Galectin-3 Mediates Cross-Talk between K-Ras and Let-7c Tumor Suppressor microRNA

Abstract

BackgroundGalectin-3 (Gal-3) and active (GTP-bound) K-Ras contribute to the malignant phenotype of many human tumors by increasing the rate of cell proliferation, survival, and migration. These Gal-3-mediated effects result from a selective binding to K-Ras.GTP, causing increased nanoclustering in the cell membrane and leading to robust Ras signaling. Regulation of the interactions between Gal-3 and active K-Ras is not fully understood.Methods and FindingsTo gain a better understanding of what regulates the critical interactions between these two proteins, we examined the role of Gal-3 in the regulation of K-Ras by using Gal-3-knockout mouse embryonic-fibroblasts (Gal-3-/- MEFs) and/or Gal-3/Gal-1 double-knockout MEFs. We found that knockout of Gal-3 induced strong downregulation (∼60%) of K-Ras and K-Ras.GTP. The downregulation was somewhat more marked in the double-knockout MEFs, in which we also detected robust inhibition(∼50%) of ERK and Akt activation. These additional effects are probably attributable to inhibition of the weak interactions of K-Ras.GTP with Gal-1. Re-expression of Gal-3 reversed the phenotype of the Gal-3-/- MEFs and dramatically reduced the disappearance of K-Ras in the presence of cycloheximide to the levels seen in wild-type MEFs. Furthermore, phosphorylation of Gal-3 by casein kinase-1 (CK-1) induced translocation of Gal-3 from the nucleus to the cytoplasm and the plasma membrane, leading to K-Ras stabilization accompanied by downregulation of the tumor suppressor miRNA let-7c, known to negatively control K-Ras transcription.ConclusionsOur results suggest a novel cross-talk between Gal-3-mediated downregulation of let 7c microRNA (which in turn negatively regulates K-Ras transcription) and elucidates the association among Gal-3 let-7c and K-Ras transcription/translation, cellular compartmentalization and activity.

The Efficacy of Raf Kinase Recruitment to the GTPase H-ras Depends on H-ras Membrane Conformer-specific Nanoclustering

“…They were grown to a confluency of 80% (8 ϫ 10 7 cells/ml) and subcultured every 2-3 days. Gal-1 Ϫ/Ϫ MEFs were a kind gift from the laboratory of Prof. Yoel Kloog (35). For Western blotting analysis and fluorescence recovery after photobleaching (FRAP) experiments, 200,000 cells were seeded in a 6-well plate (Cellstar catalog no.…”

Galectin 3 as a guardian of the tumor microenvironment

“…Perhaps the best example of Galectin 3 regulation of signal transduction involves RAS (86)(87)(88)(89)(90)(91)(92). (86,89).…”

“…In our studies , we have observed leukemia cells can also induce Galectin 3 in MSC suggesting that the induction of Galectin 3 between cells can be mutual (Ruvolo et al unpublished).Galectin 3 Intracellular functionsGalectin 3 as an anti-apoptotic moleculeGalectin 3 can function as an anti-apoptotic molecule(19,(27)(28)(29)(30)(77)(78)(79)(80)(81)(82)(83). Galectin 3 influences many diverse signal transduction cascades and pro-survival processes that include major oncogenes such as RAS, BCL2, and MYC(19,(27)(28)(29)(30)(77)(78)(79)(80)(81)(82)(83)(84)(85)(86)(87)(88)(89)(90)(91)(92). The tumor suppressor function of anti-apoptotic function is important in some cancer cells(85,(93)(94)(95)(96).…”

A Unique Galectin Signature in Human Prostate Cancer Progression Suggests Galectin-1 as a Key Target for Treatment of Advanced Disease

“…Extracellularly, galectins interact with cell surface glycoconjugates and trigger cellular signaling to control migration, immunity, and angiogenesis. Intracellularly, galectins can control tumor transformation, proliferation, and survival (7,8).…”