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. Author manuscript; available in PMC: 2009 Nov 2.
Published in final edited form as: J Invest Dermatol. 2008 Aug 28;129(3):635–640. doi: 10.1038/jid.2008.266

Lack of evidence for activation of the Hedgehog pathway in psoriasis

JE Gudjonsson 1, A Aphale 1, M Grachtchouk 1, J Ding 2, RP Nair 1, T Wang 1, JJ Voorhees 1, AA Dlugosz 1, JT Elder 1,3
PMCID: PMC2771222  NIHMSID: NIHMS112832  PMID: 18754037

Abstract

Recent reports have suggested that the Hedgehog (Hh) pathway is activated in lesional psoriatic skin, and that treatment with the Hh pathway antagonist cyclopamine may lead to rapid resolution of the disease. To assess Hh pathway activity in psoriasis, we isolated RNA from lesional and uninvolved skin of 58 psoriatic patients, and from 63 normal control subjects, and subjected these samples to global gene expression profiling on Affymetrix HU133 Plus 2.0 gene arrays. We were especially interested in Hh target genes (PTCH1, and GLI1), whose expression is elevated in response to Hh signaling. The microarray data demonstrated down-regulation of PTCH1 expression in uninvolved and lesional skin (1.1-fold and 2-fold respectively, p<0.0001). Additionally GLI1 mRNA was down-regulated in lesional skin (1.7 fold p<0.05). No significant changes were observed between lesional and uninvolved skin for the Hh ligands or Smoothened (SMO). QT-PCR confirmed these findings. In situ hybridization for GLI1 and PTCH1 was positive in BCC tumor cells, but was negligible in uninvolved or lesional psoriatic skin. The absence of elevated Hh target gene expression in lesional psoriatic skin indicates that the Hh pathway is not activated in this disease, raising questions regarding the proposed use of Hh antagonists as anti-psoriatic agents.

Keywords: Psoriasis, GLI, PTCH1, sonic hedgehog pathway

INTRODUCTION

Psoriasis is a common chronic inflammatory skin disease characterized by complex alterations in epidermal growth, differentiation and multiple, immunological and vascular abnormalities. Psoriasis was historically considered to be a primary disorder of keratinocytes, but over the past two decades it has been firmly established that psoriasis is an immune disorder mediated by activated T cells (Gudjonsson et al, 2004; Liu et al, 2007). How activated T cells mediate the altered differentiation and hyperproliferation of keratinocytes and other changes observed in psoriasis is still unknown but is thought to involve a highly complex, yet incompletely understood, interaction of multiple cytokines and growth factors with multiple cellular effectors present within the psoriatic lesion. Additionally, the intercellular signaling pathways mediating these changes remain to be fully elucidated, although reports have indicated involvement of the signal transducer and activator of transcription 1 (STAT1) (Bowcock et al, 2001), STAT3 (Sano et al, 2005), mitogen-activated protein kinase (MAPK) (Johansen et al, 2005b), activator protein 1 (AP-1) (Johansen et al, 2004) and the NF-kB pathways (Johansen et al, 2005a; Lizzul et al, 2005).

Recent reports have suggested that the Hedgehog (Hh) pathway is activated in lesional psoriatic skin (Kuenzli et al, 2004; Tas and Avci, 2004; Endo et al, 2006; Meth and Weinberg, 2006), and that pharmacological inhibition of this pathway using cyclopamine may lead to rapid resolution of the disease (Kuenzli et al, 2004; Tas and Avci, 2004; Meth and Weinberg, 2006). The Hh signaling pathway is one of the major signaling pathways involved in embryonic development (Ingham and Placzek, 2006). During physiologic Hh signaling, Hh proteins bind to the cell surface receptor Patched (PTCH1), thereby releasing Smoothened (SMO) from PTCH-mediated inhibition. SMO activation then triggers a series of intracellular events, culminating in alterations in gene expression mediated by the Gli family of transcription factors (GLI1, GLI2 and GLI3) (Ruiz i Altaba et al, 2007) (Figure 1). The transcripts for PTCH1 and GLI1 are reliable markers for both physiologic and pathologic Hh signaling activity as they are consistently induced when the Hh pathway is activated (McMahon et al, 2003; Hutchin et al, 2005). This pathway has been shown to be a crucial regulator of hair follicle growth and sebaceous gland biology (Allen et al, 2003; Niemann et al, 2003). On the other hand, sustained activation of the Hh pathway appears to be the driving force for BCC development (Daya-Grosjean and Couve-Privat, 2005).

