Cloning and expression of cDNA encoding human betacellulin, a new member of the EGF family

Molecular cloning and expression of rat betacellulin cDNA

The cDNA encoding an entire open reading frame of rat betacellulin has been cloned from rat kidney. Expression of this cDNA in COS7 cells showed a significant amount of mitogenic activity in the culture media. Western blotting of the cell lysates suggested that the membrane-anchored precursor was cleaved to release its ectodomain very efficiently.

Molecular aspects of pancreatic cancer and future perspectives

Pancreatic cancer has one of the worst prognoses of all human malignancies and the molecular mechanisms underlying this aggressive disease have been extensively investigated in the past years. Tyrosine kinase growth factor receptors and their ligands act to influence tumor cell growth, differentiation, invasion, metastasis, and angiogenesis. In pancreatic cancer a variety of these growth factor receptors and ligands are expressed at increased levels and this overexpression influences the clinical course of the disease. For example, the concomitant presence of the EGF receptor and its ligands EGF, TGF-alpha, and/or amphiregulin is associated with enhanced tumor aggressiveness and shorter survival periods following tumor resection. Furthermore, the growth inhibitory effects of the TGF-beta superfamily of serine-threonine kinase receptors and their ligands are often blocked in pancreatic cancer cells. In addition to these alterations, mutations of the p53 tumor-suppressor gene, the K-ras proto-oncogene, and the Smad4 gene are frequently present in these tumors. Taken together, the abundance of growth-promoting factors, the disturbance of growth inhibitory pathways, and the presence of gene mutations combine to give pancreatic cancer cells a distinct growth advantage which clinically results in rapid tumor progression and poor survival.

The EGF domain: requirements for binding to receptors of the ErbB family

Epidermal growth factor (EGF) has been the prototype growth-stimulating peptide for many years. It has a characteristic structure with three disulfide bridges, which is essential for its activity. However, many other proteins, including both growth factors and proteins with unrelated functions, have similar EGF-like domains. This indicates that besides a characteristic conformation provided by the EGF-like domain, specific amino acids are required to provide specificity in protein functioning. Currently, more than 10 different growth factors with an EGF-like domain have been characterized which all exert their action by binding to the four members of the erbB family of receptors. In this review, studies are described on the structure-function relationship of these EGF-like growth factor molecules in an attempt to analyze the individual amino acids that determine their binding specificity to the individual members of the erbB family.

Identification of an alternatively spliced mRNA transcript of human betacellulin lacking the C-loop of the EGF motif and the transmembrane domain

This paper describes the cloning and characterization of a novel cDNA encoding a short form of betacellulin (BTC-beta), and reports the expression of this mRNA in a variety of human tissues and cell types. BTC-beta is likely the result of alternative splicing. This splicing event leads to the generation of an mRNA encoding an unusual BTC precursor in which the C-loop of the EGF domain and the transmembrane domain are deleted while the remainder of the mature molecule is fused in-frame to the C-terminal cytoplasmic tail.

Cloning of rat betacellulin and characterization of its expression in the gastrointestinal tract

Betacellulin (BTC) is relatively a more recently discovered member of the EGF family of growth factors. As a prelude to its expression and functional studies in rat models of gut damage/repair, we have cloned rat BTC and examined its expression in the gastrointestinal tract. Rat BTC was found to be nearly identical to mouse betacellulin. A single 3 kb mRNA species was detected by Northern blotting, and ribonuclease protection analysis showed that its expression was ubiquitous but low in abundance throughout the gut. BTC mRNA and protein were found expressed in the gastric surface and upper pit epithelium as well as in some cells of gastric glands. In the jejunum, BTC mRNA and protein were localised to the crypt epithelium and in villous goblet cells. In the colon, BTC mRNA and protein were found produced in crypt and surface epithelium as well as in goblet cells. Taken together, the wide spread expression in the gut epithelium and in mucous cells in particular suggests an important and unique role for BTC in the gastrointestinal tract.

