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Query: UNIPROT:P06889 (Mol)
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Beginning at the fifth week of fetal life, successive generations of individual nephrons are induced by contact between metanephric mesenchyme and ureteric bud. Following phenotypic transformation, cells of each primitive renal vesicle undergo a phase of rapid cell division. In order to identify genes which might regulate nephron development in man, we screened adult and fetal kidney RNA for expression of a panel of growth-related genes. Among the genes which were expressed at higher levels in fetal kidney was the epidermal growth factor (EGF) receptor. There is controversy as to the most likely physiologic EGF receptor ligand in fetal kidney; we were able to identify a transcript for transforming growth factor-alpha (TGF-alpha) but not EGF on Northern blots of fetal kidney RNA. Since the abundance of TGF-alpha mRNA is low, we confirmed its presence by polymerase chain reaction amplification. Using specific radioimmunoassays, we also provide direct evidence for TGF-alpha but not EGF peptide in extracts of fetal kidney and mid-gestational amniotic fluid. We suggest that TGF-alpha/EGF receptor interactions may serve an important function in development of human fetal kidney.
Mol Cell Endocrinol 1991 May
PMID:Expression of transforming growth factor-alpha and epidermal growth factor receptor in human fetal kidneys. 172 55

We have reported previously that human group C adenoviruses down-regulate the epidermal growth factor (EGF) receptor (EGF-R) (C. R. Carlin, A. E. Tollefson, H. A. Brady, B. L. Hoffman, and W. S. M. Wold, Cell 57:135-144, 1989). Expression of a 13.7-kDa protein encoded by a gene in the E3 transcription unit is necessary and sufficient for this effect (Carlin et al., Cell, 1989; B. L. Hoffman, A. Ullrich, W. S. M. Wold, and C. R. Carlin, Mol. Cell. Biol. 10:5521-5524, 1990). We show here that EGF-R down-regulation is accelerated in cells which overexpress the receptor when these cells are infected with virus mutants that overproduce the 13.7-kDa protein compared with wild-type virus. This is in contrast to EGF stimulation, for which others have shown that high concentrations of ligand are associated with low rates of receptor internalization in EGF-R-overexpressing cells (D. Kuppuswamy and L. J. Pike, J. Biol. Chem. 264:3357-3363, 1989; H. S. Wiley, J. Cell Biol. 107:801-810, 1988). We also show that the E3 protein is not present in media conditioned by infected cells and that it does not induce secretion of an EGF-like autocrine factor. Moreover, while mature membrane-bound EGF-R is down-regulated, the precursor of the membrane-bound form is not. Adenovirus infection also does not affect receptor-related molecules expressed in the secretory pathway. Interestingly, adenovirus-induced down-regulation is not regulated by concentrations of EGF associated with a slow rate of internalization in A431 cells. This suggests that 13.7-kDa protein expression triggers receptor entry by a novel ligand-independent pathway or, alternatively, that it compensates for a cellular factor that may be rate limiting during EGF-mediated endocytosis.
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PMID:Evidence for intracellular down-regulation of the epidermal growth factor (EGF) receptor during adenovirus infection by an EGF-independent mechanism. 172 83

The present studies examine whether the Ah receptor mediates the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on the binding capacity of the hepatic epidermal growth factor (EGF) receptor in congenic strains of C57BL/6J mice that differ only at the Ah locus. The Ah locus is believed to encode the Ah receptor, which mediates the induction of cytochrome P4501A1 by TCDD and appears to mediate many of the toxic effects of TCDD. TCDD produced an 80-90% decrease in the maximum binding capacity (both high and low affinity sites) of the hepatic EGF receptor in female Ah-responsive (Ahb/b) and Ah-nonresponsive (Ahd/d) C57BL/6 mice. However, the ED50 for the effects of TCDD on the binding capacity of the EGF receptor was 10-fold higher in the Ah-nonresponsive mice, compared with the Ah-responsive mice (7 versus 0.7 micrograms/kg). TCDD did not affect the hepatic content of two EGF receptor mRNA transcripts (10 and 6 kb), indicating that the effects on the EGF receptor are not pretranslational. Similarly, TCDD did not affect the hepatic content of mRNA for transforming growth factor-alpha, an alternate ligand for the EGF receptor that is synthesized in the liver. In contrast, TCDD markedly increased the hepatic content of the mRNA for cytochrome P4501A1, which is known to be regulated transcriptionally by TCDD. The ED50 for this effect was 10-fold higher in Ah-nonresponsive mice than in Ah-responsive mice (13 versus 1.3 micrograms/kg). This study indicates that the effects of TCDD on EGF receptor ligand binding are mediated by the Ah receptor. However, unlike the effect of TCDD on cytochrome P4501A1, the effects of TCDD on the EGF receptor do not involve changes in the levels of the mRNA for this protein or changes in the mRNA for transforming growth factor-alpha, an alternate ligand for the EGF receptor.
Mol Pharmacol 1991 Mar
PMID:Influence of the Ah locus on the effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin on the hepatic epidermal growth factor receptor. 184 54