Figure 1.

Figure 1

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The involvement of the Hh pathway in psoriasis was first suggested by the marked and rapid improvement observed in a clinical trial, in which 31 individual psoriatic lesions in 7 patients, all with an established diagnosis of plaque or guttate psoriasis, were treated with topical cyclopamine (Tas and Avci, 2004). Furthermore, the authors asserted that topical cyclopamine was more effective than the potent topical steroid clobetasol-17 propionate, a typical first-line therapy (Tas and Avci, 2004). Cyclopamine is a steroid alkaloid that acts as an inhibitor of the Hh pathway by binding directly to SMO and thus blocking activation of the pathway. Cyclopamine is a potent teratogen that can lead to severe fetal malformations including cyclopia (holoprosencephaly) (Belloni et al, 1996; Roessler et al, 1996). With application of cyclopamine to the lesional skin marked improvement was seen within 24 hours with near complete clinical and histological clearance observed in 96 hours (Tas and Avci, 2004). In another recent study it was demonstrated by immunohistochemistry that GLI1 was overexpressed in lesional skin whereas no expression was detected in either uninvolved or control skin (Endo et al, 2006). Taken together, these data suggested that Hh pathway activation is proximal to other events in the pathogenesis of psoriasis and that therapeutic manipulation of this pathway may lead to rapid and possibly sustained improvement of psoriasis.

Despite these data, detailed evaluation of this pathway, and its activation status, in psoriasis has been lacking. We have collected large datasets on gene expression in psoriasis to evaluate and dissect the pathogenic basis of this enigmatic disease. Here, we investigate the principal components of the Hh pathway in lesional, uninvolved and normal skin and expression of its downstream signature target genes.

RESULTS

Microarray Data

Several of the genes involved in the Hh Pathway showed modest changes in expression between control, uninvolved and lesional skin (Figure 2), but in no case did we detect evidence for activation of Hh signaling activity in psoriasis. Expression of the PTCH1 gene was only slightly down-regulated in uninvolved psoriatic skin (89% of control, p<0.0001) with more pronounced down-regulation in lesional skin (51% of uninvolved, p<0.0001) (table 1), compared to control skin. No changes were observed in the expression levels of the PTCH2 gene. Both GLI1 and GLI2 were significantly down-regulated in lesional psoriatic skin (60% and 68% of uninvolved, p<0.05 and p<0.0001 respectively) (table 1). Cyclin D1 (CCND1) was significantly down-regulated compared to uninvolved (2.2 fold, p<0.0001) in lesional psoriatic skin whereas CCND2, CDC2 and cyclin B1 (CCNB1) were up-regulated relative to uninvolved skin (1.5-fold, 3.7-fold and 5.9-fold respectively, p<0.0001). The Sonic hedgehog (SHH) and the Indian hedgehog (IHH) gene expressions were minimally up-regulated in uninvolved psoriatic skin relative to control (1.06 and 1.05 fold, p<0.05) whereas no change was observed for the Desert hedgehog (DHH) gene. No significant changes were observed between lesional and uninvolved skin for the Hh ligands or SMO (table 1). Molecular network mapping performed by Ingenuity Pathway Analysis demonstrated complete lack of activation of the Sonic Hedgehog Pathway (data not shown)

Figure 2.

Figure 2

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Table 1.

