Modulation of interleukin-1 alpha mRNA expression in mouse epidermis by tumor promoters and antagonists

The Role of Interleukin-1 in Inflammatory and Malignant Human Skin Diseases and the Rationale for Targeting Interleukin-1 Alpha

Inflammation plays a major role in the induction and progression of several skin diseases. Overexpression of the major epidermal proinflammatory cytokines interleukin (IL) 1 alpha (IL-1α) and 1 beta (IL-1β) is positively correlated with symptom exacerbation and disease progression in psoriasis, atopic dermatitis, neutrophilic dermatoses, skin phototoxicity, and skin cancer. IL-1β and the interleukin-1 receptor I (IL-1RI) have been used as a therapeutic target for some autoinflammatory skin diseases; yet, their system-wide effects limit their clinical usage. Based on the local effects of extracellular IL-1α and its precursor, pro-IL-1α, we hypothesize that this isoform is a promising drug target for the treatment and prevention of many skin diseases. This review provides an overview on IL-1α and IL-β functions, and their contribution to inflammatory and malignant skin diseases. We also discuss the current treatment regimens, and ongoing clinical trials, demonstrating the potential of targeting IL-1α, and not IL-1β, as a more effective strategy to prevent or treat the onset and progression of various skin diseases.

Molecular mechanisms of mouse skin tumor promotion

Multiple molecular mechanisms are involved in the promotion of skin carcinogenesis. Induction of sustained proliferation and epidermal hyperplasia by direct activation of mitotic signaling pathways or indirectly in response to chronic wounding and/or inflammation, or due to a block in terminal differentiation or resistance to apoptosis is necessary to allow clonal expansion of initiated cells with DNA mutations to form skin tumors. The mitotic pathways include activation of epidermal growth factor receptor and Ras/Raf/mitogen-activated protein kinase signaling. Chronic inflammation results in inflammatory cell secretion of growth factors and cytokines such as tumor necrosis factor-α and interleukins, as well as production of reactive oxygen species, all of which can stimulate proliferation. Persistent activation of these pathways leads to tumor promotion.

IL-1R-MyD88 signaling in keratinocyte transformation and carcinogenesis

Constitutively active RAS plays a central role in the development of human cancer and is sufficient to induce tumors in two-stage skin carcinogenesis. RAS-mediated tumor formation is commonly associated with up-regulation of cytokines and chemokines that mediate an inflammatory response considered relevant to oncogenesis. In this study, we report that mice lacking IL-1R or MyD88 are less sensitive to topical skin carcinogenesis than their respective wild-type (WT) controls. MyD88(-/-) or IL-1R(-/-) keratinocytes expressing oncogenic RAS are hyperproliferative and fail to up-regulate proinflammatory genes or down-regulate differentiation markers characteristic of RAS-expressing WT keratinocytes. Although RAS-expressing MyD88(-/-) keratinocytes form only a few small tumors in orthotopic grafts, IL-1R-deficient RAS-expressing keratinocytes retain the ability to form tumors in orthotopic grafts. Using both genetic and pharmacological approaches, we find that the differentiation and proinflammatory effects of oncogenic RAS in keratinocytes require the establishment of an autocrine loop through IL-1α, IL-1R, and MyD88 leading to phosphorylation of IκBα and NF-κB activation. Blocking IL-1α-mediated NF-κB activation in RAS-expressing WT keratinocytes reverses the differentiation defect and inhibits proinflammatory gene expression. Collectively, these results demonstrate that MyD88 exerts a cell-intrinsic function in RAS-mediated transformation of keratinocytes.

Silybin from Silybum Marianum Seeds Inhibits Confluent-Induced Keratinocytes Differentiation as Effectively as Retinoic Acid without Inducing Inflammatory Cytokine

Retinoic acid (RA) has been effective for improving wrinkles. However, it has also been reported that RA induces skin irritation. In this study, we explored new botanical compounds that show RA-like activity, but do not induce inflammation in vitro. Keratinocytes were maintained in a confluent condition and induced differentiation. Under this condition keratinocytes were treated with many botanical extracts and their morphological change were observed and compared with RA-treated. We found that silybin, which is a major flavonolignan from Silybum Marianum seeds, induced RA-like morphological change and prevented differentiation. We showed that silybin, like RA, reduced the expression of keratinocyte terminal differentiation markers and stimulated the expression of basement membrane component proteins. In contrast, silybin, unlike RA, did not stimulate the secretion of IL-1α, which is a skin irritation mediator. These results suggest that silybin has RA-like activity on keratinocytes and has the potential to improve winkle without inducing skin irritation.

