抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

In contrast to normal differentiated cells, which rely primarily on mitochondrial oxidative phosphorylation to generate the energy needed for cellular processes, most cancer cells instead rely on aerobic glycolysis, a phenomenon termed “the Warburg effect.” Aerobic glycolysis is an inefficient way to generate adenosine 5′-triphosphate (ATP), however, and the advantage it confers to cancer cells has been unclear. Here we propose that the metabolism of cancer cells, and indeed all proliferating cells, is adapted to facilitate the uptake and incorporation of nutrients into the biomass (e.g., nucleotides, amino acids, and lipids) needed to produce a new cell. Supporting this idea are recent studies showing that (i) several signaling pathways implicated in cell proliferation also regulate metabolic pathways that incorporate nutrients into biomass; and that (ii) certain cancer-associated mutations enable cancer cells to acquire and metabolize nutrients in a manner conducive to proliferation rather than efficient ATP production. A better understanding of the mechanistic links between cellular metabolism and growth control may ultimately lead to better treatments for human cancer.

/pdf/understanding-the-warburg-effect-the-metabolic-requirements-t1cwrmjv80.pdf

Understanding the Warburg Effect: The Metabolic Requirements of Cell Proliferation

I MicroRNAs (miRNAs) are an abundant class of small non-protein-coding RNAs that function as negative gene regulators. They regulate diverse biological processes, and bioinformatic data indicates that each miRNA can control hundreds of gene targets, underscoring the potential influence of miRNAs on almost every genetic pathway. Recent evidence has shown that miRNA mutations or mis-expression correlate with various human cancers and indicates that miRNAs can function as tumour suppressors and oncogenes. miRNAs have been shown to repress the expression of important cancer-related genes and might prove useful in the diagnosis and treatment of cancer.

Oncomirs : microRNAs with a role in cancer

MicroRNAs (miRNAs) are an abundant class of small non-protein-coding RNAs that function as negative gene regulators They regulate diverse biological processes, and bioinformatic data indicates that each miRNA can control hundreds of gene targets, underscoring the potential influence of miRNAs on almost every genetic pathway Recent evidence has shown that miRNA mutations or mis-expression correlate with various human cancers and indicates that miRNAs can function as tumour suppressors and oncogenes miRNAs have been shown to repress the expression of important cancer-related genes and might prove useful in the diagnosis and treatment of cancer

/pdf/oncomirs-micrornas-with-a-role-in-cancer-4ryo1mpf3s.pdf

Oncomirs — microRNAs with a role in cancer

AKT/PKB signaling: navigating downstream.

Cancer cells frequently display high rates of aerobic glycolysis in comparison to their nontransformed counterparts, although the molecular basis of this phenomenon remains poorly understood. Constitutive activity of the serine/threonine kinase Akt is a common perturbation observed in malignant cells. Surprisingly, although Akt activity is sufficient to promote leukemogenesis in nontransformed hematopoietic precursors and maintenance of Akt activity was required for rapid disease progression, the expression of activated Akt did not increase the proliferation of the premalignant or malignant cells in culture. However, Akt stimulated glucose consumption in transformed cells without affecting the rate of oxidative phosphorylation. High rates of aerobic glycolysis were also identified in human glioblastoma cells possessing but not those lacking constitutive Akt activity. Akt-expressing cells were more susceptible than control cells to death after glucose withdrawal. These data suggest that activation of the Akt oncogene is sufficient to stimulate the switch to aerobic glycolysis characteristic of cancer cells and that Akt activity renders cancer cells dependent on aerobic glycolysis for continued growth and survival.

https://cancerres.aacrjournals.org/content/canres/64/11/3892.full.pdf

Akt stimulates aerobic glycolysis in cancer cells

MicroRNAs (miRNAs) are small RNAs that regulate gene expression posttranscriptionally. To block all miRNA formation in zebrafish, we generated maternal-zygotic dicer (MZdicer) mutants that disrupt the Dicer ribonuclease III and double-stranded RNA-binding domains. Mutant embryos do not process precursor miRNAs into mature miRNAs, but injection of preprocessed miRNAs restores gene silencing, indicating that the disrupted domains are dispensable for later steps in silencing. MZdicer mutants undergo axis formation and differentiate multiple cell types but display abnormal morphogenesis during gastrulation, brain formation, somitogenesis, and heart development. Injection of miR-430 miRNAs rescues the brain defects in MZdicer mutants, revealing essential roles for miRNAs during morphogenesis.