The role of the epidermal growth factor receptor in microbial infections of the gastrointestinal tract

The epidermal growth factor receptor (EGFr) is a transmembrane glycoprotein with an intrinsic tyrosine kinase. Ligand-binding to the EGFr activates cell signaling, phosphorylates protein kinases, and rearranges cytoskeletal proteins - responses that resemble those induced by microbial attachment to cell surfaces, a process known to be mediated by host cell receptors in a number of cases. This article critically reviews the possible role played by the EGFr in microbial colonization, and discusses how modulation of the EGF-EGFr axis may affect infection of the gastrointestinal tract.

Adsorption of EGF receptor ligands to test tubes--a factor with implications for studies on the potency of these peptides

Studies on the relative potency of ligands for the epidermal growth factor receptor are usually performed with highly purified ligand specimens. However, adsorption of ligands to glass and plastic surfaces may affect the results by reducing the ligand concentration in an unpredictable way. The aim of this study was to examine the adsorption of four epidermal growth factor (EGF) receptor ligands, EGF, transforming growth factor alpha (TGF-alpha), heparin binding-EGF (HB-EGF) and betacellulin, to commonly used test tubes of polyethylene, polystyrene and glass, respectively. The ligands were kept in a sodium phosphate buffer, both with and without 0.1% human albumin as carrier protein. Adsorption was examined after 20 minutes at room temperature as well as after overnight storage at 4 degrees C. The ligands were quantitated by ELISAs. In the buffer not containing 0.1% human albumin there was a marked adsorption, which differed both among the ligands and among the test tubes. After 20 minutes the ligand concentrations were reduced to 33-73% in polyethylene tubes, to 15-46% in polystyrene tubes and to 12-29% in glass tubes. The adsorption was even more pronounced after storage overnight. The use of 0.1% human albumin in the buffer solved the problem in polyethylene and polystyrene tubes, but not in glass tubes. The results demonstrate that adsorption to surfaces can be a significant problem for EGF receptor ligands and emphasize the need for controlling the growth factor concentration in the final experimental setting.

Purification and characterization of a recombinant human cripto-1 protein

Cripto-1 (CR-1) is a novel protein that contains a modified EGF-like motif and that does not directly bind to any of the known erb B type-1 receptor tyrosine kinase receptors. To more clearly define the biological effects of CR-1 and to more adequately compare the structure-function relationships of CR-1 with other members of the EGF family of growth factors, we have expressed a modified, full-length recombinant human CR-1 protein (rhCR-1) in E. coli and have devised a procedure for the solubilization, refolding and purification of a biologically active form of this protein. We have generated the mature form of hCR-1 from computer assisted predictions of potential signal peptide cleavage sites. Expression of the modified rhCR-1 protein in E. coli was limited to the inclusion bodies. The rhCR-1 protein was found to be expressed at high levels in bacterial cells when fused to a histidine-tag sequence. Refolding of rhCR-1 was found to be difficult because of the large number of cysteine residues in the protein which results in protein aggregation. By chemically modifying the cysteine residues in the rhCR-1 protein with 3-trimethylammoniopropyl methanethiosulfonate, additional positive charges have been introduced into the protein by this disulfiding reagent. This modification facilitates solubilization of the protein when rhCR-1 is denatured. The solubilized, denatured protein was then purified by CM cation exchange and C4 reverse phase HPLC chromatography and refolded in a redox buffer. The refolded, modified rhCR-1 protein was found to be biologically active by its ability to inhibit beta-casein expression, to stimulate the tyrosine phosphorylation of Shc and the activation of MAPK and by its capacity to facilitate branching growth of mouse mammary epithelial cells in type I collagen gels.

Role of heparin-binding EGF-related peptides in proliferation and apoptosis of activated ras-stimulated intestinal epithelial cells