Fold changes between uninvolved (U) and control skin (N), and lesional psoriatic (P) vs. uninvolved.

Genes Fold changes Fold changes
U vs. N (p-value) P vs. U (p-value)
PTCH1 0.89 (p<0.0001) 0.51 (p<0.0001)
PTCH2 1.03 (ns) 1.00 (ns)
GLI1 1.03 (ns) 0.60 (p<0.05)
GLI2 0.92 (ns) 0.68 (p<0.0001)
HHIP 1.02 (ns) 1.00 (ns)
SHH 1.06 (p<0.05) 1.01 (ns)
DHH 1.00 (ns) 1.01 (ns)
IHH 1.05 (p<0.05) 1.06 (ns)
SMO 0.93 (ns) 1.06 (ns)
CCND1 0.96 (ns) 0.45 (p<0.0001)
CCND2 0.92 (ns) 1.47 (p<0.0001)
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Real-time quantitative PCR Data

For confirmation of the microarray data, quantitative real-time PCR was performed on RNA isolated from 10 control skin biopsies, 10 paired uninvolved and lesional psoriatic skin biopsies, and 12 basal cell carcinoma samples, which served as positive controls for Hh pathway activation. The expression of the principal Hh pathway factors, GLI1 and PTCH1 were significantly lower in lesional psoriatic skin than in BCC (p<0.001) (Figure 3). Furthermore, expression of these two genes was lower in lesional skin compared to uninvolved skin (p=0.10 (GLI1), p<0.05 (PTCH1)). Expression of PTCH2 and HHIP were significantly lower in lesional, uninvolved and control skin compared to BCC (p<0.01) (not shown), whereas the expression of KRT1B and CCND1 was decreased in both lesional skin and basal cell carcinomas compared to normal and uninvolved skin (p<0.001, p<0.01 respectively) (data not shown). CCND2 and MYCN expression levels were significantly lower in BCC compared to lesional, uninvolved and control samples (P<0.01) whereas no difference was observed for GLI2, SMO or the ligands SHH, IHH and DHH (data not shown).

Figure 3.

Figure 3

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In situ hybridization

In situ hybridization for GLI1 and PTCH1 was strongly positive in BCC tumor cells, which served as positive controls. In contrast, negligible expression of GLI1 and PTCH1 was detected in uninvolved or lesional psoriatic skin, whereas staining for the control transcript, HPRT1, was positive for all samples analyzed (Figure 4).

Figure 4.

Figure 4

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DISCUSSION

Psoriasis is characterized by marked hyperproliferation of keratinocytes and influx of T-cells with activated CD4+ T-cells predominating in the upper dermis and CD8+ T-cells in the epidermis. The pathogenesis is highly complex with involvement and participation of multiple cell types (Bowcock and Krueger, 2005). However, despite the inherent complexity of the psoriatic process is has been shown to be critically dependent on T-cell activation, as medications inhibiting T-cell function can lead to remission of the disease (Liu et al, 2007).

The Hh pathway is one of the main signaling pathways in the developing embryo (Ingham and Placzek, 2006) and has been shown to be crucial for the regulation and development of hair follicles, sebaceous glands and maintenance of stem cell populations in the skin (Levy et al, 2005). Its role in human diseases, such as developmental disorders and cancer (Xie et al, 1998; Mullor et al, 2002; Rubin and de Sauvage, 2006), has been firmly established. Activation of the pathway in keratinocytes has been shown to induce hyperproliferation and resistance to exhaustion of replicative growth capacity (Fan and Khavari, 1999). Additionally, the Hh pathway has also been implicated in modulation of immune function of peripheral CD4+ T-cells in a pro-inflammatory manner (Lowrey et al, 2002; Stewart et al, 2002; Chan et al, 2006), suggesting that the involvement of this pathway in psoriasis pathogenesis might be plausible.

