Comparative expression of novel vascular endothelial growth factor/vascular permeability factor transcripts in skin, papillomas, and carcinomas of v-Ha-ras Tg.AC transgenic mice and FVB/N mice

One of the most frequently detected changes in human solid tumors is the mutation of the ras oncogene, which has been associated with production of angiogenic growth factors such as vascular endothelial growth factor/vascular permeability factor (VEGF/VPF). Using the v-Ha-ras Tg-AC transgenic mice and the background FVB/N strain of inbred mice, the pattern of expression of specific VEGF/VPF transcripts was characterized in major organs and in skin, papillomas, and carcinomas during multi-stage skin carcinogenesis. Three VEGF/VPF transcripts were found to be constitutively expressed in skin as well as the major organs in both mouse strains, which corresponded in size and sequence to previously reported murine VEGF120 with a bp size of 331, VEGF164 with a bp size of 333, and VEGF188 with a bp size of 407. A previously unreported fourth murine transcript was also detected in skin and major tissues from both mouse strains which corresponded to rat VEGF144, with a bp size of 404. In addition, a unique 425 bp VEGF transcript which corresponded to human VEGF205 was present in highly vascularized tissues including heart, lung, liver, kidney, brain, as well in papillomas and carcinomas isolated from v-Ha-ras Tg.AC mice. In contrast, VEGF205 was present only in carcinomas derived from FVB/N mice. An antibody generated from a peptide sequence designed to detect each of the five VEGF/VPF peptides defined by RT-PCR analysis confirmed the existence of these five peptides and confirmed that the murine VEGF205 peptide was selectively expressed in papillomas and carcinomas derived from v-Ha-ras Tg.AC mice. These results demonstrate that there is significant alternative splicing of the murine VEGF/VPF gene during multi-stage carcinogenesis, which results in four commonly expressed VEGF transcripts. In addition, these studies identified a fifth VEGF transcript and peptide at the later stages of tumor promotion and in progression which appears to be linked to the presence of v-Ha-ras.

Inhibitory effects of pentoxifylline on ultraviolet B light-induced cutaneous inflammation

It is now recognized that ultraviolet (UV) radiation is a potent environmental insult capable of interfering with immunity to skin cancers and modifying certain immunologic reactions within both locally irradiated skin and distant, unexposed sites. Exposure to UVB light (290-320 nm) induces a potent cutaneous inflammatory response that involves the infiltration of leukocytes into the dermis as well as the production of proinflammatory cytokines by both resident epidermal keratinocytes and dermal cells. Tumor necrosis factor-alpha (TNF-alpha) is a proinflammatory cytokine that has been shown to be a major mediator of UVB light effects on cutaneous immunity. Recent studies have demonstrated that pentoxifylline (PTX), a xanthine-derived phosphodiesterase inhibitor, has the ability to inhibit synthesis of TNF-alpha. To examine the effects of PTX on UVB-mediated cutaneous inflammation, Skh/hr hairless mice were injected intraperitoneally with either phosphate-buffered saline or 50 microg/g PTX 1 h before exposure to 2240 J/m2 UVB. Reverse transcription-polymerase chain reaction and immunohistochemical techniques were used to demonstrate that 24 h to 1 wk after UVB-light irradiation, PTX inhibited UVB-induced TNF-alpha gene expression, inhibited the increase in epidermal TNF-alpha protein synthesis, blocked the increase in epidermal proliferation observed after exposure to UVB light, and decreased production of myeloperoxidase by neutrophils infiltrating into the dermis. These studies demonstrated that PTX modifies epidermal responses after acute UVB light exposure and suggest that PTX treatment may be used clinically to modulate the deleterious effects of long-term UVB-light irradiation.

Beta2 integrin/ICAM-1 adhesion molecule interactions in cutaneous inflammation and tumor promotion