The ras mutation is a common and critical step in carcinogenesis. Autocrine growth factors are also known to play an important role in cancer cell growth and transformation. However, the contribution of autocrine growth factors in regulation of proliferation and apoptosis of activated ras-stimulated intestinal epithelium is not fully understood. Therefore, we constructed activated ras-transfected intestinal epithelial cell clones (IEC-ras) to examine the role of epidermal growth factor (EGF)-related peptides in the behavior of IEC-ras. Overexpression of EGF family growth factors (transforming growth factor alpha, heparin-binding EGF-like growth factor, amphiregulin and betacellulin) and stronger phosphorylation of the EGF receptor was observed in IEC-ras compared with control cells. IEC-ras proliferated more rapidly than control cells, and a specific EGF receptor kinase inhibitor, AG 1478, abolished the increased proliferation of IEC-ras. Heparitinase and chlorate also prevented increased proliferation of IEC-ras. Additionally, IEC-ras expressed more bcl-2 and was more resistant to apoptosis induction by UV radiation and mitomycin C. AG 1478 suppressed bcl-2 expression and inhibited resistance to apoptosis of IEC-ras. Heparitinase and chlorate had effects similar to those of AG 1478. Our data indicate that heparin-binding EGF family growth factors play an important role in both increased proliferation and resistance to apoptosis of ras-stimulated intestinal epithelial cells.

Expression of betacellulin and epiregulin genes in the mouse uterus temporally by the blastocyst solely at the site of its apposition is coincident with the "window" of implantation

In the mouse, the process of implantation is initiated by the attachment reaction between the blastocyst trophectoderm and uterine luminal epithelium that occurs at 2200-2300 h on day 4 (day 1 = vaginal plug) of pregnancy. Several members of the EGF family are considered important in embryo-uterine interactions during implantation. This investigation demonstrates that the expression of two additions to the family, betacellulin and epiregulin, are exquisitely restricted to the mouse uterine luminal epithelium and underlying stroma adjacent to the implanting blastocyst. These genes are not expressed during progesterone-maintained delayed implantation, but are rapidly switched on in the uterus surrounding the implanting blastocyst following termination of the delay by estrogen. These results provide evidence that expression of betacellulin and epiregulin in the uterus requires the presence of an active blastocyst and suggest an involvement of these growth factors in the process of implantation.

Neuregulin-3 (NRG3): a novel neural tissue-enriched protein that binds and activates ErbB4

We describe the identification of Neuregulin-3 (NRG3), a novel protein that is structurally related to the neuregulins (NRG1). The NRG1/neuregulins are a diverse family of proteins that arise by alternative splicing from a single gene. These proteins play an important role in controlling the growth and differentiation of glial, epithelial, and muscle cells. The biological effects of NRG1 are mediated by receptor tyrosine kinases ErbB2, ErbB3, and ErbB4. However, genetic studies have suggested that the activity of ErbB4 may also be regulated in the central nervous system by a ligand distinct from NRG1. NRG3 is predicted to contain an extracellular domain with an epidermal growth factor (EGF) motif, a transmembrane domain, and a large cytoplasmic domain. We show that the EGF-like domain of NRG3 binds to the extracellular domain of ErbB4 in vitro. Moreover, NRG3 binds to ErbB4 expressed on cells and stimulates tyrosine phosphorylation of this receptor. The expression of NRG3 is highly restricted to the developing and adult nervous system. These data suggest that NRG3 is a novel, neural-enriched ligand for ErbB4.

Distribution of mRNA for human epiregulin, a differentially expressed member of the epidermal growth factor family

We have recently identified epiregulin as a new growth regulator and a member of the epidermal growth factor (EGF) family. Epiregulin has certain characteristics that are different from those of the classical members of the EGF family, EGF and transforming growth factor alpha, including mitogenic responses on several normal cells and binding to EGF receptors on epidermoid carcinoma A431 cells. In the present study we cloned and identified the expression of human epiregulin transcript. The human epiregulin gene encoded a 163-residue putative transmembrane precursor containing an EGF-like domain in the internal segment, and the structural organization was similar to that of other members of the EGF family that bind to EGF receptors. Northern blot analysis showed the expression of human epiregulin to be mainly on peripheral blood macrophages and the placenta in normal tissues, and was highest on epithelial tumour cell lines in various types of tumour cell lines. The expression profile was quite different from that of other members of the EGF family in normal and tumour cells. Recombinant expression in mammalian cells also showed that human epiregulin was secreted as a soluble form of approx. 5 kDa that is biologically active on the basis of the stimulation of DNA synthesis. Our findings suggest that epiregulin is involved in certain physiological processes such as maintenance or development of normal cell growth, and the progression of carcinomas.

