The CHD1L protein regulates cell activation by controlling lipid-related metabolism in B cells

Abstract Clinical observation has found that the increase of B-cell infiltration (TIL-B) and the formation of mature tertiary lymphoid structures (TLS) in the tumor microenvironment are positively correlated with the good prognosis of patients. However, TIL-B cells have dual properties, and how to guide them to generate positive responses to promote more effective anti-tumor immunity is a breakthrough problem that deserves attention. Here, we show that targeting the poly-ADP-ribosylation (PARr) recognition factor CHD1L is a novel potential target for promoting B-cell activity and enhancing antitumor immune responses. CHD1L is a newly confirmed oncogene. We found that in the tumor microenvironment (TME) of human solid tumors, there are regions with high CHD1L expression in B cells which show two states: scattered distribution and concentrated distribution in the germinal center (GC) region. To assess the role that CHD1L expression playing in B-cell, we used B cell-specific CHD1L knockout (CHD1LF/F-CD19-Cre+) mice (CKO-B mice) to investigate the effect of CHD1L on B-cell function in response to inflammatory and tumor stimuli. Under physiological homeostatic conditions, development, migration and homing, differentiation, and tissue distribution of B cell in CKO-B mice did not change significantly, as well as the basic expression level of antibodies. However, in CKO-B mice with inflammatory induction (OVA intraperitoneal injection; sheep red blood cell intraperitoneal injection), the proportion of CD95+GL7+B cells in the germinal center of spleen was significantly increased, the differentiation of plasma cells in spleen, lymph nodes and bone marrow was also enhanced, and the expression of IgA, IgG1, IgG2b, IgE and other antibody subclass was significantly up-regulated. There was also a significant increase in the number of B effector and B memory cells. These results suggest that CHD1L may act as an immunosuppressive factor in B cells under in a particular microenvironment and that elimination of CHD1L is able to promote B cell-triggered germinal center responses. In addition, we also studied the function of CKO- B cells by using MC38 or B16 cells subcutaneous transplantation tumor model and AOM + DSS induced colorectal cancer model. We found that the rate of tumor formation was significantly reduced in CKO-B mice compared with control mice, and the infiltration of CD4+ T and GzmB+CD8+ T cells in the tumors was significantly increased. Single-cell sequencing analysis of cancerous rectal tissues from mice with colorectal cancer revealed a significant increase in activated CKO-B cell subsets, which mainly include follicular B cells, germinal center B cells, and IgA plasma cell subsets. In addition, the infiltration of T cells, CD74+ macrophages and neutrophils was also increased, which was beneficial to the overall antitumor immune function. Cells interaction analysis showed that the activity of ligand-receptor pairs such as MHCI, CD74, and APP was upregulated between B cells and other cells. These results suggest that depletion of CHD1L in B cells can significantly improve and promote the formation of anti-tumor immune microenvironment.To explore the specific mechanism of CHD1L gene knock out in B cells, we analyzed the difference protein expression between the CKO - B cells and wild type B cells. KEGG and GO annotations showed that CHD1L knockdown had profound effects on the metabolic pathways of B cells, with significant upregulation of the key protein FABP5, which is associated with intracellular fatty acid transport. Combined with differential metabolites analysis, we found that CHD1L knockdown increased the level of fatty acid oxidative metabolism, as well as mitochondrial tricarboxylic acid cycle (TCA) products, such as α-ketoglutarate. These results suggest that CHD1L knockout may promote mitochondrial lipid oxidation for energy supply by increasing the expression of intracellular lipid transporter FABP5 and turning on the expression of key genes by increasing the expression of α-ketoglutaric acid, an intermediate of the tricarboxylic acid cycle which decreases histone methylation and increases chromatin accessibility. Thus, it promotes the activation of B cell function. Our findings suggest that CHD1L is a novel regulator of B cell activity and may open new avenues for TIL-B based tumor immunotherapy.