Patent Application: US-18827594-A

Abstract:
a human μ opiate receptor cdna has been identified from a cerebral cortical cdna library using sequences from the rat μ opiate receptor cdna . the human μ opiate receptor shares 95 % amino acid identity with the rat sequence . the expressed μor1 recognizes tested opiate drugs and opioid peptides in a sodium - and gtp - sensitive fashion with affinities virtually identical to those displayed by the rat μ opiate receptor . effects on cyclic amp are similar to those noted for the rat μ opiate receptor . overlapping genomic clones spanning 50 kilobasepairs and hybridizing with the hμor1 cdna contains exon sequences encoding the entire open reading frame of the human a opiate receptor are described . analysis of hybridization to dna prepared from human rodent hybrid cell lines and chromosomal in situ hybridization studies indicate localization to 6q24 - 25 . an mspi polymorphism , producing a 3 . 7 kb band , is being used to assess this gene &# 39 ; s involvement in neuropsychiatric disorders involving opiatergic systems .

Description:
the medicinal and addictive properties of opium have been recognized since victorian times . the modern derivative , morphine , is well - known as a powerful analgesic . codeine is also an opiate commonly encountered in cough syrups . heroin is yet another opiate well - known to the layman as a drug of abuse . all of these compounds produce their effects on the body upon interaction with a cell surface receptor . several receptors for opiates have been found . all are structurally related , being members of the family of receptors having seven transmembrane segments “ stitched ” through the cell surface membrane . of course , these receptors did not evolve in humans in anticipation of people ingesting products from opium poppies or modern , synthetic compounds derived from them . rather , the body produces a number of endogenous ligands , collectively known as enkephalins or endorphins , which bind to opiate receptors . enkephalins are short peptides , processed from a larger polyprotein ( pomc ), first discovered in the pituitary . the peptide yggfm (“ met - enkephalin ”, seq . i . d . no . 12 ) is one well - known enkephalin . also , synthetic enkephalin derivatives are known , e . g . d - ala 2 , n - methyl - phe 4 , glycol 5 enkephalin ( damgo ). additional synthetic ligands of opiate receptors are also known , such as levorphanol and naloxone . as noted above , opiate receptors form a family of proteins , the members of which can be distinguished by differential binding of various peptide and non - peptide opioids . μ receptors recognize morphine with high affinity , δ receptors have high affinity for enkephalin peptides but poor affinities for morphine , and κ receptors display preferential affinity for dynorphin peptides . the distribution of various opiate receptor classes varies from tissue to tissue . the present invention resides , in part , in cloned dna molecules encoding a human μ opiate receptor . a cloned cdna encoding a human μ opiate receptor has the nucleotide sequence shown in seq id no : 1 . however , the present invention is not to be limited strictly to the sequence shown in seq id no : 1 . rather the invention encompasses alterations of that sequence including degenerate nucleotide sequences which would still encode the amino acid sequence shown as seq id no : 2 . furthermore , variants such as substitutions , small deletions , insertions or inversions , which nevertheless encode proteins having substantially the biochemical activities associated with the human a opiate receptor , are encompassed by the present invention . sequences which are able to hybridize to the nucleotide sequence of seq id no : 1 , under conditions typically associated with gene isolation experiments or southern blotting experiments , are preferred . example 1 describes one set of such conditions ; hybridization was performed in 29 % formamide , 6 × sspe , at 30 ° c . those sequences which will hybridize under “ stringent ” conditions of hybridization and washing are especially preferred . in looking to sequences which are preferred variants , one of skill in the art would compare the amino acid sequences of the human μ opiate receptor with the amino acid sequence of the μ opiate receptor of other species . the amino acid sequence of the rat and human μ receptors are highly conserved . all but one of the amino acid differences not located