Regulation of epidermal growth factor receptor levels by thyroid hormone

Prognostic and Predictive Factors for Renal Cell Carcinoma

Metastatic renal cell carcinoma (mRCC) is an incurable malignancy, characterized by its resistance to traditional chemotherapy, radiation, and hormonal therapy. Treatment perspectives and prognosis of patients with mRCC have been significantly improved by advances in the understanding of its molecular pathogenesis, which have led to the development of targeted therapeutics. Different molecular factors derived from the tumor or the host detected in both tissue or serum could be predictive of therapeutic benefit. Some of them suggest a rational selection of patients to be treated with certain therapies, though none have been validated for routine use. This article provides an overview of both clinical and molecular factors associated with predictive or prognostic value in mRCC and emphasizes that both should be considered in parallel to provide the most appropriate, individualized treatment and achieve the best outcomes in clinical practice.

The Retinol Circulating Complex Releases Hormonal Ligands During Acute Stress Disorders

Intensive care workers actively participate in very hot debates aiming at defining the true metabolic, hormonal and nutritional requirements of critically ill patients, the contributory roles played by thyroid and retinoid ligands being largely underestimated. The present article makes up for redressing the balance on behalf of these last hormonal compounds. The retinol circulating complex is transported in the bloodstream in the form of a trimolecular edifice made up of transthyretin (TTR), retinol-binding protein (RBP) and its retinol ligand. TTR reflects the size of the lean body mass (LBM) and is one of the 3 carrier-proteins of thyroid hormones whereas RBP is the sole conveyor of retinol in human plasma. In acute inflammatory disorders, both TTR and RBP analytes experience abrupt cytokine-induced suppressed hepatic synthesis whose amplitude is dependent on the duration and severity of the inflammatory burden. The steep drop in TTR and RBP plasma values releases thyroxine and retinol ligands in their physiologically active forms, creating free pools estimated to be 10-20 times larger than those described in healthy subjects. The peak endocrine influence is reached on day 4 and the freed ligands undergo instant cellular overconsumption and urinary leakage of unmetabolized fractions. As a result of these transient hyperthyroid and hyperretinoid states, helpful stimulatory and/or inhibitory processes are set in motion, operating as second frontlines fine-tuning the impulses primarily initiated by cytokines. The data explain why preexisting protein malnutrition, as assessed by subnormal LBM and TTR values, impairs the development of appropriate recovery processes in critically ill patients. These findings have survival implications, emphasizing the need for more adapted therapeutic strategies in intensive care units.

Epidermal growth factor receptor plays a role in the regulation of liver and plasma lipid levels in adult male mice

Dsk5 mice have a gain of function in the epidermal growth factor receptor (EGFR), caused by a point mutation in the kinase domain. We analyzed the effect of this mutation on liver size, histology, and composition. We found that the livers of 12-wk-old male Dsk5 heterozygotes (+/Dsk5) were 62% heavier compared with those of wild-type controls (+/+). The livers of the +/Dsk5 mice compared with +/+ mice had larger hepatocytes with prominent, polyploid nuclei and showed modestly increased cell proliferation indices in both hepatocytes and nonparenchymal cells. An analysis of total protein, DNA, and RNA (expressed relative to liver weight) revealed no differences between the mutant and wild-type mice. However, the livers of the +/Dsk5 mice had more cholesterol but less phospholipid and fatty acid. Circulating cholesterol levels were twice as high in adult male +/Dsk5 mice but not in postweaned young male or female mice. The elevated total plasma cholesterol resulted mainly from an increase in low-density lipoprotein (LDL). The +/Dsk5 adult mouse liver expressed markedly reduced protein levels of LDL receptor, no change in proprotein convertase subtilisin/kexin type 9, and a markedly increased fatty acid synthase and 3-hydroxy-3-methyl-glutaryl-CoA reductase. Increased expression of transcription factors associated with enhanced cholesterol synthesis was also observed. Together, these findings suggest that the EGFR may play a regulatory role in hepatocyte proliferation and lipid metabolism in adult male mice, explaining why elevated levels of EGF or EGF-like peptides have been positively correlated to increased cholesterol levels in human studies.

Central role of the EGF receptor in neurometabolic aging

A strong connection between neuronal and metabolic health has been revealed in recent years. It appears that both normal and pathophysiological aging, as well as neurodegenerative disorders, are all profoundly influenced by this "neurometabolic" interface, that is, communication between the brain and metabolic organs. An important aspect of this "neurometabolic" axis that needs to be investigated involves an elucidation of molecular factors that knit these two functional signaling domains, neuronal and metabolic, together. This paper attempts to identify and discuss a potential keystone signaling factor in this "neurometabolic" axis, that is, the epidermal growth factor receptor (EGFR). The EGFR has been previously demonstrated to act as a signaling nexus for many ligand signaling modalities and cellular stressors, for example, radiation and oxidative radicals, linked to aging and degeneration. The EGFR is expressed in a wide variety of cells/tissues that pertain to the coordinated regulation of neurometabolic activity. EGFR signaling has been highlighted directly or indirectly in a spectrum of neurometabolic conditions, for example, metabolic syndrome, diabetes, Alzheimer's disease, cancer, and cardiorespiratory function. Understanding the positioning of the EGFR within the neurometabolic domain will enhance our appreciation of the ability of this receptor system to underpin highly complex physiological paradigms such as aging and neurodegeneration.

