Molecular and cellular pharmacology最新文献

Neurodegenerative diseases caused by abnormal accumulation of the microtubule associated protein tau (MAPT, tau) are collectively called tauopathies. The most devastating tau related disorder is Alzheimer's disease (AD). Molecular chaperones such as heat shock proteins (Hsp) have emerged as critical regulators of tau stability. Several studies from our group and others have shown that the chaperone network can be targeted for the development of therapeutic strategies for AD and other neurodegenerative diseases. Here we will discuss a recent paper and current work from our laboratory where we have manipulated the ATPase activity of the 70-kDa heat shock protein (Hsp70) to regulate tau turnover. A high-throughput screening assay revealed several compounds that activated or inhibited Hsp70's ATPase activity. Inhibitors dramatically and rapidly reduced tau levels, whereas activators stabilized tau, both in cells and brain tissue. Moreover, increased levels of Hsp70 improved ATPase inhibitor efficacy, suggesting that therapies aimed at inducing Hsp70 levels followed by inhibition of its ATPase activity may be a very effective strategy to treat AD. These findings demonstrate that Hsp70 ATPase activity can be targeted to modify the pathologies of AD and other tauopathies.

The nucleolus is a highly dynamic nuclear substructure that was originally described as the site of ribosome biogenesis. The advent of proteomic analysis has now allowed the identification of over 4500 nucleolus associated proteins with only about 30% of them associated with ribogenesis (1). The great number of nucleolar proteins not associated with traditionally accepted nucleolar functions indicates a role for the nucleolus in other cellular functions such as mitosis, cell-cycle progression, cell proliferation and many forms of stress response including DNA repair (2). A number of recent reviews have addressed the pivotal role of the nucleolus in the cellular stress response (1, 3, 4). Here, we will focus on the role of Nucleolin and Nucleophosmin, two major components of the nucleolus, in response to genotoxic stress. Due to space constraint only a limited number of studies are cited. We thus apologize to all our colleagues whose works are not referenced here.

Myelination in the peripheral nervous system (PNS) is induced by close contact signaling between axons and Schwann cells. Previous studies have identified membrane-bound neuregulin-1 (Nrg1) type III, expressed on the axons, as the key instructive signal that regulates Schwann cell myelination. In our recent study, we show that recombinant soluble Nrg1 elicits a similar pro-myelinating effect on Schwann cells, albeit in a dosage-dependent manner: Nrg1 promotes myelination at low concentrations but inhibits it at high concentrations. The inhibitory effect of Nrg1 is mediated through its activation of the Ras/Raf/Erk pathway in Schwann cells, and inhibition of the pathway using a pharmacologic inhibitor restores myelination. We also show that soluble Nrg1 enhances myelination on axons that do not express sufficient amount of Nrg1 type III needed for robust myelination. These findings are significant as they suggest that combined therapies aimed at enhancing Nrg1 signaling and blocking the Ras/Raf/Erk activation may be an effective strategy for improving remyelination on adult axons, which, as shown in our recent data, express low levels of Nrg1 type III. In this report we provide an overview of our recent findings and discuss the therapeutic potential of soluble Nrg1.

The therapeutic usefulness of anticancer agents relies on their ability to exert maximal toxicity to cancer cells and minimal toxicity to normal cells. The difference between these two parameters defines the therapeutic index of the agent. Towards this end, much research has focused on the design of anticancer agents that have optimized potency against a variety of cancer cell types; however, much less effort is spent on the design of drugs that are minimally toxic to normal cells. We have previously described a concept for a novel drug delivery platform that relies on the propensity of drugs with optimal physicochemical properties to distribute differently in normal versus cancer cells due to differences in intracellular pH gradients. Specifically, we demonstrated in vitro that certain weakly basic anticancer agents had the propensity to distribute to intracellular locations in normal cells that prevent interaction with the drug target, and to intracellular locations in cancer cells that promote drug-target interactions. We refer to this concept broadly as intracellular distribution-based drug targeting. Here we will discuss current in vivo work from our laboratory that examined the role of lysosome pH on the intracellular distribution and toxicity of inhibitors of the Hsp90 molecular chaperone in mice.

