Gene for familial psoriasis susceptibility mapped to the distal end of human chromosome 17q

HLA-DQA1 and DQB1 alleles are associated with genetic susceptibility to psoriasis vulgaris in Chinese Han

BACKGROUND

Psoriasis vulgaris is a chronic skin disorder characterized by infiltration of inflammatory elements, keratinocyte hyperproliferation and altered differentiation. Although the pathogenesis of psoriasis is not fully understood, there is solid evidence of a susceptibility locus in the human leukocyte antigen (HLA) region.

OBJECTIVES

To investigate whether HLA-DQA1 and DQB1 alleles are associated with genetic susceptibility to psoriasis vulgaris in Chinese Han.

PATIENTS AND METHODS

The polymerase chain reaction-sequence-specific primer (PCR-SSP) method was used to analyse the distribution of HLA-DQA1 and DQB1 alleles in 189 patients with psoriasis and 273 healthy controls.

RESULTS

The HLA-DQA1*0104 (OR = 2.33, P = 0.0001154, Pc = 2.0 x 10-3), DQA1*0201 (OR = 3.36, P < 1.0 x 10-7, Pc < 1.0 x 10-6), DQB1*0201 (OR = 1.64, P = 0.0192, Pc > 0.05) and DQB1*0303 (OR = 1.55, P = 0.0377, Pc > 0.05) alleles were more prevalent in patients with psoriasis vulgaris than in controls, and HLA-DQA1*0501 (OR = 0.30, P = 0.0000039, Pc < 4.0 x 10-5) alleles were less prevalent. The HLA-DQA1*0104 (OR = 2.42, P = 0.0001159, Pc < 2.0 x 10-3), DQA1*0201 (OR = 3.74, P < 1.0 x 10-7, Pc < 1.0 x 10-6) and DQA1*0501 (OR = 0.30, P = 0.0000374, Pc < 4.0 x 10-4) alleles were only associated with type I psoriasis. HLA-DQA1*0104 and DQA1*0201 were more prevalent in patients with or without a family history of psoriasis. However, the DQA1*0501 allele was only more prevalent in patients without a family history of psoriasis.

CONCLUSION

HLA-DQA1*0104 and DQA1*0201 alleles may be psoriasis susceptibility genes or may be in close linkage with the susceptibility genes. The HLA-DQA1*0501 allele seems to have a protective effect against the development of psoriasis vulgaris in Chinese Han. There may be a difference in genetic background between psoriasis patients with and without a family history of psoriasis.

CD4+ T cell-associated pathophysiology critically depends on CD18 gene dose effects in a murine model of psoriasis

In a CD18 hypomorphic polygenic PL/J mouse model, the severe reduction of CD18 (beta(2) integrin) to 2-16% of wild-type levels leads to the development of a psoriasiform skin disease. In this study, we analyzed the influence of reduced CD18 gene expression on T cell function, and its contribution to the pathogenesis of this disease. Both CD4(+) and CD8(+) T cells were significantly increased in the skin of affected CD18 hypomorphic mice. But only depletion of CD4(+) T cells, and not the removal of CD8(+) T cells, resulted in a complete clearance of the psoriasiform dermatitis. This indicates a central role of CD4(+) T cells in the pathogenesis of this disorder, further supported by the detection of several Th1-like cytokines released predominantly by CD4(+) T cells. In contrast to the CD18 hypomorphic mice, CD18 null mutants of the same strain did not develop the psoriasiform dermatitis. This is in part due to a lack of T cell emigration from dermal blood vessels, as experimental allergic contact dermatitis could be induced in CD18 hypomorphic and wild-type mice, but not in CD18 null mutants. Hence, 2-16% of CD18 gene expression is obviously sufficient for T cell emigration driving the inflammatory phenotype in CD18 hypomorphic mice. Our data suggest that the pathogenic involvement of CD4(+) T cells depends on a gene dose effect with a reduced expression of the CD18 protein in PL/J mice. This murine inflammatory skin model may also have relevance for human polygenic inflammatory diseases.

A putative RUNX1 binding site variant between SLC9A3R1 and NAT9 is associated with susceptibility to psoriasis

Psoriasis (OMIM 177900) is a chronic inflammatory skin disorder of unknown pathogenesis affecting approximately 2% of the Western population. It occurs more frequently in individuals with human immunodeficiency virus, and 20-30% of individuals with psoriasis have psoriatic arthritis. Psoriasis is associated with HLA class I alleles, and previous linkage analysis by our group identified a second psoriasis locus at 17q24-q25 (PSORS2; ref. 7). Linkage to this locus was confirmed with independent family sets. Additional loci have also been proposed to be associated with psoriasis. Here we describe two peaks of strong association with psoriasis on chromosome 17q25 separated by 6 Mb. Associated single-nucleotide polymorphisms (SNPs) in the proximal peak lie in or near SLC9A3R1 (also called EBP50 and NHERF1) and NAT9, a new member of the N-acetyltransferase family. SLC9A3R1 is a PDZ domain-containing phosphoprotein that associates with members of the ezrin-radixin-moesin family and is implicated in diverse aspects of epithelial membrane biology and immune synapse formation in T cells. The distal peak of association is in RAPTOR (p150 target of rapamycin (TOR)-scaffold protein containing WD-repeats). Expression of SLC9A3R1 is highest in the uppermost stratum Malpighi of psoriatic and normal skin and in inactive versus active T cells. A disease-associated SNP lying between SLC9A3R1 and NAT9 leads to loss of RUNX1 binding. This is the second example of loss of a RUNX1 binding site associated with susceptibility to an autoimmune disease. It also suggests defective regulation of SLC9A3R1 or NAT9 by RUNX1 as a susceptibility factor for psoriasis.

Molecular cloning and characterization of alternatively spliced mRNA isoforms from psoriatic skin encoding a novel member of the S100 family

In an effort to identify psoriasis-associated genes, we compared gene expression in normal and psoriatic skin, using differential display RT-PCR technique. Sequence analysis of a 650-bp cDNA fragment (clone 110) that was highly up-regulated in lesional skin revealed homology to a noncoding cDNA (NICE-2). By subsequent cDNA cloning, using RNA from psoriatic skin, we have identified two alternatively spliced mRNA-isoforms (0.5 and 4.4 kb), which differ in composition of their untranslated regions. By sequence comparison, we have mapped the novel gene, named S100A15, to the S100 gene cluster within the epidermal differentiation complex (chromosome 1q21). Analysis of the deduced amino acid sequence revealed a protein of 101 amino acids containing two potential EF-hand motifs with high homology to the S100A7. Northern blot hybridization and semiquantitative RT-PCR analysis confirmed the S100A15 overexpression in psoriasis, showing different levels of expression of the S100A15 mRNA isoforms. In situ hybridization of the S100A15 revealed a markedly increased staining of basal and suprabasal epidermal layers of psoriatic skin compared with healthy tissue. Our data suggest an involvement of the novel S100A15 in epidermal differentiation and inflammation and might therefore be important for the pathogenesis of psoriasis and other diseases.

