BackgroundInformation | I.TESTPRINCIPLE: ThecolorimetricSTAR(SignalTransductionAssayReaction)ELISAkitisasolidphasesandwichenzymelinkedimmunosorbentassaythatprovidesafast,sensitivemethodtodetectspecificlevelsofsignalingtargetsinwholecellextracts.TheIκBplateiscoatedwithaspecificmousemonoclonalIκBcaptureantibodyonthemicrowellsofthe96-wellclearplate.SamplelysateorthestandardincludedinthekitareincubatedinthemicrowellsallowingIκBantigentobecapturedintheplatewells.Theplateisthenwashedtoremoveanyun-boundnonspecificmaterial.Aspecificrabbitanti-phospho-IκBantibodyisaddedtodetectthecapturedIκBontheplatewellthatisphosphorylatedonSer32.TheunbounddetectionantibodyiswashedawayfollowedbyincubationwithanHRP-conjugatedanti-rabbitantibody.Thisallowsforasensitiveenzymaticdetectionofthesample.AftertheadditionofTMBsubstrateandstopsolutiontheabsorbanceismeasuredat450nmusingaplatereader. Theentireassaytakeslessthan5hourstocompletewithminimalhands-ontime.Manyofthereagentsaresuppliedinready-touseformulationsforeaseofuse.ThekitalsoincludesastandardthatisrunasbothapositivecontrolandtogenerateastandardcurveforIκBmeasurement.
II.BACKGROUND: NFκBsignalingisacriticalregulatornotonlyofimmunefunction,butalsoofproliferationversusapoptosisinresponsetovariousstimuli.Inamajorityofunstimulatedcells,theNFκBtranscriptionfactorsexistintheirinactiveformandareretainedinthecytoplasmbytheboundinhibitoryIκBproteinsthatpreventitfromenteringthenucleus,thuskeepingNFκBinaninactivestate.Uponstimulationbymultipleinducersincludingvirusesorcytokines,suchasTNFα,IL-1,orPMA,IκBαisrapidlyphosphorylatedbyIKK(IκBKinase),whichphosphorylatesIκBonserines32and36,allowingrecognitionbytheubiquitinligasemachinery,leADIngtoitspolyubiquinationanddegradation,resultinginthereleaseoftheNFκBcomplex.OnceIκBisdegraded,NFκBisabletoinitiatetranscription.TheNFκBcomplexthentranslocatestothenucleuswhereitactivatesgenetranscription.NFκBinducesthetranscriptionofitsowninhibitor,IκBα,causinganautoregulatorymechanismofNFκBactivityandgeneratingtheinactiveformofNFκB.ThenewlyformednuclearNFκB-IκBαcomplexesarethenexportedouttothecytoplasm,therebyreestablishingthecytoplasmicpoolofinactiveNFκBcomplexesprimedforanotherroundofactivationtotakeplace.ThewidevarietyofgenesregulatedbyNFκBincludesthoseencodingcytokines,chemokines,adhesionmolecules,acutephaseproteins,andinducIBLeeffectorenzymes.MutantIκBinwhichserines32and36arechangedtoalanines,isnotphosphorylated,andthereforenotdegraded.CellsexpressingthisproteinarenotabletoactivateNFκB,providingausefultooltostudytheroleofNFκBinvariouspathwaysandprocesses. |