Altered differentiation and paracrine stimulation of mammary epithelial cell proliferation by conditionally activated Smoothened

摘要

TheHedgehog(Hh)signalingnetworkiscriticalforpatterningandorganogenesisinmammals,andhasbeenimplicatedinavarietyofcancers.Smoothened(Smo),thegeneencodingtheprincipalsignaltransducer,isoverexpressedfrequentlyinbreastcancer,andconstitutiveactivationinMMTV-SmoM2transgenicmicecausedalterationsinmammaryglandmorphology,increasedproliferation,andchangesinstem/progenitorcellnumber.Bothintransgenicmiceandinclinicalspecimens,proliferativecellsdidnotusuallyexpressdetectableSmo,suggestingthehypothesisthatSmofunctionedinanon-cellautonomousmannertostimulateproliferation.Here,weemployedageneticallytaggedmousemodelcarryingaCre-recombinase-dependentconditionalalleleofconstitutivelyactiveSmo(SmoM2)totestthishypothesis.MMTV-Cre-oradenoviral-Cre-mediatedSmoM2expressionintheluminalepithelium,butnotinthemyoepithelium,wasrequiredforthehyper-proliferativephenotypes.Highlevelsofproliferationwereobservedincellsadjacentorinclose-proximitytoSmoexpressingcellsdemonstratingthatSmoM2expressingcellswerestimulatingproliferationviaaparacrineorjuxtacrinemechanism.Incontrast,Smoexpressionalteredluminalcelldifferentiationinacell-autonomousmanner.SmoM2expressingcells,purifiedbyfluorescenceactivatedcellsorting(FACS)viathegeneticfluorescenttag,expressedhighlevelsofPtch2,Gli1,Gli2,Jag2andDll-1,andlowerlevelsofNotch4andHes6,incomparisontowildtypecells.ThesestudiesprovideinsightintothemechanismofSmoactivationinthemammaryglandanditspossiblerolesinbreasttumorigenesis.Inaddition,theseresultsalsohavepotentialimplicationsfortheinterpretationofproliferativephenotypescommonlyobservedinotherorgansasaconsequenceofhedgehogsignalingactivation./p/div