Role of TGF alpha and its receptor in proliferation of immortalized rat tracheal epithelial cells: studies with tyrphostin and TGF alpha antisera

We have shown in the present study and in studies reported previously that preneoplastic and neoplastic rat tracheal epithelial (RTE) cell lines express TGF alpha and do so regardless of the mechanism by which they were transformed. In order to determine whether TGF alpha is an autocrine growth regulator of immortalized RTE cells, we have examined the function of TGF alpha/EGF receptors and the growth requirements for TGF alpha in these cells. The level of immunoprecipitated TGF alpha/EGF receptor protein in immortalized RTE cells was similar to or less than levels in primary RTE cells, indicating that chemically induced transformation of RTE cells does not involve overexpression of TGF alpha/EGF receptors. Scatchard analysis of TGF alpha/EGF receptors in the neoplastic EGV5T cell line revealed the presence of high-affinity (Kd = 0.4 nM) and low-affinity (Kd = 9.8 nM) binding sites. A tyrphostin TGF alpha/EGF receptor tyrosine kinase inhibitor decreased in a dose-dependent manner the proliferation as well as EGF-induced autophosphorylation of the TGF alpha/EGF receptor of transformed RTE cells. The inhibitory effect of tyrphostin on proliferation and receptor kinase activity was attenuated in late log and plateau phase cultures. The phosphotyrosine content of several other EGF-dependent and independent phosphoproteins was also decreased by the tyrphostin. Proliferation of transformed RTE cells was also inhibited when TGF alpha antisera was added to the media of growing cells. These data are consistent with the hypothesis that proliferation of transformed RTE cells involves autocrine regulation by TGF alpha and its receptor.     

TGF beta 2, LIF and FGF2 cooperate to induce nephrogenesis

The metanephric kidney develops from interactions between the epithelial ureteric bud and adjacent metanephric mesenchyme, which is induced by the bud to form the epithelia of the nephron. We have found that leukemia inhibitory factor (LIF) and transforming growth factor beta 2 (TGF beta 2) are secreted by inductive rat bud cells and cooperate to enhance and accelerate renal tubule formation in uninduced rat metanephric mesenchymal explants. LIF alone or TGF beta 2 with fibroblast growth factor 2 induced numerous tubules in isolated mesenchymes over an 8 day period, while (in combination) all three caused abundant tubule formation in 72 hours. Furthermore, neutralization of Wnt ligands with antagonist-secreted Frizzled-related protein 1 abrogated these responses and combinatorial cytokine/growth factor stimulation of explants augmented nuclear activation of Tcf1/Lef1, suggesting that LIF and TGF beta 2/FGF2 cooperate to regulate nephrogenesis through a common Wnt-dependent mechanism.     

Expression of transforming growth factor alpha (TGF alpha) in differentiated rat mammary tumors: estrogen induction of TGF alpha production

Primary well-differentiated dimethylbenzene alpha-anthracene (DMBA)-or nitrosomethylurea (NMU)-induced rat mammary adenocarcinomas that are estrogen dependent possess biologically active and immunoreactive transforming growth factor alpha (TGF alpha), which can be detected in a sort agar growth-promoting assay and by a specific liquid-phase competitive RIA, respectively. In contrast, tissue extracts prepared from transplantable undifferentiated DMBA-I and NMU-II rat mammary carcinomas that are estrogen independent and metastatic exhibit low or undetectable levels of TGF alpha. In addition, the primary DMBA- and NMU-induced rat mammary adenocarcinomas express a specific 4.8-kilobase TGF alpha mRNA species, whereas little or no TGF alpha mRNA can be detected in the transplantable DMBA-I and NMU-II tumors. Primary tumors synthesize type IV basement membrane collagen, whereas the transplantable tumors elaborate very little type IV collagen. Either TGF alpha or estrogens can differentially enhance the synthesis of type IV collagen by 0.5- to 4-fold over total protein synthesis in primary cultures of normal mouse mammary epithelial cells or in primary NMU-induced tumor cells, respectively. Therefore, TGF alpha could function as an estrogen-inducible autocrine growth factor for well differentiated rat mammary tumor cells by its ability to selectively regulate type IV collagen synthesis. Estrogens can modulate TGF alpha production in vivo in primary DMBA-induced rat mammary tumors, because ovariectomy results in a rapid decline (within 6 h) of TGF alpha mRNA levels. This response to estrogens can also be observed in vitro. Primary DMBA- or NMU-induced rat mammary tumor cells cultured in the presence of 17 beta-estradiol (10(-8) M) for 4 days show an increase in the level of TGF alpha mRNA over cells not treated with estrogen. This increase in TGF alpha mRNA is paralleled by a 2- to 3-fold increase in the levels of immunoreactive TGF alpha that can be detected and in the conditioned medium from estrogen-treated cells. These results suggest that TGF alpha may be an adjunct marker for those mammary tumors that are well differentiated adenocarcinomas and estrogen dependent and that estrogen-independent tumors do not constitutively produce TGF alpha or express TGF alpha mRNA.     

