Overexpression of epidermal growth factor induced hypospermatogenesis in transgenic mice

Epidermal growth factor represses differentiation of mouse trophoblast stem cells into spongiotrophoblast cells via epidermal growth factor receptor

The mouse placenta is composed of three different trophoblast layers that are occupied by particular trophoblast subtypes to maintain placental function and pregnancy. Accurate control of trophoblast differentiation is required for proper placental function; however, the molecular mechanisms underlying cell fate decisions in trophoblast stem cells remain poorly understood. Epidermal growth factor (EGF) signaling is involved in multiple biological processes including cell survival, proliferation, and differentiation. The effect of EGF on trophoblast function has been reported in various species; however, the role of EGF signaling in mouse trophoblast specification remains unclear. In this study, we aimed to elucidate the role of EGF signaling in mouse trophoblast differentiation using mouse trophoblast stem cells (mTSCs) in an in vitro culture system. EGF stimulation at the early stage of differentiation repressed mTSC differentiation into spongiotrophoblast cells (SpT). Gene deletion and inhibitor experiments showed that the effect of EGF exposure went through epidermal growth factor receptor (Egfr) activity in mTSCs. EGF stimuli induced acute downstream activation of MAPK/ERK, PI3K/AKT, and JNK pathways, and inhibition of the MAPK/ERK pathway, but not others, alleviated EGF-mediated repression of SpT differentiation. Moreover, expression of Mash2, a master regulator of SpT differentiation, was repressed by EGF stimulation, and MAPK/ERK inhibition counteracted this repression. The Mash2 overexpression recovered SpT marker expression, indicating that the decrease in Mash2 expression was due to abnormal SpT differentiation in EGF-treated mTSCs. Our findings suggest that the EGF-Egfr-MAPK/ERK-Mash2 axis is a core regulatory mechanism for the EGF-mediated repression of SpT differentiation.

Trade‐offs between male fertility reduction and selected growth factors or the klotho response in a lipopolysaccharide-dependent mouse model

The increasing number of depression cases leads to a greater need for new antidepressant treatment development. It is postulated that antidepressants may harm male fertility, but the cellular mechanism is still poorly understood. The role of growth factors and klotho protein in maintaining normal male reproductive function is well documented. Hence, the study aimed to investigate the effect of the antidepressant drug – imipramine (tricyclic AD), and other substances with antidepressant potential (ALS), administered in combination or in combination with LPS (an animal model of depression) on gene expression and protein synthesis of IGF-2 (insulin-like growth factor 2), TGF-β1 (transforming growth factor β1), NGF (nerve growth factor), KGF (keratinocyte growth factor) and protein synthesis of VEGF-A (vascular endothelial growth factor A), IGF-IR (insulin-like growth factor receptor 1), EGFR (epidermal growth factor receptor) and klotho in the testis of mice. Mice were injected intraperitoneally with selected ALS and LPS or 10% DMSO (controls) (n = 7/group) once a day for 14 days. Animals were decapitated and testes collected for RNA and protein purification. PCR and western blot methods were employed for the evaluation of growth factors and klotho expression. The results obtained indicated a decreased level of most of the analyzed genes and proteins, except KGF; its expression increased after treatment with MTEP and IMI administrated individually and after NS-398, and IMI in combination with LPS. Our results may suggest that the tested ALS and LPS can contribute to a reduction of male fertility, but NS-398, IMI, and IMI+NS-398 may also act as stimulants after LPS.

Post-weaning xenohormone intake affects adult rat submandibular gland in a sex-dependent manner

OBJECTIVES

We previously reported that maternal exposure to genistein and vinclozolin, ingested alone or in combination, affects submandibular salivary glands of rat offspring. Here, we investigated the responsiveness of submandibular gland when such xenohormone exposure occurs later in life.

MATERIALS AND METHODS

Chemicals were given orally to male and female Wistar rats (1 mg/kg body weight per day), from weaning to adulthood. Submandibular glands and plasma were collected at postnatal day 100 for histologic and molecular analysis.

RESULTS

Whereas no effect was observed in females, increases in granular convoluted tubules area coupled with a modification of salivary secretions were found in male submandibular glands. Genistein and vinclozolin similarly increased the mRNA expression of Cystatin C, Mucin 10, Growth factors, and plasmatic EGF. Negative correlations were found between the expressions of androgen receptor and EGF (-0.34; p < 0.05), TGFα (-0.52; p < 0.01), Mucin 10 (-0.43; p < 0.05), and Cystatin C (-0.42; p < 0.05) as well as between progesterone receptor and EGF (-0.56; p < 0.01). The Spearman correlation test revealed also a positive correlation between salivary EGF-mRNA expression and EGF in plasma (+0.32; p < 0.05).

CONCLUSION

Our findings confirm the sex-dependent sensitivity of submandibular salivary glands to dietary xenohormones and underline the influence of the exposure period.

The role of epidermal growth factor receptor (EGFR) signaling in SARS coronavirus-induced pulmonary fibrosis

Many survivors of the 2003 outbreak of severe acute respiratory syndrome (SARS) developed residual pulmonary fibrosis with increased severity seen in older patients. Autopsies of patients that died from SARS also showed fibrosis to varying extents. Pulmonary fibrosis can be occasionally seen as a consequence to several respiratory viral infections but is much more common after a SARS coronavirus (SARS-CoV) infection. Given the threat of future outbreaks of severe coronavirus disease, including Middle East respiratory syndrome (MERS), it is important to understand the mechanisms responsible for pulmonary fibrosis, so as to support the development of therapeutic countermeasures and mitigate sequelae of infection. In this article, we summarize pulmonary fibrotic changes observed after a SARS-CoV infection, discuss the extent to which other respiratory viruses induce fibrosis, describe available animal models to study the development of SARS-CoV induced fibrosis and review evidence that pulmonary fibrosis is caused by a hyperactive host response to lung injury mediated by epidermal growth factor receptor (EGFR) signaling. We summarize work from our group and others indicating that inhibiting EGFR signaling may prevent an excessive fibrotic response to SARS-CoV and other respiratory viral infections and propose directions for future research.

