Fibroblast growth factor-2 but not Mel-CAM and/or beta3 integrin promotes progression of melanocytes to melanoma

A variety of melanoma-associated antigens have been identified that mediate adhesion, growth, proteolysis, and modulation of immune response. However, the mechanisms by which human normal melanocytes become malignant are not clearly understood. Among the most consistent observations is the up-regulation of fibroblast growth factor-2 (FGF-2) and of the adhesion molecules beta3 integrin and Mel-CAM during melanoma progression. To evaluate the potential role of FGF-2, beta3 integrin and Mel-CAM in melanoma development we overexpressed FGF-2, beta3 integrin and Mel-CAM in normal human melanocytes using replication-deficient adenoviruses as a gene delivery vehicle. Fibroblast growth factor-2 overexpressing melanocytes in monolayer culture displayed cytological atypia. Furthermore, in human skin reconstructs where the physiological milieu is recreated in vitro, FGF-2-overexpressing melanocytes exhibited marked proliferation, upwards migration, cluster formation and type IV collagen expression within the epidermal compartment, simulating early radial growth phase melanoma. In contrast, overexpression of beta3 integrin and/or Mel-CAM in melanocytes did not affect their biological behaviour in human skin reconstructs. The described results of the current and previous studies emphasise the key role of FGF-2 in melanoma development and progression, underscoring the promise of FGF-2 as a target for therapy.     

Role of protease-activated receptors in human skin fibrosis and scleroderma

Proteases and their receptors have poorly understood roles in skin fibrosis and systemic scleroderma (SSc). We examined the role of protease-activated receptors (PAR(1) and PAR(2) ) in the pathophysiology of human SSc and skin fibrosis. Immunohistochemistry showed that PAR(1) immunoreactivity was positive in fibroblasts of SSc skin and healthy skin. PAR(2) immunoreactivity was positive in SSc skin, but negative in endothelial cells and fibroblasts of healthy skin. Double immunofluorescence using an antibody against smooth muscle actin (α-SMA) as a marker for myofibroblasts verified a certain percentage of myofibroblasts positive for PAR(1) and PAR(2) in SSc skin. In human dermal cultured fibroblasts (HDF), PAR(1) stimulation with or without bleomycin pretreatment mobilized intracellular calcium, indicating that the expressed PARs are functional and have effects on downstream signalling by calcium release. PAR(2) -induced intracellular calcium mobilization was only measurable in HDF after bleomycin pretreatment. Thus, PAR(1) - and PAR(2) -positive fibroblasts are increased in SSc, indicating a regulatory role. Intriguingly, bleomycin activated PAR(2) in HDF indicating that fibrosis-promoting factors have a direct effect on PAR(2) expression and functionality.     

Agonists of proteinase-activated receptor-2 stimulate upregulation of intercellular cell adhesion molecule-1 in primary human keratinocytes via activation of NF-kappa B

Proteinase-activated receptor-2 (PAR2) belongs to a new G protein-coupled receptor subfamily that is activated by various serine proteases. Recent knowledge indicates that PAR2 is involved in cutaneous inflammation and immune response. PAR2 is highly expressed by human keratinocytes (KTC). The underlying mechanisms of PAR2-mediated KTC function and cutaneous immune response are, however, still incomplete. Therefore, we investigated the activation of important signaling cascades in primary human KTC after PAR2-stimulation using specific agonists. Moreover, we compared PAR2-immunoreactivity in the epidermis of inflammatory dermatoses and normal human skin. Electrophoretic mobility shift assays and morphological transduction studies revealed PAR2-induced activation and translocation of nuclear factor kappa B (NF-kappaB) in primary human KTC with a maximum after 1 h. Supershift analysis demonstrated acivation of the p50/p65 heterodimer complex. PAR2 agonists also induced upregulation of intercellular adhesion molecule-1 (ICAM-1) RNA, as shown by RT-PCR. Use of NF-kappaB inhibitors prevented upregulation of the cell adhesion molecule ICAM-1 in KTC indicating a direct role of NF-kappaB in PAR2-mediated upregulation of ICAM-1. Fluorescence-activated cell sorter analysis confirmed PAR2-induced and NF-kappaB-mediated upregulation of ICAM-1 protein after 13 h. Moreover, increased expression of PAR2 was detected in KTC of patients with atopic dermatitis suggesting a role of PAR2 in human skin inflammation. In conclusion, PAR2 induces upregulation of cell adhesion molecules such as ICAM-1 in primary human KTC via NF-kappaB activation, and is upregulated in KTC during cutaneous inflammation. Thus, PAR2 may play an important regulatory role of human KTC during inflammation and immune response.     

