Galectin-9 was first isolated from mouse embryonic kidney in 1997 as a 36 kDa beta-galactoside lectin protein. [3] Human galectin-9 is encoded by the LGALS9 gene. [4] [5]
Galectin-9 was first isolated from mouse embryonic kidney in 1997 as a 36 kDa beta-galactoside lectin protein. [3] Human galectin-9 is encoded by the LGALS9 gene. [4] [5]
The protein has N- and C- terminal carbohydrate-binding domains connected by a link peptide. Multiple alternatively spliced transcript variants have been found for this gene. [5]
Galectin-9 is one of the most studied ligands for HAVCR2 (TIM-3) and is expressed on various tumor cells. However, it can also interact with other proteins (CLEC7A, [6] CD137, [7] CD40 [8] ). For example, an interaction with CD40 on T-cells inhibits their proliferation and induces cell death. [8]
Galectin-9 also has important cytoplasmic, intracellular functions and controls AMPK [9] [10] in response to lysosomal damage that can occur upon exposure to endogenous and exogenous membrane damaging agents such as crystalline silica, cholesterol crystals, microbial toxins, proteopathic aggregates such as tau fibrils and amyloids, and signaling pathways inducing lysosomal permeabilization such as those initiated by TRAIL. [11] Mild lysosomal damage, such as that caused by the anti-diabetes drug metformin [10] may contribute to the therapeutic action of metformin by activating AMPK. The mechanism of how Galectin-9 activates AMPK involves recognition of exposed lysosomal lumenal glycoproteins such as LAMP1, LAMP2, SCRAB2, TMEM192, etc., repulsion of deubiquitinating enzyme USP9X, increased K63 ubiquitination of TAK1 (MAP3K7) kinase, which in turn phopshorylates AMPK and activates it. [10] This signaling cascade directly links Galectin-9 intracellular function with ubiqutin systems. Galectin-9, through its regulation of AMPK, a kinase that negatively regulates mTOR, cooperates with Galectin-8-based effects to inactivate mTOR downstream of the lysosomal damaging agents and conditions. [9] [10]
The expression of galectin-9 has been detected on various hematological malignancies, such as CLL, [12] MDS, [13] Hodgkin and Non-Hodgkin lymphomas, [14] AML [15] or solid tumors, such as lung cancer, [16] breast cancer, [17] and hepatocellular carcinoma. [18]
HAVCR2/ galectin-9 interaction attenuated T-cell expansion and effectors function in tumor microenvironment and chronic infections. [19] [15] Moreover, galectin-9 contributed to tumorigenesis by tumor cell transformation, cell-cycle regulation, angiogenesis, and cell adhesion. [20] The correlative studies analyzing the expression of galectin-9 and malignant clinical features showed controversial results. This can be explained as that galectin-9 can promote tumor immune escape as well as inhibit metastasis by promoting endothelial adhesion. [18] Therefore many factors such as tumor type, stage, and the involvement of different galectins should be take into consideration when correlating the expression level and the malignancy.
Galectin-9, through its cytoplasmic action in control of AMPK, [9] [10] may affect various health conditions impacted by AMPK, including metabolism, obesity, diabetes, cancer, immune responses, and may be a part of the mechanism of action of the widely-prescribed anti-diabetis drug metformin. [10]
Natural killer cells, also known as NK cells or large granular lymphocytes (LGL), are a type of cytotoxic lymphocyte critical to the innate immune system. They belong to the rapidly expanding family of known innate lymphoid cells (ILC) and represent 5–20% of all circulating lymphocytes in humans. The role of NK cells is analogous to that of cytotoxic T cells in the vertebrate adaptive immune response. NK cells provide rapid responses to virus-infected cell and other intracellular pathogens acting at around 3 days after infection, and respond to tumor formation. Most immune cells detect the antigen presented on major histocompatibility complex (MHC) on infected cell surfaces, but NK cells can recognize and kill stressed cells in the absence of antibodies and MHC, allowing for a much faster immune reaction. They were named "natural killers" because of the notion that they do not require activation to kill cells that are missing "self" markers of MHC class I. This role is especially important because harmful cells that are missing MHC I markers cannot be detected and destroyed by other immune cells, such as T lymphocyte cells.
5' AMP-activated protein kinase or AMPK or 5' adenosine monophosphate-activated protein kinase is an enzyme that plays a role in cellular energy homeostasis, largely to activate glucose and fatty acid uptake and oxidation when cellular energy is low. It belongs to a highly conserved eukaryotic protein family and its orthologues are SNF1 in yeast, and SnRK1 in plants. It consists of three proteins (subunits) that together make a functional enzyme, conserved from yeast to humans. It is expressed in a number of tissues, including the liver, brain, and skeletal muscle. In response to binding AMP and ADP, the net effect of AMPK activation is stimulation of hepatic fatty acid oxidation, ketogenesis, stimulation of skeletal muscle fatty acid oxidation and glucose uptake, inhibition of cholesterol synthesis, lipogenesis, and triglyceride synthesis, inhibition of adipocyte lipogenesis, inhibition of adipocyte lipolysis, and modulation of insulin secretion by pancreatic β-cells.
Autophagy is the natural, conserved degradation of the cell that removes unnecessary or dysfunctional components through a lysosome-dependent regulated mechanism. It allows the orderly degradation and recycling of cellular components. Although initially characterized as a primordial degradation pathway induced to protect against starvation, it has become increasingly clear that autophagy also plays a major role in the homeostasis of non-starved cells. Defects in autophagy have been linked to various human diseases, including neurodegeneration and cancer, and interest in modulating autophagy as a potential treatment for these diseases has grown rapidly.
