Mitogenic Effect Of TGF-alpha Research Articles

Activation of the human transforming growth factor alpha (TGF-alpha) gene by the hepatitis B viral X protein (HBx) through AP-2 sites.

The HBx protein is known as a transactivator and potential oncogene, and TGF-alpha as a potent mitogen in hepatocellular carcinoma. By assays of serial deletion of the promoter of TGF-alpha gene and the cotransfection of HBx and AP-2 expression vectors, we observed that the HBx significantly activated the promoter activity through AP-2 sites located in the proximal region of the TGF-alpha promoter (-136 to -30). This effect was also observed in the heterologous promoter assay system containing AP-2 sites. The mutation analyses of three AP-2 sites in the promoter revealed that all three AP-2 sites contributed to the activation of the TGF-a gene in the presence of HBx. Accordingly, the mRNA level of TGF-alpha was significantly elevated in the HBx-expressing cell, HepG2-HBx and the HBV-producing cell, HepG2-K8. These results suggest that the HBx protein could increase the mitogenic effect of TGF-alpha by the transactivation of the gene through AP-2 binding sites and consequently, these interactions may accelerate the process of hepatocarcinogenesis.

Epidermal growth factor receptor mRNA and protein are expressed in progenitor cells of the olfactory epithelium.

Olfactory receptor neurons are continuously replaced postnatally through the initiation of the division and terminal differentiation of progenitor cells located in the basal layer of the olfactory epithelium. Although the factors that regulate this process in vivo are not known, recent in vitro studies demonstrated that members of the epidermal growth factor (EGF) family including transforming growth factor-alpha (TGF alpha) and EGF are highly potent in promoting the proliferation of progenitor cells, suggesting a role for the EGF receptor (EGFR), which is the molecular receptor for both mitogens. We have examined the expression of EGFR mRNA and protein in the olfactory epithelium by using reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis and have examined their cellular localization with in situ RT-PCR and immunocytochemistry. RT-PCR and Southern blot analysis demonstrated that EGFR mRNA is expressed in the olfactory mucosa and also in the positive control tissues, kidney and tongue. The 170-kDa EGFR protein was identified with Western blot analysis in the olfactory epithelium and control tissues. Our results using in situ RT-PCR localized EGFR mRNA-expressing cells more extensively in the basal cell layer of the epithelium than did the immunocytochemical methods. These results suggest that EGFR mediates the mitogenic effect of TGF alpha and/or EGF on the quiescent basal cells to initiate the cell cycle.

Tyrosine kinase activity is necessary for growth factor-stimulated rabbit type II pneumocyte proliferation.

Tyrosine kinases are important in the signal transduction of a number of growth factors. As shown previously, transforming growth factor (TGF)-alpha stimulated proliferation of type II cells in vitro. The mitogenic effect of TGF-alpha could be blocked by the addition of the tyrosine kinase inhibitors genistein or tyrphostin. Tyrosine phosphorylation in type II cells exposed to growth factors was examined using an antiphosphotyrosine antibody. After addition of TGF-alpha, phosphorylation of a tyrosine protein with a molecular mass of 170 kD, presumed to be the epidermal growth factor receptor (EGF-R), peaked by 5 min, returning to baseline by 30 min. As expected, genistein or tyrphostin decreased the TGF-alpha-induced phosphorylation of the EGF-R. Addition of TGF-beta resulted in no newly phosphorylated tyrosine proteins. TGF-beta decreased the TGF-alpha-induced phosphorylation of the EGF-R. Previous work has shown that TGF-beta blocks the TGF-alpha stimulation of type II cell proliferation. It appears that TGF-beta interferes with TGF-alpha-induced phosphorylation of the EGF-R.

TGF-alpha can act as morphogen and/or mitogen in a colon-cancer cell line.

Transforming growth factor alpha (TGF-alpha) has multifunctional biological effects on a variety of mesenchymal and epithelial cells. It is a potent mitogen for a number of normal and transformed cell types, regulates extracellular matrix (ECM) production and promotes breast, kidney and lung morphogenesis. To clarify the role of ECM proteins in the morphogenetic and mitogenic effects of TGF-alpha, we have used a human colon carcinoma cell line (SW1222) which expresses EGF receptor. Here we show that TGF-alpha at 1 ng/ml increases the proliferation of SW1222 cells, but only when they are cultured on plastic rather than collagen-coated plates. Higher concentrations of TGF-alpha (10 ng/ml) did not increase cell proliferation but significantly enhanced the crypt-like glandular differentiation when cells were grown in 3-dimensional collagen gel (p = 0.027). These effects were accompanied by increased expression of alpha 2 beta 1 and alpha 3 beta 1 integrin molecules, which are receptors for extracellular matrix proteins, and by a statistically significant increase in binding of SW1222 cells to type-1 collagen. The effects of TGF-alpha both on binding to type-1 collagen and on morphological differentiation in 3-dimensional collagen gel were inhibited by monoclonal antibodies recognizing the alpha 2 beta 1 integrin. These data indicate that the morphogenetic or mitogenic activities of TGF-alpha are critically dependent on cellular interactions with extracellular matrix proteins and are primarily mediated by the alpha 2 beta 1 integrin receptor. Inappropriate expression of this growth factor, seen in tumours whose cell-matrix interactions are greatly impaired, could have deleterious effects on the maintenance of normal tissue architecture and growth control.

Growth factors alter neonatal type II alveolar epithelial cell proliferation.

The type II alveolar epithelial cell plays a critical role in the repair of lung injury by repopulating the entire damaged alveolar epithelium. We report our studies of the effects of known growth factors on the in vitro proliferation of isolated neonatal rabbit type II cells. Transforming growth factor-alpha (TGF-alpha) and epidermal growth factor (EGF) increased [3H]thymidine incorporation, cell number, and labeling index above control. Transforming growth factor-beta (TGF-beta) decreased [3H]thymidine incorporation, cell number, and labeling index compared with control. When added simultaneously, TGF-beta blocked the stimulatory effect of TGF-alpha or EGF. If TGF-alpha is added before TGF-beta, the ability of TGF-beta to block the mitogenic effect of TGF-alpha was diminished the later in time TGF-beta was added. If TGF-beta was added first, later addition of TGF-alpha had no effect. The current work demonstrates that specific growth factors, including some known to be produced by other lung cells, alter the proliferation in vitro of isolated neonatal rabbit type II alveolar epithelial cells.

Effect of TGF‐Alpha on growth of normal human breast epithelial cells in serum‐free primary culture using 3‐dimensional collagen gels.

The mitogenic effect of TGF-alpha, acidic-FGF, basic-FGF and lithium on normal human breast epithelial cells was studied in a collagen gel culture system using a serum-free 1:1 mixture of Ham's F12 and DME medium containing insulin, cholera toxin and bovine serum albumin. TGF-alpha elicited a strong mitogenic response in a dose dependent manner. Addition of cortisol to TGF-alpha stimulated growth over and above that achieved with TGF-alpha alone. A consistent observation has been the effect of a combination of TGF-alpha and cortisol on growth stimulation of normal human breast epithelial cells resulting in 3-12 fold growth after 11-13 days in culture. Acidic-FGF, basic-FGF and lithium were not growth promoting.