Mutations and regulatory anomalies effecting tumor cell immune functions

The immune system is capable of interacting with tumor cells in such a way as to lead to tumor cell death, and this knowledge has inspired therapies to manipulate patient immune systems to eradicate cancer. However, tumor cells are able to mitigate the antitumor immune response, a fact that has rarely been addressed in the design of immunotherapies. There are many different tumor cell immune functions that play a role in mitigating the antitumor immune response. In some cases, these functions appear to be intimately associated with the tumor cell abnormalities that lead to loss of growth control, such as the cases where classical tumor suppressor proteins regulate tumor cell immune function genes. In other cases, tumor cell mutations appear to affect only the antitumor response, such as tumor cell mutations that eliminate MHC class I expression. Here I review the bases for tumor cell immune functions, noting in particular where tumor cell mutations, the gold standard for identifying a tumor-specific function, are known to be responsible for the tumor cell immune function. This review also discusses other known regulatory anomalies, in the absence of a known mutation, that are apparently important for tumor development and that regulate tumor cell immune functions. Surprisingly, in many cases where the tumor cell immune function is well understood in terms of its effect on the antitumor immune response, the tumor abnormality underlying the tumor cell immune function is completely uncharacterized.     

Acetoacetate Accelerates Muscle Regeneration and Ameliorates Muscular Dystrophy in Mice

Acetoacetate (AA) is a ketone body and acts as a fuel to supply energy for cellular activity of various tissues. Here, we uncovered a novel function of AA in promoting muscle cell proliferation. Notably, the functional role of AA in regulating muscle cell function is further evidenced by its capability to accelerate muscle regeneration in normal mice, and it ameliorates muscular dystrophy in mdx mice. Mechanistically, our data from multiparameter analyses consistently support the notion that AA plays a non-metabolic role in regulating muscle cell function. Finally, we show that AA exerts its function through activation of the MEK1-ERK1/2-cyclin D1 pathway, revealing a novel mechanism in which AA serves as a signaling metabolite in mediating muscle cell function. Our findings highlight the profound functions of a small metabolite as signaling molecule in mammalian cells.     

Valproic Acid Improves Glucose Homeostasis by Increasing Beta‐Cell Proliferation,Function, and Reducing its Apoptosis through HDAC Inhibition in Juvenile Diabetic Rat

Recent evidence highlighted that there is a link between type‐1 diabetes mellitus and histone deacetylases (HDACs) due to their involvement in beta‐cell differentiation, proliferation, and function. The present study aimed to investigate the protective role of valproic acid (VPA) on beta‐cell proliferation, function, and apoptosis in juvenile diabetic rat. Diabetes was induced in juvenile Sprague–Dawley rats by streptozotocin (75 mg/kg, i.p.) and VPA was administered at the doses of 150 and 300 mg/kg/day for 3 weeks by oral route. Various biochemical parameters, cellular alterations, and protein expression as well as apoptosis were assessed using different assays. VPA treatment significantly decreased plasma glucose, beta‐cell damage, and apoptosis as well as increased the beta‐cell function, insulin level/expression. The present study demonstrated that VPA improves beta‐cell proliferation and function as well as reduces beta‐cell apoptosis through HDAC inhibition. Our findings provide evidence that VPA may be useful for the treatment of juvenile diabetes.     

C. elegans HLH-2/E/Daughterless controls key regulatory cells during gonadogenesis

The Caenorhabditis elegans distal tip cell (DTC) provides a niche for germline stem cells in both hermaphrodites and males. The hermaphrodite distal tip cell (hDTC) also provides “leader” function to control gonadal elongation and shape, while in males, leader function is allocated to the linker cell (LC). Therefore, the male distal tip cell (mDTC) serves as a niche but not as a leader. The C. elegans homolog of E/Daughterless, HLH-2, was previously implicated in hDTC specification. Here we report that HLH-2 is also critical for hDTC maintenance, hDTC niche function and hDTC expression of a lag-2/DSL ligand reporter. We also find that HLH-2 functions in males to direct linker cell specification and to promote both mDTC maintenance and the mDTC niche function. We conclude that HLH-2 functions in both sexes to promote leader cell specification and DTC niche function.     

