Showing papers by "James R. Woodgett published in 2012"

GSK3β mediates muscle pathology in myotonic dystrophy

Abstract: Myotonic dystrophy type 1 (DM1) is a complex neuromuscular disease characterized by skeletal muscle wasting, weakness, and myotonia. DM1 is caused by the accumulation of CUG repeats, which alter the biological activities of RNA-binding proteins, including CUG-binding protein 1 (CUGBP1). CUGBP1 is an important skeletal muscle translational regulator that is activated by cyclin D3–dependent kinase 4 (CDK4). Here we show that mutant CUG repeats suppress Cdk4 signaling by increasing the stability and activity of glycogen synthase kinase 3β (GSK3β). Using a mouse model of DM1 (HSALR), we found that CUG repeats in the 3′ untranslated region (UTR) of human skeletal actin increase active GSK3β in skeletal muscle of mice, prior to the development of skeletal muscle weakness. Inhibition of GSK3β in both DM1 cell culture and mouse models corrected cyclin D3 levels and reduced muscle weakness and myotonia in DM1 mice. Our data predict that compounds normalizing GSK3β activity might be beneficial for improvement of muscle function in patients with DM1.

Glycogen Synthase Kinase-3α Limits Ischemic Injury, Cardiac Rupture, Post–Myocardial Infarction Remodeling and Death

Abstract: Background—The molecular pathways that regulate the extent of ischemic injury and post–myocardial infarction (MI) remodeling are not well understood. We recently demonstrated that glycogen synthase kinase-3α (GSK-3α) is critical to the heart's response to pressure overload. However, the role, if any, of GSK-3α in regulating ischemic injury and its consequences is not known. Methods and Results—MI was induced in wild-type (WT) versus GSK-3α(−/−) (KO) littermates by left anterior descending coronary artery ligation. Pre-MI, WT, and KO hearts had comparable chamber dimensions and ventricular function, but as early as 1 week post-MI, KO mice had significantly more left ventricular dilatation and dysfunction than WT mice. KO mice also had increased mortality during the first 10 days post-MI (43% versus 22%; P=0.04), and postmortem examination confirmed cardiac rupture as the cause of most of the deaths. In the mice that survived the first 10 days, left ventricular dilatation and dysfunction remained worse in t...

The Effects of Glycogen Synthase Kinase-3beta in Serotonin Neurons

Abstract: Glycogen synthase kinase-3 (GSK3) is a constitutively active protein kinase in brain. Increasing evidence has shown that GSK3 acts as a modulator in the serotonin neurotransmission system, including direct interaction with serotonin 1B (5-HT1B) receptors in a highly selective manner and prominent modulating effect on 5-HT1B receptor activity. In this study, we utilized the serotonin neuron-selective GSK3β knockout (snGSK3β-KO) mice to test if GSK3β in serotonin neurons selectively modulates 5-HT1B autoreceptor activity and function. The snGSK3β-KO mice were generated by crossbreeding GSK3β-floxed mice and ePet1-Cre mice. These mice had normal growth and physiological characteristics, similar numbers of tryptophan hydroxylase-2 (TpH2)-expressing serotonin neurons, and the same brain serotonin content as in littermate wild type mice. However, the expression of GSK3β in snGSK3β-KO mice was diminished in TpH2-expressing serotonin neurons. Compared to littermate wild type mice, snGSK3β-KO mice had a reduced response to the 5-HT1B receptor agonist anpirtoline in the regulation of serotonergic neuron firing, cAMP production, and serotonin release, whereas these animals displayed a normal response to the 5-HT1A receptor agonist 8-OH-DPAT. The effect of anpirtoline on the horizontal, center, and vertical activities in the open field test was differentially affected by GSK3β depletion in serotonin neurons, wherein vertical activity, but not horizontal activity, was significantly altered in snGSK3β-KO mice. In addition, there was an enhanced anti-immobility response to anpirtoline in the tail suspension test in snGSK3β-KO mice. Therefore, results of this study demonstrated a serotonin neuron-targeting function of GSK3β by regulating 5-HT1B autoreceptors, which impacts serotonergic neuron firing, serotonin release, and serotonin-regulated behaviors.