GTPase-activating protein (GAP) stimulates the ability of p21ras to hydrolyze GTP to GDP. Since GAP is phosphorylated by a variety of activated or oncogenic protein-tyrosine kinases, it may couple tyrosine kinases to the Ras signaling pathway. The epidermal growth factor (EGF) receptor cytoplasmic domain phosphorylated human GAP in vitro within a single tryptic phosphopeptide. The same GAP peptide was also apparently phosphorylated on tyrosine in EGF-stimulated rat fibroblasts. Circumstantial evidence suggested that residue 460 might be the site of GAP tyrosine phosphorylation. This possibility was confirmed by phosphorylation of a synthetic peptide corresponding to the predicted tryptic peptide containing Tyr-460. Alteration of Tyr-460 to phenylalanine by site-directed mutagenesis diminished the in vitro phosphorylation of a bacterial GAP polypeptide by the EGF receptor. We conclude that Tyr-460 is a site of GAP tyrosine phosphorylation by the EGF receptor in vitro and likely in vivo. GAP Tyr-460 is located immediately C terminal to the second GAP SH2 domain, suggesting that its phosphorylation might have a role in regulating protein-protein interactions.
Mol Cell Biol 1991 May
PMID:The epidermal growth factor receptor phosphorylates GTPase-activating protein (GAP) at Tyr-460, adjacent to the GAP SH2 domains. 185 98

We and others have previously reported that transforming growth factor-alpha (TGF alpha) expression is hormonally responsive and its expression is coregulated with that of its receptor [the epidermal growth factor (EGF) receptor]. The 5'-flanking region of the TGF alpha gene was characterized to determine whether it could confer hormone responsiveness to a reporter gene (luciferase) in human mammary carcinoma cells (MDA468). This segment of the gene is GC rich and contains an element strikingly similar to the core element of the EGF receptor gene that has been shown to mediate both basal and hormone-stimulated expression of the EGF receptor. We now report that a 313-basepair (bp) proximal element of the TGF alpha 5'-flanking region (-373 to -59 relative to the TGF alpha translation start codon) is capable of conferring responses to phorbol ester and EGF. This gene segment does not contain the EGF receptor gene homolog or potential AP-2-binding sites, suggesting that these elements are not necessary for basal and EGF- or phorbol ester-responsive TGF alpha gene expression. This 313-bp proximal element also confers proper transcriptional initiation to the chimeric TGF alpha-luciferase reporter construct, indicating it is the TGF alpha promoter. A 1.1-kilobase segment of the TGF alpha 5'-flanking region also confers retinoic acid, thyroid hormone, and glucocorticoid responsiveness despite the absence of recognizable steroid hormone receptor-binding sites. These hormones stimulate reporter expression 1.5- to 2-fold in a dose-dependent manner. Extension of the 5'-flanking region to -3500 results in marked suppression of reporter gene expression. These results indicate that the TGF alpha gene 5'-flanking sequence contains the elements responsible for hormonal responsiveness of this gene and that these elements are distinct from those that regulate the expression of the EGF receptor gene.
Mol Endocrinol 1991 Apr
PMID:Transcriptional regulation of the human transforming growth factor-alpha gene. 192 84

An increasing body of evidence suggests that breast tumour growth is mediated by oncogene products and growth factors which are or which act through cell surface receptors. The aims of the present study were to determine how three of these receptors, c-erbB-2 protein, epidermal growth factor receptor (EGFr) and the beta-subunit of platelet-derived growth factor receptor (PDGFr-beta-subunit), can effectively be demonstrated by immunohistochemical methods in breast tumors, how these receptors are distributed at the cellular level and how their expression correlates with well-established prognostic indicators including hormone receptors and proliferative index. We examined frozen tissue sections of 50 invasive human breast carcinomas, including 45 ductal, four lobular, and one mucinous tumours, by immunocytochemical methods to determine the in situ distributions of c-erbB-2, EGFr, and PDGFr-beta-subunit. We compared staining for c-erbB-2 protein in frozen sections with that in paraffin sections of the same 50 tumours. The immunohistochemical labelling results were compared with tissue hormone receptor content and growth fraction determined by Ki-67 labelling. Strong labelling of tumour cells in frozen sections was detected in 22% of cases, all of the ductal type, stained with rabbit antiserum to c-erbB-2. Labelling for c-erbB-2 protein was generally weaker in paraffin sections than in frozen sections and in six of 11 positive cases, specific staining could be detected only in frozen sections. In immunostains with monoclonal antibody to EGFr, rare cells within tumour were labelled in 60% of the carcinomas. Using a monoclonal antibody to the beta-subunit of PDGFr, consistent labelling of fibrillary cellular processes in the walls of blood vessels and in fibrous stroma around tumour cell nests was detected, but there was no labelling of tumour cells themselves. C-erbB-2 oncoprotein positive tumours were found to be more often oestrogen receptor negative (P less than 0.005) or oestrogen and progesterone receptor negative (P less than 0.01) than c-erbB-2 negative tumours. No significant correlation was observed between c-erbB-2 expression and Ki-67 growth fraction.
Mol Cell Probes 1990 Feb
PMID:In situ distribution of oncogene products and growth factor receptors in breast carcinoma: c-erbB-2 oncoprotein, EGFr, and PDGFr-beta-subunit. 196 11

