Understanding the Role of Device Level Interoperability in Promoting Health - Lessons Learned from the SmartPersonalHealth Project

To summarize lessons learned from the European Commission (EC) co-funded project SmartPersonalHealth, a project to promote a greater understanding of the value of interoperability among Personal Health Systems (PHS) and between them and other eHealth systems, in the landscape of continuity of care and across multi-cultural environments in Europe.

Key concepts in PHS interoperability, challenges, barriers and benefits were discussed with stakeholders (policy makers, regulators, procurers, healthcare providers, health professionals, patient representatives, industry, researchers) in three consultation workshops and a final conference. The results were synthesized in final report to the European Commission.

The survey and analysis presented, which are designed to set the scene on the key requirements of device level interoperability within a context of using sensors, signals and imaging informatics in healthcare, set out key interoperability standards for PHS as provided for in the Continua Health Alliance Guidelines and explores further the need for wider organisational and regulatory aspects of interoperability.

Achieving interoperability of eHealth systems is a complex process involving various actors and challenges far beyond technical and standardisation issues. For harnessing the key benefits of PHS, any interoperability scenario needs to account for value-based business cases for all stakeholders involved. It must foresee to enable seamless and consistent data and information flows by integrating and mixing devices used by patients/consumers at home, for remote monitoring, for home hospitalisation and/or within the hospital.

Understanding the role of device level interoperability in promoting health - lessons learned from the SmartPersonalHealth Project

OBJECTIVES

To summarize lessons learned from the European Commission (EC) co-funded project SmartPersonalHealth, a project to promote a greater understanding of the value of interoperability among Personal Health Systems (PHS) and between them and other eHealth systems, in the landscape of continuity of care and across multi-cultural environments in Europe.

METHODS

Key concepts in PHS interoperability, challenges, barriers and benefits were discussed with stakeholders (policy makers, regulators, procurers, healthcare providers, health professionals, patient representatives, industry, researchers) in three consultation workshops and a final conference. The results were synthesized in final report to the European Commission.

RESULTS

The survey and analysis presented, which are designed to set the scene on the key requirements of device level interoperability within a context of using sensors, signals and imaging informatics in healthcare, set out key interoperability standards for PHS as provided for in the Continua Health Alliance Guidelines and explores further the need for wider organisational and regulatory aspects of interoperability.

CONCLUSION

Achieving interoperability of eHealth systems is a complex process involving various actors and challenges far beyond technical and standardisation issues. For harnessing the key benefits of PHS, any interoperability scenario needs to account for value-based business cases for all stakeholders involved. It must foresee to enable seamless and consistent data and information flows by integrating and mixing devices used by patients/consumers at home, for remote monitoring, for home hospitalisation and/or within the hospital.

Hepatitis B virus X protein interferes with cell viability through interaction with the p127-kDa UV-damaged DNA-binding protein

The hepatitis B virus X protein (HBx) is essential for establishing natural viral infection and has been implicated in the development of liver cancer associated with chronic infection. The basis for HBx function in either process is not understood. In cell culture, HBx exhibits pleiotropic activities affecting transcription, DNA repair, cell growth, and apoptotic cell death. Numerous cellular proteins including the p127-kDa subunit of UV-damaged DNA-binding activity have been reported to interact with HBx but the functional significance of these interactions remains unclear. Here we show that the binding of HBx to p127 interferes with cell viability. Mutational analysis reveals that HBx contacts p127 via a region to which no function has been assigned previously. An HBx variant bearing a single-charge reversal substitution within this region loses p127 binding and concomitant cytotoxicity. This mutant regains activity when directly fused to p127. These studies confirm that p127 is an important cellular target of HBx, and they indicate that HBx does not exert its effect by sequestering p127, and thereby preventing its normal function, but instead by conferring to p127 a deleterious activity.