Effects of substratum morphology on cell physiology

Among the host of substratum properties that affect animal cell behavior, surface morphology has received relatively little attention. The earliest effect of surface morphology on animal cells was discovered almost a century ago when it was found that cells became oriented in response to the underlying topography. This phenomenon is now commonly known as contact guidance. From then until very recentrly, little progress has been made in understanding the role of surface morphology on cell behavior, primarily due to a lack of defined surfaces with uniform morphologies. This problem has been solved recently with the development of photolithographic techniques to prepare substrata with well defined and uniform surface morphologies. Availability of such surfaces has facilitated systematic in vitro experiments to study influence of surface morphology on diverse cell physiological aspects such as adhesion, growth, and function. For example, these studies have shown that surfaces with uniform multipls parallel grooves can enhance cell adhesion by confining cells in grooves and by mechanically interlocking them. Several independent studies have demosterated that cell shape is a major determinant of cell growth and function. Because surface morphology has been shown to modulate the extent of cell spreading and cell shape, its effects on cell growth and function appear to be mediated via this biological coupling between cell shape and function. New evidence in the cell biology literature is emerging to suggest that surface morphology could affect other cell behavioral properties such as post-translational modifications. Further elucidation of such effects will enable better designs for implant and cell culture substrata.     

Scrib, a tumor suppressor gene involved in cell polarity

Polarity is a fundamental feature of all organisms both during development and in the adult. This reflects the key role of cell polarity during basic fundamental processes such as cell division, cell differentiation and cell migration. The control of cell polarity relies on functionally conserved proteins. Among these, Scribble, initially identified as a tumor suppressor gene in Drosophila, has been first involved in epithelial polarity. More recently Scribble function has been implicated in neuronal polarity and polarized cell migration. Scribble joins the growing family of tumor suppressors that play a key and conserved function in cell polarity. Scribble illustrates the more and more obvious link between regulation of cell polarity, cell transformation and tumor formation.     

The RhoGEF Pebble is required for cell shape changes during cell migration triggered by the Drosophila FGF receptor Heartless

The FGF receptor Heartless (HTL) is required for mesodermal cell migration in the Drosophila gastrula. We show that mesoderm cells undergo different phases of specific cell shape changes during mesoderm migration. During the migratory phase, the cells adhere to the basal surface of the ectoderm and exhibit extensive protrusive activity. HTL is required for the protrusive activity of the mesoderm cells. Moreover, the early phenotype of htl mutants suggests that HTL is required for the adhesion of mesoderm cells to the ectoderm. In a genetic screen we identified pebble (pbl) as a novel gene required for mesoderm migration. pbl encodes a guanyl nucleotide exchange factor (GEF) for RHO1 and is known as an essential regulator of cytokinesis. We show that the function of PBL in cell migration is independent of the function of PBL in cytokinesis. Although RHO1 acts as a substrate for PBL in cytokinesis, compromising RHO1 function in the mesoderm does not block cell migration. These data suggest that the function of PBL in cell migration might be mediated through a pathway distinct from RHO1. This idea is supported by allele-specific differences in the expressivity of the cytokinesis and cell migration phenotypes of different pbl mutants. We show that PBL is autonomously required in the mesoderm for cell migration. Like HTL, PBL is required for early cell shape changes during mesoderm migration. Expression of a constitutively active form of HTL is unable to rescue the early cellular defects in pbl mutants, suggesting that PBL is required for the ability of HTL to trigger these cell shape changes. These results provide evidence for a novel function of the Rho-GEF PBL in HTL-dependent mesodermal cell migration.     

Regulation by the precompetent cell culture of the appearance of spontaneous and induced competence

Biochemical and biophysical changes in the precompetent cell culture, rather than merely the cell size, regulate the appearance of competence. The more physiologically mature the incompetent cell culture is, the less competence substance is required for maximal induction of competence. The kinetics of induction of competence as the function of the physiological state of the incompetent culture and as the function of the concentration of the competence substance seems to support the idea that the competent cell is a temporary spheroplast.     

Cell surface changes and Rous sarcoma virus gene expression in synchronized cells

We have investigated whether cell surface changes associated with growth control and malignant transformation are linked to the cell cycle. Chicken embryo cells synchronized by double thymidine block were examined for cell-cycle-dependent alterations in membrane function (measured by transport of 2-deoxyglucose, uridine, thymidine, and mannitol), in cell surface morphology (examined by scanning electron microscopy), and in the ability of tumor virus gene expression to induce a transformation-specific change in membrane function. We reach the following conclusions: (a) The high rate of 2-deoxyglucose transport seen in transformed cells and the low rates of 2-deoxyglucose and uridine transport characteristic of density-inhibited cells do not occur in normal growing cells as they traverse the cell cycle. (b) Although there are cell cycle-dependent changes in surface morphology, they are not reflected in corresponding changes in membrane function. (c) Tumor virus gene expression can alter cell membrane function at any stage in the cell cycle and without progression through the cell cycle.     

