title: Mitogen-activated protein kinase inhibition induces translocation of Bmf to promote apoptosis in melanoma.
abstract: Constitutive activation of the mitogen-activated protein kinase (MAPK) pathway is implicated in the development and progression of many human cancers, including melanoma. Mutually exclusive activating mutations in NRAS or BRAF have been identified in approximately 85% of melanomas, and components of this pathway have been developed as molecular targets for therapeutic intervention. We and others have shown that inhibition of this pathway with specific small molecule MAPK/extracellular signal-regulated kinase kinase (MEK) inhibitors induces a wide range of apoptotic responsiveness in human melanoma cells both in vitro and in vivo. To define the molecular mechanism underlying variable apoptotic sensitivity of melanoma cells to MEK inhibition, we examined the expression and subcellular localization of Bcl-2 family members in a comprehensive set of human melanoma cell lines. Whereas the proapoptotic protein Bim was activated and localized to the mitochondrial membrane in all cell lines regardless of apoptotic sensitivity, Bmf activation and cytosolic translocation was exclusive to sensitive cells. In resistant cells, Bmf remained sequestered to the cytoskeleton through dynein light chain 2 (DLC2) binding. Overexpression of Bmf in resistant cells did not enhance apoptosis, whereas expression of mutant BmfA69P, which has decreased binding to DLC2, promoted cell death. Expression of BmfA69P mutants possessing the Bcl-2 homology 3 (BH3) domain mutation L138A, which impairs BH3 interactions, did not enhance apoptosis in resistant cells. RNA interference targeting Bim and Bmf provided protection from apoptosis induced by MEK inhibition. These results show a novel role for Bmf in promoting apoptosis and provide insight into the mechanism of apoptotic resistance to MEK inhibition in melanoma.
authors.affiliation: Drug Development Department, Nevada Cancer Institute, Las Vegas, Nevada 89135, USA.
authors.forename: Matthew W
authors.initials: MW
authors.lastname: VanBrocklin
authors.forename: Monique
authors.initials: M
authors.lastname: Verhaegen
authors.forename: Maria S
authors.initials: MS
authors.lastname: Soengas
authors.forename: Sheri L
authors.initials: SL
authors.lastname: Holmen
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism*; D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000502:physiology; D000072224:Bcl-2-Like Protein 11; D001549:Benzamides / Q000494:pharmacology; D001713:Biphenyl Compounds / Q000494:pharmacology; D020169:Caspases / Q000502:physiology; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D048049:Extracellular Signal-Regulated MAP Kinases / Q000037:antagonists & inhibitors; D006801:Humans; D008545:Melanoma / Q000188:drug therapy* / Q000401:mortality / Q000473:pathology; D008565:Membrane Proteins / Q000502:physiology; D020929:Mitogen-Activated Protein Kinase Kinases / Q000037:antagonists & inhibitors*; D009596:Nitrophenols / Q000494:pharmacology; D010879:Piperazines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology*; D021381:Protein Transport / Q000187:drug effects; D011518:Proto-Oncogene Proteins / Q000502:physiology; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000032:analysis; D013449:Sulfonamides / Q000494:pharmacology
chemical_list: C120227:2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide; C501332:ABT-737; D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; C486655:BMF protein, human; D000072224:Bcl-2-Like Protein 11; D001549:Benzamides; D001713:Biphenyl Compounds; D008565:Membrane Proteins; D009596:Nitrophenols; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D013449:Sulfonamides; D048049:Extracellular Signal-Regulated MAP Kinases; D020929:Mitogen-Activated Protein Kinase Kinases; D020169:Caspases