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Patients who survived SARS coronavirus infection often developed pulmonary fibrosis.

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Mouse models of SARS-CoV infection recapitulate fibrotic lesions seen in humans.

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Epidermal growth factor receptor (EGFR) may modulate the wound healing response to SARS-CoV.

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The EGFR pathway is a prime target for therapeutic interventions to reduce fibrosis after respiratory virus infection.

Androgen receptor in Sertoli cells regulates DNA double-strand break repair and chromosomal synapsis of spermatocytes partially through intercellular EGF-EGFR signaling

Spermatogenesis does not progress beyond the pachytene stages of meiosis in Sertoli cell-specific AR knockout (SCARKO) mice. However, further evidence of meiotic arrest and underlying paracrine signals in SCARKO testes is still lacking. We utilized co-immunostaining of meiotic surface spreads to examine the key events during meiotic prophase I. SCARKO spermatocytes exhibited a failure in chromosomal synapsis observed by SCP1/SCP3 double-staining and CREST foci quantification. In addition, DNA double-strand breaks (DSBs) were formed but were not repaired in the mutant spermatocytes, as revealed by γ-H2AX staining and DNA-dependent protein kinase (DNA-PK) activity examination. The later stages of DSB repair, such as the accumulation of the RAD51 strand exchange protein and the localization of mismatch repair protein MLH1, were correspondingly altered in SCARKO spermatocytes. Notably, the expression of factors that guide RAD51 loading onto sites of DSBs, including TEX15, BRCA1/2 and PALB2, was severely impaired when either AR was down-regulated or EGF was up-regulated. We observed that some ligands in the epidermal growth factor (EGF) family were over-expressed in SCARKO Sertoli cells and that some receptors in the EGF receptor (EGFR) family were ectopically activated in the mutant spermatocytes. When EGF-EGFR signaling was repressed to approximately normal by the specific inhibitor AG1478 in the cultured SCARKO testis tissues, the arrested meiosis was partially rescued, and functional haploid cells were generated. Based on these data, we propose that AR in Sertoli cells regulates DSB repair and chromosomal synapsis of spermatocytes partially through proper intercellular EGF-EGFR signaling.

Understanding the Impact of ErbB Activating Events and Signal Transduction on Antigen Processing and Presentation: MHC Expression as a Model

Advances in molecular pathology have changed the landscape of oncology. The ability to interrogate tissue samples for oncogene amplification, driver mutations, and other molecular alterations provides clinicians with an enormous level of detail about their patient's cancer. In some cases, this information informs treatment decisions, especially those related to targeted anti-cancer therapies. However, in terms of immune-based therapies, it is less clear how to use such information. Likewise, despite studies demonstrating the pivotal role of neoantigens in predicting responsiveness to immune checkpoint blockade, it is not known if the expression of neoantigens impacts the response to targeted therapies despite a growing recognition of their diverse effects on immunity. To realize the promise of 'personalized medicine', it will be important to develop a more integrated understanding of the relationships between oncogenic events and processes governing anti-tumor immunity. One area of investigation to explore such relationships centers on defining how ErbB/HER activation and signal transduction influences antigen processing and presentation.

Expression and Function of the Epidermal Growth Factor Receptor in Physiology and Disease

The epidermal growth factor receptor (EGFR) is the prototypical member of a family of membrane-associated intrinsic tyrosine kinase receptors, the ErbB family. EGFR is activated by multiple ligands, including EGF, transforming growth factor (TGF)-α, HB-EGF, betacellulin, amphiregulin, epiregulin, and epigen. EGFR is expressed in multiple organs and plays important roles in proliferation, survival, and differentiation in both development and normal physiology, as well as in pathophysiological conditions. In addition, EGFR transactivation underlies some important biologic consequences in response to many G protein-coupled receptor (GPCR) agonists. Aberrant EGFR activation is a significant factor in development and progression of multiple cancers, which has led to development of mechanism-based therapies with specific receptor antibodies and tyrosine kinase inhibitors. This review highlights the current knowledge about mechanisms and roles of EGFR in physiology and disease.

EGFR Signaling in Liver Diseases

The epidermal growth factor receptor (EGFR) is a transmembrane receptor tyrosine kinase that is activated by several ligands leading to the activation of diverse signaling pathways controlling mainly proliferation, differentiation, and survival. The EGFR signaling axis has been shown to play a key role during liver regeneration following acute and chronic liver damage, as well as in cirrhosis and hepatocellular carcinoma (HCC) highlighting the importance of the EGFR in the development of liver diseases. Despite the frequent overexpression of EGFR in human HCC, clinical studies with EGFR inhibitors have so far shown only modest results. Interestingly, a recent study has shown that in human HCC and in mouse HCC models the EGFR is upregulated in liver macrophages where it plays a tumor-promoting function. Thus, the role of EGFR in liver diseases appears to be more complex than what anticipated. Further studies are needed to improve the molecular understanding of the cell-specific signaling pathways that control disease development and progression to be able to develop better therapies targeting major components of the EGFR signaling network in selected cell types. In this review, we compiled the current knowledge of EGFR signaling in different models of liver damage and diseases, mainly derived from the analysis of HCC cell lines and genetically engineered mouse models (GEMMs).