Spatial and temporal expression patterns of GDNF family receptor alpha4 in the developing chicken retina

GDNF family receptor alpha (GFRalpha) receptors are involved in the regulation of different aspects of embryonic development such as proliferation, migration, differentiation and survival. To determine the possible role of GFRalpha4 in retinal development, we analysed its expression in the developing chicken retina. We found that GFRalpha4 is temporally co-expressed with c-ret. Both, the temporal and spatial expression of GFRalpha4 is developmentally regulated during retinogenesis and is first detected in cells of the ganglion cell layer at E6. As development of the retina proceeds, the expression of GFRalpha4 extends to cells of the inner half of the inner nuclear layer and to cells of the outermost cell row of the inner nuclear layer. Later on, GFRalpha4 expression is also found in additional cells of the outer half of the inner nuclear layer and in a subpopulation of photoreceptors. A central-to-peripheral gradient of retinal differentiation is evident, as the onset of GFRalpha4 expression is first detectable in the central retina, while it is delayed by two days in its periphery.     

The effect of TGF alpha on intestinal solute transport.

The effect of transforming growth factor alpha (TGF alpha) and epidermal growth factor (EGF) on 3-O-methylglucose transport was examined in vitro under short-circuited conditions in stripped rabbit jejunum. Mucosal EGF, 60 ng/ml, stimulated a significant increase in net 3-O-methylglucose transport (Jnet 0.67 +/- 0.15 vs. 0.90 +/- 0.15 microEq/cm2/h; P less than 0.03; n = 6) due to an increased mucosal to serosal flux (Jms 1.2 +/- 0.2 vs. 1.5 +/- 0.2 microEq/cm2/h; P less than 0.03). In contrast, TGF alpha, when applied to both mucosal and serosal surfaces at concentrations of either 60 (n = 6) or 150 (n = 9) ng/ml had no effect on either mucosal to serosal (Jms) or net transport (Jnet) of 3-O-methylglucose. TGF alpha did induce a significant increase in the serosal to mucosal flux (Jsm 60 ng/ml 0.44 +/- 0.02 vs. 0.51 +/- 0.03, 150 ng/ml 0.55 +/- 0.03 vs. 0.64 +/- 0.05 microEq/cm2/h; P less than 0.05). When brush border surface area was examined after exposure to either 60 ng/ml TGF alpha or saline vehicle for 2 h in in vivo isolated jejunal loops no significant difference was found (control 53 +/- 1.9; n = 35 vs. TGF alpha 52 +/- 1.9 microns 2; n = 29). Bioactivity of transforming growth factor alpha was assessed by an gastric acid secretion bioassay and found to be intact. These data provide further evidence for separate and distinct functional roles for these peptides in some biological systems.     

Transforming growth factor-beta (TGF beta) inhibits TGF alpha expression in bovine anterior pituitary-derived cells.

