Opposite effects of transforming growth factor alpha and epidermal growth factor on mouse placental lactogen I secretion

Cited1 is required in trophoblasts for placental development and for embryo growth and survival

Cited1 is a transcriptional cofactor that interacts with Smad4, estrogen receptors alpha and beta, TFAP2, and CBP/p300. It is expressed in a restricted manner in the embryo as well as in extraembryonic tissues during embryonic development. In this study we report the engineering of a loss-of-function Cited1 mutation in the mouse. Cited1 null mutants show growth restriction at 18.5 days postcoitum, and most of them die shortly after birth. Half the heterozygous females, i.e., those that carry a paternally inherited wild-type Cited1 allele, are similarly affected. Cited1 is normally expressed in trophectoderm-derived cells of the placenta; however, in these heterozygous females, Cited1 is not expressed in these cells. This occurs because Cited1 is located on the X chromosome, and thus the wild-type Cited1 allele is not expressed because the paternal X chromosome is preferentially inactivated. Loss of Cited1 resulted in abnormal placental development. In mutants, the spongiotrophoblast layer is irregular in shape and enlarged while the labyrinthine layer is reduced in size. In addition, the blood spaces within the labyrinthine layer are disrupted; the maternal sinusoids are considerably larger in mutants, leading to a reduction in the surface area available for nutrient exchange. We conclude that Cited1 is required in trophoblasts for normal placental development and subsequently for embryo viability.

Effects of tumor necrosis factor-alpha, epidermal growth factor and transforming growth factor-alpha on interleukin-8 production by, and human rhinovirus replication in, bronchial epithelial cells

Previous studies have shown that the epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha), members of the EGF growth factor family, regulate processes involved in airway repair after injury. Our studies were conducted to determine whether EGF and TGF-alpha directly control processes involved in the pathogenesis of airway inflammation and/or modulate the inflammatory effects of TNF-alpha in the airway mucosa. We have found that these cell growth factors directly induced interleukin-8 (IL-8) production by an immortalized human bronchial epithelial cell line (BEAS-2B cells). Furthermore, EGF and TGF-alpha enhanced tumor necrosis factor-alpha (TNF-alpha) induced IL-8 production by BEAS-2B cells. On the other hand, EGF but not TGF-alpha increased viral replication by BEAS-2B cells exposed to HRV-14. Moreover, TNF-alpha increased viral replication in the presence of EGF but not TGF-alpha. In conclusion, this study demonstrates that both EGF and TGF-alpha play an active role in the pathogenesis of airway inflammation.

Chronic ethanol ingestion impairs TGF-alpha-stimulated receptor autophosphorylation

The effects of chronic ethanol feeding on the binding of transforming growth factor-alpha (TGF-alpha) and TGF-alpha-stimulated receptor autophosphorylation were investigated in isolated rat hepatocytes. When hepatocytes were isolated from rats that were fed an ethanol liquid diet for 6-8 weeks, these cells exhibited a marked impairment of TGF-alpha-stimulated autophosphorylation of the receptor that binds this growth factor compared with hepatocytes from the pair-fed controls. This impaired autophosphorylation of receptor tyrosine residues was accompanied by significant decreases in the amount of surface-bound TGF-alpha. Immunoanalysis indicated no changes in receptor number, indicating that decreased receptor content was not responsible for decreased TGF-alpha binding in the hepatocytes from the ethanol-fed rats. In conclusion, chronic ethanol feeding reduced TGF-alpha binding to hepatocytes with a concomitant decrease in the ability of the receptor tyrosine kinase to autophosphorylate its tyrosine residues. These changes were not accompanied by decreased receptor protein content. These defects could lead to altered signal transduction and to impaired reparative and regenerative processes in the liver.

Regulation of mouse placental lactogen-II secretion by transforming growth factor-alpha after midpregnancy

We investigated whether transforming growth factor-alpha (TGF-alpha) regulates mouse placental lactogen-II (mPL-II) secretion by cells from day 12 of pregnancy. TGF-alpha significantly inhibited mPL-II secretion by the third and fourth day of culture, and then stimulated mPL-II secretion from the sixth day. The inhibitory and stimulatory effects of TGF-alpha on mPL-II secretion were dose-dependent, and the lowest concentration of TGF-alpha-which caused significant inhibition or stimulation of mPL-II secretion was 10 ng/ml. When TGF-alpha treatment of placental cells was begun on the fifth day of the culture, significant stimulation of mPL-II secretion was observed 3 days later. TGF-alpha inhibited steady-state levels of mPL-II mRNA on the third day of culture but stimulated steady-state levels of mPL-II mRNA on the seventh day of culture. These results suggest that TGF-alpha biphasically regulates mPL-II secretion through regulation of mPL-II gene expression after midpregnancy.