B-Cell coactivator OBF-1 exhibits unusual transcriptional properties and functions in a DNA-bound Oct-1-dependent fashion

Eukaryotic transcriptional activators generally comprise both a DNA-binding domain that recognizes specific cis-regulatory elements in the target genes and an activation domain which is essential for transcriptional stimulation. Activation domains typically behave as structurally and functionally autonomous modules that retain their intrinsic activities when directed to a promoter by a variety of heterologous DNA-binding domains. Here we report that OBF-1, a B-cell-specific coactivator for transcription factor Oct-1, challenges this traditional view in that it contains an atypical activation domain that exhibits two unexpected functional properties when tested in the yeast Saccharomyces cerevisiae. First, OBF-1 by itself has essentially no intrinsic activation potential, yet it strongly synergizes with other activation domains such as VP16 and Gal4. Second, OBF-1 exerts its effect in association with DNA-bound Oct-1 but is inactive when attached to a heterologous DNA-binding domain. These findings suggest that activation by OBF-1 is not obtained by simple recruitment of the coactivator to the promoter but requires interaction with DNA-bound Oct-1 to stimulate a step distinct from those regulated by classical activation domains.

The Oct-1 POU domain activates snRNA gene transcription by contacting a region in the SNAPc largest subunit that bears sequence similarities to the Oct-1 coactivator OBF-1

The RNA polymerases II and III snRNA gene promoters contain an octamer sequence as part of the enhancer and a proximal sequence element (PSE) as part of the core promoter. The octamer and the PSE bind the POU domain activator Oct-1 and the basal transcription factor SNAPc, respectively. Oct-1, but not Oct-1 with a single E7R mutation within the POU domain, binds cooperatively with SNAPc and, in effect, recruits SNAPc to the PSE. Here, we show that SNAPc recruitment is mediated by an interaction between the Oct-1 POU domain and a small region of the largest subunit of SNAPc, SNAP190. This SNAP190 region is strikingly similar to a region in the B-cell-specific Oct-1 coactivator, OBF-1, that is required for interaction with octamer-bound Oct-1 POU domain. The Oct-1 POU domain-SNAP190 interaction is a direct protein-protein contact as determined by the isolation of a switched specificity SNAP190 mutant that interacts with Oct-1 POU E7R but not with wild-type Oct-1 POU. We also show that this direct protein-protein contact results in activation of transcription. Thus, we have identified an activation target of a human activator, Oct-1, within its cognate basal transcription complex.

The large subunit of basal transcription factor SNAPc is a Myb domain protein that interacts with Oct-1

The human RNA polymerase II and III snRNA promoters have similar enhancers, the distal sequence elements (DSEs), and similar basal promoter elements, the proximal sequence elements (PSEs). The DSE, which contains an octamer motif, binds broadly expressed activator Oct-1. The PSE binds a multiprotein complex referred to as SNAPc or PTF. On DNAs containing both an octamer site and a PSE, Oct-1 and SNAPc bind cooperatively. SNAPc consists of at least four stably associated subunits, SNAP43, SNAP45, SNAP50, and SNAP190. None of the three small subunits, which have all been cloned, can bind to the PSE on their own. Here we report the isolation of cDNAs corresponding to the largest subunit of SNAPc, SNAP190. SNAP190 contains an unusual Myb DNA binding domain consisting of four complete repeats (Ra to Rd) and a half repeat (Rh). A truncated protein consisting of the last two SNAP190 Myb repeats, Rc and Rd, can bind to the PSE, suggesting that the SNAP190 Myb domain contributes to recognition of the PSE by the SNAP complex. SNAP190 is required for snRNA gene transcription by both RNA polymerases II and III and interacts with SNAP45. In addition, SNAP190 interacts with Oct-1. Together, these results suggest that the largest subunit of the SNAP complex is involved in direct recognition of the PSE and is a target for the Oct-1 activator. They also provide an example of a basal transcription factor containing a Myb DNA binding domain.

