Transforming growth factor-alpha. A model for membrane-anchored growth factors

The Role of Anti-Müllerian Hormone in Ovarian Function

Anti-Müllerian hormone (AMH) is a member of the transforming growth factor β (TGFβ) superfamily, whose actions are restricted to the endocrine-reproductive system. Initially known for its role in male sex differentiation, AMH plays a role in the ovary, acting as a gatekeeper in folliculogenesis by regulating the rate of recruitment and growth of follicles. In the ovary, AMH is predominantly expressed by granulosa cells of preantral and antral follicles (i.e., post primordial follicle recruitment and prior to follicle-stimulating hormone (FSH) selection). AMH signals through a BMP-like signaling pathway in a manner distinct from other TGFβ family members. In this review, the latest insights in AMH processing, signaling, its regulation of spatial and temporal expression pattern, and functioning in folliculogenesis are summarized. In addition, effects of AMH variants on ovarian function are reviewed.

Entanglement of MAPK pathways with gene expression and its omnipresence in the etiology for cancer and neurodegenerative disorders

Mitogen Activated Protein Kinase (MAPK) is one of the most well characterized cellular signaling pathways that controls fundamental cellular processes including proliferation, differentiation, and apoptosis. These cellular functions are consequences of transcription of regulatory genes that are influenced and regulated by the MAP-Kinase signaling cascade. MAP kinase components such as Receptor Tyrosine Kinases (RTKs) sense external cues or ligands and transmit these signals via multiple protein complexes such as RAS-RAF, MEK, and ERKs and eventually modulate the transcription factors inside the nucleus to induce transcription and other regulatory functions. Aberrant activation, dysregulation of this signaling pathway, and genetic alterations in any of these components results in the developmental disorders, cancer, and neurodegenerative disorders. Over the years, the MAPK pathway has been a prime pharmacological target, to treat complex human disorders that are genetically linked such as cancer, Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis. The current review re-visits the mechanism of MAPK pathways in gene expression regulation. Further, a current update on the progress of the mechanistic understanding of MAPK components is discussed from a disease perspective.

JNK2 Promotes Progression of Esophageal Squamous Cell Carcinoma via Inhibiting Axin2

INTRODUCTION

The dysregulation of the c-Jun NH2-terminal kinase (JNK) pathway has been increasingly reported in human malignancies. Aberrant expression of the JNK pathway has also been implicated in the progression of Esophageal Squamous Cell Carcinoma (ESCC). However, the specific role and regulatory mechanisms of JNK2 in ESCC have not been extensively investigated.

METHODS

In this study, we examined JNK2 expression in patient samples and performed experiments involving the knockdown and inhibition of the JNK2 in ESCC cell lines.

RESULTS

Higher JNK2 expression was observed in tumor tissues compared to adjacent tissues. JNK2 overexpression was associated with advanced disease stages and poor prognosis. Furthermore, knockdown or inhibition of JNK2 in ESCC cell lines resulted in a decrease in cell proliferation and migration.

CONCLUSION

Additionally, a significant decrease in the expression of β-catenin and vimentin, along with an increase in the expression of Axin2, was observed upon downregulation of JNK2. Our study provides insight into the role of JNK2 in ESCC and its potential regulatory mechanism, offering a potential therapeutic strategy for ESCC patients with aberrant JNK2 expression.

Shifting the Focus of Signaling Abnormalities in Colon Cancer

Colon cancer tumorigenesis occurs incrementally. The process involves the acquisition of mutations which typically follow an established pattern: activation of WNT signaling, activation of RAS signaling, and inhibition of TGF-β signaling. This arrangement recapitulates, to some degree, the stem cell niche of the intestinal epithelium, which maintains WNT and EGF activity while suppressing TGF-β. The resemblance between the intestinal stem cell environment and colon cancer suggests that the concerted activity of these pathways generates and maintains a potent growth-inducing stimulus. However, each pathway has a myriad of downstream targets, making it difficult to identify which aspects of these pathways are drivers. To address this, we utilize the cell cycle, the ultimate regulator of cell proliferation, as a foundation for cross-pathway integration. We attempt to generate an overview of colon cancer signaling patterns by integrating the major colon cancer signaling pathways in the context of cell replication, specifically, the entrance from G1 into S-phase.

In vivo and in vitro activation of dormant primordial follicles by EGF treatment in mouse and human

In the mammalian ovaries, dormant primordial follicles represent the reproductive reserve of individual females. Recently, stimulating the activation of primordial follicles in vitro has been practiced, making the utilization of those dormant follicles to treat female infertility possible. However, there are still lacks of effective upstream molecule and strategy to elevate follicle activation in vivo. In the current study, we revealed that growth factor EGF improved a transiently primordial follicle activation in mice by elevating the CDC42-PI3K signaling activity, and EGF treatment also improved the activation and development of human follicles in ovarian cortical pieces. Using a liquid-solid phase transition bio-gel as a carrier, an efficient in vivo activation system was established by ovarian topical EGF administration to living mice. We found that EGF treatment led to an increase of primordial follicle activation in short time but had no effect on long-term fertility in females. By establishing an inducible premature ovarian insufficiency (POI) mouse model through selectively ablating growing follicles in Zp3-Cre;iDTR mice, we further revealed that our in vivo EGF treatment system improved primordial follicle activation and ovulation of POI ovaries significantly. Taken together, our results revealed that in situ ovarian EGF administration could improve the activation of primordial follicles in living animals, and manipulating activation and development of primordial follicles in vivo might be an efficient approach to improve reproductive health in women.

Testosterone levels after treatment with urofollitropin in infertile patients with idiopathic mild reduction of testicular volume

INTRODUCTION

A reduction of testicular volume (TV) represents an important clinical sign, which may hide sperm abnormalities and predispose to hypogonadism.

AIM

The primary purpose of this study was to evaluate the serum levels of total testosterone after treatment with urofollitropin in selected patients with male infertility and idiopathic mild reduction of testicular volume.

METHODS

In this 1-year-long prospective design, patients with abnormal sperm parameters, mild reduction in TV (8-12 mL) and normal gonadotropin, and total testosterone (TT) serum levels were recruited in this study. Patients treated for 4 months with urofollitropin were included in group A, those treated with intracytoplasmatic sperm injection due to a female-factor infertility were included in group B. Hormone values, sperm parameters, and TV were detected at baseline (T0), after 4 (T1) and 12 months (T2) in group A and at T0 and T2 in group B.

RESULTS

Group A (n = 80) showed increased follicle-stimulating hormone (FSH) at T1 and sperm morphology at T1 and T2 compared to T0 (all p < 0.05). Group B (n = 50) had lower TT and higher FSH levels at T2 compared to T0 (all p < 0.05). At T2, TT, VT, total sperm count, progressive motility, total motility, and sperm morphology were higher in group A compared to group B (all p < 0.05).

CONCLUSION

Reduced TV may predispose to infertility and hypogonadism. FSH treatment may improve Sertoli and Leydig cell function and prevent the development of hypogonadism.