Epidermal growth factor, from gene organization to bedside

In 1962, epidermal growth factor (EGF) was discovered by Dr. Stanley Cohen while studying nerve growth factor (NGF). It was soon recognized that EGF is the prototypical member of a family of peptide growth factors that activate the EGF receptors, and that the EGF/EGF receptor signaling pathway plays important roles in proliferation, differentiation and migration of a variety of cell types, especially in epithelial cells. After the basic characterization of EGF function in the first decade or so after its discovery, the studies related to EGF and its signaling pathway have extended to a broad range of investigations concerning its biological and pathophysiological roles in development and in human diseases. In this review, we briefly describe the gene organization and tissue distribution of EGF, with emphasis on its biological and pathological roles in human diseases.

Endogenous EGF maintains Sertoli germ cell anchoring junction integrity and is required for early recovery from acute testicular ischemia/reperfusion injury

Administration of exogenous epidermal growth factor (EGF) improves testicular injury after acute ischemia–reperfusion (IR) stress, but the molecular basis is poorly understood. The role of endogenous EGF in testicular recovery and the underlying intracellular signaling pathways involved were herein investigated. In mice, testicular IR injury significantly enhanced the expression level of endogenousEgfat the very beginning of reperfusion. Expression of EGF receptor (Egfr(ErbB1)) was accordingly upregulated 3 h after reperfusion. Deprivation of majority of circulated EGF by sialoadenectomy aggravated testicular detriment (especially in pachytene spermatocytes), enhanced germ cell apoptosis, and thereafter resulted in impaired meiotic differentiation after IR insult. Mechanistically, endogenous EGF signaling appeared to be indispensable for the proper maintenance of Sertoli germ cells anchoring junction dynamics during the early testicular recovery. We also provided thein vitroevidences in a well-established rat Sertoli germ cell co-cultures model that the pro-survival effect of endogenous EGF on germ cells in response to testicular IR insult is mediated, at least in part, via the phosphatidylinositol 3-kinase/pAkt pathway. Collectively, our results suggest that the augment of endogenous EGF during the early testicular recovery may act on top of an endocrinous cascade orchestrating the intimate interactions between Sertoli cells and germ cells and may operate as indispensable defensive mechanism in response to testicular IR stress. Future studies in this field would shed light on this complicated pathogenesis.

Presence, distribution and steroidogenic effect of the peptides orexin A and receptor 1 for orexins in the testis of the South American camelid alpaca (Vicugna pacos)

The orexins A (oxA) and B are peptides discovered in the rat hypothalamus and successively found in some peripheral organs of the mammalian body. They binds two protein G-coupled receptors defined receptor 1 (ox1r) and 2 for orexins, the first of which is highly specific for oxA while the second binds both the peptides with equal affinity. This work aimed to detect the presence of oxA and ox1r in the testis of the South American camelid alpaca (Vicugna pacos) and investigate the role played by them on Leydig cell steroidogenesis. The species alpaca acquired, in the last years, increasing zootechnical interest for the quality of the wool produced and its breeding spread from the country of origin to USA, Australia and Europe. Immunohistochemistry allowed us to detect oxA in Leydig and Sertoli cells, spermatogonia, resting spermatocytes, round and oval spermatids. Ox1r-immunoreactivity was found in Leydig cells and round, oval and elongated spermatids. The expression of the two peptides in tissue extracts was established by using Western blotting technique. Such results demonstrated that in the alpaca testis exists in a cellular complex able to produce and/or internalize oxA. Finally, the effect of oxA on steroidogenesis was investigated by means of in vitro cultured thin testis slices which were added with oxA or/and Müllerian Inhibiting Substance (MIS), a steroidolitic agent basally produced by the Sertoli cell. OxA evoked increase of testosterone production while MIS a decrease. The consecutive addition of oxA and MIS, or vice versa, highlighted an antagonistic interplay between the two substances which has been thought to be the main molecular event at the basis of the oxA-stimulated steroidogenesis mechanism.

TGF-alpha mediates genetic susceptibility to chronic kidney disease

The mechanisms of progression of chronic kidney disease (CKD) are poorly understood. Epidemiologic studies suggest a strong genetic component, but the genes that contribute to the onset and progression of CKD are largely unknown. Here, we applied an experimental model of CKD (75% excision of total renal mass) to six different strains of mice and found that only the FVB/N strain developed renal lesions. We performed a genome-scan analysis in mice generated by back-crossing resistant and sensitive strains; we identified a major susceptibility locus (Ckdp1) on chromosome 6, which corresponds to regions on human chromosome 2 and 3 that link with CKD progression. In silico analysis revealed that the locus includes the gene encoding the EGF receptor (EGFR) ligand TGF-α. TGF-α protein levels markedly increased after nephron reduction exclusively in FVB/N mice, and this increase preceded the development of renal lesions. Furthermore, pharmacologic inhibition of EGFR prevented the development of renal lesions in the sensitive FVB/N strain. These data suggest that variable TGF-α expression may explain, in part, the genetic susceptibility to CKD progression. EGFR inhibition may be a therapeutic strategy to counteract the genetic predisposition to CKD.

