肿瘤在树突状细胞中诱导NR4A1转录程序，导致免疫耐受与癌症进展

The induction of effective anti-tumor immune responses is reliant upon efficient dendritic cell (DC)-mediated activation of T cells. Furthermore, DCs are necessary for the efficacy of checkpoint inhibitors. However, during tumor progression, transcriptional reprogramming of DCs occurs leading to the development of dysfunctional DCs which potentiates tolerance within the tumor microenvironment (TME). This process is facilitated by the release of metabolites and soluble factors by tumor cells leading to the activation of transcriptional states that suppress the capacity of DCs to stimulate T cells. In prior studies, we have demonstrated that tumor-derived lactate activates SREBP2 in DCs within the TME, promoting the development of pro-tolerogenic mature regulatory DCs (mregDCs) that can inhibit antigen cross-presentation and facilitate tumor progression. Despite this work, our understanding of the exact transcriptional programs that govern the development of immunotolerant DC states, the mechanisms driving the suppressive functions of DCs, and the importance of intersecting transcription factor networks remain unclear. Insights into these mechanisms hold great promise for the development of novel immunotherapeutic strategies. In this project, we investigated DC regulatory programs that are induced during tumor progression using transgenic mouse models of melanoma. Single cell assay for transposase accessible chromatin sequencing (scATACseq) and transcription factor binding motif analysis of DCs isolated from the tumor-draining lymph nodes (TDLNs) of BRAF V600E PTEN -/- transgenic melanoma mice revealed an enrichment in the accessibility of NR4A1 transcription factor motifs in mregDCs relative to other conventional DC populations. Nr4a1 -GFP reporter mice show increased expression of Nr4a1 in cDCs of tumor bearing mice, particularly in mregDCs that have developed from cDC1s. We proceeded to characterize the role of DC-expressed NR4A1 in regulating anti-tumor immunity using both in vitro and in vivo models. Zbtb46-restricted Nr4a1 knockout mice show that loss of Nr4a1 in DCs suppresses tumor progression and promotes CD8 + T cell tumor infiltration. Furthermore, we determined that lactic acid released by tumor cells via monocarboxylate transporter 1 (MCT1) induces DC Nr4a1 gene expression in a SREBP2-dependent manner. We went on to verify that SREBP2 binds to the Nr4a1 promoter using ChIP-qPCR. Additional studies found NR4A1 inhibition to suppress DC expression of Ido1 and Il4i1 while also inhibiting mregDC-dependent FoxP3 + regulatory T cell development and activation. Collectively, this data demonstrates a previously unknown role for NR4A1 in DCs. Ultimately, we have identified a DC regulatory program centered around a lactate-SREBP2-NR4A1 signaling axis that represents a promising strategy for overcoming anti-PD-1 resistance in treatment refractory tumors.