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1.  RSK promotes G2/M transition through activating phosphorylation of Cdc25A and Cdc25B 
Oncogene  2013;33(18):2385-2394.
Activation of the MAPK cascade in mammalian cell lines positively regulates the G2/M transition. The molecular mechanism underlying this biological phenomenon remains poorly understood. RSK is a key downstream element of the MAPK cascade. Our previous studies established roles of RSK2 in Cdc25C activation during progesterone-induced meiotic maturation of Xenopus oocytes. In this study, we demonstrate that both recombinant RSK and endogenous RSK in Xenopus egg extracts phosphorylate all three isoforms of human Cdc25 at a conserved motif near the catalytic domain. In human HEK293 and PC-3mm2 cell lines, RSK preferentially phosphorylates Cdc25A and Cdc25B in mitotic cells. Phosphorylation of the RSK sites in these Cdc25 isoforms increases their M phase-inducing activities. Inhibition of RSK-mediated phosphorylation of Cdc25 inhibits G2/M transition. Moreover, RSK is likely to be more active in mitotic cells than in interphase cells, as evidenced by the phosphorylation status of T359/S363 in RSK. Together, these findings indicate that RSK promotes G2/M transition in mammalian cells through activating phosphorylation of Cdc25A and Cdc25B.
PMCID: PMC4026278  PMID: 23708659
RSK; Cdc25; activating phosphorylation; mitosis; G2/M transition; cell cycle
2.  The relationship between metabolism and the autophagy machinery during the innate immune response 
Cell metabolism  2013;17(6):895-900.
The innate immune response is shaped by multiple factors, including both traditional autophagy and LC3-associated phagocytosis (LAP). As the autophagic machinery is engaged during times of nutrient stress, arising from scarcity or pathogens, we examine how autophagy, specifically LAP, and cellular metabolism together influence macrophage function and the innate immune response.
PMCID: PMC3696504  PMID: 23747248
3.  Widespread mitochondrial depletion via mitophagy does not compromise necroptosis 
Cell reports  2013;5(4):878-885.
Programmed necrosis (or necroptosis) is a form of cell death triggered by the activation of receptor interacting protein kinase-3 (RIPK3). Several reports have implicated mitochondria and mitochondrial reactive oxygen species (ROS) generation as effectors of RIPK3-dependent cell death. Here, we directly test this idea by employing a method for the specific removal of mitochondria via mitophagy. Mitochondria-deficient cells were resistant to the mitochondrial pathway of apoptosis, but efficiently died via TNF-induced, RIPK3-dependent programmed necrosis or as a result of direct oligomerization of RIPK3. Although the ROS scavenger butylated hydroxyanisol (BHA) delayed TNF-induced necroptosis, it had no effect on necroptosis induced by RIPK3 oligomerization. Further, while TNF-induced ROS production was dependent on mitochondria, the inhibition of TNF-induced necroptosis by BHA was observed in mitochondria-depleted cells. Our data indicate that mitochondrial ROS production accompanies, but does not cause, RIPK3-dependent necroptotic cell death.
PMCID: PMC4005921  PMID: 24268776
4.  The Intercellular Metabolic Interplay between Tumor and Immune Cells 
Functional and effective immune response requires a metabolic rewiring of immune cells to meet their energetic and anabolic demands. Beyond this, the availability of extracellular and intracellular metabolites may serve as metabolic signals interconnecting with cellular signaling events to influence cellular fate and immunological function. As such, tumor microenvironment represents a dramatic example of metabolic derangement, where the highly metabolic demanding tumor cells may compromise the function of some immune cells by competing nutrients (a form of intercellular competition), meanwhile may support the function of other immune cells by forming a metabolic symbiosis (a form of intercellular collaboration). It has been well known that tumor cells harness immune system through information exchanges that are largely attributed to soluble protein factors and intercellular junctions. In this review, we will discuss recent advance on tumor metabolism and immune metabolism, as well as provide examples of metabolic communications between tumor cells and immune system, which may represent a novel mechanism of conveying tumor-immune privilege.
