The transforming growth factor beta (TGF-beta) family of growth factors control the development and homeostasis of most tissues in metazoan organisms. Work over the past few years has led to the elucidation of a TGF-beta signal transduction network. This network involves receptor serine/threonine kinases at the cell surface and their substrates, the SMAD proteins, which move into the nucleus, where they activate target gene transcription in association with DNA-binding partners. Distinct repertoires of receptors, SMAD proteins, and DNA-binding partners seemingly underlie, in a cell-specific manner, the multifunctional nature of TGF-beta and related factors. Mutations in these pathways are the cause of various forms of human cancer and developmental disorders.

TGF-beta signal transduction.

The healing of an adult skin wound is a complex process requiring the collaborative efforts of many different tissues and cell lineages. The behavior of each of the contributing cell types during the phases of proliferation, migration, matrix synthesis, and contraction, as well as the growth factor and matrix signals present at a wound site, are now roughly understood. Details of how these signals control wound cell activities are beginning to emerge, and studies of healing in embryos have begun to show how the normal adult repair process might be readjusted to make it less like patching up and more like regeneration.

https://science.sciencemag.org/content/sci/276/5309/75.full.pdf

Wound Healing--Aiming for Perfect Skin Regeneration

Werner, Sabine, and Richard Grose. Regulation of Wound Healing by Growth Factors and Cytokines. Physiol Rev 83: 835–870, 2003; 10.1152/physrev.00032.2002.—Cutaneous wound healing is a complex proce...

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Regulation of Wound Healing by Growth Factors and Cytokines

During the course of purifying nerve growth factor from the submaxillary gland of the mouse, Cohen (1960) and Levi-Montalcini and Cohen (1960) noticed that daily injections of certain gland extract fractions into newborn mice produced developmental changes that could not be ascribed to nerve growth factor. These changes included precocious opening of the eyelids (7 days compared to the usual 14 days) and a similar early eruption of the incisors. Using these gross anatomical changes as an assay, Cohen (1962) proceeded to isolate the active factor — a polypeptide which he termed epidermal growth factor (EGF).

Epidermal growth factor

The production of natural antibiotic peptides has emerged as an important mechanism of innate immunity in plants and animals. Defensins are diverse members of a large family of antimicrobial peptides, contributing to the antimicrobial action of granulocytes, mucosal host defence in the small intestine and epithelial host defence in the skin and elsewhere. This review, inspired by a spate of recent studies of defensins in human diseases and animal models, focuses on the biological function of defensins.

Defensins: antimicrobial peptides of innate immunity.

Epidermal regeneration following middermal injuries to skin requires both proliferation and migration of keratinocytes. Epidermal growth factor (EGF) stimulates the proliferation of keratinocytes in culture, and topical administration of EGF accelerates epidermal regeneration of partial thickness burns or split-thickness incisions in vivo. Transforming growth factor-alpha (TGF-alpha) and vaccinia growth factor (VGF) have substantial sequence homology with EGF, and all appear to bind to the same receptor protein. Whether TGF-alpha or VGF can affect epidermal wound healing in vivo is not known. The present studies show that topical administration of TGF-alpha or VGF in antibiotic cream to partial thickness burns (second degree) accelerated epidermal regeneration in comparison with untreated or vehicle-treated burns. Low levels of both TGF-alpha and VGF (0.1 microgram per milliliter) appeared to be more effective than EGF in stimulating epidermal regeneration. Regenerated epithelium from burns treated with TGF-alpha or VGF appeared normal histologically. This finding suggests that topical application of selected growth factors may be useful in accelerating healing of partial thickness injuries.

https://science.sciencemag.org/content/sci/235/4786/350.full.pdf

Epithelial wound healing enhanced by transforming growth factor-alpha and vaccinia growth factor

Recombinant type 1 transforming growth factor beta (TGF-beta) was expressed to high levels in CHO cells by using dihydrofolate reductase (dhfr) gene amplification. The expression plasmid was derived from the pSV2 vectors and contained, in tandem, the simian TGF-beta and mouse dhfr cDNAs. Transcription of both cDNAs was controlled by the simian virus 40 early promoter. Stepwise selection of transfected CHO cells in increasing concentrations of methotrexate yielded cell lines that expressed amplified TGF-beta nucleic acid sequences. The expression plasmid DNA was amplified greater than 35-fold in one of the methotrexate-selected transfectants. The major proteins secreted by these cells consisted of latent TGF-beta and TGF-beta precursor polypeptides, as judged by immunoblots by using site-specific anti-peptide antibodies derived from various regions of the TGF-beta precursor. Levels of recombinant TGF-beta protein secreted by these cells approached 30 micrograms/24 h per 10(7) cells and required prior acidification for optimal activity; nonacidified supernatants were approximately 1% as active as acidified material. Antibodies directed toward sequences present in the mature growth factor readily identified a proteolytically processed recombinant TGF-beta which, on sodium dodecyl sulfate-polyacrylamide gels, comigrated with highly purified natural TGF-beta. In addition to mature recombinant TGF-beta, site-specific antibodies demonstrated the existence of larger TGF-beta precursor polypeptides. The availability of biologically active recombinant type 1 TGF-beta and precursor forms should provide a means to examine the structure, function, and potential in vivo therapeutic use of this growth factor.