Genetic linkage studies in alopecia areata

Alopecia areata affects approximately 4.6 million individuals in the United States alone. It is typified by patchy hair loss on the scalp that can progress to cover the entire scalp (alopecia totalis) and eventually the entire body (alopecia universalis). Despite the high incidence of this condition, its genetic basis is largely unknown. It is now generally accepted, however, that it fits the paradigm of a complex trait, in which a combination of genetic and environmental factors results in the final phenotype. Genetic studies have been limited thus far to association analyses, which suggest that a permissive HLA status may potentiate the development of alopecia areata. A systematic screen for identifying the primary genetic mechanisms underlying this disorder has never before been undertaken, however. Here we discuss our approach to the identification of susceptibility genes for alopecia areata. In particular, we recently initiated a comprehensive genetic analysis by performing a genome-wide scan in a collection of alopecia families with multiple affected family members. There are currently a number of examples of complex diseases of the skin, such as psoriasis and atopic dermatitis, in which genetic studies are being undertaken that substantiate the timeliness of this approach. We anticipate that these studies will lead to the identification of the susceptibility genes and provide a foundation for understanding how they interact with each other and with other variables, such as the immune system and environmental factors.

Psoriasis Susceptibility Locus on 18p Revealed by Genome Scan in Finnish Families Not Associated with PSORS1

The major susceptibility locus for psoriasis, PSORS1, resides on chromosome 6p and includes the candidate genes HLA-C, HCR, and CDSN. Based on a nationwide collection of psoriasis patients and genotyping for the PSORS1 susceptibility haplotype, we selected for a genome scan nine families who do not show association with PSORS1 to more easily detect minor loci for psoriasis susceptibility. In the genome scan, five loci gave initial evidence of linkage and were studied with a denser marker map. After fine mapping, only one locus on 18p11.23 showed suggestive evidence of linkage (nonparametric multipoint linkage analysis score, 3.58; p = 0.0038). The bootstrapping analysis showed that one large family contributed the majority of the linkage (p = 0.0039), but was supported by other families. Haplotype sharing between the linked families and haplotype association analysis gave additional support for the locus. Further, the 18p locus has shown nominal evidence of linkage with psoriasis in the British population. Taken together, these findings confirm the presence of a minor susceptibility locus for psoriasis on 18p11.

HLA is a candidate region for psoriatic arthritis. evidence for excessive HLA sharing in sibling pairs

Psoriatic arthritis (PsA) is an inflammatory arthritis that may affect as many as 30% of patients with psoriasis (Ps). Genetic factors play an important role in the susceptibility to and the expression of PsA. The objective of this study was to identify whether haplotype sharing among affected sibling pairs of individuals with PsA is increased compared with unaffected sibling pairs. We collected 182 sibling pairs of probands affected with PsA. Extracted genomic DNA was amplified in polymerase chain reactions using locus specific primers homologous to nucleotide sequences for each of the HLA-A, -B, -C, -DR, and -DQ loci. Polymerase chain reaction amplicons were identified by reverse line blot assay using sequence-specific oligonucleotide probes. Evidence for excessive haplotype sharing was examined through Green and Woodrow's test. Results indicate that of the 182 sibling pairs, 46 were affected by PsA, 48 by Ps, and 88 were unaffected. The sharing of 2, 1, and 0 haplotypes for the PsA affected sibling pairs was 14, 27, and 5, respectively (p = 0.04); whereas the haplotype sharing for the Ps affected sibling pairs was 12, 26, and 10, respectively (p = 0.38). In conclusion, the human leukocyte antigen region on chromosome 6p is implicated as one of the candidate regions in PsA.

Polymorphisms in the SEEK1 and SPR1 genes on 6p21.3 associate with psoriasis in the Swedish population

Psoriasis is a chronic skin disease that results in red and scaly lesions. Several psoriasis susceptibility loci have been identified across the genome, of which PSORS1 on 6p21.3 is predominant. There is an ongoing debate regarding whether the HLA-C allele, Cw*0602, can be considered the major predisposing factor in this region. Investigation of other genes in the PSORS1 region with regard to psoriasis may provide alternate candidates to HLA-C. We have characterized two overlapping genes, SEEK1 and SPR1. SEEK1 encodes two putative protein isoforms: the first being one of 152 amino acids from the full-length splice-isoform (exon 1-6), and the second being one of 100 amino acids from an alternate splice-isoform (exon 1 and 6). SPR1 encodes a highly conserved protein of 134 amino acids, and in addition to characterization of human SPR1 we report the cloning of its orthologs in mouse and pig. Both SEEK1 and SPR1 are expressed in normal and psoriasis skin. In a case-control study, five of the nine single nucleotide polymorphisms (SNPs) found in SEEK1 were associated with psoriasis, while one of the four SNPs found in SPR1 showed association. Testing the Cw*0602 confounding status revealed that two of the SEEK1 SNPs showed Cw*0602-independent association, while the SPR1 SNP showed Cw*0602-dependent association. The second exon of SEEK1, containing the two Cw*0602-independent SNPs, showed the highest concentration of the psoriasis-associating SNPs, but did not appear to be translated.

The International Psoriasis Genetics Study: assessing linkage to 14 candidate susceptibility loci in a cohort of 942 affected sib pairs

In an effort to confirm previously reported linkages to psoriasis, we analyzed 942 affected sibling pairs (ASPs) from 710 pedigrees for 53 polymorphic microsatellites spanning 14 psoriasis candidate regions at an intermarker spacing of approximately 5 cM. Maximum LOD score (MLS) analysis of ASPs yielded allele sharing of 60% for markers within the major histocompatibility complex (MHC) (P=2 x 10(-14)), which yielded a gene-specific lambda(s) of 1.6. Across the remainder of the genome, the strongest evidence of allele sharing was obtained on chromosomes 16q (D16S3032; MLS=1.3; P=.007) and 10q22-q23 (D10S2327; MLS=1.1; P=.012). None of the remaining loci exceeded MLS=0.9, the value expected to occur by chance once in this study. In agreement with previous studies, strong linkage disequilibrium was also observed between psoriasis and the MHC (pedigree disequilibrium test P=3.9 x 10(-8) for D6S1014). Two psoriasis-associated MHC haplotypes were identified with the haplotype-based transmission/disequilibrium test. Analysis of only those families carrying either of these haplotypes significantly increased the chromosome 16q LOD score from 1.3 to 2.4 (P=.045). These results underscore the importance of the MHC in psoriasis and provide a rationale for more-detailed examination of candidate regions on chromosomes 16q and 10q.

