Biomedical subjects

M Blessing

Publications and source records attributed to M Blessing.

At least 19 recordsLinked to original sources

PubMed2004

Severe hepatic injury in interleukin 18 (IL-18) transgenic mice: a key role for IL-18 in regulating hepatocyte apoptosis in vivo.

BACKGROUND: Interleukin 18 (IL-18) is a cytokine with pleiotropic activity that augments T helper 1 responses and cytotoxic activity of natural killer cells. METHODS: To assess the function of IL-18 in vivo, we generated IL-18 transgenic (IL-18 Tg) mice under the control of a CD2 promoter/enhancer construct. RESULTS: Macroscopically, IL-18 Tg mice showed reduced relative liver weight compared with wild-type littermates. TUNEL assays demonstrated increased hepatocyte apoptosis, and primary hepatocytes isolated from IL-18 Tg mice exhibited an increased spontaneous apoptosis rate. Furthermore, cross linking of Fas increased significantly the apoptosis rate in hepatocytes isolated from wild- type mice but to a much lesser extent in IL-18 Tg mice, suggesting spontaneous activation of the Fas pathway in the latter mice. In fact, in vivo blockade of Fas signal transduction by an adenovirus overexpressing the dominant negative form of the Fas associated death domain rescued hepatocytes from undergoing apoptosis. Finally, adoptive transfer of CD4(+) T cells from IL-18 Tg mice but not from wild-type littermates in SCID mice resulted in severe liver failure with massive periportal fibrosis due to hepatocyte apoptosis. CONCLUSION: IL-18 plays a fundamental role in regulating hepatocyte apoptosis. Furthermore, our transgenic model provides a novel tool to study the mechanisms of IL-18 dependent liver injury in vivo.

Adoptive Transfer↗

PubMed2001

Overexpression of bone morphogenetic protein-6 (BMP-6) in murine epidermis suppresses skin tumor formation by induction of apoptosis and downregulation of fos/jun family members.

Bone morphogenetic protein-6 (BMP-6) is a member of the transforming growth factor-beta superfamily. In murine skin, BMP-6 is highly expressed in postmitotic keratinocytes from day 15.5 p.c. till day 6 p.p. Expression in adult skin remains at very low levels, but pathological conditions such as wounding induce the expression of BMP-6. We demonstrate that tumor promotion by TPA (12-O-tetradecanoylphorbol-13-acetate) also induces expression of BMP-6 in suprabasal keratinocytes. This induction is due to post-transcriptional regulation since the level of BMP-6 mRNA remained unchanged. We performed two-stage skin carcinogenesis experiments with transgenic mice epidermally overexpressing BMP-6. These mice display augmented mitotic indices in normal and TPA-treated epidermis when compared to controls. Despite this hyperproliferation, BMP-6 transgenics showed a delayed development and strong suppression of benign and malignant skin tumor formation. In order to resolve this paradox we determined apoptotic frequencies as well as the expression of constituents of AP-1 (activator protein-1) which is essential for tumor promotion. A higher rate of apoptotic keratinocytes was detectable in transgenic mice versus controls and a downregulation of mRNA for jun/fos family members in transgenic skin after TPA-treatment. Thus expression of BMP-6 augments apoptosis and downregulates the transcription of AP-1 family members thereby establishing tumor resistance.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2001

Regulation of IL-12 p40 promoter activity in primary human monocytes: roles of NF-kappaB, CCAAT/enhancer-binding protein beta, and PU.1 and identification of a novel repressor element (GA-12) that responds to IL-4 and prostaglandin E(2).

Appropriate regulation of IL-12 expression is critical for cell-mediated immune responses. In the present study, we have analyzed the regulation of IL-12 p40 promoter activity in primary human monocytes in vivo. Accordingly, we analyzed the p40 promoter by in vivo footprinting in resting and activated primary human blood CD14(+) monocytes. Interestingly, footprints at binding sites for trans-activating proteins such as C/EBP, NF-kappaB, and ETS were only found upon stimulation with LPS and IFN-gamma. In contrast, a footprint over a purine-rich sequence at -155, termed GA-12 (GATA sequence in the IL-12 promoter), was observed in resting, but not activated, cells. Further characterization of this site revealed specific complex formation at a protected GATA core motif in unstimulated primary monocytes and RAW264.7 macrophages. Mutagenesis within the GA-12 sequence caused a significant up-regulation of inducible IL-12 p40 promoter activity in both transient and stable transfection systems, suggesting a repressor function of this site. Furthermore, binding activity of the GA-12 binding protein GAP-12 was increased by treatment with two potent inhibitors of IL-12 expression, IL-4 and PGE(2). Finally, we observed that IL-4-mediated repression of IL-12 p40 promoter activity is critically dependent on an intact GA-12 sequence. In summary, our data underline the complex regulation of the human IL-12 p40 promoter and identify GA-12 as a potent, novel repressor element that mediates IL-4-dependent suppression of inducible promoter activity in monocytes. Regulation of GAP-12 binding may thus modulate IL-12 p40 gene expression.

