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Proliferating cells, including cancer ceils, require altered metabolism to efficiently incorporate nutrients such as glucose into biomass. The M2 isoform of pyruvate kinase (PKM2) promotes the metabolism of glucose by aerobic glycolysis and contributes to anabolic metabolism. Paradoxically, decreased pyruvate kinase enzyme activity accompanies the expression of PKM2 in rapidly dividing cancer ceils and tissues. We demonstrate that phosphoenolpyruvate (PEP), the substrate for pyruvate kinase in cells, can act as a phosphate donor in mammalian cells because PEP participates in the phosphorylation of the glycolytic enzyme phosphoglycerate mutase (PGAM1) in PKM2-expressing ceils. We used mass spectrometry to show that the phosphate from PEP is transferred to the catalytic histidine ([His.sup.11]) on human PGAM1. This reaction occurred at physiological concentrations of PEP and produced pyruvate in the absence of PKM2 activity. The presence of histidine-phosphorylated PGAM1 correlated with the expression of PKM2 in cancer cell lines and tumor tissues. Thus, decreased pyruvate kinase activity in PKM2-expressing cells allows PEP-dependent histidine phosphorylation of PGAM1 and may provide an alternate glycolytic pathway that decouples adenosine triphosphate production from PEP-mediated phosphotransfer, allowing for the high rate of glycolysis to support the anabolic metabolism observed in many proliferating cells. 10.1126/science.1188015

Elevated leukocyte cell numbers (leukocytosis), and monocytes in particular, promote atherosclerosis; however, how they become increased is poorly understood. Mice deficient in the adenosine triphosphate-binding cassette (ABC) transporters ABCA1 and ABCG1, which promote cholesterol efflux from macrophages and suppress atherosclerosis in hypercholesterolemic mice, displayed leukocytosis, a transplantable myeloproliferative disorder, and a dramatic expansion of the stem and progenitor cell population containing [Lin.sup.-]Sca-[1.sup.+][Kit.sup.+] (LSK) in the bone marrow. Transplantation of [Abca1.sup.-/-] [Abcg1.sup.-/-] bone marrow into apolipoprotein A-1 transgenic mice with elevated levels of high-density lipoprotein (HDL) suppressed the LSK population, reduced leukocytosis, reversed the myeloproliferative disorder, and accelerated atherosclerosis. The findings indicate that ABCA1, ABCG1, and HDL inhibit the proliferation of hematopoietic stem and multipotential progenitor cells and connect expansion of these populations with leukocytosis and accelerated atherosclerosis. 10.1126/science.1189731

The mammalian target of rapamycin complex 1 (mTORC1) integrates mitogen and nutrient signals to control celt proLiferation and cell size. Hence, mTORC1 is implicated in a large number of human diseases--including diabetes, obesity, heart disease, and cancer--that are characterized by aberrant cell growth and proliferation. Although eukaryotic translation initiation factor 4E-binding proteins (4E-BPs) are critical mediators of mTORC1 function, their precise contribution to mTORC1 signaling and the mechanisms by which they mediate mTORC1 function have remained unclear. We inhibited the mTORC1 pathway in cells tacking 4E-BPs and analyzed the effects on cell size, cell proliferation, and cell cycle progression. Although the 4E-BPs had no effect on cell size, they inhibited cell proliferation by selectively inhibiting the translation of messenger RNAs that encode proliferation-promoting proteins and proteins involved in cell cycle progression. Thus, control of cell size and cell cycle progression appear to be independent in mammalian cells, whereas in lower eukaryotes, 4E-BPs influence both cell growth and proliferation. doi: 10.1126/science.118532

A long-standing question in biology is whether there is an intrinsic mechanism for coordinating growth and the cell cycle in metazoan cells. We examined cell size distributions in populations of lymphoblasts and applied a mathematical analysis to calculate how growth rates vary with both cell size and the cell cycle. Our results show that growth rate is size-dependent throughout the cell cycle. After initial growth suppression, there is a rapid increase in growth rate during the [G.sub.1] phase, followed by a period of constant exponential growth. The probability of cell division varies independently with cell size and cell age. We conclude that proliferating mammalian cells have an intrinsic mechanism that maintains cell size.