In this study, which is the largest and most detailed yet on the function and activity of this pathway in psoriasis, we failed to find any evidence of activation of the Hh pathway. Importantly, no expression of GLI1 or PTCH1, the established target genes of this pathway, could be observed in either the inflammatory infiltrate or in the hyperproliferative epidermis. In contrast to the expected upregulation of this pathway, our results suggest that the activity of this pathway is in fact slightly suppressed in lesional psoriatic skin. However, if the Hh pathway is suppressed in lesional psoriatic skin, how can the clinical efficacy of topical applied cyclopamine (Tas and Avci, 2004) be explained? Cyclopamine is a steroidal alkaloid derived from the false hellebore, or corn lily; Veratrum californicum [reviewed in (Kuenzli et al, 2004; McFerren, 2006)]. It is a potent teratogen that on ingestion can lead to severe fetal malformations including cyclopia and holoprosencephaly (Cooper et al, 1998; Incardona et al, 2000). It has been demonstrated that cyclopamine inhibits Hh pathway activation by binding directly to SMO and this inhibition is the underlying mechanisms whereby this compound mediates its teratogenic effect (Chen et al, 2002) as well as its inhibitory effect on basal cell carcinomas (Taipale et al, 2000). Whether the molecular effects of cyclopamine on basal cell carcinomas and psoriatic lesions share a common mechanism is not known. Supporting such a common mechanism is a recently published study where evidence of increased Hh pathway activation in lesional psoriatic skin was provided using immunohistochemistry to show upregulation of GLI1 expression in lesional psoriatic skin (Endo et al, 2006). However, the staining was weak and only found diffusely in the upper spinous layer, and Hh pathway activation was not confirmed using other markers (Endo et al, 2006). As immunohistochemistry is prone to a variety of artifacts, we believe that it cannot be considered a reliable marker for Hh pathway activity unless accompanied by other supportive data. We could not find evidence for increased activity of the Hh pathway in psoriasis, as determined by gene microarray analysis, molecular pathway analyses, QT-PCR and in situ hybridization. Thus, our data indicates that the effect of this compound, if truly effective in psoriasis, is likely to be mediated through some other mechanism than blockade of Hh signaling.

In conclusion, we could not confirm previously published studies on the activation of the Hh pathway in lesional psoriasis; in fact our results indicate that this pathway may be modestly suppressed. Given the potential for harmful effects of Hh antagonists, and the lack of evidence for Hh pathway activation in psoriasis, our study raises questions regarding the proposed use of these compounds as anti-psoriatic agents.

MATERIALS AND METHODS

Biopsies, reagent and gene chips

Fifty-eight patients and sixty-three controls were included in the study. This study was approved by the University of Michigan Institutional Review Board and all patients signed an informed consent before inclusion into the study. The patients had not received any topical or systemic treatment for two weeks prior to the study. After local anesthesia with 1% lidocaine HCl and 1:100,000 epinephrine (Hospira, Inc. Lake Forest, IL, USA) two 6mm punch biopsies were obtained from each study subject. From patients, one biopsy was obtained from lesional skin and the other from uninvolved skin, taken at least 10cm away from any active plaque. The non-lesional biopsies were taken from the buttocks or upper thighs of patients and controls. Basal cell carcinoma samples were obtained from Mohs micrographic surgery. The biopsies were snap frozen in liquid nitrogen and stored at −80°C. At processing the biopsy samples were homogenized while still frozen and total RNA extraction was performed using the RNeasy kit protocol (Qiagen, Chatsworth, CA, USA). RNA quantity and quality was measured on the Agilent 2100 Bioanalyzer (Agilent Technologies, Palo Alto, CA). RNA stabilization, isolation, and microarray sample labeling were performed using standard methods for reverse transcription and one round of in vitro transcription on 5µg of total RNA. Samples were run on HU133 Plus 2.0 and processed per the manufacturer’s protocol (Affymetrix, Foster City, CA). The raw data from the microarrays were processed using the Robust Multichip Average (RMA) method (Irizarry et al, 2003) and then normalized to account for gender and batch effects. Specifically, we used a linear model to estimate gender and batch effect and then subtracted them from the raw expression data to get the normalized data.