Animals↗

PubMed2001

Hepatocellular expression of a dominant-negative mutant TGF-beta type II receptor accelerates chemically induced hepatocarcinogenesis.

The potent growth-inhibitory activity of cytokines of the transforming growth factor-beta (TGF-beta) superfamily and their widespread expression in epithelia suggest that they may play an important role in the maintenance of epithelial homeostasis. To analyse TGF-beta mediated tumor suppressor activity in the liver, we generated transgenic mice overexpressing a dominant negative type II TGF-beta receptor in hepatocytes under control of the regulatory elements of the human C-reactive protein gene promoter. Transgenic animals exhibited constitutive and liver-specific transgene expression. The functional inactivation of the TGF-beta signaling pathway in transgenic hepatocytes was shown by reduced TGF-beta induced inhibition of DNA synthesis in primary hepatocyte cultures. Liver morphology and spontaneous tumorigenesis were unchanged in transgenic mice suggesting that interruption of the signaling of all three isoforms of TGF-beta in hepatocytes does not disturb tissue homeostasis in the liver under physiological conditions. However, following initiation with the carcinogen diethylnitrosamine and tumor-promotion with phenobarbital transgenic mice exhibited a moderate albeit significant increase in the incidence, size and multiplicity of both preneoplastic tissue lesions in the liver and of hepatocellular carcinomas. These results give in vivo evidence for a tumor suppressor activity of the endogenous TGF-beta system in the liver during chemical hepatocarcinogenesis.

Animals↗

PubMed2001

Up- and down-regulation of granulocyte/macrophage-colony stimulating factor activity in murine skin increase susceptibility to skin carcinogenesis by independent mechanisms.

The role of granulocyte-macrophage colony-stimulating factor (GM-CSF) in tumorigenesis is complex. On the one hand, GM-CSF can promote tumor cell growth, survival, and even metastasis. On the other hand, it can stimulate tumor cell rejection. In skin, it is early expressed after topic application of tumor-promoting agents and therefore may be responsible for changes that correlate with skin tumor promotion (e.g., epidermal hyperproliferation and inflammation). To analyze GM-CSF function in skin tumorigenesis, we generated transgenic mice epidermally overexpressing either GM-CSF or a GM-CSF antagonist. Both types of transgenic mice exhibited significantly increased numbers of benign tumors in a two-step skin carcinogenesis experiment using 7',12'-dimethylbenz[a]anthracene (DMBA) as initiator and 12-O-tetradecanoylphorbol-CSF displayed a significantly elevated carcinoma burden following a single-step carcinogenesis protocol consisting of tumor initiation only. Therefore, endogenous promotion is responsible for elevated tumor development in GM-CSF-overexpressing mice. In antagonist transgenic animals, an increased tumorigenicity of modified B16 tumor cells after cutaneous transplantation as compared with nontransgenic or GM-CSF transgenic mice was observed. Thus, the antitumor activity leading to the repression of tumor cell growth in control mice is GM-CSF dependent and is compromised in mice expressing the antagonist. We suggest that both, up-regulation and down-regulation of GM-CSF activity in skin, increase the incidence and growth of tumors via two independent mechanisms: endogenous tumor promotion in the case of increased GM-CSF activity and compromised tumor cell rejection in the case of decreased GM-CSF activity.

9,10-Dimethyl-1,2-benzanthracene↗

PubMed2001

The designer cytokine hyper-IL-6 mediates growth inhibition and GM-CSF-dependent rejection of B16 melanoma cells.

