Rapid development of hepatic tumors in transforming growth factor alpha transgenic mice associated with increased cell proliferation in precancerous hepatocellular lesions initiated by N-nitrosodiethylamine and promoted by phenobarbital.

The carcinogenic and tumor-promoting effects of human transforming growth factor alpha (TGF-alpha) overexpression were examined in a two-stage chemical carcinogenesis protocol using TGF-alpha transgenic mouse line MT42. Male MT42 and CD-1 mice received a single i.p. injection of 5 mg N-nitrosodiethylamine (DEN)/kg body wt at 15 days of age, and were placed on a diet containing 0.05% of phenobarbital (PB) from 4 weeks of age for 35 weeks. DEN-, PB-treated and saline-injected animals in each strain were used as controls. A total of three sequential sacrifices (at 10, 23 and 37 experimental weeks) was performed. Hepatocellular carcinomas (HCCs) developed earlier at high incidence (100%) after 23 experimental weeks in MT42 mice receiving DEN/PB, while CD-1 mice had a 40% incidence of HCCs only after week 37. HCCs also developed in the DEN-initiated MT42 mice at 80% incidence after week 23, but no HCCs were observed in the DEN-initiated CD-1 mice. PB induced preneoplastic foci (67%), adenomas (33%) and HCCs (33%) after 37 weeks in MT42 mice, but no lesions were found in CD-1 mice. Thus, the carcinogenic response to DEN and/or PB was accelerated in the MT42 transgenic mice. Furthermore, PB promotion was observed from week 10 in MT42 mice and week 23 in CD-1 mice. Thus, the promoting effect of PB was also accelerated in the MT42 transgenic mice. Proliferating cell nuclear antigen (PCNA) labeling indices of hepatocellular foci and adenomas in DEN- or DEN/PB-treated MT42 mice were significantly higher than those of CD-1 mice. TGF-alpha expression determined by immunohistochemistry revealed higher levels in these lesions than in hepatocytes of surrounding parenchyma of MT42 transgenic mice. In conclusion, TGF-alpha transgenic mice clearly demonstrated enhanced sensitivity to the development of hepatocellular carcinoma in the DEN initiation and PB promotion regime, possibly through a mechanism of increased hepatocyte proliferation in precancerous lesions (foci and adenomas), driven by high expression of the mitogen TGF-alpha in these lesions.

Pancreatic gastrin stimulates islet differentiation of transforming growth factor alpha-induced ductular precursor cells.

Gastrin is transiently expressed in fetal islets during a critical period of their development from protodifferentiated islet precursors in fetal pancreatic ducts. To examine the possible role of gastrin as an islet cell growth factor, postnatal islet growth was studied in transgenic mice which overexpress gastrin and TGF alpha in their pancreas. Overexpression of a TGF alpha transgene causes metaplastic ductules containing numerous insulin expressing cells that resemble protodifferentiated precursors of the fetal pancreas. However, islet mass of the TGF alpha transgenic mice was not increased. Pancreatic overexpression of gastrin from a chimeric insulin/gastrin transgene transcribed from the insulin promoter markedly decreased the TGF alpha-stimulated increase in pancreatic duct mass. Furthermore, pancreatic coexpression of both gastrin and TGF alpha significantly increased islet mass in mice expressing both transgenes. These findings indicate that TGF alpha and gastrin can act synergistically to stimulate islet growth, although neither peptide alone is sufficient. Islet growth may possibly be stimulated through gastrin promoting the differentiation of insulin-positive cells in the TGF alpha-induced metaplastic ducts. This transgenic study suggests that islet neogenesis can be reactivated in the ductular epithelium of the adult pancreas by local expression of two growth factors, gastrin and TGF alpha.

Molecular insights into breast cancer from transgenic mouse models.