Inflammation and cancer: an ancient link with novel potentials

Infection and chronic inflammation contribute to about 1 in 4 of all cancer cases. Mediators of the inflammatory response, e.g., cytokines, free radicals, prostaglandins and growth factors, can induce genetic and epigenetic changes including point mutations in tumor suppressor genes, DNA methylation and post-translational modifications, causing alterations in critical pathways responsible for maintaining the normal cellular homeostasis and leading to the development and progression of cancer. Recent discovery of an interaction between microRNAs and innate immunity during inflammation has further strengthened the association between inflammation and cancer.

Type I IL-1 receptor mediates IL-1 and intracellular IL-1 receptor antagonist effects in skin inflammation

The IL-1 system plays a key role in skin physiology and pathology. In this study, we used mutant mice lacking the type I IL-1 receptor (IL-1RI), lacking IL-1 receptor antagonist (IL-1Ra), or overexpressing the human intracellular (ic) IL-1Ra1 isoform, as well as combinations thereof, to dissect the role of the IL-1 system in phorbol 13-myristate 12-acetate (PMA)-induced skin inflammation. In wild-type (WT) mice, PMA application induced epidermal thickening and dermal inflammation. Skin IL-1alpha production and circulating levels of the acute-phase protein serum amyloid A (SAA) were elevated. In mice lacking IL-1RI or overexpressing icIL-1Ra1, PMA induced similar epidermal thickening as in WT mice, but dermal inflammation was partially prevented. Skin IL-1alpha mRNA expression was similar in PMA-treated IL-1RI-/- and WT mice, whereas the increase in serum SAA was suppressed in IL-1RI-/- mice. Interestingly, PMA-induced IL-1alpha mRNA expression was further enhanced by icIL-1Ra1 overexpression in an IL-1RI-dependent manner. Finally, IL-1Ra-/- mice spontaneously displayed skin lesions characterized by high IL-1beta, but not IL-1alpha, expression. In conclusion, PMA-induced epidermal thickening and skin IL-1alpha expression were independent of IL-1 signaling, in contrast to dermal inflammation and systemic inflammatory response.

The involvement of IL-1 in tumorigenesis, tumor invasiveness, metastasis and tumor-host interactions

Interleukin-1 (IL-1) includes a family of closely related genes; the two major agonistic proteins, IL-1alpha and IL-1beta, are pleiotropic and affect mainly inflammation, immunity and hemopoiesis. The IL-1Ra antagonist is a physiological inhibitor of pre-formed IL-1. Recombinant IL-1alpha and IL-1beta bind to the same receptors and induce the same biological functions. As such, the IL-1 molecules have been considered identical in normal homeostasis and in disease. However, the IL-1 molecules differ in their compartmentalization within the producing cell or the microenvironment. Thus, IL-1beta is solely active in its secreted form, whereas IL-1alpha is mainly active in cell-associated forms (intracellular precursor and membrane-bound IL-1alpha) and only rarely as a secreted cytokine, as it is secreted only in a limited manner. IL-1 is abundant at tumor sites, where it may affect the process of carcinogenesis, tumor growth and invasiveness and also the patterns of tumor-host interactions. Here, we review the effects of microenvironment- and tumor cell-derived IL-1 on malignant processes in experimental tumor models and in cancer patients. We propose that membrane-associated IL-1alpha expressed on malignant cells stimulates anti-tumor immunity, while secretable IL-1beta, derived from the microenvironment or the malignant cells, activates inflammation that promotes invasiveness and also induces tumor-mediated suppression. Inhibition of the function of IL-1 by the IL-1Ra, reduces tumor invasiveness and alleviates tumor-mediated suppression, pointing to its feasibility in cancer therapy. Differential manipulation of IL-1alpha and IL-1beta in malignant cells or in the tumor's microenvironment can open new avenues for using IL-1 in cancer therapy.