Genetics of psoriasis: the potential impact on new therapies

There is considerable epidemiologic evidence that genes play a key role in the pathogenesis of psoriasis. It is also clear that multiple genes are involved and that the disease is genetically heterogeneous. Important interactions with the environment are also implicated in its development. A number of genetic loci have been identified by genome wide linkage scans and two loci have been replicated: PSORS1 on chromosome 6, within the major histocompatibility complex, and PSORS2 on chromosome 17q. Understanding the genetic basis of psoriasis will represent a major advance in our understanding of the disease and will reveal novel disease-specific biologic pathways. This information will be used to develop more specific diagnostic and prognostic tools and also lead to the development of individualized treatment plans. Benefits of the latter include more effective and safer treatments and potentially major pharmaco-economic gain.

Association scan of the novel psoriasis susceptibility region on chromosome 19: evidence for both susceptible and protective loci

To follow up the novel psoriasis susceptibility region on chromosome 19 (PSORS6), we performed an association scan for psoriasis vulgaris using 45 evenly spaced DNA microsatellite markers. For this study, a new independent sample of 210 nuclear psoriasis families (trio design) from Northern Germany was recruited. We used the family based association test (FBAT) for an association scan over the chromosome 19 region encompassing 50.8 cM. We obtained a positive association for the markers D19S922 (allele 5, P = 0.008) and D19S916 (allele 13, P = 0.016), which correspond to the peak of the region identified in a previously performed scan. We identified two novel regions by a single marker, each showing negative association at D19S917 on 19p13.1 (allele 8, P = 0.0034) and at D19S425 (allele 9, P = 0.0005), compatible with the hypothesis of protective loci. These two novel regions were explored in more detail using novel microsatellite markers at an average distance of 100 kb. A separate analysis distinguishing between familial (n = 137) and sporadic (n = 73) psoriasis families showed that the familial trios contribute strongly in the region around D19S425 (P = 0.004), while the comparably small subset of 73 sporadic trios has a stronger effect at the locus around D19S917 (P = 0.026). These studies confirm the existence of a psoriasis susceptibility locus on chromosome 19 and give first evidence for the existence of both susceptible and protective loci in this region. Analysis of a dense marker set from these refined regions will eventually allow identification of the underlying susceptibility alleles.

Current concepts in psoriasis and its treatment

Many advances have been made in our understanding of the biology of psoriasis over the past 20 years. We are close to knowing the genetic determinants of psoriasis. There is now greater insight into the immunological mechanisms that produce the phenotype, and the possibility of intervening selectively to antagonise some of these mechanisms is becoming a reality. Nevertheless, psoriasis remains an enigmatic disease, and much of the suffering it produces is not adequately addressed. The sheer number of treatments that are used therapeutically suggests a lack of efficacy and/or toxicity of many of these approaches. In this review, we aim to briefly describe the biology of psoriasis, document the key features of treatments that are available or under development, and explain how these treatments can be used effectively to manage this chronic relapsing disease.

Connections between psoriasis and Crohn's disease

The prevalence of psoriasis in patients with Crohn's disease (CD) is higher than chance would allow if they were mutually exclusive diseases. A close examination reveals genetic and pathologic connections between these diseases. An appreciation for the role of tumor necrosis factor-alpha in both diseases has proven very important. Increased levels of this inflammatory cytokine have been measured in CD lesions, and in 1997 a clinical trial demonstrated the response of this disease to infliximab, a monoclonal antibody specific for tumor necrosis factor-alpha. A subsequent clinical trial evaluated infliximab in a patient with CD and psoriasis, another disease in which increased levels of tumor necrosis factor-alpha are seen in lesions. Scientists noticed the marked skin improvement of this patient and later demonstrated the efficacy of infliximab for psoriasis in a randomized, double-blind, placebo-controlled trial. Thus, an appreciation for connections between psoriasis and CD can suggest novel therapeutic strategies with ensuing benefits to patients. This article reviews epidemiologic, genetic, and pathologic connections between psoriasis and CD and discusses pharmaceuticals targeting inflammatory mediators common to each disease. (J Am Acad Dermatol 2003;48:805-21.)

LEARNING OBJECTIVE

At the completion of this learning activity, participants should understand how psoriasis and Crohn's disease are related at epidemiologic, genetic, and pathological levels and should appreciate how to use this knowledge to treat these diseases.

Genetic basis of psoriasis vulgaris and its pharmacogenetic potential

Psoriasis vulgaris is one of the most prevalent T cell-mediated inflammatory diseases in humans. It is multifactorial in origin and shows polygenic inheritance. Systemic immunosuppressive therapies play an important role in management of severe disease cases but are associated with variable response and toxicity. Within the last decade there have been significant advances in our understanding of the genetic basis of this complex disease and polymorphic candidate genes have been proposed. Susceptibility gene characterization together with an explosion in knowledge of its primary immune basis will further define disease pathways involved in psoriasis pathogenesis. This holds the promise of rational design of new therapeutic agents and pharmacogenetic testing to predict responders from non-responders and those at risk of toxicity.

Confirmation of PSORS psoriasis susceptibility loci in a Chinese population

We investigated 38 Chinese psoriasis families with 19 reported microsatellite markers. Families comprised a total of 96 affected and 92 unaffected individuals. Genotyping results were analyzed using parametric and nonparametric linkage analysis. Our results confirmed the published linkage with the PSORS1 locus, as well as the PSORS2 locus, which has not been previously shown in the Chinese population. Significant two-point LOD scores were obtained in a parametric linkage analysis with markers D6S1610 and D17S944. Nonparametric linkage values greater than 1.6 ( P<0.05) were obtained with markers D6S1610, D17S944 and D17S785.