We desperately need to know more of the biological details of the onset and progression of breast cancer. The disease is of startlingly high incidence (approaching 1 in 9 women), our current therapies for the disease are inadequate once it has metastasized, and the disease is characterized by excessive morbidity and mortality. Most of the growth and differentiation of the mammary gland occurs relatively late in life: during sexual maturation, and then cyclically during pregnancy and lactation. Normal as well as malignant growth is regulated by endocrine hormones as well as by local tissue factors, such as polypeptide growth factors. Cancer seems to progress as hyperplastic ductal or lobular epithelial growth, acquiring progressive genetic changes (including those of oncogenes and tumor suppressor genes) leading to clonal outgrowths of progressively more malignant cells. The nature of proliferative controls and the relevant genetic changes are the subjects of the current review.

Transgenic animals in biomedical research.

The advent of transgenic technology, in which foreign genetic information is stably introduced into the mammalian germ line, has dramatically enhanced our basic knowledge of physiologic and pathologic processes. Transgenic animals created by these genetic manipulations are being used to provide insights into gene regulation, development, pathogenesis, and the treatment of disease. Furthermore, transgenic biotechnology holds great promise for the creation of genetically superior livestock and the industrial production of precious pharmaceuticals. It is evident now that the study and use of transgenic animals will significantly improve the human condition.

Chemotherapy and chemosensitization of transgenic mice which express the human multidrug resistance gene in bone marrow: efficacy, potency, and toxicity.

A common form of multidrug resistance in human cancer results from expression of the MDR1 gene which encodes a plasma membrane energy-dependent multidrug efflux pump. We have engineered transgenic mice which express this multidrug transporter in their bone marrow cells and demonstrated that peripheral WBC of these animals provide a rapid and reliable system for assessing the bioactivity of agents that reverse multidrug resistance. Immunocytochemical analysis of bone marrow smears suggests that the activation of the MDR1 transgene has probably occurred at a very early stage of bone marrow differentiation since most bone marrow cells express the transporter. Expression of this transgene in bone marrow produces about 10-fold resistance to leukopenia induced by taxol compared to normal bone marrow. Chemosensitization of MDR1 mice to daunomycin and taxol, measured by a fall in WBC, is detectable at a dose as low as 0.01 mg/kg R-verapamil. A dose of 0.5 mg/kg R-verapamil reduces the WBC by nearly 50%. Chemosensitization of MDR-transgenic mice with 5 mg/kg R-verapamil, which is highly effective in reversing MDR and readily tolerated by mice, necessitates a reduction of the maximum tolerated dose of most chemotherapeutic agents by only 20%. In addition, detailed histopathological examination shows that treatment of mice with chemotherapeutic drugs and R-verapamil does not change the organ-related toxicity pattern but only moderately accentuates inherent toxic side effects of the chemotherapeutic agents. We conclude that MDR1-transgenic mice represent a valid model for evaluating efficacy, potency, and toxicity associated with chemotherapy and chemosensitization of multidrug-resistant cells in animals.

Inactivation of a sperm motility gene by insertion of an epidermal growth factor receptor transgene whose product is overexpressed and compartmentalized during spermatogenesis.

Transgenic mice were generated with a human epidermal growth factor (EGF) receptor cDNA driven by the chicken beta-actin gene promoter. One line (AE24) that exhibited a unique expression pattern in which dramatically elevated levels of EGF receptor RNA were found only in the testis was established, suggesting that the beta-actin promoter was being influenced by an adjacent testis-specific enhancer. EGF receptor RNA was detected in primary spermatocytes, whereas the synthesis of receptor protein was restricted to elongate spermatids, indicating that transgene expression was under translational control. At spermiation, the EGF receptor was sequestered in residual bodies and excluded from mature sperm by a compartmentalization mechanism. About half of AE24 homozygous males were sterile because of sperm paralysis, whereas heterozygous males and females of either genotype were completely fertile. Electron microscopic analysis of sperm flagella from sterile AE24 homozygotes revealed an aberrant axonemal structure in which outer doublet microtubules were missing from the middle piece, resembling changes observed in the sperm of some infertile humans. Flagellar axonemal disassembly was observed in the vas deferens and epididymis but not in the testis, suggesting that outer doublets were assembled in a grossly normal manner but possessed a latent instability. These results demonstrate that in the AE24 mouse line the EGF receptor transgene was integrated into and inactivated an endogenous autosomal gene, causing sperm flagellar axonemal disruption and male sterility.

