RESUMEN
Tumor promotion is an essential process in multistage cancer development providing the conditions for clonal expansion and genetic instability of preneoplastic and premalignant cells. It is caused by a continuous disturbance of cellular signal transduction that results in an overstimulation of metabolic pathways along which mediators of cell proliferation and inflammation as well as genotoxic by-products are generated. Among such pathways the oxidative metabolism of arachidonic acid has turned out to be of utmost importance in tumor promotion. The aberrant overexpression of cyclooxygenase-2, an inducible enzyme of prostanoid synthesis and lipid peroxidation, is a characteristic feature of more than two-thirds of all human neoplasias, and the specific inhibition of this enzyme has been found to have a substantial chemopreventive effect in both animal models and man. The prostaglandins produced by COX-2 promote tumor development by stimulating cell proliferation and angiogenesis and by suppressing programmed cell death and immune defense. In mice, a COX-2 transgene fused with the keratin 5 promoter, which is constitutively active in the basal (proliferative) compartment of stratified and simple epithelia, causes a preneoplastic and premalignant phenotype in several organs. Among these organs, skin, mammary gland, urinary bladder, and pancreas have been investigated in more detail. Histologically and biochemically, the COX-2-dependent alterations resemble an autopromoted state that--as shown for skin and urinary bladder--strongly sensitizes the tissue for carcinogenesis. In transgenic animals COX-2 expression is not restricted to keratin 5-positive cells but is seen also in adjacent keratin 5-negative cells. This spreading of the COX-2 signal indicates a paracrine mechanism of autoamplification. While cancer chemoprevention by COX-2 inhibition is a rapidly developing field, much less is known about other pathways of unsaturated fatty acid metabolism, although some of them may play a role in carcinogenesis rivaling that of prostaglandin formation. Here an urgent demand for systematic research exists.
Asunto(s)
Transformación Celular Neoplásica , Ciclooxigenasa 2/metabolismo , Modelos Biológicos , Neoplasias/prevención & control , Transducción de Señal/fisiología , Animales , Humanos , Lesiones Precancerosas/metabolismo , Lesiones Precancerosas/fisiopatologíaRESUMEN
Phylogenetically conserved toll-like receptors (TLR) recognize "pathogen-associated molecular patterns". Upon binding of ligands, TLR initiate innate immune response in immune and most likely epithelial cells. The TLR4 isoform is considered as a lipopolysaccharide (LPS) receptor. As shown here, a rat-tongue-derived epithelial cell line RTE2 expressed TLR4 mRNA and functional protein. LPS-treated RTE2 cells responded with the transient expression of inducible nitric oxide synthase (iNOS), an effector protein of TLR4 involved in the innate immune defense of monocytes. iNOS induction occurred along a nuclear factor-kappaB (NF-kappab)-dependent pathway and correlated with the increased production of NO. Moreover, LPS and lipid A were potent inhibitors of proliferation of RTE2 cells, of mouse keratinocytes, and mouse epidermis in vivo. The inhibition depended on lipid A structure, i.e., it was related to the endotoxin activity of LPS and at least in vitro was in part mediated by NF-kappaB. C57Bl/10 ScCr mice, lacking a functional TLR4, did not respond with growth inhibition, strongly suggesting a TLR4-mediated effect. RTE2 proliferation was also inhibited by transforming growth factor beta (TGFbeta) and tumor necrosis factor alpha (TNFalpha), whereas interferon gamma (IFNgamma) was a weak inhibitor. But the growth-inhibitory effect of LPS on RTE2 cells was not mediated by TNFalpha, TGFbeta, or NO. It is concluded that besides induction of innate immune responses, LPS specifically induces growth arrest in epithelial tongue cells and keratinocytes in vitro and in mouse epidermis in a TLR4-dependent but cytokine- and NO-independent manner.
