Table of Contents:
Galectin-3 is a member of the galectin family, which is characterized by its binding affinity to β-galactosides. Galectin-3 contains a chimeric structure composed of an N-terminal oligomerization domain and a C-terminal carbohydrate recognition domain. The protein is also characterized by its ubiquitious distribution in adult tissues. Depending on cell type and proliferation state, galectin-3 can accumulate in the extracellular milieu, in the cytoplasm or in the nucleus. This diffuse distribu-tion leads to a multiplicity of functions for galectin-3 which are until now not clarified. The subcellu-lar distribution is also diverse in various kinds of cancer cells. Renal clear cell carcinoma cells show an increased transport of the lectin into the nucleus. Based on these observations questions about putative nuclear interaction partners of galectin-3 and the function of these interactions arise.
In this work the heterogeneous ribonucleoprotein hnRNPA2B1 was identified as an interaction partner of galectin-3. Biochemical methods reveal that the interaction between hnRNPA2B1 and galectin-3 is RNA-independent but lactose-dependent. Moreover subcellular interaction of the two binding partners was confirmed by using the proximity ligation assay. Fluorescence microscopic analysis showed colocalizations in dot-like structures. Additional interaction partners of galectin-3, like the spliceosomal components U2AF65 or U1 70k, were found by affinity chromatography.
Further experiments showed an involvement of galectin-3 in mRNA processing and nuclear exit, since mRNA accumulated in the nucleus following a combined depletion of galectin-3 and galectin-1. RNA-sequencing then demonstrated that depletion of galectin-3 affected alternative splicing of several genes. These observations were supported by the identity of galectin-3 interaction part-ners identified in this work, which are all components of the alternative splicing machinery.