ABSTRACT
We investigated why treatment of cells with dual aurora A and B kinase inhibitors produces phenotypes identical to inactivation of aurora B. We found that dual aurora kinase inhibitors in fact potently inhibit cellular activities of both kinases, indicating that inactivation of aurora B bypasses aurora A in mitosis. RNAi experiments further established that inactivation of aurora B indeed bypasses the requirement for aurora A and leads to polyploidy. Inactivation of aurora A activates checkpoint kinase BubR1 in an aurora B-dependent manner. Our results thus show that aurora B is responsible for mitotic arrest in the absence of aurora A.
Subject(s)
Mitosis/physiology , Protein Serine-Threonine Kinases/antagonists & inhibitors , Protein Serine-Threonine Kinases/physiology , Aurora Kinase B , Aurora Kinases , Benzamides/pharmacology , Cell Cycle Proteins/metabolism , Cell Line, Tumor , Humans , Indoles/pharmacology , Mitosis/genetics , Polyploidy , Protein Kinase Inhibitors/pharmacology , Protein Kinases/metabolism , Protein Serine-Threonine Kinases/genetics , Protein Serine-Threonine Kinases/metabolism , Quinazolines/pharmacology , RNA Interference , Sulfonamides/pharmacologyABSTRACT
Protein kinase C (PKC) regulates activation of the Raf-1 signaling cascade by growth factors, but the mechanism by which this occurs has not been elucidated. Here we report that one mechanism involves dissociation of Raf kinase inhibitory protein (RKIP) from Raf-1. Classic and atypical but not novel PKC isoforms phosphorylate RKIP at serine 153 (Ser-153). RKIP Ser-153 phosphorylation by PKC either in vitro or in response to 12-O-tetradecanoylphorbol-13-acetate or epidermal growth factor causes release of RKIP from Raf-1, whereas mutant RKIP (S153V or S153E) remains bound. Increased expression of PKC can rescue inhibition of the mitogen-activated protein (MAP) kinase signaling cascade by wild-type but not mutant S153V RKIP. Taken together, these results constitute the first model showing how phosphorylation by PKC relieves a key inhibitor of the Raf/MAP kinase signaling cascade and may represent a general mechanism for the regulation of MAP kinase pathways.