Asunto(s)
Células Epiteliales/citología , Células Epiteliales/metabolismo , Lipopolisacáridos/farmacología , Glicoproteínas de Membrana/genética , Glicoproteínas de Membrana/metabolismo , Receptores de Superficie Celular/genética , Receptores de Superficie Celular/metabolismo , Animales , División Celular/efectos de los fármacos , Células Cultivadas , Citocinas/metabolismo , Células Epidérmicas , Células Epiteliales/efectos de los fármacos , Femenino , Expresión Génica/efectos de los fármacos , Inhibidores de Crecimiento/metabolismo , Lípido A/metabolismo , Ratones , Ratones Endogámicos C57BL , FN-kappa B/metabolismo , Óxido Nítrico/metabolismo , Óxido Nítrico Sintasa/genética , Óxido Nítrico Sintasa/metabolismo , Óxido Nítrico Sintasa de Tipo II , Ratas , Receptor Toll-Like 4 , Receptores Toll-Like , Lengua/citologíaRESUMEN
Cyclooxygenase (COX)-1 and -2 catalyze the key reaction in prostaglandin biosynthesis. Whereas COX-1 is found in most tissues, COX-2, with a few exceptions, is not expressed in normal tissues but becomes transiently induced in the course of inflammatory reactions. In many neoplastic epithelia, COX-2 is constitutively overexpressed. Here we show that COX isozymes are spatiotemporally expressed during morphogenesis of dorsal skin epithelium of NMRI mice. COX-1 and COX-2 mRNA and protein were detected in embryonic and postnatal epidermal tissue by RT-PCR, northern blot, and immunoblot analysis indicating that both isoforms may contribute to prostaglandin production. Being barely detectable in interfollicular epidermis and resting hair follicles of adult mice, COX-2 protein appeared in embryonic skin first in epidermal precursor cells and later on in the basal cells and the peridermal layer of the stratified epidermis. In the course of pelage hair follicle morphogenesis, COX-2 remained expressed in the basal interfollicular compartment and, in addition, became apparent in elongated hair germs and hair pegs and later on in the outer root sheath cells of the distal and proximal hair follicles as well as in basal sebaceous gland cells. During the subsequent synchronous phases of hair cycling, COX-2 expression declined in catagen, was barely detectable in telogen, and was reinduced in the basal outer root sheath and basal sebaceous gland cells of anagen hair follicles. COX-1 immunosignals were detected predominantly in the interfollicular spinous and granular layers of the developing, neonatal, and adult epidermis but not in follicular epithelial cells of developing or cycling hair follicles. Dendritic cells in the interfollicular epidermis and distal hair follicles were also COX-1-positive. Transgenic overexpression of COX-2 under the control of a keratin 5 promoter in basal cells of the interfollicular and follicular epidermis induced a precocious entry into the first catagen stage of postnatal hair follicle cycling and a subsequent disturbance of hair follicle phasing. Furthermore, transgenic mice developed an alopecia. Inhibition of transgenic COX-2 activity by feeding the specific COX-2 inhibitor valdecoxib suppressed the development of alopecia, indicating that COX-2-mediated prostaglandin synthesis is involved in hair follicle biology.
Asunto(s)
Alopecia/fisiopatología , Folículo Piloso/enzimología , Folículo Piloso/crecimiento & desarrollo , Isoenzimas/genética , Isoenzimas/metabolismo , Prostaglandina-Endoperóxido Sintasas/genética , Prostaglandina-Endoperóxido Sintasas/metabolismo , Factores de Edad , Alopecia/genética , Animales , Animales Recién Nacidos , Animales no Consanguíneos , División Celular/fisiología , Ciclooxigenasa 1 , Ciclooxigenasa 2 , Células Epidérmicas , Epidermis/enzimología , Epidermis/crecimiento & desarrollo , Regulación del Desarrollo de la Expresión Génica , Regulación Enzimológica de la Expresión Génica , Folículo Piloso/citología , Homocigoto , Proteínas de la Membrana , Ratones , Ratones Transgénicos , ARN Mensajero/análisisRESUMEN
The mouse skin model of multistage carcinogenesis has demonstrated that cancer results from a synergism between genotoxic and nongenotoxic factors. The former induce irreversible genetic alterations, whereas the latter promote tumor development by favoring the clonal outgrowth of the genetically altered cells. While therapeutic gene repair is a still unrealized dream, tumor promotion provides an attractive target for cancer prevention. A key event in epithelial tumor development is an aberrant constitutive overexpression of cyclooxygenase-2 (COX-2), being detectable already in premalignant lesions and leading to an overproduction of prostaglandins. In the mouse skin model, prostaglandin F2alpha has been identified as an endogenous tumor promoter. The well-established chemopreventive effect of nonsteroidal anti-inflammatory drugs seems to be mainly due to COX-2 inhibition. Targeted transgenic overexpression of COX-2 in mouse epidermis induces a preneoplastic phenotype and renders the tissue extremely sensitive to genotoxic carcinogens; i.e., for the induction of skin tumor development, tumor promoter treatment can be omitted in those animals. It is concluded that COX-2 acts as an endogenous tumor promoter and that its overexpression represents a first order risk factor for cancer development. Conversely, specific COX-2 inhibitors rank among the most promising agents for cancer chemoprevention.
