SMAD3 and neoplasm: Smad3 phosphorylation can be classified into C-terminal phosphorylation (pSmad3C), which is directly activated by TGF-β receptors and mediates tumour-suppressive signalling, and linker-region phosphorylation (pSmad3L), which is activated via the MAPK pathways (including ERK, JNK, and p38) and is associated with tumour progression [98,99,100].