Mitogen-regulated protein/proliferin mRNA induction following single applications of tumor promoters to murine skin

Mitogen-regulated protein/proliferin (mrp/plf) gene family transcripts rise in abundance as a response to diverse chemical and physical agents that promote morphological transformation in the murine C3H/10T1/2 cultured cell model of multi-step carcinogenesis. To determine if proliferin genes respond to tumor promoters in vivo, RNA was extracted from the whole skin of SENCAR mice after single applications of 2 or 20 microg 12-O-tetradecanoylphorbol-13-acetate (TPA); 3.2 or 32 nmole), 20 or 40 mg benzoyl peroxide (BPO; 83, 165 micromole), or acetone vehicle alone (2.72 mmole). RNA samples were prepared from treated skin areas, 2-48 h after painting. Mrp/plf-mRNA was not detected in Northern blot hybridizations, but large increases in mRNAs for ornithine decarboxylase gene and mRNA (odc), v-jun oncogene-related transcription factor gene and mRNA (junB), egr1 (early growth response protein gene and mRNA) were measured relative to beta 2 microglobulin gene and mRNA (b2m) mRNA in response to TPA. BPO induced small relative changes in these mRNAs. Reverse transcriptase (RT)-polymerase chain reactions (PCR) detected fully-processed MRP/plf-mRNA 16-48 h after TPA treatments in five of six animals, and in three of six BPO-treated animals. The MRP/plf-mRNA species expressed in the skin were predominantly plf1 and mrp3 as determined by gene-specific restriction enzyme sites within the RT-PCR products. Expression was either undetectable or found at low levels in acetone-painted controls and was not detected during the anagen phase of the normal hair growth cycle in unpainted animals. These results demonstrate that mrp/plf-mRNA is differentially expressed in murine skin in response to mechanistically distinct tumor promoters and has potential utility as a short-term biomarker for tumor promoting effects in chemical carcinogenesis.

Cytokines in cancer immunity and immunotherapy

The concept that the immune system recognizes and controls cancer was first postulated over a century ago, and cancer immunity has continued to be vigorously debated and experimentally tested. Mounting evidence in humans and mice supports the involvement of cytokines in tumor initiation, growth, and metastasis. The idea that the immune system detects stressed, transformed, and frankly malignant cells underpins much of the excitement currently surrounding new cytokine therapies in cancer treatment. In this review, we define the contrasting roles that cytokines play in promoting tumor immunity, inflammation, and carcinogenesis. We also discuss the more promising aspects of clinical cytokine use in cancer patients.

Expression of activated MEK1 in differentiating epidermal cells is sufficient to generate hyperproliferative and inflammatory skin lesions

Epidermal activation of Erk MAPK is observed in human psoriatic lesions and in a mouse model of psoriasis in which beta1 integrins are expressed in the suprabasal epidermal layers. Constitutive activation of the upstream kinase MEK1 causes hyperproliferation and perturbed differentiation of human keratinocytes in culture. It is not known, however, whether Erk activation in differentiating keratinocytes is sufficient to trigger hyperproliferation of basal keratinocytes and a skin inflammatory infiltrate. To investigate this, we expressed constitutively active MEK1 in the suprabasal epidermal layers of transgenic mice. Proliferation in the epidermal basal layer was stimulated and epidermal terminal differentiation was perturbed. Some older mice also developed papillomas. There was a large increase in T lymphocytes, dendritic cells, and neutrophils in the skin. The effects of suprabasal MEK1 on basal keratinocytes and leukocytes, cells that were transgene negative, suggested that MEK1 activity might stimulate cytokine release. Transgenic keratinocytes expressed elevated IL-1alpha and crossing the mice with mice overexpressing the IL-1 receptor in the epidermal basal layer led to exacerbated hyperproliferation and inflammation. These data suggest that activation of MEK1 downstream of beta1 integrins plays an important role in epidermal hyperproliferation and skin inflammation.

