The Molecular Insight Into PD-L1 And CD47 Regulated By Histone Deacetylases In B-cell Lymphoma And Therapeutic Implications

HDAC inhibitors(HDACi)have been shown to alter the immunogeneticity and enhance antitumor immune responses in multiple types of tumor cells.Consistant with this,we found that the HDAC inhibitor up-regulated the expression of key costimulatory factors including CD80,CD86,MHCI and MHCII in B-cell lymphoma cell lines.Unexpectedly,the key coinhibitory factor PD-L1 was also remarkably upregulated by SAHA in a time-and dose-dependent manner.Mechanistically,HDAC inhibitor treatment increased the histone acetylation and the subsequent recruitment of bromodomain-containing protein Brd4 at the promoter region of PD-L1.While JQ1,a BET-Bromodomain specific inhibitor,decreased the occupation of Brd4 on PD-L1 promoters and thereby inhibited PD-L1 up-regulation.SAHA alone had only minor effects on an syngeneic murine A20 lymphoma model.However,SAHA was effective in the PD-L1-deficent A20 syngeneic lymphoma model.More interestingly,combining HDAC inhibition with BETi JQ1 almost eliminated the lymphoma in our model in vivo.Our findings demonstrate a potential HDACi-resistant mechanism in human B-cell lymphomas and suggest a promising HDAC inhibition-based combined therapeutic strategy for this disease.This study focuses on the mechanism of resistance to histone deacetylase inhibitors(HDACi)mediated by CD47 in B-cell lymphoma.After treatment with HDACi(SAHA)at different doses for different time courses,cell surface expression of CD47 in mouse B lymphoma cell line A20 was detected by FACS.Then Trizol was used to extract RNA from SAHA-treated mouse and human B lymphoma cell lines for determination of CD47 m RNA levels.In order to explore the underlying molecular mechanisms,we used chromatin immunoprecipitation assay to detect the binding of H3K4 ac,H3K9ac and H3K27 ac at the promoter region of CD47.Finally,CD47 levels were measured by FACS after combined treatment with SAHA and BRD4 inhibitor JQ1.The results showed that the levels of CD47 protein and m RNA were positively correlated with the dose of SAHA and time of treatment.Moreover,the acetylation levels of H3K4,H3K9 and H3K27 at the promoter region of CD47 were significantly increased by SAHA treatment.The combined usage of SAHA and JQ1 significantly reversed the up-regulated CD47 by SAHA.Taken together,SAHA up-regulates CD47 expression through enhancement of its transcription,while inhibition of BRD4 can reverse SAHA-mediated up-regulation of CD47.