Interferon gamma (IFN-γ) is a dimerized soluble cytokine that is the only member of the type II class of interferons. The existence of this interferon, which early in its history was known as immune interferon, was described by E. F. Wheelock as a product of human leukocytes stimulated with phytohemagglutinin, and by others as a product of antigen-stimulated lymphocytes. It was also shown to be produced in human lymphocytes. or tuberculin-sensitized mouse peritoneal lymphocytes challenged with Mantoux test (PPD); the resulting supernatants were shown to inhibit growth of vesicular stomatitis virus. Those reports also contained the basic observation underlying the now widely employed IFN-γ release assay used to test for tuberculosis. In humans, the IFN-γ protein is encoded by the IFNG gene.
Galectins are a class of proteins that bind specifically to β-galactoside sugars, such as N-acetyllactosamine, which can be bound to proteins by either N-linked or O-linked glycosylation. They are also termed S-type lectins due to their dependency on disulphide bonds for stability and carbohydrate binding. There have been about 15 galectins discovered in mammals, encoded by the LGALS genes, which are numbered in a consecutive manner. Only galectin-1, -2, -3, -4, -7, -7B, -8, -9, -9B, 9C, -10, -12, -13, -14, and -16 have been identified in humans. Galectin-5 and -6 are found in rodents, whereas galectin-11 and -15 are uniquely found in sheep and goats. Members of the galectin family have also been discovered in other mammals, birds, amphibians, fish, nematodes, sponges, and some fungi. Unlike the majority of lectins they are not membrane bound, but soluble proteins with both intra- and extracellular functions. They have distinct but overlapping distributions but found primarily in the cytosol, nucleus, extracellular matrix or in circulation. Although many galectins must be secreted, they do not have a typical signal peptide required for classical secretion. The mechanism and reason for this non-classical secretion pathway is unknown.
CD137, a member of the tumor necrosis factor (TNF) receptor family, is a type 1 transmembrane protein, expressed on surfaces of leukocytes and non-immune cells. Its alternative names are tumor necrosis factor receptor superfamily member 9 (TNFRSF9), 4-1BB, and induced by lymphocyte activation (ILA). It is of interest to immunologists as a co-stimulatory immune checkpoint molecule, and as a potential target in cancer immunotherapy.
Vojo Deretic, is distinguished professor and chair of the Department of Molecular Genetics and Microbiology at the University of New Mexico School of Medicine. Deretic was the founding director of the Autophagy, Inflammation and Metabolism (AIM) Center of Biomedical Research Excellence. The AIM center promotes autophagy research nationally and internationally.
Lysosome-associated membrane protein 2 (LAMP2), also known as CD107b and Mac-3, is a human gene. Its protein, LAMP2, is one of the lysosome-associated membrane glycoproteins.
Psychosine receptor is a G protein-coupled receptor (GPCR) protein that in humans is encoded by the GPR65 gene. GPR65 is also referred to as TDAG8.
LIGHT, also known as tumor necrosis factor superfamily member 14 (TNFSF14), is a secreted protein of the TNF superfamily. It is recognized by herpesvirus entry mediator (HVEM), as well as decoy receptor 3.
Programmed cell death protein 1(PD-1),. PD-1 is a protein encoded in humans by the PDCD1 gene. PD-1 is a cell surface receptor on T cells and B cells that has a role in regulating the immune system's response to the cells of the human body by down-regulating the immune system and promoting self-tolerance by suppressing T cell inflammatory activity. This prevents autoimmune diseases, but it can also prevent the immune system from killing cancer cells.
Lysosomal-associated membrane protein 1 (LAMP-1) also known as lysosome-associated membrane glycoprotein 1 and CD107a, is a protein that in humans is encoded by the LAMP1 gene. The human LAMP1 gene is located on the long arm (q) of chromosome 13 at region 3, band 4 (13q34).
Galectin-8 is a protein of the galectin family that in humans is encoded by the LGALS8 gene.
V-set domain-containing T-cell activation inhibitor 1 is a protein that in humans is encoded by the VTCN1 gene.
Programmed cell death 1 ligand 2 is a protein that in humans is encoded by the PDCD1LG2 gene. PDCD1LG2 has also been designated as CD273. PDCD1LG2 is an immune checkpoint receptor ligand which plays a role in negative regulation of the adaptive immune response. PD-L2 is one of two known ligands for Programmed cell death protein 1 (PD-1).
Hepatitis A virus cellular receptor 2 (HAVCR2), also known as T-cell immunoglobulin and mucin-domain containing-3 (TIM-3), is a protein that in humans is encoded by the HAVCR2 (TIM-3)gene. HAVCR2 was first described in 2002 as a cell surface molecule expressed on IFNγ producing CD4+ Th1 and CD8+ Tc1 cells. Later, the expression was detected in Th17 cells, regulatory T-cells, and innate immune cells. HAVCR2 receptor is a regulator of the immune response.
Maternal embryonic leucine zipper kinase (MELK) is an enzyme that in humans is encoded by the MELK gene. MELK is a serine/threonine kinase belonging to the family of AMPK/Snf1 protein kinases. MELK was first identified present as maternal mRNA in mouse embryos. MELK expression is elevated in a number of cancers and is an active research target for pharmacological inhibition.
Galectin-3 is a protein that in humans is encoded by the LGALS3 gene. Galectin-3 is a member of the lectin family, of which 14 mammalian galectins have been identified.
Myeloid-derived suppressor cells (MDSC) are a heterogeneous group of immune cells from the myeloid lineage.
Gabriel A. Rabinovich is an Argentine biochemist who is currently a professor at the School of Exact and Natural Sciences at the University of Buenos Aires. He is also the deputy director of Immunopathology Laboratories, and the head of Structural and Functional Glycomic Laboratories.