Type 1 transforming growth factor beta: amplified expression and secretion of mature and precursor polypeptides in Chinese hamster ovary cells.

Epidermal growth factor (EGF) and transforming growth factor type I (TGF) are polypeptides of 53 and 50 amino acid residues, respectively1,2. Both bind to EGF receptor, a 1,200-residue transmembranous glycoprotein3, leading to phosphorylation of the receptor, enhancement of its tyrosine-specific kinase activity and ultimately to stimulation of cell growth4,5. We report here that a 140-residue polypeptide encoded by one of the early genes of vaccinia virus (VV)6 is related closely to EGF and TGF. The presence of putative signal and transmembranous sequences further suggests that the viral protein might be an integral membrane protein, but that, as in the case of EGF itself7,8, the membrane-associated form may be the precursor of a soluble growth factor. Production of EGF-like growth factors by virally infected cells could account for the proliferative diseases associated with members of the poxvirus family such as Shope fibroma virus9, Yaba tumour virus10, and molluscum contagiosum virus (MCV)11.

Vaccinia virus encodes a polypeptide homologous to epidermal growth factor and transforming growth factor.

The vaccinia virus growth factor (VGF) gene encodes a polypeptide with amino acid sequence homology to epidermal growth factor (EGF) and transforming growth factor alpha and is present twice, once at each end of the virus genome within the inverted terminal repetition. Recombination procedures were used to replace more than half of both VGF genes with a beta-galactosidase cassette which served as a color indicator for isolating an unconditionally viable VGF- mutant. The VGF- mutant genotype and phenotype were confirmed by Southern blot analysis and assays for functional growth factor. The plaque-forming efficiencies of VGF- and wild-type (WT) viruses were similar in a variety of cell types containing low or high densities of EGF receptors, suggesting a lack of a specific requirement for either VGF or the EGF receptor in the initiation of virus infection. The yield of VGF- virus was similar to that of WT virus in growing BS-C-1 and Swiss 3T3 cells, but lower in resting Swiss 3T3 cells. The greatest differences between VGF- and WT virus occurred in vivo: higher doses of VGF- virus than WT virus were required for intracranial lethality in mice and for production of skin lesions in rabbits. Thus, expression of the VGF gene is important to the virulence of vaccinia virus. Images

Deletion of the vaccinia virus growth factor gene reduces virus virulence.

We have obtained a cDNA clone coding for human transforming growth factor (TGF)-β2. The clone was isolated from a tamoxifen-treated human prostatic adenocarcinoma cell line (PC-3) using oligonucleotide probes based on the partial amino acid sequence of purified TGF-β2. The cDNA sequence predicts that TGF-β2 is synthesized as a 442-amino-acid polypeptide precursor from which the mature 112-amino-acid TGF-β2 subunit is derived by proteolytic cleavage. The proteins coded for by the human TGF-β1 and TGF-β2 cDNAs show an overall homology of 41%. The mature and amino-terminal precursor regions show 71% and 31% homology, respectively. Northern blot analysis identified TGF-β2 transcripts of 4.1, 5.1, and 6.5 kb using mRNA from several different sources. Analysis of polyadenylated RNA from tamoxifen-treated PC-3 cells showed that these cells contain higher numbers of transcripts for TGF-β1 than for TGF-β2, although they produce more TGF-β2 protein than TGF-β1. This suggests that there is a post-transcript...

Daniel R. Twardzik

Papers

Epithelial wound healing enhanced by transforming growth factor-alpha and vaccinia growth factor

Type 1 transforming growth factor beta: amplified expression and secretion of mature and precursor polypeptides in Chinese hamster ovary cells.

Vaccinia virus encodes a polypeptide homologous to epidermal growth factor and transforming growth factor.

Deletion of the vaccinia virus growth factor gene reduces virus virulence.

Transforming growth factor-beta 2: cDNA cloning and sequence analysis.