Effects of vitamin D and calcium on expression of MSH2 and transforming growth factors in normal-appearing colorectal mucosa of sporadic colorectal adenoma patients: A randomized clinical trial

Abnormal expression of the DNA mismatch repair protein MSH2 and autocrine/paracrine transforming growth factors TGFα (growth promoter) and TGFβ₁ (growth inhibitor) is common during colorectal carcinogenesis. To estimate vitamin D and calcium effects on these biomarkers in the normal-appearing colorectal mucosa of sporadic colorectal adenoma patients, we conducted a pilot, randomized, double-blinded, placebo-controlled, modified 2 × 2 factorial chemoprevention clinical trial (N = 104) of supplemental vitamin D₃ (1000 IU daily) and calcium (1200 mg daily), alone and in combination, versus placebo over 1 year. The expression of the three biomarkers and Ki-67/mib-1 in colorectal crypts in biopsies of normal-appearing rectal mucosa were detected using automated immunohistochemistry and quantified using image analysis. In the vitamin D₃ and vitamin D₃ plus calcium groups, relative to their reference groups, in the upper 40% (differentiation zone) of crypts, it was estimated that, respectively, the MSH2/mib-1 ratio increased by 47% (P = 0.14) and 62% (P = 0.08), TGFβ₁ expression increased by 41% (P = 0.25) and 78% (P = 0.14), and the TGFα/TGFβ₁ ratio decreased by 25% (P = 0.31) and 44% (P = 0.13). Although not statistically significant, these results support further research into (i) whether supplemental vitamin D₃ , alone or in combination with calcium, may increase DNA mismatch repair relative to proliferation, increase TGFβ₁ expression, and decrease autocrine/paracrine growth promotion relative to growth inhibition in the colorectal epithelium, all hypothesized to reduce risk for colorectal carcinogenesis; and (ii) the expression of MSH2 relative to mib-1, TGFβ₁ alone, and TGFα relative to TGFβ₁ in the normal-appearing rectal mucosa as potential modifiable, pre-neoplastic markers of risk for colorectal neoplasms.

Tumor-linked HER2 expression: association with obesity and lipid-related microenvironment

Obesity is associated with the risk of several health disorders including certain cancers. Among obesity-related cancers, postmenopausal breast carcinoma is a well-studied one. Apart from an increase in certain types of lipids in obesity, excess adipose tissue releases many hormone-like cytokines/adipokines, which are usually pro-inflammatory in nature. Leptin is one of such adipokines and significantly linked with the intracellular signaling pathways of other growth factors such as insulin-like growth factor-1 (IGF-1), vascular endothelial growth factor (VEGF), human epidermal growth factor receptor 2 (HER2). In general, HER2 is overexpressed in roughly 30% of breast carcinomas; its presence indicates aggressive tumor behavior. Conversely, HER2 has certain effects in normal conditions such as differentiation of preadipocytes, cardiovascular health and vitamin D metabolism. HER2 has no known endogenous ligand, but it may form dimers with other three members of the epidermal growth factor receptor (EGFR) family and can activate downstream signaling pathways. Furthermore, HER2 is intimately connected with several enzymes, e.g. fatty acid synthase (FASN), phosphatidylinositol 3-kinase (PI3K), AKT and mechanistic target of rapamycin (mTOR), all of which play significant regulatory roles in lipogenic pathways or lipid metabolism. In obesity-related carcinogenesis, characteristics like insulin resistance and elevated IGF-1 are commonly observed. Both IGF-1 and leptin can modulate EGFR and HER2 signaling pathways. Although clinical studies have shown mixed results, the behavior of HER2+ tumor cells including HER2 levels can be altered by several factors such as obesity, leptin and fatty acids. A precise knowledge is useful in new therapeutic approaches against HER+ tumors.

The role of the Hes1 crosstalk hub in Notch-Wnt interactions of the intestinal crypt

The Notch pathway plays a vital role in determining whether cells in the intestinal epithelium adopt a secretory or an absorptive phenotype. Cell fate specification is coordinated via Notch's interaction with the canonical Wnt pathway. Here, we propose a new mathematical model of the Notch and Wnt pathways, in which the Hes1 promoter acts as a hub for pathway crosstalk. Computational simulations of the model can assist in understanding how healthy intestinal tissue is maintained, and predict the likely consequences of biochemical knockouts upon cell fate selection processes. Chemical reaction network theory (CRNT) is a powerful, generalised framework which assesses the capacity of our model for monostability or multistability, by analysing properties of the underlying network structure without recourse to specific parameter values or functional forms for reaction rates. CRNT highlights the role of β-catenin in stabilising the Notch pathway and damping oscillations, demonstrating that Wnt-mediated actions on the Hes1 promoter can induce dynamic transitions in the Notch system, from multistability to monostability. Time-dependent model simulations of cell pairs reveal the stabilising influence of Wnt upon the Notch pathway, in which β-catenin- and Dsh-mediated action on the Hes1 promoter are key in shaping the subcellular dynamics. Where Notch-mediated transcription of Hes1 dominates, there is Notch oscillation and maintenance of fate flexibility; Wnt-mediated transcription of Hes1 favours bistability akin to cell fate selection. Cells could therefore regulate the proportion of Wnt- and Notch-mediated control of the Hes1 promoter to coordinate the timing of cell fate selection as they migrate through the intestinal epithelium and are subject to reduced Wnt stimuli. Furthermore, mutant cells characterised by hyperstimulation of the Wnt pathway may, through coupling with Notch, invert cell fate in neighbouring healthy cells, enabling an aberrant cell to maintain its neighbours in mitotically active states.

Tethering of rhBMP-2 upon calcium phosphate cement via alendronate/heparin for localized, sustained and enhanced osteoactivity

rhBMP-2 was tethered on surface of calcium phosphate cement via alendronate–heparin. This novel delivery system can concurrently satisfy high bioactive immobilization and sustainable release of rhBMP-2, and consequently induce rapid bone regeneration.

Transforming growth factor β (CiTGF-β) gene expression is induced in the inflammatory reaction of Ciona intestinalis

Transforming growth factor (TGF-β) is a well-known component of a regulatory cytokines superfamily that has pleiotropic functions in a broad range of cell types and is involved, in vertebrates, in numerous physiological and pathological processes. In the current study, we report on Ciona intestinalis molecular characterisation and expression of a transforming growth factor β homologue (CiTGF-β). The gene organisation, phylogenetic tree and modelling supported the close relationship with the mammalian TGF suggesting that the C. intestinalis TGF-β gene shares a common ancestor in the chordate lineages. Functionally, real-time PCR analysis showed that CiTGF-β was transcriptionally upregulated in the inflammatory process induced by LPS inoculation, suggesting that is involved in the first phase and significant in the secondary phase of the inflammatory response in which cell differentiation occurs. In situ hybridisation assays revealed that the genes transcription was upregulated in the pharynx, the main organ of the ascidian immune system, and expressed by cluster of hemocytes inside the pharynx vessels. These data supported the view that CiTGF-β is a potential molecule in immune defence systems against bacterial infection.

Covalently conjugated transforming growth factor-β1 in modular chitosan hydrogels for the effective treatment of articular cartilage defects

Approaches to control precisely growth factor presentation to a tissue defect in a sustained fashion are of increasing interest for a number of complex tissue engineering applications. Although transforming growth factor beta-1 (TGF-β1) plays a key role in promoting chondrogenesis, the therapeutic use of TGF-β1 is limited by its inherent protein instability, requiring high amounts of the protein that can cause adverse side effects with inefficient cartilage formation. In this work, we have developed strategies to stabilize TGF-β1 signaling in the injectable, visible blue light inducible chitosan (MeGC) hydrogel system for specific use in cartilage regeneration. We successfully modulated delivery of TGF-β1 with reduced burst release in a complex biological environment of serum and cells by covalently conjugating the protein to MeGC hydrogels with preserving type II collagen, one of the major cartilaginous extracellular matrix (ECM) components. The hydrogel system supported cellular condensation and deposition of cartilaginous ECM by encapsulating adipose derived stem cells in vitro. We confirmed further the ability of these TGF-β1 functionalized hydrogel systems to promote cartilage regeneration in challenging healing environments such as in a rat partial-thickness chondral defect model which present a limited source of subchondral bone marrow elements. These results suggest a new injectable delivery modality of therapeutic agents to improve clinical cartilage repair.

