Antibodies

Autophagy is a process by which cells degrade and recycle damaged organelles or misfolded proteins. These various cargo are engulfed in a double-membrane structure called the autophagosome. The autophagosome then fuses with the lysosome to facilitate the degradation of the cargo. This process requires the concerted effort of an extensive network of proteins. One of the early steps of autophagosome assembly is the formation of the large multimeric ATG12-ATG5-ATG16 complex.

Autophagy is an essential cellular process whereby damaged proteins and organelles are degraded and recycled. Autophagy, while happening constantly at a basal level, is tightly regulated and can be further induced under cellular stress. One of the regulators of the early steps of autophagy is ATG4. The ATG4 family of cysteine proteases consists of 4 homologs: ATG4A, ATG4B, ATG4C, and ATG4D.

The heat-shock protein 90 (HSP90) family is a group of highly conserved molecular chaperones with important functions in protein folding and in signal transduction. The HSP90 protein structure is so well conserved that some HSP90 antibodies are reactive with a broad range of species from humans to chickens (1). In humans there are 17 known genes encoding the HSP90 family members. The HSP90 family consists of 4 different classes: HSP90AA, HSP90AB, HSP90B, and TRAP.

The heat shock protein 70 (Hsp70) family are a group of chaperones involved in various cellular processes including protein folding and protein degradation. In addition to maintaining normal cellular homeostasis by processing newly synthesized protein, the Hsp70 family is also important in controlling intracellular signaling pathways by regulating the folding and activity of signaling proteins. The various groups within the Hsp70 family are characterized by their expression levels, activities, and subcellular localization (1).

Fms-like tyrosine kinase-3 (FLT3) is a Type III receptor tyrosine kinase expressed by hematopoietic progenitor cells. FLT3 is also sometimes referred to as FLK2 or CD135. The FLT3 protein exists in two states- membrane bound (160 kDa) and cytoplasmic (140 kDa) (1). The FLT3 ligand induces autophosphorylation of FLT3 which allows binding of scaffold and effector molecules. Activated FLT3 is capable of phosphorylating and activating PI3K, PLC-γ, Shc, Grb2, and Src (2). FLT3 signaling ultimately activates the AKT and MAPK pathways to promote cell growth and survival.

Akt1 is one of three isoforms of Akt belonging to the AGC family of serine/threonine kinases (Akt1, Akt2, and Akt3). All Akt isoforms contain an N-terminal Plekstrin Homology (PH) domain, a C-terminal regulatory domain, and a central catalytic kinase domain (1). Akt is a major downstream target of the PI3-K signaling pathway. The Akt1 isoform is fully activated by phosphorylation at three sites- T308, T450, and S473. Akt1 resides in an inactive state due to intramolecular interactions between the PH domain and the kinase domain.

Caspases are a family of cysteine-aspartic acid proteases that cleave caspase proenzymes as well as other protein substrates. Caspases are well known for their role in apoptosis, but they also play a significant role in other cellular processes including inflammation (1). Apoptotic caspases include Caspases-3, -6, -7, -8, and -9. Meanwhile, human inflammatory caspases include Caspases-1, -4, -5, and -12.

TSC2 is a tumor suppressor gene that encodes a 200 kDa protein called tuberin. TSC2 heterodimerizes with TSC1 to form a complex with GTPase-activating protein (GAP) activity. The C-terminus of TSC2 contains the GAP domain responsible for this catalytic activity. The complex was first discovered through its role in the tumor-forming condition Tuberous Sclerosis. Mutations in TSC1 and TSC2 can either destabilize the complex or compromise the GAP activity. The TSC1-TSC2 complex acts as a GAP for the small G-protein Rheb, expressed ubiquitously throughout the body (1).

Autophagy can be broken down into 4 main stages: phagophore nucleation, autophagosome elongation, autophagosome docking and fusion with a lysosome, and vesicle breakdown and degradation. ATG4B is one of four ATG4 homologs (ATG4A, ATG4B, ATG4C, and ATG4D) involved in autophagosome elongation. ATG4B encodes a 48 kDa protein called autophagin-1 that is a member of the C54 family of cysteine proteases.

TSC1 is a tumor suppressor gene that encodes a 130 kDa protein called hamartin. TSC1 was first identified as an oncogenic driver of Tuberous Sclerosis, a condition characterized by numerous benign tumors of the skin, brain, heart, and lungs. A mutation in TSC1 is responsible for the uncontrolled growth characteristic of these tumors. This discovery led to a greater understanding of the physiologic role of TSC1 as a negative cell cycle regulator. The distinct but related gene TSC2 encodes a 200 kDa protein called tuberin.