Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P17931 (galectin-3)
 2,860 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Galectin-3 is a member of the beta-galactoside-binding protein family shown to be involved in tumor progression and metastasis. It has a unique primary structure consisting of three domains: a 12-amino acid leader sequence containing a casein kinase I serine phosphorylation site, which is preceded by a collagenase-sensitive Pro-Gly-rich motif, and a COOH-terminal half encompassing the carbohydrate-binding site. To study the functional role of the unusual leader sequence of galectin-3, a mutant cDNA that causes an 11-amino acid deletion in the NH2-terminal region was generated and expressed in galectin-3-null BT-549 human breast carcinoma cells. Deletion of the NH2 terminus resulted in abolition of the secretion of truncated galectin-3, loss of nuclear localization, and reduced carbohydrate-mediated functions compared with the wild-type protein. When green fluorescent protein was fused to the galectin-3 leader sequence and transiently transfected into BT-549 cells, the uniform cellular distribution of native green fluorescent protein was changed mainly to a nuclear pattern. To further investigate whether the functional changes observed in a galectin-3 with the 11 NH2-terminal amino acids deleted were due to loss of phosphorylation at Ser6, two point mutations were created at this serine: Ser6-->Ala and Ser6-->Glu. No obvious difference was observed in cellular localization between wild-type and Ser6-mutated transfectants. These results suggest a structural role for the NH2 terminus leader motif of galectin-3 in determining its cellular targeting and biological functions independent of phosphorylation.
 ...
PMID:The NH2 terminus of galectin-3 governs cellular compartmentalization and functions in cancer cells. 1062 18

The beta-galactoside-binding protein galectin-3 has pleiotropic biological functions and has been implicated in cell growth, differentiation, adhesion, RNA processing, apoptosis, and malignant transformation. Galectin-3 may be phosphorylated at N-terminal Ser(6), but the role of phosphorylation in determining interactions of this endogenous lectin with its ligands remains to be elucidated. We therefore studied the effect of phosphorylation on binding of galectin-3 to two of its reported ligands, laminin and purified colon cancer mucin. Human recombinant galectin-3 was phosphorylated in vitro by casein kinase I, and separated from the native species by isoelectric focusing for use in solid phase binding assays. Non-phosphorylated galectin-3 bound to laminin and asialomucin in a dose-dependent manner with half-maximal binding at 1.5 microg/ml. Phosphorylation reduced saturation binding to each ligand by >85%. Ligand binding could be fully restored by dephosphorylation with protein phosphatase type 1. Mutation of galectin-3 at Ser(6) (Ser to Glu) did not alter galectin ligand binding. Metabolic labeling or separation by isoelectric focusing confirmed the presence of phosphorylated galectin-3 species in vivo in the cytosol of human colon cancer cells from which ligand mucin was purified. Phosphorylation significantly reduces the interaction of galectin-3 with its ligands. The process by which phosphorylation modulates protein-carbohydrate interactions has important implications for understanding the biological functions of this protein, and may serve as an "on/off" switch for its sugar binding capabilities.
 ...
PMID:Phosphorylation of the beta-galactoside-binding protein galectin-3 modulates binding to its ligands. 1096 87