The relationship between human epidermal growth-like factor receptor expression and cellular transformation in NIH3T3 cells

A collection of cell lines expressing each human epidermal growth factor receptor (HER) family member alone or in all pairwise combinations in a clone of NIH3T3 cells (3T3-7d) devoid of detectable epidermal growth factor receptor family members has been generated. Transformation, as measured by growth in soft agar, occurred only in the presence of appropriate ligand and only in cells expressing two different HER family members. Transfection of oncogenic neu (Tneu), conferred ligand-independent transformation only in cells which co-expressed HER1, HER3, or HER4, but not when expressed alone or with HER2. Cell lines were also tested for their ability to form tumors in animals. None of the cell lines expressing single HER family members was able to form tumors in animals with the exception of HER1, which was weakly tumorigenic. Although unable to form tumors when expressed alone, HER2 was tumorigenic when expressed with HER1 or HER3, but not HER4. Of all complexes analyzed, cells expressing HER1 + HER2 were the most aggressive. The relationship between HER1 activation, intracellular calcium fluxes, and phospholipase Cgamma1 activation is well established. We found that activation of HER1 was required for the induction of a calcium flux and the phosphorylation of phospholipase Cgamma1. These activities were independent of, and unaffected by, the co-expression of any other family member. Further, heregulin stimulation of all cell lines including those containing HER1 did not demonstrate any effect on intracellular calcium levels or phospholipase Cgamma1 phosphorylation. This demonstrates that heregulin induced cellular transformation by activating HER3- and HER4-containing complexes does not require the activation of either phospholipase Cgamma1 or the mobilization of intracellular calcium.

Characterization of the mouse epidermal growth factor promoter and 5'-flanking region. Role for an atypical TATA sequence

As a step toward delineating mechanisms that regulate its activity, we have characterized the mouse epidermal growth factor (EGF) promoter. Primer extension and S1 nuclease analyses identified prominent (+1/+2) and minor (+28) transcription start sites, with the dominant +1/+2 site located 33 bases downstream from a TTTAAA sequence. A restriction fragment that spanned these start sites and contained 390 base pairs of 5'-flanking sequence directed transcription from the +1/+2 site in vitro in the presence of HeLa cell nuclear extracts. Additionally, it promoted expression of a coupled luciferase reporter gene in transfected cell lines. The inclusion of additional 5'-flanking sequence either stimulated or inhibited luciferase expression depending on the cell line. Approximately 2 kilobases of EGF 5'-flanking sequence was determined and found to contain several motifs with partial homology to steroid hormone response elements. Despite this fact and evidence that EGF expression might be regulated by androgens in vivo, EGF promoter-luciferase constructs were not steroid-responsive in cells cotransfected with steroid receptor expression vectors. An oligonucleotide containing the aforementioned TTTAAA sequence specifically bound TATA-binding protein and TFIIA in gel shift assays, and an EGF promoter-luciferase construct in which the core TA dinucleotide was mutated to CG was not active in transfected cells. These data suggest that the TTTAAA sequence functions as an atypical TATA box.

Co-expression of heparin-binding EGF-like growth factor and related peptides in human gastric carcinoma

Heparin-binding epidermal growth factor (EGF)-like growth factor (HB-EGF) is a member of the EGF family of polypeptide growth factors, which includes EGF, transforming growth factor alpha(TGF-alpha), amphiregulin (AR) and betacellulin (BTC). To assess the potential role of HB-EGF in human gastric carcinomas, the expression of HB-EGF and EGF receptor (EGF-R) was examined in normal and cancerous gastric tissues and cultured gastric cancer cell lines. By Northern blot analysis, there was a 4.7-fold increase in HB-EGF mRNA levels in human gastric cancers compared with normal gastric tissues. There was a concomitant 3.9-fold increase in EGF-R mRNA levels in these cancers. Immunostaining revealed co-localization in 72% of the cancer cells of HB-EGF and EGF-R. AR and BTC moieties were not evident by Northern blot analysis. However, using PCR, both AR and BTC mRNA species were demonstrated in normal and cancerous gastric tissues. By Northern blot analysis, HB-EGF, TGF-alpha, AR, BTC and EGF-R mRNA moieties were co-expressed in KATO III and NCI-N87 gastric cancer cell lines. Furthermore, HB-EGF, EGF and TGF-alpha enhanced the growth of both cell lines in a dose-dependent manner. Our findings suggest that HB-EGF is relatively abundant in human gastric cancers and that co-expression of the EGF ligand family may lead to excessive activation of EGF-R in this disorder.

