15-deoxy-Delta12, 14-prostaglandin J2 activates the expression of p15INK4b gene, a cyclin-dependent kinase inhibitor.

15-deoxy-Delta12, 14-prostaglandin J2 (15-d-PGJ2) inhibits cellular proliferation primarily in the G1 phase of the cell cycle. However, the molecular mechanism responsible for this effect has not been sufficiently elucidated. Here, we show that the treatment of human immortalized keratinocyte HaCaT cells with 15-d-PGJ2 arrests the cell cycle at the G1 phase. We also show that inhibition of the proliferation of HaCaT cells by 15-d-PGJ2 correlates with induction of the expression of p15INK4b protein, a cyclin-dependent kinase inhibitor. 15-d-PGJ2 also induces p15INK4b mRNA and its promoter activity, suggesting that 15-d-PGJ2 transcriptionally activates p15INK4b gene expression. Deletion and mutation analyses indicated that one of the elements responsible for 15-d-PGJ2-mediated induction is located between nucleotides -385 and -373 upstream of the initiation codon. An electrophoretic mobility shift assay revealed the specific binding of an unknown protein to this element, and that the binding is augmented by the treatment of 15-d-PGJ2. Although 15-d-PGJ2 is a natural ligand of the peroxisome proliferator-activated receptor gamma (PPARgamma), treatment with ciglitazone, a synthetic PPARgamma ligand, had no effect on p15INK4b gene expression. Collectively, these results indicate that 15-d-PGJ2 activates p15INK4b gene expression through a novel 15-d-PGJ2-responsive element in the p15INK4b promoter in a PPARgamma-independent manner.