Toxicity as a biomarker of efficacy of molecular targeted therapies: focus on EGFR and VEGF inhibiting anticancer drugs

In addition to being present in tumor cells, many targets of signal transduction inhibitors are also found in normal tissue. Side effects attributable to the mechanism of action of molecular targeted agents thus represent "on-target" modulation in normal tissues. These mechanism-based toxicities can be pharmacodynamic effects of pathway inhibition and, in tumors depending on the inhibited pathway for proliferation, might be biomarkers of efficacy. The development of rash with tyrosine kinase inhibitors or monoclonal antibodies targeting the epidermal growth factor receptor is associated with superior outcomes in lung, head and neck, colorectal, and pancreatic cancer studies. Correlated with superior efficacy in retrospective analyses of large studies in advanced colorectal, breast, and renal cell carcinoma, arterial hypertension as an adverse event of antiangiogenic agents may also be a marker of effective target inhibition. An association between hypothyroidism and the activity of multitargeted tyrosine kinase inhibitors has been identified in renal cell carcinoma patients. Tumor growth addiction to the specific pathway that is effectively targeted may be the link between a mechanism-based toxicity and efficacy. The biological basis for this correlation can be pharmacological, with higher drug exposure being associated with greater toxicity and antitumor activity, and can also be genetic, because single nucleotide polymorphisms play an important role in drug pharmacokinetic and pharmacodynamic processes. Investigators have proposed that interpatient differences and associated toxicities can be exploited for dose selection and titration, and clinical trials are currently exploring intrapatient "dosing-to-toxicity" strategies. Ultimately, the predictive value of a side effect of molecular targeted therapies requires validation in prospective trials.

Hypothyroidism in patients with renal cell carcinoma: blessing or curse?

BACKGROUND

Sunitinib and sorafenib are tyrosine kinase inhibitors that have important antitumor activity in metastatic renal cell carcinoma (mRCC). Hypothyroidism constitutes a commonly reported side effect of both drugs, and particularly of sunitinib. The objective of this analysis was to investigate whether the occurrence of hypothyroidism during treatment with sunitinib and sorafenib affects the outcome of patients with mRCC.

METHODS

Eighty-seven consecutive patients with mRCC who were to receive treatment with sunitinib or sorafenib were included in a prospective analysis. Thyroid function was assessed in each patient every 4 weeks during the first 2 months of treatment and every 2 to 4 months thereafter. Assessment included serum levels of thyroid-stimulating hormone (TSH), tri-iodthyronine (T3), and thyroxine (T4). Subclinical hypothyroidism was defined as an increase in TSH above the upper limit of normal (>3.77 μM/mL) with normal T3 and T4 levels.

RESULTS

Subclinical hypothyroidism was evident in 5 patients at baseline and occurred in 30 patients (36.1%) within the first 2 months after treatment initiation. There was a statistically significant correlation between the occurrence of subclinical hypothyroidism during treatment and the rate of objective remission (hypothyroid patients vs euthyroid patients: 28.3% vs 3.3%, respectively; P < .001) and the median duration of survival (not reached vs 13.9 months, respectively; hazard ratio, 0.35; 95% confidence interval, 0.14-0.85; P = .016). In multivariate analysis, the development of subclinical hypothyroidism was identified as an independent predictor of survival (hazard ratio, 0.31; P = .014).

CONCLUSIONS

The current results indicated that hypothyroidism may serve as a predictive marker of treatment outcome in patients with mRCC. Thus, the interpretation of hypothyroidism during treatment with sunitinib and sorafenib as an unwanted side effect should be reconsidered.

Reduced expression of epidermal growth factor receptors in rat liver during aging

Proliferative responsiveness of hepatocytes to epidermal growth factor (EGF) declines during aging. The role of EGF receptors in mediating age-dependent changes of EGF-induced mitogenic signaling in liver remains incompletely understood. We assessed EGF receptor expression levels in whole liver specimens as well as in freshly isolated and cultured hepatocytes from young adult and senescent Fischer 344 male rats. Hepatic EGF receptor messenger RNA and protein levels, and the number of high- and low-affinity receptor binding sites, decreased with aging. Ligand-induced EGF receptor activation, determined by receptor dimerization and tyrosine phosphorylation, was reduced in old animals in parallel with the age-related decline in receptor expression. Stimulation of the extracellular signal-regulated kinase pathway by EGF was also attenuated in hepatocytes from old animals. Our results implicate decreased expression of EGF receptors as a key determinant of reduced mitogenic signaling responsive to EGF stimulation of liver during aging.

Diverse expression of ErbB receptor proteins during rat liver development and regeneration

BACKGROUND & AIMS

The protein expression and interactions of the ErbB receptors were examined in different liver proliferation models in vivo and in vitro, including ontogeny and regeneration following partial hepatectomy.

METHODS

Expression and tyrosine phosphorylation status of specific ErbB proteins were studied by immunologic methods.

RESULTS

The epidermal growth factor receptor, ErbB2, and ErbB3 were the only ErbB proteins detected in the liver parenchyma on embryonic day 19. ErbB2 disappeared by the third week after birth and could not be appreciably induced in the adult animal by partial hepatectomy. ErbB2 was also detected in multipotent stem (RLE) and hepatoma (H4IIe) cell lines as well as in fetal, but not adult, hepatocyte cultures. Only epidermal growth factor receptor and ErbB3 were detected in adult liver, and both showed circadian variation in protein expression. ErbB4 was not detected in any model. Patterns of ligand-induced ErbB phosphorylation differed between fetal and adult hepatocytes.

CONCLUSIONS

Complex and independent programs regulate the ErbB receptors, with implications for differential cell signaling in hepatic development and regeneration.

