Down-regulation of the phosphoenolpyruvate carboxykinase gene in human colon tumors and induction by omega-3 fatty acids

Emerging roles of cytosolic phosphoenolpyruvate kinase 1 (PCK1) in cancer

Although it was traditionally believed that gluconeogenesis enzymes were absent from cancers that did not originate in gluconeogenic organs, numerous investigations have shown that they are functionally expressed in a variety of tumors as mediators of shortened forms of Gluconeogenesis. One of the isomers of PEPCK, the first-rate limiting enzyme in gluconeogenesis, is PCK 1, which catalyzes the conversion of oxaloacetate (OAA) and GTP into PEP, CO2, and GDP. It is also known as PEPCK-C or PCK1, and it is cytosolic. Despite being paradoxical, it has been demonstrated that, in addition to its enzymatic role in normal metabolism, this enzyme also plays a role in tumors that arise in gluconeogenic and non-gluconeogenic organs. According to newly available research, it has metabolic and non-metabolic roles in tumor progression and development. Thus, this review will give insight into PCK1 relationship, function, and mechanism in or with different types of cancer using contemporary findings.

ZNF692 promotes colon adenocarcinoma cell growth and metastasis by activating the PI3K/AKT pathway

Despite considerable recent advancements in colorectal cancer (CRC) therapy, the prognosis of patients with advanced disease remains poor. Further understanding of the molecular mechanisms and treatment strategies of this disease is required. Zinc finger protein 692 (ZNF692), also known as AREBP and Zfp692, was first reported to have an important role in gluconeogenesis. A recent study demonstrated that ZNF692 is overexpressed in lung adenocarcinoma (LUAD) tissues and that ZNF692 knockdown inhibited LUAD cell proliferation, migration, and invasion both in vitro and in vivo. However, the role of ZNF692 in colon adenocarcinoma (COAD) remains unclear. The present study revealed that ZNF692 was upregulated in COAD tissues and cells and that high ZNF692 expression was significantly correlated with lymph node metastasis, distant metastasis and tumor stage in COAD patients. Gain- and loss-of-function experiments were employed to identify the function of ZNF692 in COAD progression. In vitro and in vivo assays revealed that ZNF692 promoted COAD cell proliferation, migration and invasion. Furthermore, western blot analysis demonstrated that the effects of ZNF692 were mediated by upregulating cyclin D1, cyclin-dependent kinase 2 (CDK2) and matrix metalloproteinase-9 (MMP-9) and by downregulating p27^Kip1 through the phosphoinositide 3-kinase/AKT signaling pathway. Collectively, these data indicated that ZNF692 may serve as a novel oncogene and a potential treatment target in COAD patients.

Dietary fat and fiber interact to uniquely modify global histone post-translational epigenetic programming in a rat colon cancer progression model

Dietary fermentable fiber generates short-chain fatty acids (SCFA), for example, butyrate, in the colonic lumen which serves as a chemoprotective histone deacetylase inhibitor and/or as an acetylation substrate for histone acetylases. In addition, n-3 polyunsaturated fatty acids (n-3 PUFA) in fish oil can affect the chromatin landscape by acting as ligands for tumor suppressive nuclear receptors. In an effort to gain insight into the global dimension of post-translational modification of histones (including H3K4me3 and H3K9ac) and clarify the chemoprotective impact of dietary bioactive compounds on transcriptional control in a preclinical model of colon cancer, we generated high-resolution genome-wide RNA (RNA-Seq) and "chromatin-state" (H3K4me3-seq and H3K9ac-seq) maps for intestinal (epithelial colonocytes) crypts in rats treated with a colon carcinogen and fed diets containing bioactive (i) fish oil, (ii) fermentable fiber (a rich source of SCFA), (iii) a combination of fish oil plus pectin, or (iv) control, devoid of fish oil or pectin. In general, poor correlation was observed between differentially transcribed (DE) and enriched genes (DERs) at multiple epigenetic levels. The combinatorial diet (fish oil + pectin) uniquely affected transcriptional profiles in the intestinal epithelium, for example, upregulating lipid catabolism and beta-oxidation associated genes. These genes were linked to activated ligand-dependent nuclear receptors associated with n-3 PUFA and were also correlated with the mitochondrial L-carnitine shuttle and the inhibition of lipogenesis. These findings demonstrate that the chemoprotective fish oil + pectin combination diet uniquely induces global histone state modifications linked to the expression of chemoprotective genes.

