Our previous studies conducted in MCF7-ptsp53 cells have demonstrated that overexpression of the wild-type (wt) p53 at permissive temperature 32 degrees C leads to growth arrest at the G2/M phase of the cell cycle. To identify novel p53-regulated genes that are responsible for the p53-induced G2/M arrest, we conducted cDNA microarray analyses. The array results indicated that the mRNA level of protein regulator of cytokinesis (PRC1) was significantly decreased when the p53 transactivation activity was turned on, suggesting that PRC1 transcription could be downregulated by p53. In this study, we have extensively examined the functional role of p53 in the regulation of PRC1, a cell cycle protein that plays important roles during cytokinesis. We demonstrate that increased expression of the wt p53 either by exogenous transfection or chemical induction results in reduced mRNA and protein expression of PRC1 in HCT116 p53(+/+), HCT116 p53(-/-), MCF-7, T47D, and HeLa cells. Importantly, we show that the decreased PRC1 expression is accompanied by the appearance of binucleated cells, indicating the process of cell division after mitosis being inhibited. By isolation and characterization of a 3 kb genomic fragment containing the 5'-flanking region and part of exon 1 of PRC1 gene, we demonstrate that p53 directly suppresses PRC1 gene transcription. We further locate the p53-responsive sequence to the proximal promoter region -214 to -163, relative to the transcriptional start site. The in vivo interaction of p53 with PRC1 gene promoter is further demonstrated by chromatin immunoprecipitation assay. Taken together, these new findings suggest that p53 may have important roles in the regulation of cytokinesis through controlling the transcription of PRC1.