p38MAPKα Stromal Reprogramming Sensitizes Metastatic Breast Cancer to Immunotherapy.

Metastatic breast cancer is an intractable disease that responds poorly to immunotherapy. We show that p38MAPKα inhibition (p38i) limits tumor growth by reprogramming the metastatic tumor microenvironment in a CD4+ T cell-, IFNγ-, and macrophage-dependent manner. To identify targets that further increased p38i efficacy, we utilized a stromal labeling approach and single-cell RNA sequencing. Thus, we combined p38i and an OX40 agonist that synergistically reduced metastatic growth and increased overall survival. Intriguingly, patients with a p38i metastatic stromal signature had better overall survival that was further improved by the presence of an increased mutational load, leading us to ask if our approach would be effective in antigenic breast cancer. The combination of p38i, anti-OX40, and cytotoxic T-cell engagement cured mice of metastatic disease and produced long-term immunologic memory. Our findings demonstrate that a detailed understanding of the stromal compartment can be used to design effective antimetastatic therapies. SIGNIFICANCE: Immunotherapy is rarely effective in breast cancer. We dissected the metastatic tumor stroma, which revealed a novel therapeutic approach that targets the stromal p38MAPK pathway and creates an opportunity to unleash an immunologic response. Our work underscores the importance of understanding the tumor stromal compartment in therapeutic design. This article is highlighted in the In This Issue feature, p. 1275.

IRF2BP2: A new player in the regulation of cell homeostasis.

The IRF2BP2 (IFN regulatory factor 2 binding protein 2) protein was identified as a nuclear protein that interacts with IFN regulatory factor 2 (IRF-2) and is an IRF-2-dependent transcriptional repressor. IRF2BP2 belongs to the IRF2BP family, which includes IRF2BP1, IRF2BP2, and IRF2BPL (EAP1). Recently, IRF2BP2 has emerged as an important new transcriptional cofactor in different biological systems, acting as a positive and negative regulator of gene expression. IRF2BP2 plays a role in different cellular functions, including apoptosis, survival, and cell differentiation. Additionally, IRF2BP2 may be involved in cancer development. Finally, it has been recently reported that IRF2BP2 may play a role in macrophage regulation and lymphocyte activation, highlighting its function in innate and adaptive immune responses. However, it has become increasingly clear that IRF2BP2 and its isoforms can have specific functions. In this review, we address the possible reasons for these distinct roles of IRF2BP2 and the partner proteins that interact with it. We also discuss the genes regulated by IRF2BP2 during the immune response and in other biological systems.

Intrinsic LINE-1 Hypomethylation and Decreased Brca1 Expression are Associated with DNA Repair Delay in Irradiated Thyroid Cells.

Exposure to ionizing radiation greatly increases the risk of developing papillary thyroid carcinoma (PTC), especially during childhood, mainly due to gradual inactivation of DNA repair genes and DNA damages. Recent molecular characterization of PTC revealed DNA methylation deregulation of several promoters of DNA repair genes. Thus, epigenetic silencing might be a plausible mechanism for the activity loss of tumor suppressor genes in radiation-induced thyroid tumors. Herein, we investigated the impact of ionizing radiation on global methylation and CpG islands within promoter regions of homologous recombination (HR) and non-homologous end joining (NHEJ) genes, as well as its effects on gene expression, using two well-established normal differentiated thyroid cell lines (FRTL5 and PCCL3). Our data reveal that X-ray exposure promoted G2/M arrest in normal thyroid cell lines. The FRTL5 cells displayed a slower kinetics of double-strand breaks (DSB) repair and a lower long interspersed nuclear element-1 (LINE-1) methylation than the PCCL3 cells. Nevertheless, acute X-ray exposure does not alter the expression of genes involved in HR and NHEJ pathways, apart from the downregulation of Brca1 in thyroid cells. On the other hand, HR and NHEJ gene expressions were upregulated in radiation-induced senescent thyroid cells. Taken together, these data suggest that FRTL5 cells intrinsically have less efficient DNA DSB repair machinery than PCCL3 cells, as well as genomic instability, which could predispose the FRTL5 cells to unrepaired DSB lesions and, therefore, gene mutations.

Interferon regulatory factor 2 binding protein 2 is a new NFAT1 partner and represses its transcriptional activity.

The nuclear factor of activated T cells (NFAT) family of transcription factors is expressed in a wide range of cell types and regulates genes involved in cell cycle, differentiation, and apoptosis. NFAT proteins share two well-conserved regions, the regulatory domain and the DNA binding domain. The N- and C-terminal ends are transactivation sites and show less sequence similarity, whereas their molecular functions remain poorly understood. Here, we identified a transcriptional repressor, interferon regulatory factor 2 binding protein 2 (IRF-2BP2), which specifically interacts with the C-terminal domain of NFAT1 among the NFAT family members. IRF-2BP2 was described as a corepressor by inhibiting both enhancer-activated and basal transcription. Gene reporter assays demonstrated that IRF-2BP2 represses the NFAT1-dependent transactivation of NFAT-responsive promoters. The ectopic expression of IRF-2BP2 in CD4 T cells resulted in decreased interleukin-2 (IL-2) and IL-4 production, supporting a repressive function of IRF-2BP2 for NFAT target genes. Furthermore, NFAT1 and IRF-2BP2 colocalized in the nucleus in activated cells, and the mutation of a newly identified nuclear localization signal in the IRF-2BP2 rendered it cytoplasmic, abolishing its repressive effect on NFAT1 activity. Collectively, our data demonstrate that IRF-2BP2 is a negative regulator of the NFAT1 transcription factor and suggest that NFAT1 repression occurs at the transcriptional level.