The low immunogenic B16 melanoma cell line was transfected with a mammalian expression vector containing the complementary DNA for a sIL-6R/IL-6 fusion protein, termed Hyper-IL-6 (H-IL-6), which was shown to have biological activities at 100-1000-fold lower concentrations than IL-6 in combination with sIL-6R. The secreted p84 glycoprotein was detected in the supernatant of transfected cells and was fully active on BAF3/gp130 cells, which respond to IL-6/sIL-6R but not to IL-6 alone. Administration of recombinant H-IL-6 to C57BL/6 mice resulted in a prolonged acute phase protein gene expression indicating long systemic persistence of the fusion protein. Transfected B16 cells (B16/H-IL6 cells) showed morphological alterations in combination with a dramatic growth inhibition in vitro. Subcutaneous injection in C57BL/6 mice resulted in an almost complete rejection of B16/H-IL6 cells. This effect was partially abolished in FVB/BL/6 mice transgenic for a GM-CSF receptor antagonist, indicating a GM-CSF-dependent rejection of H-IL-6 transfected B16 cells. These results demonstrate that the anti-tumor effect of cytokines like IL-6 which are secreted by transfected melanoma cells at least in part depends on GM-CSF activity.

Animals↗

PubMed2001

Keratinocyte-derived granulocyte-macrophage colony stimulating factor accelerates wound healing: Stimulation of keratinocyte proliferation, granulation tissue formation, and vascularization.

Chronic, nonhealing wounds represent a major clinical challenge to practically all disciplines in modern medicine including dermatology, oncology, surgery, and hematology. In skin wounds, granulocyte-macrophage colony stimulating factor (GM-CSF) is secreted by keratinocytes shortly after injury and mediates epidermal cell proliferation in an autocrine manner. Many other cells involved in wound healing including macrophages, lymphocytes, fibroblasts, endothelial cells, and dendritic cells synthesize GM-CSF and/or are targets of this cytokine. Therefore, GM-CSF is a pleiotropic cytokine evoking complex processes during wound repair. Despite this complexity and the scarcity of mechanistic understanding GM-CSF has been employed in trials of clinical treatment of skin wounds with some success. In this study, we evaluated a transgenic mouse model in order to analyze the effects of an excess of keratinocyte-derived GM-CSF on excisional wound healing in the skin. Transgenic mice constitutively overexpressing GM-CSF in the basal layer of the epidermis displayed accelerated reepithelialization of full-thickness skin wounds. In the early stages of wound repair, transgenic mice exhibited significantly higher numbers of proliferating keratinocytes at the wound edges and increased formation of granulation tissue with enhanced neovascularization. As a potential mechanism of these beneficial changes, we identified the differential temporal regulation of cytokines such as transforming growth factor-beta, a known angiogenetic factor, interferon-gamma, a proinflammatory cytokine, and interleukin 6, an essential factor for reepithelialization, in transgenic mice versus controls. We propose that the beneficial effects observed in GM-CSF transgenics are due not only to direct GM-CSF action but in addition to indirect processes via the induction of secondary cytokines.

Animals↗

PubMed2000

Epidermal overexpression of granulocyte-macrophage colony-stimulating factor induces both keratinocyte proliferation and apoptosis.

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is released by keratinocytes in sizeable amounts only under pathological conditions, e.g., after topical application of a tumor promoter, in atopic dermatitis (AD), and after wounding. To study the biological function of this cytokine release, we generated transgenic mice that constitutively overexpress GM-CSF in the epidermis. An increase in the numbers of mast cells and Langerhans cells (LCs) in transgenics versus nontransgenic controls was observed but no severe inflammation. This is consistent with a central role of this cytokine in the development and maturation of LCs. Mitotic activity in the epidemnis of transgenic mice was elevated, but epidermal thickness and differentiation were normal. Homeostasis is maintained by an increase of apoptosis in the epidermis. We describe the differential expression of regulators of apoptosis and discuss a potential mechanism for this novel proapoptotic activity of GM-CSF on keratinocytes. Both stimulation of proliferation and promotion of apoptosis are of great relevance to tumorigenesis. The latter may be a means of removing damaged cells after genotoxic stress or injury.

Animals↗

PubMed1999

Cutting edge: chronic intestinal inflammation in STAT-4 transgenic mice: characterization of disease and adoptive transfer by TNF- plus IFN-gamma-producing CD4+ T cells that respond to bacterial antigens.