Galectin-3, a beta-galactoside-binding protein, is implicated in cell growth, adhesion, differentiation, and tumor progression by interactions with its ligands. Recent studies have revealed that galectin-3 suppresses apoptosis and anoikis that contribute to cell survival during metastatic cascades. Previously, it has been shown that human galectin-3 undergoes post-translational signaling modification of Ser(6) phosphorylation that acts as an "on/off" switch for its sugar-binding capability. We questioned whether galectin-3 phosphorylation is required for its anti-apoptotic function. Serine to alanine (S6A) and serine to glutamic acid (S6E) mutations were produced at the casein kinase I phosphorylation site in galectin-3. The cDNAs were transfected into a breast carcinoma cell line BT-549 that innately expresses no galectin-3. Metabolic labeling revealed that only wild type galectin-3 undergoes phosphorylation in vivo. Expression of Ser(6) mutants of galectin-3 failed to protect cells from cisplatin-induced cell death and poly(ADP-ribose) polymerase from degradation when compared with wild type galectin-3. The non-phosphorylated galectin-3 mutants failed to protect cells from anoikis with G(1) arrest when cells were cultured in suspension. In response to a loss of cell-substrate interactions, only cells expressing wild type galectin-3 down-regulated cyclin A expression and up-regulated cyclin D(1) and cyclin-dependent kinase inhibitors, i.e. p21(WAF1/CIP1) and p27(KIP1) expression levels. These results demonstrate that galectin-3 phosphorylation regulates its anti-apoptotic signaling activity.
 ...
PMID:Galectin-3 phosphorylation is required for its anti-apoptotic function and cell cycle arrest. 1172 77

To study the signaling pathway involved in the regulation of galectin-3 expression we used phorbol ester to stimulate macrophage differentiation of THP-1 cells. Treatment with phorbol 12-myristate 13-acetate (PMA) increased significantly the level of expression of galectin-3 in THP-1 cells. PMA-induced galectin-3 overexpression was blocked by: protein kinase C inhibitors staurosporine, calphostin C, and apigenin; tyrosine-specific protein kinase inhibitors genistein and tyrphostin A25; PD 98059, a selective inhibitor of mitogen-activated protein kinase (MAPK) kinase 1 (MEK1 or MKK1); and SB 203580, a specific inhibitor of p38 MAPK. Galectin-3 up-regulation was not affected by exposure to two inhibitors of cAMP-dependent protein kinase (PKA), H-89 and KT5720. Co-transfection of pPG3.5, a plasmid vector containing the rabbit galectin-3 promoter and the constructs pMCL-MKK1 N3 or pRC-RSV-MKK3Glu that constitutively express MKK1 and MKK3, raised the activity of galectin-3 promoter by 185% and 110%, respectively. Co-transfection with a Ha-Ras expression vector stimulated galectin-3 promoter activity approximately 10-fold. Expression of c-Jun or v-Jun raised the level of galectin-3 promoter activity more the three- and fourfold, respectively. Co-transfection of c-Jun and pPG3.5 5'-upstream deletion mutants resulted in a reduction of the galectin-3 promoter activity by 50% to 80%. Transfection of c-Jun, v-Jun or Ha-Ras increased significantly galectin-3 protein in THP-1 cells. These findings indicated that Ras/MEKK1/MKK1-dependent/AP-1 signal transduction pathway plays an important role in the expression of galectin-3 in PMA-stimulated macrophages. We further investigated the effect of modified lipoproteins on galectin-3 expression in macrophages. Murine resident peritoneal macrophages loaded with acetylated low-density lipoprotein (AcLDL) or oxidized LDL (OxLDL) showed increased galectin-3 protein and mRNA. These results showed that treatment of macrophages with PMA or modified lipoproteins results in galectin-3 overexpression. These findings may explain the enhanced expression of galectin-3 in atherosclerotic foam cells and suggest that Ras/MAPK signal transduction pathway is involved in controlling this gene.
 ...
PMID:Galectin-3 expression in macrophages is signaled by Ras/MAP kinase pathway and up-regulated by modified lipoproteins. 1278 25