Synergistic and promoter-selective activation of transcription by recruitment of transcription factors TFIID and TFIIB

Eukaryotic transcriptional activators may function by stimulating formation of RNA polymerase II preinitiation complexes at the core promoter of genes. In this case, their mode of action will intrinsically depend on how these complexes assemble on promoters in living cells, an issue that remains largely unexplored. Here we show that in yeast the basal transcription machinery is brought to the promoter in the form of at least two subcomplexes, TFIID and a complex comprising TFIIB and other essential components. Individual recruitment of either complex by artificial contact with a transcriptionally inactive, sequence-specific DNA-binding protein suffices to trigger transcriptional activation from a wild-type core promoter bearing the appropriate binding site. In contrast, activation from a promoter containing a weakened TATA element is only observed upon recruitment of TFIID. Tethering TFIIB on that promoter remains without effect, but the simultaneous recruitment of both components leads to strong synergistic activation. These findings suggest a simple mechanism whereby two activators that contact distinct subcomplexes of the basal machinery may stimulate transcription synergistically and differentially depending on the nature of the promoter.

A consensus motif in the RFX DNA binding domain and binding domain mutants with altered specificity

The RFX DNA binding domain is a novel motif that has been conserved in a growing number of dimeric DNA-binding proteins, having diverse regulatory functions, in eukaryotic organisms ranging from yeasts to humans. To characterize this novel motif, we have performed a detailed dissection of the site-specific DNA binding activity of RFX1, a prototypical member of the RFX family. First, we have performed a site selection procedure to define the consensus binding site of RFX1. Second, we have developed a new mutagenesis-selection procedure to derive a precise consensus motif, and to test the accuracy of a secondary structure prediction, for the RFX domain. Third, a modification of this procedure has allowed us to isolate altered-specificity RFX1 mutants. These results should facilitate the identification both of additional candidate genes controlled by RFX1 and of new members of the RFX family. Moreover, the altered-specificity RFX1 mutants represent valuable tools that will permit the function of RFX1 to be analyzed in vivo without interference from the ubiquitously expressed endogenous protein. Finally, the simplicity, efficiency, and versatility of the selection procedure we have developed make it of general value for the determination of consensus motifs, and for the isolation of mutants exhibiting altered functional properties, for large protein domains involved in protein-DNA as well as protein-protein interactions.

Stimulation of RNA polymerase II transcription initiation by recruitment of TBP in vivo

Eukaryotic transcriptional activators may stimulate RNA polymerase II activity by promoting assembly of preinitiation complexes on promoters through their interactions with one or more components of the basal machinery. On the basis of its central role in initiating transcription-complex formation upon binding to the TATA box, the general transcription factor TFIID, which includes the TATA-binding protein (TBP) and several TBP-associated factors, has been implicated as a target for activators. Consistent with this idea, an increasing number of activators have been reported to bind directly to TBP. To assess the functional importance of these in vitro interactions for transcriptional regulation in vivo, we made use of a novel strategy in yeast to show that a physical interaction with TBP is sufficient for a sequence-specific DNA-binding protein to increase initiation of transcription by RNA polymerase II. These results imply that binding of TFIID to promoter elements is a limiting step in transcription complex assembly in vivo.

OBF-1, a novel B cell-specific coactivator that stimulates immunoglobulin promoter activity through association with octamer-binding proteins

Recent biochemical and genetic studies indicate that in addition to the octamer-binding proteins Oct-1 and Oct-2, other B cell components are required for lymphoid-restricted, octamer site-mediated immunoglobulin gene promoter activity. Using a genetic screen in yeast, we have isolated B cell-derived cDNAs encoding Oct-binding factor 1 (OBF-1), a novel protein that specifically associates with Oct-1 and Oct-2. Biochemical studies demonstrate that OBF-1 has no intrinsic DNA-binding activity and recognizes the POU domains of Oct-1 and Oct-2, but not those of Oct-4 and Oct-6. The OBF-1 mRNA is expressed in a highly cell-specific manner, being most abundant in B cells and essentially absent in most of the other cells or tissues tested. Furthermore, expression of OBF-1 in HeLa cells selectively stimulates the activity of a natural immunoglobulin promoter in an octamer site-dependent manner. Thus, OBF-1 has all the properties expected for a B cell-specific transcriptional coactivator protein.