IL-1 alpha, innate immunity, and skin carcinogenesis: the effect of constitutive expression of IL-1 alpha in epidermis on chemical carcinogenesis

Tumor promoters such as the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) are proinflammatory agents, and their mechanism of action in epithelial carcinogenesis has been linked to the release of IL-1 alpha and the induction of chronic inflammation in skin. To test the role of IL-1 alpha and inflammation in models of cutaneous carcinogenesis, we used our previously described FVB/N transgenic mice overexpressing 17-kDa IL-1 alpha in the epidermis under the keratin 14 (K14) promoter. Strikingly, the K14/IL-1 alpha mice were completely resistant to papilloma and carcinoma formation induced by a two-stage DMBA/TPA protocol, while littermate controls developed both tumor types. K14/IL-1 alpha mice crossed with the highly sensitive TG.AC mice, constitutively expressing mutant Ha-Ras, also failed to develop papillomas or carcinomas. When the K14/IL-1 alpha transgene was bred onto a recombinase-activating gene-2-deficient background, the resistance persisted, indicating that innate, but not acquired, mechanisms may be involved in the resistance to the initiation/promotion model. As an alternative approach, a complete carcinogenesis protocol using repetitive application of DMBA alone was applied. Surprisingly, although the IL-1 alpha mice still did not develop papillomas, they did develop carcinomas de novo at an accelerated rate compared with controls. We conclude that constitutive IL-1 alpha expression rendered FVB mice completely resistant to carcinomas that required evolution from prior papillomas, but facilitated carcinomas that did not evolve from papillomas, as in the complete carcinogenesis protocol. Thus, the role of IL-1 alpha and, by extension that of other proinflammatory factors, in epithelial carcinogenesis are more complex than previously appreciated. These mice may provide a mechanism to investigate the validity of these models of human skin tumorigenesis.

Flavonoid antioxidant silymarin and skin cancer

Oxidative stress is one of the key players in skin carcinogenesis, and therefore identifying nontoxic strong antioxidants to prevent skin cancer is an important area of research. In both animal and cell culture studies, we have shown that silymarin, a naturally occurring polyphenolic flavonoid antioxidant, exhibits preventive and anticancer effects against skin cancer. For example, silymarin strongly prevents both photocarcinogenesis and skin tumor promotion in mice, in part, by scavenging free radicals and reactive oxygen species and strengthening the antioxidant system. We also found that this effect of silymarin is by inhibiting endogenous tumor promoter tumor necrosis factor alpha in mouse skin, a central mediator in skin tumor promotion. In mechanistic studies, silymarin inhibits mitogenic and cell survival signaling and induces apoptosis. Furthermore, silymarin effectively modulates cell-cycle regulators and check points toward inhibition of proliferation, and growth arrest in G0-G1 and G2-M phases of the cell cycle. Thus, due to its mechanism-based chemopreventive and anticancer effects in experimental models, silymarin is an important candidate for the prevention and/or therapy of skin cancer, as well as other cancers of epithelial origin in humans.

Interleukin-1--a major pleiotropic cytokine in tumor-host interactions

Interleukin-1 (IL-1) represents a family of two agonistic proteins, IL-1alpha and IL-1beta, that are pleiotropic and affect hemopoiesis, inflammation, and immunity. In the context of the producing cell, IL-1beta is solely active in its secreted form, whereas IL-1alpha is active as an intracellular precursor, as a membrane-associated cytokine and to a lesser extent as a secreted molecule. IL-1 is abundant at tumor sites, where it may not only affect the growth and invasiveness of malignant cells, but where it may also induce antitumor immunity. Here we review the effects of microenvironmental and tumor cell-associated IL-1 on malignant processes, in experimental tumor models and in cancer patients.