Galectin-3 (Gal-3), a member of the beta-galactoside binding protein family containing the NWGR antideath motif of the Bcl-2 protein family, is involved in various aspects of cancer progression. Previously, it has been shown that the antiapoptotic activity of Gal-3 is regulated by the phosphorylation at Ser(6) by casein kinase 1 (CK1). Here we questioned how phosphorylation at Ser(6) regulates Gal-3 function. We have generated serine-to-alanine (S6A) and serine-to-glutamic acid (S6E) Gal-3 mutants and transfected them into the BT-549 human breast carcinoma cell line, which does not express Gal-3. BT-549 cell clones expressing wild-type (wt) and mutant Gal-3 were exposed to chemotherapeutic anticancer drugs. In response to the apoptotic insults, phosphorylated wt Gal-3 was exported from the nucleus to the cytoplasm and protected the BT-549 cells from drug-induced apoptosis while nonphosphorylated mutant Gal-3 neither was exported from the nucleus nor protected BT-549 cells from drug-induced apoptosis. Furthermore, leptomycin B, a nuclear export inhibitor, increased the cisplatin-induced apoptosis of Gal-3 expressing BT-549 cells. These results suggest that Ser(6) phosphoryaltion acts as a molecular switch for its cellular translocation from the nucleus to the cytoplasm and, as a result, regulates the antiapoptotic activity of Gal-3.
 ...
PMID:Nuclear export of phosphorylated galectin-3 regulates its antiapoptotic activity in response to chemotherapeutic drugs. 1512 58

Depending on the cellular context, Ras can activate characteristic effectors by mechanisms still poorly understood. Promotion by galectin-1 of Ras activation of Raf-1 but not of phosphoinositide 3-kinase (PI3-K) is one such mechanism. In this report, we describe a mechanism controlling selectivity of K-Ras4B (K-Ras), the most important Ras oncoprotein. We show that galectin-3 acts as a selective binding partner of activated K-Ras. Galectin-3 co-immunoprecipitated significantly better with K-Ras-GTP than with K-Ras-GDP, H-Ras, or N-Ras and colocalized with green fluorescent protein-K-Ras(G12V), not with green fluorescent protein-H-Ras(G12V), in the cell membrane. Co-transfectants of K-Ras/galectin-3, but not of H-Ras/galectin-3, exhibited enhanced and prolonged epidermal growth factor-stimulated increases in Ras-GTP, Raf-1 activity, and PI3-K activity. Extracellular signal-regulated kinase (ERK) activity, however, was attenuated in K-Ras/galectin-3 and in K-Ras(G12V)/galectin-3 co-transfectants. Galectin-3 antisense RNA inhibited the epidermal growth factor-stimulated increase in K-Ras-GTP but enhanced ERK activation and augmented K-Ras(G12V) transformation activity. Thus, unlike galectin-1, which prolongs Ras activation of ERK and inhibits PI3-K, K-Ras-GTP/galectin-3 interactions promote, in addition to PI3-K and Raf-1 activation, a third inhibitory signal that attenuates active ERK. These experiments established a novel and specific mechanism controlling the duration and selectivity of signals of active K-Ras, which is extremely important in many human tumors.
 ...
PMID:Galectin-3 augments K-Ras activation and triggers a Ras signal that attenuates ERK but not phosphoinositide 3-kinase activity. 1520 67

Galectin-3, a factor involved in the splicing of pre-mRNA, shuttles between the nucleus and the cytoplasm. Previous studies have shown that incubation of fibroblasts with leptomycin B resulted in the accumulation of galectin-3 in the nucleus, suggesting that the export of galectin-3 from the nucleus may be mediated by the CRM1 receptor. A candidate nuclear export signal fitting the consensus sequence recognized by CRM1 can be found between residues 240 and 255 of the murine galectin-3 sequence. This sequence was engineered into the pRev(1.4) reporter system, in which candidate sequences can be tested for nuclear export activity in terms of counteracting the nuclear localization signal present in the Rev(1.4) protein. Rev(1.4)-galectin-3(240-255) exhibited nuclear export activity that was sensitive to inhibition by leptomycin B. Site-directed mutagenesis of Leu247 and Ile249 in the galectin-3 nuclear export signal decreased nuclear export activity, consistent with the notion that these two positions correspond to the critical residues identified in the nuclear export signal of the cAMP-dependent protein kinase inhibitor. The nuclear export signal activity was also analyzed in the context of a full-length galectin-3 fusion protein; galectin-3(1-263; L247A) showed more nuclear localization than wild-type, implicating Leu247 as critical to the function of the nuclear export signal. These results indicate that residues 240-255 of the galectin-3 polypeptide contain a leucine-rich nuclear export signal that overlaps with the region (residues 252-258) identified as important for nuclear localization.
 ...
PMID:Transport of galectin-3 between the nucleus and cytoplasm. II. Identification of the signal for nuclear export. 1647 34

