| Tumor suppressor p53 plays a key role in regulating tumor suppression during tumor progression.According to an increasing number of studies,the p53-mediated canonical DNA damage responses,including cell cycle arrest,apoptosis and senescence,are dispensable for tumor suppression mediated by p53.In recent years,accumulating studies indicated that multiple p53-mediated processes such as metabolism,autophagy,ferroptosis and immune might crucially contribute to tumor suppression.However,it is still unclear which biological process plays a vital role for p53-mediated tumor suppression,and whether there exists in potential downstream targets of p53 regulating tumor suppression.Based on these questions,this study focused on the molecular mechanism of p53-mediated tumor suppression to explore potential target genes in regulating p53-mediated tumor behavior,to search for the targeted drugs inhibiting tumor growth,and eventually to provide new strategies for cancer therapy.To explore potential target genes involved in p53-mediated tumor suppression,the differentially expressed genes of p53+/-and p53-/-mice after ionizing radiation were screened via a RNA-sequencing(RNA-seq)technique.We discovered that there were more than 300 p53-dependent differentially expressed genes in response to DNA damage analysed by bioinformatics.Gene ontology(GO)analysis revealed that most of these genes were correlated to stress response and cell death,and among them,PD-1 involved in regulating biological processes including cell death,apoptosis and immune.However,it is unclear about the correlation between p53 and PD-1 at present.In this study,we found that PD-1 was expressed in tumor cells besides immune cells,and the mRNA and protein levels of PD-1 were detected after p53 activation in response to DNA damage in tumor and normal cells.Moreover,ChIP,EMSA and luciferase reporter assays were preformed to further identify that PD-1 is a direct downstream target of p53.Since phosphorylation and acetylation of p53 mainly affect transcriptional activity of p53 during response to DNA damage,it is essential to study the mechanism of p5 3-mediated PD-1 transcriptional activation via phosphorylation and acetylation of p53.We observed that acetylation at the lysine 120 or 164 residue of p53 DNA-bind domain played a critical role in p53-mediated PD-1 transcriptional activation,and acetyltransferases like p300/CBP or TIP60,contributed to p53-mediated PD-1 transcription.On the other side,p300/CBP or TIP60 respectively catalyzed histone H3K18/27 or H4K16 acetylation near the PD-1 promoter under the recruitment of acetylated p53,to promote the chromatin opening of PD-1 promoter,thus activating PD-1 transcription.In function,we confirmed that re-expression of PD-1 in cancer cell inhibited tumor growth through immune deficiency mice xenograft experiments in an immunity-independent manner,and the biological function was associated with inhibition of AKT-mTOR pathway in tumor cell.Meanwhile,depletion of tumor cell-intrinsic PD-1 remarkably impaired p53-mediated tumor suppression.In addition,histone deacetylase inhibitors(HDACi)promoted PD-1 transcription in an acetylated p53-dependent manner,and further inhibited tumor cell growth through synergistic effect with p53.In conclusion,our study revealed that the molecular mechanism by which p53 and its acetylation transcriptionally activates tumor cell-intrinsic PD-1,and indicated that p53-PD-1 axis regulates tumor progression of tumor cells in an immunity-independent manner.Moreover,our study designed that HDACi synergizes with p53 on tumor suppression via stimulating cancer cell-intrinsic PD-1,and thereby providing a new strategy for cancer therapy. |