The transforming gene product of avian erythroblastosis virus, v-erbB, is derived from the epidermal growth factor (EGF) receptor but has lost its extracellular ligand-binding domain and was mutated in its cytoplasmic portion, which is thought to be responsible for biological signal generation. We have repaired the deletion of extracellular EGF-binding sequences and investigated the functional consequences of cytoplasmic erbB mutations. Within the resulting EGF receptors, the autophosphorylation activities of the cytoplasmic domains of v-erbB-H and v-erbB-ES4 were fully ligand dependent in intact cells. However, the mitogenic and transforming signaling activities of an EGF receptor carrying v-erbB-ES4 (but not v-erbB-H) cytoplasmic sequences remained ligand independent, whereas those of a receptor with a v-erbB-H cytoplasmic domain were regulated by EGF or transforming growth factor alpha. Thus, structural alterations in the cytoplasmic domain of growth factor receptor tyrosine kinases may induce constitutive signaling activity without autophosphorylation. These findings provide new insight into the mechanism of receptor-mediated signal transduction and suggest a novel alternative for subversion of cellular control mechanisms and proto-oncogene activation.
Mol Cell Biol 1990 Jun
PMID:Epidermal growth factor receptor cytoplasmic domain mutations trigger ligand-independent transformation. 197 19

While the normal human erbB-2 gene is potently transforming when overexpressed in NIH 3T3 cells, its rat homolog, the neu gene, seems to acquire transforming properties only upon alteration of its coding sequence. In this study, we compared the effects of different levels of expression of normal erbB-2 and neu in NIH 3T3 cells. Our results revealed that the normal rat neu gene acts as a potent oncogene when sufficiently overexpressed in NIH 3T3 cells.
Mol Cell Biol 1990 Jun
PMID:Transformation of NIH 3T3 cells by overexpression of the normal coding sequence of the rat neu gene. 197 20

The relationship between terminal cell differentiation and changes in the subcellular levels of the HER-2/neu antigen was investigated in cultured human breast cancer cells: AU-565 cells (which overexpress the HER-2/neu gene) and MCF-7 cells (which do not overexpress this gene). Differentiation was achieved by treating the cells with mycophenolic acid (MPA), phorbol 12-myristate 13-acetate (PMA), retinoic acid (RA), or the TA-1 monoclonal antibody to the extracellular domain of the HER-2/neu protein. Ten to twenty percent of the cells in untreated, sparsely growing AU-565 cultures exhibited morphological maturation characterized by large lacy nuclei surrounded by sizable flat cytoplasms. A fraction of these cells harbored milk factors such as casein and large lipid droplets. Treatment of the AU-565 cells for 4 d with 9 microM MPA, 1.6 nM PMA, 2.5 microM RA, or 1 microgram/mL TA-1 antibody resulted in cell growth inhibition and an increase in the percentage of cells (48-97%) that exhibit a mature phenotype. MCF-7 cells were also susceptible to differentiation by MPA and RA, but to a lesser degree than the AU-565 cells. Differentiation in the AU-565 and MCF-7 cells was associated with reduced immunostaining for the HER-2/neu protein at the cell surface membrane and with a transient increased diffuse immunostaining for this protein in the cytoplasm.
Mol Carcinog 1990
PMID:Differentiation of cultured human breast cancer cells (AU-565 and MCF-7) associated with loss of cell surface HER-2/neu antigen. 198 May 88

Raf-1 serine- and threonine-specific protein kinase is transiently activated in cells expressing the epidermal growth factor (EGF) receptor upon treatment with EGF. The stimulated EGF receptor coimmunoprecipitates with Raf-1 kinase and mediates protein kinase C-independent phosphorylation of Raf-1 on serine residues. Hyperphosphorylated Raf-1 has lower mobility on sodium dodecyl sulfate gels and has sixfold-increased activity in immunocomplex kinase assay with histone H1 or Raf-1 sequence-derived peptide as a substrate. Raf-1 activation requires kinase-active EGF receptor; a point mutant lacking tyrosine kinase activity in inactive in Raf-1 coupling and association. It is noteworthy that tyrosine phosphorylation of c-Raf-1 induced by EGF was not detected in these cells. These observations suggest that Raf-1 kinase may act as an important downstream effector of EGF signal transduction.
Mol Cell Biol 1991 Feb
PMID:Epidermal growth factor (EGF) stimulates association and kinase activity of Raf-1 with the EGF receptor. 199 Feb 91


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