Enhanced expression of heregulin in c-erb B-2 and c-Ha-ras transformed mouse and human mammary epithelial cells

Heregulin beta 1 was found to stimulate the anchorage-dependent, serum-free growth of nontransformed human MCF-10A mammary epithelial cells. Unlike epidermal growth factor, transforming growth factor alpha, or amphiregulin, heregulin beta 1 was also able to induce the anchorage-independent growth of MCF-10A cells. In contrast, the anchorage-independent, serum-free growth of c-Ha-ras or c-erb B-2 transformed MCF-10A cells was unaffected by heregulin beta 1, whereas heregulin beta 1 was able to stimulate the anchorage-independent growth of these cells. c-Ha-ras or c-erb B-2 (c-neu) transformed MCF-10A or mouse NOG-8 mammary epithelial cells express elevated levels of 2.5, 5.0, 6.5, 6.8, and 8.5 kb heregulin mRNA transcripts and/or synthesize cell-associated 25, 29, 50, and 115 kDa isoforms of heregulin. Since the MCF-10A cells and transformants also express c-erb B-3, these data suggest that endogenous heregulin might function as an autocrine growth factor for Ha-ras or erb B-2 transformed mammary epithelial cells.

Human betacellulin, a member of the EGF family dominantly expressed in pancreas and small intestine, is fully active in a monomeric form

Betacellulin (BTC) was found to be expressed mainly in human pancreas and small intestine. This finding suggests that BTC possesses some specific function distinguished from the other members of epidermal growth factor (EGF) family. To clarify this function, the released form of human BTC has been expressed in E.coli, purified, and characterized. The recombinant human BTC was produced as an inclusion body. This material was dissolved in guanidine-HCl under reducing conditions, refolded, and purified through sequential liquid chromatography. Purified BTC was electrophoresed under reducing conditions and a molecular size of 18 kDa was determined, which is the supposed size of a dimer of the peptide. However, chemical analysis failed to show a covalently linked dimer. The molecular mass of BTC analyzed by mass spectrometry revealed it to be 9 kDa, which is consistent with theoretical value for a monomer. Recombinant BTC showed growth promoting activity for mouse fibroblasts and rat aortic smooth muscle cells which was equivalent to EGF On the other hand, BTC was found to exhibit a growth inhibitory effect on the cells overexpressing EGF receptor.

A sensitive enzyme-linked immunosorbent assay used for quantitation of epidermal growth factor receptor protein in head and neck carcinomas: evaluation, interpretations and limitations

The EGF receptor is a transmembrane glycoprotein exerting mitogenic effects on epithelial cells. The purpose of the present study was to develop a sensitive enzyme-linked immunosorbent assay (ELISA) for determination of the epidermal growth factor receptor (EGFR) protein to examine whether the receptor was overexpressed in head and neck squamous cell carcinomas compared with the normal counterpart, and to establish whether clinicopathological correlations were present by investigating a broad spectrum of parameters (tumour size, clinical stage, positive lymph nodes, tumour site, histological grade, keratinisation, preoperative irradiation and clinical outcome). The assay employs two commercially available monoclonal antibodies, both detecting protein epitopes. The material comprises 60 head and neck carcinomas, corresponding normal tissue and normal oral mucosa from healthy individuals. The study demonstrates significantly higher receptor levels in tumours compared with normal tissue (P < 0.002) and a range in tumours and normal tissues of 0.4-10.5 and 0.1-4.3 nmol g-1 membrane protein respectively. Quantitation of receptors in normal mucosa emphasises the importance of using the patients' corresponding normal tissue, because using the patients' mucosa resulted in 83% overexpression, while using normal mucosa from healthy individuals only demonstrated overexpression in 50% of cases. No significant clinicopathological correlations could be established, although the mean values for EGFR increased with tumour size and advanced clinical stage. Furthermore, the prognostic value concerning disease-free survival, recurrence and the time interval for recurrence were investigated but no significance could be demonstrated. In conclusion, the investigation supports the theory of overexpression of EGFR protein as a common motif for malignant epithelial tumours, but limitations in interpretations are demonstrated and discussed further.

