Sequences of the swine 21-hydroxylase gene (CYP21) and a portion of the opposite-strand overlapping gene of unknown function previously described in human

Molecular cloning and expression of guinea pig cytochrome P450c21 cDNA (steroid 21-hydroxylase) isolated from the adrenals

In mammals, the P450c21 enzyme mediates 21-hydroxylase activity by transforming progesterone and 17-hydroxyprogesterone into deoxycorticosterone (DOC) and 11-deoxycortisol (11-DOC), respectively. Previous studies have shown that among the adrenal steroid hydroxylase enzymes involved in C19 steroid and glucocorticoid syntheses, P450c21 plays an important role, because it is localized at the key branch between glucocorticoids and C19 steroid production. Its implication in congenital adrenal hyperplasia is also of great clinical interest. In this study, in addition to describing the isolation of the P450c21 cDNA from guinea pig (GP) adrenal and comparing it to those from other species, we report on its tissue-distribution and on the activity of the recombinant protein towards progesterone and 17-hydroxyprogesterone. The guinea pig P450c21 includes the full-length coding region (1464 nucleotide) that is translated to a protein of 488 amino acids. The clone shares highly conserved regions with other species. The guinea pig P450c21 cDNA hybridized with a major transcript of 2.1kb and with two minor related transcripts of 1.8 and 1.5 kb and was found to be adrenal-specific among the various tissues analyzed. Characterization of the enzymatic activity by transient transfection of the guinea pig P450c21 cDNA in human embryonic kidney 293 cells indicated a net preference for the 21-hydroxylation of 17-hydroxyprogesterone in comparison to the progesterone substrate. Assays showed a maximum conversion rate of 12.5% for the conversion of progesterone into deoxycorticosterone (mineralocorticoid pathway), whereas the guinea pig P450c21 demonstrated a higher activity with 17alpha-hydroxyprogesterone, with 55% of 11-deoxycortisol formation (glucocorticoid pathway) after 48 h. Adrenocorticotropin and an analogue of the second messenger cyclic adenosine monophosphate specifically increased the abundance of P450c21 mRNA levels in guinea pig adrenal cells.

Adhesive defect in extracellular matrix tenascin-X-null fibroblasts: a possible mechanism of tumor invasion

Extracellular matrix tenascin-X (TNX)-null mice, generated by disruption of the Tnx gene, display augmented invasion and metastasis of B16-BL6 melanoma tumor cells due to increased activities of matrix metalloproteinase (MMP)-2 and MMP-9. In this study, we investigated cell-matrix and cell-cell adhesions using TNX-null fibroblasts and wild-type fibroblasts. TNX-null fibroblasts exhibited a decreased attachment to fibronectin compared with that of wild-type fibroblasts. B16 melanoma cells were cocultured with wild-type or TNX-null fibroblasts, and the adhesion of B16 melanoma to the fibroblasts was assessed. B16 melanoma cells on wild-type fibroblasts proliferated and spread out in a horizontal direction, whereas those on TNX-null fibroblasts overlapped each other rather than migrating horizontally. These overlapping B16 melanoma cells on TNX-null fibroblasts peeled off faster than those on wild-type fibroblasts. To determine whether the decreased cell-matrix and cell-cell adhesions on TNX-null fibroblasts were due to increased MMP activity, the activities of MMPs in wild-type and TNX-null fibroblasts were compared by gelatinolytic assays. The analysis of MMPs from conditioned media demonstrated that almost the same levels of MMP activities were detected between wild-type and TNX-null fibroblasts. However, contrary to our expectations the activities of MMPs from conditioned media of B16 melanoma cells cocultured on TNX-null fibroblasts were rather reduced than those of B16 melanoma cells cocultured on wild-type. We concluded that the absence of TNX in the extracellular environment might play an important role in enhancement of the detachment of B16 melanoma cells.

Cloning of canine 21-hydroxylase gene and its polymorphic analysis as a candidate gene for congenital adrenal hyperplasia-like syndrome in Pomeranians

A Strong breed predisposition to canine congenital adrenal hyperplasia-like syndrome (CAH-LS) exists and implies there is an hereditary cause. Pomeranians, one of the most predisposed breeds, have been reported to have partial adrenal dysfunction that could be associated with the pathogenesis of CAH-LS. In this study, the full-length complementary DNA (cDNA) of canine 21-OH, whose mutations are most likely responsible for the adrenal dysfunction in Pomeranians, was initially obtained from adrenal gland RNA by reverse transcription-polymerase chain reaction (RT-PCR), and its nucleotide sequence was determined. Genomic DNA samples from 16 Pomeranians and 30 control dogs, of seven different breeds, were tested for 21-OH gene polymorphisms by direct sequencing. No mutations affecting the primary structure and the transcriptional level of the 21-OH enzyme were found in Pomeranians. Our results indicate that the adrenal dysfunction in Pomeranians is not due to mutations of the 21-OH gene. This contrasts with the human form of CAH where 21-OH gene mutations are the major cause of the disease.