The stressful condition as a nutritionally dependent adaptive dichotomy

The injured body manifests a cascade of cytokine-induced metabolic events aimed at developing defense mechanisms and tissue repair. Rising concentrations of counterregulatory hormones work in concert with cytokines to generate overall insulin and insulin-like growth factor 1 (IGF-1), postreceptor resistance and energy requirements grounded on lipid dependency. Salient features are self-sustained hypercortisolemia persisting as long as cytokines are oversecreted and down-regulation of the hypothalamo-pituitary-thyroid axis stabilized at low basal levels. Inhibition of thyroxine 5'-deiodinating activity (5'-DA) accounts for the depressed T3 values associated with the sparing of both N and energy-consuming processes. Both the liver and damaged territories adapt to stressful signals along up-regulated pathways disconnected from the central and peripheral control systems. Cytokines stimulate liver 5'-DA and suppress the synthesis of transthyretin (TTR), causing the drop of retinol-binding protein (RBP) and the leakage of increased amounts of T4 and retinol in free form. TTR and RBP thus work as prohormonal reservoirs of precursor molecules which need to be converted into bioactive derivatives (T3 and retinoic acids) to reach transcriptional efficiency. The converting steps (5'-DA and cellular retinol-binding protein-I) are activated by T4 and retinol, themselves operating as limiting factors of positive feedback loops. Healthy adults with normal macrophage functioning and liver parenchymal integrity, who submitted to a stress of medium severity, are characterized by TTR-RBP plasma levels reduced by half and an estimated ten-fold increase in free ligand disposal to target cells during the days ensuing injury. This transient hyperthyroid and hyperretinoid climate creates a second defense line strengthening and fine-tuning the effects primarily initiated by cytokines. The suicidal behavior of thyroxine-binding globulin (TBG), corticosteroid-binding globulin (CBG), and IGFBP-3 allows the occurrence of peak endocrine and mitogenic influences at the site of inflammation. The production rate of TTR by the liver is the main determinant of both the hepatic release and blood transport of holoRBP, which explains why poor nutritional status concomitantly impairs thyroid- and retinoid-dependent acute-phase responses, hindering the stressed body to appropriately face the survival crisis. The prognostic significance of low TT4 blood levels may be assigned to the exhaustion of extrathyroidal hormonal pools normally stored in liver and plasma but markedly shrunken in protein-depleted states. These data offer new insights into the mechanisms whereby preexisting malnutrition and stressful complications are interrelated, emphasizing the pivotal role played by TTR in that context.

Species variability in angiotensin receptor expression by cultured cardiac fibroblasts and the infarcted heart

Cardiac fibroblasts, an abundant cell of the left ventricle (LV), proliferate and synthesize collagen in the heart after acute injury and during pressure overload hypertrophy. From many studies, angiotensin II (ANG II) receptors have been implicated in promoting collagen formation by the rat cardiac fibroblast. The present study examined species variability in ANG II receptor expression. Cultured rat fibroblasts expressed 43,000 +/- 15,000 ANG II (AT1-specific) receptors per cell (dissociation constant = 0.92 +/- 0.34 nM), whereas rabbit and neonate human cardiac fibroblast cultures expressed few receptors. Angiotensin increased intracellular Ca2+ concentration in rats but not in rabbit or human cardiac fibroblasts and stimulated arachidonic acid release in rat but not rabbit fibroblasts. In situ, 6 days after coronary artery ligation, angiotensin receptor expression was increased 34.8 +/- 13.4-fold in the infarcted area relative to the noninfarcted tissue in the rat LV, whereas rabbit hearts demonstrated only a 3.2 +/- 1.6-fold increase in ANG II binding within the infarcted tissue. These species differences in receptor expression raise questions as to the role of angiotensin as a mediator of collagen formation across species and as a direct target of angiotensin-converting enzyme inhibitors to regulate cardiac fibroblast function.

Down-regulation of epidermal growth factor receptors by nerve growth factor in PC12 cells is p140(trk)-, Ras-, and Src-dependent

Nerve growth factor (NGF) treatment causes a profound down-regulation of epidermal growth factor receptors during the differentiation of PC12 cells. This process is characterized by a progressive decrease in epidermal growth factor (EGF) receptor level measured by 125I-EGF binding, tyrosine phosphorylation, and Western blotting. Treatment of the cells with NGF for 5 days produces a 95% reduction in the amount of [35S]methionine-labeled EGF receptors. This down-regulation does not occur in PC12nnr5 cells, which lack the p140(trk) NGF receptor. However, in PC12nnr5 cells stably transfected with p140(trk), the NGF-induced heterologous down-regulation of EGF receptors is reconstituted in part. NGF-induced heterologous down-regulation, but not EGF-induced homologous down-regulation of EGF receptors, is blocked in Ras- and Src-dominant-negative PC12 cells. Treatment with either pituitary adenylate cyclase-activating peptide (PACAP) or staurosporine stimulates neurite outgrowth in PC12 cell variants, but neither induces down-regulation of EGF receptors. NGF treatment of PC12 cells in suspension induces down-regulation of EGF receptors in the absence of neurite outgrowth. These results strongly suggest a p140(trk)-, Ras- and Src-dependent mechanism of NGF-induced down-regulation of EGF receptors and separate this process from NGF-induced neurite outgrowth in PC12 cells.

EGF receptor expression, regulation, and function in breast cancer

Epidermal growth factor receptor (EGFR) overexpression correlates with both loss of estrogen receptor (ER) and poor prognosis in breast cancer. Interestingly, in normal breast EGFR appears to be expressed more frequently than in malignant tissue, and there may be a different relationship between ER and EGFR. A variety of cellular regulators, such as EGF, TGF alpha, phorbol esters, and steroid hormones, are capable of altering the level of EGFR expression in breast cells. However, much work remains to be done on the mechanistic details of EGFR regulation in this disease. The significance of EGFR as an oncogene in breast cancer is compounded by its potential interactions with other oncogenes such as c-erbB-2 and c-myc. Additionally, several recent studies have placed EGFR prominently in the signal transduction pathway, demonstrating that the EGFR-ligand system may play important roles throughout the course of malignant progression in breast cancer.

Mechanisms of EGF receptor regulation in breast cancer cells

Overexpression of the EGF receptor in breast cancer correlates with poor prognosis and failure on endocrine therapy for both ER-/EGFR+ and ER+/EGFR+ tumors, suggesting a role for EGFR in the progression to hormone independence. The identification of specific DNAse I hypersensitive site patterns for the EGFR gene in ER+ vs. ER- cells implicates regions of the EGFR first intron in up-regulation of EGFR, while estrogen regulation studies indicate the involvement of a repressor(s) in the maintenance of low levels of EGFR. Based on these findings, a multi-step model is proposed for the progression of breast cancer from a hormone-dependent, ER+/EGFR-phenotype to an aggressive, hormone-independent, ER-/EGFR+ stage.