Transforming growth factor-beta 1 (TGF beta 1) is a multifunctional regulator of cell growth and differentiation. We report here that TGF beta 1 decreased the proliferation of nontransformed bovine anterior pituitary-derived cells grown in culture. We have previously demonstrated that these cells express both TGF alpha and its receptor [the epidermal growth factor (EGF) receptor] and that expression can be stimulated by phorbol ester (TPA) and EGF. TGF beta 1 treatment over a 2-day period decreased the proliferation of pituitary cells. This decreased growth rate was accompanied by a decrease in the TGF alpha mRNA level. The effect of TGF beta 1 on TGF alpha mRNA down-regulation was both dose dependent (maximal effect observed at 1.0 ng/ml TGF beta 1) and time dependent (minimum of 2-day treatment with TGF beta 1 was required before a decrease in TGF alpha mRNA was observed). Studies on TGF alpha mRNA stability indicated that TGF beta 1 did not alter the TGF alpha mRNA half-life. Treatment of the TGF beta 1 down-regulated cells with EGF resulted in the stimulation of TGF alpha mRNA levels; thus, the TGF beta 1-treated cells remained responsive to EGF. The decreased proliferation in response to TGF beta 1 could be only partially reversed by simultaneous treatment of the cells with EGF (10(-9)M) and TGF beta 1 (3.0 ng/ml). Qualitatively, the TGF beta 1-induced reduction of TGF alpha mRNA content was independent of cell density. TGF beta 1 treatment of the anterior pituitary-derived cells also reduced the levels of c-myc and EGF receptor mRNA. These results represent the first demonstration of the down-regulation of TGF alpha synthesis by a polypeptide growth factor and suggest that TGF beta 1 may be a physiological regulator of TGF alpha production in vivo.     

Mechanisms by which EGF receptor and TGF alpha contribute to malignant transformation

Alterations affecting the epidermal growth factor/transforming growth factor alpha-responsive mitogenic pathway are frequently detected in malignancies. In particular, the epidermal growth factor receptor has been found overexpressed in a number of human tumors. Production and secretion of transforming growth factor type alpha has also been shown in several tumor cells but not in their normal counterparts. In this review we describe the establishment of in vitro model systems to study the transforming potential of these molecules and summarize our current understanding of the mechanisms involved in transformation by genes encoding a growth factor and a growth factor receptor.     

Control of the intracellular signaling induced by fibroblast growth factors (FGF) over the proliferation and survival of retinal pigment epithelium cells: example of the signaling regulation of growth factors endogenous to the retina ]

Retinal pigmented epithelium (RPE) cells are of central importance in the maintenance of neural retinal function. RPE cell apoptosis is responsible for the development of a variety of retinal degeneration. The role of FGF2 was investigated on RPE cell proliferation and apoptosis in vitro. In the absence of serum, RPE cells died by apoptosis, while the addition of FGF2 greatly reduces apoptosis over a 7-day culture period. This is due to an autocrine loop involving secretion of endogenous FGF1 in the mechanism that govern FGF2-induced resistance to apoptosis. FGF2 induces long-term activation of FGFR1 and ERK1/2, and production of the anti-apoptotic protein BcL-x. Because FGF1 has no classical signal sequence to direct its secretion, we investigated the effects of FGF1 secretion on RPE proliferation and apoptosis in the absence of exogenous FGF2. Forced secretion of endogenous FGF1 by adding a signal peptide to the FGF1 molecule induces FGF1 secretion and cell proliferation in the presence of serum, while in FGF1 stops to be secreted and cell die in the absence of serum. Conversely, in cells cultured in the presence of serum, FGF1 without signal peptide is not secreted, but is secreted and rescue RPE cell from apoptosis when cells are cultured without serum. Thus, the proliferation and survival activities of endogenous FGF1 depend on the secretion of FGF1 which is determined by the cell environment.     

