Enzymes, proteins, riboproteins and signaling pathways.


The phosphatidylinositide-3-OH kinase (PI3K)/3-phosphoinositide-dependent protein kinase-1 (PDK1)/Akt and the Raf/mitogen-activated protein kinase (MAPK/ERK) kinase (MEK)/mitogen-activated protein kinase (MAPK) pathways play central roles in the regulation of survival and proliferation of cells.

The mTOR protein kinase receives stimulatory signals from nutrients as well as Ras and phosphatidylinositol-3-OH kinase (PI(3)K) downstream from growth factors. Functioning as a critical growth-control node, mTOR is the 'mammalian target of rapamycin', a fungal derivative that halts protein synthesis by complexing with immunophilin FK-506 binding protein FKBP12 peptide prolyl cis/trans isomerase.

Phosphatidylinositide-3' (PI 3)-kinase participates in Kit-ligand (KL)-induced adhesion of bone marrow-derived mast cells (BMMCs) to fibronectin. The Kit receptor tyrosine kinase is a member of the PDGF receptor subfamily that mediates diverse responses including proliferation, survival, chemotaxis, migration, differentiation, and adhesion to extracellular matrix. PKCs play a dual role as both positive and negative regulators of Kit function by acting as downstream mediators in addition to participating in a negative feedback loop that down-regulates Kit receptor activity. PKC is activated by diacylgylcerol and by products of PI-3 kinase. Kit participates in the secretion of inflammatory mediators in connective tissue mast cells. Receptor-proximal PI 3-kinase activation and activation of a PKC isoform appear to have a role in Kit-mediated secretory enhancement, adhesion, and cytoskeletal reorganization.[r]

Agonist stimulation of phosphatidylinositide 3-kinase (PI 3-kinase) activates a pathway that leads to activation of ADP-ribosylation factor (ARF) 6, which regulates plasma membrane trafficking and cortical actin formation by cycling between inactive GDP and active GTP-bound conformations.

Components of the Ras and PI(3)K signalling pathways are mutated in most human cancers. The high frequency of mutations in these pathways suggests that the loss of growth-control checkpoints and the promotion of cell survival in nutrient-limited conditions may be an obligate event in carcinogenesis.[r]

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