GTPases in bacterial cell polarity and signalling

In bacteria, large G domain GTPases have well-established functions in translation, protein translocation, tRNA modification and ribosome assembly. In addition, bacteria also contain small Ras-like GTPases consisting of stand-alone G domains. Recent data have revealed that small Ras-like GTPases as well as large G domain GTPases in bacteria function in the regulation of cell polarity, signal transduction and possibly also in cell division. The small Ras-like GTPase MglA together with its cognate GAP MglB regulates cell polarity in Myxococcus xanthus, and the small Ras-like GTPase CvnD9 in Streptomyces coelicolor is involved in signal transduction. Similarly, the large GTPase FlhF together with the ATPase FlhG regulates the localization and number of flagella in polarly flagellated bacteria. Moreover, large dynamin-like GTPases in bacteria may function in cell division. Thus, the function of GTPases in bacteria may be as pervasive as in eukaryotes.     

The replicometer is broken: telomeres activate cellular senescence in response to genotoxic stresses

Telomeres, the ends of our linear chromosomes, can function as ‘replicometers’, capable of counting cell division cycles as they progressively erode with every round of DNA replication. Once they are critically short, telomeres become dysfunctional and consequently activate a proliferative arrest called replicative senescence. For many years, telomeres were thought to be autonomous structures, largely isolated from cell intrinsic and extrinsic signals, whose function is to prevent limitless cellular proliferation, a characteristic of most cancer cells. It is becoming increasingly evident, however, that telomeres not only count cell divisions, but also function as sensors of genotoxic stresses to stop cell cycle progression prematurely and long before cells would have entered replicative senescence. This stable growth arrest, triggered by dysfunctional telomeres that are not necessarily critically short, likely evolved as a tumor‐suppressing mechanism as it prevents proliferation of cells that are at risk for acquiring potentially hazardous and transforming mutations both in vitro and in vivo. Here, we review studies supporting the concept that telomeres are important cellular structures whose function not only is to count cell divisions, but also to act as molecular switches that can rapidly stop cell cycle progression permanently in response to a variety of stresses, including oncogenic signals.     

A junctional problem of apical proportions: epithelial tube-size control by septate junctions in the Drosophila tracheal system

The size of epithelial tubes is critical for the function of organs such as the lung, kidney and vascular system. However, the molecular mechanisms regulating tube size are largely unknown. Recent work in the Drosophila tracheal system reveals that septate junctions play a previously unsuspected role in tube-size control. Surprisingly, this tube-size function is distinct from the established diffusion barrier function of septate junctions, and involves regulation of cell shape rather than cell number. Possible tube-size functions of septate junctions include patterning of the apical extracellular matrix and regulation of conserved cell polarity genes such as Scribble and Discs Large.     

Mst1 deletion reduces hyperglycemia-mediated vascular dysfunction via attenuating mitochondrial fission and modulating the JNK signaling pathway

Diabetes is a leading cause of microvascular complications, such as nephropathy and retinopathy. Recent studies have proposed that hyperglycemia-induced endothelial cell dysfunction is modulated by mitochondrial stress. Therefore, our experiment was to detect the upstream mediator of mitochondrial stress in hyperglycemia-treated endothelial cells with a focus on macrophage-stimulating 1 (Mst1) and mitochondrial fission. Our data illuminated that hyperglycemia incubation reduced cell viability, as well as increased apoptosis ratio in endothelial cell, and this alteration seemed to be associated with Mst1 upregulation. Inhibition of Mst1 via transfection of Mst1 siRNA into an endothelial cell could sustain cell viability and maintain mitochondrial function. At the molecular levels, endothelial cell death was accompanied with the activation of mitochondrial oxidative stress, mitochondrial apoptosis, and mitochondrial fission. Genetic ablation of Mst1 could reduce mitochondrial oxidative injury, block mitochondrial apoptosis, and repress mitochondrial fission. Besides, we also found Mst1 triggered mitochondrial dysfunction as well as endothelial cell damage through augmenting JNK pathway. Suppression of JNK largely ameliorated the protective actions of Mst1 silencing on hyperglycemia-treated endothelial cells and sustain mitochondrial function. The present study identifies Mst1 as a primary key mediator for hyperglycemia-induced mitochondrial damage and endothelial cell dysfunction. Increased Mst1 impairs mitochondrial function and activates endothelial cell death via opening mitochondrial death pathway through JNK.     

