title: A proline-rich loop mediates specific functions of human sialidase NEU4 in SK-N-BE neuronal differentiation.
abstract: Human sialidase NEU4 long (N4L) is a membrane-associated enzyme that has been shown to be localized in the outer mitochondrial membrane. A role in different cellular processes has been suggested for this enzyme, such as apoptosis, neuronal differentiation and tumorigenesis. However, the molecular bases for these roles, not found in any of the other highly similar human sialidases, are not understood. We have found that a proline-rich sequence of 81 amino acids, unique to NEU4 sequence, contains potential Akt and Erk1 kinase motifs. Molecular modeling, based on the experimentally determined three-dimensional structure of cytosolic human NEU2, showed that the proline-rich sequence is accommodated in a loop, thus preserving the typical beta-barrel structure of sialidases. In order to investigate the role of this loop in neuronal differentiation, we obtained SK-N-BE neuroblastoma cells stably overexpressing either human wild-type N4L or a deletion mutant lacking the proline-rich loop. Our results demonstrate that the proline-rich region can also enhance cell proliferation and retinoic acid (RA)-induced neuronal differentiation and it is also involved in NEU4 interaction with Akt, as well as in substrate recognition, modifying directly or through the interaction with other protein(s) the enzyme specificity toward sialylated glycoprotein(s). On the whole, our results suggest that N4L could be a downstream component of the PI3K/Akt signaling pathway required for RA-induced differentiation of neuroblastoma SK-N-BE cells.
authors.affiliation: Department of Biotechnologies and Biosciences, University of Milan-Bicocca, 20126 Milan, Italy.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Bigi
authors.forename: Cristina
authors.initials: C
authors.lastname: Tringali
authors.forename: Matilde
authors.initials: M
authors.lastname: Forcella
authors.forename: Alessandra
authors.initials: A
authors.lastname: Mozzi
authors.forename: Bruno
authors.initials: B
authors.lastname: Venerando
authors.forename: Eugenio
authors.initials: E
authors.lastname: Monti
authors.forename: Paola
authors.initials: P
authors.lastname: Fusi
mesh_terms: D002454:Cell Differentiation / Q000187:drug effects; D049109:Cell Proliferation; D006801:Humans; D008958:Models, Molecular; D009439:Neuraminidase / Q000737:chemistry* / Q000378:metabolism*; D009447:Neuroblastoma / Q000378:metabolism / Q000473:pathology*; D011392:Proline / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D014212:Tretinoin; D011392:Proline; C491428:NEU4 protein, human; D009439:Neuraminidase
keywords: Akt signaling pathway; NEU4; neuronal differentiation; proline-rich region; sialidase