The peroxisome proliferator-activated receptor α (PPARα, or NR1C1) is a nuclear hormone receptor activated by a structurally diverse array of synthetic chemicals known as peroxisome proliferators. Endogenous activation of PPARα in liver has also been observed in certain gene knockout mouse models of lipid metabolism, implying the existence of enzymes that either generate (synthesize) or degrade endogenous PPARα agonists. For example, substrates involved in fatty acid oxidation can function as PPARα ligands. PPARα serves as a xenobiotic and lipid sensor to regulate energy combustion, hepatic steatosis, lipoprotein synthesis, inflammation and liver cancer. Mainly, PPARα modulates the activities of all three fatty acid oxidation systems, namely mitochondrial and peroxisomal β-oxidation and microsomal ω-oxidation, and thus plays a key role in energy expenditure. Sustained activation of PPARα by either exogenous or endogenous agonists leads to the development of hepatocellular carcinoma resulting from sustained oxidative and possibly endoplasmic reticulum stress and liver cell proliferation. PPARα requires transcription coactivator PPAR-binding protein (PBP)/mediator subunit 1(MED1) for its transcriptional activity.

Peroxisome proliferator-activated receptor (PPAR)α, β (also known as δ), and γ function as sensors for fatty acids and fatty acid derivatives and control important metabolic pathways involved in the maintenance of energy balance. PPARs also regulate other diverse biological processes such as development, differentiation, inflammation, and neoplasia. In the nucleus, PPARs exist as heterodimers with retinoid X receptor-α bound to DNA with corepressor molecules. Upon ligand activation, PPARs undergo conformational changes that facilitate the dissociation of corepressor molecules and invoke a spatiotemporally orchestrated recruitment of transcription cofactors including coactivators and coactivator-associated proteins. While a given nuclear receptor regulates the expression of a prescribed set of target genes, coactivators are likely to influence the functioning of many regulators and thus affect the transcription of many genes. Evidence suggests that some of the coactivators such as PPAR-binding protein (PBP/PPARBP), thyroid hormone receptor-associated protein 220 (TRAP220), and mediator complex subunit 1 (MED1) may exert a broader influence on the functions of several nuclear receptors and their target genes. Investigations into the role of coactivators in the function of PPARs should strengthen our understanding of the complexities of metabolic diseases associated with energy metabolism.

Pdx1-Cre x LSL-Kras G12D x LSL-TP53 R172H (KPC), Pdx1-Cre x LSL-Kras G12D x LSL-TP53 R172H+/+ (KPPC), Gemcitabine resistant (GR), Anti-PD-1 (αPD-1).

Pancreatic ductal adenocarcinoma (PDAC) remains remarkably lethal with a 5-year survival rate of 8%. This is mainly attributed to the late stage of presentation, as well as widespread resistance to conventional therapy. In addition, PDAC tumors are largely nonimmunogenic, and most patients have displayed incomplete responses to cancer immunotherapies. Our group has previously identified TGFb as a crucial repressor of antitumor immune function in PDAC, particularly with respect to cytotoxic T lymphocytes. However, pharmacologic inhibition of TGFb signaling has had limited efficacy in clinical trials, failing to promote a significant antitumor immune response. Hence, in this work, we extend our analysis to identify and circumvent the mechanisms of resistance to TGFb signal inhibition in PDAC. Consistent with our previous observations, adoptive transfer of TGFb-insensitive CD8 þ T cells led to the near complete regression of neoplastic disease in vivo. However, we demonstrate that this cannot be recapitulated via global reduction in TGFb signaling, through either genetic ablation or pharmacologic inhibition of TGFBR1. In fact, tumors with TGFb signal inhibition displayed increased PD-L1 expression and had no observable change in antitumor immunity. Using genetic models of advanced PDAC, we then determined that concomitant inhibition of both TGFb and PD-L1 receptors led to a reduction in the neoplastic phenotype, improving survival and reducing disease-associated morbidity in vivo. Combined, these data strongly suggest that TGFb and PD-L1 pathway inhibitors may synergize in PDAC, and this approach warrants clinical consideration. Analysis and interpretation of data (e.g., statistical analysis, biostatistics, computational analysis):

Fatty acyl-coenzyme A oxidase 1 (ACOX1) knockout (ACOX1(-/-)) mice manifest hepatic metabolic derangements that lead to the development of steatohepatitis, hepatocellular regeneration, spontaneous peroxisome proliferation, and hepatocellular carcinomas. Deficiency of ACOX1 results in unmetabolized substrates of this enzyme that function as biological ligands for peroxisome proliferator-activated receptor-α (PPARα) in liver. Here we demonstrate that sustained activation of PPARα in ACOX1(-/-) mouse liver by these ACOX1 substrates results in endoplasmic reticulum (ER) stress. Overexpression of transcriptional regulator p8 and its ER stress-related effectors such as the pseudokinase tribbles homolog 3, activating transcription factor 4, and transcription factor CCAAT/-enhancer-binding protein homologous protein as well as phosphorylation of eukaryotic translation initiation factor 2α, indicate the induction of unfolded protein response signaling in the ACOX1(-/-) mouse liver. We also show here that, in the liver, p8 is a target for all three PPAR isoforms (-α, -β, and -γ), which interact with peroxisome proliferator response elements in p8 promoter. Sustained activation of p8 and unfolded protein response-associated ER stress in ACOX1(-/-) mouse liver contributes to hepatocyte apoptosis and liver cell proliferation culminating in the development of hepatocarcinogenesis. We also demonstrate that human ACOX1 transgene is functional in ACOX1(-/-) mice and effectively prevents metabolic dysfunctions that lead to ER stress and carcinogenic effects. Taken together, our data indicate that progressive PPARα- and p8-mediated ER stress contribute to the hepatocarcinogenesis in ACOX1(-/-) mice.