Three novel mutations in CYP21 gene in Brazilian patients with the classical form of 21-hydroxylase deficiency due to a founder effect

Three different new mutations were found after CYP21 gene sequencing in three unrelated patients with the classical form of the 21-hydroxylase deficiency. These mutations were also screened in their affected relatives. In one patient and her brother, both affected with the simple virilizing form and in their aunt, with the nonclassical form, an AG>GG transition was found in the acceptor site of intron 2. In another patient with the salt wasting form, we found a 1003 1004 insA, in exon 4, that altered the reading frame and created a stop codon in codon 297. In the third patient and his sister, we found a C>T transition in codon 408. This transition led to the substitution of arginine by cysteine (R408C) in a conserved region where arginine is conserved in at least four different species. These siblings with the R408C mutation, both affected with the salt wasting form, have the IVS2-13A/C>G mutation in the other allele, suggesting that the R408C should lead to complete impairment of enzymatic activity. To rule out the possibility of polymorphism, R408C was screened through allele specific PCR, and it was not found in 100 normal alleles. The screening of these three new mutations by allele-specific PCR or enzymatic restriction in 212 CAH patients disclosed their presence in 2.3% (9/387) of the alleles. All three new mutations were found in compound heterozygous state with previously known mutations. Microsatellite studies, using markers flanking CYP21 gene, revealed that each new mutation presents the same haplotype, suggesting a gene founder effect, similar to what was previously observed with the G424S mutation also described in our population. Although microconversion events are the main cause of mutations in the CYP21 gene, random mutations with a common origin can also be the cause of 21-hydroxylase deficiency.

Opposite regulation of tenascin-C and tenascin-X in MeLiM swine heritable cutaneous malignant melanoma

Interactions between tumour cells and surrounding extracellular matrix (ECM) influence the growth of tumour cells and their ability to metastasise. It is thus interesting to compare ECM composition in tumours and healthy tissues. Using the recently described MeLiM miniature pig model of heritable cutaneous malignant melanoma, we studied the expression of two ECM glycoproteins, the tenascin-C (TN-C) and tenascin-X (TN-X), in normal skin and melanoma. Using semiquantitative RT-PCR, we observed a 3.6-fold mean increase of TN-C RNAs in melanoma compared to normal skin. Both stromal and tumour cells synthesise TN-C. On the contrary, TN-X RNAs decreased 30-fold on average in melanoma. This opposite regulation of TN-C and TN-X RNAs was confirmed at the protein level by indirect immunofluorescence. Whereas pig normal skin displayed a discrete TN-C signal at the dermo-epidermal junction, around blood vessels and hair bulbs, the swine tumour showed enhanced expression of TN-C in these areas and around stromal and tumour cells. In contrast, normal skin showed a strong TN-X staining at the dermo-epidermal junction and in the dermis, whereas this signal almost completely disappeared in the tumour. The results presented here describe a dramatic alteration of the ECM composition in swine malignant melanoma which might have a large influence on tumourigenesis or invasion and metastasis of melanoma cells.

The major histocompatibility complex in swine

In swine, the major histocompatibility complex (Mhc) or swine leukocyte antigen (SLA) is located on chromosome 7 and divided by the centromere. Thus, the telomeric class I and more centromeric class III regions are located on the p arm and the class II region is located on the q arm. The SLA region spans about 2 Mb, in which more than 70 genes have so far been characterized. Despite its division by the centromere, the spatial relationships between the genes in the class II and class III regions, and between the well-conserved non-class I genes of the class I region, are similar to those found in the human HLA complex. On the other hand, no orthologous relationships have been found between the Mhc class I genes in man and swine. In swine, the 12 SLA class I sequences constitute two distinct clusters. One cluster comprises six classical class I-related sequences, while the other comprises five class I-distantly related sequences including two swine homologous genes of the HLA Mhc class I chain-related gene (MIC) sequence family. The number of functional SLA classical class I genes, as defined by serology, probably varies from one to four, depending on the haplotype. Some of the SLA class I-distantly related sequences are clearly transcribed. As regards the SLA class II genes, some of them clearly code for at least one functional SLA-DR and one SLA-DQ heterodimer product, but none code for any DP product. The amino acid alignment of the variable domains of 33 SLA classical class I chains, and 62 DR beta and 20 DQ beta chains confirmed the exceptionally polymorphic pattern of these polypeptides. Among the class II genes, the genes are either monomorphic, like the DRA gene, or oligomorphic, like the DQA genes. In contrast, the DRB and DQB genes display considerable polymorphism, which seems more marked in DRB than DQB genes.