New potent verapamil derivatives that reverse multidrug resistance in human renal carcinoma cells and in transgenic mice expressing the human MDR1 gene.

Multidrug resistance in human renal cell carcinoma is mainly caused by expression of the MDR1 gene and is characterized by a broad spectrum cross resistance to many natural product chemotherapeutic agents. This resistance can be overcome by applying chemosensitizers which inhibit the function of the MDR1 gene product P-glycoprotein. The development of new reversing agents with fewer side effects and a higher potency in modifying resistance is a high priority of research on drug resistance. We have evaluated four new verapamil derivatives on 21 primary human renal cell carcinomas in vitro, and also tested them in an MDR-transgenic mice model. These mice express the human MDR1 gene in their bone marrow cells and measurement of their white blood counts provides a simple, rapid and reliable system to screen for the potency of MDR-reversing agents in vivo. We demonstrate here that all four drugs are effective in reversing multidrug resistance in primary cultures of human renal cell carcinomas when used in combination with vinblastine chemotherapy, and to a lesser extent with doxorubicin or daunomycin chemotherapy. Our in vivo data indicate that two of these reversing agents display low toxicity at high concentrations and are more effective at low, clinically achievable concentrations, than the other two drugs and R-verapamil. These results make the two new drugs attractive candidates to be taken into clinical trials.

Transgenic mice that express the human multidrug-resistance gene in bone marrow enable a rapid identification of agents that reverse drug resistance.

The development of preclinical models for the rapid testing of agents that circumvent multidrug resistance in cancer is a high priority of research on drug resistance. A common form of multidrug resistance in human cancer results from expression of the MDR1 gene, which encodes a Mr 170,000 glycoprotein that functions as a plasma membrane energy-dependent multidrug efflux pump. We have engineered transgenic mice that express this multidrug transporter in their bone marrow and demonstrated that these animals are resistant to leukopenia by a panel of anticancer drugs including anthracyclines, vinca alkaloids, etoposide, taxol, and actinomycin D. Differential leukocyte counts indicate that both neutrophils and lymphocytes are protected. Drugs such as cisplatin, methotrexate, and 5-fluorouracil, which are not handled by the multidrug transporter, produce bone marrow suppression in both normal and transgenic mice. The resistance conferred by the MDR1 gene can be circumvented in a dose-dependent manner by simultaneous administration of agents previously shown to be inhibitors of the multidrug transporter in vitro, including verapamil isomers, quinidine, and quinine. Verapamil and quinine, both at levels suitable for human trials that produced only partial sensitization of the MDR1-transgenic mice, were fully sensitizing when used in combination. We conclude that MDR1-transgenic mice provide a rapid and reliable system to determine the bioactivity of agents that reverse multidrug resistance in animals.

Epidermal growth factor receptor regulation and function.

The epidermal growth factor (EGF) receptor is a transmembrane, cell-surface glycoprotein that mediates the mitogenic action of a family of ligands, including EGF and transforming growth factor alpha (TGF alpha). Perturbation of this signal transduction pathway by exposure to excess ligand, by overproduction of the normal EGF receptor, or by the presence of specific mutated forms of this receptor can result in dramatic alterations in cellular phenotype, including malignant transformation. Overstimulation of normal cells is avoided by precise control of the synthesis and degradation of EGF receptors. Regulation occurs at multiple levels, including transcriptional control. A number of DNA-binding proteins have now been identified which positively and negatively modulate EGF receptor gene transcription.

TGF alpha overexpression in transgenic mice induces liver neoplasia and abnormal development of the mammary gland and pancreas.