Mice homozygous for a single tyrosine mutation in LAT (linker for activation of T cells) exhibited an early Mock in T cell maturation but later developed a polyclonal lymphoproferative disorder and signs of autoimmune disease. T cell antigen receptor (TCR)-induced activation of phospholipase C-γ1 (PLC-γ1) and of nuclear factor of activated T cells, calcium, influx, interleukin-2 production, and cell death were reduced or abrogated in T cells from LAT mutant mice. In contrast, TCR-induced Erk activation was intact. These results identify a critical role for integrated PLC-γ1 and Ras-Erk signaling through LAT in T cell development and homeostasis., LAT is a transmembrane scaffolding protein that, after TCR engagement, becomes tyrosine-phosphorylated and recruits multiple signaling molecules important for T cell activation (1-5). The distal four tyrosine residues of LAT [...]

Aberrant centrosome duplication is observed in many tumor ceils and may contribute to genomic instability through the formation of multipolar mitotic spindles. Cyclin-dependent kinase 2 (Cdk2) is required for multiple rounds of centrosome duplication in Xenopus egg extracts but not for the initial round of replication. Egg extracts undergo periodic oscillations in the level of free calcium. We show here that chelation of calcium in egg extracts or specific inactivation of calcium/calmodulin-dependent protein kinase II (CaMKII) blocks even initial centrosome duplication, whereas inactivation of Cdk2 does not. Duplication can be restored to inhibited extracts by addition of CaMKII and calmodulin. These results indicate that calcium, calmodulin, and CaMKII are required for an essential step in initiation of centrosome duplication. Our data suggest that calcium oscillations in the cell cycle may be linked to centrosome duplication., Centrosome duplication occurs once and only once during the cell cycle, ensuring the formation of bipolar spindles that distribute replicated chromosomes equally to daughter cells. Overduplication of centrosomes causes multipolar [...]

Induction of apoptosis by oncogenes like c-myc may be important in restraining the emergence of neoplasia. However, the mechanism by which c-myc induces apoptosis is unknown. CD95 (also termed Fas or APO-1) is a cell surface transmembrane receptor of the tumor necrosis factor receptor family that activates an intrinsic apoptotic suicide program in cells upon binding either its ligand CD95L or antibody. c-myc-induced apoptosis was shown to require interaction on the cell surface between CD95 and its ligand. c-Myc acts downstream of the CD95 receptor by sensitizing cells to the CD95 death signal. Moreover, IGF-I signaling and Bcl-2 suppress c-myc-induced apoptosis by also acting downstream of CD95. These findings link two apoptotic pathways previously thought to be independent and establish the dependency of Myc on CD95 signaling for its killing activity., Most human tumors have genetic alterations in myc proto-oncogene family members that result in deregulation of myc expression (1). However, growth-promoting oncogenes like c-myc are also effective inducers of apoptosis, [...]

A new class of protein tyrosine kinase inhibitors was identified that is based on an oxindole core (indolinones). Two compounds from this class inhibited the kinase activity of fibroblast growth factor receptor 1 (FGFR1) and showed differential specificity toward other receptor tyrosine kinases. Crystal structures of the tyrosine kinase domain of FGFR1 in complex with the two compounds were determined. The oxindole occupies the site in which the adenine of adenosine triphosphate binds, whereas the moieties that extend from the oxindole contact residues in the hinge region between the two kinase lobes. The more specific inhibitor of FGFR1 induces a conformational change in the nucleotide-binding loop. This structural information will facilitate the design of new inhibitors for use in the treatment of cancer and other diseases in which cell signaling by tyrosine kinases plays a crucial role in disease pathogenesis., Protein tyrosine kinases (PTKs) are critical components of signaling pathways that control cell proliferation and differentiation. Enhanced PTK activity due to activating mutations or overexpression has been implicated in many [...]