The effects of sulfur mustard on expression of TGF-βs variants in lung epithelial cell line

Sulfur mustard (SM) is a blister-forming agent and can cause damages in various momentous human organs. Previous studies have demonstrated that chemical and mechanical injuries of epithelial cells cause to give rise the secretion of TGF-β1 and TGF-β2. These cytokines play a key role in respiratory remodeling due to SM. In this study, we investigated the impact of SM on the expression level of TGF-β isoforms and their receptors in vitro using reverse transcriptase polymerase chain reaction and western blotting. Our finding revealed the significant increase at concentrations of 25 μl/ml SM for 30 min and 60 min and also 100 μl/ml for 60 min for TGF-β1, 25, 50 and 100 μl/ml SM for 30 min for TGF-βr1 and after exposing with 100 μl/ml SM for both 30 and 60 min for TGF-β2 (p < 0.05). Data from western blotting showed the increase of TGF-β1 expression at the level of protein as the same pattern as the mRNA level. In vitro short-time exposure of fibroblast to SM can induce the expression of TGF-β1, TGF-β2 and TGF-βR1 denoting that over-expression of TGF-β isoforms and their receptors leads to differentiation and collagen production, causing in airway remodeling and fibrosis.

Cell and molecular biology of epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) has been one of the most intensely studied cell surface receptors due to its well-established roles in developmental biology, tissue homeostasis, and cancer biology. The EGFR has been critical for creating paradigms for numerous aspects of cell biology, such as ligand binding, signal transduction, and membrane trafficking. Despite this history of discovery, there is a continual stream of evidence that only the surface has been scratched. New ways of receptor regulation continue to be identified, each of which is a potential molecular target for manipulating EGFR signaling and the resultant changes in cell and tissue biology. This chapter is an update on EGFR-mediated signaling, and describes some recent developments in the regulation of receptor biology.

Gene expression of growth factors and growth factor receptors for potential targeted therapy of canine hepatocellular carcinoma

The purpose of this study was to evaluate the gene expression of growth factors and growth factor receptors of primary hepatic masses, including hepatocellular carcinoma (HCC) and nodular hyperplasia (NH), in dogs. Quantitative real-time reverse transcriptase-polymerase chain reaction was performed to measure the expression of 18 genes in 18 HCCs, 10 NHs, 11 surrounding non-cancerous liver tissues and 4 healthy control liver tissues. Platelet-derived growth factor-B (PDGF-B), transforming growth factor-α, epidermal growth factor receptor, epidermal growth factor and hepatocyte growth factor were found to be differentially expressed in HCC compared with NH and the surrounding non-cancerous and healthy control liver tissues. PDGF-B is suggested to have the potential to become a valuable ancillary target for the treatment of canine HCC.

Evaluation of endostatin and EGF serum levels in patients with gastric cancer

THE AIM OF THE STUDY was to assess angiogenesis markers - endostatin and endothelial growth factor (EGF) as markers of detection of gastric carcinoma. MATERIAL AND METHODS. The study involved 20 patients with colorectal cancer (10 women, 10 men) aged 35 - 75 years, mean age = 55 years ± 11.2 who referred to the 2nd Department of General Surgery, Medical University in Lublin between June 2008 and June 2009. The control group comprised 10 volunteers (6 women, 4 men) who underwent upper gastrointestinal (GI) endoscopy due to the reflux disease and in whom gastric cancer was not diagnosed. RESULTS. The mean endostatin concentration in controls was 5.21 ng/mL ± 1.37. Mean concentrations in patients with gastric cancer were higher than those in controls - 5.91 ng/mL ± 1.5. The difference was not statistically significant (p= 0.714). The EGF concentration in the control group was 28.19 pg/mL ± 12.94. EGF concentrations in patients with gastric cancer were higher compared to the control group - 28.8 pg/mL ± 12.63. The difference was not statistically significant (p= 0.85). The mean concentration of endostatin before the operation was 5.91 ng/mL ± 1.5 and after surgery was 5.33 ng/mL ± 2.01, the difference was not statistically significant. CONCLUSIONS. Blood endostatin and EGF quantitative determinations probably is not useful for detection of gastric carcinoma and effectiveness of treatment.

The impact of immobilization of BMP-2 on PDO membrane for bone regeneration

Poly(dioxanone) (PDO) is colorless, crystalline, a biodegradable synthetic polymers that is used for biomedical applications, such as surgical sutures, cardiovascular applications, orthopedics, and plastic surgery. Recently, bone morphogenetic protein-2 (BMP-2) is widely used for bone tissue engineering. For the first time we report here on the in vitro performance of an electrospun PDO membrane immobilized with BMP-2. Immobilized BMP-2 on PDO membrane enhanced ALPase activity, the osteogenic differentiation gene expressions as well as cell attachment, except cell proliferation when compared to that of PDO membrane alone. These results suggest that PDO membrane with BMP-2 is helpful to promote bone healing and regeneration.

The Caenorhabditis elegans synthetic multivulva genes prevent ras pathway activation by tightly repressing global ectopic expression of lin-3 EGF

The Caenorhabditis elegans class A and B synthetic multivulva (synMuv) genes redundantly antagonize an EGF/Ras pathway to prevent ectopic vulval induction. We identify a class A synMuv mutation in the promoter of the lin-3 EGF gene, establishing that lin-3 is the key biological target of the class A synMuv genes in vulval development and that the repressive activities of the class A and B synMuv pathways are integrated at the level of lin-3 expression. Using FISH with single mRNA molecule resolution, we find that lin-3 EGF expression is tightly restricted to only a few tissues in wild-type animals, including the germline. In synMuv double mutants, lin-3 EGF is ectopically expressed at low levels throughout the animal. Our findings reveal that the widespread ectopic expression of a growth factor mRNA at concentrations much lower than that in the normal domain of expression can abnormally activate the Ras pathway and alter cell fates. These results suggest hypotheses for the mechanistic basis of the functional redundancy between the tumor-suppressor-like class A and B synMuv genes: the class A synMuv genes either directly or indirectly specifically repress ectopic lin-3 expression; while the class B synMuv genes might function similarly, but alternatively might act to repress lin-3 as a consequence of their role in preventing cells from adopting a germline-like fate. Analogous genes in mammals might function as tumor suppressors by preventing broad ectopic expression of EGF-like ligands.

Extracellular signals that drive cells to divide must be carefully restricted so that only the correct cells receive those signals. Failure to properly control the expression of signaling molecules can lead to aberrant development and cancer. Studies of vulval development in the nematode Caenorhabditis elegans have helped define various multi-step signaling pathways involved in cancer. Here we report that two groups of proteins that control the EGF/Ras/MAP kinase pathway of vulval development act by tightly repressing the spatial expression of the gene lin-3, which encodes an EGF-like signaling molecule. Using a technique that detects single mRNA molecules, we show that inactivation of these proteins causes a low ectopic expression of lin-3 in many cells. In response, the EGF/Ras/MAP kinase pathway is activated in cells normally not exposed to the lin-3 signal, and vulval development is abnormal. This process is analogous to the cancerous growth that occurs in humans when mutations cause both tumor cells and the microenvironment surrounding the tumor cells to ectopically express factors that drive cellular proliferation. We propose that mammalian genes analogous to those that repress lin-3 expression in C. elegans vulval development act as tumor suppressors by preventing broad ectopic expression of EGF-like ligands.

