title: The methionine salvage pathway compound 4-methylthio-2-oxobutanate causes apoptosis independent of down-regulation of ornithine decarboxylase.
abstract: 4-Methylthio-2-oxobutanoic acid (MTOB) is the final compound of the methionine salvage pathway that converts the polyamine byproduct methylthioadenosine to adenine and methionine. Here we find that MTOB inhibits growth of several human cell lines in a dose-dependent manner. Growth inhibition was specific for MTOB as we did not observe any inhibition with other chemically related compounds. MTOB treatment causes apoptosis and reduction of ornithine decarboxylase (ODC) activity but not ODC mRNA. To determine if MTOB exerts its effects primarily via ODC inhibition, we compared the effects of MTOB with the ODC-specific inhibitor difluoromethylornithine (DFMO). We found that MTOB was a more potent inducer of apoptosis than DFMO, lacked activation of caspase 3/7, and was able to induce apoptosis in cells lacking p53. Our results show that MTOB-induced growth inhibition and apoptosis is not simply secondary due to ODC inhibition and implies that MTOB activates apoptosis via other mechanisms.
authors.affiliation: Division of Population Science, Fox Chase Cancer Center, 333 Cottman Avenue, Philadelphia, PA 19111, USA.
authors.forename: Baiqing
authors.initials: B
authors.lastname: Tang
authors.forename: Yuwaraj
authors.initials: Y
authors.lastname: Kadariya
authors.forename: Maureen E
authors.initials: ME
authors.lastname: Murphy
authors.forename: Warren D
authors.initials: WD
authors.lastname: Kruger
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects; D000518:Eflornithine / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D006131:Growth Inhibitors / Q000494:pharmacology; D006801:Humans; D008715:Methionine / Q000031:analogs & derivatives* / Q000494:pharmacology; D009955:Ornithine Decarboxylase / Q000235:genetics / Q000378:metabolism; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines / Q000145:classification / Q000494:pharmacology; D011506:Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism
chemical_list: D006131:Growth Inhibitors; D065108:Ornithine Decarboxylase Inhibitors; D011073:Polyamines; D011506:Proteins; D012333:RNA, Messenger; D016159:Tumor Suppressor Protein p53; C031017:ornithine decarboxylase antizyme; C014632:2-keto-4-methylthiobutyric acid; D008715:Methionine; C505407:CASP3 protein, human; C505520:CASP7 protein, human; D053148:Caspase 3; D053179:Caspase 7; D020169:Caspases; D009955:Ornithine Decarboxylase; D000241:Adenosine; D000518:Eflornithine