Aging-related changes in astrocytes in the rat retina: imbalance between cell proliferation and cell death reduces astrocyte availability

The aim of this study was to investigate changes in astrocyte density, morphology, proliferation and apoptosis occurring in the central nervous system during physiological aging. Astrocytes in retinal whole-mount preparations from Wistar rats aged 3 (young adult) to 25 months (aged) were investigated qualitatively and quantitatively following immunofluorohistochemistry. Glial fibrillary acidic protein (GFAP), S100 and Pax2 were used to identify astrocytes, and blood vessels were localized using Griffonia simplicifoli a isolectin B4. Cell proliferation was assessed by bromodeoxyuridine incorporation and cell death by TUNEL-labelling and immunolocalization of the apoptosis markers active caspase 3 and endonuclease G. The density and total number of parenchymal astrocytes in the retina increased between 3 and 9 months of age but decreased markedly between 9 and 12 months. Proliferation of astrocytes was detected at 3 months but virtually ceased beyond that age, whereas the proportion of astrocytes that were TUNEL positive and relative expression of active caspase 3 and endonuclease G increased progressively with aging. In addition, in aged retinas astrocytes exhibited gliosis-like morphology and loss of Pax2 reactivity. A small population of Pax2⁺/GFAP⁻ cells was detected in both young adult and aged retinas. The reduction in the availability of astrocytes in aged retinas and other aging-related changes reported here may have a significant impact on the ability of astrocytes to maintain homeostasis and support neuronal function in old age.     

Inhibition of cell proliferation by cytosin-arabinoside and its interference with spatial and temporal differentiation patterns in the chick retina

Summary Incubation of chick embryos with 200 nmoles/ egg of cytosine arabinoside (AraC) completely inhibits cell proliferation in the embryo. At an age older than embryonic day 4 (E4) more than 90% of the embryos survive this treatment. The drug induces various malformations; in particular the retina is heavily affected. This simple method offers the possibility to study the effect of a more or less decreased cell production on processes of further differentiation and histogenesis of retinal tissue.The following results are obtained: (1) In spite of the inhibition of cell proliferation in the retina by AraC an abnormally thick basal lamina is found and the expansion of the eye still proceeds, indicating that eye growth is not only dependent on retinal cell numbers. (2) Stereotyped malformations of retinal histogenesis are induced and categorized into three groups: in addition to areas of normal structure cells are found arranged in rosettes and in half-rosettes sometimes linked by areas of undefined transient cell arrangements. The results point to a strong tendency of a severely diminished cell population to form regularly laminated retinal-like structures as long as a minimal ratio of cell types is given. (3) The spatio-temporal appearance of the type of retinal malformation in a given retinal area is dependent on the time of AraC exposure and thus on the degree of differentiation reached at a spatio-temporal spot: Full rosettes develop at earlier, and half-rosettes at later stages of AraC interference. Furthermore, deformities first appear on temporal and ventral sides. Thus, the establishment of these malformations follows and reflects the normal sequence of differentiation within the retina. (4) Cells within rosettes organize in specific layers and start to differentiate normally. This shows that earlier formed cells are not dependent on the influence of factors derived from cells that are formed later for their proper differentiation.Abbreviations AChE acetylcholinesterase - AraC cytosin arabinoside - d'cyt 2 desoxycytidine - FITC-Con A fluorescent concanavalin A - FITC-PNA fluorescent peanut agglutinin - GCL ganglion cell layer - INL inner nuclear layer - IPL inner plexiform layer - LY Lucifer Yellow Recipient of a grant from the Alexander von Humboldt-Stiftung     

Characterization of a scintillation proximity assay to detect modulators of transforming growth factor alpha (TGF alpha) binding.

A scintillation proximity assay (SPA) for transforming growth factor alpha (TGF alpha) using SPA beads coated with A431 membranes has been studied. Binding of TGF alpha to the beads was characteristic of a receptor interaction. A class of high-affinity receptors for [125I]-TGF alpha (Kd = 0.10-0.26 nM) was detected by competition studies between [125I]TGF alpha and cold TGF alpha and by analysis of association and dissociation rate constants. An antibody to the epidermal growth factor receptor (clone 528) inhibited binding of [125I]TGF alpha (IC50 = 0.20 micrograms/ml), but an anti-TGF alpha antibody (clone 134A-2B3) (less than 25 micrograms/ml) did not block binding. Suramin inhibited [125I]-TGF alpha binding (IC50 = 0.20 mM). The ether lipids 1-O-hexadecyl-2-O-methyl-sn-glycero-3-phosphocholine, 1-O-octadecyl-2-O-methyl-sn-glycero-3-phosphocholine, and rac-lyso-platelet activating factor inhibited TGF alpha binding (IC50 values of 49, 69, and 57 microM, respectively). SPA is a convenient method for identifying agents that may act by interfering with TGF alpha binding.     

