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Posts Tagged ‘cancer

New Switch Of The Immune System Discovered

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At the Institut Curie, Inserm researchers, in collaboration with collegues from Dynavax(1), have discovered a new mechanism controlling the choice in humans between two lines of defense in the event of attack. In the presence of viruses or bacteria, the immune system can trigger a response that is rapid but devoid of memory – innate immunity – or a response that takes longer to put in place but is more specifically targeted – adaptive immunity.

PI3-kinase, a protein essential to the activation of the innate response immune in this image, immune cells responding to attack: IRF-7 (red) is in the nucleus and so can trigger the innate immune response. (Credit: Copyright Cristiana Guiducci/Institut Curie)

The essential prerequisite to the proper functioning of innate immunity is the “turning on” of the protein PI3-kinase. Once PI3-kinase is activated, the immune response is triggered, leading to the production of type I interferons, the spearhead of innate immunity, which destroy the body’s invaders. This discovery opens up new therapeutic prospects since it may suggest ways of restoring the function of innate immunity, which is overactivated in autoimmune diseases and inhibited in certain cancers.

The body is often faced with attacks from outside (viral or bacterial infection) and sometimes from inside, because of the dysfunction of its own cells (cancer), and defends itself by activating its immune system. There are two types of defence. The first is innate immunity: this has no memory, and is permanently on guard to detect and destroy abnormal cells, tumor cells, or virus-infected cells. The second, which takes longer to initiate, is adaptive immunity, which specifically targets an invader. This response requires a education phase during which the cells of the immune system learn to recognize their enemy.

Dendritic cells, the body’s “sentinels”, are the first line of defence against invading pathogens: they recognize viruses and bacteria and then trigger an immune response, which, depending on the case, may be innate or adaptive. In response to an intruder, the so-called plasmacytoid dendritic cells can either produce large amounts of interferons, molecules that trigger a rapid response against viral infections, or “specialize” and become cells able to teach the immune system to recognize the pathogens.

At the Institut Curie, Vassili Soumelis(2) and his team (“Immunity and Cancer”, Inserm/Institut Curie Unit 653) have discovered how the dendritic cells choose between the two types of immune response. First, whatever the response, the presence of an intruder stimulates the TLR receptor inside the dendritic cells. Only then is the choice made between the two types of response. The PI3-kinase signaling pathway is activated, and the innate response is triggered. Kinase PI3 is the switch that turns on a whole cascade of proteins inside the cell. Information on the presence of an intruder in the body is thus transmitted to its final destination, in the cell’s nucleus, where the protein IRF-7 (transcription factor) modifies the expression of specific genes and so alters the cell’s behavior. In this specific case, IRF-7 induces the production of type 1 interferons (interferon-alpha, for example), which will bring about the destruction of the viruses and strongly activate various cells of the immune system.

Vassili Soumelis MD, PhD at the Institut Curie explains: “Activation of the protein PI3-kinase is one of the very first steps needed for the production of large quantities of type 1 interferons, leading to the triggering or strengthening of the innate immune response.”

In certain autoimmune diseases this innate response overstimulated, leading to an abnormal defense reaction of the immune system, which attacks its own cells, tissues, or organs. In some cancers, on the other hand, the innate response is virtually absent. It may be that the cancer cells are able to block the PI3-kinase signaling pathway. Through this discovery, Vassili Soumelis and his collaborators hope, in time, to develop new treatments for use in autoimmune diseases and oncology. By acting on PI3-kinase, it may be possible to adapt the innate response, so as to inhibit it in the treatment of autoimmune diseases and boost it in cancer treatment.

J Exp Med. 2008 Feb 18;205(2):315-22. Epub 2008 Jan 28.
PI3K is critical for the nuclear translocation of IRF-7 and type I IFN production by human plasmacytoid predendritic cells in response to TLR activation.

Dynavax Technologies Corporation, Berkeley, CA 94710, USA.

Plasmacytoid predendritic cells (pDCs) are the main producers of type I interferon (IFN) in response to Toll-like receptor (TLR) stimulation. Phosphatidylinositol-3 kinase (PI3K) has been shown to be activated by TLR triggering in multiple cell types; however, its role in pDC function is not known. We show that PI3K is activated by TLR stimulation in primary human pDCs and demonstrate, using specific inhibitors, that PI3K is required for type I IFN production by pDCs, both at the transcriptional and protein levels. Importantly, PI3K was not involved in other proinflammatory responses of pDCs, including tumor necrosis factor alpha and interleukin 6 production and DC differentiation. pDCs preferentially expressed the PI3K delta subunit, which was specifically involved in the control of type I IFN production. Although uptake and endosomal trafficking of TLR ligands were not affected in the presence of PI3K inhibitors, there was a dramatic defect in the nuclear translocation of IFN regulatory factor (IRF) 7, whereas nuclear factor kappaB activation was preserved. Thus, PI3K selectively controls type I IFN production by regulating IRF-7 nuclear translocation in human pDCs and could serve as a novel target to inhibit pathogenic type I IFN in autoimmune diseases.

