Evolution of neoplastic development in the liver of transgenic mice co-expressing c-myc and transforming growth factor-alpha.

We have previously shown that co-expression of c-myc and transforming growth factor (TGF)-alpha as transgenes in mouse liver results in major enhancement of neoplastic development in this organ as compared with expression of either of these transgenes alone. In this report we describe in detail the progression from liver cell dysplasia to hepatocellular carcinomas (HCCs) occurring in the liver of c-myc/TGF-alpha and c-myc transgenic mice. Despite morphological similarities in the sequence of events between the two transgenic lines, the dramatic acceleration, extent, and severity of hepatic lesions in c-myc/TGF-alpha mice clearly demonstrated the synergistic effects of this transgenic combination. Although c-myc/TGF-alpha and c-myc females displayed longer latency and lower tumor incidence, the pathological changes were the same as those seen in the male mice, including the formation of HCCs, which are absent in TGF-alpha single-transgenic females. Tumors in single- and double-transgenic mice showed induction of the endogenous c-myc and TGF-alpha and, most frequently, unchanged or decreased epidermal growth factor receptor, further indicating the collaborative role of c-myc and TGF-alpha in providing a selective growth advantage to tumor cells independently of the epidermal growth factor receptor levels. To identify possible tumor precursors, we focused particularly on the dysplastic changes preceding and accompanying the appearance of preneoplastic and neoplastic lesions in the double-transgenic mice. Early on, these changes were characterized by the appearance of large dysplastic hepatocytes, mostly pericentrally, expressing high levels of TGF-alpha and uPA, as well as TGF-beta 1, particularly in apoptotic cells. After a short period of replication and expansion into the liver parenchyma, as well as penetration into the central veins, these cells underwent apoptotic cell death while preneoplastic and neoplastic lesions were forming. The peritumorous tissues also contained small dysplastic hepatocytes and oval-like cells, similar to those found in the tumors. Transplantation of the transgenic liver tissues harboring only dysplasia with or without vascular lesions onto nude mice was able to yield HCCs composed of small diploid cells, suggesting that initiated cells are generated during the early dysplastic phase and can progress to HCC. It is therefore likely that large dysplastic hepatocytes undergo apoptosis, which may be closely associated with the up-regulation of TGF-beta 1 and uPA, whereas other cells evolve into the precursor population for HCC. Due to the simultaneous presence of c-myc, TGF-alpha, and dysplasia in premalignant human liver diseases, our transgenic mouse system appears to be an appropriate model for studying human hepatocarcinogenesis.     

Nonrandom cytogenetic alterations in hepatocellular carcinoma from transgenic mice overexpressing c-Myc and transforming growth factor-alpha in the liver

Identification of specific and primary chromosomal alterations during the course of neoplastic development is an essential part of defining the genetic basis of cancer. We have developed a transgenic mouse model for liver neoplasia in which chromosomal lesions associated with both the initial stages of the neoplastic process and the acquisition of malignancy can be analyzed. Here we analyze chromosomal alterations in 11 hepatocellular carcinomas from the c-myc/TGF-alpha double-transgenic mice by fluorescent in situ hybridization with whole chromosome probes, single-copy genes, and 4'-6-diamidino-2-phenylindole (DAPI-) and G-banded chromosomes and report nonrandom cytogenetic alterations associated with the tumor development. All tumors were aneuploid and exhibited nonrandom structural and numerical alterations. A balanced translocation t(5:6)(G1;F2) was identified by two-color fluorescent in situ hybridization in all tumors, and, using a genomic probe, the c-myc transgene was localized near the breakpoint on derivative chromosome der 6. Partial or complete loss of chromosome 4 was observed in all tumors with nonrandom breakage in band C2. Deletions of chromosome 1 were observed in 80% of the tumors, with the most frequent deletion at the border of bands C4 and C5. An entire copy of chromosome 7 was lost in 80% of the tumors cells. Eighty-five percent of the tumor cells had lost one copy of chromosome 12, and the most common breakpoint on chromosome 12 occurred at band D3 (28%). A copy of chromosome 14 was lost in 72%, and band 14E1 was deleted in 32% of the tumor cells. The X chromosome was lost in the majority of the tumor cells. The most frequent deletion on the X chromosome involved band F1. We have previously shown that breakages of chromosomes 1, 6, 7, and 12 were observed before the appearance of morphologically distinct neoplastic liver lesions in this transgenic mouse model. Thus breakpoints on chromosome 4, 9, 14, and X appear to be later events in this model of liver neoplasia. This is the first study to demonstrate that specific sites of chromosomal breakage observed during a period of chromosomal instability in early stages of carcinogenesis are later involved in stable rearrangements in solid tumors. The identification of the 5;6 translocation in all of the tumors has a special significance, being the first balanced translocation reported in human and mouse hepatocellular carcinoma and having the breakpoint near a tumor susceptibility gene and myc transgene site of integration. Moreover, its early occurrence indicates that this is a primary and relevant alteration to the initiation of the neoplastic process. In addition, the concordance between the breakpoints observed during the early dysplastic stage of hepatocarcinogenesis and the stable deletions of chromosomes 1, 4, 6, 7, 9, and 12 in the tumors provides evidence for preferential site of genetic changes in hepatocarcinogenesis.     