We generated transgenic mice for STAT-4, a regulatory protein specifically associated with IL-12 signaling, under the control of a CMV promoter. These mice expressed strikingly increased nuclear STAT-4 levels in lamina propria CD4+ T lymphocytes upon systemic administration of dinitrophenyl-keyhole limpet hemocyanin and developed chronic transmural colitis characterized by infiltrates of mainly CD4+ T lymphocytes. The latter cells produced predominantly TNF and IFN-gamma but not IL-4 upon activation with alphaCD3/CD28 or autologous bacterial Ags, consistent with a Th1-type cell response. Furthermore, chronic colitis in STAT-4 transgenic mice could be adoptively transferred to SCID mice by colonic and splenic CD4+ T cells that were activated with Ags from autologous bacterial flora. These data establish a critical molecular signaling pathway involving STAT-4 for the pathogenesis of chronic intestinal inflammation, and targeting of this pathway may be relevant for the treatment of colitis in humans.

Adoptive Transfer↗

PubMed1999

TGF-beta1 in liver fibrosis: an inducible transgenic mouse model to study liver fibrogenesis.

Transforming growth factor-beta1 (TGF-beta1) is a powerful stimulus for collagen formation in vitro. To determine the in vivo effects of TGF-beta1 on liver fibrogenesis, we generated transgenic mice overexpressing a fusion gene [C-reactive protein (CRP)/TGF-beta1] consisting of the cDNA coding for an activated form of TGF-beta1 under the control of the regulatory elements of the inducible human CRP gene promoter. Two transgenic lines were generated with liver-specific overexpression of mature TGF-beta1. After induction of the acute phase response (15 h) with lipopolysaccharide (100 microgram ip), plasma TGF-beta1 levels reached >600 ng/ml in transgenic animals, which is >100 times above normal plasma levels. Basal plasma levels of uninduced transgenic animals were about two to five times above normal. As a consequence of hepatic TGF-beta1 expression, we could demonstrate marked transient upregulation of procollagen I and procollagen III mRNA in the liver 15 h after the peak of TGF-beta1 expression. Liver histology after repeated induction of transgene expression showed an activation of hepatic stellate cells in both transgenic lines. The fibrotic process was characterized by perisinusoidal deposition of collagen in a linear pattern. This transgenic mouse model gives in vivo evidence for the important role of TGF-beta1 in stellate cell activation and liver fibrogenesis. Due to the ability to control the level of TGF-beta1 expression, this model allows the study of the regulation and kinetics of collagen synthesis and fibrolysis as well as the degree of reversibility of liver fibrosis. The CRP/TGF-beta1 transgenic mouse model may finally serve as a model for the testing of antifibrogenic agents.

Animals↗

PubMed1998

Expression of a dominant negative type II TGF-beta receptor in mouse skin results in an increase in carcinoma incidence and an acceleration of carcinoma development.

The role of Transforming growth factor beta (TGF-beta) in carcinogenesis is complex. There are reports on both tumor inhibition and tumor promotion by TGF-beta. To elucidate the complex role of TGF-beta in epithelial carcinogenesis, we generated transgenic mice overexpressing a dominant negative type II TGF-beta receptor in the basal cell compartment and in follicular cells of the skin. Despite the reduced responsiveness of transgenic keratinocytes to TGF-beta, both proliferation and differentiation were normal in non-irritated epidermis of these transgenic mice. Thus, interruption of signaling of all three isoforms of TGF-beta in basal and follicular cells does not disturb tissue homeostasis. However, during tumor promotion transgenic mice showed an elevated level of proliferation in the epidermis. This hyperproliferation correlated with a very early onset of carcinoma development and a malignant conversion frequency of 30% from benign papillomas to carcinomas. By comparison, the conversion frequency in wild-type mice of this strain has previously been reported as 5.5%. Even without induction of hyperproliferation by tumor promoters, transgenic mice developed far more carcinomas as controls when treated with a carcinogen. This result indicates that there is a synergistic effect between loss of TGF-beta responsiveness and mutations caused by initiation with a carcinogen leading to an endogenous tumor promotion in initiated cells only.

Animals↗

PubMed1998

Hepatocellular hyperplasia, plasmacytoma formation, and extramedullary hematopoiesis in interleukin (IL)-6/soluble IL-6 receptor double-transgenic mice.