Conserved and nonconserved functions of the yeast and human TATA-binding proteins

Although the TATA-binding protein (TBP) is highly conserved throughout the eukaryotic kingdom, human TBP cannot functionally replace yeast TBP for cell viability. To investigate the basis of this species specificity, we examine the in vivo transcriptional activity of human TBP at different classes of yeast promoters. Consistent with previous results, analysis of yeast/human hybrid TBPs indicates that growth defects are not correlated with the ability to promote TATA-dependent polymerase II (Pol II) transcription or to respond to acidic activator proteins. Human TBP partially complements the growth defects of a yeast TBP mutant with altered TATA element-binding specificity, suggesting that it carries out sufficient Pol II function to support viability. However, human TBP does not complement the defects of yeast TBP mutants that are specifically defective in transcription by RNA polymerase III. Three independently isolated derivatives of human TBP that permit yeast cell growth replace arginine 231 with lysine; the corresponding amino acid in yeast TBP (lysine 133) has been implicated in RNA polymerase III transcription. Transcriptional analysis indicates that human TBP functions poorly at promoters recognized by RNA polymerases I and III and at RNA Pol II promoters lacking a conventional TATA element. These observations suggest that species specificity of TBP primarily reflects evolutionarily diverged interactions with TBP-associated factors (TAFs) that are necessary for recruitment to promoters lacking TATA elements.

Yeast and human TFIID with altered DNA-binding specificity for TATA elements

TFIID is the highly conserved, but species-specific, component of the RNA polymerase II transcription machinery that binds specifically to the TATA element (consensus TATAAA). Using a genetic selection, we isolated an altered specificity derivative of yeast TFIID that permits transcription from promoters containing a mutated TATA element (TGTAAA). Biochemical analysis indicates that this TFIID derivative has specifically gained the ability to bind TGTAAA efficiently. The mutant protein contains three substitutions within a 12 amino acid region; two of these are necessary and primarily responsible for the altered specificity. An analogous version of human TFIID, generated by introducing the same amino acid substitutions in the corresponding region of the protein, can support basal and GCN4-activated transcription in yeast cells from a TGTAAA-containing promoter. These results define a surface of TFIID that directly interacts with the TATA element, and they indicate that human TFIID can respond to acidic activator proteins in conjunction with the other components of the yeast transcription machinery.

Nuclear targeting of the transcription factor PTF1 is mediated by a protein subunit that does not bind to the PTF1 cognate sequence

The pancreas-specific transcription factor PTF1 is a heterooligomer that exists as two variants, alpha and beta, both of which bind DNA. The nucleus contains exclusively alpha while the cytoplasm contains both forms. Alpha and beta differ in protein composition. Reconstitution of alpha in vitro requires, in addition to the DNA-binding subunits common to both forms, a 75 kd glycosylated protein that apparently does not bind DNA. Here we show that this protein is essential for targeting PTF1 to the nucleus. Upon injection into frog oocytes, alpha is translocated quantitatively to the nucleus while beta remains in the cytoplasm. However, if beta is coinjected with purified 75 kd protein or a particular size fraction of pancreatic mRNA, it can be converted to alpha and imported into the nucleus.

Functional differences between yeast and human TFIID are localized to the highly conserved region

TFIID, the general transcription factor that binds TATA promoter elements, is highly conserved throughout the eukaryotic kingdom. TFIIDs from different organisms contain C-terminal core domains that are at least 80% identical and display similar biochemical properties. Despite these similarities, yeast cells containing human TFIID instead of the endogenous yeast protein grow extremely poorly. Surprisingly, this functional distinction reflects differences in the core domains, not the divergent N-terminal regions. The N-terminal region is unimportant for the essential function(s) of yeast TFIID because expression of the core domain permits efficient cell growth. Analysis of yeast-human hybrid TFIIDs indicates that several regions within the conserved core account for the phenotypic difference, with some regions being more important than others. This species specificity might reflect differences in DNA-binding properties and/or interactions with activator proteins or other components of the RNA polymerase II transcription machinery.