Strain background alters mammary gland lesion phenotype in transforming growth factor-alpha transgenic mice

Whey acidic protein (WAP)-transforming growth factor (TGF)-alpha transgenic mice acquire both cancerous and noncancerous mammary lesions. For this study, we evaluated the effect of mouse strain background on the incidence, latency, and histotype of two noncancerous lesions, hyperplastic alveolar nodules (analogous to typical hyperplasias in women), and macrocysts. These lesions display characteristics of fibrocystic changes observed in breasts of women, and in both mice and humans are associated with an uncertain risk of progression to neoplasia. Virgin transgenic mice of the (C57BL/6J;SJL)F2 background developed very few hyperplastic alveolar nodules and no macrocysts. In contrast, when the WAP-TGF-alpha transgene was carried on the FVB/N strain, congenic virgin transgenic mice acquired both lesion types with approximately 100% penetrance. In the (FVB;C57BL/6J)F1 background, hyperplastic alveolar nodule incidence was reduced to approximately the nontransgenic mouse level, and macrocyst latency was increased dramatically. Crossing into C57BL/6 resulted in elimination of the macrocyst phenotype. Finally, FVB strain transgenic mammary epithelium transplanted into nontransgenic recipients of the FVB/N or (FVB;C57BL/6J)F1 backgrounds displayed macrocyst latency characteristic of the recipient, and not donor, mouse strain. Quantitative real-time polymerase chain reaction analysis demonstrated that, despite the difference in macrocyst incidence between (FVB;C57BL/6J)F1 and C57BL/6 virgin transgenic mice (81% versus 0%), the level of TGF-alpha expression was not different. FVB strain transgenic mice expressed only twofold more TGF-alpha than the other backgrounds. These findings indicate that C57BL/6J modifier alleles inhibit mammary lesion incidence and macrocyst latency in a semidominant manner, and that suppression of lesion development can involve host factors that are independent of mammary epithelial genotype.     

Dose-related protection from nickel-induced lung injury in transgenic mice expressing human transforming growth factor-alpha

To determine the role of transforming growth factor-alpha (TGF-alpha) in protecting the lung from aerosolized nickel injury, transgenic mouse lines expressing human TGF-alpha in the pulmonary epithelium, under control of the human surfactant protein-C gene promoter, were tested. Higher expressing TGF-alpha transgenic mouse lines, expressing distinct levels of TGF-alpha, survived longer than nontransgenic control mice. Increased survival correlated with levels of TGF-alpha expression in the lung. After 72 h of nickel exposure (70 microg Ni/m3), transgenic lines with intermediate levels of the TGF-alpha expression demonstrated attenuation of lung injury. The highest expressing line (line 28) demonstrated reduced lung inflammation and edema, reduced lung wet-to-dry weight ratios, decreased bronchoalveolar lavage (BAL) protein and neutrophils, reduced interleukin (IL)-1beta, interleukin-6, and macrophage inflammatory protein-2, and maintained surfactant protein-B (SP-B) levels compared with nontransgenic controls. In the TGF-alpha transgenic mouse model, TGF-alpha protects against nickel-induced acute lung injury, at least in part, by attenuating the inflammatory response, reducing pulmonary edema, and preserving levels of SP-B.     