Role of intracellular interleukin-1 receptor antagonist in skin carcinogenesis

Interleukin 1 (IL-1) is a major mediator of inflammation and exerts pleiotropic effects on many systems. To elucidate the role of its endogenous inhibitor, intracellular IL-1 receptor antagonist (icIL-1Ra), in mouse skin, we produced an icIL-1Ra-overexpressing skin carcinoma cell line (icIL-1Ra-JWF2). Altered expression of icIL-1Ra did not change IL-1alpha mRNA levels in these transfected cells. In icIL-1Ra-JWF2 cells, however, cyclooxygenase-2 mRNA levels were dramatically reduced and shown to be transcriptionally regulated by icIL-1Ra. To determine the effect of icIL-1Ra on cell proliferation, cell counts were done 24 h after plating equal numbers of cells. Cells from three icIL-1Ra-JWF2 clones showed significantly reduced growth rates compared with parental JWF2 cells. We subcutaneously injected five independent clones of icIL-1Ra-JWF2 cells into nude mice and measured the tumor doubling time by weekly measurements of tumor volume. IcIL-1Ra appeared to significantly slow the growth of tumors in vivo. Collectively these observations suggest that IL-1Ra has antiproliferative effects in murine skin carcinoma cells.

Anti-tumor promoting potential of naturally occurring diarylheptanoids structurally related to curcumin

In recent years, there have been considerable efforts to search for naturally occurring substances for intervention of carcinogenesis. Many components from medicinal or dietary plants have been identified to possess potential chemopreventive properties. For instance, curcumin, a yellow colouring agent from turmeric (Curcuma longa Linn., Zingiberaceae) has been shown to inhibit tumor formation in diverse animal models. Alpinia oxyphylla Miquel that also belongs to ginger family has been used in oriental herbal medicine. In the present work, we have evaluated the anti-tumor promoting potential of yakuchinone A (1-[4'-hydroxy-3'-methoxyphenyl]-7-phenyl-3-heptanone) and yakuchinone B (1-[4'-hydroxy-3'-methoxyphenyl]-7-phenylhept-1-en-3-one), major pungent ingredients of A. oxyphylla. Thus, topical application of yakuchinone A or B significantly suppressed TPA-induced epidermal ornithine decarboxylase activity. They also reduced TPA-stimulated production of tumor necrosis factor-alpha in cultured human promyelocytic leukemia (HL-60) cells. Both compounds blunted the TPA-induced superoxide generation in differentiated HL-60 cells in a concentration-related manner and also inhibited lipid peroxidation in rat brain homogenates. Furthermore, yakuchinone A and yakuchinone B nullified the activation of the activator protein-1 (AP-1) in immortalized mouse fibroblast cells in culture. These findings indicate that pungent diarylheptanoids from A. oxyphylla have anti-tumor promotional properties that can contribute to their chemopreventive potential.

Differential regulation of epidermal cell tumor-antigen presentation by IL-1alpha and IL-1beta

IL-1 exists in two forms, termed IL-1alpha and IL-1beta, which exert similar effects in a number of biologic models. Recently, there have been reports of some differences in the activities of these two species in some systems. To address this issue with regard to Langerhans cells, Langerhans cell-enriched preparations of epidermal cells were treated with either IL-1alpha or IL-1beta before pulsing with S1509a tumor-associated antigens and subsequent use for immunization of naive mice to S1509a. While epidermal cells treated with 100 U IL-1beta per ml were able to induce protective tumor immunity (as indicated by the rejection of a subsequent tumor challenge with viable S1509a tumor cells), epidermal cells treated with 100 U IL-1alpha per ml failed to confer protective immunity. At 1000 U per ml, IL-1beta also inhibited the ability of epidermal cells to induce tumor immunity. To investigate the effects of the two IL-1 forms on elicitation of tumor immunity, naive mice were immunized against the S1509a tumor by s.c. injection of dead S1509a cells. Epidermal cells enriched for Langerhans cells were treated with either 100 U IL-1alpha or IL-1beta per ml before tumor-associated antigens-pulsing. Epidermal cells were then washed and injected into a hind footpad of tumor immune mice and 24 h footpad swelling was assessed as a measure of delayed-type hypersensitivity. Exposure to IL-1alpha led to suppressed elicitation of delayed-type hypersensitivity, whereas IL-1beta treated epidermal cells elicited a normal (100 U per ml) or enhanced (1000 U per ml) level of delayed-type hypersensitivity. Previous experiments indicated that the suppressive effects of IL-1alpha on induction of immunity may be mediated by TNF alpha. Therefore, the ability of IL-1alpha or IL-1beta to induce epidermal cell production of TNF alpha was assessed. IL-1alpha induced epidermal cells to secrete significantly higher amounts of TNF alpha protein compared with stimulation with IL-1beta. IL-1alpha and IL-1beta appear to differentially regulate epidermal cell antigen presenting capability.