Evidence for a major psoriasis susceptibility locus at 6p21(PSORS1) and a novel candidate region at 4q31 by genome-wide scan in Chinese hans

Psoriasis is a heterogeneous disease with seven major psoriasis susceptibility loci reported so far on chromosomes 1p, 1q, 3q, 4q, 6p, 17q, and 19p, respectively. To investigate the psoriasis susceptibility loci in Chinese Hans, a genome-wide scan was performed with two-point and multipoint parametric and nonparametric linkage analyses in 61 multiplex families. These families were Chinese Hans residing in east and south-east China, comprising 189 affected and 166 unaffected individuals. We detected evidence for linkage at 6p21 (PSORS1) with nonparametric linkage scores > 3 in the range of 39.9-62.3 cM and a maximum multipoint nonparametric linkage score of 4.58 (p=0.000032). Parametric analysis revealed a maximum two-point heterogeneity lod score of 4.30 with 58% as the proportion of linked families (alpha) and a maximum multipoint heterogeneity lod score of 4.25 (alpha=53%) under the assumption of a dominant model. We could not confirm a previous reported locus (PSORS3) on distal chromosome 4q; however, a region of highly suggestive linkage was identified proximal to this proposed locus. Multipoint nonparametric analysis demonstrated nonparametric linkage scores > 3 throughout a region between 152.5 cM and 165.1 cM (from pter) with a maximum peak of 3.69 (p=0.00033) at 157.9 cM, which locates D4S413. A maximum multipoint heterogeneity lod score of 2.31 (alpha=46%) was reached at 163.1 cM. With two-point parametric linkage analysis, we observed the highest lod score of 2.43 and heterogeneity lod score of 3.94 (alpha=77%) at marker D4S1597. Our results showed that chromosomes 6p and 4q may contain genes involved in the susceptibility to psoriasis vulgaris in a Chinese Han population. Other regions with weaker evidence for linkage could also hide minor susceptibility genes.

Genetics and genomics of asthma and allergic diseases

Asthma and eczema (atopic dermatitis) are characterized by a number of unexplained phenomena: the familial aggregation of disease, the initiation of disease by apparently trivial exposure to allergens, the preferential transmission of disease from affected mothers and the large increase in prevalence of disease in Westernized societies in the last century. A number of genes and chromosomal regions have been identified that consistently show linkage to asthma and its related phenotypes. Known loci modify the strength of the atopic response, nonspecific inflammation, the ability to respond to particular allergens and nonspecific airway reactivity. Eczema has been shown to be due to a different set of genetic loci that are shared with other skin diseases such as psoriasis and leprosy. Genetic and genomic studies both provide evidence that epithelial surfaces are active in the induction of allergic disease.

Identification of the hRDH-E2 gene, a novel member of the SDR family, and its increased expression in psoriatic lesion

To identify novel psoriasis-associated genes, we focused on several ESTs (expressed sequence tags) whose expression was predominantly increased in the affected skin in patients with psoriasis vulgaris, as assessed by microarray assay. In this paper, a full-length cDNA corresponding to one of those ESTs (AI440266) was isolated by screening of cultured human keratinocyte cDNA libraries. This cDNA has an open reading frame of a 309-amino-acid protein, sharing significant homology to one of the short-chain alcohol dehydrogenase/reductase (SDR) families that can catalyze the first and rate-limiting step that generates retinaldehyde from retinol. So, this gene was designated as hRDH-E2 (human epidermal retinal dehydrogenase 2). The hRDH-E2 gene has a single functional copy on chromosome 8q12.1, spanning approximately 20kb with seven exons. The deduced amino acid sequence contains three motifs that are conserved in the SDR family. Qualitative RT-PCR demonstrated that the mRNA levels of hRDH-E2 were significantly elevated in the affected skin in psoriasis patients as compared to the unaffected skin in patients and the normal skin in healthy individual. These results suggest that hRDH-E2 may be involved in the pathogenesis of psoriasis through its critical role in retinol metabolism in keratinocyte proliferation.

The genetics of atopic dermatitis

PURPOSE OF REVIEW

Atopic dermatitis is typified by itchy, inflamed skin. It is increasingly common in the developed world and is a major cause of morbidity in infants and young children. Most children with the disease have high levels of immunoglobulin E and many have concomitant asthma. The cause of the disease is unknown, but it is highly heritable. Identification of the genes and genetic variants underlying atopic dermatitis may lead to new treatments and better classification of children with the disease.

RECENT FINDINGS

Preliminary genetic studies have identified genes or clusters of genes that are expressed in the outermost layer of the skin to be just as important as genes that may modify the atopic process. These genes may influence other diseases, including psoriasis. Genome screens in mouse models seem to indicate involvement of some of the equivalent chromosomal regions as for human disease.

SUMMARY

The findings suggest that atopy in atopic dermatitis may be a secondary process, rather than the cause of the disease. The barrier function of the skin is seen not to be merely passive. Identification of the genes underlying atopic dermatitis is feasible and likely within a few years.

Psoriasis is associated with a SNP haplotype of the corneodesmosin gene (CDSN)

A psoriasis susceptibility locus has been mapped to the HLA region in the proximity of the HLA-C locus. This critical region also contains the CDSN gene coding for the corneodesmosin protein. In a case-control association study of psoriasis in the Sardinian population, we analyzed the allele distribution of eight intragenic SNPs (positions 619, 767, 1215, 1118, 1236, 1243, 1331, 1593) of the CDSN gene and the six haplotypes that are coded by these SNPs. Our study showed that these CDSN haplotypes are very stable and well-conserved in the Sardinian population. The CDSN2 haplotype was found to be associated with susceptibility to psoriasis. The association did not depend upon any one of the intragenic SNPs taken separately. At the HLA-C locus, the Cw6 and Cw7 alleles were dragged along by linkage disequilibrium with the CDSN2 haplotype and only revealed a trend towards association with the disease. Therefore, the intragenic SNPs of the CDSN gene and the HLA-Cw6 and Cw7 alleles are not directly involved in susceptibility to psoriasis. However, the strong association of the CDSN2 haplotype suggests a possible role for the CDSN gene and its chromosome region in susceptibility to psoriasis.

Susceptibility locus for epidermodysplasia verruciformis not linked to cervical cancer in situ

Cervical cancer is strongly associated with infection by oncogenic forms of human papillomavirus (HPV), mainly HPV 16 and HPV 18. The aim of this study was to test if a locus previously mapped to a region on chromosome 17 qter in patients with epidermodysplasia verucciformis (EV) and psoriasis and considered to be responsible for an increased susceptibility to HPV 5, also is linked to increased HPV susceptibility in cervical cancer in situ. We also wanted to test whether HPV 16 positivity cluster in families with cervical cancer. DNA was extracted from formalin fixed biopsies of 224 affected from 77 families diagnosed with cervical cancer in situ. Two microsatellite markers (D17S939 and D17S802) containing the locus were genotyped and linkage analysis was performed. No linkage was found to any of the two markers, neither when considering all cancer cases as affected nor when only considering HPV 16 infected cancer cases as affected in the analysis. We conclude that the susceptibility locus for HPV 5 infections associated with EV and psoriasis does not seem to affect susceptibility to HPV 16, frequently detected in cervical cancer. Also, positivity for HPV 16 did not show a significant clustering in families.