The cell-specific transcription factor PTF1 contains two different subunits that interact with the DNA

The cognate sequence of transcription factor PTF1, which plays a key role in pancreas-specific gene expression, has a bipartite organization. Two separate DNA domains, the A and the B boxes, are required for efficient binding of the factor. The structure of PTF1 was elucidated by cross-linking purified PTF1 to DNA templates that had been differentially substituted with azido-deoxyuridine (N3.dU). This site-directed UV cross-linking shows that PTF1 contains two DNA-binding proteins, distinct in size and sensitivity to Staphylococcus aureus V8 protease. A 64-kD protein is cross-linked with DNA containing N3.dU substitutions in the A box, and a 48-kD protein is cross-linked with DNA containing N3.dU substitutions in the B box. Both proteins bind simultaneously to the same DNA molecule. The data indicate that PTF1 is a heteromeric oligomer and that its cell-specific DNA-binding potential is the result of a concerted activity of two DNA-binding subunits.

Identification of a cell-specific DNA-binding activity that interacts with a transcriptional activator of genes expressed in the acinar pancreas

Footprint analysis of the 5'-flanking regions of the alpha-amylase 2, elastase 2, and trypsina genes, which are expressed in the acinar pancreas, showed multiple sites of protein-DNA interaction for each gene. Competition experiments demonstrated that a region from each 5'-flanking region interacted with the same cell-specific DNA-binding activity. We show by in vitro binding assays that this DNA-binding activity also recognizes a sequence within the 5'-flanking regions of elastase 1, chymotrypsinogen B, carboxypeptidase A, and trypsind genes. Methylation interference and protection studies showed that the DNA-binding activity recognized a bipartite motif, the subelements of which were separated by integral helical turns of DNA. The alpha-amylase 2 cognate sequence was found to enhance in vivo transcription of its own promoter in a cell-specific manner, which identified the DNA-binding activity as a transcription factor (PTF 1). The observation that PTF 1 bound to DNA sequences that have been defined as transcriptional enhancers by others suggests that this factor is involved in the coordinate expression of genes transcribed in the acinar pancreas.

Alternative splicing and alternative initiation of translation explain the four forms of the Ia antigen-associated invariant chain

The Ia antigen-associated invariant chain (In) exists in humans as four related polypeptides, p33, p35, p41 and p43, all associated with HLA-class II antigens. As described previously, two of these forms of In chain, p33 and p35, result from the use of two in-phase initiation AUG codons on the unique In p33 mRNA. In addition to cDNA clones derived from In p33 mRNA, we have isolated a new cDNA clone, called p41-1, which differs from p33-1 by an additional segment in the coding region. The DNA sequence encoding the segment unique to p41-1 was identified in the genomic sequence in the intron between exon 6 and 7, and we refer to it as exon 6b. Cells transfected with a full length p41 cDNA clone in an expression vector synthesize the two larger forms of the In chain, p41 and p43. We propose that the larger mRNA, encoding p41, results from alternative splicing of exon 6b, and that p41 and p43 result from the use of the two functional initiation AUG codons identified in p33 mRNA. Alternative splicing, together with alternative initiation of translation, allows therefore the synthesis of four related In chain polypeptides from a single gene.

Two forms of the Ia antigen-associated invariant chain result from alternative initiations at two in-phase AUGs

The Ia antigen-associated invariant chain (In) exists in humans as two major related forms, p33 and p35. The mRNA for In contains two in-phase AUGs, at positions 8 and 56 from the cap site. Cells transfected with a full-length cDNA clone in an expression vector synthesize both p33 and p35. Cell-free translation of mRNA synthesized in vitro from cDNA also produces both forms. When the first ATG is deleted from the cDNA clone, only the smallest form of In is produced. Mutations introduced at the second ATG lead to synthesis of the large form only. The alternative use of two in-phase AUGs on a unique mRNA is thus responsible for the synthesis of p33 and p35. This is the first documented example of such a mechanism in nonviral systems.

