35,36,37].

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