Asunto(s)
Antiinflamatorios no Esteroideos/uso terapéutico , Inhibidores de la Ciclooxigenasa/uso terapéutico , Modelos Animales de Enfermedad , Isoenzimas/metabolismo , Neoplasias Experimentales/prevención & control , Neoplasias Experimentales/terapia , Prostaglandina-Endoperóxido Sintasas/metabolismo , Animales , Ciclooxigenasa 2 , Inhibidores de la Ciclooxigenasa 2 , Expresión Génica/efectos de los fármacos , Isoenzimas/genética , Ratones , Ratones Transgénicos , Neoplasias Experimentales/enzimología , Fenotipo , Lesiones Precancerosas/patología , Prostaglandina-Endoperóxido Sintasas/genética , Prostaglandinas/biosíntesis , Piel/efectos de los fármacos , Piel/enzimología , Piel/patología , Neoplasias Cutáneas/enzimología , Neoplasias Cutáneas/prevención & control , Neoplasias Cutáneas/terapiaAsunto(s)
Inhibidores de la Ciclooxigenasa/uso terapéutico , Isoenzimas/fisiología , Prostaglandina-Endoperóxido Sintasas/fisiología , Neoplasias Cutáneas/enzimología , Neoplasias Cutáneas/prevención & control , Animales , Ciclooxigenasa 2 , Inhibidores de la Ciclooxigenasa 2 , Dermatitis/enzimología , Regulación Enzimológica de la Expresión Génica , Humanos , Isoenzimas/análisis , Isoenzimas/genética , Queratinocitos/enzimología , Proteínas de la Membrana , Ratones , Ratones Noqueados , Prostaglandina-Endoperóxido Sintasas/análisis , Prostaglandina-Endoperóxido Sintasas/genética , Piel/enzimologíaRESUMEN
The recently identified mouse 8(S)-lipoxygenase almost exclusively directs oxygen insertion into the 8(S) position of arachidonic acid and, with lower efficiency, into the 9(S) position of linoleic acid. The protein of 677 amino acids displays 78% sequence identity to human 15(S)-lipoxygenase-2 which is considered to be its human orthologue. The 8(S)-lipoxygenase gene, Alox15b, consisting of 14 exons and spanning 14.5 kb is located within a gene cluster of related epidermis-type lipoxygenases at the central region of mouse chromosome 11. 8(S)-Lipoxygenase is predominantly expressed in stratifying epithelia of mice, constitutively in the hair follicle, forestomach, and foot-sole and inducible in the back skin with strain-dependent variations. The expression is restricted to terminally differentiating keratinocytes, in particular the stratum granulosum and 8(S)-lipoxygenase activity seems to be involved in terminal differentiation of mouse epidermis. Tumor-specific up-regulation of 8(S)-lipoxygenase expression and activity indicate a critical role of this enzyme in malignant progression during tumor development in mouse skin.
Asunto(s)
Araquidonato Lipooxigenasas/metabolismo , Animales , Araquidonato Lipooxigenasas/química , Araquidonato Lipooxigenasas/clasificación , Araquidonato Lipooxigenasas/genética , Diferenciación Celular/fisiología , Humanos , Ácidos Hidroxieicosatetraenoicos/metabolismo , Queratinocitos/fisiología , Neoplasias/metabolismo , Filogenia , Especificidad por Sustrato , Distribución TisularRESUMEN
In addition to their proinflammatory activities, prostaglandins recently have been shown to be beneficial in the resolution of tissue injury and inflammation. Thus, inhibition of cyclooxygenase-2, the predominant prostaglandin endoperoxide synthase under these conditions, may not only result in attenuating the inflammatory response but also in delaying tissue regeneration and repair. To this end, we investigated cyclooxygenase isozyme expression and the effects of cyclooxygenase inhibitors on wound healing upon full-thickness incisions in mouse skin. Immunohistochemical analysis revealed prominent expression of cyclooxygenase isozymes in keratinocytes of the hyperplastic epithelium, with cyclooxygenase-1 immunosignals predominating in the suprabasal compartment and cyclooxygenase-2 immunosignals spread throughout the whole epidermis. Moreover, dendritic cells, resembling Langerhans cells, as well as endothelial cells and macrophages in the vicinity of or within the granulation tissue were found to express both isozymes. Inhibition of prostaglandin E2 synthesis by oral administration of the cyclooxygenase-1-selective inhibitor SC-560 or the cyclooxygenase-2-selective inhibitor valdecoxib did not retard wound healing in mouse skin macroscopically. Except for a slight transient retardation of epithelialization early after wounding wound-induced neoangiogenesis, collagen deposition, and the restoration of tensile strength were not delayed by these agents. Likewise, the nonselective inhibitor indomethacin had no effect on the tensile strength of incisional skin wounds.