Mammary carcinogenesis is preceded by altered epithelial cell turnover in transforming growth factor-alpha and c-myc transgenic mice

Identification of biomarkers that indicate an increased risk of breast cancer or that can be used as surrogates for evaluating treatment efficacy is paramount to successful disease prevention and intervention. An ideal biomarker would be identifiable before lesion development. To test the hypothesis that changes in cell turnover precede mammary carcinogenesis, we evaluated epithelial cell proliferation and apoptosis in mammary glands from transgenic mice engineered to develop mammary cancer due to expression in mammary epithelia of transforming growth factor α (TGF-α) or c-myc. In transgenic glands, before lesion development, epithelial cell turnover was enhanced overall compared with nontransgenic glands, indicating that aberrant cell turnover in normal epithelia may contribute to tumorigenesis. In addition, in tumor-containing glands, proliferation in normal epithelia was higher than in tumor-free transgenic glands, suggesting these cell populations influence one another. Finally, although c-myc glands displayed a uniformly high epithelial cell turnover regardless of age, cell turnover was reduced with aging in nontransgenic and TGF-α mice, indicating that some growth and death regulatory mechanisms remain intact in TGF-α epithelia. These observations support the evaluation of cell turnover as a biomarker of cancer risk and indicator of prevention/treatment efficacy in preclinical models and warrant validation in human breast cancer.     

Transforming growth factor-alpha deficiency reduces pulmonary fibrosis in transgenic mice

Despite evidence that implicates transforming growth factor-alpha (TGF-alpha) in the pathogenesis of acute lung injury, the contribution of TGF-alpha to the fibroproliferative response is unknown. To determine whether the development of pulmonary fibrosis depends on TGF-alpha, we induced lung injury with bleomycin in TGF-alpha null-mutation transgenic mice and wild-type mice. Lung hydroxyproline content was 1.3, 1.2, and 1.6 times greater in wild-genotype mice than in TGF-alpha-deficient animals at Days 10, 21, and 28, respectively, after a single intratracheal injection of bleomycin. At Days 7 and 10 after bleomycin treatment, lung total RNA content was 1.5 times greater in wild-genotype mice than in TGF-alpha-deficient animals. There was no significant difference between mice of the two genotypes in lung total DNA content or nuclear labeling indices after bleomycin administration. Wild-genotype mice had significantly higher lung fibrosis scores at Days 7 and 14 after bleomycin treatment than did TGF-alpha-deficient animals. There was no significant difference between TGF-alpha-deficient mice and wild-genotype mice in lung inflammation scores after bleomycin administration. To determine whether expression of other members of the epidermal growth factor (EGF) family is increased after bleomycin-induced injury, we measured lung EGF and heparin-binding- epidermal growth factor (HB-EGF) mRNA levels. Steady-state HB-EGF mRNA levels were 321% and 478% of control values in bleomycin-treated lungs at Days 7 and 10, respectively, but were not significantly different in TGF-alpha-deficient and in wild-genotype mice. EGF mRNA was not detected in normal or bleomycin-treated lungs of mice of either genotype. These results show that TGF-alpha contributes significantly to the pathogenesis of pulmonary fibrosis after bleomycin-induced injury, and that compensatory increases in other EGF family members do not occur in TGF-alpha-deficient mice.     

Distinctive patterns of hyperplasia in transgenic mice with mouse mammary tumor virus transforming growth factor-alpha. Characterization of mammary gland and skin proliferations.