PMCID: PMC4112791  PMID: 25120544
metabolism; tumor; tumor immunity; antagonism; symbiosis
5.  c-Myc is a universal amplifier of expressed genes in lymphocytes and embryonic stem cells 
Cell  2012;151(1):68-79.
The c-Myc HLH-bZIP protein has been implicated in physiological or pathological growth, proliferation, apoptosis, metabolism and differentiation at the cellular, tissue or organismal levels via regulation of numerous target genes. No principle yet unifies Myc action due partly to an incomplete inventory and functional accounting of Myc’s targets. To observe Myc target expression and function in a system where Myc is temporally and physiologically regulated, the transcriptomes and the genome-wide distributions of Myc, RNA polymerase II and chromatin modifications were compared during lymphocyte activation and in ES cells as well. A remarkably simple rule emerged from this quantitative analysis: Myc is not an on-off specifier of gene activity, but is a non-linear amplifier of expression, acting universally at active genes, except for immediate early genes that are strongly induced before Myc. This rule of Myc action explains the vast majority of Myc biology observed in literature.
PMCID: PMC3471363  PMID: 23021216
6.  Metabolic reprogramming and metabolic dependency in T cells 
Immunological reviews  2012;249(1):14-26.
Upon activation, quiescent naive T cells undergo a growth phase followed by massive clonal expansion and differentiation that are essential for appropriate immune defense and regulation. Accumulation of cell biomass during the initial growth and rapid proliferation during the expansion phase is associated with dramatically increased bioenergetic and biosynthetic demands. This not only requires a metabolic rewiring during the transition between resting and activation, but also ‘addicts’ active T cells to certain metabolic pathways in ways that naive and memory T cells are not. We consider such addiction in terms of the biological effects of deprivation of metabolic substrates or inhibition of specific pathways in T cells. In this review, we illustrate the relevant metabolic pathways revealed by recent metabolic flux analysis and discuss the consequences of metabolic intervention on specific metabolic pathways in T lymphocytes.
PMCID: PMC3422760  PMID: 22889212
metabolism; T lymphocytes; T-cell activation
7.  The transcription factor Myc controls metabolic reprogramming upon T lymphocyte activation 
Immunity  2011;35(6):871-882.
To fulfill the bioenergetic and biosynthetic demand of proliferation, T cells reprogram their metabolic pathways from fatty acid β-oxidation and pyruvate oxidation via the TCA cycle to the glycolytic, pentose-phosphate, and glutaminolytic pathways. Two of the top-ranked candidate transcription factors potentially responsible for the activation-induced T cell metabolic transcriptome, HIF1α and Myc, were induced upon T cell activation, but only the acute deletion of Myc markedly inhibited activation-induced glycolysis and glutaminolysis in T cells. Glutamine deprivation compromised activation-induced T cell growth and proliferation, and this was partially replaced by nucleotides and polyamines, implicating glutamine as an important source for biosynthetic precursors in active T cells. Metabolic tracer analysis revealed a Myc-dependent metabolic pathway linking glutaminolysis to the biosynthesis of polyamines. Therefore, a Myc-dependent global metabolic transcriptome drives metabolic reprogramming in activated, primary T lymphocytes. This may represent a general mechanism for metabolic reprogramming under patho-physiological conditions.
PMCID: PMC3248798  PMID: 22195744
8.  Disrupting the CH1 domain structure in the acetyltransferases CBP and p300 results in lean mice with increased metabolic control 
Cell metabolism  2011;14(2):219-230.
