FIG. 2.

Repression of cyclin D1 expression and kinase activity by 15d-PGJ₂ requires PPARγ. (A) Western blot analysis for cyclin D1 and GDI of HeLa cells selected by magnetic cell sorting after transfection with PPARγ and treated with 15d-PGJ₂ (10 μM) for 24 h. (B) Activity of the cyclin D1-dependent serine-threonine kinase was assessed by IP kinase assays using GST-pRB as substrate in MCF-7 (top) or HeLa (bottom) cells. Cells were treated with 15d-PGJ₂ (10 μM) for the time points indicated. (C) Cell cycle analysis was performed with MCF-7 cells transfected with either pRC-CMV–cyclin D1 or the control empty vector cassette, followed by treatment with 10 μM 15d-PGJ₂ for 24 h. FACS analysis was performed to compare the effect of 15d-PGJ₂ or vehicle on S phase. Values represent the percentage of cells in S phase. Cyclin D1 overexpression abrogates the inhibition of S phase by 15d-PGJ₂ (5.4 versus 12.4%).