Transforming growth factor-beta stimulates the expression of fibronectin and collagen and their incorporation into the extracellular matrix.

The partial amino-acid sequence of purified human transforming growth factor-beta (TGF-beta) was used to identify a series of cDNA clones encoding the protein. The cDNA sequence indicates that the 112-amino acid monomeric form of the natural TGF-beta homodimer is derived proteolytically from a much longer precursor polypeptide which may be secreted. TGF-beta messenger RNA is synthesized in various normal and transformed cells.

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Human transforming growth factor-beta complementary DNA sequence and expression in normal and transformed cells.

This study examines the potential role of transforming growth factor beta (TGF-beta) in the regulation of human T lymphocyte proliferation, and proposes that TGF-beta is an important autoregulatory lymphokine that limits T lymphocyte clonal expansion, and that TGF-beta production by T lymphocytes is important in T cell interactions with other cell types. TGF-beta was shown to inhibit IL-2-dependent T cell proliferation. The addition of picograms amounts of TGF-beta to cultures of IL-2-stimulated human T lymphocytes suppressed DNA synthesis by 60-80%. A potential mechanism of this inhibition was found. TGF-beta inhibited IL-2-induced upregulation of the IL-2 and transferrin receptors. Specific high-affinity receptors for TGF-beta were found both on resting and activated T cells. Cellular activation was shown to result in a five- to sixfold increase in the number of TGF-beta receptors on a per cell basis, without a change in the affinity of the receptor. Finally, the observations that activated T cells produce TGF-beta mRNA and that TGF-beta biologic activity is present in supernatants conditioned by activated T cells is strong evidence that T cells themselves are a source of TGF-beta. Resting T cells were found to have low to undetectable levels of TGF-beta mRNA, while PHA activation resulted in a rapid increase in TGF-beta mRNA levels (within 2 h). Both T4 and T8 lymphocytes were found to make mRNA for TGF-beta upon activation. Using both a soft agar assay and a competitive binding assay, TGF-beta biologic activity was found in supernatants conditioned by T cells; T cell activation resulted in a 10-50-fold increase in TGF-beta production. Thus, TGF-beta may be an important antigen-nonspecific regulator of human T cell proliferation, and important in T cell interaction with other cell types whose cellular functions are modulated by TGF-beta.

/pdf/production-of-transforming-growth-factor-beta-by-human-t-2kr5ba93ll.pdf

Production of transforming growth factor beta by human T lymphocytes and its potential role in the regulation of T cell growth.

The ability of cancer cells to produce and to respond to their own growth factors (autocrine secretion) has become a central concept linking oncogene and growth factor research. Oncogenes confer growth factor autonomy on cells not only by coding directly for autocrine peptide growth factors or their receptors, but also by amplifying the mitogenic signals generated by a growth factor at its receptor. Antagonists of positive autocrine growth factors can inhibit growth of cancer cells in experimental animals. Recently identified negative autocrine growth factors might themselves control aberrant cell growth.

Autocrine growth factors and cancer.

Publisher Summary This chapter discusses the development of follicles in the mammalian ovary. The unresolved issues in follicular development are focused. Folliculogenesis culminates in the production of fully ripe, preovulatory follicles visible to the naked eye as large bulges on the surface of the ovary. Each ripe follicle contains thousands of highly differentiated cells. This complex, functional miniature organ arises from the handful of cells that constitute a simple primordial follicle, a structure so small that it is invisible at the lower magnifications of a light microscope. All regulatory influences can only permit or prevent cells from completing the full maturation process; they cannot change the course of differentiation. A plethora of modulating influences act as permissive inducers, impeding or propelling the committed follicular cells through the process of clonal expansion. As each follicle progresses through its program of limited clonal expansion and maturation, its cells proliferate more and more rapidly. With every passing generation, the proliferative potential of the granulosa and theca cells continues to diminish, while the state of maturation increases.

Development of Follicles in the Mammalian Ovary

The structural features of the heterodimeric glycoprotein hormones (LH, FSH, TSH, and hCG) are briefly reviewed. Removal of carbohydrate chains does not reduce binding of the hormones to membrane receptors, but markedly reduces biological responses. The glycopeptides from the hormone do not reduce binding of native hormone to receptors but do reduce biological responses. Newer data concerned with replication of different regions of the peptide chains of these molecules using synthetic peptides are reviewed and presented. These studies indicate that two regions on the common alpha subunit are involved with receptor binding of the LH, hCG, and TSH molecules. These regions are alpha 26 to 46 and alpha 75-92. Two synthetic disulfide loop peptides from the hCG beta subunit beta 38-57 and beta 93-100 also block binding of hCG to its receptor. In addition, the beta 38-57 peptide stimulates testosterone production by Leydig cells. These data indicate that glycoprotein hormone binding to plasma membrane receptors ...

https://faseb.onlinelibrary.wiley.com/doi/pdf/10.1096/fasebj.2.11.2456242

The glycoprotein hormones: recent studies of structure-function relationships.