Betacellulin inhibits osteogenic differentiation and stimulates proliferation through HIF-1alpha

Cellular signaling via epidermal growth factor (EGF) and EGF-like ligands can determine cell fate and behavior. Osteoblasts, which are responsible for forming and mineralizing osteoid, express EGF receptors and alter rates of proliferation and differentiation in response to EGF receptor activation. Transgenic mice over-expressing the EGF-like ligand betacellulin (BTC) exhibit increased cortical bone deposition; however, because the transgene is ubiquitously expressed in these mice, the identity of cells affected by BTC and responsible for increased cortical bone thickness remains unknown. We have therefore examined the influence of BTC upon mesenchymal stem cell (MSC) and pre-osteoblast differentiation and proliferation. BTC decreases the expression of osteogenic markers in both MSCs and pre-osteoblasts; interestingly, increases in proliferation require hypoxia-inducible factor-alpha (HIF-alpha), as an HIF antagonist prevents BTC-driven proliferation. Both MSCs and pre-osteoblasts express EGF receptors ErbB1, ErbB2, and ErbB3, with no change in expression under osteogenic differentiation. These are the first data that demonstrate an influence of BTC upon MSCs and the first to implicate HIF-alpha in BTC-mediated proliferation.

Betacellulin inhibits osteogenic differentiation and stimulates proliferation through HIF-1alpha

Cellular signaling via epidermal growth factor (EGF) and EGF-like ligands can determine cell fate and behavior. Osteoblasts, which are responsible for forming and mineralizing osteoid, express EGF receptors and alter rates of proliferation and differentiation in response to EGF receptor activation. Transgenic mice over-expressing the EGF-like ligand betacellulin (BTC) exhibit increased cortical bone deposition; however, because the transgene is ubiquitously expressed in these mice, the identity of cells affected by BTC and responsible for increased cortical bone thickness remains unknown. We have therefore examined the influence of BTC upon mesenchymal stem cell (MSC) and pre-osteoblast differentiation and proliferation. BTC decreases the expression of osteogenic markers in both MSCs and pre-osteoblasts; interestingly, increases in proliferation require hypoxia-inducible factor-alpha (HIF-α), as an HIF antagonist prevents BTC-driven proliferation. Both MSCs and pre-osteoblasts express EGF receptors ErbB1, ErbB2, and ErbB3, with no change in expression under osteogenic differentiation. These are the first data that demonstrate an influence of BTC upon MSCs and the first to implicate HIF-α in BTC-mediated proliferation.

The C-terminal cytoplasmic domain of human proEGF is a negative modulator of body and organ weights in transgenic mice

We generated transgenic mice to study the in vivo role of the cytoplasmic domain of human proEGF (proEGFcyt). Post-pubertal proEGFcyt transgenic (tg) mice displayed an up to 15% reduction in body weight, including smaller kidney and brain weights as compared to control littermates. Renal histology, gene expression profiles, and functional parameters were normal. In both sexes, serum levels of IGFBP-3 were reduced. Circulating IGF-I/IGF-II levels were unchanged. Histomorphological analysis revealed isolated foci of liver necrosis specific to proEGFcyt tg mice. In conclusion, we identified proEGF cytoplasmic domain as a novel modulator of whole body and organ-specific growth in mice.

The epidermal growth factor receptor ligands at a glance

The epidermal growth factor receptor (EGFR) regulates key processes of cell biology, including proliferation, survival, and differentiation during development, tissue homeostasis, and tumorigenesis. Canonical EGFR activation involves the binding of seven peptide growth factors. These ligands are synthesized as transmembrane proteins comprising an N-terminal extension, the EGF module, a short juxtamembrane stalk, a hydrophobic transmembrane domain, and a carboxy-terminal fragment. The central structural and functional feature is the EGF module, a sequence containing six cysteines in a conserved spacement which is responsible for binding to the EGFR. While the membrane-anchored peptide can be biologically active by juxtacrine signaling, in most cases the EGF module is proteolytically cleaved (a process termed ectodomain shedding) to release the soluble growth factor, which may act in an endocrine, paracrine, or autocrine fashion. This review summarizes the structural and functional properties of these fascinating molecules and presents selected examples to illustrate their roles in development, physiology, and pathology.

Epidermal growth factor mediates spermatogonial proliferation in newt testis

The complex processes of spermatogenesis are regulated by various factors. The aim of the current study is to determine the effect of epidermal growth factor (EGF) on spermatogonial proliferation and clarify the mechanism causing the proliferation in newt testis. In the organ culture, EGF stimulated spermatogonial proliferation, but not their differentiation into spermatocytes. cDNA cloning identified 3 members of the EGF receptors, ErbB1, ErbB2, and ErbB4, in the testis. RT-PCR showed that all the receptors cloned were expressed in both Sertoli and germ cells at the spermatogonial stage. In the organ cultures with inhibitors for the EGF receptors, mitogen-activated protein kinase (MAPK), and phosphoinositide 3-kinase (PI3K), the EGF-induced spermatogonial proliferation was suppressed. Furthermore, when the organ culture was exposed to EGF, the expressions of stem cell factor (SCF), immunoglobulin-like domain containing neuregulin1 (Ig-NRG1), and ErbB4 mRNA were increased. These results suggested that, since the spermatogonia are sequestered within cysts by the blood-testis barrier consisted of Sertoli cells, EGF possibly mediates spermatogonial proliferation in an endocrine manner through the receptors including ErbB1, ErbB2, and ErbB4 expressed on Sertoli cells via activation of MAPK cascade or/and PI3K cascade by elevating the expressions of SCF, Ig-NRG1, and ErbB4.

Localization of the epidermal growth factor (EGF) and epidermal growth factor receptor (EGFR) in the bovine testis

In the last few decades, several growth factors were identified in the testis of various mammalian species. Growth factors are shown to promote cell proliferation, regulate tissue differentiation, and modulate organogenesis. In the present investigation we have studied the localization of EGF and EGFR in the adult bovine testis by means of immunohistochemical method. Our results demonstrated that EGF and EGFR were localized solely to the bovine testicular germ cells (spermatogonia, spermatocytes, and round spermatids). In contrast, the somatic testicular cells (i.e., Sertoli, Leydig, and myofibroblast cells) exhibited no staining affinity. EGF and EGFR were additionally detected in the epithelial lining of straight tubules and rete testis. Interestingly, the distribution of EGF and EGFR in the germ cells was mainly dependent upon the cycle of the seminiferous epithelium since their localization appeared to be preponderant during the spermatogonia proliferation and during the meiotic and spermiogenic processes. In conclusion, such findings may suggest that EGF and EGFR are important paracrine and/or autocrine regulators of spermatogenesis in bovine.

