Background: Microglia cells are resident macrophages of the brain that survey the brain environment and dynamically respond to maintain brain homeostasis. Microglial responses include phagocytosis of cellular debris, restricting sites injury or pathology, and/or releasing inflammatory signals to initiate an immune response. Such responses are important during normal development and during diseased states (1).Recently, the role of microglia in neurodegenerative disease pathology, particularly Alzheimer’s disease (AD), has been of intense investigation. Much of this work is driven by human genetic data that links microglia-enriched genes with AD progression (2). The triggering receptor expressed on myeloid cells 2 (TREM2) protein is an innate immune receptor that is expressed on the cell surface of microglia (3). TREM2 plays a role in innate immunity, and a rare functional variant (R47H) of the TREM2 gene is associated with the late-onset risk of AD (3,4). How TREM2 contributes to disease function is currently an active area of research (4,5), but might drive a number of microglial cellular functions ranging from microgliosis, phagocytosis, and cytokine release via a variety of signaling cascades triggered by TREM2.The TREM2 receptor is a single-pass type I membrane glycoprotein that consists of an extracellular immunoglobulin-like domain, a transmembrane domain, and a cytoplasmic tail. Ligands for TREM2 include phospholipids, apolipoproteins, and lipoproteins. Upon activation, TREM2 interacts with the tyrosine kinase-binding protein DNAX-activating protein 12 (DAP12, TYROBP) to form a receptor-signaling complex (6). Ligand binding by DAP12-associated receptors, including TREM2, results in phosphorylation of tyrosine residues within the DAP12 immunoreceptor tyrosine-based activation motif (ITAM) by Src family kinases; ITAM phosphorylation leads to activation of spleen tyrosine kinase (Syk) and downstream signaling cascades (7). Tyr525 and Tyr526 are located in the activation loop of the Syk kinase domain and phosphorylation at these residues (equivalent to Tyr519/520 of mouse Syk) is essential for Syk function (8). Syk phosphorylation is also a readout for β-amyloid triggered TREM2 activity (9). Phosphoinositide-specific phospholipase C γ 1/2 (PLCγ1/2) is reported to be down stream of Syk (10). Tyr352 of Syk is involved in the association of PLCγ1 (11); Syk-mediated phosphorylation PLCγ1 at Tyr783 activates PLCγ1 enzymatic activity (12). Interestingly, mutations in the microglia-enriched PLCγ2 gene are associated with AD (13,14,15).
Background: Syk is a protein tyrosine kinase that plays an important role in intracellular signal transduction in hematopoietic cells (1-3). Syk interacts with immunoreceptor tyrosine-based activation motifs (ITAMs) located in the cytoplasmic domains of immune receptors (4). It couples the activated immunoreceptors to downstream signaling events that mediate diverse cellular responses, including proliferation, differentiation, and phagocytosis (4). There is also evidence of a role for Syk in nonimmune cells and investigators have indicated that Syk is a potential tumor suppressor in human breast carcinomas (5). Tyr323 is a negative regulatory phosphorylation site within the SH2-kinase linker region in Syk. Phosphorylation at Tyr323 provides a direct binding site for the TKB domain of Cbl (6,7). Tyr352 of Syk is involved in the association of PLCγ1 (8). Tyr525 and Tyr526 are located in the activation loop of the Syk kinase domain; phosphorylation at Tyr525/526 of human Syk (equivalent to Tyr519/520 of mouse Syk) is essential for Syk function (9).
Background: Senescence is characterized by stable stress-induced proliferative arrest and resistance to mitogenic stimuli, as well as the secretion of proteins such as cytokines, growth factors and proteases. These secreted proteins comprise the senescence-associated secretory phenotype (SASP). Senescent cells are thought to accumulate as an organism ages, and contribute to age-related diseases, including cancer, through promotion of inflammation and disruption of normal cellular function (1,2). The composition of the SASP varies, and SASP components can be either beneficial or deleterious in human disease, depending on the context (3).Senescence Associated Secretory Phenotype (SASP) Antibody Sampler Kit provides a collection of antibodies to various SASP components, including TNF-alpha, interleukin-6 (IL-6), the multifunctional cytokine IL-1beta, the chemokines CXCL10, RANTES/CCL5 and MCP-1, the matrix metalloprotease MMP3, and the serine-protease inhibitor PAI-1.
Background: Phosphoinositide 3-kinase (PI3K) catalyzes the production of phosphatidylinositol-3,4,5-triphosphate by phosphorylating phosphatidylinositol (PI), phosphatidylinositol-4-phosphate (PIP), and phosphatidylinositol-4,5-bisphosphate (PIP2). Growth factors and hormones trigger this phosphorylation event, which in turn coordinates cell growth, cell cycle entry, cell migration, and cell survival (1). PTEN reverses this process, and research studies have shown that the PI3K signaling pathway is constitutively activated in human cancers that have loss of function of PTEN (2). PI3Ks are composed of a catalytic subunit (p110) and a regulatory subunit. Various isoforms of the catalytic subunit (p110α, p110β, p110γ, and p110δ) have been isolated, and the regulatory subunits that associate with p110α, p110β, and p110δ are p85α and p85β (3). In contrast, p110γ associates with a p101 regulatory subunit that is unrelated to p85. Furthermore, p110γ is activated by βγ subunits of heterotrimeric G proteins (4).