Reciprocal Changes in Phosphoenolpyruvate Carboxykinase and Pyruvate Kinase with Age Are a Determinant of Aging in Caenorhabditis elegans

Aging involves progressive loss of cellular function and integrity, presumably caused by accumulated stochastic damage to cells. Alterations in energy metabolism contribute to aging, but how energy metabolism changes with age, how these changes affect aging, and whether they can be modified to modulate aging remain unclear. In locomotory muscle of post-fertile Caenorhabditis elegans, we identified a progressive decrease in cytosolic phosphoenolpyruvate carboxykinase (PEPCK-C), a longevity-associated metabolic enzyme, and a reciprocal increase in glycolytic pyruvate kinase (PK) that were necessary and sufficient to limit lifespan. Decline in PEPCK-C with age also led to loss of cellular function and integrity including muscle activity, and cellular senescence. Genetic and pharmacologic interventions of PEPCK-C, muscle activity, and AMPK signaling demonstrate that declines in PEPCK-C and muscle function with age interacted to limit reproductive life and lifespan via disrupted energy homeostasis. Quantifications of metabolic flux show that reciprocal changes in PEPCK-C and PK with age shunted energy metabolism toward glycolysis, reducing mitochondrial bioenergetics. Last, calorie restriction countered changes in PEPCK-C and PK with age to elicit anti-aging effects via TOR inhibition. Thus, a programmed metabolic event involving PEPCK-C and PK is a determinant of aging that can be modified to modulate aging.

PEPCK Coordinates the Regulation of Central Carbon Metabolism to Promote Cancer Cell Growth

Phosphoenolpyruvate carboxykinase (PEPCK) is well known for its role in gluconeogenesis. However, PEPCK is also a key regulator of TCA cycle flux. The TCA cycle integrates glucose, amino acid, and lipid metabolism depending on cellular needs. In addition, biosynthetic pathways crucial to tumor growth require the TCA cycle for the processing of glucose and glutamine derived carbons. We show here an unexpected role for PEPCK in promoting cancer cell proliferation in vitro and in vivo by increasing glucose and glutamine utilization toward anabolic metabolism. Unexpectedly, PEPCK also increased the synthesis of ribose from non-carbohydrate sources, such as glutamine, a phenomenon not previously described. Finally, we show that the effects of PEPCK on glucose metabolism and cell proliferation are in part mediated via activation of mTORC1. Taken together, these data demonstrate a role for PEPCK that links metabolic flux and anabolic pathways to cancer cell proliferation.

An exploration of pathways involved in lung carcinoid progression using gene expression profiling

Pulmonary carcinoids comprise a well-differentiated subset of neuroendocrine tumors usually associated with a favorable prognosis, but mechanisms underlying disease progression are poorly understood. In an explorative approach to identify pathways associated with progression, we compared gene expression profiles of tumors from five patients with a favorable and five with a poor disease outcome. Differentially expressed genes were validated using quantitative real-time PCR on 65 carcinoid tumors, in combination with survival analysis. One of the identified pathways was further examined using immunohistochemistry. As compared with other chromosomal locations, a significantly higher number of genes downregulated in carcinoids with a poor prognosis were located at chromosome 11q (P = 0.00017), a region known to be frequently lost in carcinoids. In addition, a number of upregulated genes were found involved in the mitotic spindle checkpoint, the chromosomal passenger complex (CPC), mitotic kinase CDC2 activity and the BRCA-Fanconi anemia pathway. At the individual gene level, BIRC5 (survivin), BUB1, CD44, IL20RA, KLK12 and OTP were independent predictors of patient outcome. For survivin, the number of positive nuclei was also related to poor prognosis within the group of carcinoids. Aurora B kinase and survivin, major components of the CPC, were particularly upregulated in high-grade carcinomas and may therefore comprise therapeutic targets for these tumors. To our knowledge, this is the first expression profiling study focusing specifically on pulmonary carcinoids and progression. We have identified novel pathways underlying malignant progression and validated several genes as being strong prognostic indicators, some of which could serve as putative therapeutic targets.

Characterization of a (pckA) mutant of the non-nodulating bacterium Rhizobium pusense NRCPB10 induced by transposon Tn5 mutagenesis

Phosphoenolpyruvate carboxykinase (PCK) catalyzes the decarboxylation and phosphorylation of oxaloacetate to phosphoenolpyruvate in the gluconeogenic pathway in most organisms. A pckA gene encoding PCK was cloned and sequenced from strain Rhizobium pusense NRCPB100, a spontaneous rifampicin resistant mutant of R. pusense NRCPB10^T (JCM16209^T) of a recently described new species of a non-nodulating and non-tumorigenic bacterium. The mapping of the pck gene region following Tn5 mutagenesis located the gene downstream of a transcriptional regulatory protein gene (chvI) and upstream of a conserved hypothetical protein gene. The pck of 1,611 bp was deduced to encode 536 amino acids and showed high homology to the genes of known ATP-dependent PCK enzymes. Phylogenetic analysis of the gene placed it in a cluster with pck of other known members of Rhizobiales. Amino acid sequences of the putative functional regions of the deduced enzyme were found to be conserved.