Seasonally activated spermatogenesis is correlated with increased testicular production of testosterone and epidermal growth factor in mink (Mustela vison)

Seasonal changes in spermatogenesis were studied with respect to testicular production of both testosterone and epidermal growth factor (EGF) in mink. The testes were collected in November (n = 15; testis recrudescence), February (n = 15; before breeding season), March (n = 14; breeding season), and May (n = 11; testis involution) and the following parameters of testicular activity were quantified: testicular mass, number of testicular spermatozoa, percentages of haploid, diploid, and tetraploid (G2/M-phase) cells and content of testosterone and EGF. The growth factor was immunohistochemically localized in the parenchyma. Testis mass, spermatogenic activity, and the production of both testosterone and EGF were maximal in March, but were not significantly different from the levels in February. The correlation between testis weight and sperm per testis was r = 0.825 (P < 0.001). Testosterone and EGF levels were correlated to each other (r = 0.78; P < 0.001) and had significant positive correlations to testis mass, number of sperm and proportion of haploid cells; and negative correlations to percentages of mitotic cells. EGF was localized in interstitial cells and in the luminal region of seminiferous tubules, where it occurred during the last steps of spermiogenesis. We inferred that intensified seasonal spermatogenesis was stimulated by testosterone and by autocrine/paracrine effects of EGF.

In vitro effects of epidermal growth factor, follicle stimulating hormone and testosterone on mouse spermatogonial cell colony formation

The complex process of spermatogenesis is regulated by various factors. In the present study, the in vitro effects of epidermal growth factor (EGF), follicle stimulating hormone (FSH) and testosterone on spermatogonial cell colony formation were investigated, and the best colonising factor was chosen for treating cells before transplantation. Sertoli and spermatogonial cells were isolated from neonatal mouse testes. The identity of the cells was confirmed through analysis of morphology, alkaline phosphatase activity, immunoreactivity and transplantation. Co-cultured Sertoli and spermatogonial cells were treated with EGF, FSH and testosterone before colony assay. Results indicated that EGF is the best factor for in vitro colonisation of spermatogonial cells, but transplantation of the EGF-treated group did not show any significant change compared with the control groups. In conclusion, EGF increased in vitro colonisation of spermatogonial cells, but, as a result of differential effects, did not influence transplantation efficiency.

Betacellulin overexpression in transgenic mice causes disproportionate growth, pulmonary hemorrhage syndrome, and complex eye pathology

The EGF family comprises a network of ligands and receptors that regulate proper development and elicit diverse functions in physiology and pathology. Betacellulin (BTC) is a rather poorly characterized member of the EGF family whose in vivo effects have been linked mainly to endocrine pancreas, intestine, and mammary gland function. In vitro studies revealed that this growth factor is a potent mitogen for diverse cell types and suggested unique receptor-binding properties. Genetic ablation of BTC in mice yielded a mild phenotype, probably because of opportunistic compensation by other EGF receptor ligands. To study the biological capabilities of BTC in vivo, we generated transgenic mice overexpressing BTC ubiquitously, with highest expression levels in heart, lung, brain, and pancreas. Mice overexpressing BTC exhibit high early postnatal mortality, reduced body weight gain, and impaired longitudinal growth. In addition, a variety of pathological alterations were observed. Cataract and abnormally shaped retinal layers as well as bone alterations leading to a dome-shaped, round head form were hallmarks of BTC transgenic mice. The most important finding and the cause of reduced life expectancy of BTC transgenic mice were severe alterations of the lung. Pulmonary pathology was primarily characterized by alveolar hemorrhage, thickening of the alveolar septa, intraalveolar accumulation of hemosiderin-containing macrophages, and nodular pulmonary remodeling. Thus, our model uncovers multiple consequences of BTC overexpression in vivo. These transgenic mice provide a useful model for examining the effects of BTC excess on different organs.

Angiotensin II and EGF receptor cross-talk in chronic kidney diseases: a new therapeutic approach

Mechanisms of progression of chronic renal diseases, a major healthcare burden, are poorly understood. Angiotensin II (AngII), the major renin-angiotensin system effector, is known to be involved in renal deterioration, but the molecular pathways are still unknown. Here, we show that mice overexpressing a dominant negative isoform of epidermal growth factor receptor (EGFR) were protected from renal lesions during chronic AngII infusion. Transforming growth factor-alpha (TGF-alpha) and its sheddase, TACE (also known as ADAM17), were induced by AngII treatment, TACE was redistributed to apical membranes and EGFR was phosphorylated. AngII-induced lesions were substantially reduced in mice lacking TGF-alpha or in mice given a specific TACE inhibitor. Pharmacologic inhibition of AngII prevented TGF-alpha and TACE accumulation as well as renal lesions after nephron reduction. These findings indicate a crucial role for AngII-dependent EGFR transactivation in renal deterioration and identify in TACE inhibitors a new therapeutic strategy for preventing progression of chronic renal diseases.