Can a Two-Faced Kinase be Exploited for Osteosarcoma?

Abstract: There are 518 protein kinases in the human genome, many of which act as important nodes in signal transduction pathways (1). Members of this class of important regulatory enzymes are also, unsurprisingly, frequently mutated or dysregulated in cancer and many other diseases. They have thus become the target of therapeutic interventions, with many successes. What is often overlooked, however, is that there are fewer than 15 signaling pathways for transmitting extracellular information into the cell. This paucity of communication routes is responsible for extracting appropriate cellular responses to a myriad of external cues. If it sounds as though too many eggs are in a limited number of baskets, the situation is further exacerbated by sharing of several transduction components between pathways. The most egregious example is that of glycogen synthase kinase-3 (GSK-3), a protein kinase first identified as a regulator of glycogen synthesis (2). This innocuously named protein is anything but because it plays a central role in at least four of these signaling pathways—the Wnt, Notch, Hedgehog, and nuclear factor-kB (NF-kB) pathways—with important roles in at least six more—the ras/mitogen-associated protein kinase (RAS/MAPK), cyclic-AMP, transforming growth factor-b/activin (TGF-b), phosphatidylinositol -3-kinase (PI3K), jun kinase/stressactivated protein kinase (JNK/SAPK), and janus kinase/signal transducer and activator of transcription (JAK/STAT) pathways. There are two highly related isoforms of GSK-3 (termed a and b) encoded by distinct genes, but that is still a substantial responsibility assigned to a particular protein kinase begging the question of why and how pathways maintain the authenticity of their signals if relying on the same molecules (3). Only the cyclic GMP, p38 mitogen-activated protein kinase (p38 MAPK), Ca 2+ , calmodulin, and Hippo pathways, and the intracellular DNA damage response and unfolded protein response pathways currently lack known roles for GSK-3. In this issue of the Journal, Tang et al. (4) report that suppression of GSK-3b interferes with the growth and viability of osteosarcoma cells, likely by inhibition of NF-kB. This transcription factor plays a critical role in inflammatory responses and has been directly implicated in the promotion of tumorigenesis (5). An important connection between GSK-3 and NF-kB was revealed upon the generation of mice that were genetically engineered to lack GSK-3b (6). GSK-3b null embryos frequently died before birth of extensive apoptosis in the liver, a phenotype reminiscent of mice that were engineered to lack RelA, a subunit of NF-kB (7). Mouse embryo fibroblasts derived from the GSK-3 b null mice displayed a substantial deficit in the ability of tumor necrosis factor alpha (TNF-a) to induce activation of NF-kB and its regulation of anti-apoptotic gene expression. (TNF-a-mediated induction of the caspase pathway was unaffected; hence, the hepatocytes were sensitized to programmed cell death.) Interestingly, mice engineered to lack GSK-3a are viable and NF-kB signaling is normal (8). The molecular mechanism by which GSK-3b selectively regulates and is required for NF-kB function remains unclear, but this kinase modifies the spectrum of genes regulated by NF- kB (9). Both isoforms of GSK-3 are negatively regulated by serine phosphorylation (ie, Serine 21 of GSK-3a and Serine 9 of GSK-3b), and this is one mechanism by which the cyclic-AMP and phosphatidylinositol-3- kinase pathways suppress GSK-3 activity. Tang et al. (4) observed that the level of inhibitory phosphorylation of GSK-3b at Serine 9 was low in several osteosarcoma lines compared with that in a normal osteoblast cell line, suggesting that GSK-3 activity was higher than normal, although this was not directly measured. They also found that b-catenin levels (a target of the Wnt pathway) were increased in some lines, but this finding is unlikely to be related to GSK-3b phosphorylation for several reasons. First, agonists that induce serine phosphorylation of GSK-3 do not typically affect b-catenin (10,11), probably because

We must be open about our mistakes

Abstract: Greater transparency about the scientific process and a closer focus on correcting defective data are the way forward, says Jim Woodgett.