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).
Background: A number of studies have identified distinct complexes involving Beclin-1 and PI3K Kinase Class III with specific roles in autophagy and vesicle trafficking (1,2). These complexes commonly contain Beclin-1, PI3KC3/VSP34, and PIK3R4/VPS15 and function to catalyze the phosphorylation of phosphatidylinositol at the D3 position, producing phosphatidylinositol-3-phosphate. Specificity of PI3KC3 activity is regulated by additional binding partners. Complex 1 contains Atg14 which is required for early stages of autophagosome nucleation (3,4). Complex 2 lacks Atg14, but instead contains UVRAG, and is important for autophagosome maturation and endocytic trafficking (4-6). A third complex, containing both UVRAG and Rubicon, negatively regulates canonical autophagy (7,8). Importantly, this complex containing Rubicon is critical for a related process of LC3-associated phagocytosis (LAP) in which extracellular pathogens binding to cell surface receptors are engulfed by a single membrane phagosome and degraded by the lysosome (9,10).
Background: Anaplastic lymphoma kinase (ALK) is a tyrosine kinase receptor for pleiotrophin (PTN), a growth factor involved in embryonic brain development (1-3). In ALK-expressing cells, PTN induces phosphorylation of both ALK and the downstream effectors IRS-1, Shc, PLCγ, and PI3 kinase (1). ALK was originally discovered as a nucleophosmin (NPM)-ALK fusion protein produced by a translocation (4). Investigators have found that the NPM-ALK fusion protein is a constitutively active, oncogenic tyrosine kinase associated with anaplastic lymphoma (4). Research literature suggests that activation of PLCγ by NPM-ALK may be a crucial step for its mitogenic activity and involved in the pathogenesis of anaplastic lymphomas (5).A distinct ALK oncogenic fusion protein involving ALK and echinoderm microtubule-associated protein like 4 (EML4) has been described in the research literature from a non-small cell lung cancer (NSCLC) cell line, with corresponding fusion transcripts present in some cases of lung adenocarcinoma. The short, amino-terminal region of the microtubule-associated protein EML4 is fused to the kinase domain of ALK (6-8).