TGF-beta Receptor

Transforming growth factor-beta receptors (TGF-βR) are the serine/threonine kinase receptors that mediate signaling of the TGF-β family. The system is built on two cooperating kinases: TGFBR2 (type II receptor), which constitutively active, first binds TGF-β1/2/3 and then recruits and phosphorylates TGFBR1 (ALK5, type I receptor); TGFBR1 then phosphorylates receptor-regulated SMAD2 and SMAD3, which complex with SMAD4 and translocate to the nucleus to govern genes controlling proliferation arrest, extracellular matrix production, epithelial-mesenchymal transition and immune suppression. TGF-β receptors also activate non-canonical routes including p38, JNK, ERK, Rho GTPases and PI3K-AKT. TGFBR1/2 are ubiquitously expressed; their loss releases tumor cells from TGF-β growth inhibition, while excessive signaling drives fibrosis and cancer metastasis. Germline TGFBR1/TGFBR2 mutations cause Marfan syndrome type 2 and Loeys-Dietz syndrome with arterial aneurysms, and small-molecule TGFBR1 inhibitors (galunisertib) are under evaluation in cancer and fibrosis.