Chemically-conjugated bone morphogenetic protein-2 on three-dimensional polycaprolactone scaffolds stimulates osteogenic activity in bone marrow stromal cells

Poly(ε-caprolactone) (PCL) has received considerable attention in bone tissue engineering. However, the lack of osteoinductive ability of PCL limits its application. The aim of this study was to directly attach bone morphogenetic protein-2 (BMP-2) to PCL scaffolds by a crosslinking conjugation method and to investigate whether the bound BMP-2 maintained bioactivity in vitro. Immunofluorescent staining against BMP-2 and quantitative enzyme-linked immunosorbent assay measurements demonstrated that BMP-2 was successfully immobilized on the PCL three-dimensional scaffold by aminolysis and subsequent chemical conjugation. Conjugation produced much higher immobilization efficiency than the physical adsorption. Conjugated BMP-2 release from the PCL scaffolds was significantly slower than that from BMP-2-adsorbed PCL scaffolds over 15 days, which resulted in more BMP-2 locally retained on the conjugated scaffold. Further, the downstream Smads pathway was upregulated in bone marrow stromal cells cultured on the BMP-2-conjugated PCL scaffolds. Finally, gene expression of osteogenic markers (alkaline phosphatase, osteoclacin, and type I collagen) was upregulated in bone marrow stromal cells cultured on the PCL scaffolds with BMP-2 conjugation, but not on PCL scaffolds after BMP-2 adsorption. Therefore, our finding demonstrated that BMP-2 conjugation on polyester scaffolds is a feasible way to impart scaffolds with osteoinductive capability.

Putative association of transforming growth factor-alpha polymorphisms with clearance of hepatitis B virus and occurrence of hepatocellular carcinoma in patients with chronic hepatitis B virus infection

Previous studies showed that several genetic polymorphisms might influence the clinical outcome of chronic hepatitis B virus (HBV) infection, including HBV clearance or development of hepatocellular carcinoma (HCC). The aim of this study was to determine whether polymorphisms of the transforming growth factor-alpha (TGF-alpha) gene are associated with clinical outcome of HBV infection. A total of 1096 Korean subjects having either present or past evidence of HBV infection were prospectively enrolled between January 2001 and August 2003. Among 16 genetic variants in TGFA gene, nine variants were genotyped using TaqMan assay and the genetic association with HBV clearance and HCC occurrence was analysed. Statistical analyses revealed that TGFA+103461T>C, TGFA+106151C>G and TGFA-ht2 were marginally associated with clearance of HBV infection. However, only TGFA-ht2 retained significance after multiple correction (OR = 0.39, P(corr) = 0.007 in recessive model). Although no variants were significant after multiple correction, TGFA+88344G>A and TGFA+103461T>C were weakly associated in recessive model in the analysis of HCC occurrence. In addition, Cox relative hazards model also revealed that TGFA+88344G>A was associated with onset age of HCC occurrence in subjects (RH = 1.46, P(corr) = 0.04). TGF-alpha polymorphisms might be an important factor in immunity, progression of inflammatory process and carcinogenesis, which explains the variable outcome of HBV infection at least in part. Further biological evidence is warranted in the future to support these suggestive associations.

Regulation of renal sodium handling through the interaction between serine proteases and serine protease inhibitors

Sodium balance, extracellular fluid volume, and ultimately blood pressure are maintained by precise regulation of the activity of epithelial sodium channels (ENaC). Multiple mechanisms such as hormones, intracellular factors, and other regulatory factors contribute to regulation of ENaC activity. Prostasin, a glycosylphosphatidylinositol-anchored serine protease, has been identified as an activator of ENaC that increases its open probability. Furin cleaves αENaC at two sites and γENaC at one site at the Golgi. Prostasin cleaves γENaC at one site that is distinct from the furin site at the plasma membrane. Dual cleavage of α- and γ-subunit releases inhibitory segments from ENaC, leading to channel activation. Protease nexin-1 (PN-1), an endogenous prostasin inhibitor, inhibits ENaC activity through suppression of prostasin activity. Aldosterone and transforming growth factor-β1 reciprocally regulate expression of prostasin, PN-1, and ENaC in renal epithelial cell, resulting in sodium retention or natriuresis, respectively. These findings strongly suggest the possibility that coordinated regulation of serine protease, serpin, and ENaC expression plays a key role in sodium handling in the kidney.

The genotype-phenotype relationship in multicellular pattern-generating models--the neglected role of pattern descriptors

Background

A deep understanding of what causes the phenotypic variation arising from biological patterning processes, cannot be claimed before we are able to recreate this variation by mathematical models capable of generating genotype-phenotype maps in a causally cohesive way. However, the concept of pattern in a multicellular context implies that what matters is not the state of every single cell, but certain emergent qualities of the total cell aggregate. Thus, in order to set up a genotype-phenotype map in such a spatiotemporal pattern setting one is actually forced to establish new pattern descriptors and derive their relations to parameters of the original model. A pattern descriptor is a variable that describes and quantifies a certain qualitative feature of the pattern, for example the degree to which certain macroscopic structures are present. There is today no general procedure for how to relate a set of patterns and their characteristic features to the functional relationships, parameter values and initial values of an original pattern-generating model. Here we present a new, generic approach for explorative analysis of complex patterning models which focuses on the essential pattern features and their relations to the model parameters. The approach is illustrated on an existing model for Delta-Notch lateral inhibition over a two-dimensional lattice.

Results

By combining computer simulations according to a succession of statistical experimental designs, computer graphics, automatic image analysis, human sensory descriptive analysis and multivariate data modelling, we derive a pattern descriptor model of those macroscopic, emergent aspects of the patterns that we consider of interest. The pattern descriptor model relates the values of the new, dedicated pattern descriptors to the parameter values of the original model, for example by predicting the parameter values leading to particular patterns, and provides insights that would have been hard to obtain by traditional methods.

Conclusion

The results suggest that our approach may qualify as a general procedure for how to discover and relate relevant features and characteristics of emergent patterns to the functional relationships, parameter values and initial values of an underlying pattern-generating mathematical model.

Amphiregulin as a novel target for breast cancer therapy

Amphiregulin, an EGF family growth factor, binds and activates the epidermal growth factor receptor (EGFR or ErbB1). Activation of the EGFR by amphiregulin can occur through autocrine, paracrine and juxtacrine mechanisms. Amphiregulin plays a role in several biological processes including nerve regeneration, blastocyst implantation, and bone formation. Amphiregulin also plays an important role in mammary duct formation as well as the outgrowth and branching of several other human tissues such as the lung, kidney and prostate. This effect is most likely due to the induction of genes involved in invasion and migration such as cytokines and matrix metalloproteases. Clinical studies have suggested that amphiregulin also plays a role in human breast cancer progression and its expression has been associated with aggressive disease. Therefore, amphiregulin may be a novel and effective target for the treatment of breast cancer and could represent an alternative to targeting the EGFR.