The beta2 integrin (CD 18/CD 11 a, b, c) family of proteins mediate adherence of leukocytes to vascular endothelium and the associated ligand, intercellular adhesion molecule-1 (ICAM-1; CD 54), interacts with beta2 integrin proteins to allow transendothelial migration of leukocytes into sites of inflammation. The present study examines the function of these proteins in a murine model of acute cutaneous inflammation induced following topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) to the dorsal epidermis of SENCAR mice and in a model of skin multistage carcinogenesis. At 24 h following topical application of TPA to the dorsal epidermis of mice, dermal leukocytes expressed higher levels of beta2 integrin protein compared with the lower levels of beta2 integrin protein expression by peripheral blood leukocytes. ICAM-1 protein was localized to epidermal keratinocytes and vascular endothelium in TPA-treated skin and to proliferating papilloma cells. Intravenous (i.v.) injection of either 50 microg anti-beta2 integrin antibody alone or in combination with anti-ICAM-1 antibody significantly inhibited both TPA-stimulated neutrophil infiltration into the dermis (P < 0.001) and myeloperoxidase (MPO) activity (P < 0.03 anti-beta2 integrin antibody; P < 0.01 anti-beta2 integrin + ICAM-1 adhesion molecule antibodies), but had no effect on TPA-induced epidermal hyperplasia. In addition, injection of either anti-ICAM-1 adhesion molecule antibody alone (P < 0.004) or in combination with anti-beta2 integrin antibody (P < 0.001) significantly inhibited TPA-induced production of 7,8-dihydroxy-2'-deoxyguanosine (8-OHdG) immunoreactive proteins by epidermal keratinocytes. Beta2 integrin/ICAM-1 adhesion molecules work in concert to regulate migration, retention and functional activation of leukocytes within the dermis during TPA-induced skin inflammation and within stromal tissue of papillomas that form during multi-stage carcinogenesis. Agents that inhibit these receptor/ligand interactions may be useful in defining the roles of specific cell populations in cutaneous inflammation and multistage carcinogenesis and may also have potential as anti-promoting and anti-progression agents.

Sensitivity of human hepatocytes in culture to reactive nitrogen intermediates

The cytotoxic effects of 3-morpholinosydnonimine (Sin-1) and S-nitroso-N-acetylpenicillamine-amine (SNAP) on replicatively active human hepatocyte cells in culture was determined as a function of oxidant type. Both Sin-1 which yields nitric oxide and peroxynitrite following the generation of superoxide anion plus nitric oxide, and SNAP which generates nitric oxide, induced dose dependent decreases in the colony forming capabilities of the human hepatocytes. Sin-1 was much more cytotoxic (LD50 = 400 microM) than SNAP (LD50 = 1250 microM). Comparatively, both compounds were much less cytotoxic than H2O2 (LD50 = 96 microM). Sin-1 induced 4-fold higher levels of cellular nitrite than that generated by the chemical in cell free medium. Nitrotyrosine, a marker of peroxynitrite formation in cells, was immunohistochemically detected in hepatocytes treated with both Sin-1 and SNAP. The formation of 3-nitrotyrosine by hepatocytes incubated with SNAP, suggests that hepatocytes generate intracellular superoxide which reacts with the exogenous nitric oxide derived from SNAP to produce intracellular peroxynitrite, resulting in the SNAP cytotoxicity. The enhanced levels of Sin-1 cytotoxicity on the hepatocytes is suggested to be due both to the chemical generation of peroxynitrite and superoxide anion by Sin-1. These data indicate that peroxynitrite is formed in cultured human hepatocytes inhibiting their replication, and that peroxynitirite may play a significant role in the pathogenesis of liver disease.

Gene expression and cellular sources of inducible nitric oxide synthase during tumor promotion

The present studies examined the temporal sequence of inducible nitric oxide synthase (iNOS) gene expression and the cellular sources of iNOS protein and of 3-nitrotyrosine, as a marker of production of nitric oxide-derived reactive nitrogen intermediates during murine multi-stage carcinogenesis. Levels of iNOS mRNA in dorsal skin isolated from acetone-treated female Sencar mice were 2.5-fold higher than iNOS gene expression detected in cutaneous tissue isolated from Sencar mice at 1, 3, 6, 10, 16 and 22 weeks after exposure to a single topical application of 25 nmol 7,12-dimethylbenz[a]anthracene (DMBA) followed by repetitive applications of 2 microgram 17-O-tetradecanoylphorbol-13-acetate (TPA). Papillomas isolated at 16 and 22 weeks of a tumor promotion protocol also had low levels of iNOS mRNA. The diminished levels of iNOS mRNA inversely correlated with the extent of TPA-induced epidermal hyperplasia. In acetone-treated mouse skin, iNOS immunospecific antibody binding was localized to the stratum corneum and suprabasal keratinocytes. In contrast, iNOS protein was present in lower amounts and was localized to the upper-most suprabasal keratinocytes in cutaneous tissue isolated at 22 weeks following a single exposure to either 25 nmol DMBA or acetone and repetitive applications of 2 microgram TPA. At all time points examined over the 22 week time period of papilloma growth, infiltrating neutrophils within the dermis bound significant levels of anti-iNOS antibodies. The production of iNOS by neutrophils within the dermis correlated with the formation of protein nitrotyrosination within the dermal tissue, as detected by 3-nitrotyrosine-specific antibodies. The present studies indicate that NOS and reactive nitrogen intermediates, including peroxynitrite, are produced specifically by dermal neutrophils during the tumor promotion process at time points that correspond to simultaneous production of reactive oxygen intermediates. Conversely, iNOS is simultaneously down-regulated in hyperplastic epidermis and in papillomas.