in the extracellular amino terminal domain conserve hydrophobicity and charge , and thus are not expected to greatly affect protein function . the majority of the differences in amino acid sequence are localized in the amino terminal extracellular domain . thus , the amino terminal extracellular domain is expected to be the portion of the protein which has a large influence on the species differences , if any are observed , in biochemical characteristics of the μ opiate receptor . similarly , comparison of the amino acid sequences of the μ -, δ - and κ - opiate receptors within a single species is expected to shed light on sequence determinants of ligand discrimination . the present invention therefore encompasses those variants which can be made by switching one or more amino acids from an opiate receptor from another species into the homologous position in the human μ opiate receptor . genomic clones hybridizing to the human μ opiate receptor cdna have also been isolated ( hg3 , hg4 , hg24 and hg31 ). hg4 is an 18 kbp insert in a λ - zap ii phage vector . genomic dna fragments of 20 , 15 and 16 kbp are inserted in the genomic clones hg3 , hg24 and hg 31 , respectively . the insert dna can be excised from the vector by digestion of the clones with xho i . these four overlapping clones , which encompass the complete structural gene portion of the hor1 locus , are ordered beneath the intron - exon structure of the locus in fig4 . table i shows the portions of the structural gene which are located on each genomic clone . the nucleotide sequences at the exon - intron boundaries are shown in table ii ( seq id nos : 6 - 11 ). the cloned dna finds utility in , among other applications , the creation of cell lines which can be used to screen compounds for activity , either as ligands for the μ receptor , and therefore likely analgesics , or as antagonists to ligands of the μ receptor . compounds showing activity as antagonists of μ receptor ligands might prove useful as treatments for heroin addiction . alternatively , such compounds might also be found useful as good analgesics that would be lacking in the less desirable effects of opiate compounds . a screening assay , in its generic form , comprises contacting cells which express μ receptor , by virtue of being transformed with a dna vector carrying a gene encoding a human μ receptor , with an opioid compound . the cells are also contacted , either simultaneously in the case of a competition assay , or subsequently , in the case of a displacement assay , with the compound to be screened . either the opioid compound or the compound being screened may be labeled in some manner , e . g . by a radioisotope , so that the amount of the compound bound or displaced can be measured . binding of ligand to the μ receptor also causes a change in intracellular 3 ′, 5 ′- cyclic adenosine monophosphate ( camp ) levels . thus , the screening assay can also be performed by measuring intracellular camp levels upon addition of the compound to be screened . commercial kits for measurement of intracellular camp are widely available ( e . g . kit rpa 452 , amersham ). measurement of intracellular camp upon ligand binding to rat μ receptor is described in reference 15 . furthermore , the cellular responses of ligand binding to μ receptor appear to be mediated by coupling to a g protein . therefore , such assays as measure μ receptor - g protein interactions can also be used to assess ligand binding or antagonist competition . thus , binding activity can define the affinity of a compound for the μ receptor . the ability to inhibit adenyl cyclase can establish whether a compound is an agonist ( and thus expected to produce morphine - like effects ) or an antagonist ( able to block opiate effects ). also , it is not necessary to use whole cells for the binding assays . it is sufficient to prepare membranes from the transformed cells , which can then be used as the substrate for binding , in place of the whole cells . preparation of membranes retaining receptor binding activity is well known in the art , as exemplified by wang et al . [ 15 ]. also , it is not necessary to use cells which are stably transformed with the μ receptor expression vector , transiently expressing cells can be used . however , a stably expressing cell line is preferred , due to the more reproducible results one obtains using such a cell line . also , it is clearly preferable to use a cell line stably expressing