Timely deactivation of kinase cascades is crucial to the normal control of cell signaling and is partly accomplished by protein phosphatase 2A (PP2A). The catalytic ([Alpha]) subunit of the serine-threonine [...]

During early development in many species, maternally supplied gene products permit the cell cycle to run at maximum velocity, subdividing the fertilized egg into smaller and smaller cells. As development proceeds, zygotic controls are activated that first limit divisions to defined spatial and temporal domains, coordinating them with morphogenesis, and then halt proliferation altogether, to allow cell differentiation. Analysis of the regulation of cyclin-dependent kinases (Cdks) in Drosophila has provided insights into how this embryonic program of cell proliferation is controlled at the molecular level and how it is linked to developmental cues. Recent studies have also begun to reveal how cell proliferation is controlled during the second phase of Drosophila development, which occurs in imaginal tissues. In contrast to their embryonic progenitors, imaginal cells proliferate with a cycle that requires cell growth and is linked to patterning processes controlled by secreted cell signaling molecules. The functions of these signaling molecules appear to be nearly as conserved between vertebrates and invertebrates as the cell cycle control apparatus itself, suggesting that the mechanisms that coordinate growth, patterning, and cell proliferation in developing tissues have ancient origins., During the development of multicellular creatures, up to 10[15] cells can be generated. How is such massive cell proliferation coordinated with morphogenesis? Present models are based largely on experiments with [...]

Most nonmalignant cells are anchorage-dependent; they require substrate attachment for growth and, in some instances, survival. This requirement is lost on oncogenic transformation. The cyclin E-CDK2 complex, which is required for the [G.sub.1]-S transition of the cell cycle, was activated in late [G.sub.1] phase in attached human fibroblasts, but not in fibroblasts maintained in suspension. In transformed fibroblasts the complex was active regardless of attachment. The lack of cyclin E-CDK2 activity in suspended cells appeared to result from increased expression of CDK2 inhibitors and a concomitant decrease in phosphorylation of CDK2 on threonine-160. Suppression of cyclin E-CDK2 activity may thus underlie the anchorage dependence of cell growth., Most untransformed mammalian cells fail to proliferate when they are prevented from attaching to a solid substrate, a phenomenon known as anchorage dependence of growth (1). Loss of anchorage dependence [...]

Synthesis of DNA at chromosome ends by telomerase may be necessary for indefinite proliferation of human cells. A highly sensitive assay for measuring telomerase activity was developed. In cultured cells representing 18 different human tissues, 98 of 1 00 immortal and none of 22 mortal populations were positive for telomerase. Similarly, 90 of 1 01 biopsies representing 12 human tumor types and none of 50 normal somatic tissues were positive. Normal ovaries and testes were positive, but benign tumors such as fibroids were negative. Thus, telomerase appears to be stringently repressed in normal human somatic tissues but reactivated in cancer, where immortal cells are likely required to maintain tumor growth., Telomeres are specialized structures at the ends of eukaryotic chromosomes that appear to function in chromosome protection, positioning, and replication (1, 2). In vertebrates, telomeres consist of hundreds to thousands [...]

In this study, a protein that interacts with sequences encoded by the first exon of the protein kinase Bcr was cloned. The Bcr-associated protein 1 (Bap-1) is a member of the family of proteins. Bap-1 interacts with full-length c-Bcr and with the chimeric Bcr-Abl tyrosine kinase of Philadelphia chromosome ([Ph.sup.1])-positive human leukemias. Bap-1 is a substrate for the Bcr serine-threonine kinase and is also phosphorylated on tyrosine by Bcr-Abl but not by c-Abl. Bap-1 may function in the regulation of c-Bcr and may contribute to the transforming activity of Bcr-Abl in vivo. 14-3-3 proteins are essential for cell proliferation and have a role in determining the timing of mitosis in yeast. Through direct binding to sequences present in Bcr and in other proteins implicated in signaling, the mammalian 14-3-3 proteins may link specific signaling protein components to mitogenic and cell-cycle control pathways., The product of the bcr gene is a 160-kD protein with multiple functional and structural domains. Among the functional domains ascribed to c-bcr are a serine-threonine kinase encoded by the [...]