Searching for the major histocompatibility complex psoriasis susceptibility gene

Psoriasis, a common skin disorder, is widely regarded to be multifactorial in origin including gene-gene and gene-environment interactions. Genetic and allelic heterogeneity, multifactorial inheritance, and low penetrance of susceptibility alleles substantially complicate both study design and interpretation of results. Notwithstanding these difficulties, genome-wide scans for psoriasis susceptibility have generated robust evidence for a major locus lying within the major histocompatibility complex (PSORS1, Psoriasis Susceptibility 1), on the short arm of chromosome 6. Subsequent studies have sought to refine the PSORS1 boundaries by means of linkage disequilibrium fine mapping. Studies of positional candidate genes have also been undertaken, focusing on HLA-C, corneodesmosin, and alpha-helix coiled-coil rod homolog genes. Methodologic approaches, results, and interpretations of these studies are discussed, as well as future research objectives. In particular, we emphasize the importance of characterizing PSORS1 linkage disequilibrium patterns and developing functional assays for disease-associated alleles.

Combined segregation and linkage analysis of HLA markers in familial psoriasis

Marker-based segregation analysis (MBSA) is a modification of a published method of combined linkage and segregation analysis (Am J Hum Genet 51: 1111-1126, 1992), to determine whether a candidate gene known to be associated with the disease of interest is truly segregating with the disease in families. Here we outline the conceptual basis of MBSA and present a Monte Carlo method for significance testing. The method is applied to PSORS1, a locus within the major histocompatibility complex (MHC) for which linkage and linkage disequilibrium with psoriasis has already been demonstrated. The results are very consistent with our current knowledge of PSORS1, and suggest that MBSA can provide useful information on genotype-phenotype relationships such as penetrance and allelic heterogeneity.

The evaluation of the sociodemographic and clinical features of Turkish psoriasis patients

BACKGROUND

Psoriasis is a common, chronic and recurrent, inflammatory disease of the skin. With no sociodemographic psoriasis data available in Turkey, we decided to investigate the clinical features and distribution of this disease in our country.

METHODS

The records of 329 patients with psoriasis were retrospectively reviewed.

RESULTS

Psoriasis constituted 1.3% of the total dermatological disorders. Sixty-one per cent of the patients were female, and 39% were male. The mean age at onset of disease was 25 +/- 16 years in females, and 28 +/- 15 years in males. Family history was positive 30% of the patients. A positive family history was observed in 25% of the females and 37% of the males. 312 cases (95%) had psoriasis vulgaris, 17 cases (5%) had pustular psoriasis. Of the patients with psoriasis vulgaris, 212 (68%) had plaque, 73 (23%) guttate, 18 (6%) palmoplantar, 9 (3%) inverse type. The mean and median PASI score were 3.7 +/- 3.8 & 2.7 for females, 5.4 +/- 6.1 & 3.5 for males, respectively. 1.5% of patients had psoriatic arthropathy. Nail changes were seen in 54 (16%) of the cases. The various nail involvement types observed in descending frequency were: pitting (13%), subungual hyperkeratoses (7%), onycholysis (2%), discoloration (1.5%), oily spot (1%) and splinter hemorrhages (0.3%).

CONCLUSIONS

The prevalence of psoriasis in Turkey is similar to numbers reported in South America and Germany. Females were predominant, and the mean age of onset was lower in women. Positive family history was more frequent in males. Plaque type psoriasis was the most common presentation. The difference between mean PASI scores of female and male patients was not statistically significant. Psoriatic arthritis was extremely rare in Turkish psoriasis patients. Pitting was the most common abnormality of the nails.

Identification of a psoriasis susceptibility candidate gene by linkage disequilibrium mapping with a localized single nucleotide polymorphism map

Psoriasis is a chronic inflammatory disease of the skin with both genetic and environmental risk factors. Here we describe the creation of a single-nucleotide polymorphism (SNP) map spanning 900-1200 kb of chromosome 3q21, which had been previously recognized as containing a psoriasis susceptibility locus, PSORS5. We genotyped 644 individuals, from 195 Swedish psoriatic families, for 19 polymorphisms. Linkage disequilibrium (LD) between marker and disease was assessed using the transmission/disequilibrium test (TDT). In the TDT analysis, alleles of three of these SNPs showed significant association with disease (P<0.05). A 160-kb interval encompassing these three SNPs was sequenced, and a coding sequence consisting of 13 exons was identified. The predicted protein shares 30-40% homology with the family of cation/chloride cotransporters. A five-marker haplotype spanning the 3' half of this gene is associated with psoriasis to a P value of 3.8<10(-5). We have called this gene SLC12A8, coding for a member of the solute carrier family 12 proteins. It belongs to a class of genes that were previously unrecognized as playing a role in psoriasis pathogenesis.

HLA-Cw6-positive and HLA-Cw6-negative patients with Psoriasis vulgaris have distinct clinical features

Psoriasis is associated with HLA-Cw6, and Caucasians who carry this allele have about a 10-fold increased risk of developing psoriasis. We have HLA-C typed 369 patients with familial psoriasis and compared the clinical features of the patients carrying HLA-Cw6 against those carrying other HLA-C types. Some striking clinical differences were observed between the two groups. Patients who are Cw6 positive had a lower age at onset (p=3x10(-7)). Cw6-positive women had an earlier disease onset than Cw6-positive men (p =0.02), but such a difference was not observed for the Cw6-negative patients. The guttate-type onset of psoriasis was mostly confined to this group (p=2x10(-4)) and persistent disseminated guttate-like papules were also predominantly observed in the Cw6-positive patients (p <10(-)4). The Cw6-positive patients also had more extensive plaques on their arms, legs, and trunk (p =0.001), more severe disease (p =0.003), higher incidence of the Koebner's phenomenon (p =0.005), reported more often that their psoriasis got worse during or after throat infections (p =0.02), and more often a favorable response to sunlight (p =0.008) In contrast, dystrophic nail changes were more common in the Cw6-negative patients (p =0.002) and also psoriatic arthritis, although this was not significant (p =0.135). It is concluded that patients with psoriasis have different clinical features depending on whether they are HLA-Cw6 positive or negative.