Opposing activities of acetyltransferases and deacetylases help regulate energy balance. Mice heterozygous for the acetyltransferase CREB binding protein (CBP) are lean and insulin-sensitized but how CBP regulates energy homeostasis is unclear. In one model, the main CBP interaction with the glucagon-responsive factor CREB is not limiting for liver gluconeogenesis, whereas a second model posits that Ser436 in the CH1 (TAZ1) domain of CBP is required for insulin and the anti-diabetic drug metformin to inhibit CREB-mediated liver gluconeogenesis. Here we show that conditional knockout of CBP in liver does not decrease fasting blood glucose or gluconeogenic gene expression, consistent with the first model. However, mice where the CBP CH1 domain structure is disrupted by deleting residues 342-393 (ΔCH1) are lean and insulin-sensitized, as are p300ΔCH1 mutants. CBPΔCH1/ΔCH1 mice remain metformin responsive. An intact CH1 domain is thus necessary for normal energy storage, but not for the blood glucose-lowering actions of insulin and metformin.
PMCID: PMC3163393  PMID: 21803292
9.  The immune diet: meeting the metabolic demands of lymphocyte activation 
During the adaptive immune response, lymphocytes undergo dramatic changes in metabolism that accompany the proliferative burst and differentiation into functional subsets. This brief overview focuses on recent advances in understanding the mechanisms of this metabolic reprogramming in T lymphocytes.
PMCID: PMC3342832  PMID: 22615715
10.  HIF1α–dependent glycolytic pathway orchestrates a metabolic checkpoint for the differentiation of TH17 and Treg cells 
The Journal of Experimental Medicine  2011;208(7):1367-1376.
HIF1α induction by mTOR represents a metabolic checkpoint for the differentiation of TH17 and Treg cells.
Upon antigen stimulation, the bioenergetic demands of T cells increase dramatically over the resting state. Although a role for the metabolic switch to glycolysis has been suggested to support increased anabolic activities and facilitate T cell growth and proliferation, whether cellular metabolism controls T cell lineage choices remains poorly understood. We report that the glycolytic pathway is actively regulated during the differentiation of inflammatory TH17 and Foxp3-expressing regulatory T cells (Treg cells) and controls cell fate determination. TH17 but not Treg cell–inducing conditions resulted in strong up-regulation of the glycolytic activity and induction of glycolytic enzymes. Blocking glycolysis inhibited TH17 development while promoting Treg cell generation. Moreover, the transcription factor hypoxia-inducible factor 1α (HIF1α) was selectively expressed in TH17 cells and its induction required signaling through mTOR, a central regulator of cellular metabolism. HIF1α–dependent transcriptional program was important for mediating glycolytic activity, thereby contributing to the lineage choices between TH17 and Treg cells. Lack of HIF1α resulted in diminished TH17 development but enhanced Treg cell differentiation and protected mice from autoimmune neuroinflammation. Our studies demonstrate that HIF1α–dependent glycolytic pathway orchestrates a metabolic checkpoint for the differentiation of TH17 and Treg cells.
PMCID: PMC3135370  PMID: 21708926
11.  Dissecting the M Phase–specific Phosphorylation of Serine–Proline or Threonine–Proline Motifs 
Molecular Biology of the Cell  2010;21(9):1470-1481.
Mitotic induction tightly associates with increased reactivity to mitotic phosphoprotein antibody MPM-2. Here we report that phosphorylation of TP motifs surrounded by hydrophobic residues at the −1 and +1 positions plays a dominant role in M phase–associated MPM-2 reactivity. The majority of these motifs are not phosphorylated by mitotic Cdk or MAPK.
M phase induction in eukaryotic cell cycles is associated with a burst of protein phosphorylation, primarily at serine or threonine followed by proline (S/TP motif). The mitotic phosphoprotein antibody MPM-2 recognizes a significant subset of mitotically phosphorylated S/TP motifs; however, the required surrounding sequences of and the key kinases that phosphorylate these S/TP motifs remain to be determined. By mapping the mitotic MPM-2 epitopes in Xenopus Cdc25C and characterizing the mitotic MPM-2 epitope kinases in Xenopus oocytes and egg extracts, we have determined that phosphorylation of TP motifs that are surrounded by hydrophobic residues at both −1 and +1 positions plays a dominant role in M phase–associated burst of MPM-2 reactivity. Although mitotic Cdk and MAPK may phosphorylate subsets of these motifs that have a basic residue at the +2 position and a proline residue at the −2 position, respectively, the majority of these motifs that are preferentially phosphorylated in mitosis do not have these features. The M phase–associated burst of MPM-2 reactivity can be induced in Xenopus oocytes and egg extracts in the absence of MAPK or Cdc2 activity. These findings indicate that the M phase–associated burst of MPM-2 reactivity represents a novel type of protein phosphorylation in mitotic regulation.