Expression of the soluble vascular endothelial growth factor receptor-1 in cutaneous melanoma: role in tumour progression

Background Vascular endothelial growth factor (VEGF)‐A, placenta growth factor (PlGF) and their corresponding membrane receptors are involved in autocrine and paracrine regulation of melanoma growth and metastasis. Besides the membrane receptors, a soluble form of the VEGF receptor (VEGFR)‐1 (sVEGFR‐1) has been identified, that behaves both as a decoy receptor, sequestering VEGF‐A and PlGF, and as an extracellular matrix (ECM) molecule, promoting endothelial cell adhesion and migration through the interaction with α5β1 integrin. Objectives To analyse whether sVEGFR‐1 plays a role during melanoma progression. Methods sVEGFR‐1 expression was evaluated in a panel of 36 melanoma cell lines and 11 primary human melanocyte cultures by quantitative real‐time polymerase chain reaction analysis and in specimens of primary or metastatic melanoma lesions from 23 patients by immunohistochemical analysis. Results sVEGFR‐1 expression was highly upregulated in melanoma cell lines with respect to human melanocytes. Interestingly, cell lines obtained from cutaneous metastases showed a significant reduction of sVEGFR‐1 expression, as compared with cell lines derived from primary tumours. These results were confirmed by immunohistochemical analysis of sections from primary skin melanomas and the corresponding cutaneous metastases, suggesting that modulation of sVEGFR‐1 expression influences ECM invasion by melanoma cells and metastasis localization. Moreover, we provide evidence that adhesion of melanoma cells to sVEGFR‐1 is favoured by the activation of a VEGF‐A/VEGFR‐2 autocrine loop. Conclusions Our data strongly suggest that sVEGFR‐1 plays a role in melanoma progression and that low sVEGFR‐1/VEGF‐A and sVEGFR‐1/transmembrane VEGFR‐1 ratios might predict a poor outcome in patients with melanoma.     

Matrix metalloproteinases in human melanoma

Cutaneous melanoma is a highly invasive and metastatic tumor. Degradation of basement membranes and extracellular matrix is an essential step in melanoma cell migration, invasion, and metastasis formation. Matrix metalloproteinases and their tissue inhibitors play a crucial role in these complex multistep processes. Melanoma cells may express a number of matrix metalloproteinase family members (MMP-1, MMP-2, MMP-9, MMP-13, and MT1-MMP) as well as their tissue inhibitors (TIMP-1, TIMP-2, and TIMP-3). Numerous studies have examined matrix metalloproteinases, their tissue inhibitors, and the molecules that regulate their expression and/or activation in melanoma cell lines in vitro and in vivo, and in human melanocytic lesions. Recent results have indicated that adhesion molecules such as CD44 and integrin alphavbeta3 are involved in positioning activated matrix metalloproteinase molecules on the cell surface of invasive tumor cells. In this review we evaluate these novel aspects of the role of matrix metalloproteinases and their tissue inhibitors in melanoma progression. We conclude that the balance between levels of activated matrix metalloproteinases and expression levels of their tissue inhibitors, and the coexpression of activated matrix metalloproteinases and adhesion molecules are important factors in determining melanoma cell invasion, tumor growth, and metastasis formation.     

IL-23/Th17相关细胞因子在基底细胞癌中的表达水平及意义

目的探讨IL-23/Th17相关细胞因子在基底细胞癌(BCC)疾病进展中的作用。方法采用免疫组织化学染色的方法检测35例BCC组织及10例正常皮肤组织中IL-17、IL-22及IL-23的表达水平。结果IL-17在基底细胞癌中的表达水平高于正常皮肤组织(P<0.05),IL-17在基底细胞癌组织细胞和肿瘤间质细胞胞质中均有表达。IL-23在基底细胞癌中的表达水平高于正常皮肤组织(P<0.05),IL-23主要在基底细胞癌组织细胞胞质表达,部分位于肿瘤间质细胞胞质中。IL-22在基底细胞癌和正常皮肤组织的表达水平差异无统计学意义(P>0.05)。基底细胞癌中IL-17和IL-23的表达水平呈正相关(P<0.05)。结论IL-23/Th17相关细胞因子可能参与基底细胞癌的发生、发展。IL-23可能通过诱导Th17细胞的发育和增殖,促进IL-17分泌并在基底细胞癌的发生、发展中发挥协同作用。     

