eThe integrated stress response (ISR) controls cellular adaptations to nutrient deprivation, redox imbalances, and endoplasmic reticulum (ER) stress. ISR genes are upregulated in stressed cells, primarily by the bZIP transcription factor ATF4 through its recruitment to cis-regulatory C/EBP:ATF response elements (CAREs) together with a dimeric partner of uncertain identity. Here, we show that C/EBP␥:ATF4 heterodimers, but not C/EBP␤:ATF4 dimers, are the predominant CARE-binding species in stressed cells. C/EBP␥ and ATF4 associate with genomic CAREs in a mutually dependent manner and coregulate many ISR genes. In contrast, the C/EBP family members C/EBP␤ and C/EBP homologous protein (CHOP) were largely dispensable for induction of stress genes. Cebpg ؊/؊ mouse embryonic fibroblasts (MEFs) proliferate poorly and exhibit oxidative stress due to reduced glutathione levels and impaired expression of several glutathione biosynthesis pathway genes. Cebpg ؊/؊ mice (C57BL/6 background) display reduced body size and microphthalmia, similar to ATF4-null animals. In addition, C/EBP␥-deficient newborns die from atelectasis and respiratory failure, which can be mitigated by in utero exposure to the antioxidant N-acetylcysteine. Cebpg ؊/؊ mice on a mixed strain background showed improved viability but, upon aging, developed significantly fewer malignant solid tumors than WT animals. Our findings identify C/EBP␥ as a novel antioxidant regulator and an obligatory ATF4 partner that controls redox homeostasis in normal and cancerous cells.A variety of stresses, such as amino acid limitation, protein misfolding in the endoplasmic reticulum (ER), oxidative stress, hypoxia, and intracellular pathogens, activate gene expression programs collectively known as the integrated stress response (ISR) (1). Stress-induced genes are involved in multiple cellular processes that include nutrient uptake, amino acid synthesis, metabolic changes, antioxidant defenses, and cell survival, leading to cell recovery and alleviation of stress. However, prolonged or irresolvable stress can trigger cell death (2).Protein misfolding and ER stress are associated with several diseases, including diabetes and neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease, and Huntington's disease (3). The ISR also plays an important role in cancer as tumor cells frequently experience nutrient deprivation, hypoxia, and oxidative stress and require stress response regulators such as the transcription factor (TF) ATF4 to thrive under adverse conditions (4, 5). Elevated levels of reactive oxygen species (ROS) can initiate oncogenesis by causing DNA mutations and genome instability (6). However, recent studies have shown that, once established, tumor cells are reliant on antioxidant pathways for growth and survival (7,8). Moreover, radio-and chemotherapies induce death or senescence of cancer cells partly by increasing ROS. Thus, acquiring a detailed understanding of the pathways and mechanisms that regulate stress response genes may le...

Purpose Uveal melanoma (UM) is a rare melanoma variant with no effective therapies once metastases develop. Although durable cancer regression can be achieved in metastatic cutaneous melanoma (CM) with immunotherapies that augment naturally existing anti-tumor T cell responses, the role of these treatments for metastatic UM remains unclear. We sought to define the relative immunogenicity of these two melanoma variants and determine whether endogenous anti-tumor immune responses exist against UM. Experimental Design We surgically procured liver metastases from UM (n=16) and CM (n=35) patients and compared the attributes of their respective tumor cell populations and their infiltrating T cells (TIL) using clinical radiology, histopathology, immune assays and whole exomic sequencing. Results Despite having common melanocytic lineage, UM and CM metastases differed in their melanin content, tumor differentiation antigen expression, and somatic mutational profile. Immunologic analysis of TIL cultures expanded from these divergent forms of melanoma revealed CM TIL were predominantly composed of CD8+ T cells, while UM TIL were CD4+ dominant. Reactivity against autologous tumor was significantly greater in CM TIL compared to UM TIL. However, we identified TIL from a subset of UM patients which had robust anti-tumor reactivity comparable in magnitude to CM TIL. Interestingly, the absence of melanin pigmentation in the parental tumor strongly correlated with the generation of highly reactive UM TIL. Conclusions The discovery of this immunogenic group of UM metastases should prompt clinical efforts to determine whether patients who harbor these unique tumors can benefit from immunotherapies that exploit endogenous anti-tumor T cell populations.

The epithelial–mesenchymal transition (EMT), considered essential for metastatic cancer, has been a focus of much research, but important questions remain. Here, we show that silencing or removing H2A.X, a histone H2A variant involved in cellular DNA repair and robust growth, induces mesenchymal-like characteristics including activation of EMT transcription factors, Slug and ZEB1, in HCT116 human colon cancer cells. Ectopic H2A.X re-expression partially reverses these changes, as does silencing Slug and ZEB1. In an experimental metastasis model, the HCT116 parental and H2A.X-null cells exhibit a similar metastatic behaviour, but the cells with re-expressed H2A.X are substantially more metastatic. We surmise that H2A.X re-expression leads to partial EMT reversal and increases robustness in the HCT116 cells, permitting them to both form tumours and to metastasize. In a human adenocarcinoma panel, H2A.X levels correlate inversely with Slug and ZEB1 levels. Together, these results point to H2A.X as a regulator of EMT.