PMCID: PMC2861607  PMID: 20219976
12.  Differentiation potential of STRO-1+ dental pulp stem cells changes during cell passaging 
BMC Cell Biology  2010;11:32.
Dental pulp stem cells (DPSCs) can be driven into odontoblast, osteoblast, and chondrocyte lineages in different inductive media. However, the differentiation potential of naive DPSCs after serial passaging in the routine culture system has not been fully elucidated.
DPSCs were isolated from human/rat dental pulps by the magnetic activated cell sorting based on STRO-1 expression, cultured and passaged in the conventional culture media. The biological features of STRO-1+ DPSCs at the 1st and 9th passages were investigated. During the long-term passage, the proliferation ability of human STRO-1+ DPSCs was downregulated as indicated by the growth kinetics. When compared with STRO-1+ DPSCs at the 1st passage (DPSC-P1), the expression of mature osteoblast-specific genes/proteins (alkaline phosphatase, bone sialoprotein, osterix, and osteopontin), odontoblast-specific gene/protein (dentin sialophosphoprotein and dentin sialoprotein), and chondrocyte-specific gene/protein (type II collagen) was significantly upregulated in human STRO-1+ DPSCs at the 9th passage (DPSC-P9). Furthermore, human DPSC-P9 cells in the mineralization-inducing media presented higher levels of alkaline phosphatase at day 3 and day 7 respectively, and produced more mineralized matrix than DPSC-P9 cells at day 14. In vivo transplantation results showed that rat DPSC-P1 cell pellets developed into dentin, bone and cartilage structures respectively, while DPSC-P9 cells can only generate bone tissues.
These findings suggest that STRO-1+ DPSCs consist of several interrelated subpopulations which can spontaneously differentiate into odontoblasts, osteoblasts, and chondrocytes. The differentiation capacity of these DPSCs changes during cell passaging, and DPSCs at the 9th passage restrict their differentiation potential to the osteoblast lineage in vivo.
PMCID: PMC2877667  PMID: 20459680
13.  Roles of Greatwall Kinase in the Regulation of Cdc25 Phosphatase 
Molecular Biology of the Cell  2008;19(4):1317-1327.
We previously reported that immunodepletion of Greatwall kinase prevents Xenopus egg extracts from entering or maintaining M phase due to the accumulation of inhibitory phosphorylations on Thr14 and Tyr15 of Cdc2. M phase–promoting factor (MPF) in turn activates Greatwall, implying that Greatwall participates in an MPF autoregulatory loop. We show here that activated Greatwall both accelerates the mitotic G2/M transition in cycling egg extracts and induces meiotic maturation in G2-arrested Xenopus oocytes in the absence of progesterone. Activated Greatwall can induce phosphorylations of Cdc25 in the absence of the activity of Cdc2, Plx1 (Xenopus Polo-like kinase) or mitogen-activated protein kinase, or in the presence of an activator of protein kinase A that normally blocks mitotic entry. The effects of active Greatwall mimic in many respects those associated with addition of the phosphatase inhibitor okadaic acid (OA); moreover, OA allows cycling extracts to enter M phase in the absence of Greatwall. Taken together, these findings support a model in which Greatwall negatively regulates a crucial phosphatase that inhibits Cdc25 activation and M phase induction.
PMCID: PMC2291418  PMID: 18199678

Results 1-13 (13)