Maria C. Birchenall-Roberts

Transcriptional regulation of the transforming growth factor beta 1 promoter by v-src gene products is mediated through the AP-1 complex.

Growth factor-independent 32D-src and 32D-abl cell lines, established by infecting the interleukin-3-dependent myeloid precursor cell line (32D-123) with retroviruses containing the src or abl oncogene, were used to study transcriptional regulation of transforming growth factor beta 1 (TGF-beta 1) mRNA. Analysis of different TGF-beta 1 promoter constructs regulated by pp60v-src indicated that sequences responsive to high levels of src induction contain binding sites for AP-1. Both src and serum induced expression of the c-fos and c-jun genes in myeloid cells, resulting in transcriptional activation of the TGF-beta 1 gene. We found that serum treatment increased TGF-beta 1 mRNA levels in 32D-123 cells and that the v-Src protein could replace the serum requirement by stimulating binding to the AP-1 complex of the TGF-beta 1 promoter, thereby mediating the induction of TGF-beta 1 transcription.

28. – Transforming Growth Factor β1

Publisher Summary This chapter focuses on transforming growth factor-β1 (TGF-β1). The human TGF-β1 precursor is encoded by seven exons and has a very GC-rich region with several Sp1 binding sites. The TGF-β1 precursor is 390 amino acids (aa) long and contains an amino-terminal hydrophobic signal sequence (aa 1–23) for translocation to the endoplasmic reticulum to undergo exocytosis. TGF-β1 regulates the adhesiveness of cells at various levels that include increased synthesis of extracellular matrix protein expression, control of matrix-degrading proteases and protease inhibitors, and increased expression of cell surface receptors (integrins) for cell adhesion proteins. The genes for murine TGF-β1 are located on chromosome 7, and these genes encode seven exons ranging in size from 78 to 357 bp with all the intron–exon junctions conserved except the exon 6/7 junction. The primary and secondary structures of murine TGF-β1 are virtually identical to those of the human molecule. Mouse embryos of 9–16 days old express TGF-β1 mRNAs in their bone liver and hematopoietic cells, with high levels seen in megakaryocytes, osteoclasts, and mesenchymal and epithelial tissues. Among mammals, the TGF-β1 protein is highly conserved, and it is identical in man, pig, and cow but differs by only one aa in mice. The primary and secondary structure of murine TGF-β1 is virtually identical to that of the human molecule.

Transforming growth factor-beta1 in heart development

Abstract Defined biochemical stimuli regulating neonatal ventricular myocyte (cardiomyocyte) development have not been established. Since cardiomyocytes stop proliferating during the first 3–5 days of age in the rodent, locally generated ‘anti-proliferative’ and/or differentiation signals can be hypothesized. The transforming growth factor-beta (TGF-β) family of peptides are multifunctional regulators of proliferation and differentiation of many different cell types. We have determined in neonatal and maturing rat hearts that TGF- β 1 gene expression occurs in pups of both normotensive (Wistar Kyoto, WKY) and hypertrophy-prone rats (spontaneously hypertensive, SHR). TGF- β 1 transcript levels were readily apparent in total ventricular RNA from SHR pups within 1 day of age and elevated in 3–7 day old WKY and SHR hearts when cardiomyocyte proliferation indices are diminished. TGF- β 1 transcript levels remain at a ‘relatively’ high level throughout maturation and into adulthood in both strains. Further, TGF- β 1 transcripts were localized to cardiomyocytes of neonatal rat ventricular tissue sections by in situ hybridization. Immunoreactive TGF-β was co-localized to the intracellular compartment of neonatal cardiomyocytes at the light and electron microscopic level. In vitro analysis using primary cultures of fetal and neonatal cardiomyocytes indicated that TGF-βs inhibit mitogen stimulated DNA synthesis and thymidine incorporation. From these data, we propose that locally generated TGF-βs may act as autocrine and/or paracrine regulators of cardiomyocyte proliferation and differentiation as intrinsic components of a multifaceted biochemical regulatory process governing heart development.

Role of Transforming Growth Factor‐β1 in Regulation of Hematopoiesisab

The data presented above suggest that one possible clinical use of TGF-beta would be to protect the bone marrow from the effects of myelosuppressive chemotherapeutic drugs by preventing entry or removing primitive stem cells from the cell cycle. It may also have the additional benefit of reducing the drug-induced neutrophil nadir by stimulating granulopoiesis. The availability of large quantities of recombinant TGF-beta will allow study of the pharmacokinetics with different routes of administration, dosage effects, and details of the pleiotropic effects on other cell systems. Experiments are in progress to determine whether TGF-beta will allow the delivery of higher amounts or more frequent doses of chemotherapeutic drugs and thus allow increased antitumor efficacy in tumor-bearing animals.

Nuclear localization of v-Abl leads to complex formation with cyclic AMP response element (CRE)-binding protein and transactivation through CRE motifs.

Deregulated expression of v-abl and BCR/abl genes has been associated with myeloproliferative syndromes and myelodysplasia, both of which can progress to acute leukemia. These studies identify the localization of the oncogenic form of the abl gene product encoded by the Abelson murine leukemia virus in the nuclei of myeloid cells and the association of the v-Abl protein with the transcriptional regulator cyclic AMP response element-binding protein (CREB). We have mapped the specific domains within each of the proteins responsible for this interaction. We have shown that complex formation is a prerequisite for transcriptional potentiation of CREB. Transient overexpression of the homologous cellular protein c-Abl also results in the activation of promoters containing an intact CRE. These observations identify a novel function for v-Abl, that of a transcriptional activator that physically interacts with a transcription factor.