Inhibition of pro-inflammatory cytokine gene expression and papilloma growth during murine multistage carcinogenesis by pentoxifylline

Topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA) to the dorsal epidermis of Sencar mice induces synthesis of pro-inflammatory cytokines, including interleukin-1 alpha (IL-1 alpha) and tumor necrosis factor-alpha (TNF-alpha). These proteins differentially regulate proliferation of epidermal keratinocytes, as well as stimulate chemotaxis, migration and production of reactive oxygen and nitrogen intermediates by leukocytes. Studies over the past several years have demonstrated that pentoxifylline ([1-(5-oxohexyl)-3,7-dimethyl-xanthine], oxpentifylline), which is a methylxanthine derivative used clinically for treatment of vascular insufficiency, has the unique ability to inhibit synthesis of pro-inflammatory cytokines. The present studies were performed to examine the effects of acute and chronic administration of pentoxifylline on TPA-induced cutaneous inflammation in female Sencar mice treated once with 10 micrograms TPA and also to determine the ability of pentoxifylline to inhibit the tumor promotion process in mice treated with a single application of 25 nmol 7,12-dimethylbenz[a]anthracene (DMBA) followed for 8 weeks by twice weekly topical application of TPA. Intraperitoneal injection of 50 micrograms/g pentoxifylline at 30 min prior to topical application of 10 micrograms TPA to the dorsal epidermis of Sencar mice inhibited TPA-induced IL-1 alpha and TNF-alpha gene expression 24 h after TPA treatment. Administration of pentoxifylline also significantly inhibited all parameters of acute TPA-induced inflammatory response examined 24 h later, including skin thickening (P < 0.005), infiltration of neutrophils into the dermis (P < 0.001), the corresponding dermal myeloperoxidase activity (P < 0.01) and epidermal hyperplasia (P < 0.001). Injection of 50 micrograms/g pentoxifylline over an 8 week time period significantly inhibited DMBA/TPA-induced papilloma growth (P < 0.05). These results indicate that administration of pentoxifylline is an effective means of inhibiting acute TPA-induced cutaneous inflammation and pro-inflammatory cytokine gene expression, as well as is effective as an antipromoter that inhibits papilloma growth.

Temporal sequence of pulmonary cytokine gene expression in response to endotoxin in C3H/HeN endotoxin-sensitive and C3H/HeJ endotoxin-resistant mice