In situ hybridization

In situ hybridization was performed using 5 µm sections cut from NBF-fixed, paraffin embedded tissue as previously described (Grachtchouk et al, 2003). Plasmid DNA, containing full length cDNA, to make riboprobe against human HPRT1 was purchased from Invitrogen (Clone ID 3163726). BglII or EcoRI digestions followed by in vitro transcription using Sp6 or T7 promoters were used to generate sense or senti-sense probes (respectively).

Real-time PCR

Quantitative (QT) real-time PCR was performed on paired lesional and uninvolved samples from 10 psoriatic patients, 10 normal controls and 11 BCC samples. The RNA used was from the same samples used for the gene microarrays. Primers for the genes GLI1, GLI2, PTCH1, PTCH2, SMO, CCND1, CCND2, IHH, SHH, DHH, HHIP, RPLPO were obtained from Superarray Biosciences (Frederick, MD, USA). Results were normalized to the expression of the housekeeping gene; Ribosomal protein, large, P0 (RPLPO). The reverse transcription reaction was performed on 0.5µg of RNA template and cDNA was synthesized using anchored-oligo(dT)18 primers as instructed by the manufacturer (Roche Diagnostics, Mannheim, Germany). QT-real-time PCR was carried out on the LightCycler™ 2.0 system (Roche Diagnostics, Mannheim, Germany). LightCycler® FastStart DNA MasterPLUS SYBR Green I was used for all PCR reactions as instructed by the manufacturer (Roche Diagnostics, Mannheim, Germany). The reaction profile consisted of an initial denaturation at 95°C for 15 minutes followed by 40 cycles of PCR at 95°C for 10 seconds (denaturation), 58°C for 10 seconds (annealing) and 72°C for 10 seconds (extension). The fluorescence emitted was captured at the end of the extension step of each cycle at 530nm.

Statistical analysis

Student’s T-test was used to analyze differences between the 3 groups. Bonferroni correction was used p-values generated from the microarray data. Paired T-test was used when uninvolved and lesional psoriatic datasets were compared. The Sonic Hedgehog Pathway network of genes and network analysis of microarray data was performed using Ingenuity Pathway Analysis (Ingenuity Systems: www.analysis.ingenuity.com).

ACKNOWLEDGMENTS

This work was supported by the Dermatology Foundation (JEG), the American Skin Association (JEG), the National Institute of Arthritis, Musculoskeletal, and Skin Diseases (AR052889)(JTE). We acknowledge Dr. D. Thomas for generously contributing reagents. The authors thank the volunteers who provided blood and skin samples for this study, and acknowledge the skilled technical assistance of Linda Hodges, Kathleen McCarthy and Suzan Rehbine.

