title: p27Kip1 mediates addiction of ovarian cancer cells to MYCC (c-MYC) and their dependence on MYC paralogs.
abstract: The MYCC (c-MYC) gene is amplified in 30-60% of human ovarian cancers. We assessed the functional significance of MYCC amplification by siRNA inhibition of MYCC or MYC paralogs in a panel of ovarian cancer cell lines expressing varying levels of MYCC. Inactivation of MYCC inhibited cell proliferation and induced replicative senescence only in lines with amplified MYCC, indicating that these cells are addicted to continued MYCC overexpression. In contrast, siRNA knockdown of all three MYC isoforms inhibited proliferation of MYCC non-amplified ovarian cancer cells without inducing replicative senescence, and did not inhibit the proliferation of telomerase-immortalized ovarian surface epithelial cells. The arrest induced by MYCC knockdown was accompanied by an increase in the level of the Cdk inhibitor p27(Kip1) and a decrease in cyclin A expression and Cdk2 activity, and could be reversed by RNAi knockdown of p27(Kip1) or Rb, or by overexpression of cyclin A/Cdk2. The arrest induced by knockdown of all three MYC isoforms could similarly be reversed by p27(Kip1) knockdown. Our findings indicate that the addiction of MYCC-amplified ovarian cancer cells to MYCC differs from the dependence of MYCC non-amplified cancer cells on MYC paralogs, but both are mediated, at least in part, by p27(Kip1). They also suggest that growth of ovarian cancers may be blocked by inhibition of MYCC or MYC paralogs.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, California 94720, USA.
authors.forename: Tulsiram
authors.initials: T
authors.lastname: Prathapam
authors.forename: Alexey
authors.initials: A
authors.lastname: Aleshin
authors.forename: Yinghui
authors.initials: Y
authors.lastname: Guan
authors.forename: Joe W
authors.initials: JW
authors.lastname: Gray
authors.forename: G Steven
authors.initials: GS
authors.lastname: Martin
mesh_terms: D000818:Animals; D002453:Cell Cycle; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D019925:Cyclin A / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27 / Q000378:metabolism*; D005260:Female; D006801:Humans; D010051:Ovarian Neoplasms / Q000235:genetics / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D047428:Protein Kinase Inhibitors / Q000378:metabolism*; D016271:Proto-Oncogene Proteins c-myc / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000235:genetics / Q000378:metabolism
chemical_list: D019925:Cyclin A; C489427:MYC protein, human; D020033:Protein Isoforms; D047428:Protein Kinase Inhibitors; D016271:Proto-Oncogene Proteins c-myc; D034741:RNA, Small Interfering; D050760:Cyclin-Dependent Kinase Inhibitor p27; C495894:CDK2 protein, human; D051357:Cyclin-Dependent Kinase 2