Expression of activated N-ras in a primary melanoma cell line counteracts growth inhibition by transforming growth factor-beta

One critical factor in melanoma progression is the change from radial growth phase to vertical growth phase. We previously showed a high incidence of ras mutations in progressing but not early human melanomas. We also found that stable expression of activated Ras in a primary human melanoma cell line (WM35) led to enhanced proliferation, anchorage-independent survival, migration and invasion in vitro and enhanced subcutaneous tumor formation in vivo, transforming the melanoma phenotype from the radial growth phase to the vertical growth phase. Inhibitory cytokines, especially transforming growth factor-beta, are important in homeostasis of normal human melanocytes. Proliferation of early melanoma cells can be inhibited by transforming growth factor-beta, whereas more aggressive stages lose this response. Using a transforming growth factor-beta activated luciferase reporter transiently transfected into WM35, WM35N-ras, and WM35H-ras (WM35 transfected with mutant N-ras or H-ras genes), we demonstrated significant decreases (p < 0. 04) in transforming growth factor-beta induced reporter expression in both ras transfected cell lines. Transforming growth factor-beta also induced significant decreases (p < 0.002) in the proportion of WM35 cells in S-phase of the cell cycle; this effect was not observed in WM35N-ras cells. Furthermore, we demonstrated that an important controlling factor in transforming growth factor-beta inhibition of cell cycle progression, the phosphorylation of the Rb protein, was altered in WM35N-ras; transforming growth factor-beta caused a marked relative increase in hypophosphorylated pRb in WM35 cells, but not in WM35N-ras. These data suggest that activated Ras plays an important part in melanoma progression from the radial growth phase to the vertical growth phase by counteracting inhibition by cytokines such as transforming growth factor-beta, thus providing a growth advantage.     

Stromal Fibroblast-Specific Expression of ADAM-9 Modulates Proliferation and Apoptosis in Melanoma Cells In Vitro and In Vivo

ADAMs are members of the zinc metalloproteinase superfamily characterized by the presence of disintegrin and metalloprotease domains. In human melanoma, ADAM-9 is expressed in focalized areas of the tumor-stroma border in both melanoma and stromal cells. However, the role of ADAM-9 in melanoma progression remains elusive. To analyze the role of stromal-derived ADAM-9 for the growth and survival of melanoma cells, we have used in vitro coculture systems of melanoma cells and ADAM-9(-/-) fibroblasts. Coculture of melanoma cells in the presence of ADAM-9(-/-) fibroblasts led to increased melanoma cell proliferation and reduced apoptosis as compared with control cocultures. We identified TIMP-1 and sTNFRI as the two relevant factors expressed in increased amounts in culture supernatants from ADAM-9(-/-) fibroblasts. TIMP-1 was associated with induced melanoma cell proliferation, whereas soluble TNFR1 mediated the reduced cellular apoptosis in vitro. In vivo, injection of murine melanoma cells into the flank of ADAM-9(-/-) animals resulted in the development of significantly larger tumors than in wild-type animals as a result of increased proliferation and decreased apoptosis of melanoma cells. Taken together, stromal expression of ADAM-9 during melanoma development modulates the expression of TIMP-1 and sTNFR1, which in turn affect tumor cell proliferation and apoptosis.     

Endothelin-1 induces CXCL1 and CXCL8 secretion in human melanoma cells

The endothelin pathway plays a critical role in melanoma tumor progression by a variety of mechanisms that enhance tumor cell growth, invasion, and metastasis. Here, we investigate the effect of this pathway on CXC chemokine expression in human melanoma cells and melanocytes. As determined by ELISA, endothelin-1 (ET-1) induces CXCL1 and CXCL8 secretion in three human melanoma cell lines in a concentration-dependent fashion. These responses are mediated by the endothelin-B receptor and are sustained over a 40 h time course. ET-1 does not induce CXCL1 secretion in primary human melanocytes but ET-3, an endothelin isoform, induces a low level of CXCL1 secretion in certain cultures. Neither ET-1 nor ET-3 induces secretion of CXCL8 in primary human melanocytes; thus, this response may be specific for melanocytic cells that have undergone malignant transformation. We have previously demonstrated that ET-1 induces changes in the expression of adhesion molecules in melanoma cells such that invasion and metastasis are favored. This study demonstrates that ET-1 additionally induces secretion of CXC chemokines critical for melanoma metastasis and tumor progression.     

