Metabolic adaptations in rat hepatomas: altered regulation of serine dehydratase synthesis by glucose and amino acids in hepatocellular carcinomas.

[CANCERRESEARCH30,387—392,February1970]SUMMARYTheforcedfeedingofaminoacidmixturestoratsbearingtheMorris5123hepatomahadvirtuallynoeffectonchangingthealreadyhighlevelsofserinedehydratasepresentinthisneoplasm.OntheotherhandasimilarregimendidstimulateanincreaseinthelevelofserinedehydrataseintheMorris7800andReuberH-35hepatomas.Glucoseadministrationtogetherwiththeaminoacidshadvirtuallynoeffectonchangingorinhibitingthestimulatedlevelsoftheaminoacidsinthehepatomas.Byquantitativeprecipitintechniquesandpulselabelingwithvaline-14C,itwasdemonstratedthattherateofsynthesisofserinedehydrataseintheMorrishepatoma5123wasextremelyhighrelativetototalsolubleproteinsynthesisandthattheadministrationofaminoacidsorglucosehadnoeffectonvalineincorporationintoserinedehydratase.Theresultsobtainedapparentlywerenottheresultofadramaticallydifferentstructureoftheserinedehydratase oftheneoplasms,norweretheyaresultoftherelativeunavailabilityofglucosetotheneoplasmsbecauseoftheirdifferentbloodsupplies.Thedatapresentedindicateaderangedeffectofglucoseonenzymesynthesis,probablytheresultofalteredmechanismsofthetranslationalcontrolofenzymesynthesis.INTRODUCTIONEarlierstudiesfromthis(12,14,17)andotherlaboratories(20)havedemonstratedthatthehormonalandsubstrateregulationofenzymelevelsinhepatomasisingeneralalteredincomparisonwiththesamemechanismsseeninnormalliver.Examplesofthishavebeenseenwiththeregulationofserinedehydratase (L-serinehydro-lyase,EC4.2.1.13)intheMorrishepatoma 5123and7793.Theenzymewasshowntobeatextremelyhighlevelsintumorsgrowingin1TheworkreportedhereinwassupportedinpartbyNationalCancerInstituteGrantCA-07175andAmericanCancerSocietyGrantP-314.2Presentaddress:DivisionofResearch,NationalJewishHospital,Denver,Cob.80206.3CareerDevelopmentAwardee(CA-40415)oftheNationalCancerInstitute.ReceivedJanuary27,1969;acceptedJune10,1969.intacthosts.Adrenalectomy ofthetumor-bearinghostresultedinamarkedloweringofthelevelsofserinedehydrataseinthetumorsbuthadverylittleeffectontheenzymeinthelivers(1).Withotherenzymessuchastyrosinetransaminasetheactivitywashighinmosthepatomasandalsolowereduponadrenalectomyofthehost.Administrationofcorticosteroidsresultedinamarkedincreaseintheleveloftheenzymeactivityinbothtumorandliver.Thefeedingwithhigh-proteindiets(5,13)alsofailedtostimulateincreasesinthelevelsofserinedehydrataseinmosttumors.AnexceptiontothiswastheMorrishepatoma7800(1),whichdidrespondtoahigh-proteindietbyanincreasedserinedehydrataselevel.Inmostoftheexperimentspreviouslydescribedtheenzymesstudiedwerethoseinvolvedingluconeogenesis.Studiesfromthislaboratoryhavedemonstratedthattheadministrationofglucosetoanimalsbeingorhavingbeengivenlargeamountsofproteinresultsinacompletecessationofthesynthesisoftheenzyme,serinedehydratase(6,9,13).Theexperimentsdescribedinthispaperweredesignedtotestwhetherornotglucoserepressionofserinedehydrataseisactiveornonfunctional inseveralhighlydifferentiatedhepatocellularcarcinomas.MATERIALSANDMEThODSThetumorsusedintheseexperimentsweretheMorris5123and7800hepatomasandReuberhepatomaH-35.TheMorrishepatomawascarriedinBuffalostrainratsandtheReuberhepatomawascarriedinACI/Nrats.Transplantationofalltheseneoplasmswasperformedinthislaboratoryviatrocarintramuscularly inthehindlegsoftheanimals.Inductionofserinedehydratasewasperformedbyintraperitonealinjectionsofanequimolarmixtureof10essentialaminoacidsatalevelof300mgin5ml0.9%NaClsolution/doseevery6hr(8).Theglucose,givenatthevarioustimesindicatedorgiven6hraftertheinitialaminoacidadministration, wasadministeredthroughastomachtubewiththemiceunderslightetheranesthesia.Thedosewas2gglucose/100gbodyweight.Atthetimeindicatedineachexperimenta‘4C-labeledaminoacidwasinjectedintraperitoneallyandtheratswerekilledafter30min(6).Ahigh-speedcentrifugateoftheliverandtumorhomogenate@ waspreparedandthe4C-labeledaminoacidincorporationintoimmunochemicallyprecipitableenzymewasdetermined.FEBRUARY1970 387