Immunohistochemical investigation of epidermal growth factor receptor expression during periods of accelerated rat incisor eruption

The effect of accelerated odontogenesis of the rat mandibular incisor on the expression of receptors for epidermal growth factor (EGF) was examined using specific monoclonal antibodies to the receptor molecule. Acceleration of odontogenesis was achieved by regular trimming of the tooth crown. At normal eruption rates the major area of cross-reactivity was over the secretory ameloblasts. Some labelling of the papilla and preameloblasts was evident. When proliferation was increased the major area of effect was at the preodontoblast/odontoblast boundary where there was a marked increase in labelling, initially at the proximal end of the cell adjacent to the basal lamina. The ameloblasts did not show such a dramatic increase in receptor numbers. Increase in labelling was also evident in the remainder of the papilla. The results suggest that an increase in proliferation with normal morphogenesis is associated with an overall increase in the numbers of EGF receptors, particularly in a population of cells immediately before and after elongation and differentiation of odontoblasts.

Modulation of the expression of the VIP receptor by serum factors on the human melanoma cell line IGR39

IGR39 cells, isolated from a human superficial melanoma, display at their surface high and low affinity receptors for the vasoactive intestinal peptide (VIP). When grown in DME medium supplemented with 10% fetal calf serum, cells display 1.6 x 10(5) high affinity (Kd 0.74 nM) and 5.6 x 10(5) low affinity (Kd 55 nM) VIP binding sites per cell. When cultured in a chemically defined medium containing EGF, transferrin, and selenium, IGR39 cells display many neurite-like extensions. Following these morphological changes, the specific [125I]VIP binding is increased four- to fivefold after 6 days in culture. This phenomenon is reversible and is the result of an increased number of VIP binding sites available at the cell surface, without modification of their affinities. The molecular mass of the binding sites is also unchanged whatever cell culture conditions. Increase in [125I]VIP binding is inversely correlated to the serum concentration in the culture medium. When added to the chemically defined medium, sera from various origins as well as some serum substitutes reduce [125I]VIP binding to the same extent as that of the serum. The total cAMP production by VIP-stimulated IGR39 cells is enhanced by a factor of six to seven when cells are cultured in serum-free medium, in good correlation with the increase of VIP binding capacity. These data suggest that factor(s) present in fetal calf serum inhibit(s) the expression of VIP receptor, thus demonstrating the importance of a strict control of cell culture conditions for in vitro studies.

Molecular mechanisms of tubulointerstitial hypertrophy and hyperplasia

Adult kidneys, which are principally composed of tubulointerstitium, do not normally regenerate or expand their working pool of functional cells at a very high rate. Loss of kidney tissue, however, can lead to some compensatory renal enlargement. The catalytic forces initiating such exchanges have not been fully articulated by current experimental endeavors. Increasing evidence, nevertheless, does suggest that factors other than simple changes in renal hemodynamics may be involved in this process. Different cellular elements in the tubulointerstitial microenvironment probably modulate changes in tubular enlargement or size through a complex cytokine network. Autocrine and paracrine stimulation of enlargement by different local growth factors also seem to play a pivotal role. After binding to cellular receptors, these factors activate signal transduction pathways resulting in expression of immediate early genes, which by themselves can synchronize the expression of subsequent genes through the medium of transacting factors. The renal enlargement response can also be modified by endocrine hormones that can activate such genes directly and/or stimulate other adjunctive processes, like receptor expression for the regional binding of growth factors. Furthermore, renal enlargement is under negative feedback of inhibitory factors like TGF beta. It is possible, for example, that special genes exist which are only expressed to arrest enlargement. It has been further suggested that activation of the Na+/H+ antiporter is a common denominator in renal enlargement. Recent findings, however, indicate that the activation of this antiporter is not always necessary, and might rather be a parallel event rather than a key phenomena in tubular enlargement. G0/G1 transition of tubular cells seems to involve similar factors in tubular hypertrophy and hyperplasia. The factors which are responsible for the final determination of the enlargement pattern (hypertrophy vs. proliferation) are unknown. The separation between hypertrophy and hyperplasia, although suggested by striking differences in cellular regulation, may be somewhat artificial, since responses leading to tubular enlargement also exist in circumstances where hyperplasia and hypertrophy are combined events. Recently it has been proposed that growth factors stimulate gluconeogenesis in proximal tubular cells producing hyperplasia, whereas factors inhibiting gluconeogenesis might induce hypertrophy. Whether the common pathway message of this intriguing hypothesis is correct still requires further validation.(ABSTRACT TRUNCATED AT 400 WORDS)

Characterization of epidermal growth factor receptor in normal and neoplastic human endometrium

Growth factors, including epidermal growth factor (EGF), have been implicated in the growth of several types of cancer. This study compares EGF receptors in normal and neoplastic endometrium. Membrane fractions were isolated from surgical specimens. Radioreceptor assays demonstrated the presence of receptors with a dissociation constant of 0.64 nmol/l in normal endometrium. Affinity cross-linking revealed receptor molecular weight of 150 to 170 kiloDaltons (KD). A survey of samples (n = 37) revealed progressive decrease of EGF receptors in cancers of increasing grade: Grade 1-2 adenocarcinoma decreased 34% from control (n = 6, P less than 0.01), whereas Grade 3 adenocarcinoma decreased 90% (n = 7, P less than 0.01) and sarcoma decreased by 72% (n = 3, P less than 0.01). The dissociation constant and molecular weight of the receptor in neoplastic endometrium did not differ significantly from normal. The inverse relationship with grade suggests receptor alteration or down regulation by hormones and/or growth factors.

