Autophagy, also known as macroautophagy, supplies alternative fuel for cells that are under environmental stress conditions (including starvation, growth factor deprivation, and hypoxia). This highly regulated and catabolic cell process recycles and repurposes pre-existing organelles as well as existing macromolecules and is a very evolutionarily conserved and fundamental process to preserve cells under adverse conditions. The LC3B protein is a subunit of the LC3 autophagy complex that associates with the microtubule-associated proteins (MAPs) 1A and 1B. LC3B, along with its associated molecules, helps guide and regulates autophagosome assembly and formation. In its inactive and resting state, LC3B is found in the cytosol, but upon activation LC3B is localized to the autophagosomal membrane. LC3B and caspase-3 were used as biomarkers by scientists in a unique three-dimensional bovine mammary epithelial cell (MEC) culture model system examined with confocal microscopy (1). There, with the LC3B antibody physiologists found that estradiol, progesterone, and TGF beta regulate mammary gland development by modulating and balancing processes such as MEC autophagy, proliferation, and apoptosis. The LC3B antibody allowed Sirois' group to validate (via immunoblot) a multidimensional proteomics method for studying vascular wall integrity and intercellular communication in the endothelium (2). In conjunction with detailed electron microscopy, apoptotic indices were assessed and caspase-3 was identified as a central component for human endothelial cell (HEC) signal transduction downstream of nutrient deficiency and apoptosis. Oncologists at MD Anderson used the LC3B antibody for complex cDNA microarray analyses on autophagic glioblastoma cell lines (3). They determined that LC3B expression is a valuable, efficient, and robust means of predicting induction of autophagy as well as patient outcome and survival rates. Additionally, oncologists at the Dana Farber Cancer Institute also employed the LC3B antibody and determined that cancers with a pancreatic origin have a distinct dependence on autophagy (4). Their results suggest that potent autophagy inhibitors such as chloroquine and other derivatives could be novel therapeutics in such patients. A Nature publication out of Efeyan's group at the Whitehead Institute relied upon the LC3B antibody to demonstrate that rapamycin complex (mTORC) regulates neonatal autophagy and growth - in response to nutrients and growth factors – through the Rag GTPase family (5).
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