https://science.sciencemag.org/content/sci/308/5723/833.full.pdf

MicroRNAs Regulate Brain Morphogenesis in Zebrafish

The serine/threonine kinase Akt is a component of many receptor signal transduction pathways and can prevent cell death following growth factor withdrawal. Here, we show that Akt inhibition of cell death is not dependent on new protein translation. Instead, Akt inhibition of cell death requires glucose hydrolysis through glycolysis. Akt was found to regulate multiple steps in glycolysis via posttranscriptional mechanisms that included localization of the glucose transporter, Glut1, to the cell surface and maintenance of hexokinase function in the absence of extrinsic factors. To test the role of glucose uptake and phosphorylation in growth factor-independent survival, cells were transfected with Glut1 and hexokinase 1 (Glut1/HK1) cells. Glut1/HK1 cells accumulated Glut1 on the cell surface and had high glucose uptake capacity similar to that of cells with constitutively active Akt (mAkt). Unlike mAkt-expressing cells, however, they did not consume more glucose, did not maintain prolonged phosphofructokinase-1 protein levels and activity, and did not maintain pentose phosphate shuttle activity in the absence of growth factor. Nevertheless, expression of Glut1 and HK1 promoted increased cytosolic NADH and NADPH levels relative to those of the control cells upon growth factor withdrawal, prevented activation of Bax, and promoted growth factor-independent survival. These data indicate that Bax conformation is sensitive to glucose metabolism and that maintaining glucose uptake and phosphorylation can promote cell survival in the absence of growth factor. Furthermore, Akt required glucose and the ability to perform glycolysis to prevent Bax activation. The prevention of Bax activation by posttranscriptional regulation of glucose metabolism may, therefore, be a required aspect of the ability of Akt to maintain long-term cell survival in the absence of growth factors.

Akt-Directed Glucose Metabolism Can Prevent Bax Conformation Change and Promote Growth Factor-Independent Survival

Growth factor withdrawal results in the termination of factor-dependent transcription. One transcript that declines rapidly following growth factor deprivation of hematopoietic cells is the serine/threonine kinase pim-2. When constitutively expressed, Pim-2 conferred long-term resistance to a variety of apoptotic stimuli including growth factor withdrawal and endogenous levels of Pim-2 contributed to growth factor-mediated apoptotic resistance. Pim-2 expression maintained cell size and mitochondrial potential independently of the PI3K/Akt/TOR pathway. Pim-2-dependent maintenance of cell size and survival correlated with its ability to maintain rapamycin-resistant phosphorylation of the translational repressor 4E-BP1 and phosphorylation of the BH3 protein BAD. These results establish Pim-2 as a direct link between growth factor-induced transcription and a novel, kinase-dependent pathway that promotes cell-autonomous survival.

/pdf/the-serine-threonine-kinase-pim-2-is-a-transcriptionally-1wwnwg0dlq.pdf

The serine/threonine kinase Pim-2 is a transcriptionally regulated apoptotic inhibitor

Bak and Bax are required and redundant regulators of an intrinsic mitochondrial cell death pathway. To analyze this pathway in T cell development and homeostasis, we reconstituted mice with Bak−/−Bax−/− hematopoietic cells. We found that the development and selection of Bak−/−Bax−/− thymocytes was disrupted, with altered representation of thymic subsets and resistance to both death-by-neglect and antigen receptor–induced apoptosis. Elimination of Bak−/−Bax−/− T cells that responded to endogenous superantigen was also reduced. Despite more efficient early reconstitution and apoptotic resistance of Bak−/−Bax−/− thymocytes, thymic cellularity declined over time. Reduced thymic cellularity resulted from a progressive cessation of thymopoiesis. However, animals developed splenomegaly as a result of accumulated memory T cells that were not deleted after antigen-driven expansion. These data indicate that Bak and Bax are required for thymic selection and peripheral lymphoid homeostasis and suggest that thymopoiesis can be negatively regulated by the accumulation of cells that would normally be eliminated by pro-apoptotic Bcl-2–related genes.

Ryan M. Cinalli

Papers

Akt stimulates aerobic glycolysis in cancer cells

MicroRNAs Regulate Brain Morphogenesis in Zebrafish

Akt-Directed Glucose Metabolism Can Prevent Bax Conformation Change and Promote Growth Factor-Independent Survival

The serine/threonine kinase Pim-2 is a transcriptionally regulated apoptotic inhibitor

Deficiency in Bak and Bax perturbs thymic selection and lymphoid homeostasis.