Intracellular signaling from receptor tyrosine kinases in mammalian cells results in activation of a signal cascade that includes the guanine nucleotide-binding protein Ras and the protein kinases Raf, MEK [mitogen-activated [...]

Conversion of external signals into proliferative responses may be mediated by interactions between signaling pathways that control cell proliferation. Interactions between Gα.sub.a], th α subunit of the heterotrimeric guanine nucleotide binding protein that stimulates adenylyl cyclase, and Ras, an important element in growth factor signaling, were studied. Expression of activated G[α.sub.s], in NIH 3T3 cells increased intracellular concentrations of adenosine 3',5'-monophosphate (cAMP) and inhibited H-Ras-stimulated DNA synthesis and mitogen-activated protein kinase activity. Activated Gas and 8-Br-cAMP suppressed H-Ras-induced transformation of NIH 3T3 cells. Apparently, G[α.sub.s] inhibits proliferative signals from Ras by stimulating cAMP production and activating protein kinase A., Many heterotrimeric guanine nucleotide binding proteins (G proteins) participate in mitogenic signaling (1). Of these, the [G.sub.s] and its signaling pathway are probably the most enigmatic. In a few systems, [...]

Cell adhesion has an essential role in regulating proliferation during the [G.sub.1] phase of the cell cycle, and loss of this adhesion requirement is a classic feature of oncogenic transformation. The appearance of cyclin A messenger RNA and protein in late [G.sub.1] was dependent on cell adhesion in both NRK and NIH 3T3 fibroblasts. In contrast, the expression of Cdc2, Cdk2, cyclin D1, and cyclin E was independent of adhesion in both cell lines. Transfection of NRK cells with a cyclin A complementary DNA resulted in adhesion-independent accumulation of cyclin A protein and cyclin A--associated kinase activity. These transfected cells also entered S phase and complete multiple rounds of cell division in the absence of cell adhesion. Thus, cyclin A is a target of the adhesion-dependent signals that control cell proliferation., Adhesion to substratum is required for the proliferation of most mammalian cell types; nonadherent cells fail to proliferate despite the presence of growth factors and nutrients (1)(2). In NRK and [...]

The development of an immunodeficiency syndrome of mice caused by a replication-defective murine leukemia virus (MuLV) is paradoxically associated with a rapid activation and proliferation of [CD4.sup.+] T cells that [...]

The proliferative potential of human diploid endothelial cells is finite, and cellular senescence in vitro is accompanied by the failure of the endothelial cell to respond to exogenous growth factors. Senescence human endothelial cells were shown to contain high amounts of the transcript for the cytokine interleukin-α (IL-1α) a potent inhibitor of endothelial cell proliferation in vitro. In contrast, tranformed human endothelial cells did not contain detectable IL-α messenger RNA. Treatment of human endothelial cell populations with an antisense oligodeoxynucleotide to the human IL-1α transcript prevented cell senescence and extend the proliferative life-span of the cells in vetro. Removal of the IL-1α antisense oligomer resulted in the generation of the senescent phenotype and loss of proliferative potential. These data suggest that human endothelial cell senescence in vitro is a dynamic process regulated by the potential intracellular activity of IL-1α., The Number of Cell Divisions that human diploid fibroblasts undergo in vitro is both finite and a function of the number of cumulative population doublings [1]. The lifetime of human [...]

Cell Proliferation in Carcinogenesis CERTAIN CHEMICALS HAVE LONG BEEN ASSOCIATED WITH cancer in humans, and animal models have been developed to study processes involved in the transition from a normal [...]