Cytoplasmic citrate is the prime carbon source for fatty acid, triacylglycerol, and cholesterol biosyntheses, and also regulates glucose metabolism via its allosteric inhibition of phosphofructokinase. It originates either via the efflux of citrate from the mitochondrial matrix on the inner membrane citrate transport protein (CTP) or via the influx of extracellular citrate on the plasma membrane citrate transporter (PMCT). Despite their common substrate, the two transport proteins share little sequence similarity and they transport citrate via fundamentally different mechanisms. We tested the ability of a set of previously identified CTP inhibitors, to inhibit the PMCT. We found that of the top 10 CTP inhibitors only one substantially inhibited the PMCT. Conversely, we identified two other inhibitors that inhibited the PMCT but had little effect on the CTP. All three identified PMCT inhibitors displayed a noncompetitive mechanism. Furthermore, models to explain inhibitor interactions with the CTP are proposed. As part of the present studies a PMCT homology model has been developed based on the crystal structure of the leucine transporter, and a possible citrate binding site has been identified and its composition compared with the two known citrate binding sites present within the CTP. The ability to selectively inhibit the PMCT may prove key to the pharmacologic amelioration of metabolic disorders resulting from the synthesis of excess lipid, cholesterol, and glucose, including human obesity, hyperlipidemia, hyper-cholesterolemia, and Type 2 diabetes.

About 15 years ago, several groups including ours had used matched pairs of cell lines carrying wild type or mutant p53 genes to ascertain a role for p53 in cell survival. These were isogenic cell lines differing only by p53 status. The trend at that time was to support p53-mediated apoptosis. Accordingly, p53-wildtype cells were sensitive to DNA damage compared to p53-mutant cells which were thought to evade apoptosis. However, this finding was not universal. In particular, after UV-radiation, p53-mutant cells were more sensitive than their wild type p53 counterparts in several studies. The finding that p53 controlled a major DNA repair pathway, nucleotide excision repair (NER) which repairs UV-damage, provided a mechanism for the observations. We coined the term "the two faces of tumor suppressor p53" to illustrate that p53 can on one hand induce apoptosis leading to cell sensitivity, but p53 can also enhance the rate of DNA repair thereby protecting cells from DNA damage. This concept has gained acceptance and has been expanded to other DNA-damaging agents. New insights into how p53 is "switched" from a protective function to an apoptotic function are reviewed.

Nuclear factor of activated T cells (NFAT) is a transcription factor that translocates from cytosol to nucleus following dephosphorylation by the Ca(2+)/calmodulin dependent protein phosphatase calcineurin (CN). In nervous tissue, aberrant CN signaling is increasingly linked to a variety of pathologic features associated with Alzheimer's disease (AD), including synaptic dysfunction, glial activation, and neuronal death. Consistent with this linkage, our recent work on postmortem human hippocampal tissue discovered increased nuclear accumulation of select NFAT isoforms at different stages of AD. Some of these changes occurred at the early stages of the disease process and/or paralleled diminishing cognitive status. In addition, inhibition of astrocytic NFAT activity in primary cultures of neurons and glia dampened glutamate levels and alleviated neuronal death in response to pathogenic amyloid-β peptides. In this article, we discuss our recent findings and expand upon the possible isoform specific contributions of NFATs to the progression of AD. We also consider the possible benefits of using NFAT inhibitors to treat AD and other neurodegenerative disorders, as well.

Cellular response to DNA damage is multifacted in nature and involves a complex signaling network in which p53 functions as a "molecular node" for converging signals. p53 has been implicated in a variety of cellular processes primarily functioning as a transcription factor and also in a transcription-independent manner. It is rapidly activated following DNA damage with phosphorylation as one of the initial signals. Cellular context as well as the type and severity of DNA damage determine p53 activation code, and its activities are regulated predominantly through protein degradation, post-translational modification and interactions with various cellular co-factors. These events are crucial in decision making by p53 as it has the ability to receive, assess and integrate different signals and route them accordingly to induce cell death or promote cell survival. In this decision making process, its transcriptional role to activate a specific subset of target genes linked to inducing cell cycle arrest or apoptosis is critical that is further fine-tuned by its transcription-independent function. This article reviews the current state of knowledge about the role of p53 in determining the fate of cells that have incurred DNA damage.