Genomewide scans of complex human diseases: true linkage is hard to find

Many "complex" human diseases, which involve multiple genetic and environmental determinants, have increased in incidence during the past 2 decades. During the same time period, considerable effort and expense have been expended in whole-genome screens aimed at detection of genetic loci contributing to the susceptibility to complex human diseases. However, the success of positional cloning attempts based on whole-genome screens has been limited, and many of the fundamental questions relating to the genetic epidemiology of complex human disease remain unanswered. Both to review the success of the positional cloning paradigm as applied to complex human disease and to investigate the characteristics of the whole-genome scans undertaken to date, we created a database of 101 studies of complex human disease, which were found by a systematic Medline search (current as of December 2000). We compared these studies, concerning 31 different human complex diseases, with regard to design, methods, and results. The "significance" categorizations proposed by Lander and Kruglyak were used as criteria for the "success" of a study. Most (66.3% [n=67]) of the studies did not show "significant" linkage when the criteria of Lander and Kruglyak (1995) were used, and the results of studies of the same disease were often inconsistent. Our analyses suggest that no single study design consistently produces more-significant results. Multivariate analysis suggests that the only factors independently associated with increased study success are (a) an increase in the number of individuals studied and (b) study of a sample drawn from only one ethnic group. Positional cloning based on whole-genome screens in complex human disease has proved more difficult than originally had been envisioned; detection of linkage and positional cloning of specific disease-susceptibility loci remains elusive.

Papulosquamous disorders of the elderly

Several papulosquamous skin conditions occur in the elderly, including inherited and acquired ichthyoses, psoriasis, cutaneous lymphoma, and cutaneous connective tissue diseases. The clinical presentations can be quite helpful in diagnosing these conditions, and confirmatory histology and immunologic testing can often better define the specific entities. Treatment often involves identifying underlying systemic causes, as well as specific approaches based on the diagnosis and severity of clinical presentation.

Disease mechanisms in psoriasis and psoriatic arthritis

Any hypothesis that tries to explain disease mechanisms in psoriasis and psoriatic arthritis (PsA) must take into account the containment of the inflammatory process to three specific sites: the skin, synovium, and enthesis. This article reviews the recent literature that advances our understanding of disease mechanisms at these specific sites. Additional progress will be achieved by research that focuses on common pathogenic pathways at these sites, in particular when searching for foreign candidates or auto-antigens triggering the T-cell-mediated immune response.

Skin disorders and thyroid diseases

Thyroid disorders have a high prevalence in medical practice; they are associated with a wide range of diseases with which they may or may not share etiological factors. One of the organs which best show this wide range of clinical signs is the skin. This review is an attempt to approach most of the dermopathies reflecting several degrees of harmfulness, coming directly or indirectly from thyroid abnormalities, as well as to update current knowledge on the relationship between the thyroid and skin. We have proposed a primary classification of skin disorders, regarding thyroid involvement, into two main groups: 1) dermopathies associated with thyroid abnormalities, mainly with autoimmune thyroid diseases, like melasma, vitiligo, Sjogren's syndrome, alopecia, idiopathic hirsutism, pre-menstrual acne, bullous diseases, connective tissue diseases, hamartoma syndrome, atopy, leprosy and DiGeorge anomaly; and 2) dermopathies depending on the nature of the thyroid disorder, in which the evolution and outcome of the skin disorder depend on the thyroidal treatment in most cases, such as trophism and skin blood flow, myxedema, alopecia, onychodystrophy, hypo- and hyperhidrosis, xanthomas, intraepidermal bullae, carotenodermia, pruritus, flushing, pyodermitis, palmoplantar keratoderma, ecchymosis, etc. In some other cases, the skin disease which developed as a consequence of the thyroid abnormality can remain unaltered despite functional treatment of the thyroid problem, such as pretibial myxedema, thyroid acropachy and some cutaneous manifestations of multiple endocrine neoplasia types 2A and 2B.

Psoriatic arthritis: clinical aspects, genetics, and the role of T cells

In the last 2 years there has been considerable progress in investigating the genetic and immunologic background of psoriasis and psoriatic arthritis. This review focuses on genetics and the role of T-cells in the immunopathogenesis of the disease, with particular reference to psoriatic arthritis.

Genetic aspects of psoriasis

Epidemiological studies indicate that genes play an important role in the pathogenesis of psoriasis. Multiple genes are likely to be involved, interacting not only with each other but also with the environment to cause disease expression. Molecular genetic studies indicate that there are multiple susceptibility loci present throughout the human genome. It is clear that a gene or genes of major impact on psoriasis is present on chromosome 6 within the major histocompatibility complex (MHC). Linkage disequilibrium studies indicate this gene to reside within a 300 kb interval centred around the centromeric end of class I MHC. Known candidate genes in this region are HLA-C, corneodesmosin and HCR, although novel genes, as yet unknown, may also exist. There is accumulating evidence that HLA-C is not itself the causative gene but rather a marker for it. Identification of the genes involved in psoriasis susceptibility will represent a step forward in our understanding of the disease and our future ability to help patients with psoriasis.

Antagonistic effects of the staphylococcal enterotoxin a mutant, SEA(F47A/D227A), on psoriasis in the SCID-hu xenogeneic transplantation model

Psoriasis is a T-cell-mediated immune dermatosis probably triggered by bacterial superantigens. This pathomechanism has been experimentally reproduced in a SCID-hu xenogeneic transplantation model. We analyzed the effects of different bacterial superantigens on the induction of psoriasis in this model. Staphylococcal enterotoxin B and exfoliative toxin triggered the onset of psoriasis when administered repetitively intracutaneously over a period of 2 wk, whereas staphylococcal enterotoxin A representing a distinct subfamily of staphylococcal enterotoxins only mimicked certain aspects of psoriasis. The biologic effects of staphylococcal enterotoxin A were more pronounced when a mutated form, SEA(H187A), of this superantigen with reduced affinity to major histocompatibility complex class II was coinjected. Another mutated variant, SEA(F47A/D227A), exhibiting no measurable major histocompatibility complex class II affinity blocked the effects triggered by wild-type staphylococcal enterotoxin A when injected in a 10-fold higher dose. Inhibition was specific as induction of psoriasiform epidermal changes by staphylococcal enterotoxin B could not be blocked. As staphylococcal enterotoxin A, in contrast to the other superantigens tested, is capable of inducing epidermal thickening but not the typical appearance of psoriasis, we conclude that bacterial superantigens may differ with regard to their effects on human nonlesional psoriatic skin. Staphylococcal-enterotoxin-A-mediated effects were blocked by a genetically engineered superantigen highlighting the potential therapeutic use of mutated superantigens.