Crosslinking of CD66 antigens on the neutrophil surface induces functional responses such as aggregation of the cells and protein kinase activity. Although CD66b (carcinoembryonic antigen-related cell adhesion molecule-8) has been reported as a candidate receptor for galectin-3, its natural ligand is still unknown and therefore its physiologic function remains to be elucidated. We were able to detect the storage of intracellular interleukin-8 (IL-8) in unstimulated human neutrophils and its secretion in response to the crosslinking of CD66b. In contrast to lipopolysaccharide (LPS), the stimulation via CD66b does not induce a de novo synthesis of cytokines but rather a directed release of the preformed IL-8. This process may represent a very low state of activation for the neutrophil. As it extravasates into the tissue, the neutrophil might interact with the extracellular matrix via CD66b. In response to this interaction, polymorphonuclear neutrophils (PMN) release their preformed IL-8, establishing a chemotactic track for other cells to follow. By contact with pathogenic stimuli such as LPS in the infected tissue, the neutrophil then becomes fully activated and is able to synthesize cytokines de novo to release greater quantities.
 ...
PMID:Crosslinking of CD66B on peripheral blood neutrophils mediates the release of interleukin-8 from intracellular storage. 1700 97

Galectin-3 has a unique modular design. Its short N-terminal stretch can be phosphorylated, relevant for nuclear export and anti-anoikis/apoptosis activity. Enzymatic modification by casein kinase 1 at constant ATP concentration yielded mg quantities of mono- and diphosphorylated derivatives at Ser5/Ser11 in a 2:1 ratio. Their carbohydrate-inhibitable binding to asialofetuin, cell surfaces of three tumor lines, rabbit erythrocytes leading to haemagglutination and cytoplasmic sites in fixed tissue sections was not markedly altered relative to phosphate-free galectin-3. Spectroscopically, phosphorylation induced alterations in the far UV CD, indicative of an increase in ordered structure. This is accompanied by changes in the environment of aromatic amino acids signified by shifts in the near UV CD.
 ...
PMID:Phosphorylated human galectin-3: facile large-scale preparation of active lectin and detection of structural changes by CD spectroscopy. 1830 43

The organization of Ras proteins into plasma membrane nanoclusters is essential for high-fidelity signal transmission, but whether the nanoscale environments of different Ras nanoclusters regulate effector interactions is unknown. We show using high-resolution spatial mapping that Raf-1 is recruited to and retained in K-Ras-GTP nanoclusters. In contrast, Raf-1 recruited to the plasma membrane by H-Ras is not retained in H-Ras-GTP nanoclusters. Similarly, upon epidermal growth factor receptor activation, Raf-1 is preferentially recruited to K-Ras-GTP and not H-Ras-GTP nanoclusters. The formation of K-Ras-GTP nanoclusters is inhibited by phosphorylation of S181 in the C-terminal polybasic domain or enhanced by blocking S181 phosphorylation, with a concomitant reduction or increase in Raf-1 plasma membrane recruitment, respectively. Phosphorylation of S181 does not, however, regulate in vivo interactions with the nanocluster scaffold galectin-3 (Gal3), indicating separate roles for the polybasic domain and Gal3 in driving K-Ras nanocluster formation. Together, these data illustrate that Ras nanocluster composition regulates effector recruitment and highlight the importance of lipid/protein nanoscale environments to the activation of signaling cascades.
 ...
PMID:Electrostatic interactions positively regulate K-Ras nanocluster formation and function. 1845 61


1 2 3 Next >>