Heterobifunctional poly(ethylene glycol)-tethered bone morphogenetic protein-2-stimulated bone marrow mesenchymal stromal cell differentiation and osteogenesis

We describe a biomimetic mode of insoluble signaling stimulation to provide target delivery of bone morphogenetic protein-2 (BMP-2), with the aim of prolonging the retention of BMP-2 use in bone tissue engineering and to enable its localized release in response to cellular activity. In our novel localization process, we used heterobifunctional acrylate-N-hydroxysuccinimide poly(ethylene glycol) (PEG) as a spacer to tether BMP-2 onto a poly(lactide-co-glycolide) scaffold. Use of PEG-tethered BMP-2 was feasible because BMP-2 retained its activity after covalent conjugation. The PEG-tethered BMP-2 conjugate sustained stimulation and retained its mitogenic activity, notably affecting pluripotent stem cell proliferation and differentiation. We seeded the scaffolds with bone marrow-derived mesenchymal stromal cells as progenitor cells to evaluate their morphology and phenotypic expression. We also created bilateral, full-thickness cranial defects in rabbits to investigate the osteogenic effect of cultured mesenchymal stromal cells on bone regeneration in vivo. Histomorphometry and histology demonstrated that the PEG-tethered BMP-2 conjugate enhanced de novo bone formation after surgery. Our work revealed the potential for biomimetic surface engineering by entrapping signaling growth factor to stimulate osteogenesis. Our technique may provide a new platform for bone-engineered stem cell therapies.

Targeted delivery system for juxtacrine signaling growth factor based on rhBMP-2-mediated carrier-protein conjugation

We propose a model of artificial juxtacrine signaling for the controlled release of recombinant human bone morphogenetic protein-2 (rhBMP-2) suitable for guided bone regeneration. A porous three-dimensional scaffold of poly-(lactide-co-glycolide) was fabricated by means of gel molding and particulate leaching. Collagen immobilization onto the scaffold surface was produced by performing photo-induced graft polymerization of acrylic acid, and rhBMP-2 was tethered to the collagenous surface by covalent conjugation. On pharmacokinetic analysis, in vitro enzyme-linked immunosorbent and alkaline phosphatase assays revealed sustained, slow release of rhBMP-2 over 28 days, with a cumulative release of one third of the initial load diffusing out of the scaffold. Conjugation of rhBMP-2 inhibited the free lateral diffusion and internalization of the activated complex of rhBMP-2 and the bone morphogenetic protein receptor. Osteoprogenitor cells were used as bone precursors to determine the expression of biosignaling growth factor in regulating cell proliferation and differentiation. To identify the phenotype of cells seeded on the rhBMP-2-conjugated scaffold, cellular activity was evaluated with scanning electron microscopy and with viability, histological, and immunohistochemical testing. The rhBMP-2-conjugated scaffold prolonged stimulation of intracellular signal proteins in cells. Enhancement of cell growth and differentiation was considered a consequence of juxtacrine signaling transduction. Animal studies of rhBMP-2-containing filling implants showed evidence of resorption and de novo bone formation. The present study revealed the potential of biomimetic constructs with co-immobilized adhesion and growth factors to induce osteoinduction and osteogenesis. Such constructs may be useful as synthetic bone-graft materials in orthopaedic tissue engineering.

An unexpected inverse correlation between soluble epidermal growth factor receptor and interleukin-6 in metastatic malignant melanoma patients

The exact role of the soluble form of epidermal growth factor receptor (sEGF-R) in melanoma disease remains to be determined. We focused this study on the detection of circulating levels of sEGF-R in metastatic malignant melanoma patients and on the possible relationship between sEGF-R and clinicobiological parameters including circulating interleukin-6 (IL-6) and survival. sEGF-R and IL-6 levels were determined using a highly sensitive enzyme-linked immunosorbent assay in serum from 75 metastatic malignant melanoma patients and 30 healthy controls. In our patients, median sEGF-R level was significantly elevated (P < 0.0001) compared with that of healthy controls (173.4 vs. 91.9 fm/ml). Age or sex was not associated with sEGF-R levels. Regarding tumor burden, in contrary to the detected IL-6 levels, we found that median sEGF-R levels were significantly (P = 0.045) lower in patients with high tumor burden (163 fm/ml) than in those with low tumor burden (193.8 fm/ml). An inverse correlation between IL-6 levels and sEGF-R was observed (r =-0.33; P = 0.040). No relationship between sEGF-R and time to progression or overall survival was observed while circulating IL-6 was found as a predictive factor of survival. Our results showed that sEGF-R level was elevated in metastatic malignant melanoma patients but not related to time to progression or survival and demonstrated an inverse correlation between sEGF-R and IL-6 levels. These findings imply a better understanding of EGF-R and IL-6 cross-talk function in melanoma.

Integrative roles of transforming growth factor-alpha in the cytoprotection mechanisms of gastric mucosal injury

Background

Transforming growth factor α (TGFα) protects against gastric mucosal injury and facilitates wound healing. However, its overexpression is known to induce hypertrophic gastropathy resembling Menetrier's disease in transgenic (TG) mice on an FVB background, as one of the authors reported previously. We studied another TGFα-expressing mouse line on a CD1 background, whose gastric mucosa appears normal. Since this TG mouse had a strong resistance to ethanol-induced gastric injury, we considered the long-term effect of TGFα on several gastric protection mechanisms.

Methods

TGFα-expressing transgenic (TG) mouse lines bearing human TGFα cDNA under the control of the mouse metallothionein gene I promoter were generated on a CD1 mouse background, and analyzed their ethanol injury-resistant phenotypes produced by TGFα.

Results

In the TG mucosa, blood flow was well maintained after ethanol injury. Further, neural and inducible types of NO synthases were consistently and widely expressed in the TG mucosa, compared with the limited distribution of neural type NO synthase in the luminal pit region of the wild-type (WT) mucosa. COX-2 and its upstream transcription factor NfkB were constitutively elevated in the TG mucosa even before ethanol administration, whereas they were induced in the same region of the WT mucosa only after ethanol injury. Two anti-apoptotic proteins, HSP70 and Bcl-2, were upregulated in the TG mucosa even before ethanol administration, while they were not expressed in the WT mucosa before the injury. Furthermore, pro-caspase 3 activation was inhibited in the TG mucosa, while it was converted to the active form in the WT mucosa following ethanol administration.

Conclusion

We conclude that TGFα maintains the gastric mucosal defense against gastric injury by integrating other cytoprotective mechanisms.

Modulation of different stress pathways after styrene and styrene-7,8-oxide exposure in HepG2 cell line and normal human hepatocytes

Styrene is one of the most important monomers produced worldwide. IARC classified styrene as a possible carcinogen to humans (group 2B). Styrene-7,8-oxide (SO) is the main reactive metabolite of styrene, and it is found to be genotoxic in several in vitro test systems. Styrene and styrene-7,8-oxide (SO) toxicity to HepG2 cells was investigated by evaluating end-points such as heat shock proteins (Hsps), metallothioneins (MT), apoptosis-related proteins, accumulation of styrene within the cells and expression of two isoforms of cytochrome P450. The potential activity of styrene and styrene-7,8-oxide in modulating gene expression was also investigated. The results showed induction of Hsp70, metallothioneins, BclX(S/L) and c-myc expression and a decrease in Bax expression in HepG2 after treatments, confirming that these compounds activated protective mechanisms. Moreover, up-regulation of TGFbeta2 and TGFbetaRIII in HepG2 cells was found after exposure to styrene, while in human primary hepatocytes these genes were down-regulated after both treatments. Finally, it was found that styrene and SO treatments did not induce CYP1A2 and CYP2E1 protein expression. In conclusion, both compounds caused toxic stress in HepG2 cells, with SO being more toxic; in the meantime, a different effect of the two compounds in HepG2 cells and primary human hepatocytes was observed regarding their activity in gene modulation.