Regulation of mouse placental lactogen secretion by G proteins before midpregnancy

To determine whether G proteins are involved in the regulation of mouse placental lactogen-I (mPL-I) and/or mPL-II secretion before midpregnancy, mouse placental tissue from day 7 of pregnancy was dispersed with collagenase, cells were fractionated on a percoll gradient, and the purified trophoblast cells were cultured in a serum-free medium with cholera toxin (CTX) or pertussis toxin (PTX) which modulate the activities of distinct G proteins for 5 days. CTX inhibited both mPL-I and mPL-II secretion, but PTX inhibited mPL-I secretion and stimulated mPL-II secretion in a time- and dose-dependent manner. Addition of both CTX and PTX additionally inhibited mPL-I secretion but did not affect mPL-II secretion. 8-Bromo cAMP, which increases intracellular cAMP accumulation, inhibited both mPL-I and mPL-II secretion similarly to CTX. In contrast, H8, an inhibitor of cAMP-dependent protein kinase A, stimulated both mPL-I and mPL-II secretion. Addition of PTX and H8 synergistically stimulated mPL-II secretion. These findings suggest that G proteins play important roles in regulation of mPL-I and mPL-II secretion before midpregnancy.

Lipopolysaccharides selectively inhibit mouse placental lactogen-II secretion through stimulation of interleukin-1 alpha (IL-1 alpha) and IL-6 production

To determine whether lipopolysaccharides (LPS) regulate mouse placental lactogen-I (mPL-I), mPL-II, and mouse GHRF (mGHRF) secretion, mouse placental tissue from days 7, 9, and 12 of pregnancy was dispersed with collagenase and the purified trophoblast cells were cultured in a serum-free medium with or without LPS for 5 days. LPS significantly inhibited mPL-II secretion by cells from days 9 and 12 of pregnancy. However, LPS did not affect mPL-II secretion by cells from day 7 of pregnancy, mPL-I secretion by cells from days 7 and 9 of pregnancy, or mGHRF secretion by cells from day 12 of pregnancy. The inhibitory effect of LPS on mPL-II secretion by cells from day 12 of pregnancy was dose-dependent. Steady-state levels of mPL-II mRNA were significantly reduced by incubation of placental cells from day 12 of pregnancy with LPS. The inhibitory effect of LPS on mPL-II secretion was abolished by the addition of antibodies to IL-1 alpha and IL-6. These findings suggest that LPS selectively inhibit mPL-II secretion, at least partly through increases in IL-1 and IL-6 production, after midpregnancy.

Enhanced modulation of keratinocyte motility by transforming growth factor-alpha (TGF-alpha) relative to epidermal growth factor (EGF)

Epidermal growth factor (EGF) and transforming growth factor (TGF)-alpha are high-affinity polypeptide ligands for the EGF receptor, which mediates their biologic activities. In this study, we directly compared the actions of both ligands in promoting keratinocyte motility. We found that normal and tumorigenic human keratinocytes responded to activation of the EGF receptor by either EGF or TGF-alpha; however, the two ligands did not elicit identical responses with regard to cell locomotion. TGF-alpha was more effective than EGF at promoting colony dispersion (cell scattering), in vitro wound closure, and single-cell migration as assessed by phagokinetic track analysis. In contrast, EGF and TGF-alpha evoked identical profiles for DNA synthesis with regard to concentration dependence and magnitude of response in normal keratinocytes and in a squamous cell carcinoma line. The overall pattern of tyrosine phosphorylation of intracellular substrates was similar when cells were stimulated with either growth factor; however, a limited number of differences in the kinetics or magnitude of protein phosphorylation were detected in subcellular fractions. These findings demonstrate that two growth factors implicated in promoting mitogenesis and locomotion may elicit divergent responses with regard to one biologic activity while retaining similar responses for other activities. This suggests that ligand-mediated mitogenic responses may not be tightly coupled to motogenic activity and further illustrates the multifunctional roles of polypeptide growth factors.

Transforming growth factor-alpha regulates subpopulation of giant cells which secrete mouse placental lactogen-I (mPL-I) and/or mPL-II at midpregnancy

The aim of this study was to determine whether transforming growth factor-alpha (TGF-alpha) regulates expression of mouse placental lactogen-I (mPL-I) and mPL-II at midpregnancy in vitro. Treatment of placental cells from day 9 of pregnancy with TGF-alpha resulted in stimulation of mPL-I secretion and inhibition of mPL-II secretion in a time- and dose-dependent manner without changing the amount of newly synthesized trichloroacetic acid precipitable proteins and cell viability. Moreover, TGF-alpha increased the intra-cellular mPL-I concentration and immuno-precipitable newly synthesized mPL-I concentration both in the medium and cells. TGF-alpha increased the number of cells containing only mPL-I and cells containing both mPL-I and mPL-II, but decreased that of the cells containing only mPL-II assessed by double immunocytochemistry. TGF-alpha increased the number of cells releasing only mPL-I but decreased the number of cells releasing only mPL-II, however TGF-alpha did not affect the number of cells releasing both mPL-I and mPL-II assessed by sequential reverse hemolytic plaque assay (RHPA). TGF-alpha decreased the expression of mPL-II mRNA, but did not change the expression of mPL-I mRNA. In situ hybridization for epidermal growth factor receptor (EGF-R) after RHPA for mPL-I indicated that giant cells releasing mPL-I express EGF-R mRNA. These findings suggest that TGF-alpha regulates the subpopulation of giant cells which produces and releases mPL-I and mPL-II and it results in an increase of mPL-I secretion and decrease of mPL-II secretion, and suggests possible post-transcriptional stimulation of mPL-I secretion and transcriptional inhibition of mPL-II secretion by TGF-alpha. Giant cells releasing mPL-I express EGF-R mRNA, suggesting direct regulation of giant cell differentiation by EGF and TGF-alpha at midpregnancy.