Target Information
Extracellular signal-regulated kinase (ERK) is the founding member and a key component of the classical Mitogen-Activated Protein Kinase (MAPK) pathway. ERK1 (p44, MAPK3) and ERK2 (p42, MAPK2) are both activated via the MAPK/ERK pathway, which is downstream of various Receptor Tyrosine Kinases (RTKs) or GPCRs. MEK, a Ser/Thr and Tyr kinase, activates ERK by phosphorylation of its TxY motifs, namely Thr202/Tyr204 and Thr185/Tyr187 of ERK1 and ERK2, respectively. Once activated, ERK phosphorylates a variety of proteins that regulate cellular processes such as cell division, proliferation, survival, differentiation, apoptosis, motility, and metabolism. AKT, which exists as multiple isoforms, is one of the principle kinases activated by phosphoinositide 3-kinase (PI3K). Activation of PI3K results in the generation of phosphatidylinositol (3,4,5)-triphosphate (PIP3). These lipid second messengers bind to the pleckstrin homology domain of AKT to promote its translocation to the plasma membrane for activation via phosphorylation at Thr308 and Ser473 by PDK1 and the mTOR TORC2 complex, respectively. Phosphorylation at both these sites is required for full activation of AKT Ser/Thr kinase activity. AKT phosphorylates over 50 known substrates, including GSK3, AS160, PRAS40, TSC 1, TCS 2, Raf-1, Bad, the FOXO family of transcription factors, and PFK2. Due to its established critical role in numerous biological processes, AKT is a frequent target for oncology-related drug development.