VCAM-1-, ELAM-1-, and ICAM-1-independent adhesion of melanoma cells to cultured human dermal microvascular endothelial cells.

We have examined the mechanisms by which tumor cells bind to endothelial cells utilizing cultured melanoma cells and microvascular endothelial cells derived from human dermis (HDMEC). The ability of biologic response modifiers (BRM) to modulate the adhesion of melanoma cells to HDMEC was defined and those results were compared with results from human umbilical vein endothelial cells (HUVEC). SK-MEL-2, WM266-4, and Hs 294T melanoma cells all bound to HDMEC and HUVEC monolayers and adherence of melanoma cells was enhanced in a dose- and time-dependent manner by the treatment of HDMEC with interleukin 1 (IL-1) alpha or tumor necrosis factor (TNF) alpha. Similar increases in binding to HDMEC or HUVEC were induced after BRM stimulation, although baseline melanoma cell binding to HUVEC tended to be slightly higher than to HDMEC. In contrast, whereas phorbol 12-myristate 13-acetate (PMA) augmented melanoma cell adherence to HDMEC, PMA failed to increase adherence to HUVEC. The alterations in melanoma cell binding were induced only after pretreatment of endothelial and not melanoma cells with PMA. Studies of the expression of cell adhesion molecules (CAM) on HDMEC and HUVEC using enzyme-linked immunosorbent assay showed that vascular cell adhesion molecule 1 (VCAM-1) is not induced by PMA on HDMEC and intercellular adhesion molecule 1 (ICAM-1) is downregulated on HDMEC by PMA treatment. Endothelial leukocyte adhesion molecule 1 (ELAM-1) is induced by PMA, IL-1 alpha, or TNFalpha, but its expression does not correlate with increased melanoma cell binding MoAb recognizing VCAM-1-inhibited TNFalpha-induced increases in melanoma cell binding to HUVEC. However, anti-VCAM-1 antibody failed to clock melanoma cell binding to PMA or IL-1 alpha-stimulated HDMEC and only partially inhibited melanoma cell binding to TNF alpha-stimulated HDMEC. This study demonstrates that PMA and IL-1 alpha-induced increases in melanoma cell adherence to HDMEC are not mediated via known CAM, including ICAM-1, VCAM-1, or ELAM-1, and may be affected through microvessel-specific novel proteins not previously described on endothelial cells.     

恶性黑素瘤细胞中的谷氨酸信号通路及其与细胞骨架蛋白分子的作用机制

目的 探讨谷氨酸受体通路对恶性黑素瘤(恶黑)细胞树突形态以及细胞骨架蛋白的作用.方法 激光共聚焦显微镜及原子力显微镜分析微管相关蛋白2a(MAP2a)、离子型谷氨酸受体(NMDAR2A)、代谢型谷氨酸受体(mGluR1)在人侵袭性恶黑细胞中的亚细胞定位,以及NMDAR拮抗剂MK-801及mGluR1拮抗剂CPCCOEt对微管蛋白分布、细胞树突形态的作用.测定细胞生长曲线,观察MK-801及CPCCOEt对恶黑细胞增殖的影响.结果 研究发现,上述分子具有相似的亚细胞分布:均主要位于细胞树突内;MK-801及CPCCOEt均可使细胞树突内微管密度增加,使恶黑细胞树突化;且与MAP2a具有协同作用;MK-801及CPCCOEt均对恶黑细胞增殖具有显著抑制作用.结论 谷氨酸受体通路参与恶黑细胞树突发育的生理功能,谷氨酸受体拮抗剂可抑制恶黑细胞增殖.     