Spatial and temporal expression of heparan sulfate in mouse development regulates FGF and FGF receptor assembly

Heparan sulfate (HS) interacts with diverse growth factors, including Wnt, Hh, BMP, VEGF, EGF, and FGF family members, and is a necessary component for their signaling. These proteins regulate multiple cellular processes that are critical during development. However, a major question is whether developmental changes occur in HS that regulate the activity of these factors. Using a ligand and carbohydrate engagement assay, and focusing on FGF1 and FGF8b interactions with FGF receptor (FR)2c and FR3c, this paper reveals global changes in HS expression in mouse embryos during development that regulate FGF and FR complex assembly. Furthermore, distinct HS requirements are identified for both complex formation and signaling for each FGF and FR pair. Overall, these results suggest that changes in HS act as critical temporal regulators of growth factor and morphogen signaling during embryogenesis.     

EGF and TGF alpha influence in vitro lung development by the induction of matrix-degrading metalloproteinases.

Remodeling of the extracellular matrix by matrix-degrading metalloproteinases (MMPs) has been implicated in the early morphogenesis of branched organs. Growth factors such as EGF and TGF alpha are known to regulate the expression of MMPs in a variety of systems. We therefore examined the effects of EGF, TGF alpha, and collagenase upon in vitro branching of the embryonic lung. Lung rudiments from 11.5 day post coitum mice underwent extensive growth and repetitive branching during a 3-day period in organ culture. Lungs treated with EGF or TGF alpha were larger than controls, yet displayed fewer branches along with markedly dilated end buds which lacked clefts, indicating that these growth factors inhibit normal lung branching. Addition of purified mammalian collagenase to lung cultures similarly inhibited epithelial branching and produced end bud enlargement. In addition, gelatin-substrate enzymography of the conditioned medium from EGF- and TGF alpha-treated lungs revealed a marked induction of a metalloproteinase activity which most likely corresponds to the 72kDa type IV collagenase/gelatinase which degrades basement membrane collagens. Lungs maintained in the presence of both TGF alpha and TIMP, a specific inhibitor of MMPs, branched repeatedly and displayed normal, narrow end buds as seen with controls, suggesting that TIMP is capable of preventing or reversing the observed growth factor mediated effects upon lung branching. Taken together, these results provide evidence that the growth factors EGF and TGF alpha guide lung development, at least in part, by inducing the expression of matrix-degrading metalloproteinases.     

Spatial and temporal localization of FGF receptors in Xenopus laevis

Summary Mesoderm formation is a result of cell-cell interactions between the vegetal and animal hemisphere and is thought to be mediated by inducing peptide growth factors including members of the FGF and TGF superfamilies. Our immunochemical study analyses the distribution of FGF receptors coded by the human flg gene during embryogenesis of Xenopus laevis. Immunostaining was detected in the dorsal and ventral ectoderm and also in the marginal zone of early cleavage, blastula and gastrula stages. Signals were very strong in the mid and late blastula (stage 8 and 9) and declined slightly in the early gastrula (stage 10). A dramatic decrease was observed up to the late gastrula (stage 11⁺). In stage 13 embryos, immunostaining was only found in cells around the blastopore. Isolated ectoderm cultured in vitro showed a similar temporal expression and decrease of the signal as the normal embryos. These results indicate that receptor expression is independent of the interaction of the animal cells with the vegetal part of the embryo. Of interest is the fact that the signal cannot only be found at or near the cell surface but also within the cell. This suggests the presence of an intracellular isoform of the receptor resulting from the endogenous expression of splice variants and the internalization of transmembrane receptor. Taken together our results suggest that the loss of competence (for bFGF around stage 10) is not directly correlated with the presence of receptors. The possible roles of heparan sulphate glucosaminoglycans (low affinity receptors) and control mechanisms in the intracellular signalling pathway downstream of the receptor level should be taken into consideration.     