Cell surface expression of class II histocompatibility antigens occurs in the absence of the invariant chain

The invariant chain is a glycoprotein transiently associated with the alpha and beta subunits of class II antigens of the major histocompatibility complex during their transport to the cell surface. An expression assay with cDNA clones transfected into simian COS cells was used to test whether the invariant chain is required for assembly and transport of human class II antigens. COS cells do not express detectable levels of RNA from the endogenous invariant chain gene. Cell surface expression of the DP, DQ, and DR antigens was observed in COS cells transfected with the respective alpha and beta chain cDNA clones. Analysis of RNA from the transfected cells showed that the human genes were transcribed in COS cells and that the endogenous simian class II and invariant chain genes were not induced. Cotransfections with an invariant chain cDNA clone did not alter the levels of class II antigens at the cell surface. Biosynthetic labeling and immunoprecipitation demonstrated that the invariant chain cDNA was expressed into a protein which associated with DR alpha and beta chains. Efficient expression of DR antigen in absence of invariant chain was also observed at the surface of a human fibroblast line stably transfected with DR alpha and beta cDNA. This study demonstrates that expression of all three human class II antigens can be achieved with cDNAs cloned in expression vectors. Furthermore, cell surface expression of class II major histocompatibility complex antigens can occur in absence of invariant chain. The postulated role of the invariant chain in class II antigen transport to the cell surface must be reevaluated. The invariant chain may rather be involved in functional properties of class II molecules such as antigen presentation.

Serological and immunochemical analysis of the products of a single HLA DR-alpha and DR-beta chain gene expressed in a mouse cell line after DNA-mediated cotransformation reveals that the beta chain carries a known supertypic specificity

Using a mouse cell line transformed with and expressing a single HLA DR-alpha and DR-beta chain gene, we present evidence that the product of the DR-beta chain gene carries a supertypic determinant, BR3, previously defined by serology. The amino acid sequence of this beta chain gene is determined from the DNA sequence. Another DR-associated supertypic specificity defined by monoclonal antibody MCS7 was not encoded by this DR-beta chain gene. This provides formal proof that a supertypic specificity can be associated with a product of a distinct DR-beta locus. We propose that haplotypes sharing such specificities are evolutionarily related.

The complete sequence of the mRNA for the HLA-DR-associated invariant chain reveals a polypeptide with an unusual transmembrane polarity

A non-polymorphic polypeptide is associated intracellularly with the alpha and beta chains of murine Ia antigens and of human HLA-DR antigens. The exact role and the structure of this invariant chain have not been determined so far. A cDNA clone encoding the 33 000 dalton human invariant chain has been isolated. The nucleotide sequence of a near full-length cDNA clone, together with the sequence of the 5' portion of the mRNA determined by primer-extension, are reported here. The protein structure deduced from that sequence shows an unusual feature: the presence of a hydrophobic transmembrane region near the NH2 terminus, and of two glycosylation sites near the middle, indicates that the invariant chain has a polarity of membrane insertion which is inverted relative to histocompatibility antigens and most transmembrane proteins.

Molecular analysis of the genes for human class II antigens of the major histocompatibility complex

Different cDNA clones have been isolated that encode each of the three chains of HLA-DR antigens: alpha, intermediate and beta, as well as another beta chain, most likely DC. Whereas the DR alpha and intermediate chains seem encoded by single genes, the DR and DC beta chains are most likely encoded by multiple genes; furthermore, their polymorphism can be readily detected by restriction analysis of cellular DNA. Several genomic DNA clones were isolated for the DR and DC beta chain genes and for the intermediate chain gene. The sum of all distinct cDNA clones and genomic DNA clones for HLA-DR beta chains, isolated from a heterozygous cell line, represent five genes. This implies the existence of at least three nonallelic DR beta chain genes in addition to the DC beta chain genes. The complete sequence of one of the DR beta chains is presented. A genomic DNA clone for a DR beta chain was transferred into mouse L cells and found to be expressed into RNA of the same size as DR beta mRNA. The finding, among the genes for class II antigens, of multiple genes for the beta chain of HLA-DR, distinct from those of other known subregions such as DC, emphasizes the importance of gene transfer experiments, where individual genes can be expressed and tested for their functional role in the immune response.