皮肤病中蛋白激酶D1研究进展

蛋白激酶D1是一种在体内多个重要器官广泛表达的钙离子/钙调蛋白依赖性的丝氨酸/苏氨酸蛋白激酶,参与多种重要的生理和病理活动,在许多肿瘤组织中表达异常。PKD1促进角质形成细胞增殖,抑制其分化,对表皮伤口愈合及肿瘤的形成具有促进作用,与UVB、ROS等影响皮肤疾病发生发展的重要因素之间都有密切联系。因此PKD1可能成为治疗某些皮肤病甚至皮肤肿瘤更有效的分子靶点。     

CELL PROLIFERATION AND CYTOKINE INDUCTION BY TNF-�� OF PSORIATIC KERATINOCYTES ARE NOT DIFFERENT FROM NORMAL KERATINOCYTES IN VITRO

Background:

Recent studies indicate that various cytokines including tumor necrosis factor-α (TNF-α) play an essential role in the induction and maintenance of psoriatic lesion.

Aims:

To compare the cell proliferation of keratinocytes by various cytokines and TNF-α-induced cytokine secretion among normal keratinocytes, uninvolved, and involved keratinocytes.

Methods:

The keratinocytes from normal skin, uninvolved, and involved psoriasis were cultured in the presence of IL-6, IL-8, epidermal growth factor (EGF), hepatocyte growth factor (HGF), transforming growth factor-α (TGF-α) epiregulin, amphiregulin, and TNF-α and then MTT assay for keratinocytes proliferation was performed. Furthermore, TNF-α-induced secretion of IL-6, IL-8, EGF, HGF, TGF-α, epiregulin, and amphiregulin were compared among these keratinocytes.

Results:

IL-6, IL-8, EFG, TGF-α, epiregulin, and amphiregulin, but not TNF-α increased keratinocyte proliferation of normal, psoriatic uninvolved, and involved skin. The increased cell proliferation by these cytokines and growth factors were not different among the keratinocytes derived from normal skin, uninvolved, and involved psoriasis. The significant induction of TNF-α increased IL-6, IL-8, EGF, HGF, TGF-α, epiregulin, and amphiregulin, but the increase in these cytokines and growth factors were not different among normal skin, uninvolved, and involved psoriasis.

Conclusion:

Cell proliferation by various cytokines and growth factors and TNF-α-induced cytokine secretion are not different between normal and psoriatic keratinocytes.     

Erythroid differentiation regulator 1, an interleukin 18-regulated gene, acts as a metastasis suppressor in melanoma

Erythroid differentiation regulator (Erdr1) was first discovered in mouse leukemia cell lines and functions as a stress-related survival factor. This study investigated whether Erdr1 regulates murine melanoma progression, as well as the mechanism involved in Erdr1-regulated metastasis. The expression of Erdr1 is negatively correlated with IL-18 expression, which has a pro-cancer effect in melanoma. To study the role of Erdr1 as an anti-cancer factor, cell migration, invasion, and proliferation were measured. Erdr1 overexpression markedly inhibited the level of cell migration, invasion, and proliferation in B16F10 cells in vitro. In addition, Erdr1 overexpression significantly suppressed melanoma lung colonization, metastasis, and tumor growth in vivo. To identify the factors involved in Erdr1-reduced metastasis, heat shock protein 90 (HSP90), a well-known stress protein and contributor to tumor metastasis, was examined. We found that HSP90 was significantly decreased in Erdr1-overexpressing cells. Functional analysis demonstrated that HSP90 small-interfering RNA transfection reduced the migration ability and metastasis of melanoma. In conclusion, Erdr1 shows a powerful anti-metastasis effect that leads to the ability to reduce the metastatic potential of murine malignant melanoma cells. Erdr1 is an anti-metastatic factor that may be a possible therapeutic target for treatment of melanoma.     

G2A plays proinflammatory roles in human keratinocytes under oxidative stress as a receptor for 9-hydroxyoctadecadienoic acid

G2A is a stress-inducible G protein-coupled receptor for oxidized free fatty acids, such as 9-hydroxyoctadecadienoic acid (HODE). As skin is routinely and pathologically exposed to many oxidative stresses such as UV radiation, chemical agents, and inflammation that might induce both G2A expression and production of G2A ligands, we examined G2A function in human keratinocytes. G2A was expressed in human epidermis, normal human epidermal keratinocytes (NHEK), and an immortalized human keratinocyte cell line (HaCaT). 9(S)-HODE evoked intracellular calcium mobilization and secretion of cytokines, including IL-6, IL-8, and GM-CSF in NHEK cells. These responses became prominent in HaCaT cells by overexpression of G2A. 9(S)-HODE inhibited proliferation of NHEK cells by suppressing DNA synthesis and arresting the cell cycle in the G0/1-phase. On the other hand, 13(S)-HODE, another major oxidative product from linoleate, showed little or no effect on either cytokine secretion or on proliferation in NHEK cells. A small interfering RNA designed to downregulate G2A caused suppression of 9(S)-HODE-induced inhibitory effects on proliferation of NHEK cells. UVB and H(2)O(2) induced G2A expression and caused oxidation of linoleate to produce 9-HODE in HaCaT cells. These results suggest that 9-HODE-G2A signaling plays proinflammatory roles in skin under oxidative conditions.     