μ receptor as a source of membranes for binding format screening assays . since the μ receptor is a glycoprotein , it is preferable for expression to be obtained in a eukaryotic cell line . several vectors for expressing the dna of the present invention in mammalian cells are known . vectors can be plasmid vectors , such as the pcdna and prep plasmids , available commercially from invitrogen . alternatively , “ defective ” ( replication incompetent ) retroviruses and associated packaging cells lines , e . g . pzipneosvx and its associated ψ2 proliferation cell line ( 42 ) and pa 317 packaging cell lines ( atcc crl 9078 , american type culture collection ) are known in the art . expression of dna encoding μ receptor in yeast can be accomplished using one of the large number of yeast expression vectors commercially available . one might wish to obtain the human μ receptor polypeptide in non - glycosylated form , for example as an immunogen to raise antibodies specific for μ receptor . such a protein can be expressed in bacteria , e . g . in e . coli , by any of the bacterial expression systems typically used in the art . there have been a number of recent reports documenting association of human genotypes with behaviors . we have previously reported an association of the presence of particular alleles of the dopamine receptor protein with drug abuse in polyabusing individuals ( 34 ). consequently , another utility of the cloned dna of the present invention resides in testing , by restriction fragment length polymorphism ( rflp ) analysis , the genotypes of individuals for presence of alleles of the μ receptor ( μor1 ) locus that are associated with opiate abuse behaviors . examples iii and iv , below , describe the identification of one rflp ( msp i ) which identifies two different alleles ( a1 and a2 ) of the μor1 locus and describe a search for a behavior - associated allele in a population of polyabusers who prefer heroin , respectively . it is expected that other polymorphisms of the μor1 locus will be found . general description of the means for identifying rflps is provided in references 43 and 44 . the general problems to be overcome in performing the association analysis , together with solutions for them , is presented in our study of the association of dopamine receptor alleles and cocaine preference behavior ( 34 and copending application u . s . ser . no . 07 / 889 , 723 , continued as u . s . ser . no . 08 / 301 , 722 hereby incorporated by reference ). isolation of cdna and genomic clones encoding human μ opiate recedtor candidate human μ opiate receptor cdnas were obtained using several cdna libraries screened with fragments of the rat opiate receptor rμor1 radiolabeled by random priming to specific activities of 10 9 dpm / μg . phμor1 was a 2 . 1 kb cdna obtained from a human cerebral cortical cdna library prepared by random and oligo - dt priming in λ - zap ii ( stratagene ). filters were hybridized at 30 ° c . in 29 % formamide , 6 × sspe , washed at 42 ° in 0 . 4 × sspe / 0 . 1 % sds , and exposed overnight to x - ray film . plasmids were autoexcised from λ - zap ii phage dna grown from positive plaques as described and analyzed by restriction mapping and cdna sequencing . phμor1 was subjected to complete sequencing using automated and manual methods as described [ 29 ], with sequence analyses using gcg software [ 30 ], and the insert was subcloned into the expression plasmid pcdnal to yield pcdna1hμor1 . phg4 was an 18 kb hμor1 genomic clone isolated from a human genomic library prepared in λ - zap ii phage ( stratagene ) using hybridization with the phμor1 cdna and analysis by sequencing as described [ 30 ]. cos cells were transfected by electroporation with 20 μg / 10 7 cells of plasmid pcdna1hμor1 , grown for two to three days and tested for opiate receptor expression by radioligand binding as described [ 15 ], except that whole cell suspensions were used . adenyl cyclase activities were assessed by radioimmunoassay as described [ 15 ]. cells transfected with the pcdna1 vector alone served as negative controls . although several partial length cdnas were obtained from other libraries , the 2 . 