N-terminal cleavage of proTGFalpha occurs at the cell surface by a TACE-independent activity

ProTGFalpha (transforming growth factor alpha precursor) maturation and conversion into soluble TGFalpha is a complex process that involves three proteolytic steps. One, that occurs co-translationally, eliminates the signal sequence. Another, occurring at the juxta-membrane domain, solubilizes TGFalpha. A third cleavage removes the N-terminal extension of proTGFalpha. This latter step has been poorly studied, mainly because of the rapid kinetics of this cleavage. In the present study, we have designed a strategy to analyse several aspects regarding this N-terminal cleavage. In vivo treatment with the hydroxamate-based metalloprotease inhibitors BB3103 or TAPI-2 (tumour necrosis factor-alpha protease inhibitor 2) reversibly induced accumulation of forms of proTGFalpha that included the N-terminal extension. N-terminal shedding was rapid, and occurred at the cell surface. However, the machinery responsible for the N-terminal cleavage was inactive in other cellular sites, such as the endoplasmic reticulum. Experiments of proTGFalpha expression and maturation in cells deficient in TACE (tumour-necrosis-factor-alpha-converting enzyme) activity indicated that this protease was dispensable for N-terminal processing of proTGFalpha in vivo, but was required for regulated cleavage at the C-terminus. These findings indicate that TACE is not involved in N-terminal processing of proTGFalpha, and suggest differences in the machineries that control the cleavage at both ends of TGFalpha within its precursor.

RNF11 is a multifunctional modulator of growth factor receptor signalling and transcriptional regulation

Our laboratory has found that the 154aa RING finger protein 11 (RNF11), has modular domains and motifs including a RING-H2 finger domain, a PY motif, an ubiquitin interacting motif (UIM), a 14-3-3 binding sequence and an AKT phosphorylation site. RNF11 represents a unique protein with no other known immediate family members yet described. Comparative genetic analysis has shown that RNF11 is highly conserved throughout evolution. This may indicate a conserved and non-redundant role for the RNF11 protein. Molecular binding assays using RNF11 have shown that RNF11 has important roles in growth factor signalling, ubiquitination and transcriptional regulation. RNF11 has been shown to interact with HECT-type E3 ubiquitin ligases Nedd4, AIP4, Smurf1 and Smurf2, as well as with Cullin1, the core protein in the multi-subunit SCF E3 ubiquitin ligase complex. Work done in our laboratory has shown that RNF11 is capable of antagonizing Smurf2-mediated inhibition of TGFbeta signalling. Furthermore, RNF11 is capable of degrading AMSH, a positive regulator of both TGFbeta and EGFR signalling pathways. Recently, we have found that RNF11 can directly enhance TGFbeta signalling through a direct association with Smad4, the common signal transducer and transcription factor in the TGFbeta, BMP, and Activin pathways. Through its association with Smad4 and other transcription factors, RNF11 may have a role in direct transcriptional regulation. Our laboratory and others have found nearly 80 protein interactions for RNF11, placing RNF11 at the cross-roads of cell signalling and transcriptional regulation. RNF11 is highly expressed in breast tumours. Deregulation of RNF11 function may prove to be harmful to patient therapeutic outcomes. RNF11 may therefore provide a novel target for cancer therapeutics. The purpose of this review is to discuss the role of RNF11 in cell signalling and transcription factor modulation with special attention given to the ubiquitin-proteasomal pathway, TGFbeta pathway and EGFR pathway.

Detection of transforming growth factor-alpha and epidermal growth factor receptor mRNA and immunohistochemical localization of the corresponding proteins in the canine uterus during the estrous cycle

Uterine expression of the epidermal growth factor (EGF) family of growth factors has not been studied in the dog. The present study looks at the presence of mRNA transcripts and immunohistochemical localization for transforming growth factor-alpha (TGF-alpha), which is the potent EGF family member, and for EGF receptor (EGF-R) in the canine uterus during the estrous cycle. The reverse transcriptase-polymerase chain reaction together with sequencing of the products confirmed the presence of their mRNA transcripts in the endometrium throughout the estrous cycle. Immunohistochemical analysis found clear positive staining for TGF-alpha and EGF-R in the luminal and glandular epithelia at proestrus and estrus. Immunoreactivity decreased at the early stage of diestrus. In the mid stage of diestrus, clear staining for TGF-alpha was again found in the glands of the luminal region, and staining for EGF-R was observed in all glands. Very little staining was seen at anestrus for either TGF-alpha or EGF-R. These results suggest that TGF-alpha expressed in the uterus may be involved in regulating growth, differentiation and regression in the endometrial epithelial cells during the estrous cycle in the dog.

Inhibition of prostasin expression by TGF-beta1 in renal epithelial cells

BACKGROUND

Prostasin has been shown to be involved in the regulation of sodium handling in the kidney. TGF-beta1 has been demonstrated to suppress alphaENaC expression and sodium uptake. Therefore, we hypothesized that TGF-beta1 may regulate prostasin expression to modulate sodium reabsorption in the kidney.

METHODS

To determine if TGF-beta1 has an effect on prostasin expression, we isolated 2.9 kb of the rat prostasin promoter, and measured its transcriptional activity with a luciferase assay in mouse cortical collecting duct cell line (M-1). The effect of TGF-beta1 on the mRNA and protein abundance of prostasin, and amiloride-sensitive (22)Na uptake was determined.

RESULTS

Treatment of M-1 cells with 20 ng/mL of TGF-beta1 for 24 hours significantly decreased the promoter activity by 50 +/- 1%, and the inhibitory effect was dose dependent over the range of 0.1 to 20 ng/mL. We identified a 50 bp region (-410 to -360) containing c-Rel-like sequence in prostasin promoter that is responsible for the TGF-beta1-mediated inhibition, and found that TGF-beta1 increases IkappaBalpha expression in M-1 cells. TGF-beta1 reduced endogenous prostasin mRNA and protein expression in M-1 cells by 50 +/- 12% and 44 +/- 12%, respectively, and the amiloride-sensitive (22)Na uptake by 35.9 +/- 4.8%.

CONCLUSION

Our findings indicate the possibility that TGF-beta1 transcriptionally inhibits prostasin expression by the induction of IkappaBalpha and the subsequent inhibition of NF-kappaB/Rel activity in M-1 cells, and also suggest the possibility that TGF-beta1 might inhibit sodium reabsorption through a reduction in prostasin expression and subsequent inhibition of ENaC activity.

Distinct roles of EGF repeats for the Notch signaling system

Notch is a single-pass transmembrane receptor that mediates cell fate choice in various species and developmental contexts. The Notch signal is transduced by its intracellular domain, which acts as a transcriptional activator, and is released from the plasma membrane by proteolytic cleavages. This process is initiated by intercellular association of the epidermal growth factor (EGF) repeats between Notch and the DSL (Delta, Serrate, Lag-2) ligands but the detailed mechanism is yet to be clarified. Here we demonstrate that Notch1 can form homodimers, which is achieved by its EGF motifs. The Notch1 dimer formation increased in response to ligand presentation and HES1 promoter was stimulated, implying that receptor homodimerization is an important initial step in Notch signal transduction. EGF motifs also serve as a protection against proteases, including TNF-alpha converting enzyme, which prevents Notch1 from ligand-independent activation. Multiple functions of the Notch EGF motifs, such as the prevention of constitutive activation, reciprocal interaction with the ligands and lateral interaction for homodimerization, appear to constitute crucial elements of the Notch signaling system.

