Inhibition of Cell-Free Splicing by Saccharides That Bind Galectins and SR Proteins

Galectin-3 does not interact with RNA directly

Galectin-3, well characterized as a glycan binding protein, has been identified as a putative RNA binding protein, possibly through participation in pre-mRNA maturation through interactions with splicosomes. Given recent developments with cell surface RNA biology, the putative dual-function nature of galectin-3 evokes a possible non-classical connection between glycobiology and RNA biology. However, with limited functional evidence of a direct RNA interaction, many molecular-level observations rely on affinity reagents and lack appropriate genetic controls. Thus, evidence of a direct interaction remains elusive. We demonstrate that antibodies raised to endogenous human galectin-3 can isolate RNA-protein crosslinks, but this activity remains insensitive to LGALS3 knock-out. Proteomic characterization of anti-galectin-3 IPs revealed enrichment of galectin-3, but high abundance of hnRNPA2B1, an abundant, well-characterized RNA-binding protein with weak homology to the N-terminal domain of galectin-3, in the isolate. Genetic ablation of HNRNPA2B1, but not LGALS3, eliminates the ability of the anti-galectin-3 antibodies to isolate RNA-protein crosslinks, implying either an indirect interaction or cross-reactivity. To address this, we introduced an epitope tag to the endogenous C-terminal locus of LGALS3. Isolation of the tagged galectin-3 failed to reveal any RNA-protein crosslinks. This result suggests that the galectin-3 does not directly interact with RNA and may be misidentified as an RNA-binding protein, at least in HeLa where the putative RNA associations were first identified. We encourage further investigation of this phenomenon employ gene deletions and, when possible, endogenous epitope tags to achieve the specificity required to evaluate potential interactions.

Thiodigalactoside shows antitumour activity by beta-galactoside-binding protein and regulatory T cells inhibition in oral squamous cell carcinoma

OBJECTIVE

Thiodigalactoside (TDG), a synthetic inhibitor of β-galactoside-binding protein (β-GBP) suppresses tumour growth by inhibiting multiple cancer enhancing activities of β-GBP. Hence, we attempted to understand whether disruption of β-GBP functions and indirect inhibition of Treg cells by TDG affect the growth and establishment of oral cancer cells.

METHOD

The growth, morphology, cell cycle regulation, apoptosis induction and angiogenesis of oral cancer cell lines (SCC-4, SCC-9, SCC-25) via MACS-purified Treg cells were performed by MTT, propidium iodide (PI) staining, annexin-V-binding assay and ELISA respectively.

RESULTS

Treatment with β-GBP showed growth-promoting effects on Tregs and oral cancer cells. However, the treatment with its inhibitor TDG resulted in inhibition of Treg subsets and also decreased the frequency of IL10(+) and IL35(+) Tregs indicating its immunomodulatory effects. Additionally, TDG treatment significantly (P < 0.001) inhibited the growth of OSCC cells with a concomitant induction of apoptosis, cell cycle arrest and anti-angiogenesis.

CONCLUSION

It appears that TDG concurrently prevents many tumour-promoting effects of β-GBP in oral cancer cells possibly by Treg inhibition. This offers a preclinical proof of the concept that therapeutic targeting of β-GBP can overcome Treg -mediated tumour promotion and immunosuppression in oral cancer patients.

Identification of Lectins from Metastatic Cancer Cells through Magnetic Glyconanoparticles

Cancer cells can have characteristic carbohydrate binding properties. Previously, it was shown that a highly metastatic melanoma cell line B16F10 bound to galacto-side-functionalized nanoparticles much stronger than the corresponding less metastatic B16F1 cells. To better understand the carbohydrate binding properties of cancer cells, herein, we report the isolation and characterization of endogenous galactose binding proteins from B16F10 cells using magnetic glyconanoparticles. The galactose-coated magnetic glyconanoparticles could bind with lectins present in the cells and be isolated through magnet-mediated separation. Through Western blot and mass spectrometry, the arginine/serine rich splicing factor Sfrs1 was identified as a galactose-selective endogenous lectin, overexpressed in B16F10 cells, compared with B16F1 cells. In addition, galactin-3 was found in higher amounts in B16F10 cells. Finally, the glyconanoparticles exhibited a superior efficiency in lectin isolation, from both protein mixtures and live cells, than the corresponding more traditional microparticles functionalized with carbohydrates. Thus, the magnetic glyconanoparticles present a useful tool for discovery of endogenous lectins, as well as binding partners of lectins, without prior knowledge of protein identities.

The lectin-binding pattern of nucleolin and its interaction with endogenous galectin-3

Unlike nuclear nucleolin, surface-expressed and cytoplasmic nucleolin exhibit Tn antigen. Here, we show localization-dependent differences in the glycosylation and proteolysis patterns of nucleolin. Our results provide evidence for different paths of nucleolin proteolysis in the nucleus, in the cytoplasm, and on the cell surface. We found that full-length nucleolin and some proteolytic fragments coexist within live cells and are not solely the result of the preparation procedure. Extranuclear nucleolin undergoes N- and O-glycosylation, and unlike cytoplasmic nucleolin, membrane-associated nucleolin is not fucosylated. Here, we show for the first time that nucleolin and endogenous galectin-3 exist in the same complexes in the nucleolus, the cytoplasm, and on the cell surface of melanoma cells. Assessments of the interaction of nucleolin with galectin-3 revealed nucleolar co-localization in interphase, suggesting that galectin-3 may be involved in DNA organization and ribosome biogenesis.