Developmental changes of epidermal growth factor-like immunoreactivity in the human fetal brain

We investigated the immunohistochemical localization of epidermal growth factor (EGF) in the developing human brain from 6 weeks of gestation to 3 months postpartum. EGF-like immunoreactivity varied in its localization and intensity according to the stage of development. At 10 - 20 weeks of gestation, EGF-like immunoreactivity appeared in proliferating and migrating cells in the cerebrum, disappeared thereafter, and appeared again in cortical neurons after 27 weeks of gestation. Astrocytes also showed EGF-like immunoreactivity from 27 weeks of gestation. These results suggest developmental regulation of EGF expression in the human brain, suggesting its physiological role in both neuronal and glial cells.

Frequent expression of genes for receptor tyrosine kinases and their ligands in human pancreatic cancer cells

Limited information is available concerning the involvement of growth factor receptors and their ligands in the pathogenesis of human pancreatic cancer. We analyzed 12 human pancreatic cancer cell lines by Northern blot analysis for the expression of 9 receptor tyrosine kinase (RTKs) and 6 growth factors. The effect of a monoclonal antibody (MAb) against transforming growth factor-alpha (TGF-alpha) on in vitro pancreatic cancer cell growth was also assessed, mRNA for EGF-R, c-erbB-2 and c-erbB-3 was expressed in 12 (100%), 12 (100%), and 7 (58%), respectively, of the cell lines examined. In addition, 8 (67%) cell lines expressed the c-met/receptor for hepatocyte growth factor. As for ligands, TGF-alpha mRNA was detected in 10 (83%) cell lines; MAb against TGF-alpha inhibited growth of the 2 cell lines examined. Furthermore, mRNA for amphiregulin (AR) was expressed in 10 (83%) cell lines. Coexpression of TGF-alpha, AR, and EGF-R was observed in 9 (75%) cell lines. These results support the concept that several specified types of RTKs and their ligands are closely involved in regulation of the growth of human pancreatic cancer cells.

Carboxyl-terminal truncation of leucine76 converts heparin-binding EGF-like growth factor from a heparin-enhancible to a heparin-suppressible growth factor

Previous studies have indicated that heparin differentially regulates heparin-binding EGF-like growth factor (HB-EGF) and amphiregulin (AR) mitogenic activity. To further explore this phenomenon, these mitogens were compared under identical cell culture conditions in two different assays. The results of our present investigation demonstrated that AR-mediated mitogenic activity in the murine AKR-2B fibroblast-like cell line was inhibited by heparin, while HB-EGF activity was enhanced. However, the absolute effect of heparin appeared to be cell type specific since HB-EGF mitogenic activity was not dramatically affected by coincubation with heparin when tested on human dermal fibroblasts. Several studies have indicated that mutation of a conserved leucine in the carboxyl-terminal region of both EGF and transforming growth factor-alpha results in decreased affinity for EGF receptors. Since this leucine is present in the analogous position of HB-EGF, but absent in AR, we examined the effect of deleting this residue by carboxyl-terminal truncation of HB-EGF. Analysis of recombinant forms of HB-EGF demonstrated that HB-EGF can be converted to a heparin-inhibited growth factor if the putative mature form of the protein is truncated by two residues (leucine76 and proline77) at the carboxyl terminus. Further analysis demonstrated that only leucine76 appears to be required for heparin-dependent enhancement of HB-EGF-mediated mitogenic activity, indicating that this amino acid may play a pivotal role in controlling the response of HB-EGF to heparin or related glycosaminoglycan sulfates. Our results also suggest that expression of different HB-EGF forms in vivo could result in the production of HB-EGFs with divergent responses to sulfated glycosaminoglycans and proteoglycans.

Regulation of terminal differentiation of zymogenic cells by transforming growth factor alpha in transgenic mice

BACKGROUND/AIMS

Transforming growth factor (TGF) alpha affects the growth of gastric mucosa. Its overexpression alters the mucosa. The aim of this study was to test the possibility that it regulates differentiation of gland cells.

