Atherosclerosis, the principal cause of heart attack, stroke and gangrene of the extremities, is responsible for 50% of all mortality in the USA, Europe and Japan. The lesions result from an excessive, inflammatory-fibroproliferative response to various forms of insult to the endothelium and smooth muscle of the artery wall. A large number of growth factors, cytokines and vasoregulatory molecules participate in this process. Our ability to control the expression of genes encoding these molecules and to target specific cell types provides opportunities to develop new diagnostic and therapeutic agents to induce the regression of the lesions and, possibly, to prevent their formation.

The pathogenesis of atherosclerosis: a perspective for the 1990s

The recent identification of the SMAD family of signal transducer proteins has unravelled the mechanisms by which transforming growth factor-beta (TGF-beta) signals from the cell membrane to the nucleus. Pathway-restricted SMADs are phosphorylated by specific cell-surface receptors that have serine/threonine kinase activity, then they oligomerize with the common mediator Smad4 and translocate to the nucleus where they direct transcription to effect the cell's response to TGF-beta. Inhibitory SMADs have been identified that block the activation of these pathway-restricted SMADs.

TGF-beta signalling from cell membrane to nucleus through SMAD proteins

Transforming growth factor-beta 1 (TGF-beta 1) is a multifunctional growth factor that has profound regulatory effects on many developmental and physiological processes. Disruption of the TGF-beta 1 gene by homologous recombination in murine embryonic stem cells enables mice to be generated that carry the disrupted allele. Animals homozygous for the mutated TGF-beta 1 allele show no gross developmental abnormalities, but about 20 days after birth they succumb to a wasting syndrome accompanied by a multifocal, mixed inflammatory cell response and tissue necrosis, leading to organ failure and death. TGF-beta 1-deficient mice may be valuable models for human immune and inflammatory disorders, including autoimmune diseases, transplant rejection and graft versus host reactions.

Targeted disruption of the mouse transforming growth factor-β1 gene results in multifocal inflammatory disease

Epidermal growth factor-related peptides and their receptors in human malignancies

Wound healing is an evolutionarily conserved, complex, multicellular process that, in skin, aims at barrier restoration. This process involves the coordinated efforts of several cell types including keratinocytes, fibroblasts, endothelial cells, macrophages, and platelets. The migration, infiltration, proliferation, and differentiation of these cells will culminate in an inflammatory response, the formation of new tissue and ultimately wound closure. This complex process is executed and regulated by an equally complex signaling network involving numerous growth factors, cytokines and chemokines. Of particular importance is the epidermal growth factor (EGF) family, transforming growth factor beta (TGF-beta) family, fibroblast growth factor (FGF) family, vascular endothelial growth factor (VEGF), granulocyte macrophage colony stimulating factor (GM-CSF), platelet-derived growth factor (PDGF), connective tissue growth factor (CTGF), interleukin (IL) family, and tumor necrosis factor-alpha family. Currently, patients are treated by three growth factors: PDGF-BB, bFGF, and GM-CSF. Only PDGF-BB has successfully completed randomized clinical trials in the Unites States. With gene therapy now in clinical trial and the discovery of biodegradable polymers, fibrin mesh, and human collagen serving as potential delivery systems other growth factors may soon be available to patients. This review will focus on the specific roles of these growth factors and cytokines during the wound healing process.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1524-475X.2008.00410.x

Growth factors and cytokines in wound healing.

Transforming growth factor-beta (TGF beta) is produced by most cultured cells in an inactive form. Potential activation mechanisms of latent TGF beta were studied using fibroblastic (NRK-49F and AKR-MCA) cell-conditioned medium as a model. Active TGF beta was monitored by radioreceptor and soft agar assays as well as by antibody inhibition and immunoprecipitation. Little or no TGF beta was detected in untreated conditioned medium. Treatment of the medium with extremes of pH (1.5 or 12) resulted in significant activation of TGF beta as shown by radioreceptor assays, while mild acid treatment (pH 4.5) yielded only 20-30% of the competition achieved by pH 1.5. In an effort to define more physiological means of TGF beta activation, the effects of some proteases were tested. Plasmin and cathepsin D were found to generate 25-kD bands corresponding to the active form of TGF beta as shown by immunoprecipitation analysis of radiolabeled cell-conditioned medium. Plasmin treatment of the medium resulted in activity that was quantitatively similar to that of mild acid treatment as measured by radioreceptor and soft agar assays. In addition, the plasmin-generated activity was inhibited by anti-TGF beta antibodies. Sequential treatments of AKR-MCA cell-conditioned medium with mild acid followed by plasmin or plasmin followed by mild acid gave activation comparable to either treatment alone. The data suggest that conditioned medium may contain at least two different pools of latent TGF beta. One pool is resistant to mild acid and/or plasmin and requires strong acid or alkali treatment for activation. A second pool is activated by mild pH change and/or plasmin. Activation of this form of latent TGF beta may take place by dissociation or proteolytic digestion from a precursor molecule or hypothetical TGF beta-binding protein complex.