Proliferation and differentiation are the cell's most fundamental responses to extracellular stimuli. The two outcomes are poles apart: Proliferating cells divide into more of the same kind, whereas differentiating cells [...]

Insulin stimulation was found to promote association of the [α.sub.v][β.sub.3] integrin (a vitronectin receptor) with insulin receptor substrate-1 (IRS-1), an intracellular protein that mediates insulin signaling by binding other signaling molecules, including growth factor receptor-bound protein 2 (Grb2) and phosphatidylinositol-3' kinase. Insulin-treated cells expressing the [α.sub.v][β.sub.3] integrin showed 2.5 times more DNA synthesis when plated on vitronectin than on other substrates, whereas cells expressing another vitronectin receptor, [α.sub.v][β.sub.5], did not show this difference. The association between integrin and IRS-1 may be a mechanism for the synergistic action of growth factor and extracellular matrix receptors., Adhesion of cells to extracellular matrix (ECM) is mainly mediated by the integrin family of cell surface receptors (1) and is a prerequisite for cell proliferation and survival (2). The [...]

Lymphocytes must proliferate and differentiate in response to low concentrations of a vast array of antigens. The requirements of broad specifically and sensitivity conflict because the former is met by low-affinity antigen receptors, which precludes achieving the latter with high-affinity receptors. Coligation of the membrane protein CD 19 with the antigen receptor of B lymphocytes decreased the threshold for antigen receptor - dependent stimulation by two orders of magnitude magnitude. B lymphocytes proliferated when approximately 100 antigen receptors per cell, 0.03 percent of the total, were coligated with CD19. The B cell resolves its dilemma by having an accessory protein that enables activation when few antigen receptors are occupied., The immune system must respond to low concentrations of antigen for the efficient elimination of infections. The growth and differentiation of lymphocytes are mediated by antigen receptors that have low [...]

ONE OF THE PHYSIOLOGIC EFFECTS of the neuroendocrine hormone PRL is regulation of the immune system [1]. Ablation of PRL secretion in vivo diminishes immune response [2], and proliferation of [...]

ALTHOUGH FACTOR-DEPENDENT human T cell lines and clones have been available for more than a decade, all attempts to reproducibly generate factor-dependent human B cell lines have failed [1], and [...]

Influx of calcium through membrane channels is an important initial step in signal transduction of growth signals. Therefore, the effects of Ras protein injection on calcium currents across the soma [...]

The [Alpha] subunit of a prototypical heterotrimeric GTP-binding protein (G protein), which is encoded by a single gene (GPA1) in Arabidopsis, is a modulator of plant cell proliferation, gpa1 null mutants have reduced cell division in aerial tissues throughout development. Inducible overexpression of GPA1 in Arabidopsis confers inducible ectopic cell division. GPA1 overexpression in synchronized BY-2 cells causes premature advance of the nuclear cycle and the premature appearance of a division wail Results from loss of function and ectopic expression and activation of GPA1 indicate that this subunit is a positive modulator of cell division in plants., Heterotrimeric G proteins regulate cell growth, differentiation, and transformation in animal cells (1). Many growth factors activate receptors that transmit signals to the cytoplasm through heterotrimeric G proteins. Of the [...]

Mitogenesis in Response to PDGF and Bombesin Abolished by Microinjection of Antibody to PIP.sub.2 MUCH ATTENTION HAS BEEN PAID to inositol phospholipids recently because of their crucial, although so far [...]

Directing Cell Division During Development GROWTH AND CELL PROLIFERATION MUST BE REGULATED to produce an organism having a defined form and coherent structure. The speed of the cell division cycle [...]

S Phase of the Cell Cycle DURING THE S PHASE OF THE CELL CYCLE THE ENTIRE DNA content of the nucleus must be replicated completely and precisely in a period [...]

Blocking of EGF-Dependent Cell Proliferation by EGF Receptor Kinase Inhibitors MANY ONCOGENE PRODUCTS EXHIBIT protein tyrosine kinase (PTK) activity that is essential for their biological function. Similarly, early events in [...]