Development and characterization of monoclonal antibodies to a specific domain of human estrogen receptor

We have synthesized three peptides with amino acid sequences identical to those spanning amino acids 201-215, 231-245, and 247-261 of the human estrogen receptor (hER). These peptides were conjugated to keyhole limpet hemocyanin and used as immunogens to develop monoclonal antibodies (MoAbs) to hER. Antibody responses were only elicited by the peptide with amino acid sequence 247-261. Splenocytes from immunized mice were used for hybridoma production. Of the seven MoAbs that recognized the native (functional) form of the ER, four (MoAbs 16, 33, 114, and 213) recognized the ER with high affinity, as demonstrated by the increased sedimentation coefficient of the antibody-complexed ER in sucrose density gradients. Antibodies 318, 35, and 36 bound to ER with low affinity since they immunoprecipitated ER, but the ER-antibody complex appeared to dissociate on sucrose density gradients. The high-affinity MoAbs appear to be site-specific since the peptide competed effectively for binding of the receptor by the antibody. The fact that they reacted with ER from human breast cancer and calf, rat, and mouse uterine tissues suggests that this epitope of the receptor is conserved in these species. Although the DNA-binding region appears to be conserved among the various steroid receptors, these MoAbs did not recognize the native forms of progesterone, androgen, or glucocorticoid receptors. These MoAbs bound to the KCl-activated 4S ER and heat-transformed 5S ER, suggesting that the antibody-binding site is accessible in the monomeric and dimeric forms of ER. The antibodies did not recognize the untransformed 8S ER in the presence of molybdate and without KCl, suggesting that the antibody-binding site in the oligomeric form of ER is inaccessible. The fact that the antibodies did bind to the unoccupied 4S ER was demonstrated by the data obtained with sucrose density gradient analysis followed by postlabeling of ER with [3H]estradiol. The antibodies bound to ERs with high affinity (KD = 0.4 to 1.8 nM). At a fixed concentration of antibody, ERs ranging from 20 to 1,000 fmol were detectable. These MoAbs did not inhibit nuclear or DNA binding of ER in vitro. This can be attributed to the dissociation of the antibodies from ER when the latter interacts with its acceptor site. These results demonstrate the development of site-specific MoAbs to the native form of the hER using synthetic peptides as immunogens.

Modulation of transforming growth factor alpha-dependent expression of epidermal growth factor receptor gene by transforming growth factor beta, triiodothyronine, and retinoic acid

We have investigated the actions of transforming growth factor (TGF) type alpha on epidermal growth factor (EGF) receptor mRNA expression in MDA-468 human mammary carcinoma cells in serum-free media. We found that exposure of MDA-468 cells to TGF alpha results in elevated levels of EGF receptor mRNA. This increase in mRNA accumulation showed time and dose dependence. Addition of TGF beta 1 enhanced the accumulation of EGF receptor mRNA induced by TGF alpha in a time- and dose-dependent manner. We also found that triiodothyronine at physiological concentrations exerts synergistic control on the action of TGF alpha alone, or in association with TGF beta 1, on EGF receptor mRNA expression. Similarly, retinoic acid treatment also enhanced in a time- and dose-dependent manner the TGF alpha-dependent response of EGF receptor mRNA and acted synergistically with TGF beta 1. The results described here suggest that optimum regulation of EGF receptor gene expression by TGF alpha is a complex process involving synergistic interactions with heterologous growth factors and hormones.

Noradrenaline and thyroid function regulate (Na+,K+)-adenosine triphosphatase independently in vivo

We investigated interactions between noradrenaline and thyroid hormone status in the regulation of (Na+,K+)-ATPase in vivo. Treatment with the beta-adrenoceptor antagonist propranolol or with the neurotoxin 6-hydroxydopamine did not prevent the increases in heart (Na+,K+)-ATPase associated with triiodothyronine treatment. Administration of methimazole did not prevent the increase in (Na+,K+)-ATPase indices in cerebral cortex and heart associated with subacute noradrenergic stimulation by yohimbine. There was no evidence for synergistic effects between thyroid hormone administration and noradrenergic stimulation by yohimbine. Thyroid hormone, unlike noradrenaline, mainly increased (Na+,K+)-ATPase activity with low affinity for ouabain. These results show that noradrenaline and thyroid hormone regulate (Na+,K+)-ATPase by largely independent mechanisms, and may regulate different populations of enzyme molecules.

Epidermal growth factor receptors in spontaneous ovarian granulosa cell tumors of SWR-derived mice

Epidermal growth factor (EGF) receptor binding properties were examined in spontaneous ovarian granulosa cell (GC) tumors from SWR and SWR-derived strains of mice. EGF binding was measured at room temperature in tissue homogenates from GC tumors and normal ovaries from adult randomly cycling mice. GC tumor tissue displayed significantly increased EGF binding and 2 receptor populations (R1 and R2). Normal ovarian tissue appeared to have only one receptor population with a dissociation constant (KD) similar to the R1 (high-affinity) receptor in GC tumors. In subsequent experiments, GC tumor and normal granulosa cells from immature mice were analyzed in primary cultures for EGF binding, immunofluorescence microscopy for receptors, and cell proliferation. After 24 hr in culture, the GC tumors bound 10-fold more EGF/micrograms protein than did normal granulosa cells. GC tumor cells, but not normal granulosa cells, showed specific immunofluorescence when reacted with a polyclonal antibody to mouse EGFR. During 96 hr in culture, GC tumor cells, but not normal cells, showed a significant proliferative response to EGF. In conclusion, the EGF binding capacity is markedly increased in GC tumor cells and the proliferation data suggest that this growth factor supports tumor growth in the SWR model system.