METHODS

Transgenic mice that overexpress TGF-alpha were used to detect its effect on zymogenic (chief) cells in the stomach. To test for a general regulatory role of TGF-alpha in differentiation of zymogen-producing cells, salivary glands from transgenic mice were studied.

RESULTS

In these mice, messenger RNA for pepsinogen C is present in the stomach at normal levels during the neonatal period and then decreases markedly. Zymogenic cells are present in the stomach during the neonatal period but are missing in transgenic adults. The bases of gastric glands, normally rich in zymogenic cells, are occupied by undifferentiated cells and mucous neck cells, the precursors of zymogenic cells. Zymogen granules in submandibular glands of transgenic female mice are reduced in number. Zymogen granule-containing cells in the parotid gland undergo redifferentiation to form tubular complexes, collections of ductularlike structures like those formed in the transgenic pancreas.

CONCLUSIONS

TGF-alpha is a major participant in the regulation of terminal differentiation of zymogenic cells in the stomach and salivary glands.

The role of growth factors in vascular cell development and differentiation

The control of vascular growth and differentiation is a complex system of activity and interaction between positive and negative modulators of these processes. A number of important stimulators and inhibitors of both smooth muscle cells and endothelial cells have now been purified and biochemically characterized. Imbalances in the activity of these factors can result in serious pathologies. In this chapter, we briefly discuss the biology of blood vessel development and growth, review the current literature which describes these stimulators and inhibitors, and discuss current therapeutic strategies designed around these growth modulators.

Interaction of pancreatic ductal carcinoma with nerves leads to nerve damage

BACKGROUND/AIMS

Perineural extension of pancreatic adenocarcinoma has been explained as a mechanical extension along planes of least resistance. This study tests whether the cancer is limited to following these planes and if substances involved in cell signaling are involved in the interaction of cancer cells with nerves.

METHODS

Samples of tissue from patients undergoing resection of pancreatic cancer were studied by electron microscopy and light microscopy. Transforming growth factor alpha (TGF-alpha) and epidermal growth factor receptor (EGFR) were localized in sections.

RESULTS

The adenocarcinoma is not confined to the periphery of nerves. It penetrates the perineurium and becomes intimately associated with Schwann cells and axons in the endoneurium. Neural elements are damaged. Neural invasion likely is a factor in associated pain. TGF-alpha is abundant in nerves in the pancreas. EGFR is prominent in the cells of the adenocarcinoma.

CONCLUSIONS

The interaction of pancreatic cancer with nerves involves more than the cancer following a perineural space. Interaction of TGF-alpha in nerves with EGFR on cancer cells constitutes a possible paracrine mechanism that provides a growth advantage for pancreatic adenocarcinoma and serves as an example of potential interactions that might be active in biological interaction of cancer with nerves.

The heparin-binding domain of amphiregulin necessitates the precursor pro-region for growth factor secretion

The five members of the human epidermal growth factor (EGF) family (EGF, transforming growth factor alpha [TGF-alpha], heparin-binding EGF-like growth factor [HB-EGF], betacellulin, and amphiregulin [AR]) are synthesized as transmembrane proteins whose extracellular domains are proteolytically processed to release the biologically active mature growth factors. These factors all activate the EGF receptor, but in contrast to EGF and TGF-alpha, the mature forms of HB-EGF and AR are also glycosylated, heparin-binding proteins. We have constructed a series of mutants to examine the influence of the distinct precursor domains in the biosynthesis of AR. The transmembrane and cytoplasmic domains of the precursor are not required for secretion of bioactive AR from either COS or mammary epithelium-derived cells, although proteolytic removal of the N-terminal pro-region is less efficient in the absence of the membrane anchor. Deletion of the N-terminal pro-region, however, results in rapid intracellular degradation of the molecule with no detectable secretion of active growth factor. AR secretion is preserved by replacing the native pro-region with the corresponding domain of the HB-EGF precursor but not with that of the TGF-alpha precursor. In the absence of any N-terminal pro-region, secretion of the molecule is restored by deleting the N-terminal heparin-binding domain of mature AR. Both EGF and TGF-alpha, in contrast, can be secreted without their pro-regions. However, if the protein is fused with the AR heparin-binding domain, TGF-alpha secretion is inhibited unless the AR pro-region is also present. We propose that the heparin-binding domain of mature AR necessitates the presence of a specific structural motif in an N-terminal pro-region to permit proper folding, and thus secretion, of a bioactive molecule.