Abbreviations

AP

activator protein

STAT

signal transducer and activator of transcription

MAPK

mitogen-activated protein kinase

CCND1

cyclin D1

CCND2

cyclin D2

SHH

Sonic hedgehog

IHH

Indian hedgehog

DHH

Desert hedgehog

MYCN

myc myelocytomatosis viral related oncogene, neuroblastoma derived

SMO

Smoothened

Hh

Hedgehog

BCC

basal cell carcinoma

KRT1b

keratin 1b

QT

quantitative

PCR

polymerase chain reaction

DNA

deoxyribonucleic acid

RNA

ribonucleic acid

REFERENCES

  1. Allen M, Grachtchouk M, Sheng H, Grachtchouk V, Wang A, Wei L, Liu J, Ramirez A, Metzger D, Chambon P, Jorcano J, Dlugosz AA. Hedgehog signaling regulates sebaceous gland development. Am J Pathol. 2003;163:2173–2178. doi: 10.1016/S0002-9440(10)63574-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Belloni E, Muenke M, Roessler E, Traverso G, Siegel-Bartelt J, Frumkin A, Mitchell HF, Donis-Keller H, Helms C, Hing AV, Heng HH, Koop B, Martindale D, Rommens JM, Tsui LC, Scherer SW. Identification of Sonic hedgehog as a candidate gene responsible for holoprosencephaly. Nat Genet. 1996;14:353–356. doi: 10.1038/ng1196-353. [DOI] [PubMed] [Google Scholar]
  3. Bowcock AM, Krueger JG. Getting under the skin: the immunogenetics of psoriasis. Nat Rev Immunol. 2005;5:699–711. doi: 10.1038/nri1689. [DOI] [PubMed] [Google Scholar]
  4. Bowcock AM, Shannon W, Du F, Duncan J, Cao K, Aftergut K, Catier J, Fernandez-Vina MA, Menter A. Insights into psoriasis and other inflammatory diseases from large-scale gene expression studies. Hum Mol Genet. 2001;10:1793–1805. doi: 10.1093/hmg/10.17.1793. [DOI] [PubMed] [Google Scholar]
  5. Chan VS, Chau SY, Tian L, Chen Y, Kwong SK, Quackenbush J, Dallman M, Lamb J, Tam PK. Sonic hedgehog promotes CD4+ T lymphocyte proliferation and modulates the expression of a subset of CD28-targeted genes. Int Immunol. 2006;18:1627–1636. doi: 10.1093/intimm/dxl096. [DOI] [PubMed] [Google Scholar]
  6. Chen JK, Taipale J, Cooper MK, Beachy PA. Inhibition of Hedgehog signaling by direct binding of cyclopamine to Smoothened. Genes Dev. 2002;16:2743–2748. doi: 10.1101/gad.1025302. [DOI] [PMC free article] [PubMed] [Google Scholar]
  7. Cooper MK, Porter JA, Young KE, Beachy PA. Teratogen-mediated inhibition of target tissue response to Shh signaling. Science. 1998;280:1603–1607. doi: 10.1126/science.280.5369.1603. [DOI] [PubMed] [Google Scholar]
  8. Daya-Grosjean L, Couve-Privat S. Sonic hedgehog signaling in basal cell carcinomas. Cancer Lett. 2005;225:181–192. doi: 10.1016/j.canlet.2004.10.003. [DOI] [PubMed] [Google Scholar]
  9. Endo H, Momota Y, Oikawa A, Shinkai H. Psoriatic skin expresses the transcription factor Gli1: possible contribution of decreased neurofibromin expression. Br J Dermatol. 2006;154:619–623. doi: 10.1111/j.1365-2133.2005.06975.x. [DOI] [PubMed] [Google Scholar]
  10. Fan H, Khavari PA. Sonic hedgehog opposes epithelial cell cycle arrest. J Cell Biol. 1999;147:71–76. doi: 10.1083/jcb.147.1.71. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Grachtchouk V, Grachtchouk M, Lowe L, Johnson T, Wei L, Wang A, de Sauvage F, Dlugosz AA. The magnitude of hedgehog signaling activity defines skin tumor phenotype. Embo J. 2003;22:2741–2751. doi: 10.1093/emboj/cdg271. [DOI] [PMC free article] [PubMed] [Google Scholar]
