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The pancreatic tumor microenvironment drives deregulated nutrient availability. Accordingly, pancreatic cancer cells require metabolic adaptations to survive and proliferate. Pancreatic cancer subtypes have been characterized by transcriptional and functional differences, with subtypes reported to exist within the same tumor. However, it remains unclear if this diversity extends to metabolic programming. Here, using metabolomic profiling and functional interrogation of metabolic dependencies, we identify two distinct metabolic subclasses among neoplastic populations within individual human and mouse tumors. Furthermore, these populations are poised for metabolic cross-talk, and in examining this, we find an unexpected role for asparagine supporting proliferation during limited respiration. Constitutive GCN2 activation permits ATF4 signaling in one subtype, driving excess asparagine production. Asparagine release provides resistance during impaired respiration, enabling symbiosis. Functionally, availability of exogenous asparagine during limited respiration indirectly supports maintenance of aspartate pools, a rate-limiting biosynthetic precursor. Conversely, depletion of extracellular asparagine with PEG-asparaginase sensitizes tumors to mitochondrial targeting with phenformin.

Cancer-associated fibroblasts (CAF) may exert tumor-promoting and tumor-suppressive functions, but the mechanisms underlying these opposing effects remain elusive. Here, we sought to understand these potentially opposing functions by interrogating functional relationships among CAF subtypes, their mediators, desmoplasia, and tumor growth in a wide range of tumor types metastasizing to the liver, the most common organ site for metastasis. Depletion of hepatic stellate cells (HSC), which represented the main source of CAF in mice and patients in our study, or depletion of all CAF decreased tumor growth and mortality in desmoplastic colorectal and pancreatic metastasis but not in nondesmoplastic metastatic tumors. Single-cell RNA-Seq in conjunction with CellPhoneDB ligand-receptor analysis, as well as studies in immune cell-depleted and HSC-selective knockout mice, uncovered direct CAF-tumor interactions as a tumor-promoting mechanism, mediated by myofibroblastic CAF-secreted (myCAF-secreted) hyaluronan and inflammatory CAF-secreted (iCAF-secreted) HGF. These effects were opposed by myCAF-expressed type I collagen, which suppressed tumor growth by mechanically restraining tumor spread, overriding its own stiffness-induced mechanosignals. In summary, mechanical restriction by type I collagen opposes the overall tumor-promoting effects of CAF, thus providing a mechanistic explanation for their dual functions in cancer. Therapeutic targeting of tumor-promoting CAF mediators while preserving type I collagen may convert CAF from tumor promoting to tumor restricting.

It is now recognized that cell identity is more fluid, and tissues more plastic, than previously thought. The plasticity of cells is relevant to diverse fields, most notably developmental and stem cell biology, regenerative medicine, and cancer biology. To date, a comprehensive and uniform nomenclature to define distinct cell states and their injury-induced interconversions has been elusive. The first Keystone Symposium devoted exclusively to cellular plasticity in regeneration and tumorigenesis was held on January 2019 in Keystone, Colorado, and featured a workshop on terminology in the cell plasticity field. Definitions for terms such as plasticity, de- and transdifferentiation, reversion, and paligenosis were discussed. Here, we summarize the content and tenor of the symposium and nomenclature-focused workshop with regard to terms in the field. We outline the challenges with current definitions and recommend best practices and approaches to developing an accurate and acceptable nomenclature in the future.

Pioneer transcription factors, by virtue of their ability to target nucleosomal DNA in silent chromatin, play crucial roles in eliciting cell fate decisions during development and cellular reprogramming. In addition to their well‐established role in chromatin opening to activate gene expression programs, recent studies have demonstrated that pioneer factors have the complementary function of being able to silence the starting cell identity through targeted chromatin repression. Given recent discoveries regarding the repressive aspect of pioneer function, we discuss the basis by which pioneer factors can suppress alternative lineage programs in the context of cell fate control. [ABSTRACT FROM AUTHOR]

A number of studies have demonstrated that it is possible to directly convert one cell type to another by factor-mediated transdifferentiation, but in the vast majority of cases, the resulting reprogrammed cells are unable to maintain their new cell identity for prolonged culture times and have a phenotype only partially similar to their endogenous counterparts. To better understand this phenomenon, we developed an analytical approach for better characterizing trans-differentiation-associated changes in DNA methylation, a major determinant of long-term cell identity. By examining various models of transdifferentiation both in vitro and in vivo, our studies indicate that despite convincing expression changes, transdifferentiated cells seem unable to alter their original developmentally mandated methylation patterns. We propose that this blockage is due to basic developmental limitations built into the regulatory sequences that govern epigenetic programming of cell identity. These results shed light on the molecular rules necessary to achieve complete somatic cell reprogramming. [ABSTRACT FROM AUTHOR]