Transforming growth factor alpha (TGF-alpha) and other targets of tumor necrosis factor-alpha converting enzyme (TACE) in murine polycystic kidney disease

Transforming growth factor-alpha (TGF-alpha) is abnormally expressed in autosomal recessive polycystic kidney disease (ARPKD). Tumor necrosis factor-alpha converting enzyme (TACE), a metalloproteinase, mediates TGF-alpha processing. In this study, we sought to determine whether TGF-alpha was an absolute requirement for renal cystogenesis and whether its absence would modulate disease severity or related growth factors/receptors expression. Bpk heterozygotes were bred with TGF-alpha null mice to produce cystic and noncystic offspring with or without TGF-alpha. Assessments included kidney weight (KW), body weight (BW), blood urea nitrogen (BUN), and kidney and liver immunohistology. Western analysis assessed kidney expression of amphiregulin (AR), epidermal growth factor (EGF), heparin-binding EGF (HB-EGF), and their receptors, EGFR and ErbB4. A PCR-based methodology for genotyping bpk mice was also developed. No significant differences in KW, BW, KW/BW%, or BUN were seen in cystic mice with versus without TGF-alpha. Cystic kidney disease and liver disease histology were similar. AR, EGF, HB-EGF, EGFR, and ErbB4 were abnormally expressed to an equal degree in kidneys of mice with versus without TGF-alpha. Although previous data suggest a critical role of TGF-alpha in murine PKD, these data show that TGF-alpha is not required for renal cyst formation or kidney or liver disease progression. We speculate that the therapeutic effect of WTACE2 could have been due to effects on several TACE targets, including TGF-alpha, AR, and ErbB4, as well as metalloproteinases other than TACE.

The ADAM-integrin-tetraspanin complex in fetal and postnatal testicular cords

New insights have emerged about the expression, during testicular cord formation, of the ADAM (a disintegrin and metalloprotease) domain family of proteins that combines both cell surface adhesion and proteolytic activity; this family includes integrins alpha3beta1 and alpha6beta1 and tetraspanins, a distinct family of proteins containing four transmembrane domains, a small and a large extracellular loop, and short cytoplasmic tails. ADAM3 (cyritestin), ADAM5, ADAM6, and ADAM15 are expressed in fetal rat testes. In contrast, the expression of the ADAM1/ADAM2 pair (fertilin alpha/fertilin beta, respectively) is not detected in fetal testis. Yet the expression of ADAM1 starts immediately after birth, and is followed within 24 hr by the expression of ADAM2. Therefore, the ADAM1/ADAM2 heterodimer is visualized far in advance of the meiotic and spermiogenic phase of spermatogenesis. A similar expression pattern was observed for integrin subunits alpha3, alpha6, and beta1, as well as for tetraspanins CD9, CD81, and CD98; the latter is a single-pass integrin subunit beta1-binding protein. ADAM2, integrin subunits alpha3, alpha6, and beta1, and tetraspanin CD9 and CD81 immunoreactive sites are observed in prespermatogonia (also known as primordial germ cells or gonocytes). A model is proposed in which the ADAM-integrin-tetraspanin complex, known to constitute a network of membrane microdomains called the tetraspanin web, may be involved in the migration of prespermatogonia from the center to the periphery of the testicular cords and in the reinitiation of mitotic activity during the initial wave of spermatogenesis. A complementary model consists in the rearrangement of the tetraspanin web in prespermatogonia/spermatogonia undergoing spontaneous or Fas-induced apoptosis upon coculturing with Sertoli cells. In this model, the cellular site involved in the formation of preapoptotic bodies is devoid of tetraspanin-integrin clusters, in contrast with nonapoptotic cells, which display a diffuse circumferential distribution. In apoptotic prespermatogonia, immunoreactive clusters are restricted to sites where the attachment of prespermatogonia/spermatogonia to Sertoli cell surfaces is still preserved.

Oncogenes as Novel Targets for Cancer Therapy (Part I)

In the past 10 years, progress made in cancer biology, genetics, and biotechnology has led to a major transition in cancer drug design and development. There has been a change from an emphasis on non-specific, cytotoxic agents to specific, molecular-based therapeutics. Mechanism-based therapy is designed to act on cellular and molecular targets that are causally involved in the formation, growth, and progression of human cancers. These agents, which may have greater selectivity for cancer versus normal cells, and which may produce better anti-tumor efficacy and lower host toxicity, can be small molecules, natural or engineered peptides, proteins, antibodies, or synthetic nucleic acids (e.g. antisense oligonucleotides, ribozymes, and siRNAs). Novel targets are identified and validated by state-of-the-art approaches, including high-throughput screening, combinatorial chemistry, and gene expression arrays, which increase the speed and efficiency of drug discovery and development. Examples of oncogene-based, molecular therapeutics that show promising clinical activity include trastuzumab (Herceptin), imatinib (Gleevec), and gefitinib (Iressa). However, the full potential of oncogenes as novel targets for cancer therapy has not been realized and many challenges remain, from the validation of novel targets, to the design of specific agents, to the evaluation of these agents in both preclinical and clinical settings. In maximizing the benefits of molecular therapeutics in monotherapy or combination therapy of cancer, it is necessary to have an understanding of the underlying molecular abnormalities and mechanisms involved. This is the first part of a four-part review in which we discuss progress made in the last decade as it relates to the discovery of novel oncogenes and signal transduction pathways, in the context of their potential as targets for cancer therapy. This part delineates the latest discoveries about the potential use of growth factors and protein tyrosine kinases as targets for therapy. Later parts focus on intermediate signaling pathways, transcription factors, and proteins involved in cell cycle, DNA damage, and apoptotic pathways.