Although previous studies suggested that tumor necrosis factor alpha (TNF-alpha) was a critical cytokine responsible for the inflammation observed after exposure to endotoxin, other mediators may also play an important role in the regulation of systemic inflammatory responses independent of TNF-alpha. The present study compared the temporal sequence of endotoxin-induced TNF-alpha, interleukin-1 alpha (IL-1 alpha), and interleukin-10 (IL-10) gene expression and cellular localization of cytokine proteins in pulmonary tissue of two strains of mice that have a genetically based differential sensitivity to endotoxin. Lung tissue and plasma were harvested from endotoxin-sensitive C3H/HeN and endotoxin-resistant C3H/HeJ mice at 15 min, 30 min, 1 h, 2 h, 4 h, 6 h, 12 h, and 24 h after intraperitoneal (i.p.) injection of 5 mg/kg endotoxin (Escherichia coli-derived lipopolysaccharide, serotype 0111:B4). There were significant elevations in both TNF-alpha gene and IL-1 alpha expression immediately (15 min) after endotoxin injection in C3H/HeN mice. Although levels of TNF-alpha mRNA in the two mouse strains were similar at 1-2 h, the IL-1 alpha gene expression in pulmonary tissue isolated from endotoxin-resistant mice was not comparable to the levels detected in C3H/HeN endotoxin-sensitive mice at the same times. The most dramatic difference in endotoxin-induced cytokine gene expression between the two strains of mice was in IL-10 mRNA levels in pulmonary tissue isolated from endotoxin-sensitive mice, compared to the lack of detectable increase in IL-10 gene expression in C3H/HeJ endotoxin-resistant mice above baseline at any time point examined. Quantitation of neutrophil infiltration into pulmonary tissue using immunochemical detection of GR-1, a myeloid differentiation-specific antibody, demonstrated that there was a significantly decreased inflammatory infiltrate in pulmonary tissue isolated from C3H/HeJ mice following endotoxin administration, which correlated with decreased levels of proinflammatory cytokine immunoreactive protein within pulmonary cells. Pulmonary cytokine synthesis and immunoreactive protein production did not directly correlate with either the magnitude or the temporal sequence of increases in plasma cytokine levels, suggesting that systemic levels of cytokines may not accurately reflect the cytokine response within the local tissue milieu. The present observations demonstrate that the differential synthesis and production of immunosuppressive cytokines as well as proinflammatory cytokines may be important variables in the determination of the extent of infiltration of inflammatory cells into the local pulmonary site in response to endotoxin and may significantly contribute to the determination of sensitivity or resistance to endotoxin in this murine model.

Interleukin-1alpha gene expression during wound healing

Interleukin-1alpha is known to be constitutively produced by epidermal keratinocytes under normal conditions, and injection of this cytokine enhances wound reepithelialization. However, no studies have characterized the temporal sequence of interleukin-1alpha gene expression over the time course of wound healing, and the cellular sources of this cytokine have not been identified. In the present studies, levels of interleukin-1alpha messenger RNA in wound tissue isolated from SKH-1 hairless mice were characterized and the cells that produced interleukin-1alpha immunoreactive protein over a 10-day time course of wound healing were defined. A time-dependent upregulation in interleukin-1alpha gene expression occurred immediately (4 hours) after a full-thickness wound was made, which represented a four-fold increase over levels of cytokine gene expression detected in nonwounded skin. Upregulation of cytokine gene expression correlated with an immediate increase in plasma interleukin-1alpha levels and was followed by an increase in interleukin-1alpha immunoreactive protein localized to keratinocytes within the leading edge of the wound and epidermis, as well as to neutrophils within the dermis. The rapid increase in local and systemic interleukin-1alpha levels correlated with the infiltration of a significant number of neutrophils into the wound site and with the proliferation of both basal keratinocytes and dermal fibroblasts. Given the known ability of interleukin-1alpha to regulate proliferation and migration of epidermal keratinocytes and to indirectly induce leukocyte chemotaxis, the results of the present studies suggest that interleukin-1alpha may be an important cytokine with both local and systemic actions that are linked to the initiation of critical cellular events early in wound healing.

Granulocyte-macrophage colony stimulating factor gene expression and function during tumor promotion

Although recent evidence suggests that granulocyte-macrophage colony stimulating factor (GM-CSF) plays a role in cutaneous inflammation induced by topical exposure of phorbol ester tumor promoters to murine epidermis, there is little information available on the temporal sequence of gene expression of this cytokine over the time course of tumor promotion or about its function in this process. The goal of the present studies was to examine the potential role of GM-CSF in tumor promotion in SENCAR mice. Competitive reverse transcriptase polymerase chain reaction (RT-PCR) studies demonstrated that a single topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA; 2 micrograms, 10 micrograms) to the dorsal epidermis of SENCAR mouse skin stimulated a dose and time dependent GM-CSF gene expression that was upregulated at 1 h after TPA exposure, peaked at 3 h and declined at 12 h. Although treatment with 7',12'-dimethylbenz[a]anthracene (DMBA) did not stimulate GM-CSF gene expression, GM-CSF gene expression was elevated in epidermal tissue isolated from SENCAR mice treated with a single application of 10 nmol DMBA followed by multiple applications of 2 micrograms TPA over a 1-22 week time course. Immunochemical and autoradiographic studies demonstrated that GM-CSF protein was produced by suprabasal keratinocytes, interfollicular cells, nonproliferating papilloma cells and leukocytes within the dermis. Intraperitoneal injection of recombinant (r) GM-CSF into SENCAR mice at 2 h prior to topical application of 10 micrograms TPA induced a significant increase in epidermal keratinocyte proliferation, leukocyte infiltration into the dermis, hydroperoxide production by circulating neutrophils and chemotactic activity present within the plasma at 24 h compared to treatment with only 10 micrograms TPA. Intravenous injection of anti-GM-CSF antibodies significantly inhibited both local and systemic inflammatory events induced by topical application of TPA. The present studies suggest that GM-CSF has a broad spectrum of activity with at least two target cell populations, epidermal keratinocytes within the proliferative compartment and leukocytes. This cytokine is actively transcribed during the tumor promotion process, acts as a signal peptide that stimulates epidermal proliferation, primes circulating neutrophils to produce hydroperoxide and regulates leukocyte migration.