Circadian variation of epidermal growth factor receptor in mouse liver

The liver undergoes a biochemical and morphological circadian transformation. In this paper, we document circadian variation in the binding parameters of the hepatic epidermal growth factor receptor (EGFR). Liver membranes were prepared from ad libitum fed or fasted male CD2F1 mice killed at different circadian phases at 4 h intervals. Bmax (maximum binding) and Kd (dissociation constant) varied in a rhythmic fashion. The range of change for Bmax along the 24 h time scale was 423%. For Kd, it was 162%. Both peaked late in the dark span, and decreased late in the light span. Fasting and EGF treatment reduced Bmax and the amplitude of circadian variation.

Epidermal growth factor receptor numbers in male and female mouse primary hepatocyte cultures

Epidermal growth factor receptors (EGF-R) were measured in adult male and female mouse primary hepatocyte cultures. On culture day 1, female hepatocytes had significantly fewer EGF-R than male hepatocytes (1.3 x 10(4) versus 6.2 x 10(5) per cell). Over the next three days, morphological changes consistent with progressive heptocyte dedifferentiation were observed. During this period, EGF-R numbers progressively increased in female cultures and decreased in male cultures, and by day 4 the sexual difference in EGF-R numbers was obliterated. These results indicate that a relationship exists between the degree of differentiation in hepatocyte cultures and the expression of EGF-R on the cell surface.

Physiological implications of estrogen receptor modulation by 2,3,7,8-tetrachlorodibenzo-p-dioxin

The interactions of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) with hormones and hormone receptors have important implications for TCDD toxicity. Evidence suggests that TCDD modulates receptors for glucocorticoids, prolactin, thyroxine, low density lipids, epidermal growth factor, and estrogens. Estrogen receptor modulation and the animal's physiological responses to this modulation appear to be particularly important effects and can explain much of the toxicity observed in TCDD-treated animals. Susceptibility of different species to TCDD correlates with their steroid glucuronidation capacity. Because of the close interactions and interdependent regulation of hormonal systems, other hormones may have a similar role in TCDD toxicity.

Ontogenesis of epidermal growth factor in liver of BALB mice

To characterize the ontogenesis of hepatic epidermal growth factor (EGF) metabolism in normal BALB mice, we measured serum and liver concentrations of EGF and liver concentrations of pre-pro EGF mRNA. Female and male animals were studied at 1, 2, 5, 7, and 10 wk of life. After death, body weight and length were measured, and serum and liver tissues were collected for EGF determinations. Immunoreactive serum EGF (means +/- SE) increased at 7 and 10 wk and was significantly higher (P less than 0.05) in males (465 +/- 58 and 683 +/- 120 pg/ml) than females (188 +/- 52 and 295 +/- 64 pg/ml). Liver EGF concentrations were low at 1, 2, and 5 wk, significantly increasing (P less than 0.01) at 10 wk to 179 +/- 36 vs. 268 +/- 49 pg/mg protein for females and males, respectively (female and male values were significantly different, P less than 0.01). Pre-pro EGF mRNA was examined at 1, 2, 3, 5, 7 and 10 wk. EGF message increased in liver to highest values at 10 wk in both males and females. There was a high correlation between serum and liver EGF concentrations during the first 10 wk (r = 0.97 and 0.85 for males and females, respectively) and a twofold increase in liver EGF mRNA between 3 and 10 wk of postnatal life. These results suggest that liver may be an important source of circulating EGF in developing BALB mice.

Epidermal growth factor and its receptor

Epidermal growth factor (EGF) binds with high affinity and specificity to a single site on the external domain of its transmembrane receptor to activate the tyrosine protein kinase activity of its cytoplasmic portion. The EGF receptor gene is amplified and over-expressed in several human tumors, suggesting that increased concentrations of the proto-oncogene leads to constitutive activity similar to that seen with oncogene erb B. Synthesis and degradation of the EGF receptor are regulated, in addition, covalent modification by phosphorylation regulates activity of the receptor protein. Intramolecular self-phosphorylation of Tyr1173 removes a competitive inhibitory constraint to enhance phosphorylation of substrates. Phosphorylation of Thr654 by protein kinase C decreases high affinity EGF binding and EGF-stimulated tyrosine protein kinase activity, providing a mechanism for heterologous regulation of the EGF receptor by tumor promoters and other ligand X receptor complexes. Extensive regulation contributes to normal growth control, abrogation of regulatory controls contributes to uncontrolled growth as seen with erb B transformation and EGF receptor gene amplification in human tumors.

Factors influencing the growth of normal and neoplastic thyroid tissue

TSH activates the adenylate cyclase and the phosphoinositide turnover-protein kinase C-calcium systems in thyroid cells and appears to have an important but variable role in controlling the growth of both normal and neoplastic thyroid tissues. Species differences, experimental conditions, and tissue or tumor cell heterogeneity may account for this variability. Although TSH seems to be an important physiologic growth factor, it is neither the exclusive growth factor for the thyroid gland nor absolutely necessary for the effect of other thyroid growth factors. TSH may work in concert with other growth factors such as EGF. Some growth factors influence thyroid growth through TSH, whereas others do not.

Effect of streptozotocin-induced diabetes on epidermal growth factor receptors in rat liver plasma membrane

The effect of streptozotocin-induced diabetes on 125I-labeled epidermal growth factor (EGF) binding was studied in microsomal membranes from rat liver. The binding of EGF in membranes from diabetic animals was significantly low, the value being about 60% of the control level. Scatchard analysis of the binding data clearly showed that the decrease in EGF binding was due to a decrease in the number of receptors. Treatment of diabetic animals with insulin restored EGF receptors to control levels, whereas the treatment with triiodothyronine had no effect. Serum EGF concentrations measured were almost the same among the control, diabetic, and insulin-treated diabetic groups. These results suggest that insulin deficiency in vivo causes a decrease in hepatic EGF receptors.