Asunto(s)
Inhibidores de la Ciclooxigenasa/farmacología , Isoenzimas/antagonistas & inhibidores , Isoxazoles/farmacología , Piel/enzimología , Sulfonamidas/farmacología , Cicatrización de Heridas/efectos de los fármacos , Enfermedad Aguda , Animales , Colágeno/metabolismo , Ciclooxigenasa 2 , Inhibidores de la Ciclooxigenasa 2 , Modelos Animales de Enfermedad , Femenino , Isoenzimas/biosíntesis , Isoenzimas/metabolismo , Ratones , Ratones Endogámicos , Neovascularización Fisiológica/efectos de los fármacos , Prostaglandina-Endoperóxido Sintasas/biosíntesis , Prostaglandina-Endoperóxido Sintasas/metabolismo , Pirazoles/farmacología , Piel/lesiones , Resistencia a la Tracción/efectos de los fármacos , Cicatrización de Heridas/fisiologíaRESUMEN
Genetic and pharmacological evidence suggests that overexpression of cyclooxygenase-2 (COX-2) is critical for epithelial carcinogenesis and provides a major target for cancer chemoprevention by nonsteroidal antiinflammatory drugs. Transgenic mouse lines with keratin 5 promoter-driven COX-2 overexpression in basal epidermal cells exhibit a preneoplastic skin phenotype. As shown here, this phenotype depends on the level of COX-2 expression and COX-2-mediated prostaglandin accumulation. The transgenics did not develop skin tumors spontaneously but did so after a single application of an initiating dose of the carcinogen 7,12-dimethylbenz[a]anthracene (DMBA). Long-term treatment with the tumor promoter phorbol 12-myristate 13-acetate, as required for tumorigenesis in wild-type mice, was not necessary for transgenics. The ratios of squamous cell carcinomas to papillomas and of sebaceous gland adenomas to papillomas plus squamous cell carcinomas were increased markedly in transgenic mice treated with DMBA alone compared with DMBA/phorbol 12-myristate 13-acetate-treated transgenic and wild-type mice. Thus, COX-2 overexpression, which leads to high levels of epidermal prostaglandin E(2), prostaglandin F(2alpha), and 15-deoxy(delta12,14)-PGJ(2), is insufficient for tumor induction but transforms epidermis into an "autopromoted" state, i.e., dramatically sensitizes the tissue for genotoxic carcinogens.
Asunto(s)
Isoenzimas/genética , Prostaglandina-Endoperóxido Sintasas/genética , Neoplasias Cutáneas/etiología , Piel/enzimología , 9,10-Dimetil-1,2-benzantraceno/toxicidad , Adenoma/etiología , Animales , Carcinógenos/toxicidad , Carcinoma de Células Escamosas/etiología , Celecoxib , Cocarcinogénesis , Ciclooxigenasa 2 , Inhibidores de la Ciclooxigenasa 2 , Inhibidores de la Ciclooxigenasa/farmacología , Modelos Animales de Enfermedad , Expresión Génica/efectos de los fármacos , Isoenzimas/metabolismo , Ratones , Ratones Transgénicos , Papiloma/etiología , Fenotipo , Lesiones Precancerosas/etiología , Prostaglandina-Endoperóxido Sintasas/metabolismo , Prostaglandinas/biosíntesis , Pirazoles , Piel/efectos de los fármacos , Piel/patología , Neoplasias Cutáneas/enzimología , Neoplasias Cutáneas/genética , Neoplasias Cutáneas/patología , Sulfonamidas/farmacología , Acetato de Tetradecanoilforbol/toxicidadRESUMEN
In contrast to other 12S-lipoxygenase (LOX) isoforms expressed in the skin of mice, epidermis-type (e) 12S-LOX was found to be transcriptionally down-regulated in the course of epidermal tumor development in NMRI mice. This may indicate that this enzyme is related to antitumorigenic rather than protumorigenic effects. To test this hypothesis, two transgenic mouse lines were generated that differentially expressed e12S-LOX under the control of the bovine keratin 6 promoter known to be constitutively up-regulated in mouse skin tumors. As compared with the wild-type, low transgene expression correlated with a decreased skin tumor response paralleled by an up-regulation of leukocyte-type 12S-LOX and an accumulation of the linoleic acid derivative 13S-hydroxyoctadecadienoic acid. In contrast, high transgene expression coincided with an increased tumor response paralleled by a strong keratin 6 promoter-driven up-regulation of the transgenic e12S-LOX and an accumulation of the arachidonic acid derivative 12S-hydroxyeicosatetraenoic acid as the predominant LOX product. These results indicate a complex interaction between different LOX isoforms and an opposite role of arachidonic acid and linoleic acid products in the modulation of skin carcinogenesis.