Proteinase-activated receptor-2 (PAR2): a tumor suppressor in skin carcinogenesis

The proteinase-activated receptor PAR(2) has been demonstrated to modulate tumor growth, invasion and metastasis in various tissues. However, the role of PAR(2) in cutaneous cancerogenesis is still unknown. Here we could show a protective role of PAR(2) in the development of epidermal skin tumors: we established a mouse skin tumor model using chemically induced carcinogenesis. Tumors started to appear after eight weeks. After 13 weeks, PAR(2)-deficient mice showed a significantly increased number of skin tumors (14 per animal on the average) in contrast to the wild type (eight tumors per mouse). Analysis of possible signal transduction pathways activated upon PAR(2) stimulation in HaCaT keratinocytes showed an involvement of extracellular signal-regulated kinase 1/2 and profound epidermal growth factor receptor transactivation, leading to secretion of the tumor-suppressing factor transforming growth factor-beta1. Thus, our results provide early experimental evidence for a tumor-protective role of PAR(2).     

Hepatocyte growth factor establishes autocrine and paracrine feedback loops for the protection of skin cells after UV irradiation

Hepatocyte growth factor (HGF) is a multifunctional cytokine, which, among various other activities, acts as a growth factor for melanocytes and has recently been implicated in the pathogenesis of malignant melanoma. In the skin, the main source for HGF is dermal fibroblasts (FB). Here, we have investigated the regulation of HGF production and secretion by cytokines derived from UV-irradiated keratinocytes (KC) and by direct UV irradiation. We demonstrate that supernatants of ultraviolet (UV)B-irradiated KC strongly induce HGF production in FB, and that this effect was mediated primarily by IL-1alpha. Direct irradiation of FB with UVB had no effect on HGF expression. In contrast, irradiation with UVA1 strongly upregulated HGF mRNA production and secretion of the functional protein. Addition of neutralizing anti-HGF antibodies after UVA1 irradiation, as well as transfection of FB with HGF small-interfering RNA (siRNA); which completely abrogated HGF secretion led to a dramatic rise of FB apoptosis demonstrating that autocrine HGF efficiently protected FB from UVA1-induced apoptosis. Our data suggest that upregulation of HGF plays a role in skin homeostasis after UV irradiation. However, a negative side effect of UV-induced HGF secretion by dermal FB might represent a decisive factor for induction and/or progression of melanoma.     

Effects of Etretinate on Keratinocyte Proliferation and Secretion of Interleukin-1α (IL-1α) and IL-8

Etretinate has proven to be effective in the treatment of psoriasis. Since abnormal proliferation and cytokine secretion are well-known features of psoriatic epidermis, we studied the in vitro effects of etretinate on these two processes using human keratinocytes. Etretinate promoted proliferation of normal human keratinocytes (NHKs) grown in keratinocyte growth medium (KGM) but not in growth factor-deficient keratinocyte basic medium (KBM). Moreover, etretinate partly overcame growth inhibition by PMA. Etretinate was shown to have an effect on either IL-1α or IL-8 secretion in unstimulated NHKs. In HSC-1, a human squamous cell carcinoma cell line cultured in 20% FCS/DMEM, inhibited IL-1α secretion and enhanced IL-8 secretion. These results indicate that the effects of etretinate on keratinocyte proliferation and cytokine secretion may depend on cell type and culture conditions. Stimulation of NHKs with PMA significantly enhanced IL-1α and IL-8 secretion, and these effects were inhibited by etretinate. However, etretinate failed to inhibit rTNFα-induced IL-8 secretion, suggesting that etretinate regulation of NHK cytokine secretion may also depend on the stimulus. As treatment of keratinocytes or epidermis with PMA can induce psoriasis-like changes, so might the experimental “anti-PMA” activity of etretinate be related to its therapeutic benefit in the treatment of psoriasis.