Cytokines interact not only with membrane anchored receptors, but also with specific soluble receptors which circulate in the bloodstream. In general, soluble cytokine receptors such as soluble tumor necrosis factor receptor, soluble interleukin 1 receptor, and soluble interleukin 4 receptor compete with their membrane-bound counterparts for the ligands and therefore act as antagonists. In contrast, soluble receptors for cytokines of the interleukin-6 (IL-6) family complex with their ligands act agonistically. Interestingly, the complex of IL-6 and the soluble interleukin 6 receptor (sIL-6R) activates target cells that do not express the membrane-bound IL-6R and therefore cannot respond to IL-6. To identify cellular responses that are due to IL-6/sIL-6R but not to IL-6 alone, IL-6/sIL-6R double-transgenic mice were generated and compared with IL-6 single-transgenic mice. IL-6/sIL-6R transgenic mice develop a severe phenotype showing 1) marked hepatocellular hyperplasia frequently surrounded by peliosis and necrosis, 2) significant acceleration and aggravation of plasmacytoma formation, and 3) excessive activation of extramedullary hematopoiesis in spleen and liver followed by a subsequent increase of all cellular components in the peripheral blood. These in vivo data suggest that the sIL-6R recruits primarily unresponsive cell populations such as hematopoietic progenitor cells and hepatocytes to IL-6-induced proliferation, but also enhances the known mitogenic effect of IL-6 on plasma cells and thereby contributes to plasmacytoma formation.

Animals↗

PubMed1998

Induction of bone morphogenetic protein-6 in skin wounds. Delayed reepitheliazation and scar formation in BMP-6 overexpressing transgenic mice.

Growth factors of the transforming growth factor-beta superfamily are involved in cutaneous wound healing. In this study we analyze the expression of the bone morphogenetic protein-6 (BMP-6) gene, a transforming growth factor-beta related gene, in skin wounds. In normal mouse skin high levels of BMP-6 mRNA and protein are expressed by postmitotic keratinocytes of stratified epidermis until day 6 after birth. BMP-6 expression is strongly reduced in adult epidermis with diminished mitotic activity. After skin injury we found large induction of BMP-6-specific RNA and protein in keratinocytes at the wound edge and keratinocytes of the newly formed epithelium as well as in fibroblast shaped cells in the wound bed. BMP-6-specific RNA was induced within 24 h after injury, whereas significant upregulation of BMP-6 on the protein level was detected only 2-3 d after injury. Protein was confined to outermost suprabasal epidermal layers, whereas BMP-6-specific RNA was distributed throughout all epidermal layers including basal keratinocytes and the leading edge of the migrating keratinocytes. We also detected high levels of BMP-6-specific RNA and protein in chronic human wounds of different etiology. In contrast to the overall distribution pattern of BMP-6-specific RNA, the protein was not detected in keratinocytes directly bordering the wound. In order to test the influence of BMP-6 abundance on the progress of wound healing, we analyzed the wound response of transgenic mice overexpressing BMP-6 in the epidermis. In these mice, reepitheliazation of skin wounds was significantly delayed, suggesting that strict spatial and temporal regulation of BMP-6 expression is necessary not only for formation but also for reestablishment of a fully differentiated epidermis.

Adult↗

PubMed1997

Cloning and targeted deletion of the mouse fetuin gene.

We proposed that the alpha2-Heremans Schmid glycoprotein/fetuin family of serum proteins inhibits unwanted mineralization. To test this hypothesis in animals, we cloned the mouse fetuin gene and generated mice lacking fetuin. The gene consists of seven exons and six introns. The cystatin-like domains D1 and D2 of mouse fetuin are encoded by three exons each, whereas a single terminal exon encodes the carboxyl-terminal domain D3. The promoter structure is well conserved between rat and mouse fetuin genes within the regions shown to bind transcription factors in the rat system. Expression studies demonstrated that mice homozygous for the gene deletion lacked fetuin protein and that mice heterozygous for the null mutation produced roughly half the amount of fetuin protein produced by wild-type mice. Fetuin-deficient mice were fertile and showed no gross anatomical abnormalities. However, the serum inhibition of apatite formation was compromised in these mice as well as in heterozygotes. In addition, some homozygous fetuin-deficient female ex-breeders developed ectopic microcalcifications in soft tissues. These results corroborate a role for fetuin in serum calcium homeostasis. The fact that generalized ectopic calcification did not occur in fetuin-deficient mice proves that additional inhibitors of phase separation exist in serum.

