Identification of Promoter Elements Responsible for Transcriptional Inhibition of Polo-like Kinase 1 and Topoisomerase IIα Genes by p21^{WAF1/CIP1/ SDI1}

Abstract

© 2 0 0 2 L a n d e s B i o s c i e n c e . N o t f o r d i s t r i b u t i o n .[Cell Cycle 1, 59-66, January 2002]; published online as a Cell Cycle "Papers In Press" at www. ABSTRACT Induction of p21 WAF1/CIP1/SDI1 , a physiological mediator of cell cycle arrest, inhibits multiple genes involved in cell division. We have investigated the determinants of p21-mediated inhibition of two of these genes, polo-like kinase 1 (PLK1) and topoisomerase IIα (TOPO IIα). p21 expression from an inducible promoter in human HT1080 cells rapidly decreases cellular levels of PLK1 and TOPO IIα RNA without decreasing their RNA stability. p21 also inhibits reporter gene expression from the PLK1 and TOPO IIα promoters in transient and stable transfection assays. Promoter mutagenesis studies show that inhibition of the PLK1 promoter by p21 is mediated in part by tandem sequences CDE (cell cycle-dependent element) and CHR (cell cycle genes homology region). p21 response of the TOPO IIα promoter was found to be mediated through CDE (but not CHR) and the inverted CCAAT box 1 (ICB1). The extent of PLK1 and TOPO IIα promoter inhibition and the effects of promoter mutations differ under the conditions of growth arrest produced by p21 induction or by mimosine, a cell cycle inhibitor that increases p21 RNA but not protein expression in HT1080 cells. These results indicate that inhibition of cell division-associated genes by p21 is mediated by different but overlapping mechanisms, which are not a general consequence of cell cycle arrest.

Nitric Oxide Down-regulates Polo-like Kinase 1 through a Proximal Promoter Cell Cycle Gene Homology Region

“…Here, we found similarly that NO ⅐ repression of PLK1 transcription appeared completely dependent on p38 MAPK activation in PMA-differentiated U937 cells. These results and previous reports demonstrating that p21/Waf1 inhibits the expression of many late phase cell cycle genes including PLK1 (9,15,34) suggested that NO ⅐ -p38 MAPK signaling might exert its repressive effect on PLK1 transcription through up-regulation of p21/Waf1. Although alternative mechanisms, such as direct NO ⅐ effects on transcription factors that regulate PLK1 remain possible, the current experiments strongly implicate the importance of p21/Waf1 induction by NO ⅐ .…”

“…p21/Waf1 is a multipotent CDK inhibitor. By binding to CDK complexes, it inhibits CDK activities, resulting in retinoblastoma-associated protein dephosphorylation and subsequent sequestration of E2F family proteins (9,34). This is widely believed to be the mechanism by which p21/Waf1 down-regulates a large group of E2F-dependent genes involved in DNA replication and cell cycle progression (9,21,34).…”

“…Expression of PLK1 mRNA and protein is coordinately regulated, steadily rising from a low level in G 1 to a peak during G 2 /M (7,8). Both transcriptional regulation (9,10) and mRNA stabilization (11) have been associated with PLK1 fluctuations during various phases of the cell cycle.…”

“…At least in part, p21/Waf1 triggers cell arrest by repressing highly synchronized target genes that collectively contain CDE/CHR promoter sites (9,10,(23)(24)(25)(26)(27). Whether or not NO ⅐ activation of p38 MAPK with subsequent stabilization of p21/Waf1 mRNA fully explains NO ⅐ repression of CDE/ CHR-regulated genes is not known.…”

“…In contrast to E2F1 and p21/Waf1 induction, NO ⅐ down-regulated a large group of G 2 /M phase cell cycle genes (15). A high proportion of these later genes including PLK1 have CDE/CHR (cell cycle-dependent element/cell cycle gene homology region) sites in their proximal promoters (9,10).…”