Eight lines of transgenic mice expressing a mouse mammary tumor virus (MMTV) human transforming growth factor-alpha (TGF alpha) fusion gene were established. Three lines with distinctive phenotypes are presented. All have proliferative changes of the mammary gland. One line has sebaceous gland hyperplasia of the skin. Five histologic patterns of mammary gland hyperplasia based on two of these lines were identified: cystic hyperplasia, solid hyperplasia, dysplasia, adenoma, and adenocarcinoma. Human TGF alpha mRNA and protein were produced in all patterns but appeared reduced in solid hyperplasia, dysplasia, and adenocarcinoma. TGF alpha immunoreactivity in the mammary tissue, cystic fluid, and serum did not show significant differences; hyperplasia developed in 65% of multiparous mice and 45% of virgin mice by 12 months of age. Adenocarcinoma developed in 40% of multiparous mice and 30% of virgin mice by 16 months of age. These transgenic lines may provide useful models of mammary and sebaceous gland hyperplasia analogous to human disease.     

The mitogenic activity of hepatocyte growth factor on rat hepatocytes is dependent upon endogenous transforming growth factor-alpha

Both transforming growth factor-alpha (TGF-alpha) and hepatocyte growth factor (HGF) induce DNA synthesis in hepatocytes in vitro and in vivo. Hepatic and circulating levels of HGF have been reported to increase before an increase in TGF-alpha levels in several rat models of liver regeneration. In addition, serum TGF-alpha levels increase after an increase in serum HGF levels in patients with either partial hepatectomy or acute hepatitis. In this study, we investigate the significance of TGF-alpha in hepatocyte proliferation. TGF-alpha contents and DNA synthesis in cultured rat hepatocytes increased in response to HGF addition to the culture medium in a dose-related manner. These increases were suppressed by the addition of anti-sense TGF-alpha mRNA oligonucleotide. Furthermore, the addition of anti-TGF-alpha rabbit IgG suppressed the increase in DNA synthesis. When the anti-TGF-alpha antibody was administered to rats after partial hepatectomy, the number of mitotic hepatocytes was reduced in comparison to rats treated with normal rabbit IgG. These results were observed even though hepatic HGF levels were increased equally in rats given either anti-TGF-alpha antibody or normal rabbit IgG. Our results suggest that HGF stimulates TGF-alpha production in rat hepatocytes, and that the mitogenic activity of HGF depends on endogenous TGF-alpha activity.     

Overexpression of tumor necrosis factor-alpha diminishes pulmonary fibrosis induced by bleomycin or transforming growth factor-beta

Tumor necrosis factor-alpha (TNF-alpha) is thought to be important in the development of pulmonary fibrosis. However, surfactant protein-C/TNF-alpha transgenic mice do not spontaneously develop pulmonary fibrosis but instead develop alveolar enlargement and loss of elastic recoil. We hypothesized that overexpression of TNF-alpha in the lung requires an additional insult to produce fibrosis. In this study we evaluated whether TNF-alpha overexpression altered the development of pulmonary fibrosis due to bleomycin or transforming growth factor-beta (TGF-beta). Either 0.2 U bleomycin or saline was administered into left lung of TNF-alpha transgenic mice and their transgene-negative littermates. To overexpress TGF-beta, an adenovirus vector containing either active TGF-beta (AdTGF-beta) or LacZ was administered at a dose of 3 x 108 plaque-forming units per mouse. Fibrosis was assessed histologically and by measurement of hydroxyproline. TNF-alpha transgenic mice tolerated bleomycin or AdTGF-beta, whereas the transgene-negative littermates demonstrated severe pulmonary fibrosis after either agent. An increase in prostaglandin E2 and downregulation of TNF receptor I expression were observed in the TNF-alpha transgenic mice. In addition, recombinant human TNF-alpha attenuated bleomycin-induced pulmonary fibrosis. TNF-alpha has a complex role in the development of pulmonary fibrosis. Endogenous TNF-alpha may be important in the development of fibrosis as indicated in other reports, but overexpression of TNF-alpha or exogenous TNF-alpha limits pulmonary fibrosis in mice.     

