TGF-beta signaling (Homo sapiens)

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The signal transduction mechanisms underlying the pathophysiological activities of transforming growth factor-خ² (TGF-خ²) have been extensively studied since its discovery nearly 30 years ago. TGF-خ² ligands belong to a large superfamily of cytokines that bears its name (TGF-خ² Superfamily) and includes bone morphogenic proteins, activins, inhibin, growth/differentiation factors, Mullerian inhibiting substance, Nodal, and several other structurally-related polypeptides. Mammals express three TGF-خ² isoforms (i.e., TGF-خ²1, TGF-خ²2, and TGF-خ²3) that are encoded by distinct genes in a tissue-specific and developmentally-regulated manner. TGF-خ² was identified originally via its stimulation of morphological transformation and anchorage-independent growth in fibroblasts; however, this cytokine is now recognized as being a potent tumor suppressor that prevents the dysregulated growth and survival of epithelial, endothelial, and hematopoietic cells. In addition, numerous studies have clearly established TGF-خ² as a multifunctional cytokine that plays essential roles in regulating virtually all aspects of mammalian development and differentiation, and in maintaining mammalian tissue homeostasis. The pleiotropic nature of TGF-خ² is highlighted by the fact that every cell in the metazoan body can produce and respond to this cytokine. Even more remarkably, malignant cells have evolved a variety of complex mechanisms capable of circumventing the tumor suppressing activities of TGF-خ², and in doing so, typically convert the functions of TGF-خ² to that of a tumor promoter, particularly the induction of carcinoma epithelial-mesenchymal transition, invasion, and dissemination to distant organ sites. This peculiar conversion in TGF-خ² function is known as the “ TGF-خ² Paradox,â€‌ which underlies the lethality of TGF-خ² in metastatic cancer cells. Thus, elucidating the effectors and signaling modules activated by TGF-خ² may offer new insights into the development of novel neoadjuvants capable of effectively targeting the TGF-خ² pathway to significantly improve the clinical course of patients with cancer, fibrosis, or immunologic disorders. TGF-خ² is secreted from cells as a latent homodimeric polypeptide that becomes tethered to the extracellular matrix by latent-TGF-خ²-binding proteins. Mature TGF-خ² isoforms are activated and liberated from extracellular matrix depots by a variety of mechanisms, including proteolysis, reactive oxygen species, changes in pH, and physical interactions with integrins, thromobspondin-1, or SPARC. Once activated, mature TGF-خ² initiates transmembrane signaling by binding to two distinct transmembrane Ser/Thr protein kinases, termed TGF-خ² type I (Tخ²R-I) and type II (Tخ²R-II) receptors. In some cells and tissues, TGF-خ² also binds to a third cell surface receptor, TGF-خ² type III (Tخ²R-III), which transfers TGF-خ² to Tخ²R-II and Tخ²R-I. Full activation of these cytokine:receptor ternary complexes transpires upon Tخ²R-II-mediated transphosphorylation and activation of Tخ²R-I, which then phosphorylates and activates the latent transcription factors, Smad2 and Smad3. Afterward, phosphorylated Smad2/3 interact physically with Smad4, with the resulting heterotrimers translocating into the nucleus to regulate the expression of TGF-خ²-responsive genes. These Smad-dependent events are subject to fine-tuning and crosstalk regulation in the cytoplasm by their interaction with a variety of adapter molecules, including SARA, Hgs, PML and Dab2, and with Smad7, whose inhibitory activity is modulated by STRAP, AMSH2, and Arkadia; and in the nucleus by their interaction with a variety of transcriptional activators and repressors that occur in a gene- and cell-specific manner. In addition to activating canonical Smad2/3-dependent signaling, accumulating evidence clearly links the development of a variety of human pathologies to aberrant coupling of TGF-خ² to its noncanonical effector molecules. Included in this ever expanding list of noncanonical signaling molecules stimulated by TGF-خ² are PI3K, AKT, mTOR, integrins and focal adhesion kinase, and members of the MAP kinase (e.g., ERK1/2, JNK, and p38 MAPK small GTP-binding proteins (e.g., Ras, Rho, and Rac1). The interactions and intersections between canonical and noncanonical TGF-خ² signaling systems are depicted in the pathway map.

Please access this pathway at NetSlim database.

If you use this pathway, you must cite following paper:

Kandasamy, K., Mohan, S. S., Raju, R., Keerthikumar, S., Kumar, G. S. S., Venugopal, A. K., Telikicherla, D., Navarro, J. D., Mathivanan, S., Pecquet, C., Gollapudi, S. K., Tattikota, S. G., Mohan, S., Padhukasahasram, H., Subbannayya, Y., Goel, R., Jacob, H. K. C., Zhong, J., Sekhar, R., Nanjappa, V., Balakrishnan, L., Subbaiah, R., Ramachandra, Y. L., Rahiman, B. A., Prasad, T. S. K., Lin, J., Houtman, J. C. D., Desiderio, S., Renauld, J., Constantinescu, S. N., Ohara, O., Hirano, T., Kubo, M., Singh, S., Khatri, P., Draghici, S., Bader, G. D., Sander, C., Leonard, W. J. and Pandey, A. (2010). NetPath: A public resource of curated signal transduction pathways. Genome Biology. 11:R3.