1 kb phμor1 appeared to contain the entire μor1 open reading frame as well as 3 ′ and 5 ′ untranslated sequences . the human cdna displayed an overall nucleotide identity of 79 % with the rat cdna ; 87 % nucleotide identity was noted in coding regions . this cdna displayed an open reading frame with 95 % indentity to amino acids encoded by the rat μ opiate receptor cdna [ 15 - 17 ], 59 % amino acid and 50 % nucleotide identity with the rat κ receptor [ 21 - 22 ] and 62 % amino acid and 59 % nucleotide identity with the rat δ receptor [ 17 ] ( fig1 ). amino acid identities with the rat somatostatin receptor [ 36 ], 40 %, and β 2 adrenergic receptor [ 37 ], 27 %, were higher in transmembrane domains . this sequence manifests five n - terminal sites for potential n - linked glycosylation , seven hydrophobic potential transmembrane domains , and sites for possible phosphorylation characteristic of members of the g - protein linked receptor family ( fig1 ). an 18 kb human genomic subclone , phg4 , displayed sequence beginning in the middle of transmembrane domain 4 at its 5 ′ end , an intron between sequences encoding its second extracellular loop , another exon containing sequence , encoding transmembrane regions 5 - 7 and the first 47 amino acids of the c - terminal domain , and a second intron ( fig4 ). the genomic clone failed to hybridize with an oligonucleotide complementary to a sequence located ca . 400 bp into the 3 ′ untranslated region of the cdna . partial sequence analysis of this genomic clone thus identified 552 bp of nucleotide sequence identical to a portion of the hμor1 cdna . expression of the hμor1 in cos cells revealed high affinity recognition of the μ opiate specific ligand [ 3 h ] damgo ( d - ala 2 , n - methyl - phe 4 , glyol 5 ) enkephalin with k d 1 . 2 +/− 0 . 13 nm ( fig2 ). this binding was displaced by a number of compounds recognizing μ receptors with high affinity . morphine ( 4 . 1 +/− 1 . 4 nm ), ctop ( dphe - cys - tyr - dtrp - orn - thr - pen - thr - nh 2 ; peninsula labs ; 16 +/− 6 nm ), levorphanol and dadle ( d - ala 2 , d - leu 5 enkephalin ; 16 +/− 1 . 3 nm ) displayed nanomolar affinities . u - 50 , 488 , dpdpe ( d - pen 2 , d - pen 5 enkephalin ), dextrorphan and dynorphin a 1 - 17 ( 284 +/− 110 nm ) each displayed low affinities of less than 100 nm . the binding of each compound could be blocked by 1 μmnaloxone . the addition of 50 μmgpp ( nh ) p reduced the affinity of damgo more then three - fold . addition of concentrations of sodium chloride as low as 5 mm reduced binding affinity by two - fold . as noted for the rat μ receptor , the human a μ receptor can couple to adenylate cyclase . addition of morphine or damgo to forskolin - stimulated cos cells expressing the human μor1 transiently resulted in greater than 30 % decreases in adenyl cyclase activity that were naloxone - reversible ( fig2 b ). these results document the nature and function of the human μ opiate receptor . the high conservation of the receptor with the rat sequence , more than 95 %, may reflect its important biological roles . the conservation also extends to function . each of the measures of opioid peptide and drug affinities and second messenger activities noted for the human receptor nicely parallels that noted for the rat . opiate receptor - mediated effects on several different second messenger systems , including adenyl cyclase , have been suggested by neuropharmacologic studies [ 8 - 14 ]. the human μor1 receptor appears to couple to adenyl cyclase , as noted for the rat receptor . interestingly , the rat μ opiate receptor peptide co - purifies with a g iα3 immunoreactive g - protein species [ 39 ]. a 1 . 2 kb 3 ′ fragment of hμor1 contained 526 bp of coding sequence beginning in the protein &# 39 ; s predicted second extracellular loop and displayed nucleotide sequence 87 % identical to the rat rμor1 nucleotide sequence . this 1 . 2 kb fragment , and the genomic clone hg4 , were radiolabeled by random priming , and used as hybridization probes in southern analyses of the somatic cell hybrid panels # 1 and # 2 ( bios labs , new haven , conn . 06511 ). these panels contain different complements of hindll digests of human chromosomes in 26 independent cell lines in 36 panels . the panels were incubated separately with each radiolabelled hybridization probe in 29 % formamide / 6 × sspe at 30 ° c . overnight , washed with 0 . 1 × sspe / 0 . 