Analysis of autoantibody epitopes on steroid 21-hydroxylase using a panel of monoclonal antibodies

A panel of five mouse monoclonal antibodies (MAbs) to human recombinant steroid 21-hydroxylase (21-OH) were produced, characterized, and used to study the interaction of 21-OH autoantibodies (AAbs) with different epitopes on human 21-OH. AAbs in patients with isolated autoimmune Addison's disease, autoimmune polyglandular syndromes types I and II, and 21-OH antibody-positive patients without overt Addison's disease (25 patients in total) were studied. Four MAbs were IgG1 subclass, one was IgG2a, and all had kappa light chains. The affinities of four of the antibodies were in the range 2.0 x 10(8) M(-1) to 7.0 x 10(8) M(-1), and the affinity of the other was 2.3 x 10(7) M(-1) 21-OH MAbs did not cross-react with 17alpha-hydroxylase (17alpha-OH)) or P450 side chain cleavage enzyme. Studies using a series of 21-OH fragments allowed the identification of short stretches of amino acids (AA) that were involved in forming the MAb binding sites. AA 391-405, defined as epitope region (ER) 1, were found to be important for binding of M21-OH1 and M21-OH2, AA 406-411 (ER2) were important for M21-OH3 and M21-OH4 binding, and AA 335-339 (ER3) for M21-OH5 binding. In addition, MAb Fab or F(ab')2 fragments were used to study 21-OH AAb epitopes in competition experiments. These investigations demonstrated that 21-OH AAbs recognize similar epitopes to the MAbs, with ER2 and ER3 being part of two distinct major epitopes, and ER 1 being part of a minor epitope. Mixtures of M21-OH antibody Fab or F(ab')2 fragments caused almost complete inhibition (80%-95%) of AAb binding in 24 out of 25 sera, and in the case of the remaining serum, the effect was marked but incomplete (67% inhibition). There were no major differences between the binding characteristics of AAbs from patients with different forms of autoimmune adrenal disease. All five 21-OH MAbs reacted with human adrenal tissue in an immunofluorescence test, but only M21-OH1 and M21-OH2 reacted with bovine adrenal tissue in these experiments. None of the MAbs reacted with human ovarian tissue in an immunofluorescence test. Overall, these studies indicate that 21-OH AAbs bind to at least three different epitopes in the C-terminal part of 21-OH, and two of these epitopes appear to be human 21-OH specific.

A detailed physical map of the porcine major histocompatibility complex (MHC) class III region: comparison with human and mouse MHC class III regions

A detailed physical map of the porcine MHC class III region on Chr 7 was constructed with a panel of probes in a series of hybridizations on genomic pulsed field gel electrophoresis (PFGE) Southern blots. A precise organization of the 700-kb segment of DNA between G18 and BAT1 can now be proposed, with more than 30 genes mapped to it. Comparison of this region with homologous regions in human and mouse showed only minor differences. The biggest difference was observed in the CYP21/C4 locus with only one CYP21 gene and one C4 gene found, whereas in human and mouse these genes are duplicated. These results show the class III region is very well conserved between pig, human, and mouse, in contrast with the class I and class II regions, which seem more prone to rearrangements.

Conservation of the RD-BF-C2 organization in the pig MHC class-III region: mapping and cloning of the pig RD gene

The RD gene, named after the arginine (R) and aspartic acid (D) repeat in the central part of its protein, was initially mapped in the mouse H-2S subregion between C4 and BF. It was later mapped in the same position in the human MHC and here we show it is also conserved in the pig MHC class III region, close to the complement BF gene. A pig RD genomic clone was isolated from a lambda-phage library. Hybridizations on genomic DNA separated with pulsed field gel electrophoresis identified common 220 kb NruI, 130 kb EagI and 200 kb MluI bands for RD, BF and C2. The RD gene has also a 17 kb Kp nI and 11 kb SacI fragment in common with BF but not with C2. The close linkage of the RD and BF genes was further established by hybridization of BF to a genomic lambda-phage clone also containing the RD gene. This genomic RD clone overlaps with a lambda-phage clone previously isolated and containing the complete BF gene and the 3' part of C2. The distance between RD and BF is about 6 kb. The junction between the two complement genes BF and C2 was sequenced and the BF 5' promoter region, overlapping the 3' noncoding region of C2, was compared with that of the human BF promoter. The overall homology was about 80% and all but one identified promoter elements were found in the same position in both genes. The results obtained demonstrate the RD-BF-C2 organization is strongly conserved between human, mouse and pig. No polymorphisms were detected in either the RD gene or in the BF promoter region using polymerase chain reaction and restriction fragment polymorphism analysis.