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Written by huehueteotl

February 26, 2008 at 10:44 am

Enzyme Structure Reveals New Drug Targets For Cancer And HIV

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If the genome is the parts list of the human cell, certain proteins are the production managers, activating and deactivating genes as needed. Scientists funded by the National Institute of General Medical Sciences (NIGMS), part of the National Institutes of Health, now have a clearer understanding of how a key protein controls gene activity and how mutations in the protein may cause disease. The work could provide new avenues to design drugs aimed at cancer, diabetes, HIV, and heart disease.

Control of gene expression occurs at four different levels starting with DNA-packaging into higher order structures controlled by ATP-dependent chromatin remodelling complexes (ATP-DRs), polycomb group (PcG) and trithorax group (TxG) genes. DNA is wrapped around nucleosomes that are assembled from dimers of the histones H2A, H2B, H3 and H4 which all contain tails that can be either acetylated (HATs) and demethylated (HDMTs) during active transcription or deactylated (HDACs) and highly methylated (HMTs) during repressed transcription. At the parts level of DNA control via DNA methylation is mediated by the DNA methylating enzymes (DNMTs), methyl-DNA binding proteins (eg MeCBPs), and cytosine deaminases which could act as demethylating enzymes. Finally transcriptional repression is also mediated by microRNAs. Viruses target DNA methyltransferase activity and p300/CBP histone acetyltransferase activity but may also target other epigenetic mechanisms to induce cancer or disease. (from Flanagan BJC 2006)

The investigators focused on a protein called p300/CBP that belongs to a family of enzymes known as histone acetyltransferases, or HATs. These enzymes activate genes by attaching chemicals called acetyl groups to histones, the spool-like proteins that hold DNA in a tightly wound form.

Mutations in p300/CBP are linked to a variety of cancers, including those of the colon, breast, pancreas, and prostate. Researchers believe that a substance that selectively inhibits p300/CBP might be the basis for an anticancer agent.

Nearly 10 years ago, Philip Cole, M.D., Ph.D., of the Johns Hopkins University School of Medicine and his coworkers designed a p300/CBP inhibitor. But the inhibitor is not active in the human body, so it has been used exclusively as a research tool.

In the new study, the investigators combined X-ray crystallography with detailed enzymology to understand how p300/CBP works.

Their three-dimensional crystal structure provides an image of how a key part of p300/CBP binds to the inhibitor. Their studies of numerous mutant versions of the enzyme reveal which amino acids in p300/CBP are essential for its activity.

The work has a number of clinical implications. Understanding the structure and behavior of p300/CBP will help scientists design a p300/CBP inhibitor that might function in human cells as an anticancer drug.

Proper functioning of p300/CBP is critical for insulin regulation and the health of heart cells. As a result, compounds that can regulate p300/CBP activity might be useful in the treatment of diabetes and heart disease.

In addition, HAT activity is necessary for the multiplication of HIV, leading at least one scientific group to suggest that targeting HATs or similar enzymes might be an new way to thwart the virus.

Finally, the article also shows that some p300/CBP mutations previously linked to certain cancers lie right where p300/CBP contacts the inhibitor. Studying how these mutations alter the enzyme’s function should shed light on why the mutations can lead to disease.

“This work illustrates how enzymology and structural biology can combine to yield both fundamental and practical insights about an important biomedical problem. The studies provide a new framework for understanding p300/CBP in health and disease,” said Jeremy M. Berg, NIGMS Director.

Nature. 2008 Feb 14;451(7180):846-50.
The structural basis of protein acetylation by the p300/CBP transcriptional coactivator.

Program in Gene Expression and Regulation, The Wistar Institute, 3601 Spruce Street, Philadelphia, Pennsylvania 19104, USA.

The transcriptional coactivator p300/CBP (CREBBP) is a histone acetyltransferase (HAT) that regulates gene expression by acetylating histones and other transcription factors. Dysregulation of p300/CBP HAT activity contributes to various diseases including cancer. Sequence alignments, enzymology experiments and inhibitor studies on p300/CBP have led to contradictory results about its catalytic mechanism and its structural relation to the Gcn5/PCAF and MYST HATs. Here we describe a high-resolution X-ray crystal structure of a semi-synthetic heterodimeric p300 HAT domain in complex with a bi-substrate inhibitor, Lys-CoA. This structure shows that p300/CBP is a distant cousin of other structurally characterized HATs, but reveals several novel features that explain the broad substrate specificity and preference for nearby basic residues. Based on this structure and accompanying biochemical data, we propose that p300/CBP uses an unusual ‘hit-and-run’ (Theorell-Chance) catalytic mechanism that is distinct from other characterized HATs. Several disease-associated mutations can also be readily accounted for by the p300 HAT structure. These studies pave the way for new epigenetic therapies involving modulation of p300/CBP HAT activity.