Inherent growth advantage of (pre)malignant hepatocytes associated with nuclear translocation of pro-transforming growth factor alpha

The pro-peptide of transforming growth factor alpha (proTGFalpha) was recently found in hepatocyte nuclei preparing for DNA replication, which suggests a role of nuclear proTGFalpha for mitogenic signalling. This study investigates whether the nuclear occurrence of the pro-peptide is involved in the altered growth regulation of (pre)malignant hepatocytes. In human hepatocarcinogenesis, the incidence of proTGFalpha-positive and replicating nuclei gradually increased from normal liver, to dysplastic nodules, to hepatocellular carcinoma. ProTGFalpha-positive nuclei almost always were in DNA synthesis. Also, in rat hepatocarcinogenesis, proTGFalpha-positive nuclei occurred in (pre)malignant hepatocytes at significantly higher incidences than in unaltered hepatocytes. For functional studies unaltered (GSTp(-)) and premalignant (GSTp(+)) rat hepatocytes were isolated by collagenase perfusion and cultivated. Again, DNA synthesis occurred almost exclusively in proTGFalpha-positive nuclei. GSTp(+) hepatocytes showed an approximately 3-fold higher frequency of proTGFalpha-positive nuclei and DNA replication than GSTp(-) cells. Treatment of cultures with the mitogen cyproterone acetate (CPA) elevated the incidence of proTGFalpha-positive nuclei and DNA synthesis in parallel. Conversely, transforming growth factor beta1 (TGFbeta1) lowered both. These effects of CPA and TGFbeta1 were significantly more pronounced in GSTp(+) than in GSTp(-) hepatocytes. In conclusion, nuclear translocation of proTGFalpha increases in the course of hepatocarcinogenesis and appears to be involved in the inherent growth advantage of (pre)malignant hepatocytes.

Intra-membrane ligand diffusion and cell shape modulate juxtacrine patterning

A key problem in developmental biology is how pattern and planar polarity are transmitted in epithelial structures. Examples include Drosophila neuronal differentiation, ommatidia formation in the compound eye, and wing hair polarization. A key component for the generation of such patterns is direct cell-cell signalling by transmembrane ligands, called juxtacrine signalling. Previous models for this mode of communication have considered homogeneous distributions in the cell membrane, and the role of polarity has been largely ignored. In this paper we determine the role of inhomogeneous protein and receptor distributions in juxtacrine signalling. We explicitly include individual membrane segments, diffusive transport of proteins and receptors between these segments, and production terms with a combination of local and global responses to ligand binding. Our analysis shows that intra-membrane ligand transport is vital for the generation of long wavelength patterns. Moreover, with no ligand transport, there is no pattern formation for lateral induction, a process in which receptor activation up-regulates ligand production. Biased production of ligand also modulates patterning bifurcations and predicted wavelengths. In addition, biased ligand and receptor trafficking can lead to regular polarity across a lattice, in which each cell has the same orientation-directly analogous to patterns of hairs in the Drosophila wing. We confirm the trends in pattern wavelengths previously observed for patterns with cellular homogeneity-lateral inhibition tends to give short-range patterns, while lateral induction can give patterns with much longer wavelengths. Moreover, the original model can be recovered if intra-membrane bound receptor diffusion is included and rapid equilibriation between the sides is considered. Finally, we consider the role of irregular cell shapes and waves in such networks, including wave propagation past clones of non-signalling cells.

The expression of thrombospondin-1 in benign prostatic hyperplasia and prostatic intraepithelial neoplasia is decreased in prostate cancer

OBJECTIVE

To evaluate the immunohistochemical expression of thrombospondin (TSP), a potent inhibitor of angiogenesis, in human benign prostatic hyperplasia (BPH) and prostate cancer.

MATERIALS AND METHODS

The expression of TSP-1, TSP-2 and CD36 receptor was assessed in 73 tissue specimens using immunohistochemistry; specimens were from 32 patients with BPH, seven with prostatic intraepithelial neoplasia (PIN) and 34 with cancer.

RESULTS

Immunohistochemistry showed that all 39 patients with BPH and PIN had TSP-1-positive glands. In contrast, none of the 34 patients with cancer had positive TSP-1 staining in the cancer tissue. All 73 patients were positive for TSP receptor CD36 and negative for TSP-2.

CONCLUSIONS

TSP is expressed in BPH, down-regulated in PIN and absent in prostate cancer tissue. This may indicate that TSP is important in prostate cancer progression. Further studies are needed to understand the significance of these findings for the malignant transformation of the prostate gland.

Membrane-bound stem cell factor is a key regulator in the initial lodgment of stem cells within the endosteal marrow region

OBJECTIVE

The transmembrane isoform of stem cell factor (tm-SCF) has been implicated in the adhesion of hemopoietic stem cells to the extracellular matrix within the bone marrow microenvironment in vitro. In addition, in vivo SCF has been shown to play a role in cell mobilization and migration. The aim of this study was to determine if SCF is an integral component of the hemopoietic "niche" of the bone marrow in situ.

MATERIALS AND METHODS

To analyze the role of tm-SCF in cell lodgment, purified populations of primitive progenitors and hemopoietic stem cells (HSC) were transplanted into a hemopoietic microenvironment devoid of tm-SCF, and the spatial distribution of engrafted cells was analyzed. In addition, populations of HSC were isolated using non-neutralizing and neutralizing antibodies to the SCF receptor c-kit, and their spatial distribution was analyzed post-transplant.

RESULTS

The data demonstrated a significant impairment in the lodgment of transplanted cells within the endosteal marrow region in mice lacking tm-SCF, with a reduction of almost 30% by 15 hours post-transplant. The role of tm-SCF was confirmed by analyzing the spatial distribution of HSC isolated using a neutralizing antibody to c-kit.

CONCLUSION

The data demonstrate that although tm-SCF does not appear to play a role in the homing of transplanted cells to the bone marrow, it is critical in the lodgment and detainment of HSC within their hemopoietic "niche."

Muc4/sialomucin complex, the intramembrane ErbB2 ligand, in cancer and epithelia: to protect and to survive

The membrane mucin Muc4, also called sialomucin complex (SMC), is a heterodimeric complex of two subunits, ASGP-1 and ASGP-2, derived from a single gene. It is produced by multiple epithelia in both membrane and soluble forms and serves as a protective agent for the epithelia. The membrane form of Muc4 acts as a steric barrier to the apical cell surface of epithelial or tumor cells. An important example is the uterus of the rat, in which Muc4 expression is downregulated for blastocyst implantation. The soluble form facilitates the protection and lubrication of epithelia by mucous gels composed of gel-forming mucins, as in the airway, where Muc4 is proposed to participate in mucociliary transport as a constituent of the periciliary fluid. The soluble form is also found in body fluids, such as milk, tears, and saliva. The transmembrane subunit ASGP-2 acts as an intramembrane ligand and activator for the receptor tyrosine kinase ErbB2. Formation of this ligand-receptor complex is proposed to repress apopotosis in epithelial and cancer cells in which the ligand-receptor complex is formed, providing a second type of cell protective mechanism. Muc4 expression is regulated in epithelial tissues in a cell- and tissue-specific manner during epithelial differentiation. In stratified epithelia, it is predominantly in the most superficial, differentiated layers, often coincident with ErbB2. Dysregulation of Muc4 expression may contribute to cell and tissue dysfunction, such as the proposed contribution of Muc4 to mammary tumor progression. These observations clearly show that Muc4 has multiple roles in epithelia, which may provide insights into aberrant behaviors of these tissues and their derivative carcinomas.