Mapping of the SLA complex class III region by pulsed field gel electrophoresis

The fine order of genes in the class III region of the swine major histocompatibility complex (MHC), the SLA complex, was examined by pulsed field gel electrophoresis (PFGE) and Southern blot analysis. Four genes, C2, HSP70, TNF alpha, and CYP21, were analyzed. The CYP21, C2, and HSP70 genes were all located within a 200-kb NotI fragment. The C2, HSP70, and TNF alpha genes cohybridized to a 420-kb SalI fragment. The TNF alpha gene is linked to the class I region by a 390-kb NotI fragment. Combined with a previous study from our lab, the order of genes in the SLA complex is class II-class III [(CYP21/C4)-(Bf/C2/HSP70)-TNF alpha]-class I. The size of the class III region from CYP21 to TNF alpha is estimated to be 500 kb. This size and the order of the genes in the swine class III region are similar to those of human, mouse, goat, and rabbit, which confirms the high conservation of class III gene organization across species.

Embryonic expression of tenascin-X suggests a role in limb, muscle, and heart development

Tenascin-X (TN-X) is the newest member of the tenascin family of extracellular matrix proteins and it is highly expressed in muscular tissues during development. To gain insight into the possible functions of TN-X during development, we evaluated its expression in the rat embryo. Using an 800 bp cDNA encoding the fibrinogen-like domain of TN-X, we show that TN-X expression begins in migrating cells of the epicardium in the E12 heart. The epicardium provides progenitors of fibrous and vascular tissue to the developing heart. After the epicardium is complete, TN-X is expressed in the sub-epicardial space in association with developing blood vessels, and later by non-myocytes dispersed through the myocardial wall. A similar pattern of TN-X expression, first in connective tissue surrounding muscle, and then by a subset of cells within muscle, was seen in para-axial, body wall, craniofacial, and appendicular muscle. This pattern suggests a role in connective tissue cell migration and late muscle morphogenesis. TN-X is also highly expressed in the interdigital space at E15 and surrounding developing tendons, suggesting an additional role in cell fate determination. Although the pattern of TN-X expression is distinct from that of tenascin C, they are frequently expressed in close proximity. Indirect genetic evidence in humans suggests an essential function for TN-X, and the pattern of TN-X expression in heart, skeletal muscle, and limb is consistent with this hypothesis.

The BAT1 gene in the MHC encodes an evolutionarily conserved putative nuclear RNA helicase of the DEAD family

The BAT1 gene has previously been identified about 30 kb upstream from the tumor necrosis factor (TNF) locus and close to a NF kappa b-related gene of the nuclear factor family in the major histocompatibility complex (MHC) of human, mouse, and pig. We now show that the BAT1 translation product is the homolog of the rat p47 nuclear protein, the WM6 Drosophila gene product, and probably also Ce08102 of Caenorhabditis elegans, all members of the DEAD protein family of ATP-dependent RNA helicases. This family has more than 40 members, including the eukaryotic translation initiation factor-4A (eIF-4A), the human nuclear protein p68, and the Drosophila oocyte polar granule component vasa. BAT1 spans about 10 kb, is split into 10 exons of varying length, and encodes a protein of 428 amino acids (approximately 48 kDa). Human and pig BAT1 cDNAs display 95.6% identity in the coding region and 80% identity in the 5' and 3' noncoding regions. Several repeat sequences of different types were identified in introns of the porcine BAT1 gene. Three different mRNAs, 4.1, 1.7, and 0.9 kb, respectively, were detected in all tissues analyzed upon hybridization with porcine BAT1 cDNA. Transfection and expression of human BAT1 cDNA after tagging with a heterologous antibody recognition epitope revealed a nuclear localization of the hybrid protein. An MspI RFLP was detected in an SLA class I typed family, confirming the localization of the BAT1 gene in the porcine MHC. BAT1 thus encodes a putative nuclear ATP-dependent RNA helicase and is likely to have an indispensable function.