Written by huehueteotl

February 18, 2008 at 12:32 pm

Cannabinoids May Inhibit Cancer Cell Invasion

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Cannabinoids may suppress tumor invasion in highly invasive cancers, according to a study published online December 25 in the Journal of the National Cancer Institute.

Schematic representation of TIMP-1 structure. TIMP1 contains 12 cysteine residues which form six loop structures through disulfide bonds. The N-terminus of TIMPs 1-4 binds to the catalytic domain of most activated MMPs and inhibits function. The C-terminus of TIMP1 and TIMP2 binds to the hemopexin domain of proMMP2 and proMMP9, respectively; this binding regulates MMP function.

Cannabinoids, the active components in marijuana, are used to reduce the side effects of cancer treatment, such as pain, weight loss, and vomiting, but there is increasing evidence that they may also inhibit tumor cell growth. However, the cellular mechanisms behind this are unknown.

Robert Ramer, Ph.D., and Burkhard Hinz, Ph.D., of the University of Rostock in Germany investigated whether and by what mechanism cannabinoids inhibit tumor cell invasion.

Cannabinoids did suppress tumor cell invasion and stimulated the expression of TIMP-1, an inhibitor of a group of enzymes that are involved in tumor cell invasion.

“To our knowledge, this is the first report of TIMP-1-dependent anti-invasive effects of cannabinoids. This signaling pathway may play an important role in the antimetastatic action of cannabinoids, whose potential therapeutic benefit in the treatment of highly invasive cancers should be addressed in clinical trials,” the authors write.

MMP and Cancer LF

Schematic diagram of interaction between cancer cells and stromal within a tumor with a focus on
role of MMPs.

J Natl Cancer Inst. 2007 Dec 25
Inhibition of Cancer Cell Invasion by Cannabinoids via Increased Expression of Tissue Inhibitor of Matrix Metalloproteinases-1.
Ramer R, Hinz B.

Affiliation of authors: Institute of Toxicology and Pharmacology, University of Rostock, Rostock, Germany.

Background Cannabinoids, in addition to having palliative benefits in cancer therapy, have been associated with anticarcinogenic effects. Although the antiproliferative activities of cannabinoids have been intensively investigated, little is known about their effects on tumor invasion. Methods Matrigel-coated and uncoated Boyden chambers were used to quantify invasiveness and migration, respectively, of human cervical cancer (HeLa) cells that had been treated with cannabinoids (the stable anandamide analog R(+)-methanandamide [MA] and the phytocannabinoid Delta(9)-tetrahydrocannabinol [THC]) in the presence or absence of antagonists of the CB(1) or CB(2) cannabinoid receptors or of transient receptor potential vanilloid 1 (TRPV1) or inhibitors of p38 or p42/44 mitogen-activated protein kinase (MAPK) pathways. Reverse transcriptase-polymerase chain reaction (RT-PCR) and immunoblotting were used to assess the influence of cannabinoids on the expression of matrix metalloproteinases (MMPs) and endogenous tissue inhibitors of MMPs (TIMPs). The role of TIMP-1 in the anti-invasive action of cannabinoids was analyzed by transfecting HeLa, human cervical carcinoma (C33A), or human lung carcinoma cells (A549) cells with siRNA targeting TIMP-1. All statistical tests were two-sided. Results Without modifying migration, MA and THC caused a time- and concentration-dependent suppression of HeLa cell invasion through Matrigel that was accompanied by increased expression of TIMP-1. At the lowest concentrations tested, MA (0.1 muM) and THC (0.01 muM) led to a decrease in invasion (normalized to that observed with vehicle-treated cells) of 61.5% (95% CI = 38.7% to 84.3%, P < .001) and 68.1% (95% CI = 31.5% to 104.8%, P = .0039), respectively. The stimulation of TIMP-1 expression and suppression of cell invasion were reversed by pretreatment of cells with antagonists to CB(1) or CB(2) receptors, with inhibitors of MAPKs, or, in the case of MA, with an antagonist to TRPV1. Knockdown of cannabinoid-induced TIMP-1 expression by siRNA led to a reversal of the cannabinoid-elicited decrease in tumor cell invasiveness in HeLa, A549, and C33A cells. Conclusion Increased expression of TIMP-1 mediates an anti-invasive effect of cannabinoids. Cannabinoids may therefore offer a therapeutic option in the treatment of highly invasive cancers.

Written by huehueteotl

December 28, 2007 at 12:47 pm