Transforming growth factor-alpha is expressed in astrocytes of the suprachiasmatic nucleus in hamster: role of glial cells in circadian clocks

Transforming growth factor-alpha (TGF-alpha) is abundantly expressed in the suprachiasmatic nucleus of several rodent species. It was recently suggested to be a clock output signal regulating the activity/rest rhythm. In this study we further characterized the cellular identity of TGF-alpha-expressing cells in the suprachiasmatic nucleus of the Syrian hamster (Mesocricetus auratus). Using confocal laser scanning fluorescence imaging on brain sections immuno-histologically processed for TGF-alpha and GFAP double staining, we observed that in the suprachiasmatic nucleus, TGF-alpha staining is located mainly in GFAP-positive cells, indicating suprachiasmatic nucleus astrocytes produce TGF-alpha. Glial expression of TGF-alpha was also observed in the 3rd ventricle tanycytes of the retrochiasmatic area. In other brain regions where the TGF-alpha message is abundant, such as in the piriform cortex, we observed that TGF-alpha staining is mainly located in neurons. Our results provide the first evidence that glial cells are involved in the regulation of output from the suprachiasmatic nucleus circadian clock through a diffusible mechanism.

Interferon-gamma activates EGF receptor and increases TGF-alpha in T84 cells: implications for chloride secretion

IFN-gamma inhibits intestinal Cl(-) secretion, in part via downregulation of CFTR and Na(+)-K(+)-ATPase activity and expression, but the proximal signaling events were unknown. We have shown that transforming growth factor-alpha (TGF-alpha) inhibits calcium-activated Cl(-) secretion, and effects of IFN-gamma in other systems are mediated via EGF family members. We tested whether IFN-gamma inhibits Cl(-) secretion via EGF receptor (EGFr) activation. IFN-gamma increased tyrosine phosphorylation in T84 cells at 24 h, including the EGFr. IFN-gamma also increased cell-associated pro-TGF-alpha, as well as free TGF-alpha in the bathing media. However, whereas IFN-gamma significantly inhibited carbachol-induced Cl(-) secretion, neither neutralizing antibodies to TGF-alpha nor an EGFr inhibitor (1 microM tyrphostin AG 1478) were able to reverse this inhibitory effect. AG 1478 also failed to reverse IFN-gamma-induced tyrosine phosphorylation of the EGFr, but receptor phosphorylation was attenuated by both the neutralizing antibody to TGF-alpha and PP2, a Src kinase inhibitor. Moreover, PP2 reversed the inhibitory effect of IFN-gamma on Cl(-) secretion. In total, our findings suggest an increase in functional TGF-alpha and activation of the EGFr in response to IFN-gamma. The release of TGF-alpha and intracellular Src activation likely combine to mediate EGFr phosphorylation, but only Src appears to contribute to the inhibition of transport. Nevertheless, because TGF-alpha plays a role in restitution and repair of the intestinal epithelium after injury, we speculate that these findings reflect a feedback loop whereby IFN-gamma modulates the extent of cytokine-induced intestinal damage.

Growth factors and steroid hormones: a complex interplay in the hypothalamic control of reproductive functions

The mechanisms through which LHRH-secreting neurons are controlled still represent a crucial and debated field of research in the neuroendocrine control of reproduction. In the present review, we have specifically considered two potential signals reaching these hypothalamic neurons: steroid hormones and growth factors. Examples of the relevant physiological role of the interactions between these two families of biologically acting molecules have been provided. In many cases, these interactions occur at the level of hypothalamic astrocytes, which are presently accepted as functional partners of the LHRH-secreting neurons. On the basis of the observations here summarized, we have formulated the hypothesis that a functional co-operation of steroid hormones and growth factors occurring in the hypothalamic astrocytic compartment represents a key factor in the neuroendocrine control of reproductive functions.

Intrapituitary regulatory system of mammotrophs in the mouse

Estrogen stimulates the proliferation of pituitary cells, in particular mammotrophs. The present study was designed to clarify involvement of transforming growth factor alpha (TGF-alpha) in the estrogen-induced growth of mouse pituitary cells in vitro. Anterior pituitary cells obtained from ICR male mice were cultured in a primary, serum-free culture system. Proliferation of pituitary cells was detected by monitoring the cellular uptake of a thymidine analogue, bromodeoxyuridine. Secretory cell types were immunocytochemically determined. Treatment with TGF-alpha (0.1 and 1 ng/ml) for 5 days stimulated cell proliferation. Since TGF-alpha binds to the epidermal growth factor (EGF)-receptor, this action may be exerted through this receptor. Estradiol-17beta (E2, 10(-9) M) stimulated proliferation of mammotrophs. RG-13022, an EGF receptor inhibitor, reduced the cell proliferation induced by EGF or E2, showing that the EGF receptor was involved in this induction of mammotroph growth. Treatment with TGF-alpha antisense oligodeoxynucleotide (ODN) inhibited the cell proliferation induced by E2, but treatment with EGF antisense ODN did not. Dual detection of TGF-alpha mRNA and growth hormone by in situ hybridization and fluorescence-immunocytochemistry demonstrated that TGF-alpha mRNA was detected in most somatotrophs. Our recent RT-PCR analysis revealed that E2 stimulated TGF-alpha-mRNA and EGF-receptor mRNA expression. These results indicate that TGF-alpha produced in somatotrophs mediates the stimulatory effect of estrogen on pituitary cell proliferation in a paracrine manner, and that EGF-receptor expression is stimulated by estrogen. These findings indicate that intrapituitary cell-to-cell interaction plays an important role in the control of pituitary secretory cells.

The transmembrane heregulin precursor is functionally active

A variety of eucaryotic polypeptide growth factors are synthesized as transmembrane precursors. Many of these precursors are released from plasma membranes by proteolytic cleavage and converted into soluble mature proteins. A number of studies, however, indicate that bound growth factor precursors can be biologically active, suggesting a role for these membrane-associated ligands in cell-cell communication. Secreted heregulin is a 45-kDa growth factor with homology to epidermal growth factor. This growth factor binds directly to HER-3 and HER-4 and activates heterodimeric receptor complexes composed of the type I receptor tyrosine kinases, i.e. HER-1, HER-2, HER-3, and HER-4. Heregulin was originally detected in the conditioned medium of the human breast cancer cell line MDA-MB-231 and purified based on its ability to stimulate phosphorylation of p185(HER-2/neu). In the current study, the biologic activity of plasma membrane-anchored heregulin was evaluated in human breast cells. Transmembrane heregulin binds to cells expressing p180(HER-3), induces p185(HER-2/neu) phosphorylation, and increases DNA synthesis in cells overexpressing the HER-2/neu gene product. In addition, when cells containing heregulin receptors are co-cultured with heregulin-producing cells, specific in vivo associations are observed. This study demonstrates that transmembrane heregulin is functionally active and suggest it is capable of playing a role in cell-cell communication and subsequent signal transduction in vivo.

Function of the Drosophila TGF-alpha homolog Spitz is controlled by Star and interacts directly with Star

Drosophila Spitz is a homolog of transforming growth factor alpha (TGF-alpha) and is an activating ligand for the EGF receptor (Egfr). It has been shown that Star is required for Spitz activity. Here we show that Star is quantitatively limiting for Spitz production during eye development. We also show that Star and Spitz proteins colocalize in Spitz sending cells and that this association is not coincident with the site of translation--consistent with a function for Star in Spitz processing or transmission. Finally, we have defined minimal sequences within both Spitz and Star that mediate a direct interaction and show that this binding can occur in vivo.