Cks1 regulates cdk1 expression: a novel role during mitotic entry in breast cancer cells.
Cks1, a small protein whose expression is strongly associated with aggressive breast tumors, is a component of cyclin-cdk complexes, as well as the SCF(Skp2) ubiquitin ligase. In these studies, we explored its roles in estrogen receptor-positive breast tumor cells. When exposed to the antiestrogen ICI 182780, these cells accumulate in G(1) by reducing the expression of Cks1, and increasing the levels of p130/Rb2, a cdk2 inhibitor and SCF(Skp2) target. Heregulin beta1 or estradiol abrogate antiestrogen effects by increasing Cks1 expression, down-regulating p130/Rb2 and inducing S phase entry. Depletion of Cks1 in these cells by RNA interference concomitantly decreased Skp2 and up-regulated p130/Rb2 and another SCF(Skp2) target, p27(Kip1). Remarkably, however, Cks1-depleted cells not only exhibit slowed G(1) progression, but also accumulate in G(2)-M due to blocked mitotic entry. Notably, we show that cdk1 expression, which is crucial for M phase entry, is drastically diminished by Cks1 depletion, and that restoration of cdk1 reduces G(2)-M accumulation in Cks1-depleted cells. cdk1 reduction in Cks1-depleted cells is a consequence of a marked decrease in its mRNA and not due to alteration in its proteolytic turnover. Both heregulin beta1 and estradiol could neither restore cdk1 nor sustain cycling in Cks1-depleted cells, although classical estrogen receptor function remained unaltered. Cks1 depletion also decreased Skp2 in human mammary epithelial cells without altering cell cycle progression. Thus, the indispensability of Cks1 to the breast cancer cell cycle, versus its redundancy in normal cells, suggests that Cks1 abrogation could be an effective interventional strategy in breast cancer.
Southern Research Institute, 2000 Ninth Avenue South, Birmingham, AL 35205, USA.
Louise
L
Westbrook
Marina
M
Manuvakhova
Francis G
FG
Kern
Norman R
NR
Estes
Harish N
HN
Ramanathan
Jaideep V
JV
Thottassery
D015152:Blotting, Northern; D001940:Breast / Q000378:metabolism / Q000473:pathology; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D016203:CDC2 Protein Kinase / Q000235:genetics / Q000378:metabolism*; D042846:CDC2-CDC28 Kinases; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects / Q000502:physiology; D050719:Crk-Associated Substrate Protein / Q000235:genetics / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D004965:Estrogen Antagonists / Q000494:pharmacology; D000077267:Fulvestrant; D006801:Humans; D015151:Immunoblotting; D047908:Intracellular Signaling Peptides and Proteins / Q000235:genetics / Q000378:metabolism; D008156:Luciferases / Q000378:metabolism; D008938:Mitosis; D020890:Neuregulin-1 / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D034741:RNA, Small Interfering / Q000494:pharmacology; D016196:S Phase / Q000187:drug effects / Q000502:physiology; D044786:S-Phase Kinase-Associated Proteins / Q000235:genetics / Q000378:metabolism
C493841:BCAR1 protein, human; C436291:CDKN1B protein, human; C093090:CKS1B protein, human; D002352:Carrier Proteins; D050719:Crk-Associated Substrate Protein; D004965:Estrogen Antagonists; D047908:Intracellular Signaling Peptides and Proteins; D020890:Neuregulin-1; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D044786:S-Phase Kinase-Associated Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; C087230:heregulin beta1; D000077267:Fulvestrant; D004958:Estradiol; D008156:Luciferases; D016203:CDC2 Protein Kinase; D042846:CDC2-CDC28 Kinases; D018844:Cyclin-Dependent Kinases