Purified type beta transforming growth factor from human platelets (TGF beta) radioiodinated with 125I-labeled Bolton and Hunter reagent was found to bind to a variety of cultured cells of both epithelial and mesenchymal origin, including normal human fibroblasts and keratinocytes. TGF beta binding sites have also been found on three mouse embryo-derived fibroblast-like cell lines with lower levels of TGF beta binding on the chemically transformed derivatives of these cell lines. A variety of human tumor cell lines was shown to have an inverse correlation between their level of TGF beta binding and their ability to form colonies in soft agar. The mouse embryo-derived AKR-2B (clone 84A) cells reached maximal binding of 125I-labeled TGF beta after 2 hr at 22 degrees C. Scatchard analysis of the equilibrium binding of TGF beta to AKR-2B (clone 84A) cells gives a Kd of 33 pM with approximately equal to 10,500 binding sites per cell. This Kd for TGF beta binding to AKR-2B (clone 84A) cells agreed well with the ED50 of 40 pM for stimulation of colony formation of these cells by TGF beta. The TGF beta binding sites on the AKR-2B cells were shown to be specific for TGF beta with no significant competition with epidermal growth factor, fibroblast growth factor, or insulin and only a small level of competition with high concentrations of platelet-derived growth factor. Partially purified preparations with TGF beta-like activity from mouse embryos and medium conditioned by mouse embryo-derived cells competed effectively for binding to the TGF beta receptor.

Specific binding to cultured cells of 125I-labeled type beta transforming growth factor from human platelets.

Publisher Summary The gonadotropins, luteinizing hormone (LH), and follicle-stimulating hormone (FSH) of pituitary origin, and chorionic gonadotropin (hCG, eCG) of placental origin, along with thyroid-stimulating hormone (TSH) constitute a family of glycoprotein hormones. The α-subunit is common to all of the hormones and shows considerable homology from one species to another. The β-subunits are unique for LH, FSH, and TSH. The s-subunits of hLH and hCG are highly homologous (85%) through the first 114 residues, but hCG β differs in that it has a C-terminus extension rich in serine and proline. This offers a chemical basis for their common biological activities. Baboon chorionic gonadotropin, and eLH and chorionic gonadotropin s-subunits also have C-terminal extensions. The glycoprotein hormone s-subunits also show regions of homology between themselves and among different species. A wide range of chemical and enzymatic modifications have been employed in efforts to define residues and sequences in the s-subunits that may be essential for receptor binding. In general, chemical modifications of reactive amino acids appear to be more tolerated in the s- than in the α-subunits.

Structure-function relationships of gonadotropins.

The free acid form of L-triiodothyronine was coupled to HSA, BSA or RSA using carbodiimide. The conjugates contained 11–17 moles of T3 per mole of protein. Rabbits were immunized separately with each conjugate. Antibodies against T3 were obtained in all animals after 6 weeks of immunization. One antiserum prepared with T3-HSA was studied in detail using a radioimmunoassay procedure. It was useful in a final dilution of 1:1000 to 1:4000 and was sufficiently sensitive to measure 50 pg of unlabeled T3 per assay tube. The ability of 30 tyrosine and thyronine derivatives to compete with T3 for binding to antibody were investigated to assess the specificity of the assay. Antibody recognition involved the following structural requirements: two phenolic rings; a 3′ iodine; 4′ hydroxyl group and a 5′ hydrogen. Alterations in the alanine side chain reduced antibody recognition, but to a much smaller extent than changes in the structure of the phenolic rings. Thus, the antiserum is highly specific for L-T3 ...

Radioimmunoassay for Triiodothyronine (T3): I. Affinity and Specificity of the Antibody for T3*

Numerous parameters of the chemical composition of porcine follicular fluid obtained at different stages of follicle development were analyzed. The concentrations of electrolytes glucose uric acid selected enzymes lipids amino acids cyclic AMP and steroid hormones were determined and compared with concentrations in serum. There were both quantitative and qualitative differences in the composition of follicular fluid and plasma. These differences are discussed with regard to follicular development.

Robert J. Ryan

Papers

The glycoprotein hormones: recent studies of structure-function relationships.

Specific binding to cultured cells of 125I-labeled type beta transforming growth factor from human platelets.

Structure-function relationships of gonadotropins.

Radioimmunoassay for Triiodothyronine (T3): I. Affinity and Specificity of the Antibody for T3*

The Porcine Ovarian Follicle: I. Selected Chemical Analysis of Follicular Fluid at Different Developmental Stages