Keratinocyte expression of the type 2 interleukin 1 receptor mediates local and specific inhibition of interleukin 1-mediated inflammation

Epidermal keratinocytes can express two types of interleukin 1 (IL-1) receptors: IL-1R1, which is active in signal transduction, and the less well characterized IL-1R2, which is incapable of transducing a signal and can be shed from cells. The binding of IL-1 in solution by IL-1R2 has been demonstrated, and it has been proposed to inhibit IL-1-mediated responses through this mechanism. We and others have reported that keratinocytes can be induced to express IL-1R2 both in vitro and in vivo, often under conditions that also favor IL-1 gene expression. We hypothesized that production of IL-1R2 by keratinocytes would be an efficient means to achieve local inhibition of IL-1-mediated responses without systemic consequences. To test this hypothesis, we have generated transgenic mice that constitutively express IL-1R2 on basal keratinocytes. Keratinocytes cultured from these animals shed the soluble form of the receptor into culture supernatants, and IL-1-inducible production of granulocyte/macrophage colony-stimulating factor was markedly inhibited. In vivo, acute cutaneous vascular leakage, as well as chronic inflammation induced by a well characterized IL-1-dependent stimulus, was significantly inhibited in IL-1R2 transgenic animals. In contrast, contact hypersensitivity was unaffected, suggesting that overexpression of IL-1R2 did not inhibit all types of inflammation globally. Finally, systemic injection of IL-1 induced equivalent levels of plasma IL-6 in IL-1R2 transgenic and nontransgenic mice, suggesting that the activity of the transgenic IL-1R2 remained predominantly local and did not influence systemic IL-1 responses. We conclude that tissue-specific production of IL-1R2 can mediate IL-1 antagonism in tissue microenvironments without systemic consequences. Our transgenic mice may be a useful tool for determining the degree to which different types of cutaneous inflammation depend on the IL-1 system.

Inhibition of 12-O-tetradecanoylphorbol-13-acetate and other skin tumor-promoter-caused induction of epidermal interleukin-1 alpha mRNA and protein expression in SENCAR mice by green tea polyphenols

Recent studies have shown that topical application of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA) to murine skin results in increased expression of the highly inflammatory cytokine interleukin (IL)-1 alpha in the epidermis. This has led to the suggestion that IL-1 alpha directly or indirectly mediates the inflammatory and hyperplastic responses elicited by TPA and possibly by other skin tumor promoters. In the current study, we investigated the effect of skin application of a polyphenolic fraction isolated from green tea (GTP) to SENCAR mice on skin tumor-promoter-caused induction of cutaneous edema and hyperplasia, and IL-1 alpha mRNA expression. Pretreatment of the skin with GTP 30 min before that of anthralin, benzoyl peroxide, mezerein, and TPA resulted in a significant (p < 0.05) inhibition of cutaneous edema and epidermal hyperplasia caused by each of these tumor promoters. Northern blot analysis indicated that topical application of TPA, anthralin, mezerein, or benzoyl peroxide to SENCAR mice resulted in an increased expression of epidermal IL-1 alpha mRNA. Pretreatment of the skin with GTP or individual epicatechin derivatives (ECDs) present therein, 30 min before that of TPA, resulted in a significant inhibition of enhanced expression of epidermal IL-1 alpha mRNA caused by skin application of TPA. These inhibitory effects were found to be dependent on the dose of GTP. Among four epicatechin derivatives present in GTP, (-)-epicatechin-3-gallate and (-)-epigallocatechin-3-gallate were more effective than (-)-epigallocatechin and (-)-epicatechin in affording this inhibition. Preapplication of GTP was also found to afford inhibition against anthralin-, benzoyl peroxide-, and mezerein-caused increased expression of epidermal IL-1 alpha mRNA and protein. Our study suggests that the inhibition of tumor-promoter-induced IL-1 alpha mRNA and protein expression in mouse epidermis by green tea in combination with other inhibitory effects may be responsible for the anti-tumor-promoting and anti-inflammatory effects of GTP.

