title: Signalling responses linked to betulinic acid-induced apoptosis are antagonized by MEK inhibitor U0126 in adherent or 3D spheroid melanoma irrespective of p53 status.
abstract: MEK1/2 inhibitors like U0126 can potentiate or antagonize the antitumor activity of cytotoxic agents such as cisplatin, paclitaxel or vinblastine, depending on the drug or the target cells. We now investigated whether U0126, differentially regulates melanoma signaling in response to UV radiation or betulinic acid, a drug lethal against melanoma. This report shows that U0126 inhibits early response (ERK) kinase activation and cyclin A expression in wt p53 C8161 melanoma exposed to either UV radiation or betulinic acid. However, U0126 does not protect from UV damage, but counteracts betulinic acid-mediated apoptosis in the same cells. Protection from the latter drug by joint treatment with U0126 was also evident in wt p53 MelJuso melanoma and mutant p53 WM164 melanoma. The latter cells were the most responsive to betulinic acid, showing a selective decline in the cdk4 protein, without a comparable change in other key cell cycle proteins like cdc2, cdk2, cdk7 or cyclin A, prior to apoptosis-associated PARP fragmentation. Laser scanning cytometry also showed that betulinic acid induced a significant increase in chromatin condensation in WM164 melanoma irrespective of whether they were in adherent form or as multicellular spheroids. All these betulinic acid-induced changes were counteracted by U0126. Our data show for the first time that (a) cdk4 protein is an early target of betulinic acid-induced apoptosis and (b) unrestricted ERK signaling favours betulinic acid-induced apoptosis, but this is counteracted by U0126, partly through counteracting chromatin condensation and restoring Akt activation decreased by betulinic acid treatment.
authors.affiliation: IVIC, Tumor Cell Biology Laboratory, Apartado 21827, Caracas 1020 A, Venezuela. mrieber@ivic.ve
authors.forename: Manuel
authors.initials: M
authors.lastname: Rieber
authors.forename: Mary Strasberg
authors.initials: MS
authors.lastname: Rieber
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D002070:Butadienes / Q000494:pharmacology*; D002448:Cell Adhesion / Q000187:drug effects; D045744:Cell Line, Tumor; D002843:Chromatin / Q000187:drug effects / Q000378:metabolism; D019925:Cyclin A / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D004249:DNA Damage / Q000187:drug effects; D015536:Down-Regulation; D004789:Enzyme Activation / Q000187:drug effects / Q000528:radiation effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D008545:Melanoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology*; D053978:Pentacyclic Triterpenes; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D014315:Triterpenes / Q000494:pharmacology*; D016159:Tumor Suppressor Protein p53 / Q000235:genetics / Q000378:metabolism*; D000094062:Betulinic Acid
chemical_list: D002070:Butadienes; D002843:Chromatin; D019925:Cyclin A; D009570:Nitriles; D053978:Pentacyclic Triterpenes; D047428:Protein Kinase Inhibitors; D014315:Triterpenes; D016159:Tumor Suppressor Protein p53; C113580:U 0126; D051057:Proto-Oncogene Proteins c-akt; D051358:Cyclin-Dependent Kinase 4; D048049:Extracellular Signal-Regulated MAP Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D000094062:Betulinic Acid