In vivo treatment with anti-I-A antibodies: differential effects on Ia antigens and antigen-presenting cell function of spleen cells and epidermal Langerhans cells

The in vivo activation of T cells by a variety of antigens can be inhibited by the administration of anti-I-A antibodies (Ab) at the time of antigen priming. This inhibition can partially be explained by the temporary loss of Ia molecules from Ia-bearing antigen-presenting cells (APC) in the spleen. In this study, the effects of i.p. injected monoclonal Ab specific for I-A glycoproteins of different H-2 haplotypes on Ia antigen expression and APC function of spleen cells and epidermal Langerhans cells were compared. It was found that anti-I-A Ab quickly bound to both spleen cell and Langerhans cell Ia antigens. Although spleen cell Ia antigens were modulated and thus temporarily disappeared, Ia antigen expression by epidermal Langerhans cells was not modulated. In functional studies, the capacity of spleen cells and epidermal cells from anti-I-A Ab treated vs control animals to function as APC for antigen-specific, I-A- or I-E-restricted T cell clones was tested. A single injection of anti-I-A Ab completely abolished the APC function of spleen cells as shown in several inbred mouse strains, F1 animals, and with the use of several different Ab and T cell clones. In contrast, Langerhans cell-dependent APC function of epidermal cells remained completely unaltered. Even multiple injections of high doses of Ab never caused any inhibition of Langerhans cell function. Experiments with anti-I-Ak or anti-I-Ad Ab in an (H-2k X H-2d)F1 animal showed abrogation of APC function of spleen cells, but again not of Langerhans cells. Thus in vivo anti-I-A Ab administration appears to differentially affect Ia antigen expression and APC function from spleen and epidermis: Ia antigens are modulated from spleen cells but not from epidermis, and APC function disappears in the spleen but not in the epidermis. The abrogation of splenic but not of Langerhans cell APC function with anti-I-A Ab will facilitate the dissection of the relative contributions of Langerhans cells as compared with other APC in the generation of cutaneous immune responses.     

The tumor-associated EpCAM regulates morphogenetic movements through intracellular signaling

Epithelial cell adhesion molecule (EpCAM) is best known as a tumor-associated protein highly expressed in carcinomas. The function of this cell surface protein during embryonic development and its potential role in cancer are still poorly understood. We identified EpCAM in a gain-of-function screen for inducers of abnormal tissue mixing during gastrulation. Elevated EpCAM levels in either the ectoderm or the mesoderm confer "invasive" properties to cells in both populations. We found that this phenotype represents an "overstimulation" of an essential activity of EpCAM in controlling cell movements during embryonic development. Surprisingly, this property is independent of the putative adhesive function of EpCAM, and rather relies on a novel signaling function that operates through down-regulation of PKC activity. We show that inhibition of novel PKCs accounts entirely for the invasive phenotype induced by abnormally high levels of EpCAM as well as for its normal function in regulating cell rearrangement during early development.     

Glycoprotein contributions to mammary gland and mammary tumor structure and function: roles of adherens junctions, ErbBs and membrane MUCs

Mammary function is dependent on its three-dimensional organization, which is established and maintained by cell adhesive junctions linked through the membrane to the cell cytoskeleton. These junctions serve not only as structural elements, but also function as initiators and integrators of cell signals. In this review we discuss three types of glycoproteins whose interactions impinge on the function of mammary cell-cell junctions, cadherins, ErbB receptor tyrosine kinases and membrane mucins, as a microcosm of events regulating mammary cell behaviors. Actions of these components are integrated by the critical signaling element beta-catenin. When functioning properly, these glycoproteins, beta-catenin and associated signaling pathways mesh into a highly structured program for development and function of the gland. However, disruption or dysfunction of these glycoproteins or the signaling elements can lead to disorganization of the epithelia and ultimately to neoplasia.     

