Transforming Growth Factor Tgf3 Family

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The crystal structure of TGF-/3 has been determined, and a computer model is shown in Figure 19-8. TGF-/3 either stimulates or inhibits cell growth or affects cellular functions distinct from mitosis. Among the activities of TGF-/3 are inhibition of proliferation of mesenchymal, epithelial, endothelial, and transformed cells, stimulation of proliferation of these cell types, control of extracellular matrix interactions, suppression of immune function, regulation of embryogenesis and cellular differentiation, fibroblast transformation, inhibition of adrenal steroidogenesis, and regulation of the biosynthesis and action of FSH. These represent many diverse activities, including several that are distinct from the effects on cellular proliferation. There are three isoforms in the mammal (TGF-/31-3), a chicken form (TGF-/34), and a frog form (TGF-/35). There are other more distant members of this family. The members of this family are related by sequence homology but, for the most part, act through separate receptors, although some of these receptors, as expected, may share some homology. TGF-/3 is found in the a-granules of platelets, and some species, such as pig, chicken, and mouse, contain isoforms. Aspects of the structure of TGF-/3 are described in Figure 19-8.

Members of the TGF-/3 family are pictured in Figure 19-9. Among the family members are inhibins, activins, Miillerian inhibitory substance (MIS), bone morpho-genetic protein, Vgl and Vgr-1 from xenopus, and DPP-C in Drosophila development. Inhibins, activins, and Miillerian inhibitory substance are discussed in Chapters 12 and 13.

TGF-/8 is generated from an inactive precursor protein. The precursors are glycosylated and substituted

FIGURE 19-3 Close-up of interfaces between hormone and receptors: (A) binding site I; (B) binding site II. The hGH is represented by a space-filling model and the receptors by a stick model. The hGH backbone atoms are cyan, side chain carbons are white, and side chain oxygens and nitrogens are red and blue, respectively. The receptor carbon atoms are in yellow, with red oxygens and blue nitrogens. Selected residues are labeled. This figure is reproduced in black and white from a colored illustration with permission from de Vos, A. M., Ultsch, M., and Mossiakoff, A. (1992). Human growth hormone and extracellular domain of its receptor: Crystal structure of the complex. Science 255, 306-212.

FIGURE 19-3 Close-up of interfaces between hormone and receptors: (A) binding site I; (B) binding site II. The hGH is represented by a space-filling model and the receptors by a stick model. The hGH backbone atoms are cyan, side chain carbons are white, and side chain oxygens and nitrogens are red and blue, respectively. The receptor carbon atoms are in yellow, with red oxygens and blue nitrogens. Selected residues are labeled. This figure is reproduced in black and white from a colored illustration with permission from de Vos, A. M., Ultsch, M., and Mossiakoff, A. (1992). Human growth hormone and extracellular domain of its receptor: Crystal structure of the complex. Science 255, 306-212.

Cytokine Receptor

Growlh Factor Receptor

Growlh Factor Receptor

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