Temporal relationship between fetal bovine skeletal growth and circulating hormonal levels

Skeletal growth and serum hormonal levels in bovine fetuses were studied cross-sectionally from late first trimester to late third trimester of gestation (corresponding approximately to 75-275 days of age, and a crown-rump (CR) 5-105 cm/in size). Measurements of tibial and femoral lengths showed that bone growth proceeds at a 30% faster rate in fetuses of 50-105 cm CR, coincident with the appearance and exponential growth (y = 0.000207 e 0.12522 x; y, dried weights of ossification in grams and x, CR in cm) of a secondary center of ossification in the epiphysis. During this period there is an increase in the proportion of [3H]-thymidine-labeled nuclei (measured by autoradiography) in the proliferative zone of the epiphyseal growth plate and a progressive hypertrophy of chondrocytes in the epiphysis; in serum there is a rise in alkaline phosphatase activity, a rise in the calcium, and a decrease in the phosphorus concentrations. Cellularity (nuclei/area) and the proportion of [3H]-thymidine labeled nuclei in epiphyseal cartilage decline during the period of 15-105 cm CR, except at 25-45 cm CR when both parameters of chondrocyte growth have transiently stabilized. [35S]-Sulfate and [3H]-proline incorporation (cpm/100 micrograms DNA) in epiphyseal cartilage also decline initially during 10-25 cm CR, then attain a stable level during 25-50 cm CR; subsequently, [35S]-sulfate incorporation gradually increases and [3H]-proline incorporation remains at a constant level. The proportion of [3H]-thymidine-labeled nuclei in the epiphyseal growth plate also declines in early gestation, then becomes stabilized at 20-50 cm CR. The whole growth plate thickness varies during gestation and is maximal during 20-50 cm CR. The proliferative zone attains maximal thickness at 20-50 cm CR while the hypertrophied and degenerative zone has maximal thickness at 40-80 cm CR. Gestational changes of hormone levels were quantitated in fetal serum. Glucocorticoids and thyroxine were measured by radioimmunoassay; somatomedinlike bioactivity was measured as the capacity of a serum sample to stimulate [3H]-thymidine incorporation in chondrocytes compared to that of a control serum. Temporally related to the changes occurring in the skeletal tissues, there is a high serum level of glucocorticoids at 10-20 cm CR when the cartilaginous activities are declining, a peak level of serum somatomedinlike bioactivity at 20-50 cm CR when cartilage growth and metabolism become stabilized, and a rise of thyroxine level after 45 cm CR during which time there is an increasing rate of bone formation.(ABSTRACT TRUNCATED AT 400 WORDS)

Levels of epidermal growth factor binding in third-trimester and term human placentas: elevated binding in term placentas of male fetuses

Specific binding of iodine 125-labeled epidermal growth factor was measured in membrane homogenates of third-trimester and term human placentas of male and female fetuses. All placentas (n = 35) generated curvilinear Scatchard plots, and all placentas had similar equilibrium dissociation constants for both high-affinity (210 pmol/L) and low-affinity (830 pmol/L) binding sites. Mean maximum number of available binding sites of term placentas from male fetuses (330 +/- 110 fmol/mg protein; n = 11) was significantly higher (p less than 0.001) than that of female fetuses (170 +/- 80 fmol/mg protein, n = 13). Occupation of epidermal growth factor receptors by endogenous epidermal growth factor could not account for the difference in levels of epidermal growth factor binding. Kendall's rank order correlation test demonstrated a significant positive correlation of the gestational age in weeks with the maximum number of epidermal growth factor receptors in placentas from male fetuses (p less than 0.002; T = 0.527; n = 17) and female fetuses (p less than 0.01; T = 0.404; n = 18). These results indicate that there is a sexual dimorphism in the level of epidermal growth factor receptors in placentas of male and female fetuses during the third trimester and that the level of epidermal growth factor receptors increases during the third trimester for placentas of both male and female fetuses.

Effects of enterally fed epidermal growth factor on the small and large intestine of the suckling rat

Epidermal growth factor (EGF) has been shown to be present in the milk of several species, including the rat, and to have gastrointestinal effects when given parenterally or orally in pharmacologic doses. We investigated the effect of enteral EGF in physiologic doses on the small intestine and colon of suckling rats. Serum thyroxine (T4) levels were also measured. Rats were gavage-fed by hand with an artificial formula with or without added EGF every 3 h from 11 to 14 days of age. Intake was adjusted to deliver 30 kcal/100 g b.wt./day of formula and 16 micrograms/kg/day of EGF approximating the daily caloric intake, and about twice the estimated daily EGF intake for suckling rats. Weight gain did not differ between groups (fed EGF: 3.8 + 0.2 g; not fed EGF: 3.7 + 0.1 g). The protein content of the whole colon of rats fed an EGF-containing formula was significantly lower and the DNA content significantly higher, than in rats fed formula without added EGF. The protein/DNA ratio was therefore markedly higher in the animals fed formula without added EGF; these effects were most evident in the distal colon. In contrast, there was no effect of EGF on small intestinal protein and DNA content; lactase, sucrase, and maltase activities were likewise unaffected, as was serum T4. These data suggest a physiologic role for breast milk EGF in the development of the suckling rat colon.

Dedifferentiation of cultured thyroid cells by epidermal growth factor: some insights into the mechanism

Epidermal growth factor (EGF) has been shown to enhance both the proliferation and dedifferentiation of thyroid cells in culture, leading to a maintained dedifferentiated state, even in the presence of thyrotropin (TSH). Since this maintained loss of differentiated function is not seen with other mitogens, it may relate to a regulatory role for EGF in thyroid function. Therefore, we have examined the loci affected by the dedifferentiative actions of EGF using porcine thyroid cells in culture. EGF (10 ng/ml) induces a loss of thyrotropin (TSH) receptors with a time course identical to the loss in ability to transport iodide. This could account for the difference in extent of iodide uptake and morphological dedifferentiation seen between TSH- and cAMP-supported cells, although the fact that cAMP-supported cells also dedifferentiate implies a lesion distal to the cyclase. Reciprocal plot analysis of iodide uptake in control and EGF-treated cells shows that EGF increases the Km for iodide transport, corresponding to a decreased affinity of iodide pump sites for iodide. These effects on iodide pump affinity and TSH receptor number may result from reversal of thyroid cell polarity in monolayer culture, or they may be the result of more specific actions of EGF at these loci. It has been possible to discriminate between the proliferative and dedifferentiating actions of EGF using amiloride, a non-specific inhibitor of the Na+/H+ antiporter. An optimum concentration of amiloride (0.1 mM) was able to block EGF-stimulated incorporation of [3H]thymidine into DNA without preventing the blockade of iodide uptake, which implies that dedifferentiation is not a consequence of proliferation.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of sera, growth factors, and hormones in the in vitro production of disaturated phosphatidylcholine and propagation of undifferentiated type II alveolar cells from the fetal rabbit lung