  12. Gudjonsson JE, Johnston A, Sigmundsdottir H, Valdimarsson H. Immunopathogenic mechanisms in psoriasis. Clin Exp Immunol. 2004;135:1–8. doi: 10.1111/j.1365-2249.2004.02310.x. [DOI] [PMC free article] [PubMed] [Google Scholar]
  13. Hutchin ME, Kariapper MS, Grachtchouk M, Wang A, Wei L, Cummings D, Liu J, Michael LE, Glick A, Dlugosz AA. Sustained Hedgehog signaling is required for basal cell carcinoma proliferation and survival: conditional skin tumorigenesis recapitulates the hair growth cycle. Genes Dev. 2005;19:214–223. doi: 10.1101/gad.1258705. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Incardona JP, Gaffield W, Lange Y, Cooney A, Pentchev PG, Liu S, Watson JA, Kapur RP, Roelink H. Cyclopamine inhibition of Sonic hedgehog signal transduction is not mediated through effects on cholesterol transport. Dev Biol. 2000;224:440–452. doi: 10.1006/dbio.2000.9775. [DOI] [PubMed] [Google Scholar]
  15. Ingham PW, Placzek M. Orchestrating ontogenesis: variations on a theme by sonic hedgehog. Nat Rev Genet. 2006;7:841–850. doi: 10.1038/nrg1969. [DOI] [PubMed] [Google Scholar]
  16. Irizarry RA, Bolstad BM, Collin F, Cope LM, Hobbs B, Speed TP. Summaries of Affymetrix GeneChip probe level data. Nucleic Acids Res. 2003;31:e15. doi: 10.1093/nar/gng015. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Johansen C, Flindt E, Kragballe K, Henningsen J, Westergaard M, Kristiansen K, Iversen L. Inverse regulation of the nuclear factor-kappaB binding to the p53 and interleukin-8 kappaB response elements in lesional psoriatic skin. J Invest Dermatol. 2005a;124:1284–1292. doi: 10.1111/j.0022-202X.2005.23749.x. [DOI] [PubMed] [Google Scholar]
  18. Johansen C, Kragballe K, Rasmussen M, Dam TN, Iversen L. Activator protein 1 DNA binding activity is decreased in lesional psoriatic skin compared with nonlesional psoriatic skin. Br J Dermatol. 2004;151:600–607. doi: 10.1111/j.1365-2133.2004.06088.x. [DOI] [PubMed] [Google Scholar]
  19. Johansen C, Kragballe K, Westergaard M, Henningsen J, Kristiansen K, Iversen L. The mitogen-activated protein kinases p38 and ERK1/2 are increased in lesional psoriatic skin. Br J Dermatol. 2005b;152:37–42. doi: 10.1111/j.1365-2133.2004.06304.x. [DOI] [PubMed] [Google Scholar]
  20. Kuenzli S, Sorg O, Saurat JH. Cyclopamine, hedgehog and psoriasis. Dermatology. 2004;209:81–83. doi: 10.1159/000079588. [DOI] [PubMed] [Google Scholar]
  21. Levy V, Lindon C, Harfe BD, Morgan BA. Distinct stem cell populations regenerate the follicle and interfollicular epidermis. Dev Cell. 2005;9:855–861. doi: 10.1016/j.devcel.2005.11.003. [DOI] [PubMed] [Google Scholar]
  22. Liu Y, Krueger JG, Bowcock AM. Psoriasis: genetic associations and immune system changes. Genes Immun. 2007;8:1–12. doi: 10.1038/sj.gene.6364351. [DOI] [PubMed] [Google Scholar]
  23. Lizzul PF, Aphale A, Malaviya R, Sun Y, Masud S, Dombrovskiy V, Gottlieb AB. Differential expression of phosphorylated NF-kappaB/RelA in normal and psoriatic epidermis and downregulation of NF-kappaB in response to treatment with etanercept. J Invest Dermatol. 2005;124:1275–1283. doi: 10.1111/j.0022-202X.2005.23735.x. [DOI] [PubMed] [Google Scholar]