Psoriasis: the future

The aetiology of psoriasis is still unclear but our knowledge of the psoriatic process has grown substantially over the last two decades. The future will undoubtedly bring advances in our understanding of the pathogenesis of psoriasis and, as a consequence, new therapies. Defining the molecular genetics of psoriasis will enhance our understanding of the disease process and hopefully facilitate the development of a representative animal model. This in itself will be a key step in the development and testing of new therapies. Precise identification of the immunological events involved in psoriasis will allow specific T-cell- and cytokine-targeted, and perhaps less toxic. immunotherapies. Anti-angiogenic agents that are in development for use in oncology may also be effective in psoriasis. The adaptation of current topical therapies such as retinoids and vitamin D analogues to produce more effective and better-tolerated formulations will also play a significant role in our future first-line management of patients. The increased recognition and better management of environmental trigger factors such as psychological distress will become an important factor in future psoriasis care. The development of physical therapies including photodynamic therapy and excimer lasers has the potential to expand the remit of psoriasis therapy. There is little doubt that the future for our patients with psoriasis is bright. However, this will only be achievable by a concerted research effort to understand all facets of this enigmatic disease ranging from the molecular to the environmental.

Genetic linkage of childhood atopic dermatitis to psoriasis susceptibility loci

We have carried out a genome screen for atopic dermatitis (AD) and have identified linkage to AD on chromosomes 1q21, 17q25 and 20p. These regions correspond closely with known psoriasis loci, as does a previously identified AD locus on chromosome 3q21. The results indicate that AD is influenced by genes with general effects on dermal inflammation and immunity.

Identification of a novel psoriasis susceptibility locus at 1p and evidence of epistasis between PSORS1 and candidate loci

The pathogenesis of all forms of psoriasis remains obscure. Segregation analysis and twin studies together with ethnic differences in disease frequency all point to an underlying genetic susceptibility to psoriasis, which is both complex and likely to reflect the action of a number of genes. We performed a genome wide analysis using a total of 271 polymorphic autosomal markers on 284 sib relative pairs identified within 158 independent families. We detected evidence for linkage at 6p21 (PSORS1) with a non-parametric linkage score (NPL)=4.7, p=2 x 10(-6) and at chromosome 1p (NPL=3.6, p=1.9 x 10(-4)) in all families studied. Significant excess (p=0. 004) paternal allele sharing was detected for markers spanning the PSORS1 locus. A further three regions reached NPL scores of 2 or greater, including a region at chromosome 7 (NPL 2.1), for which linkage for a number of autoimmune disorders has been reported. Partitioning of the data set according to allele sharing at 6p21 (PSORS1) favoured linkage to chromosomes 2p (NPL 2.09) and 14q (NPL 2.0), both regions implicated in previous independent genome scans, and suggests evidence for epistasis between PSORS1 and genes at other genomic locations. This study has provided linkage evidence in favour of a novel susceptibility locus for psoriasis and provides evidence of the complex mechanisms underlying the genetic predisposition to this common skin disease.

The OTF3 gene polymorphism confers susceptibility to psoriasis independent of the association of HLA-Cw*0602

Psoriasis has been strongly associated to HLA-Cw6, but it remains unclear whether Cw6 itself or a closely linked gene is associated with the disease. The aim of this study was to clarify whether the HLA-C itself determines disease susceptibility or whether it acts only as a marker for the susceptibility allele. We examined a sample of 95 type I psoriasis patients and 104 Spanish matched controls to investigate whether HLA-Cw*0602 or other closely related class I loci, such as HLA-B and MICA (which are centromeric to HLA-C), or corneodesmosin gene and octamer transcription factor-3 genes (which are telomeric to HLA-C), might play a part in disease development. DNA samples were genotyped by polymerase chain reaction/sequence-specific primers (HLA-C), polymerase chain reaction/sequence-specific primers (HLA-B), radioactive polymerase chain reaction (MICA-TM polymorphism in the transmembrane region), and polymerase chain reaction/restriction fragment length polymorphism (protein S and octamer transcription factor-3). Our results show a significant increase of Cw*0602 in psoriasis patients (odds ratio = 3.64; pc < 0.0006). A significant association between the beta allele of octamer transcription factor-3 (HindIII) and psoriasis was also detected (odds ratio = 3.76; pc < 0.0003). The allele octamer transcription factor-3B (etiologic fraction = 0.62) was found to be more strongly associated to psoriasis vulgaris than Cw*0602 (etiologic fraction = 0.35) and the increase of octamer transcription factor-3 B allele is independent of the linkage disequilibrium with Cw*0602 as this was also found in Cw*0602 negative patients (odds ratio = 3.63; pc < 0.015, etiologic fraction = 0.55). We did not detect an association between the corneodesmosin gene and psoriasis. This fact suggests that the psoriasis susceptibility gene is located within a critical region of 147 kb, telomeric to HLA-C and centromeric to the corneodesmosin gene, and the association of Cw6 to psoriasis may be secondary to linkage disequilibrium.

Drug-induced suppression of phosphorylase kinase activity correlates with resolution of psoriasis as assessed by clinical, histological and immunohistochemical parameters

BACKGROUND

Phosphorylase kinase (PhK), also known as adenosine triphosphate (ATP)-phosphorylase b phosphotransferase, integrates multiple calcium/calmodulin-dependent signalling pathways, including those involved in cell migration and cell proliferation, while coupling these pathways to glycogenolysis and ATP-dependent phosphorylation, thus ensuring continuing energy supply for these activities.

OBJECTIVES

Our laboratory recently reported correlation of elevated PhK activity with psoriatic activity. This study further evaluates the significance of drug-induced suppression of PhK activity on psoriatic activity.

PATIENTS AND METHODS

PhK activity was assayed in four groups, each with 10 patients: (i) active untreated psoriasis; (ii) resolving psoriasis treated by calcipotriol (Dovonex(R), Bristol Myers Squibb, Princeton, NJ, U.S.A. ), a vitamin D3 analogue and an indirect inhibitor of PhK; (iii) curcumin (diferuloylmethane), a selective PhK inhibitor; and (iv) 10 normal non-psoriatic subjects.

RESULTS

PhK activity in units mg-1 protein was highest in active untreated psoriasis (1204 +/- 804.3; mean +/- SD), lower in the calcipotriol-treated group (550.7 +/- 192. 9), lower in curcumin-treated group (207.2 +/- 97.6), and lowest in normal skin (105.4 +/- 44.6). One-way analysis of variance performed on log-transformed PhK activity measure showed significant differences among the four groups, F3,36 = 48.79, P < 0.0001. Decreased PhK activity in curcumin-and calcipotriol-treated psoriasis was associated with corresponding decreases in keratinocyte transferrin receptor (TRR) expression, severity of parakeratosis and density of epidermal CD8+ T cells.