Localization of transforming growth factor-alpha in human appendageal tumors.

Transforming growth factor-alpha (TGF alpha) is a potent mitogen for epithelial cells that has been localized to normal human appendageal epithelia. To further understand the role of TGF alpha in human appendages, we examined TGF alpha expression immunohistochemically in 17 types of human appendageal tumors differentiating toward hair follicles, eccrine, apocrine, and sebaceous glands. In order of decreasing degrees of differentiation, tumors could be divided into hyperplasias, adenomas, benign epitheliomas, and primordial epitheliomas. Using an antibody that recognizes primarily the 6-kd and 13-kd forms of TGF alpha, TGF alpha immunostaining in 16 of 17 tumor types analyzed was found to follow a similar pattern, with expression in hyperplasias greater than adenomas greater than benign epitheliomas greater than primordial epitheliomas. Within a given tumor, TGF alpha expression also correlated well with the known differentiation state of the tumor cell types. The results suggest that TGF alpha expression is directly correlated with the differentiation state of hair follicle, eccrine, apocrine, and sebaceous tumors in human skin, and raises the possibility that TGF alpha may play a role in the differentiation of appendageal epithelia.     

Expression of tumor necrosis factor-alpha and transforming growth factor-beta 1 in acute liver injury

Tumor necrosis factor-alpha (TNF-alpha) and transforming growth factor-beta 1 (TGF-beta 1) have a number of in vitro functions that could be important in vivo in acute liver injury and repair. Therefore, we investigated these two cytokines in acute liver damage. Northern blots of RNA isolated from rats sacrificed at various time intervals after a single oral dose of CCl4 revealed that TNF-alpha mRNA levels were elevated within 6 hr of CCl4 administration and returned to control values by 24-32 hr. In contrast, TGF-beta 1 mRNA levels started to rise significantly at 24 hr, peaked at 48 hr, and approached baseline levels by 72 hr. Identical changes in TNF-alpha and TGF-beta 1 mRNA levels were also seen with D-galactosamine-induced hepatotoxicity. Immunohistochemical analysis using a TGF-beta 1 antibody demonstrated increased hepatic staining in CCl4-treated rats, at times corresponding to the increases in TGF-beta 1 gene expression. Therefore, there is a differential expression of these cytokines in acute CCl4 and galactosamine hepatotoxicity with an early rise in TNF-alpha, suggesting that this cytokine may affect inflammation and cell toxicity, while TGF-beta 1 peaks later, when it may regulate hepatocyte proliferation and extracellular matrix repair.     

Expression of transforming growth factor-alpha and its receptor during human liver development and maturation

We investigated the expression of transforming growth factor-alpha (TGF-) and its receptor during human liver development and maturation, using immunohistochemistry. In the fetal liver, strong immunoreactivity for TGF- and its receptor was noted in intrahepatic bile duct cells of various developmental stages; moderate immunoreactivity for TGF- and mild immunoreactivity for TGF- receptor were found in immature hepatocytes. In the postnatal liver, reactivity for TGF- in hepatocytes decreased gradually and was negative or only weakly positive in the adult liver, while reactivity for TGF- receptor in hepatocytes increased gradually and was strongly positive in the adult liver. In contrast, immunoreactivity of TGF- and its receptor in intrahepatic bile duct cells persisted in the postnatal liver and was positive in the adult liver. These data suggest that the system of TGF- and its receptor has an important role in the proliferation and differentiation of intrahepatic biliary cells and hepatocytes in the fetal liver. The decreasing expression of TGF- in hepatocytes in the postnatal liver may indicate that proliferative activity of hepatocytes gradually decreases with liver maturation. The presence of TGF- and its receptor in intrahepatic bile ducts in the postnatal liver suggests that the system of TGF- and TGF- receptor is operative postnatally.     

