title: Dissecting the roles of checkpoint kinase 1/CDC2 and mitogen-activated protein kinase kinase 1/2/extracellular signal-regulated kinase 1/2 in relation to 7-hydroxystaurosporine-induced apoptosis in human multiple myeloma cells.
abstract: The functional roles of Cdc2 and checkpoint kinase 1 (Chk1) in synergistic interactions between 7-hydroxystaurosporine (UCN-01) and mitogen-activated protein kinase kinase 1/2 (MEK1/2) inhibitors [e.g., 2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide (PD184352)] were examined in human multiple myeloma cells in relation to MEK1/2/ERK1/2 activation and lethality. Time course studies revealed that MEK1/2/extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation preceded Cdc2 dephosphorylation (Tyr15) after UCN-01 exposure. Furthermore, enforced expression of Cdc2 or small inducible RNA (siRNA)-mediated Cdc2 knockdown failed to modify ERK1/2 activation status in either the presence or absence of UCN-01, arguing against a causal relationship between these events. However, ectopic expression of Cdc2 sensitized cells to the lethality of UCN-01/MEK inhibitor regimen, whereas Cdc2 knockdown by siRNA significantly diminished the lethal effects of this combination. Conversely, Chk1 knockdown by siRNA enhanced lethality mediated by UCN-01/PD184352. It is interesting that Chk1 knockdown reduced basal ERK1/2 activation and antagonized the ability of UCN-01 to activate ERK1/2. Finally, ectopic expression of constitutively active MEK1 significantly protected cells from the UCN-01/MEK1/2 inhibitor regimen without modifying Cdc2 activation status. Together, these findings indicate that although UCN-01-mediated Chk1 inhibition and Cdc2 activation are unlikely to be responsible for MEK1/2/ERK1/2 activation, both of these events contribute functionally to enhanced lethality in cells coexposed to MEK inhibitors. They also suggest a role for Chk1 in UCN-01-induced ERK1/2 activation, implying the existence of a heretofore unrecognized link between Chk1 and ERK1/2 signaling.
authors.affiliation: Division of Hematology/Oncology, Virginia Commonwealth University/Medical College of Virginia, MCV Station Box 230, Richmond VA 23298, USA.
authors.forename: Xin-Yan
authors.initials: XY
authors.lastname: Pei
authors.forename: Weiqun
authors.initials: W
authors.lastname: Li
authors.forename: Yun
authors.initials: Y
authors.lastname: Dai
authors.forename: Paul
authors.initials: P
authors.lastname: Dent
authors.forename: Steven
authors.initials: S
authors.lastname: Grant
mesh_terms: D017209:Apoptosis / Q000187:drug effects*; D016203:CDC2 Protein Kinase / Q000378:metabolism*; D045744:Cell Line, Tumor; D000071877:Checkpoint Kinase 1; D004789:Enzyme Activation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D009101:Multiple Myeloma / Q000201:enzymology / Q000473:pathology*; D010766:Phosphorylation; D011494:Protein Kinases / Q000378:metabolism*; D034622:RNA Interference; D019311:Staurosporine / Q000031:analogs & derivatives* / Q000494:pharmacology
chemical_list: D005419:Flavonoids; C054852:7-hydroxystaurosporine; D011494:Protein Kinases; C000605867:CHEK1 protein, human; D000071877:Checkpoint Kinase 1; D016203:CDC2 Protein Kinase; D048049:Extracellular Signal-Regulated MAP Kinases; D019311:Staurosporine; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one