CONCLUSIONS

Our results demonstrate that drug-induced suppression of PhK activity is associated with resolution of psoriatic activity as assessed by clinical, histological and immunohistochemical criteria, and support the hypothesis that effective antipsoriatic activity may be achieved through modulation of PhK activity.

Genomewide scan in german families reveals evidence for a novel psoriasis-susceptibility locus on chromosome 19p13

Psoriasis is a common chronic inflammatory skin disease with a strong genetic component. Few psoriasis-susceptibility loci have been reported, and only two have been confirmed in independent data sets. This article reports results of a genomewide scan that was performed, using 370 microsatellite markers, for psoriasis-susceptibility loci in 32 German extended families, comprising 162 affected and 195 unaffected individuals. Nonparametric linkage analysis of all families provided strong evidence for a novel psoriasis-susceptibility locus on chromosome 19p (Zlr=3.50; P=.0002). Parametric analysis revealed a heterogeneity LOD score of 4.06, corresponding to a genomewide significance level of.037, under the assumption of a recessive model with high disease-allele frequency and 66% as the proportion of linked families. This study confirms linkage of psoriasis to the HLA region on chromosome 6p and suggests additional regions on chromosomes 8q and 21q for further investigations.

Advances in the search for psoriasis susceptibility genes

Psoriasis (PS) is a common skin disorder affecting approximately 2% of the Caucasian population. Despite the established influence of several environmental factors, epidemiological data and twin studies have long demonstrated a genetic basis for psoriasis susceptibility. Moreover an association between PS and HLA-Cw6 has been reported in different ethnic groups. In recent years, the availability of statistical methods for complex disease linkage analysis has prompted many researchers to carry out genome-wide scans. Their results have been conflicting and linkage replication has seldom been documented. However, a few chromosome regions have been confirmed in independent studies. In particular, compelling evidence supports the existence of a susceptibility locus within the HLA region. Moreover, loci on chromosomes 17q and 1q have been reported in at least two independent genome scans. Several groups have undertaken the refinement of regions identified during genome scans, using linkage disequilibrium data. This approach has allowed the fine mapping of the 6p21 locus, now restricted to a 60-kb genomic segment. As critical regions get smaller, candidate gene analysis becomes an attractive approach. So far, three genes have been extensively investigated: S100A7 on chromosome 1q and CDSN and HCR on chromosome 6p21. Even though several SNPs have been identified within these genes, none of them seems to meet the requirement needed to prove an involvement in PS pathogenesis. These criteria include association replication in different populations and functional studies of SNP biological significance. Thus, only a collaborative and multidisciplinary approach will allow the identification of PS susceptibility genes.

Genetics of rat neuroinflammation

The definition of genes regulating the pathogenetic pathways of autoimmune neuroinflammation, may provide targets for new therapeutic strategies. This is not easily accomplished in human disease. Such genetic dissection can more readily be done by the use of inbred rodent strains. With these, genetic heterogeneity is avoided and variation in the environmental influences is minimized. Close mimicking of the human disease characteristics is desirable in such endeavors. Chronic relapsing experimental autoimmune encephalomyelitis (EAE) with MS-like histopathology is achieved after immunization of certain rat strains with myelin oligodendrocyte glycoprotein (MOG) or spinal cord homogenate. The major histocompatibility complex (MHC) regulate the ease by which the environmental trigger in the form of immunisation induces disease. Use of intra-MHC recombinant strains demonstrated major influences from the MHC class II genome region, but additional influences from both the MHC class I and III regions. These findings now provide a basis for studies of the mechanisms for MHC-controlled autoimmune pathogenicity leading to MS-like disease. Gene mapping of F2 crosses between susceptible and resistant rat strains demonstrated nine genome regions outside the MHC which regulate different phenotypes of rat EAE. Many of these co-localize with genome regions regulating other organ-specific disease such experimental arthritis, suggesting a sharing of disease pathways. Further finemapping can lead to the exact identification of disease regulating genes. Interestingly, we have also demonstrated a non-MHC gene control of the inflammatory response, in the form of glial cell activation, and neuronal degeneration, subsequent to anterior nerve root avulsion in rats. The genetic dissection of these influences may unravel pathways controlling CNS vulnerability.

Genomic views of the immune system*

Genomic-scale experimentation aims to view biological processes as a whole, yet with molecular precision. Using massively parallel DNA microarray technology, the mRNA expression of tens of thousands of genes can be measured simultaneously. Mathematical distillation of this flood of gene expression data reveals a deep molecular and biological logic underlying gene expression programs during cellular differentiation and activation. Genes that encode components of the same multi-subunit protein complex are often coordinately regulated. Coordinate regulation is also observed among genes whose products function in a common differentiation program or in the same physiological response pathway. Recent application of gene expression profiling to the immune system has shown that lymphocyte differentiation and activation are accompanied by changes of hundreds of genes in parallel. The databases of gene expression emerging from these studies of normal immune responses will be used to interpret the pathological changes in gene expression that accompany autoimmunity, immune deficiencies, and cancers of immune cells.

Human sphingosine kinase: molecular cloning, functional characterization and tissue distribution

Sphingosine-1-phosphate (SPP), the product of sphingosine kinase, is an important signaling molecule with intra- and extracellular functions. The cDNA for the mouse sphingosine kinase has recently been reported. In this paper we describe the cloning, expression and characterization of the human sphingosine kinase (huSPHK1). Sequence analysis comparison revealed that this kinase is evolutionarily very conserved, having a high degree of homology with the murine enzyme, and presenting several conserved regions with bacteria, yeast, plant, and mammalian proteins. Expressed huSPHK1 cDNA specifically phosphorylates D-erythro-sphingosine and, to a lesser extent, D, L-erythro-dihydrosphingosine, and not at all the 'threo' isoforms of dihydrosphingosine; hydroxy-ceramide or non-hydroxy-ceramide; diacylglycerol (DAG); phosphatidylinositol (PI); phosphatidylinositol-4-phosphate (PIP); or phosphatidylinositol-4, 5-bisphosphate (PIP(2)). huSPHK1 shows typical Michaelis-Menten kinetics (V(max)=56microM and K(m)=5microM). The kinase is inhibited by D,L-threo-dihydrosphingosine (K(i)=3microM), and by N, N-dimethyl-sphingosine (K(i)=5microM). Northern blots indicate highest expression in adult lung and spleen, followed by peripheral blood leukocyte, thymus and kidney, respectively. It is also expressed in brain and heart. In addition, database searches with the stSG2854 sequence indicate that huSPHK1 is also expressed in endothelial cells, retinal pigment epithelium, and senescent fibroblasts.