Effects of Global O-GlcNAcylation on Galectin Gene-expression Profiles in Human Cancer Cell Lines

Abstract

Background/Aim: The effects of O-linked β-Nacetyl-D-glucosamine (O-GlcNAc) transferase (OGT) and O-GlcNAcase (OGA) inhibitors on galectin gene expression profiles were examined in MCF7, HT-29, and HL-60 cancer cell lines. Materials and Methods: Cell cultures were treated for 24 h with OGA inhibitor thiamet G or OGT inhibitor 2-acetamido-1,3,4,6-tetra-O-acetyl-2-deoxy-5-thio-α-Dglucopyranose, and global O-GlcNAc levels and expression of galectin genes were determined using an immunodot blot assay and real-time quantitative polymerase chain reaction. Results: Two galectin genes, LGALS3 in MCF7 cells and LGALS12 in HL-60 cells, were up-regulated by O-GlcNAc, whereas other cell-specific galectins were unresponsive to changes in O-GlcNAc level. Of interest, basal levels of O-GlcNAc in resting HL-60 and HT-29 cells were significantly higher than those in cells differentiated into neutrophilic or enterocytic lineages, respectively. Conclusion: O-GlcNAcmediated signaling pathways may be involved in regulating the expression of only a limited number of galectin genes. Additional O-GlcNAc-dependent mechanisms may work at the protein level (galectin secretion and intracellular localization) and warrant further investigation.

The Emerging Role of Galectins and O-GlcNAc Homeostasis in Processes of Cellular Differentiation

“…As galectin-1 is a possible target of specific posttranslational glycosylation with O -linked N -acetyl- d -glucosamine called O -GlcNAcylation [ 124 ], the externalization of galectin-1 could be explained in the framework concept about O -GlcNAc-mediated redistribution of galectin-1 between intra- and extra-cellular space [ 32 ]. As such, progenitor cells keep a high level of global O -GlcNAcylation in comparison to differentiated cells [ 31 ], which might prevent the secretion of soluble proteins like galectins. Similar mechanisms may work in the case of mouse 3T3-L1 pre-adipocyte to adipocyte differentiation, which is readily accompanied by an increase in galectin-1 secretion [ 37 ].…”

“…It is interesting that galectin-1-induced differentiation of astrocytes was resistant to treatments with a protein kinase A inhibitor KT5720 and a tyrosine kinase inhibitor genistein while an inhibitor of protein tyrosine phosphatase orthovanadate almost completely inhibited the stellation of astrocytes indicating a key role of global phosphorylation of relevant intracellular proteins in this process. This aspect of regulation may provide an advantage condition for competitive O -GlcNAcylation of intracellular proteins that can support the undifferentiated state of different cell types [ 31 ].…”

“…Recombinant galectin-3 binding to CD34 + progenitor myeloid cells was very efficient and resulted in a dose-dependent stimulation (<4 µg/mL) or inhibition (>4 µg/mL) of the cell proliferation, which represented biphasic activity of this galectin [ 55 ]. The increase in the expression of galectin-3 coincided with decreasing levels of O -GlcNAc in high DMSO-treated HL-60 cells leading to neutrophilic differentiation [ 23 , 31 ]. Lowering O -GlcNAc with pharmacological inhibitors also induced differentiation of acute myeloid leukemia OCI-AML3 and HL-60 cells [ 148 ].…”

“…Emerging evidence suggests that one of the hallmarks of differentiated cells in comparison with progenitor cells is a decrease in glycosylation of intracellular proteins with N -acetyl- d -glucosamine, termed O -GlcNAcylation [ 27 , 28 , 29 , 30 , 31 ]. O -GlcNAcylation is known to change the functional activities of proteins and govern the trafficking and localization of proteins in cells.…”

“…O -GlcNAcylation is known to change the functional activities of proteins and govern the trafficking and localization of proteins in cells. Recently, we have proposed that the regulatory functions of galectins toward cell self-renewal and differentiation depend on the localization of galectins in cells which may be driven by O -GlcNAc signaling mechanisms [ 31 , 32 ]. In particular, we propose that high levels of O -GlcNAc promote the intracellular accumulation of galectins in stem cells while low levels of O -GlcNAc promote galectin secretion and cell differentiation.…”