Abstract
BackgroundThe multifunctional β-galactoside-binding protein galectin-3 is found in many distinct subcellular compartments including the cell nucleus. Expression and distribution of galectin-3 between the cell nucleus and the cytosol changes during cell differentiation and cancer development. Nuclear functions of galectin-3 and how they contribute to tumorigenesis are not understood.MethodsIn order to identify nuclear galectin-3 interaction partners, we used affinity chromatography and co-immunoprecipitation. Spatial proximity in the nucleus was assessed by immunofluorescence and proximity ligation assay. We also investigated the function of galectin-3 on mRNA-export by fluorescence in situ hybridization and on mRNA-processing by RNA-sequencing.ResultsThe heterogeneous ribonucleoprotein particle component hnRNPA2B1 was identified as a novel galectin-3 binding protein that associates with the lectin in a lactose-dependent manner in the cell nucleus. Specific individual depletion of galectin-3 does not affect the mRNA distribution between cytoplasm and nucleus. A significant alteration of this distribution was observed after combined depletion of galectin-1 and −3. However, silencing of galectin-3 was sufficient to alter the splicing patterns of several genes.ConclusionsGalectin-3 and hnRNPA2B1 interact as members of the early splicing machinery. Galectin-3 and −1 have redundant functions in mRNA transport and at least in part in mRNA splicing. RNA-sequencing data points to a specific function of the hnRNPA2B1/galectin-3 interaction in the processing of transcripts coding for the nuclear oncoprotein SET.Electronic supplementary materialThe online version of this article (doi:10.1186/s12885-016-2546-0) contains supplementary material, which is available to authorized users.
Highlights
The multifunctional β-galactoside-binding protein galectin-3 is found in many distinct subcellular compartments including the cell nucleus
Nuclear extracts (NE) from RCC FG1 cells were immunoprecipitated with anti-galectin-3 antibodies, and the co-precipitated proteins were separated by SDS-PAGE followed by colloidal coomassie staining of the gels and analyzed by mass spectrometry
The column was loaded with NE from RCC FG1 cells, washed intensively and 150 mM lactose was added to release interaction partners that bind to the lactosefree form of galectin-3 [26]
Summary
The multifunctional β-galactoside-binding protein galectin-3 is found in many distinct subcellular compartments including the cell nucleus. The galectins are a family of small soluble sugar binding proteins characterized by a carbohydrate recognition domain (CRD). This CRD shows a conserved sequence motif and has a high affinity for β-galactosides [1]. Part of the lectin family is distributed in many different cell types (galectin-1, galectin-3, galectin-8, galectin-9), while galectin-2, galectin-4 and galectin-7 show a more restricted distribution According to their domain composition, galectins have been classified into three subgroups, the prototype, the tandem repeat and the chimeric type.
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