Isolation of cDNA clones for the p33 invariant chain associated with HLA-DR antigens

HLA-DR antigens are polymorphic cell surface glycoproteins involved in the control of the immune response in man. They consist of two subunits, the alpha and the beta chains. In addition, an invariant glycoprotein of Mr 33,000 (DRp33) is associated intracellularly with HLA-DR antigens. A cDNA clone for DRp33, called 33-10, was isolated. Because no amino acid sequence has yet been determined for DRp33 the identification of cDNA clone 33-10 was based on selection of mRNA by hybridization, subsequent translation in a rabbit reticulocyte lysate supplemented with microsomes, and translation in microinjected Xenopus oocytes followed by immunoprecipitation with an anti-DR antiserum. The translation products assembled with DR alpha and beta chains in oocytes coinjected with all three mRNAs. Assembly of DR alpha and beta chains was also observed in the absence of DRp33 mRNA. Furthermore, when compared with DRp33 immunoprecipitated from a human B-cell line, translation products of the hybrid-selected mRNA showed (i) identical migration in two-dimensional gel electrophoresis, (ii) identical apparent molecular weight in the absence of N-linked glycosylation, and (iii) a very similar two-dimensional peptide map. Transcription of the DRp33 gene into a mRNA 1,400 nucleotides long was observed in B cells but was undetectable in T-cell lines and was very low in liver. Thus, DRp33 appears to be coordinately expressed with DR alpha and beta chains. Hybridization to DNA of mouse-human somatic cell hybrids showed that DRp33 is encoded by a gene that is located outside the major histocompatibility complex.

Isolation of distinct cDNA clones encoding HLA-DR beta chains by use of an expression assay

cDNA clones encoding different human Ia antigen beta chains were isolated by use of a complementation-expression assay in Xenopus oocytes. The assay was based on two previous findings. First, oocytes injected with mRNA from a human B-cell line express HLA-DR antigen. The three intracellular DR chains are assembled in oocytes and can be immunoprecipitated with anti-DR monoclonal antibodies. Second, we have isolated cDNA clones encoding DR alpha and intermediate chains. In order to identify beta-chain cDNA clones, mRNA was hybrid-selected with pools of cDNA clones, mixed with mRNA for the alpha and intermediate chains, and injected into oocytes. We isolated two distinct clones that could select DR beta-chain mRNA as demonstrated by assembly of the translation product with DR alpha chains and immunoprecipitation with DR-specific monoclonal antibodies. One clone is specific for a beta chain of the DR locus. The other clone, much weaker in its ability to select DR mRNA, encodes another Ia-like beta chain. Full-length cDNA clones corresponding to the DR and Ia-like beta chains were isolated and compared. Cross-hybridization was detectable in the coding regions but not in the 3' untranslated regions. Distinct RNAs homologous to the DR and the Ia-like beta-chain clones were present in B cells but were undetectable in three T-cell lines.

Isolation of cDNA clones encoding HLA-DR alpha chains

HLA-DR antigens, the human equivalent of mouse Ia antigens, are multimeric surface glycoproteins characterized by a high degree of allelic polymorphism. They are expressed specifically on macrophages and lymphocytes and they play a key role in the regulation of the immune response. We have investigated this complex genetic system by a direct study of the genes involved through molecular cloning. This paper deals with the cloning, in plasmids, of full-length cDNA sequences for the HLA-DR alpha chain from the human B-cell line Raji. The approach relies on a translation assay of mRNA injected into frog oocytes and recognition of translation products by polyclonal and monoclonal antibodies. After enrichment of specific mRNA and cloning of cDNA, plasmid clones were analyzed by hybridization-selection of mRNA and translation in oocytes. A clone was identified and used to screen a cDNA library from which several full-length HLA-DR alpha chain plasmids were isolated. DNA sequence determination of one such clone confirmed its identity and also established the amino acid sequence of the NH2-terminal signal sequence of HLA-DR alpha chains. The translation product of HLA-DR alpha chain mRNA purified by hybridization-selection gives a single alpha chain spot on two-dimensional gels, whereas the alpha chain released from the alpha/beta HLA-DR complex gives about seven distinct spots. Finally, the results of analysis of genomic DNA by Southern blotting are compatible with the existence of a single nonpolymorphic alpha chain gene and indicate extensive cross-hybridization with a homologous gene in mouse DNA.