1 % sds for 30 min at 37 ° c . then twice for 30 min at 60 ° c . radioactive patterns were detected by phosphorimaging following overnight exposure . probes were then removed from panels by incubation in water at 90 ° c . for 20 mins , with removal assessed by overnight autoradiographic phosphorimager exposure . higher resolution mapping of the hμor1 gene was accomplished with chromosomal in situ hybridization . a genomic clone , phg4 , was nick - translated with biotin - 14 datp ( brl , gaithersburg , md . ), with 81 % incorporation as determined by tritium tracer incorporation . slides with chromosome spreads were made from normal male lymphocytes cultured with brdu [ 31 ]. fluorescence in situ hybridization was performed as described [ 32 ] with modifications . 12 . 5 μg / μl biotinylated probe in 2xsscp , 50 % formamide , 10 % dextran sulfate , 0 . 5 μg / μl cot - 1 dna and 0 . 5 μg / μl salmon sperm dna were denatured at 70 ° c . for 5 min ., preannealed at 37 ° c . for 30 min ., placed on slides and hybridized at 37 ° c . overnight . slides were washed in 50 % formamide / 2 × ssc at 43 ° c . for 20 minutes , then twice for 5 min . in 2 × ssc at 37 ° c . biotinylated probe was detected with fitc - avidin and biotinylated anti - avidin [ 33 ]; ( oncor , inc . gaithersburg , md . ), following manufacturer &# 39 ; s instructions . southern analyses revealed that both the human cdna and genomic hybridization probes hybridized to total genomic dna extracted from human but not from hamster . southern analyses of dna from 30 panels derived from 26 independent hamster / human somatic cell hybrid lines revealed that both the human cdna and genomic hybridization probes hybridized to dna from each of the six panels derived from four independent cell lines that contained human chromosome six . in studies using the cdna hybridization probe , none of the 30 panels derived from 22 independent cell lines containing material from human chromosomes other than six produced a positive hybridization signal . no other human chromosome was uniformly present in cell lines producing positive hybridization signals . hybridization patterns with the genomic clone hg4 , however , also revealed signals in four panels containing chromosome 3 and two panels containing chromosome 5 . analysis of 42 metaphase cells by fluorescent in situ hybridization demonstrated 20 cells ( 48 %) that had at least one pair of hybridization signals that involved both chromatids of a single chromosome . thirty - two paired signals were seen ; 23 ( 72 %) were located near the terminal end of the long arm of a large c - group ( chr . 6 , 7 or x ) chromosome . to determine the specific chromosome and band , cells were g - banded by fluorescence plus giemsa [ 31 ] techniques , and photographs of banding patterns aligned with photographs of the fluorescence in situ hybridization signals to determine sub - band location . eighteen signals of 27 analyzable signals ( 67 %) were on chromosome 6 , bands q24 - 25 ( fig3 a ). of the remaining 9 signals , seven were located on chromosome 3 , band q26 , while two were on other chromosomes . both somatic cell hybrid panels probed with each of two hμor1 probes and chromosomal in situ hybridization studies using the longer genomic hybridization probe produce concordant hybridzation signals associated with chromosome 6 . recognition of sequences on chromosome 3 and , in somatic cell hybrid studies , 5 by the hg4 genomic probe , but not by the cdna , could be accounted for by hybridization to apparent repetitive sequences identified in the hg4 clone , but not in the cdna . identification of a restriction fragment length polymorphism at the hμor1 locus dna isolated from the leukocytes of 49 unrelated individuals subjected to experimental protocols at the addiction research center , nida [ 34 , 35 ] was digested with bamnhi , ecori , haeiii , hindiii , hinfi , mspi , psti , rsai , and taqi and subjected to southern analyses using the 1 . 2 kb 3 ′ radiolabeled hybridization probe . only mspi digestion produced polymorphisms ; no reproducible polymorphisms were present in lanes digested with other enzymes . digestion with alui , bamhi , ecori , haeiii , hindiii , hinfi , mspi , psti , rsai , and taqi produced constant bands detectable with the 1 . 2 kb hμor1 cdna . however , mspi digestion produced hybridizing fragments of 15 . 0 , 7 . 5 , 6 . 4 , and a 3 . 7 kb that showed variability from individual to individual , creating a distinct polymorphic pattern ( fig3 b ). the 3 . 7 kb band was present in dna from 31 of 49 ( 63 %) of the caucasian individuals studied . an apparently rare variant generated by the absence of the 15 . 0 kb band ( fig3 b ) was detected in only 2 ( 4 . 1 %) of our 49 subjects . no band allelic with the 3 . 