Anti-hepatocyte growth factor antibody inhibits hepatocyte proliferation during liver regeneration

In vitro studies have shown hepatocyte growth factor (HGF) to be a potent mitogen for hepatocytes. Direct evidence of a mitogenic role in vivo was sought by inhibiting HGF activity, using continuous administration of neutralizing antibody to rats which had a stimulus for liver regeneration. Alzet osmotic mini-pumps, administering a constant supply of anti-HGF monoclonal antibody (clone D9), were inserted intraperitoneally into male Wistar rats; an irrelevant isotypical antibody was administered to controls. Forty-five animals received an intragastric bolus of 40 per cent carbon tetrachloride (CCl₄) and groups of three test and control animals were killed at 24 h intervals for 7 days. Treatment with anti-HGF monoclonal antibody significantly inhibited the levels of immunodetectable HGF in the sera of rats following CCl₄ administration. In comparison with controls, hepatocyte proliferation as assessed by bromodeoxyuridine labelling in anti-HGF-treated animals was significantly inhibited at 24 h (P<0·001), 48 h (P<0·001), and 96 h (P<0·05) post-CCl₄ administration. In contrast, sinusoidal cell proliferation was not significantly different from controls at any time point. Inhibition of the parenchymal proliferative response to acute CCl₄-induced liver injury by the in vivo neutralization of HGF provides direct evidence that this growth factor plays an important role in liver regeneration following necrosis. © 1998 John Wiley & Sons, Ltd.     

Critical stages of tumor growth regulation in transgenic mice harboring a hepatocellular carcinoma revealed by distinct patterns of tumor necrosis factor-alpha and transforming growth factor-beta mRNA production

There is now good evidence that cytokines contribute to the regulation of tumor growth. The cytokine-driven modulation of tumor growth was investigated during the progression of a hepatocellular carcinoma (HCC) in SV40 large T tumor antigen transgenic mice. In vivo, an increased rate of liver growth correlated with increased transforming growth factor (TGF)-beta 1 mRNA expression, while the greatest amounts of tumor necrosis factor (TNF)-alpha mRNA were detected earlier during tumor development. Conversely, no particular alteration of IL-1 alpha, IL-1 beta, IL-6, IL-2, IL-4 and IFN-gamma mRNA production could be reported. In vitro, hepatocyte-like tumor cell lines established at two stages, either before or after HCC differentiation, were characterized. The early-stage-derived cell line produced TNF-alpha mRNA, but had barely detectable expression of TGF-beta 1 mRNA, while later-stage- derived cell lines showed the reciprocal pattern. All cell lines displayed a lack of sensitivity to TNF-alpha, although some degree of sensitivity to TNF-alpha could be observed in the presence of actinomycin-D or after treatment with IFN-gamma. The early-stage- derived cell line was sensitive to the growth inhibitory effects of TGF- beta 1, but late-stage-derived tumor cell lines displayed a loss of sensitivity to TGF-beta 1 which correlated with the increased expression of TGF-beta 1 mRNA. Altogether, this suggests that tumor cells contribute to the discrete TNF-alpha and TGF-beta 1 expression patterns during HCC progression. This model of HCC could be of valuable interest to assess the impact of various immunotherapeutic strategies on modulation of tumor growth.      

Prolactin potentiates transforming growth factor alpha induction of mammary neoplasia in transgenic mice

Prolactin influences mammary development and carcinogenesis through endocrine and autocrine/paracrine mechanisms. In virgin female mice, pro-lactin overexpression under control of a mammary selective nonhormonally responsive promoter, neu-related lipocalin, results in estrogen receptor alpha (ERalpha)-positive and ERalpha-negative adenocarcinomas. However, disease in vivo occurs in the context of dysregulation of multiple pathways. In this study, we investigated the ability of prolactin to modulate carcinogenesis when co-expressed with the potent oncogene transforming growth factor alpha (TGFalpha) in bitransgenic mice. Prolactin and TGFalpha cooperated to reduce dramatically the latency of mammary macrocyst development, the principal lesion type induced by TGFalpha. In combination, prolactin and TGFalpha also increased the incidence and reduced the latency of other preneoplastic lesions and increased cellular turnover in structurally normal alveoli and ducts compared with single transgenic females. Bitransgenic glands contained higher levels of phosphorylated ERK1/2 compared with single TGFalpha transgenic glands, suggesting that this kinase may be a point of signaling crosstalk. Furthermore, transgenic prolactin also reversed the decrease in ERalpha induced by neu-related lipocalin-TGFalpha. Our findings demonstrate that locally produced prolactin can strikingly potentiate the carcinogenic actions of another oncogene and modify ovarian hormone responsiveness, suggesting that prolactin signaling may be a potential therapeutic target.     