The role of epidermal growth factor and its receptors in mammalian CNS

Epidermal growth factor (EGF) is a common mitogenic factor that stimulates the proliferation of different types of cells, especially fibroblasts and epithelial cells. EGF activates the EGF receptor (EGFR/ErbB), which initiates, in turn, intracellular signaling. EGFR family is also expressed in neurons of the hippocampus, cerebellum, and cerebral cortex in addition to other regions of the central nervous system (CNS). EGF enhances the differentiation, maturation and survival of a variety of neurons. Transgenic mice lacking the EGFR developed neurodegenerative disease and die within the first month of birth. EGF acts not only on mitotic cells but also on postmitotic neurons, and many studies have indicated that EGF has neuromodulatory effect on various types of neurons in the CNS. This review highlights some of the major recent findings pertinent to the EGF and ErbB family with special references to elucidating their roles in the regulation of neurogenesis, signal transduction and trafficking and degradation.

Autocrine regulation of steroidogenic function of Leydig cells by transforming growth factor-alpha

We have determined the effects of LH on the expression of transforming growth factor-alpha (TGFalpha) and epidermal growth factor receptor (EGFR) system in rat Leydig cells and investigated its role in steroidogenesis. LH and TGFalpha/epidermal growth factor (EGF) significantly increased the levels of TGFalpha mRNA and protein, and the levels of EGFR protein in immature rat Leydig cells (ILC). Treatment with TGFalpha or EGF for 24h resulted in significant increase in androgen production in ILC. The increase in androgen production in response to TGFalpha was associated with increased mRNA levels of SR-BI, steroidogenic acute regulatory (StAR) and P450scc but not of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and P450c17. TGFalpha also caused a marked increase in the levels StAR protein in ILC. EGFR inhibitor (AG1478) blocked the effects of TGFalpha while MEK-inhibitor (PD98059) potentiated TGFalpha or LH effects on steroidogenesis. A PKA inhibitor (H89) blocked both TGFalpha and LH effects on steroidogenesis. We conclude that TGFalpha plays an autocrine role in LH dependent development and function of Leydig cells.

JunD protects against chronic kidney disease by regulating paracrine mitogens

The AP-1 transcription factor, composed of Jun and Fos proteins, plays a crucial role in the fine tuning of cell proliferation. We showed previously that AP-1 complexes are activated during the proliferative response that parallels the development of renal lesions after nephron reduction, but little is known about the specific role of individual Jun/Fos components in the deterioration process. Here we used JunD knockout (JunD-/-) mice and an experimental model of chronic renal injury (75% nephron reduction) to explore the role of JunD. Nephron reduction resulted in an initial compensatory growth phase that did not require JunD. JunD, however, was essential to inhibit a second wave of cell proliferation and to halt the development of severe glomerular sclerosis, tubular dilation, and interstitial fibrosis. We show that the effects of junD inactivation are not cell autonomous and involve upregulation of the paracrine mitogen, TGF-alpha. Expression of a transgene (REM) encoding a dominant negative isoform of the EGFR, the receptor for TGF-alpha, prevented the second wave of cell proliferation and the development of renal lesions in bitransgenic JunD-/-/REM mice. We propose that JunD is part of a regulatory network that controls proliferation to prevent pathological progression in chronic renal diseases.

Male infertility and thiamine-dependent erythroid hypoplasia in mice lacking thiamine transporter Slc19a2

Thiamine-responsive megaloblastic anemia with diabetes and deafness (TRMA) is an autosomal recessive disease caused by mutations in the high-affinity thiamine transporter gene SLC19A2. To study the role of thiamine transport in the pathophysiology of TRMA syndrome and of each of the component disorders, we created a targeted disruption of the Slc19a2 gene in mice. Slc19a2 -/- mice are viable and females are fertile. Male -/- mice on a pure 129/Sv background are infertile with small testes (testis/body weight=0.13 +/- 0.04 knockout vs. 0.35 +/- 0.05 wild type, P<0.000005). The lack of developing germ cells beyond primary spermatocytes suggests an arrest in spermatogenesis prior to meiosis II. Nuclear chromatin changes indicative of apoptosis are present. No mature sperm are found in the tubules or epididymis. This phenotype suggests a previously unknown role for thiamine transport in spermatogenesis and male fertility. Slc19a2 -/- mice on a pure 129/Sv background develop reticulocytopenia after two weeks on thiamine-depleted chow with a virtual absence of reticulocytes in the peripheral blood (0.12% knockout vs. 2.58% wild type, P=0.0079). Few erythroid precursors are found in the bone marrow. Contrary to human TRMA syndrome, we see no evidence of megaloblastosis or ringed sideroblasts in the bone marrow of Slc19a2 -/- mice in thiamine-replete or thiamine-deficient dietary states. Phenotypic differences between TRMA patients and Slc19a2 -/- mice might be explained by dissimilar tissue expression patterns of the transporter, as well as by differing metabolic needs and possible different species-specific contributions of the related thiamine transporter Slc19a3.

Dietary diethylstilbestrol but not genistein adversely affects rat testicular development

Isoflavones, including genistein, contribute to the health benefits of a soy diet. However, the estrogenic activity of genistein suggests that there may be adverse effects on reproductive tract development. We investigated the potential of exposure to genistein (250 and 1000 mg/kg diet) and the synthetic estrogen and known male reproductive toxicant, diethylstilbestrol (DES, 75 micro g/kg diet) from d 21 to d 35 to alter rat testicular development. These dietary genistein concentrations resulted in serum concentrations that approximate or exceed concentrations in Asian men on a soy-containing diet. DES exposure reduced testicular weights, altered morphology and increased apoptosis in the seminiferous tubules. The effects of DES were accompanied by a reduction in androgen receptor (AR) protein concentrations, predominantly localized to Sertoli cells. Increased expression and immunostaining for the epidermal growth factor receptor (EGFR) and its downstream extracellular signal-regulated kinases (ERK) 1 and 2 in spermatagonia and spermatocytes were also observed. Immunohistochemical analysis of serial sections demonstrated that greater EGFR expression correlated with increased cellular proliferation, rather than apoptosis, and reflected impaired testicular development in DES-treated rats. Genistein in the diet did not significantly alter testicular weights, morphology, AR, EGFR and ERK expression or apoptosis. However, the higher concentration significantly reduced testicular aromatase activity, an effect that may contribute to reduced estrogen concentrations and suppression of prostate cancer development. These data suggest that exposure to genistein in the diet at concentrations that result in serum concentrations at the upper limit of humans consuming soy products does not adversely affect testicular development, but may provide health benefits.