The interleukin-1 axis and cutaneous inflammation

Since the discovery that epidermal cell-derived thymocyte-activating factor was identical to interleukin (IL)-1 alpha and -beta in 1986, these molecules have been implicated in the pathogenesis of skin diseases. In 1995, it has become clear that a group of gene products function to regulate the activity of IL-1. IL-1 alpha and mature 17-kD IL-1 beta (cleaved from precursor by IL-1 beta-converting enzyme) bind to the type 1 IL-1 receptor to transduce a signal. This process can be antagonized at the level of the receptor by two distinct forms of the IL-1 receptor antagonist, which bind to the type I receptor but do not transduce a signal. The process can also be antagonized at the level of the ligand by either cell-bound or soluble type 2 IL-1 receptor. This type 2 IL-1 receptor binds ligand but does not transduce a signal. Keratinocytes can make each of these variables in vitro, and the balance between agonists and antagonists dictates the biologic outcome of a putative IL-1-mediated event. Transgenic mice that overexpress each of these factors individually in epidermis will be useful for enhancing our understanding of the cutaneous biology of IL-1.

Augmented expression of cytokines in mouse epidermal tumor cells and its possible involvement in the induction of hematopoietic alterations

Mice with skin tumors induced either by 7,12-dimethylbenz[a]anthracene complete carcinogenesis or subcutaneous injection of a carcinogenic keratinocyte cell line showed moderate to severe splenomegaly as a result of an increase in splenic granulocyte-macrophage and erythroid (erythroid burst-forming unit) progenitors. To test whether the observed alterations involve the release of soluble factors by the epidermal component of skin tumors, we used an in vitro approach. A series of mouse keratinocyte cell lines resembling progressive stages of skin carcinogenesis and carrying either normal or activated Ha-ras genes were assayed for their ability to produce the factors required for colony growth of hematopoietic-committed progenitors. Only the conditioned media of keratinocytes harboring activated Ha-ras genes were able to support the growth of granulocyte-macrophage colony-forming units. In addition, preincubation of normal bone-marrow cells with conditioned media from the transformed epidermal cell lines stimulated in vitro amplification of the hematopoietic granulocyte-macrophage progenitor compartment. To identify the possible factors responsible for the activities detected in the keratinocyte-conditioned media, we performed northern blot analysis using the cytokine probes granulocyte colony-stimulating factor, macrophage colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, stem cell factor, interleukin-1 alpha, interleukin-3, and tumor necrosis factor-alpha. The cell lines expressed different cytokine mRNA combinations that positively correlated with the colony-stimulating activity detected in the corresponding conditioned medium. These results suggest that transformed epidermal tumor cells in vivo may alter normal hematopoiesis as a consequence of the production of cytokines that act in autocrine or paracrine loops probably related to tumor growth.

Inhibition of anthralin-caused skin tumor promotion and interleukin-1 alpha production by potent immunosuppressant FK506

The effect of FK506, a potent immunosuppressive agent, on 7,12-dimethylbenz[alpha]anthracene-initiated and anthralin-promoted skin tumor formation was examined in CD-1 mice. A topical application of 0.1 mumol FK506 to mouse skin 15 min prior to each anthralin treatment markedly inhibited skin tumor formation. Anthralin stimulated IL-1 alpha production in primary cultured mouse epidermal cells, and the peak IL-1 alpha level was observed at 6 h after the stimulation. Anthralin also stimulated IL-1 alpha release into culture medium. Both production and release of Il-1 alpha were markedly inhibited by FK506 (0.1 or 1 microM). FK506 (1 microM) alone neither affected IL-1 alpha production nor its release. It may be possible that the inhibition of IL-1 alpha production by FK506 is related to its anti-tumor-promoting action.