To define the role of TGF alpha in normal tissue function and in pathogenesis, transgenic mice have been generated bearing a fusion gene consisting of the mouse metallothionein 1 promoter and a human TGF alpha cDNA. In these mice, human TGF alpha RNA and protein are abundant in many tissues and TGF alpha is detectable in blood and urine. The effects of TGF alpha overproduction in transgenic mice are pleiotropic and tissue specific. The liver frequently contains multifocal, well-differentiated hepatocellular carcinomas that express enhanced levels of human TGF alpha RNA. The mammary gland exhibits impeded morphogenetic penetration of epithelial duct cells into the stromal fat pad. The pancreas shows progressive interstitial fibrosis and a florid acinoductular metaplasia, during which acinar cells appear to degranulate, dedifferentiate, and assume characteristics of intercalated or centroacinar duct cells. TGF alpha therefore plays an important role in cellular proliferation, organogenesis, and neoplastic transformation.

Expression of a human multidrug resistance cDNA (MDR1) in the bone marrow of transgenic mice: resistance to daunomycin-induced leukopenia.

The human multidrug resistance gene (MDR1) encodes a drug efflux pump glycoprotein (P-glycoprotein) responsible for resistance to multiple cytotoxic drugs. A plasmid carrying a human MDR1 cDNA under the control of a chicken beta-actin promoter was used to generate transgenic mice in which the transgene was mainly expressed in bone marrow and spleen. Immunofluorescence localization studies showed that P-glycoprotein was present on bone marrow cells. Furthermore, leukocyte counts of the transgenic mice treated with daunomycin did not fall, indicating that their bone marrow was resistant to the cytotoxic effect of the drug. Since bone marrow suppression is a major limitation to chemotherapy, these transgenic mice should serve as a model to determine whether higher doses of drugs can cure previously unresponsive cancers.

Nuclear factor ETF specifically stimulates transcription from promoters without a TATA box.

Transcription factor ETF stimulates the expression of the epidermal growth factor receptor (EGFR) gene which does not have a TATA box in the promoter region. Here, we show that ETF recognizes various GC-rich sequences including stretches of deoxycytidine or deoxyguanosine residues and GC boxes with similar affinities. ETF also binds to TATA boxes but with a lower affinity. ETF stimulated in vitro transcription from several promoters without TATA boxes but had little or no effect on TATA box-containing promoters even though they had strong ETF-binding sites. These inactive ETF-binding sites became functional when placed upstream of the EGFR promoter whose own ETF-binding sites were removed. Furthermore, when a TATA box was introduced into the EGFR promoter, the responsiveness to ETF was abolished. These results indicate that ETF is a specific transcription factor for promoters which do not contain TATA elements.

Cooperative function of two separate enhancers of the human epidermal growth factor receptor proto-oncogene.

Two separate enhancers were identified both upstream and downstream of the promoter of the human epidermal growth factor receptor gene. Transcriptional enhancer activity was found to be associated with a region 1172 and 852 base pairs upstream of the most upstream RNA start site, and within a 530-base pair fragment located in the first intron about 2000 base pairs downstream of the most upstream RNA start site. These two separate enhancers stimulated promoter activity cooperatively in HeLa cells synthesizing the epidermal growth factor receptor. The enhancer downstream of the promoter functioned only in the presence of the other upstream enhancer. Several areas of sequences homology with viral and cellular enhancers were noted in both the upstream and downstream enhancers. The region essential for the downstream enhancer activity has 10 nuclear factor-binding sites.

Modulation of epidermal growth factor receptor proto-oncogene transcription by a promoter site sensitive to S1 nuclease.