7 kb band could be identified in mspi digests . conceivably , the other allele could comigrate with one of the constant bands in mspi digests , or be unrecognized by the 1 . 2 kb 3 ′ hybridization probe used here . association of genotype at the μor1 locus with opiate abuse behavior classical genetic studies , including family , twin and adoption approaches , suggest that individual differences in vulnerability to substance abuse are likely to be , at least in part , genetically determined [ 40 - 41 ]. μopiate receptor systems are plausible candidate genes that might display allelic variants contributing to these individual differences . conceivably , such allelic variation could also contribute to individual differences in potency and power of opiate mediated analgesia , or to development of tolerance during chronic treatments . in order to evaluate the contribution of allelic variation at the μor1 locus to the genetic component of opiate abuse behavior , we are studying the distribution of alleles of the μor1 locus among a population of polyabusers enrolled in clinical studies at the nida addiction research center in baltimore , md . the study is performed substantially as described for the taqi polymorphism in the human dopamine transporter locus ( copending u . s . patent application ser . no . 07 / 889 , 723 , continued as u . s . ser . no . 08 / 301 , 722 hereby incorporated by reference ). in the present instance , the mspi polymorphism identified in example iii is examined in a population of 49 subjects selected from the population described in the dopamine transporter study who indicated a preference , among the several substances abused , for opiates . the invention being thus described , various modifications and changes to the materials and methods used in the practice of the invention , as set forth above , will be obvious to one of skill in the art . such modifications and changes are to be considered as within the scope of the invention as claimed herein below . this paper cites various articles of the scientific and patent literature . each article listed below , and other cited within this paper , are hereby incorporated in their entirety by reference . 1 . lord , j . a . h ., waterfield , a . a ., hughes , j . and kosterlitz , h . w . 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( 1991 ) current opinion in biotechnology 2 , 178 - 183 . asn tyr leu met gly thr trp pro phe gly thr ile leu cys lys ile cys thr met ser val asp arg tyr ile ala val cys his pro val lys ala leu asp phe arg thr pro arg asn ala lys ile ile asn val cys asn trp ile leu ser ser ala ile gly leu pro val met phe met ala thr thr lys tyr arg gln gly ser ile asp cys thr leu thr phe ser his pro thr trp tyr trp glu asn leu leu lys ile cys val phe ile phe ala phe ile met pro val leu ile ile thr val cys tyr gly leu lys ala leu val thr ile pro glu thr thr phe gln thr val ser trp his phe cys ile ala leu gly tyr thr asn ser cys leu asn pro val ser his val asp gly asn gln ser asp pro cys gly leu asn arg thr ala asp ala leu ala thr ser thr leu pro phe gln ser val asn tyr leu met gly thr trp pro phe gly thr ile leu cys lys ile val ile met ser val asp arg tyr ile ala val cys his pro val lys ala leu asp phe arg thr pro arg asn ala lys ile val asn val cys asn trp lys tyr arg gln gly ser ile asp cys thr leu thr phe ser his pro thr trp tyr trp glu asn leu leu lys ile cys val phe ile phe ala phe ile val cys trp thr pro ile his ile tyr val ile ile lys ala leu ile thr ile pro glu thr thr phe gln thr val ser trp his phe cys ile ala leu gly tyr thr asn ser cys leu asn pro val leu tyr leu gly asn val leu val met phe gly ile val arg tyr thr lys leu leu ala thr ser thr leu pro phe gln ser ala lys tyr leu met glu thr trp pro phe gly glu leu leu cys lys ala val leu ser ile asp asp arg tyr ile ala val cys his pro val lys ala leu asp phe arg asp gly ala val val cys thr leu gln phe pro ser pro ser trp tyr cys trp ala pro ile his ile phe val ile val trp thr leu val asp leu asp glu asn phe lys arg cys phe arg gln leu cys arg ala pro met glu ser pro ile gln ile phe arg gly glu pro gly pro thr cys pro phe gln ser ala val tyr leu met asn ser trp pro phe gly asp val leu cys lys ile val ile ser ile asp tyr tyr asn met phe thr ser ile phe thr leu thr met met ser val asp arg tyr ile ala val cys his pro val lys ala leu asp phe arg thr pro leu lys ala lys pro ile his ile phe ile leu val glu ala leu gly ser thr ser his thr asn ser ser leu asn pro val leu tyr ala phe leu asp glu asn