p73 competes with co-activators and recruits histone deacetylase to NF-Y in the repression of PDGF beta-receptor.

We investigated mechanisms of the p73alpha-mediated repression of the platelet-derived growth factor beta-receptor (PDGFRB) promoter caused by its interaction with NF-Y. Treatment of cells with the histone deacetylase (HDAC) inhibitor, Trichostatin A, increases PDGFRB promoter activity through the CCAAT motif and counteracts the repression caused by p73alpha. Activation of the PDGFRB promoter by the co-activator p300 also occurs through the CCAAT motif. Expression of p73alpha counteracts both p300- and P/CAF-mediated activation of the PDGFRB promoter, and expression of p300 or P/CAF attenuates the p73alpha-mediated repression of the promoter activity. In concordance, p73alpha decreases the p300-mediated acetylation of NF-YC, p300 competes with p73alpha for binding NF-YB, and P/CAF competes with p73alpha for binding NF-YB and NF-YC. Furthermore, p73alpha, but not the oncogenic DeltaNp73alpha, binds directly to HDAC1. We performed chromatin immunoprecipitation with antibodies against p73, DeltaNp73, NFYB, p300 and HDAC1 at different periods after serum stimulation in serum-starved NIH3T3 cells. A marked decrease of DeltaNp73, NF-YB and p300 was detected 6 hours after serum stimulation when the expression of PDGFRB decreased. Conversely, HDAC1 was found bound at its maximum and the anti-p73 detecting both TAp73 and DeltaNp73 was found at all time points, indicating that p73, but not DeltaNp73, remains bound at this time. Double immunofluorescence staining of TAp73 and HDAC1 revealed that both of these molecules exist in the nucleus at this time point, supporting the presence of endogenous interaction. These results suggest that p73 and DeltaNp73 behave as physiological regulators for the transcription of the PDGFRB promoter.