The epidermal growth factor (EGF) receptor is the functional target of the mitogen EGF and the cellular homolog of the avian erythroblastosis virus erbB oncogene product. Regulation of expression of the proto-oncogene encoding the EGF receptor can be elucidated by studying the structure and function of the gene promoter outside the confines of the cell. Previously, we reported the isolation of the human EGF receptor gene promoter. The promoter is highly GC rich, contains no TATA or CAAT box, and has multiple transcription start sites. An S1 nuclease-sensitive site has now been found 80 to 110 base pairs (bp) upstream from the major in vivo transcription initiation site. Two sets of direct repeat sequences were found in this area; both conform to the motif TCCTCCTCC. When deletion mutations were made in this region of the promoter by using either Bal 31 exonuclease or S1 nuclease, we found that in vivo activity dropped three- to fivefold, on the basis of transient-transfection analysis. Examination of nuclear protein binding to normal and mutated promoter DNAs by gel retardation analysis and DNase I footprinting revealed that two specific factors bind to the direct repeat region but cannot bind to the S1 nuclease-mutated promoter. One of the specific factors is the transcription factor Sp1. The results suggest that these nuclear trans-acting factors interact with the S1 nuclease-sensitive region of the EGF receptor gene promoter and either directly or indirectly stimulate transcription.

Methylation status of epidermal growth factor receptor gene in lung carcinoma cells.

The methylation status of the epidermal growth factor receptor (EGFR) gene was compared in cell lines from four major types of lung carcinoma, small cell lung carcinoma (SCLC), large cell lung carcinoma, squamous cell carcinoma and adenocarcinoma, in order to examine whether DNA methylation is responsible for the suppression of EGFR gene in SCLC cells. Southern blot analysis revealed that the structural region of the EGFR gene is methylated to various degrees regardless of the expression of EGF receptor on the surface. An 8-kilobase EcoRI fragment which contains the EGFR gene promoter region is readily digested with various methylation-sensitive restriction enzymes in all types of cells, indicating that the EGFR gene 5' region is barely methylated. Thus, a mechanism other than DNA methylation appears to control EGFR gene expression and the lack of EGFR gene expression in SCLC cells may be caused by a paucity of some transcription regulatory factor(s).

A transcription factor active on the epidermal growth factor receptor gene.

We have developed an in vitro transcription system for the epidermal growth factor receptor (EGFR) oncogene by using nuclear extracts of A431 human epidermoid carcinoma cells, which overproduce EGFR. We found that a nuclear factor, termed EGFR-specific transcription factor (ETF), specifically stimulated EGFR transcription by 5- to 10-fold. In this report, ETF, purified by using sequence-specific oligonucleotide affinity chromatography, is shown by renaturing material eluted from a NaDodSO4/polyacrylamide gel to be a protein with a molecular mass of 120 kDa. ETF binds to the promoter region, as measured by DNase I "footprinting" and gel-mobility-shift assays, and specifically stimulates the transcription of the EGFR gene in a reconstituted in vitro transcription system. These results suggest that ETF could play a role in the overexpression of the cellular oncogene EGFR.

A novel effect of EGF on mRNA stability.

Expression of the epidermal growth factor (EGF) receptor gene is stimulated by EGF and the phorbol ester, 4 beta-phorbol 12-myristate 13-acetate (PMA). PMA elevates EGF receptor mRNA levels in human KB epidermoid carcinoma cells, but does not significantly affect the half-life of this mRNA when its decay is examined after the addition of actinomycin D. In contrast, EGF greatly prolongs the half-life of EGF receptor mRNA suggesting a possible mechanism for the stimulatory effect of EGF on EGF receptor mRNA levels. EGF also stabilizes beta-tubulin and beta-actin mRNAs but has very little effect on the degradation of total mRNA.

Epidermal growth factor (EGF) receptor gene transcription. Requirement for Sp1 and an EGF receptor-specific factor.

We have studied in vitro transcription of the human epidermal growth factor (EGF) receptor proto-oncogene using nuclear extracts of A431 human epidermoid carcinoma cells, which overproduce the EGF receptor. With the in vitro system we found that Sp1 and other trans-acting factors bound to the EGF receptor promoter regions and are required for maximal expression. Fractionation showed that a DEAE-Sepharose fraction (BA) contained a novel factor, which specifically stimulated EGF receptor transcription 5- to 10-fold. The molecular mass of the native form of the factor is about 270-kDa based on its migration on Sephacryl S-300. This factor may activate transcription of the proto-oncogene through a weak or indirect interaction with the DNA template.