Interleukin-1 alpha gene expression and localization of interleukin-1 alpha protein during tumor promotion

Treatment of the dorsal epidermis of SENCAR mice with 12-O-tetradecanoylphorbol-13-acetate (TPA) induced a time- and dose-dependent stimulation of interleukin-1 alpha (IL-1 alpha) gene expression. Levels of IL-1 alpha mRNA were elevated as early as 15 min and peaked at 3-4 h after a single application of TPA (2 micrograms or 10 micrograms). IL-1 alpha gene expression increased in epidermal tissue isolated from SENCAR mice at 1, 3, 6, 10, 16, and 22 wk after a single treatment with 10 nmol 7,12-dimethylbenz[a]anthracene (DMBA) and subsequent twice-weekly application of 2 micrograms TPA. IL-1 alpha-immunoreactive protein was specifically localized within suprabasal keratinocytes in cutaneous tissue isolated from mice treated with DMBA-TPA for 1-22 wk and in nonproliferating cells located within papilloma tissue isolated from SENCAR mice at 22 wk after initiation and promotion. Basal cells within hyperplastic epidermis did not produce IL-1 alpha-immunoreactive protein. DMBA treatment alone did not induce IL-1 alpha gene expression. Injection of IL-1 alpha-specific antibodies (50 micrograms) into SENCAR mice via the tail vein 2 h before treatment with TPA (2 micrograms or 10 micrograms) significantly (P < 0.05) inhibited the skin thickening usually observed 24 h after treatment with TPA. Autoradiography studies showed that injection of anti-IL-1 alpha antibodies inhibited incorporation of [methyl-3H]thymidine by keratinocytes within the epidermis and by cells within hair follicles. It also inhibited neutrophil infiltration into the dermis, which usually results from topical application of TPA. These data suggest that IL-1 alpha is a pivotal cytokine produced by specific subpopulations of epidermal keratinocytes and that IL-1 alpha primarily regulates the epidermal proliferative response of a distinctly separate population of keratinocytes after topical exposure of murine epidermis to TPA and secondarily modulates neutrophil migration into the dermis. Consequently, manipulation of IL-1 alpha may be a way to attenuate or abrogate the cutaneous response to TPA by altering keratinocyte proliferation, the resultant hyperplasia, and a portion of the inflammatory response characterized by dermal infiltration of neutrophils.

Production of hydrogen peroxide by murine epidermal keratinocytes following treatment with the tumor promoter 12-O-tetradecanoylphorbol-13-acetate

The ability of murine epidermal cells to produce intracellular hydrogen peroxide was analyzed by flow cytometry and the measurement of 2',7'- dichlorofluorescin (DCFH) oxidation. Epidermal cells isolated from acetone-treated CD-1 mice for 24 h were relatively homogeneous in cell size and density and oxidized low levels of DCFH. However, following 12-O-tetradecanoylphorbol-13-acetate (TPA) treatment of mice (10 micrograms; 24 h), two cytokeratin-positive populations of cells were identified that were heterogeneous with respect to size and density. These two TPA-derived cell populations oxidized levels of DCFH that were time and dose dependent and were between 2- and 10-fold higher than levels of DCFH oxidized by cells isolated from acetone-treated mice. The ability of catalase, the enzyme that detoxifies hydrogen peroxide, to suppress DCFH oxidation to control levels suggested that intracellular hydrogen peroxide was responsible for the enhanced rate of DCFH oxidation in epidermal cells isolated from TPA-treated mice. The ability of mouse epidermal keratinocytes to oxidize DCFH in response to TPA treatment was confirmed using a cloned keratinocyte cell line. These results suggest that specific subpopulations of keratinocytes produce elevated levels of intracellular peroxides following treatment with TPA either in vivo or in culture.