| * Phosphorylation of c-Abl at Tyr245 is a critical marker of activation of the non-receptor tyrosine kinase c-Abl, a multifunctional signaling protein of the Abl family that regulates cellular responses to DNA damage, oxidative stress, growth factors, adhesion signaling, and cytoskeletal dynamics in both the nucleus and cytoplasm. c-Abl contains an N-terminal cap region, SH3 and SH2 regulatory domains, a linker region harboring Tyr245, a catalytic kinase domain, and an activation loop containing Tyr412, which together maintain the kinase in an autoinhibited conformation under basal conditions. Phosphorylation at Tyr245 within the SH2-kinase linker disrupts inhibitory intramolecular interactions by repositioning the SH2 domain away from the catalytic cleft, thereby enhancing kinase activity and facilitating subsequent autophosphorylation at Tyr412 to stabilize the fully active conformation. Activated phospho-c-Abl phosphorylates multiple downstream substrates, including c-Jun to enhance AP-1–dependent transcription, CrkL to regulate Rac/Cdc42-mediated cytoskeletal remodeling, and Abi1 to control WAVE complex assembly and lamellipodia formation during cell migration. In DNA damage signaling, activated c-Abl interacts with ATM and promotes phosphorylation of pro-apoptotic factors such as p73, leading to induction of apoptotic genes including Puma, whereas during growth factor signaling such as PDGF stimulation, c-Abl cooperates with adaptor proteins like Nck and PI3K to activate MAPK/ERK pathways involved in proliferation and survival. Tyr245 phosphorylation is important in neuronal development, particularly in EphB receptor-mediated growth cone collapse and axon guidance, and also contributes to stress granule regulation through phosphorylation of RNA-binding proteins such as Sam68. Phosphorylation at Tyr245 induces a conformational shift that relieves steric inhibition of the ATP-binding pocket and activation loop, enabling efficient substrate access and kinase signaling. Dysregulated or constitutive Tyr245 phosphorylation is a hallmark of oncogenic BCR-ABL fusion proteins in leukemias, where persistent c-Abl activation drives Ras, STAT5, and PI3K signaling pathways that promote uncontrolled proliferation and myeloid transformation. |
