Antibodies

WD repeat domain phosphoinositide-interacting protein 1 (WIPI) is involved in the lysosomal degradation of cytoplasmic components during starvation-induced autophagy. WIPI1 is a seven bladed beta-propeller protein that provides a scaffold for the assembly of multimeric protein complexes (1). During the assembly of the autophagosome WIPI1 interacts with the lipid phosphatidylinositol-3 phosphate (PI3P) and mediates the recruitment of the large multimeric complex of ATG12-ATG5-ATG16 (1).

VPS34, vacuolar protein sorting 34, is the only identified Class III phosphoinositide-3 kinase (PI3K) in mammals and is ubiquitously expressed in all eukaryotic cells. VPS34 is a 100 kDa protein responsible for phosphorylating phosphatidylinositol to produce phosphatidylinositol 3-phosphate (PI3P). PI3P is an important intermediate in the development of the double-membraned autophagosome during autophagy, indicating a role for VPS34 in autophagy initiation. PI3P allows VPS34 to form complexes with ATG14L during the elongation of the autophagosome membrane.

Autophagy is an important cellular process involved in degradation and recycling of cellular macromolecules in response to stress or starvation. Autophagy is carried out in four main phases: phagophore nucleation, autophagosome elongation, docking and fusion with a lysosome, and vesicle breakdown and degradation. ULK1, also known as UNC51-like autophagy activating kinase 1, is a 112 kDa protein with serine-threonine kinase activity. ULK1 is one of two mammalian homologues of the yeast ATG1 kinase, known for its role in autophagy initiation (1).

S6K is a serine/threonine kinase that is a member of the ribosomal S6 kinase (RSK) family. S6K exists in two main isoforms, S6K1 and S6K2, which can also be alternatively spliced to produce different splice forms. S6K1 has two major splicing products that are approximately 70 kDa and 85 kDa, known as p70S6K and p85S6K respectively. S6K is activated via phosphorylation by mTORC1 which relieves the autoinhibition of S6K. Active S6K phosphorylates the ribosomal S6 protein, which induces protein synthesis and cell growth and proliferation.

Autophagy is an important cellular process that maintains homeostasis by degrading and recycling damaged proteins and organelles. Autophagy receptors, such as p62/SQSTM1, recognize these intracellular cargo and mediate their engulfment by the double-membrane autophagosome. The autophagosomes are subsequently targeted to the lysosome for degradation. An early regulatory step in this process is the activation and lipidation of ATG8 related proteins such as microtubule-associated protein-1 light chain 3 (LC3).

Membrane fusion is an essential step during the trafficking of endosomes and vesicles throughout the cell. Membrane fusion events are facilitated by multisubunit tethering complexes (MTC) including CORVET and HOPS. These complexes interact with Rab GTPases and SNARE proteins to promote the fusion of endosomes and lysosomes (1). In yeast VPS41 is a component of the HOPS complex that is needed for transport of endosomes and Golgi-derived vesicles to the vacuole. The choice between these two substrates is facilitated by the phosphorylation of VPS1 by Yck3 (2). Carbrera et al.

Phosphatidylinositol 3-kinases (PI3Ks) are a group of lipid kinases with important roles in signal transduction. PI3Ks are involved in signal propagation for diverse receptors including tyrosine kinase receptors and G-protein coupled receptors. Class I PI3Ks consist of two subunits: the regulatory p85 subunit and the catalytic p110 subunit (1). p85 binds to phosphorylated tyrosine residues found on activated tyrosine kinase receptors and mediates the translocation of the p110 subunit to the cell membrane (2).

C/EBP homologous protein (CHOP) is a transcription factor that regulates apoptosis in response to cellular stress. CHOP also known as growth arrest and DNA damage 153 (GADD153) was first cloned because of its induction in response to genotoxic stress such as UV irradiation. CHOP has now been shown to be induced mainly by ER-stress (1). CHOP is normally expressed at low levels and localizes to the cytoplasm. Cellular stress triggers an upregulation of CHOP levels and accumulation in the nucleus where it can act as either a transcriptional repressor or activator (1).

T-cells infiltrating sites of inflammation of the skin typically express the cutaneous lymphocyte-associate antigen (CLA). This antigen is defined by the binding of the monoclonal CLA antibody HECA-452. The CLA antigen is a fucose-containing oligosaccharide and is found on many of the ligands that are recognized by the adhesion proteins P-selectin and E-selectin. CLA is primarily expressed by memory T-cells.

Cellular inhibitor of apoptosis protein-1 (cIAP-1) is an anti-apoptotic protein that is able to bind to caspases and inhibit their activity. Additionally cIAP-1 contains a RING domain with E3 ubiquitin ligase activity that is able to mediate the regulation of NF-kB signaling through the ubiquitination and degradation of various substrate proteins. Depending on cellular context, the RING domain of cIAP-1 can either promote or inhibit apoptosis.