Transforming growth factor-alpha expression in peritoneal macrophages elicited from SENCAR and B6C3F1 mice: responses to lipopolysaccharide and 12-O-tetradecanoylphorbol-13-acetate

Recent findings in our laboratory indicated that peritoneal macrophages (MPs) elicited from phorbol ester-sensitive SENCAR mice generated significant amounts of superoxide when stimulated by 12-O-tetradecanoylphorbol-13-acetate (TPA) in vitro; negligible responses were observed for MPs derived from relatively resistant B6C3F1 mice. We hypothesized a similar strain-dependent secretion of transforming growth factor-alpha (TGF-alpha) by TPA-stimulated MPs. TGF-alpha secreted by MPs was quantitated by competitive enzyme-linked immunosorbent assay. After 72 h (maximal secretion), for MPs derived from B6C3F1 mice, in vitro exposure to 10 microgram/mL lipopolysaccharide (LPS; non-lipid-A-detoxified) resulted in maximal induction (708 pg/mL), in vivo exposure to intraperitoneally (i.p.) administered TPA (2 micrograms/mouse) alone resulted in a minimal response (32 pg/mL), and prior in vivo exposure to TPA significantly inhibited (more than 90% suppression) the LPS-stimulated MP response in culture (i.e., to 62 pg/mL). Although significant amounts of TGF-alpha could be detected in both SENCAR- and B6C3F1-derived MPs (i.e., approximately 2-3 ng/5 x 10(6) cells), SENCAR MPs did not secrete TGF-alpha in response to either TPA or LPS. In addition, the use of the semiquantitative reverse transcription-polymerase chain reaction to detect TGF-alpha-specific mRNA did not support the strain dependency observed for LPS-stimulated TGF-alpha secretion, i.e., detectable transcripts were observed in MP RNA derived from both strains. In conclusion, although TPA itself demonstrated negligible effects on TGF-alpha expression in murine MPs, prior in vivo exposure inhibited LPS-stimulated transcriptional activation and intracellular TGF-alpha production. The negligible TGF-alpha secretion determined for LPS-stimulated SENCAR-derived MPs suggested the possibility of a strain-specific defect in the posttranslational processing of the proTGF-alpha molecule.

Altered expression of transforming growth factor-beta 1 mRNA and protein in mouse skin carcinogenesis

Transforming growth factor (TGF)-beta 1, whose gene is located on mouse chromosome 7, has been proposed to be involved in skin carcinogenesis. In the study presented here, we demonstrated that single topical treatments with different types of tumor promoters, i.e., the protein kinase C activator 12-O-tetradecanoylphorbol-13-acetate (TPA, 2 micrograms); the non-protein kinase C activators anthralin (22.6 micrograms), benzoyl peroxide (20 mg), and cumene hydroperoxide (1.2 mg); the first-stage tumor promoters 4-O-methyl-TPA (500 micrograms) and A23187 (166 micrograms); and the second-stage tumor promoter mezerein (2 micrograms) produced transient induction of TGF-beta 1 mRNA in SSIN (inbred SENCAR) mouse skin. The time of maximum induction varied from 3 to 12 h; the relative extent of induction was ranked as cumene hydroperoxide > benzoyl peroxide > anthralin > TPA > 4-O-methyl-TPA > mezerein > A23187. These findings suggested that TGF-beta 1 mRNA induction is a common response of skin to several types of complete and stage-specific promoters; however, the extent of induction did not correlate with the reported hyperplastic activity of single applications of these promoters. We also demonstrated that TGF-beta 1 mRNA expression in papillomas of SENCAR mice generally correlated with expression levels of cyclin D1, another gene on chromosome 7, and with stage of tumor progression. TGF-beta 1 mRNA expression was constitutively elevated in most squamous cell carcinomas from either initiation-promotion or complete carcinogenesis protocols. Cell lines established from carcinomas also overexpressed TGF-beta 1 mRNA. Immunohistochemical staining of tissue sections of normal and TPA-treated skin revealed the presence of extracellular TGF-beta 1 protein in the dermis and intracellular TGF-beta 1 protein in the epidermis, especially in the suprabasal layers. The staining patterns of papillomas varied, with 62 +/- 13% of the tissue showing strong intracellular staining but only 25 +/- 8% of the connective tissue staining for extracellular TGF-beta 1. Variable staining patterns were also found in carcinomas; some areas stained heavily for both the intracellular and extracellular forms of TGF-beta 1. Overall, 28 +/- 6% of the tissue of the 12 analyzed carcinomas stained for the intracellular form and 18 +/- 5% for the extracellular form of TGF-beta 1.