Roles of transforming growth factor-alpha in mammary development and disease

Transforming growth factor-alpha (TGFalpha) is a member of the epidermal growth factor (EGF) family. Expression of TGFalpha is highly regulated in response to exogenous cellular signals including cytokines and other growth factors. The growth factor has been found to be indispensable for proper development of many tissues and organs. TGFalpha has also been implicated in numerous disease states including forms of breast cancer. This minireview summarizes the basic biology of TGFalpha and its actions during normal and pathogenic development of the mammary epithelium.     

Interleukin-13 induces proliferation of human airway epithelial cells in vitro via a mechanism mediated by transforming growth factor-alpha.

Remodeling of the airways, as occurs in asthmatic patients, is associated with the continual presence of inflammatory mediators and Th2 cytokines, especially interleukin (IL)-13, during cycles of epithelial injury and repair. In this study, we examined the effect of IL-13 on well-differentiated normal human bronchial epithelial (NHBE) cells maintained in air-liquid interface culture. IL-13 induced proliferation of NHBE cells after 24 h exposure, as reflected by [(3)H]thymidine uptake and cell counts. The effects of IL-13 were mediated through the epidermal growth factor receptor (EGFR), as proliferation was attenuated by AG1478, an EGFR tyrosine kinase inhibitor. Proliferation appeared to be mediated by transforming growth factor (TGF)-alpha, a potent ligand for EGFR, which was released rapidly from NHBE cells in response to IL-13. Neutralizing antibody to TGF-alpha, but not antibodies against other potentially important growth factors (EGF, heparin binding epidermal growth factor-like growth factor [HB-EGF], platelet-derived growth factor [PDGF]), inhibited the mitogenic response to IL-13. This study provides the first experimental evidence that IL-13 can initiate a proliferative response of human airway epithelium in the absence of inflammatory cells or other cell types. The results are consistent with a mechanism whereby IL-13 induces release of TGF-alpha from the epithelial cells, which in turn binds via an autocrine/paracrine-type action to the EGFR, initiating proliferation. IL-13-induced airway remodeling in vivo may involve this epithelium-driven response.     

Chronically increased transforming growth factor-beta1 strongly inhibits hippocampal neurogenesis in aged mice

There is increasing evidence that hippocampal learning correlates strongly with neurogenesis in the adult brain. Increases in neurogenesis after brain injury also correlate with improved outcomes. With aging the capacity to generate new neurons decreases dramatically, both under normal conditions and after injury. How this decrease occurs is not fully understood, but we hypothesized that transforming growth factor (TGF)-beta1, a cell cycle regulator that rapidly increases after injury and with age, might play a role. We found that chronic overproduction of TGF-beta1 from astrocytes almost completely blocked the generation of new neurons in aged transgenic mice. Even young adult TGF-beta1 mice had 60% fewer immature, doublecortin-positive, hippocampal neurons than wild-type littermate controls. Bromodeoxyuridine labeling of dividing cells in 2-month-old TGF-beta1 mice confirmed this decrease in neuro-genesis and revealed a similar decrease in astrogenesis. Treatment of early neural progenitor cells with TGF-beta1 inhibited their proliferation. This strongly suggests that TGF-beta1 directly affects these cells before their differentiation into neurons and astrocytes. Together, these data show that TGF-beta1 is a potent inhibitor of hippocampal neural progenitor cell proliferation in adult mice and suggest that it plays a key role in limiting injury and age-related neurogenesis.