Critical role for p27Kip1 in cell cycle arrest after androgen depletion in mouse mammary carcinoma cells (SC-3).
The molecular mechanisms underlying androgen-regulated cancer growth and the frequent development of refractoriness to endocrine therapy remain unknown. In this study functional and quantitative alterations in cell cycle regulators after androgen depletion were examined in androgen-dependent mouse mammary carcinoma cells (SC-3) as a model system to clarify the initial response of cancer cells to anti-androgen therapy. FACS analysis of SC-3 cells cultured with or without 10(-7) M testosterone revealed that suppression of cell growth after hormone withdrawal was due to GI arrest. Although cyclin D1/Cdk4 activity decreased along with a reduced level of cyclin D1 protein, this was a later event (48-72 h) than the G1 arrest (24 h). Taken together with the results that constitutive expression of cyclin D1 in SC-3 cells did not overcome the growth suppression following androgen depletion, the existence of an alternative pathway(s) causing G1 arrest was suggested. Cyclin E/Cdk2 and cyclin A/Cdk2 activities decreased significantly at 24 h without apparent changes in the amounts of Cdk2, cyclin E or cyclin A. Among various Cdk inhibitors (CKIs) examined, p27Kip1 was upregulated at both mRNA and protein levels at 24 h after androgen depletion. In addition, immunoprecipitation-Western analysis showed that the amount of p27Kip1 associated with Cdk2 complexes increased as early as 24 h. These results suggest that p27Kip1 CKI is a critical target in the initial response of cancer cells to androgen depletion and plays a key role in Cdk2 inactivation through association with the kinase complex, leading to cell cycle arrest.
Menjo
M
M
Department of Geriatric Research, National Institute for Longevity Sciences, Obu, Aichi, Japan.
Kaneko
Y
Y
Ogata
E
E
Ikeda
K
K
Nakanishi
M
M
D000728:Androgens / Q000494:pharmacology*; D000818:Animals; D042846:CDC2-CDC28 Kinases; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology*; D018797:Cell Cycle Proteins; D019938:Cyclin D1 / Q000378:metabolism; D051357:Cyclin-Dependent Kinase 2; D050760:Cyclin-Dependent Kinase Inhibitor p27; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D016213:Cyclins / Q000037:antagonists & inhibitors / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D016193:G1 Phase; D008325:Mammary Neoplasms, Experimental / Q000473:pathology*; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000502:physiology*; D009363:Neoplasm Proteins / Q000502:physiology*; D009376:Neoplasms, Hormone-Dependent / Q000473:pathology*; D017346:Protein Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology; D013739:Testosterone / Q000494:pharmacology; D014162:Transfection; D014407:Tumor Cells, Cultured; D025521:Tumor Suppressor Proteins
D000728:Androgens; C493961:Cdkn1b protein, mouse; D018797:Cell Cycle Proteins; D016213:Cyclins; D004791:Enzyme Inhibitors; D008869:Microtubule-Associated Proteins; D009363:Neoplasm Proteins; D025521:Tumor Suppressor Proteins; D019938:Cyclin D1; D050760:Cyclin-Dependent Kinase Inhibitor p27; D013739:Testosterone; D017346:Protein Serine-Threonine Kinases; D042846:CDC2-CDC28 Kinases; C495893:Cdk2 protein, mouse; D051357:Cyclin-Dependent Kinase 2; D018844:Cyclin-Dependent Kinases