  24. Lowrey JA, Stewart GA, Lindey S, Hoyne GF, Dallman MJ, Howie SE, Lamb JR. Sonic hedgehog promotes cell cycle progression in activated peripheral CD4(+) T lymphocytes. J Immunol. 2002;169:1869–1875. doi: 10.4049/jimmunol.169.4.1869. [DOI] [PubMed] [Google Scholar]
  25. McFerren MA. Useful plants of dermatology. VIII. The false hellebore (Veratrum californicum) J Am Acad Dermatol. 2006;54:718–720. doi: 10.1016/j.jaad.2005.11.1075. [DOI] [PubMed] [Google Scholar]
  26. McMahon AP, Ingham PW, Tabin CJ. Developmental roles and clinical significance of hedgehog signaling. Curr Top Dev Biol. 2003;53:1–114. doi: 10.1016/s0070-2153(03)53002-2. [DOI] [PubMed] [Google Scholar]
  27. Meth MJ, Weinberg JM. Cyclopamine: inhibiting hedgehog in the treatment of psoriasis. Cutis. 2006;78:185–188. [PubMed] [Google Scholar]
  28. Mullor JL, Sanchez P, Altaba AR. Pathways and consequences: Hedgehog signaling in human disease. Trends Cell Biol. 2002;12:562–569. doi: 10.1016/s0962-8924(02)02405-4. [DOI] [PubMed] [Google Scholar]
  29. Niemann C, Unden AB, Lyle S, Zouboulis Ch C, Toftgard R, Watt FM. Indian hedgehog and beta-catenin signaling: role in the sebaceous lineage of normal and neoplastic mammalian epidermis. Proc Natl Acad Sci U S A. 2003;100 Suppl 1:11873–11880. doi: 10.1073/pnas.1834202100. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Roessler E, Belloni E, Gaudenz K, Jay P, Berta P, Scherer SW, Tsui LC, Muenke M. Mutations in the human Sonic Hedgehog gene cause holoprosencephaly. Nat Genet. 1996;14:357–360. doi: 10.1038/ng1196-357. [DOI] [PubMed] [Google Scholar]
  31. Rubin LL, de Sauvage FJ. Targeting the Hedgehog pathway in cancer. Nat Rev Drug Discov. 2006;5:1026–1033. doi: 10.1038/nrd2086. [DOI] [PubMed] [Google Scholar]
  32. Ruiz i Altaba A, Mas C, Stecca B. The Gli code: an information nexus regulating cell fate, stemness and cancer. Trends Cell Biol. 2007;17:438–447. doi: 10.1016/j.tcb.2007.06.007. [DOI] [PMC free article] [PubMed] [Google Scholar]
  33. Sano S, Chan KS, Carbajal S, Clifford J, Peavey M, Kiguchi K, Itami S, Nickoloff BJ, DiGiovanni J. Stat3 links activated keratinocytes and immunocytes required for development of psoriasis in a novel transgenic mouse model. Nat Med. 2005;11:43–49. doi: 10.1038/nm1162. [DOI] [PubMed] [Google Scholar]
  34. Stewart GA, Lowrey JA, Wakelin SJ, Fitch PM, Lindey S, Dallman MJ, Lamb JR, Howie SE. Sonic hedgehog signaling modulates activation of and cytokine production by human peripheral CD4+ T cells. J Immunol. 2002;169:5451–5457. doi: 10.4049/jimmunol.169.10.5451. [DOI] [PubMed] [Google Scholar]
  35. Taipale J, Chen JK, Cooper MK, Wang B, Mann RK, Milenkovic L, Scott MP, Beachy PA. Effects of oncogenic mutations in Smoothened and Patched can be reversed by cyclopamine. Nature. 2000;406:1005–1009. doi: 10.1038/35023008. [DOI] [PubMed] [Google Scholar]
  36. Tas S, Avci O. Rapid clearance of psoriatic skin lesions induced by topical cyclopamine. A preliminary proof of concept study. Dermatology. 2004;209:126–131. doi: 10.1159/000079596. [DOI] [PubMed] [Google Scholar]
  37. Xie J, Murone M, Luoh SM, Ryan A, Gu Q, Zhang C, Bonifas JM, Lam CW, Hynes M, Goddard A, Rosenthal A, Epstein EH, Jr, de Sauvage FJ. Activating Smoothened mutations in sporadic basal-cell carcinoma. Nature. 1998;391:90–92. doi: 10.1038/34201. [DOI] [PubMed] [Google Scholar]

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