Transforming growth factor beta (TGF-β) is a member of TGF-β superfamily that comprises a large group of structurally related growth factors involved in the control of a variety of cellular processes and responses. TGF-β is secreted in a latent form. Upon activation it binds to the TGF-β receptor (TβR) on the cell surface. Following the activation by the type II receptor (TβRII), the type I receptor (TβRI) propagates the signal to receptor-regulated Smads (R-Smads). The efficient recruitment of R-Smads to the receptor is facilitated by a protein called SARA (Smad Anchor for Receptor Activation). Ultimately, R-Smads form a complex with Co-mediator Smad (Co-Smad). The R-Smad/Co-Smad complex in combination with other co-factors regulates the transcription of target gens. The inhibitory Smads (I-Smads) play role in negative regulation of TGF-β signalling.