Extracellular potassium controls responsiveness of the noradrenergic cAMP system in the rat retina to fluphenazine

The effects of fluphenazine (FLU) on the noradrenaline (NA) induced cAMP-synthesis in intact rat retinae were studied as a function of extracellular K⁺- and Ca²⁺-ions. Thus NA-induced cAMP levels were measured after incubating intact rat retinae with 50 μM NA in the presence or absence of FLU and in the presence of 1 or 10 mM theophylline. Results were: (1) Experimental condition a: standard NA-responses were measured after incubating retinae at 0.75 mM Ca²⁺, at 10 mM theophylline, at 10 μM FLU and at 2 and 0 mM K⁺. FLU does not affect the NA-response at 2 mM K⁺ significantly; however, it inhibits the NA-response at 0 mM K⁺ in this condition. (2) Experimental condition b: NA-responses were measured after incubating retinae at 0.125 mM Ca²⁺, 10 mM theophylline, 10 μM FLU and at 2 and 0 mM K⁺. At 2 mM K⁺ FLU replaces a Ca²⁺ function probably connected with the synthesis part of the NA-cAMP system and NA-responses in this low Ca²⁺ condition are consequently enhanced by FLU; however, FLU inhibits the NA-response at 0 mM K⁺ in this condition. (3) Experimental condition c: NA-responses were measured after incubating retinae at 0.75 mM Ca²⁺, 1 mM theophylline, 10 μM FLU and at 2 and 0 mM K⁺. At 2 mM K⁺ FLU enhances the NA-response by further inhibition of the degradation part of the NA-cAMP system; FLU inhibits the NA-response at 0 mM K⁺ in this condition. (4) The inhibitions of the NA-responses by FLU at 0 mM K⁺ in all three conditions a, b and c showed an apparent K_m of 1 μM. (5) Low concentrations of K⁺ (0.4–0.8 mM) maintain the property of FLU to enhance the NA-responses at condition b (0.125 mM Ca²⁺) and at condition c (1 mM theophylline). Results suggest that the activation of NA-receptor coupled adenylate cyclases (NA-AC-ases) by NA, resulting in activation of phosphodiesterase activity by the NA-elevated cAMP-levels, is sustained by (a) membraneous factor(s) connected to the NA-receptor. This (these) factor(s) is (are) switched off in the absence of K⁺. Evidence has been presented, that Ca²⁺ and FLU do not have access to this intramembraneous factor-enzyme activating moiety of the NA-cAMP system at 0 mM K⁺. Between 0.4 and 0.8 mM K⁺ the factor-enzyme-NA-receptor complex is still intact.     

Rapidly recurring cortical seizures induce changes in neuronal responsiveness to acetylcholine.

The majority of mechanisms proposed to explain epileptic discharge suggest an excessive synaptic input into the cell or possible changes in cellular excitability which result in a decreased firing threshold and in the presence of self-sustained activity. It is likely that these changes are caused by modifications in the membrane receptor sensitivity to a specific neurotransmitter. In view of the above, the purpose of the present study has been to evaluate the sensitivity of the postsynaptic receptor by means of the microiontophoretic applications of substances whose pharmacological effect is known, thus determining its possible involvement in the epileptic process. Changes in cortical excitability were induced by electric stimuli in the sensorimotor cortex of rats anesthetized with urethane (1 g/kg intraperitoneally), immobilized with pancuronium bromide and kept alive with mechanical respiration. The electric stimuli consisted of trains of biphasic pulses, each lasting one millisecond, with a frequency of 100 pps and with a train duration of 1 second. The response of the neuron to acetylcholine was evaluated before and after the kindling had been established. The dosage was measured in nanoamperes of microiontophoretic ejecting current. Extracellular field potentials were recorded with the central barrel of 4-barrel micropipettes. Peripheral barrels were used for iontophoretic applications of Acetylcholine (Ach .1, 1M), Atropine (25mM). One of these barrels containing NaCl (2M) was used for the automatic passage of balancing current.(ABSTRACT TRUNCATED AT 250 WORDS)     