Animals↗

PubMed1997

Soluble IL-6 receptor leads to a paracrine modulation of the IL-6-induced hepatic acute phase response in double transgenic mice.

There is a growing number of soluble agonistic (IL-6, ciliary neurotropic factor, IL-11, and glia-derived neurotropic factor receptors) and antagonistic (IL-1 and TNF receptors) receptor proteins, modulating the biological functions of their cognate ligands. The physiologic role of these receptor molecules in vivo is unclear. In particular, it is not known how the specificity of function of soluble receptors after release into the blood stream is maintained. We addressed this question by studying the function of the soluble IL-6R (sIL-6R) at the cellular level in the liver. We have generated double transgenic mice coexpressing human sIL-6R and human IL-6 in the liver and have analyzed the expression patterns by in situ hybridization. The expression of the human sIL-6R, driven by the phosphoenolpyruvate carboxykinase promoter, is located mainly in periportal areas, whereas human IL-6 under the control of the metallothionein promoter is uniformly expressed throughout the liver. We show here by in situ hybridization that acute phase protein gene expression induced by human IL-6 and human sIL-6R correlated with the periportal expression of sIL-6R, indicating that sIL-6R acts mainly in an area where it is generated. We conclude that in a concentration-dependent manner, at low concentrations of sIL-6R, there is a predominantly paracrine action at the site of its generation, whereas at higher concentrations of the sIL-6R there are both local and systemic effects.

Acute-Phase Proteins↗

PubMed1996

The chromosomal mapping of four genes encoding winged helix proteins expressed early in mouse development.

Members of the winged helix family of transcription factors are required for the normal embryonic development of the mouse. Using the interspecific backcross panel from The Jackson Laboratory, we have determined the chromosomal locations of four genes that encode winged helix containing proteins. Mf1 was assigned to mouse Chromosome 8, Mf2 to Chromosome 4, Mf3 to Chromosome 9, and Mf4 to Chromosome 13. Since Mf3 is located in a region of Chromosome 9 containing many well-characterized mouse mutations such as short ear (se), ashen (ash), and dilute (d), we have analyzed deletion mutants to determine the location of Mf3 more precisely.

Animals↗

PubMed1996

Overexpression of bone morphogenetic protein-6 (BMP-6) in the epidermis of transgenic mice: inhibition or stimulation of proliferation depending on the pattern of transgene expression and formation of psoriatic lesions.

Bone morphogenetic protein-6 (BMP-6) belongs to the family of TGF-beta-related growth factors. In the developing epidermis, expression of BMP-6 coincides with the onset of stratification. Expression persists perinatally but declines after day 6 postpartum, although it can still be detected in adult skin by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. We constitutively overexpressed BMP-6 in suprabasal layers of interfollicular epidermis in transgenic mice using a keratin 10 promoter. All mice expressing the transgene developed abnormalities in the skin, indicating an active transgene-derived factor. Depending on the pattern of transgene expression, the effects on proliferation and differentiation were completely opposite. Strong and uniform expression of the BMP-6 transgene resulted in severe repression of cell proliferation in embryonic and perinatal epidermis but had marginal effects on differentiation. Weaker and patchy expression of the transgene evoked strong hyperproliferation and parakeratosis in adult epidermis and severe perturbations of the usual pattern of differentiation. These perturbations included changes in the expression of keratins and integrins. Together with an inflammatory infiltrate both in the dermis and in the epidermis, these aspects present all typical histological and biochemical hallmarks of a human skin disease: psoriasis.

Acanthosis Nigricans↗

PubMed1995

Increased frequency of spontaneous skin tumors in transgenic mice which overexpress ornithine decarboxylase.

Ornithine decarboxylase, a critical regulatory enzyme for polyamine biosynthesis, is highly inducible by growth-promoting stimuli in mouse epidermis but the enzyme level is only transiently elevated due to rapid turnover of the protein. Here we report that constitutive overexpression of the enzyme in the skin of transgenic mice causes several phenotypic abnormalities. Effects observed include development of dermal follicular cysts, excessive skin wrinkling, enhanced nail growth, alopecia, and spontaneous tumor development. These results indicate that up-regulation of polyamine biosynthesis can profoundly disturb skin homeostasis and alter susceptibility to neoplastic development.

Animals↗