Identification of the Osteopontin gene as a direct target of TP53

Abstract

The TP53 tumor suppressor gene regulates a number of genes that are involved in cell-cycle inhibition, apoptosis, and maintaining genetic stability. Recently, two genes that have a role in immunosurveillance were identified as downstream targets of TP53. These genes, TAP1 and fractalkine, may contribute to suppress tumor growth through host immunosurveillance. It has been reported that the mouse secreted phosphoprotein osteopontin (Opn) is one of the key cytokines for type 1 immune responses mediated by macrophages. It also was reported that Opn may play a role in suppressing tumor growth in vivo. Here we identified Opn as a Tp53-target gene using mRNA differential display analysis of embryonic fibroblasts from Tp53-deficient mice. Furthermore, we found that Opn expression was upregulated by DNA damage-induced Tp53 activity and by adenovirus-mediated transfer of the human TP53 gene. In addition, a luciferase assay showed that the Opn gene has a functional Tp53-responsive element in its promoter region, and a chromatin immunoprecipitation assay confirmed interaction between the Opn promoter and Tp53 protein in vivo. These results suggest that OPN is a direct transcriptional target of TP53. The TP53-directed regulation of OPN expression suggests a novel model of TP53 participation in immunosurveillance, involving interaction with the host immune system to prevent damaged cells from undergoing malignant transformation.

Sumoylation of ING2 regulates the transcription mediated by Sin3A

“…Interestingly, some of these genes have been associated with cellular processes in which ING2 is known to be involved. It is the case for the SPP1 gene that has been shown to be an effector of p53 that is upregulated by p53 in response to DNA damage (Morimoto et al, 2002). As ING2 has been previously described as being able to activate p53 in response to DNA damage, it could be interesting to investigate the potential link between the decrease in SPP1 observed after ING2 dowregulation and the activation of p53.…”

The Id2 gene is a novel target of transcriptional activation by EWS-ETS fusion proteins in Ewing family tumors

“…The chromatin immunoprecipitation (ChIP) assay was performed using a ChIP assay kit (Upstate Biotechnology, Lake Placid, NY, USA), as recommended by the manufacturer Morimoto et al, 2002). Genomic DNA and protein were cross-linked by addition of formaldehyde to 2610 6 cells.…”

Identification of pigment epithelium-derived factor as a direct target of the p53 family member genes

“…The immunoprecipitated material was amplified using primers specific for RE-PEDF, the p21 promoter or two other candidate sites (À6362 and À5996). (c) The luciferase reporter assay was performed as described previously (Ishida et al, 2000;Morimoto et al, 2002;Sasaki et al, 2002). Saos2 cells were transiently transfected with the pGL3-promoter vector (Promega) containing the RE-PEDF (wt: 5 0 -aaacttgttttaaaacaagcttgtgtaacccatgacc-3 0 ) or a mutant sequence (RE-PEDF-mut: 5 0 -aaaatttttttaaaaaaatcttgtgtaaccaattacc-3 0 ) along with phRL-TK (Promega) by using Lipofectamine plus reagent (Invitrogen).…”