Telomere dysfunction and stem cell ageing

Ageing is characterized by a decline in organ maintenance and repair. Adult stem cells contribute to tissue repair and organ maintenance. Thus it is conceivable that ageing is partly due to a decline of stem cell function. At molecular level, ageing is associated with an accumulation of damage affecting DNA, proteins, membranes, and organelles, as well as the formation of insoluble protein aggregates. Telomere shortening represents a cell intrinsic mechanism, which contributes to the accumulation of DNA damage during cellular ageing. Telomere dysfunction in response to critical telomere shortening induces DNA damage checkpoints that lead to cell cycle arrest and/or cell death. Checkpoint responses induced by telomere dysfunction have mostly been studied in somatic cells but there are emerging data on cell intrinsic checkpoints that impair the maintenance and function of adult stem cell in response to telomere dysfunction. Moreover, telomere dysfunction induces alterations in the stem cell environment that limit the function of adult stem cells. In this review we summarize our current knowledge on the role of telomere dysfunction in adult stem cell ageing.     

Beyond the cell surface: New mechanisms of receptor function

The text book view of cell surface receptors depicts them at the top of a vertical chain of command that starts with ligand binding and proceeds in a lineal fashion towards the cell nucleus. Although pedagogically useful, this view is incomplete and recent findings suggest that the extracellular domain of cell surface receptors can be a transmitter as much as a receiver in intercellular communication. GFRα1 is a GPI-anchored receptor for GDNF (glial cell line-derived neurotrophic factor), a neuronal growth factor with widespread functions in the developing and adult nervous system. GFRα1 partners with transmembrane proteins, such as the receptor tyrosine kinase RET or the cell adhesion molecule NCAM, for intracellular transmission of the GDNF signal. In addition to this canonical role, GFRα1 can also engage in horizontal interactions and thereby modify the function of other cell surface components. GFRα1 can also function as a ligand-induced adhesion cell molecule, mediating homophilic cell-cell interactions in response to GDNF. Finally, GFRα1 can also be released from the cell surface and act at a distance as a soluble factor together with its ligand. This plethora of unconventional mechanisms is likely to be a feature common to several other receptors and considerably expands our view of cell surface receptor function.     

植物果胶的生物合成与功能

果胶作为植物细胞壁多糖之一,其结构和功能非常复杂。果胶主要由同型半乳糖醛酸聚糖(HG)、鼠李半乳糖醛酸聚糖I (RGI)和鼠李半乳糖醛酸聚糖II (RGII)组成。果胶类成分在维持细胞壁结构的完整性以及细胞间黏附和信号转导等方面发挥重要作用。研究果胶类成分的结构、分布和功能,对理解细胞壁高级结构的构建和功能具有重要意义...     

The BH3 Mimetic Obatoclax Accumulates in Lysosomes and Causes Their Alkalinization

Obatoclax belongs to a class of compounds known as BH3 mimetics which function as antagonists of Bcl-2 family apoptosis regulators. It has undergone extensive preclinical and clinical evaluation as a cancer therapeutic. Despite this, it is clear that obatoclax has additional pharmacological effects that contribute to its cytotoxic activity. It has been claimed that obatoclax, either alone or in combination with other molecularly targeted therapeutics, induces an autophagic form of cell death. In addition, obatoclax has been shown to inhibit lysosomal function, but the mechanism of this has not been elucidated. We have evaluated the mechanism of action of obatoclax in eight ovarian cancer cell lines. Consistent with its function as a BH3 mimetic, obatoclax induced apoptosis in three cell lines. However, in the remaining cell lines another form of cell death was evident because caspase activation and PARP cleavage were not observed. Obatoclax also failed to show synergy with carboplatin and paclitaxel, chemotherapeutic agents which we have previously shown to be synergistic with authentic Bcl-2 family antagonists. Obatoclax induced a profound accumulation of LC-3 but knockdown of Atg-5 or beclin had only minor effects on the activity of obatoclax in cell growth assays suggesting that the inhibition of lysosomal function rather than stimulation of autophagy may play a more prominent role in these cells. To evaluate how obatoclax inhibits lysosomal function, confocal microscopy studies were conducted which demonstrated that obatoclax, which contains two basic pyrrole groups, accumulates in lysosomes. Studies using pH sensitive dyes demonstrated that obatoclax induced lysosomal alkalinization. Furthermore, obatoclax was synergistic in cell growth/survival assays with bafilomycin and chloroquine, two other drugs which cause lysosomal alkalinization. These studies explain, for the first time, how obatoclax inhibits lysosomal function and suggest that lysosomal alkalinization contributes to the cytotoxic activity of obatoclax.