Characterization of six new loci within the swine major histocompatibility complex class III region

A search for new potential coding sequences was conducted within two overlapping cosmid genomic DNA clusters of about 170 and 45 kb from the swine major histocompatibility complex class III region. The sequences were detected with various probes, including pools of swine cDNA, homologous and heterologous genomic sequences, and synthetic oligonucleotides. The 170 kb cluster was centered on the tumor necrosis factor genes (TNF), and the 45 kb cluster contained the heat-shock protein 70 genes (HSP70). The TNF cluster revealed the presence of five new genes: lymphotoxin beta, BAT1, BAT2, BAT3, and a sequence related to DNA-binding factors. No sequence homologous to B144 was found in the TNF cluster, although other unidentified coding sequences may be present in this cluster. The HSP70 cluster contained a gene identified as BAT6, that is, tRNA-valyl synthetase. These results provide new evidence that the genomic maps of these various genes in the TNF and HSP70 sub-regions are similar in swine and human.

The P450 superfamily: update on new sequences, gene mapping, accession numbers, early trivial names of enzymes, and nomenclature

We provide here a list of 221 P450 genes and 12 putative pseudogenes that have been characterized as of December 14, 1992. These genes have been described in 31 eukaryotes (including 11 mammalian and 3 plant species) and 11 prokaryotes. Of 36 gene families so far described, 12 families exist in all mammals examined to date. These 12 families comprise 22 mammalian subfamilies, of which 17 and 15 have been mapped in the human and mouse genome, respectively. To date, each subfamily appears to represent a cluster of tightly linked genes. This revision supersedes the previous updates [Nebert et al., DNA 6, 1-11, 1987; Nebert et al., DNA 8, 1-13, 1989; Nebert et al., DNA Cell Biol. 10, 1-14 (1991)] in which a nomenclature system, based on divergent evolution of the superfamily, has been described. For the gene and cDNA, we recommend that the italicized root symbol "CYP" for human ("Cyp" for mouse), representing "cytochrome P450," be followed by an Arabic number denoting the family, a letter designating the subfamily (when two or more exist), and an Arabic numeral representing the individual gene within the subfamily. A hyphen should precede the final number in mouse genes. "P" ("p" in mouse) after the gene number denotes a pseudogene. If a gene is the sole member of a family, the subfamily letter and gene number need not be included. We suggest that the human nomenclature system be used for all species other than mouse. The mRNA and enzyme in all species (including mouse) should include all capital letters, without italics or hyphens. This nomenclature system is identical to that proposed in our 1991 update. Also included in this update is a listing of available data base accession numbers for P450 DNA and protein sequences. We also discuss the likelihood that this ancient gene superfamily has existed for more than 3.5 billion years, and that the rate of P450 gene evolution appears to be quite nonlinear. Finally, we describe P450 genes that have been detected by expressed sequence tags (ESTs), as well as the relationship between the P450 and the nitric oxide synthase gene superfamilies, as a likely example of convergent evolution.

Isolation of four HSP70 genes in the pig and localization on chromosomes 7 and 14

For insight into the general organization of the swine leukocyte antigen (SLA) complex, the swine major histocompatibility complex (MHC), four sequences related to the heat-shock proteins HSP70 were characterized by screening of a pig genomic cosmid library with a swine cDNA HSP70 2.6-kb probe. This yielded three positive clones: HC2.2, HC3.2, and HC4.2. Restriction site maps revealed a large overlap of HC2.2 with HC3.2, whereas HC4.2 was independent. Southern blot hybridization with the 5' section, the central section, and the 3' section of the 2.6-kb probe and also with a swine 4.5-kb HSP70 genomic probe suggested the existence, within the overlapping clones, of three distinct HSP70 sequences encompassing a segment no longer than 22 kb. The HC4.2 clone, which hybridized with the same probes, displayed a single band of 7.3 kb, probably corresponding to one gene only. Fluorescent in situ hybridization on swine chromosome metaphases with the whole HC2.2 or HC4.2 cosmids allowed the assignment of HC2.2 to MHC region on Chromosome (Chr) 7 (Cen-p1.1), and of HC4.2 to Chr 14 (q2.4-2.5). Thus, as in humans, the swine MHC comprises three closely linked HSP70 loci. The presence of additional genes belonging to the same inducible HSP70 gene family can be expected from what is known in humans. The HSP70 gene found here on the pig Chr 14 may be one of these putative unidentified genes.