title: Rapamycin and UCN-01 synergistically induce apoptosis in human leukemia cells through a process that is regulated by the Raf-1/MEK/ERK, Akt, and JNK signal transduction pathways.
abstract: Interactions between the protein kinase C and Chk1 inhibitor UCN-01 and rapamycin in human leukemia cells have been investigated in relation to apoptosis induction. Treatment of U937 monocytic leukemia cells with rapamycin (10 nmol/L) in conjunction with a minimally toxic concentration of UCN-01 (100 nmol/L) for 36 hours resulted in marked potentiation of mitochondrial injury (i.e., loss of mitochondrial membrane potential and cytosolic release of cytochrome c, AIF, and Smac/DIABLO), caspase activation, and apoptosis. The release of cytochrome c, AIF, and Smac/DIABLO were inhibited by BOC-D-fmk, indicating that their release was caspase dependent. These events were associated with marked down-regulation of Raf-1, MEK, and ERK phosphorylation, diminished Akt activation, and enhanced phosphorylation of c-Jun NH2-terminal kinase (JNK). Coadministration of UCN-01 and rapamycin reduced the expression levels of the antiapoptotic members of the Bcl-2 family Mcl-1 and Bcl-xL and diminished the expression of cyclin D1 and p34(cdc2). Furthermore, enforced expression of a constitutively active MEK1 or, to a lesser extent, myristoylated Akt construct partially but significantly attenuated UCN-01/rapamycin-mediated lethality in both U937 and Jurkat cell systems. Finally, inhibition of the stress-related JNK by SP600125 or by the expression of a dominant-negative mutant of c-Jun significantly attenuated apoptosis induced by rapamycin/UCN-01. Together, these findings indicate that the mammalian target of rapamycin inhibitor potentiates UCN-01 cytotoxicity in a variety of human leukemia cell types and suggest that inhibition of both Raf-1/MEK/ERK and Akt cytoprotective signaling pathways as well as JNK activation contribute to this phenomenon.
authors.affiliation: Department of Medicine, MCV Station Box 230, Virginia Commonwealth University, Medical College of Virginia, Richmond, VA 23298, USA.
authors.forename: Michael
authors.initials: M
authors.lastname: Hahn
authors.forename: Weiqun
authors.initials: W
authors.lastname: Li
authors.forename: Chunrong
authors.initials: C
authors.lastname: Yu
authors.forename: Mohamed
authors.initials: M
authors.lastname: Rahmani
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis; D016203:CDC2 Protein Kinase / Q000378:metabolism; D020169:Caspases / Q000378:metabolism; D045744:Cell Line, Tumor; D019938:Cyclin D1 / Q000378:metabolism; D045304:Cytochromes c / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005799:Genes, Dominant; D006801:Humans; D015151:Immunoblotting; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism*; D019169:Jurkat Cells; D007938:Leukemia / Q000188:drug therapy*; D048369:MAP Kinase Kinase 1 / Q000378:metabolism*; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology*; D019311:Staurosporine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D013997:Time Factors; D020298:U937 Cells
chemical_list: D000903:Antibiotics, Antineoplastic; D000970:Antineoplastic Agents; D011518:Proto-Oncogene Proteins; D019938:Cyclin D1; C054852:7-hydroxystaurosporine; D045304:Cytochromes c; C494918:AKT1 protein, human; D017346:Protein Serine-Threonine Kinases; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D016203:CDC2 Protein Kinase; D048049:Extracellular Signal-Regulated MAP Kinases; D048031:JNK Mitogen-Activated Protein Kinases; D048369:MAP Kinase Kinase 1; D048670:MAP Kinase Kinase 4; D020929:Mitogen-Activated Protein Kinase Kinases; D020169:Caspases; D019311:Staurosporine; D020123:Sirolimus