Undifferentiated type II alveolar cells isolated from the fetal rabbit lung were cultured in chemically-defined medium supplemented with 10% carbon-stripped fetal bovine serum for 2-3 days and then placed in serum-free medium, or medium supplemented with either 10% carbon-stripped fetal bovine serum (sFBS) or 10% unstripped fetal bovine serum. Cells exposed to the latter treatment showed the highest growth rate but the lowest level of [3H]choline incorporation into disaturated phosphatidylcholine (DSPC). Cells in serum-free medium showed the lowest rate of growth but removal of serum components stimulated a rapid increase in radioactive precursor incorporation. Cells exposed to the stripped serum were intermediate in both measurements. Incubation of undifferentiated type II cells with EGF stimulated growth but only in the presence of sFBS. EGF also stimulated [3H]choline into DSPC after 48 hours of exposure to the peptide. This latter response could only be elicited in serum-free medium. In the presence of sFBS no effect of the peptide was detected on radioactive precursor incorporation. Similarly dexamethasone (0.55 nM) or 20% medium which had been conditioned by fetal lung fibroblast monolayers did not stimulate [3H]choline in DSPC in the presence of sFBS. In contrast these agents did evoke a significant increase in radioactive precursor incorporation when the undifferentiated type II alveolar cells were incubated in serum-free medium.

Interactions between estrogen and EGF in uterine growth and function

The rat uterus contains specific, high-affinity EGF receptors which possess a tyrosine kinase activity. As demonstrated autoradiographically, these receptors are present in the epithelial, stromal and myometrial cells of the uterus. Estrogen treatment in vivo produces a 2-3-fold increase in EGF receptor levels in the immature rat, the immature mouse and the ovariectomized adult rat; furthermore, EGF receptor levels vary throughout the estrus cycle in concert with levels of occupied nuclear estrogen receptor. This estrogen-induced increase in EGF receptor is preceded by an increase in the level of EGF receptor mRNA as judged by Northern blot analysis. In general, there is a good correlation between estrogen-induced DNA synthesis and EGF receptor levels in the uterus, although in certain situations EGF receptor levels are elevated without a subsequent increase in DNA synthesis. These observations suggest that an increase in tissue EGF receptor levels is important in estrogen-induced uterine growth, but that this increase in receptor levels alone is not sufficient to stimulate DNA synthesis. In addition to its possible role in tissue growth, we have shown very recently that EGF causes contraction of myometrial smooth muscle in a completely in vitro organ bath system. The qualitative nature of this contractile response is distinct from that produced by other classical uterotonic agents. The physiological significance of this uterine response to EGF remains to be elucidated.

Decreased expression of liver epidermal growth factor receptors in rats with alloxan and streptozotocin diabetes

Male rats (200 g) were rendered diabetic with one intraperitoneal injection of alloxan (150 mg/kg) or streptozotocin (60 mg/kg). In hyperglycemic animals within 3 hours after the injection, the binding of EGF to liver membranes decreased by 43-52%; the maximal drop was by 70% and persisted for the 20 days of the experiment. EGF receptors decreased in number with almost no changes in their affinity. Autophosphorylation of the receptors decreased parallel to the ligand binding. In animals that received lower doses and did not develop diabetes and in animals in whom diabetes was prevented by the injections of glucose (before alloxan) or nicotinamide (before streptozotocin) the binding of EGF to liver receptors remained normal. We conclude that the decreased expression of EGF receptors was caused by diabetes and not by the toxic effects of the diabetogenic compounds on the liver.

Binding characteristics of epidermal growth factor receptors in male and female rat liver cell membrane preparations

The binding characteristics of epidermal growth factor (EGF) receptors were studied in cell membrane preparations from adult male (n = 14) and female (n = 13) rat livers. Results indicate a significant lower (about 65%) number of EGF receptors in female preparations. The possibility that the decrease in EGF receptors was only a reflection of an excess free EGF in female preparations was ruled out by means of acid extraction, ultrafiltration, and measurement of EGF in the acid extracts. In view of the known role of EGF in cell differentiation, it may be important to recognize that the number of its receptors, at least in liver preparations, is markedly different between sexes.

Inhibition by estradiol of binding and mitogenic effect of epidermal growth factor in primary cultures of Xenopus hepatocytes

We demonstrate here the presence of two classes of EGF (epidermal growth factor) binding sites in primary cultures of male Xenopus liver parenchymal cells. One of these corresponds to the high-affinity receptor described in other tissues and species, and which exhibits the property of autophosphorylation. The number of EGF receptors decreased sharply in freshly prepared cultures but recovered to maximum levels within 24 h thereafter. Addition of EGF and insulin to the hepatocyte cultures enhanced the rate of DNA synthesis as measured by the incorporation of [3H]thymidine. Estrogen abolished this increase, reducing the incorporation to that seen with hydroxyurea. At the same time, the addition of estradiol reduced the number or activity of EGF receptors in a dose-dependent manner. The latter paralleled the activation of transcription of vitellogenin genes in Xenopus hepatocytes so that a high rate of DNA synthesis is unnecessary for or incompatible with the activation of the steroid hormone-induced vitellogenin genes.