Determination and characterization of novel nuclear binding partners of the neural cell adhesion molecule L1 and the HNK-1 glycan

Abstract

The neuronal cell adhesion molecule L1, also known as L1CAM, plays an important role in the development of the nervous system and the proper functioning of the adult nervous system. The L1 glycoprotein is mainly known and studied in its transmembrane form related to cell-cell interactions as neuron migration depends on the microenvironment of the neurons to guide their axons, form synapses, and regulate the synaptic structure. L1 interactions with glycan receptor proteins have been related to two main carbohydrate epitopes: LewisX and HNK-1. In the case of the mature transmembrane L1, proteolytic cleavages lead to the formation of soluble extracellular fragments, membrane-bound transmembrane fragments, and intracellular fragments. The soluble intracellular fragments in the cytoplasm can be transported to the nucleus or the mitochondria where interactions and pathways that are not yet fully understood take place. My work was based on finding possible protein-protein and glycan-receptor interactions inside of the nucleus. I used biotechnical techniques such as the production of recombinant proteins and cell culture from mouse cerebellar granule cells in addition to bioinformatics techniques such as sequence comparison and sequence conservation to try to find possible interactions happening inside of the nucleus. I found that the intracellular domain of L1 interacts with heterochromatin protein γ inside of the nucleus of cerebellar granule cells from mice and that the interaction might have a role in the regulation of genes involved in the DNA damage response. My work also revealed that receptors of the HNK-1 carbohydrate do not contain a common HNK-1 binding motif and that the HNK-1 receptors bind to the glycan via motifs unique for each receptor family.