Developmental changes in responsiveness to vitamin D metabolites

We have demonstrated that epiphyseal chondroblasts contain specific receptors for 24R,25-dihydroxy vitamin D3(24,25(OH)2D3) while diaphyseal osteoblasts contain specific receptors for 1 alpha 25-dihydroxy vitamin D3(1,25(OH)2D3). Both metabolites induce DNA synthesis and creatine kinase (CKBB) activity. We have also found that the responsiveness of rat kidney to these metabolites changes during development. In embryonic and early postnatal stages, the kidney responds to 24,25(OH)2D3, later to both 24,25(OH)2D3 and 1,25(OH)2D3, and the mature kidney only to 1,25(OH)2D3. These responses correlate with changes in the specific receptors present in the kidney. Furthermore, we have compared developmental changes in skeletal (epiphysis, diaphysis and mandibular condyle) and non-skeletal (kidney, cerebellum, cerebrum, liver and pituitary) tissue in both rat (a postnatal developer) and rabbit (a perinatal developer). Epiphyseal or diaphyseal chondroblasts at any stage of development were predominantly responsive to 24,25(OH)2D3, whereas osteoblasts were responsive to 1,25(OH)2D3. In contrast, condylar chondroblasts, kidney, cerebellum and pituitary responded to 24,25(OH)2D3 during early development and subsequently developed responsiveness to 1,25(OH)2D3. Using primary cell cultures from kidneys at different stages of maturation, we showed the same developmental pattern as in vivo. Chronic treatment of the cells with 24,25(OH)2D3, but not 1,25(OH)2D3, caused precocious development of responsiveness to 1,25(OH)2D3 in culture. We suggest that 24,25(OH)2D3 acts as a maturation factor, during early development in kidney, and probably in other tissues, possibly by induction of receptor to 1,25(OH)2D3, accompanied by down-regulation of its own receptor.     

Overexpression of TGF alpha in transgenic mice: induction of epithelial hyperplasia, pancreatic metaplasia, and carcinoma of the breast.

Metallothionein-directed expression of TGF alpha in transgenic mice induced a spectrum of changes in the growth and differentiation of certain adult tissues. First, TGF alpha promoted a uniform epithelial hyperplasia of several organs without otherwise causing major alterations in tissue architecture. Second, in pancreas it promoted proliferation of both acinar cells and fibroblasts and focally altered acinar cell differentiation. The magnitude of this response was proportional to the level of local, tissue-specific TGF alpha expression and was reproduced when expression of TGF alpha was placed under the control of the elastase promoter, implying an autocrine or paracrine mechanism. Third, TGF alpha was oncogenic in vivo. It caused dramatic hyperplasia and dysplasia of the coagulation gland epithelium, which displayed evidence of carcinoma in situ, and in postlactational mammary gland it induced secretory mammary adenocarcinomas. Thus, TGF alpha displays characteristics of both a potent epithelial cell mitogen and an oncogenic protein in vivo.     

雌激素诱发大鼠原位与移植垂体催乳素瘤中催乳素基因与TGFα和TGF …

利用本实验室建立的１７β－雌二醇诱致Ｓｐｒａｇｕｅ－Ｄａｗｌｅｙ（ＳＤ）大鼠原位垂体和异体移植于肾囊的垂体同时形成催乳素瘤的动物模型,采用Ｎｏｒｔｈｅｍ印迹杂交方法,我们观察了Ｅ２长期作用（１２０ｄ）后诱发的原位与移植垂体ＰＲＬ瘤中ＰＲＬ基因和两种转化生长因子ＴＧＦα和ＴＧＦβ１基因表达水平的改变。结果表明：在Ｅ２长期作用后,原位垂体与异体移植于肾囊,从而远离下丘脑的垂体均可形成垂体ＰＲＬ瘤;原位