Overexpression of motor protein KIF17 enhances spatial and working memory in transgenic mice

The kinesin superfamily proteins (KIFs) play essential roles in receptor transportation along the microtubules. KIF17 transports the N-methyl-d-aspartate receptor NR2B subunit in vitro, but its role in vivo is unknown. To clarify this role, we generated transgenic mice overexpressing KIF17 tagged with GFP. The KIF17 transgenic mice exhibited enhanced learning and memory in a series of behavioral tasks, up-regulated NR2B expression with the potential involvement of a transcriptional factor, the cAMP-dependent response element-binding protein, and increased phosphorylation of the cAMP-dependent response element-binding protein. Our results suggest that the motor protein KIF17 contributes to neuronal events required for learning and memory by trafficking fundamental N-methyl-d-aspartate-type glutamate receptors.

The role of expression of extracellular matrix proteins and epidermal growth factor receptor activity on fertilization capacity of testicular harvested spermatozoa

It has been suggested that multiple growth factors are crucial for spermatogenesis. We analyzed whether alterations on epidermal growth factor receptor activity and different expression pattern of extracellular matrix proteins had an impact on the fertilization capacity of spermatozoa and pregnancy rate after testicular sperm extraction and intracytoplasmic injection. Extracellular matrix proteins and epidermal growth factor receptor were immunohistochemically evaluated in testis of 88 patients with nonobstructive azoospermia. Testicular sperm extraction and intracytoplasmic injection procedure was also performed in 32 of the patients for whom mature sperm could be harvested from the testicular tissue. While collagen Type-IV and laminin activity percentages were 33.1% and 86.4% in motile sperm harvested testicular tissue, these activities were 23.3% and 89.3% in immotile sperm harvested testicular tissue, respectively. In addition, the mean epidermal growth factor receptor expression was higher in immotile than motile sperm obtained tissue (56.4% vs. 51.1%, P=0.4928). There was no statistically significant relationship between the extracellular matrix protein and epidermal growth factor receptor expression patterns and sperm motility, fertilization and pregnancy rates in testicular sperm extraction and intracytoplasmic injection. However, further studies are required to investigate the relationship between other growth factors and sperm fertilization capacity.

Transforming growth factor-alpha stimulates proliferation of rat Sertoli cells

The number of Sertoli cells is positively correlated with the number of germ cells produced in the testis, but the regulation of Sertoli cell proliferation and final density is poorly understood. Using non-aggregated Sertoli cells from 8 to 9-day-old rat testes, highly enriched by lectin binding, we explored effects of Sertoli cell growth factor candidates in vitro. Proliferation was assessed by 3H-thymidine incorporation, bromodeoxyuridine labeling and supravital staining, and FSH was used as positive control. Transforming growth factor-alpha (TGF-alpha) was found to stimulate Sertoli cell proliferation in a dose-dependent manner. Epidermal growth factor (EGF) and betacellulin mimicked the effect, demonstrating specificity of the response as they share receptors with TGF-alpha. Insulin-like growth factor I and II, acidic and basic fibroblast growth factor and stem cell factor lacked significant stimulatory effects. We conclude that EGF/TGF-alpha is a growth factor for Sertoli cells in vitro, possibly contributing to paracrine regulation of Sertoli cell proliferation in vivo.

Expression of epidermal growth factor in transgenic mice causes growth retardation

The epidermal growth factor (EGF) family of peptides signals through the erbB family of receptor tyrosine kinases and plays important roles in development and tumorigenesis. Both EGF and transforming growth factor (TGF)-alpha only bind to erbB1 and activate it. The precursor of EGF is distinct from that of TGF-alpha in having eight additional EGF-like repeats. We have recently shown that the EGF precursor without these repeats is biologically active and leads to hypospermatogenesis in transgenic mice. Here we present evidence that the growth of transgenic mice widely expressing this engineered EGF precursor is also stunted. These mice were consistently born at half the normal weight and reached almost 80% of normal weight at adulthood. The mechanism involved a reduction of serum insulin-like growth factor-binding protein-3. Chondrocyte development in the growth plate was affected, and osteoblasts accumulated in the endosteum and periosteum. Besides these novel findings on the in vivo effects of EGF on bone development, we observed no sign of tumor formation in our transgenic animals. In contrast to previous reports on TGF-alpha transgenic mice, we show that the biological functions of EGF and TGF-alpha are clearly distinct.

An efficient method of generating transgenic mice by pronuclear microinjection

Genetic transformation of mice using pronuclear microinjection was demonstrated by a number of groups in rapid succession in the early 1980's. Since that time, studies using transgenic animals have produced major advances in biomedical sciences and molecular genetics. More important, it is possible to study the molecular basis for tissue and stage-specific expression of genes. We recently used this method to generate transgenic mice. DNA fragment (transgene) was injected into the pronucleus of one-cell embryos. We describe this simplified protocol, which is reliable. With the use of buffered medium M2 for the whole process, it is not mandatory to have a CO2 incubator.