In the adult liver, the Hippo pathway mammalian STE20-like protein kinases 1 and 2 and large tumor suppressor homologs 1 and 2 (LATS1/2) control activation of the transcriptional coactivators Yes-associated protein (YAP) and WW domain containing transcription regulator 1 (TAZ) in hepatocytes and biliary epithelial cells, thereby regulating liver cell proliferation, differentiation, and malignant transformation. Less is known about the contribution of Hippo signaling to liver development. We used conditional mutagenesis to show that the Hippo signaling pathway kinases LATS1 and LATS2 are redundantly required during mouse liver development to repress YAP and TAZ in both the biliary epithelial and hepatocyte lineages. In the absence of LATS1/2, biliary epithelial cells exhibit excess proliferation while hepatoblasts fail to mature into hepatocytes, defects that result in perinatal lethality. Using an in vitro hepatocyte differentiation assay, we demonstrate that YAP activity decreases and Hippo pathway kinase activities increase upon differentiation. In addition, we show that YAP activation in vitro, resulting from either depletion of its negative regulators LATS1/2 or expression of a mutant form of YAP that is less efficiently phosphorylated by LATS1/2, results in transcriptional suppression of genes that normally accompany hepatocyte maturation. Moreover, we provide evidence that YAP activity is repressed by Hippo pathway activation upon hepatocytic maturation in vitro. Finally, we examine the localization of YAP during fetal liver development and show that higher levels of YAP are found in biliary epithelial cells, while in hepatocytes YAP levels decrease with hepatocyte maturation.ConclusionHippo signaling, mediated by the LATS1 and LATS2 kinases, is required to restrict YAP and TAZ activation during both biliary and hepatocyte differentiation. These findings suggest that dynamic regulation of the Hippo signaling pathway plays an important role in differentiation and functional maturation of the liver. (Hepatology 2016;64:1757-1772).

Crosstalk between metabolism and circadian rhythms is a fundamental building block of multicellular life, and disruption of this reciprocal communication could be relevant to disease. Here, we investigated whether maintenance of circadian rhythms depends on specific metabolic pathways, particularly in the context of cancer. We found that in adult mouse fibroblasts, ATP levels were a major contributor to signal from a clock gene luciferase reporter, although not necessarily to the strength of circadian cycling. In contrast, we identified significant metabolic control of circadian function across a series of pancreatic adenocarcinoma cell lines. Metabolic profiling of congenic tumor cell clones revealed substantial diversity among these lines that we used to identify clones to generate circadian reporter lines. We observed diverse circadian profiles among these lines that varied with their metabolic phenotype: The most hypometabolic line [exhibiting low levels of oxidative phosphorylation (OxPhos) and glycolysis] had the strongest rhythms, while the most hypermetabolic line had the weakest rhythms. Pharmacological enhancement of OxPhos decreased the amplitude of circadian oscillation in a subset of tumor cell lines. Strikingly, inhibition of OxPhos enhanced circadian rhythms only in the tumor cell line in which glycolysis was also low, thereby establishing a hypometabolic state. We further analyzed metabolic and circadian phenotypes across a panel of human patient-derived melanoma cell lines and observed a significant negative association between metabolic activity and circadian cycling strength. Together, these findings suggest that metabolic heterogeneity in cancer directly contributes to circadian function and that high levels of glycolysis or OxPhos independently disrupt circadian rhythms in these cells. [ABSTRACT FROM AUTHOR]

Resistance to immunotherapy is one of the biggest problems of current oncotherapeutics. While T cell abundance is essential for tumor responsiveness to immunotherapy, factors that define the T cell-inflamed tumor microenvironment are not fully understood. We used an unbiased approach to identify tumor-intrinsic mechanisms shaping the immune tumor microenvironment (TME), focusing on pancreatic adenocarcinoma because it is refractory to immunotherapy and excludes T cells from the TME. From human tumors, we identified ephrin-A receptor 2 (EPHA2) as a candidate tumor-intrinsic driver of immunosuppression. Epha2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy. We found that prostaglandin endoperoxide synthase 2 (PTGS2), the gene encoding cyclooxygenase- 2, lies downstream of EPHA2 signaling through TGF-[beta] and is associated with poor patient survival. Ptgs2 deletion reversed T cell exclusion and sensitized tumors to immunotherapy; pharmacological inhibition of PTGS2 was similarly effective. Thus, EPHA2/PTGS2 signaling in tumor cells regulates tumor immune phenotypes; blockade may represent a therapeutic avenue for immunotherapy-refractory cancers. Our findings warrant clinical trials testing the effectiveness of therapies combining EPHA2/TGF-[beta]/PTGS2 pathway inhibitors with antitumor immunotherapy and may change the treatment of notoriously therapy-resistant pancreatic adenocarcinoma., Introduction Immunotherapies, including immune checkpoint blockade (ICB), have led to significant improvement of clinical care for cancer patients (1-4). Patients with melanoma, lung adenocarcinoma, or kidney cancer have a 20%-40% [...]

The endocrine and exocrine cells in the adult pancreas are not static, but can change their differentiation state in response to injury or stress. This concept of cells in flux means that there may be ways to generate certain types of cells (such as insulin-producing β-cells) and prevent formation of others (such as transformed neoplastic cells). We review different aspects of cell identity in the pancreas, discussing how cells achieve their identity during embryonic development and maturation, and how this identity remains plastic, even in the adult pancreas.