EP300 Inhibition Contributes To Anti-tumor Immunity By Enhancing Autophagy

Purpose:In recent years,immunotherapy has become a hot spot in cancer treatment,but more suitable therapeutic targets need to be found.Studies show E1A binding protein p300(EP300,hereafter referred to as p300),a member of the histone acetyltransferase family,promotes transcription through acetylated histones and transcription factors,regulating tumor progression eventually.Therefore,we explored the role of p300 in anti-tumor immune responses and provided theoretical support for the translational application of p300 as an immunotherapy target.Methods:C57BL/6 mice and immunodeficient Nu/Nu mice were selected to establish a subcutaneous transplantation tumor model.The p300 gene was knocked out by using p300 inhibitor or Crispr-cas9 technology to observe the effect of p300 on tumor growth.A p300 overexpression cell line was constructed to observe the effect of p300 overexpression on tumor growth.Immunofluorescence staining,and enzyme-linked immune spot assays were utilized to detect changes in the composition and function of immune cells in the tumor microenvironment after p300 deletion.A cell line overexpressing RFP-GFP-LC3 was constructed on the basis of p300-deficient cells.The changes of autophagy flow after p300 deletion were observed by immunofluorescence,and the expression levels of key proteins of AMPK/ULK1 and autophagy-related pathways were analyzed by Western blot analysis.Results:(1)p300 overexpression could promote tumor growth in C57BL/6 mice.(2)p300 inhibitors played a certain role in the treatment of subcutaneous xenografts in C57BL/6 mice,but no effect was seen on subcutaneous xenografts in nude mice.(3)p300 gene deletion could inhibit tumor growth in C57BL/6 mice,while for nude mice,there was no inhibitory effect.(4)p300-/-tumors showed more infiltration and interference of immune cells.(5)In the condition of starving,compared with the control group,autophagy increased significantly after p300 deletion,SQSTM1/p62 expression was down-regulated,and LC3B-Ⅱ/LC3B-Ⅰ increased.In addition,inhibition of p300 could affect the expression of AMPK/ULK1 pathway-related proteins,increase phosphorylation of AMPK,and up-regulate the expression of ULK1,ATG13 and FIP200.Conclusion:p300 deletion mediates the enhancement of autophagy by enhancing the AMPK/ULK1 pathway,leading to an increase in autophagy-dependent ATP release,which in turn stimulates tumor immunogenicity and benefits for anti-tumor immune response.Effective and continuous anti-tumor immunity has become a huge potential for tumor therapy,so p300 is expected to become a new target for tumor therapy.