The heparin-binding domain of amphiregulin necessitates the precursor pro-region for growth factor secretion

The five members of the human epidermal growth factor (EGF) family (EGF, transforming growth factor alpha [TGF-alpha], heparin-binding EGF-like growth factor [HB-EGF], betacellulin, and amphiregulin [AR]) are synthesized as transmembrane proteins whose extracellular domains are proteolytically processed to release the biologically active mature growth factors. These factors all activate the EGF receptor, but in contrast to EGF and TGF-alpha, the mature forms of HB-EGF and AR are also glycosylated, heparin-binding proteins. We have constructed a series of mutants to examine the influence of the distinct precursor domains in the biosynthesis of AR. The transmembrane and cytoplasmic domains of the precursor are not required for secretion of bioactive AR from either COS or mammary epithelium-derived cells, although proteolytic removal of the N-terminal pro-region is less efficient in the absence of the membrane anchor. Deletion of the N-terminal pro-region, however, results in rapid intracellular degradation of the molecule with no detectable secretion of active growth factor. AR secretion is preserved by replacing the native pro-region with the corresponding domain of the HB-EGF precursor but not with that of the TGF-alpha precursor. In the absence of any N-terminal pro-region, secretion of the molecule is restored by deleting the N-terminal heparin-binding domain of mature AR. Both EGF and TGF-alpha, in contrast, can be secreted without their pro-regions. However, if the protein is fused with the AR heparin-binding domain, TGF-alpha secretion is inhibited unless the AR pro-region is also present. We propose that the heparin-binding domain of mature AR necessitates the presence of a specific structural motif in an N-terminal pro-region to permit proper folding, and thus secretion, of a bioactive molecule.

The mouse waved-2 phenotype results from a point mutation in the EGF receptor tyrosine kinase

Mice harboring the waved-1 (wa-1) and waved-2 (wa-2) mutations exhibit skin and eye abnormalities that are strikingly similar to those of TGF-alpha-deficient mice, and wa-1 and TGF-alpha were recently shown to be allelic. Because the wa-2 mutation was mapped previously to the vicinity of the EGF/TGF-alpha receptor (EGFR) gene on mouse chromosome 11, we hypothesized that the wa-2 phenotype might result from a defect in either the expression or activity of EGFR, or both. In the present report, we show that EGFR mRNA and protein of normal size are expressed in wa-2 liver and skin at levels that are comparable to those in the corresponding normal tissues, and that the ability of wa-2 EGFR to bind ligand is unaltered. However, ligand-dependent autophosphorylation of wa-2 EGFR is diminished 5- to 10-fold in vitro, and the ability of wa-2 EGFR to phosphorylate an exogenous substrate is reduced by > 90% compared with that of the control receptor. EGF-induced tyrosine phosphorylation, including that of EGFR itself, is also diminished in skin, particularly at lower dose of exogenous EGF. To establish the nature of the wa-2 mutation, we determined the nucleotide sequence of the coding region of normal and wa-2 murine EGFR cDNAs. A comparison of these sequences revealed a single-nucleotide transversion resulting in the substitution of a glycine for a conserved valine residue near the amino terminus of the tyrosine kinase domain. The importance of this mutation was confirmed by showing that its introduction into an otherwise normal EGFR markedly reduced the receptor's tyrosine kinase activity in transfected Chinese hamster ovary cells. Finally, in situ hybridization analysis demonstrated expression of EGFR predominantly in the outer root sheath of active hair follicles in neonatal mice. As we previously localized TGF-alpha mRNA to the inner root sheath, this pattern of EGFR expression is consistent with the effect of the wa-2 mutation on hair structure, and together with our previous characterization of TGF-alpha-deficient mice, reveals a critical role for signaling by this ligand/receptor system in skin.