https://rupress.org/jcb/article-pdf/106/5/1659/1056368/1659.pdf

Proteolytic activation of latent transforming growth factor-beta from fibroblast-conditioned medium.

Medium conditioned by Chinese hamster ovary (CHO) cells transfected with the simian pre-pro-TGF beta 1 cDNA contains high levels of latent TGF beta 1. The amino-terminal region of the TGF beta 1 precursor is secreted and can be detected in the conditioned medium by immunoblotting using peptide antibodies specific for amino-terminal peptides. Chemical cross-linking of CHO-conditioned medium using bis-(sulfosuccinimidyl)-suberate (BS3) followed by immunoblot analyses indicates that latent recombinant TGF beta 1 contains both the cleaved amino-terminal glycopeptide and mature TGF beta 1 polypeptide in a noncovalent association and that this association confers latency. The data presented here do not support the involvement of a unique TGF beta binding protein(s) in latent recombinant TGF beta 1. Plasmin treatment of CHO-conditioned medium resulted in the appearance of TGF beta competing activity. In addition, immunoblot analysis of plasmin-treated CHO-conditioned medium indicates that the amino-terminal glycopeptide is partially degraded and that mature TGF beta 1 is released. Thus, activation of latent TGF beta 1 may occur by proteolytic nicking within the amino-terminal glycopeptide thereby causing a disruption of tertiary structure and noncovalent bonds, which results in the release of active, mature TGF beta 1. Acid activation of latent TGF beta, in comparison, appears to be due to dissociation of the amino-terminal glycopeptide from the mature polypeptide.

/pdf/mechanism-of-activation-of-latent-recombinant-transforming-4t7ilkxzee.pdf

Mechanism of activation of latent recombinant transforming growth factor beta 1 by plasmin.

TGF-β1 inhibition of c-myc transcription and growth in keratinocytes is abrogated by viral transforming proteins with pRB binding domains

The cell biology of transforming growth factor β

Mechanisms of growth regulation by polypeptides include endocrine, paracrine and autocrine systems. Factors, such as hormones, which enter the circulatory system and effect target cells or tissues distant from their site of synthesis, are endocrine in nature. It has been postulated that some growth factors may function in an endocrine manner. Insulin-like growth factor, which is synthesized in the liver and enters the blood stream to affect distal tissues, is an example of endocrine action of a specific growth factor [1,2]. The paracrine mechanism of action suggests that growth factors synthesized by one cell type diffuse through the extracellular spaces to act on neighboring target cells. Finally, autocrine growth regulation may occur when cells are able to both synthesize and respond to a specific growth signal. The autocrine model of growth regulation was originated as a concept to explain the abnormal growth of cancer. This model hypothesizes that affected cells over-produce a stimulatory growth factor to which they respond, thus resulting in sustained, self-stimulated proliferation [3]. Although initially postulated to explain the unregulated growth of cancer cells, the autocrine mechanism of growth regulation, in addition to paracrine and endocrine systems, is likely to play an important role in normal cellular processes, including development, differentiation and proliferation [4, 5]. Thus local concentrations of growth factors and numbers of specific cell-surface receptors, will affect the biological response of cells to a particular growth factor. It is apparent, therefore, that regulated growth requires the complex interaction of many growth signals and that this interaction may be influenced by the synthesis and delivery of growth factors to target tissues. Of particular interest in the study of the regulation of cell proliferation are the transforming growth factors (TGF), for which paracrine and autocrine mechanisms have been postulated.

https://febs.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1432-1033.1990.tb15327.x

Russette M. Lyons

Papers

Proteolytic activation of latent transforming growth factor-beta from fibroblast-conditioned medium.

Mechanism of activation of latent recombinant transforming growth factor beta 1 by plasmin.

TGF-β1 inhibition of c-myc transcription and growth in keratinocytes is abrogated by viral transforming proteins with pRB binding domains

The cell biology of transforming growth factor β

Transforming growth factors and the regulation of cell proliferation.