Post-translational modification localizes MYC to the nuclear pore basket to regulate a subset of target genes involved in cellular responses to environmental signals.

The transcription factor MYC (also c-Myc) induces histone modification, chromatin remodeling, and the release of paused RNA polymerase to broadly regulate transcription. MYC is subject to a series of post-translational modifications that affect its stability and oncogenic activity, but how these control MYC's function on the genome is largely unknown. Recent work demonstrates an intimate connection between nuclear compartmentalization and gene regulation. Here, we report that Ser62 phosphorylation and PIN1-mediated isomerization of MYC dynamically regulate the spatial distribution of MYC in the nucleus, promoting its association with the inner basket of the nuclear pore in response to proliferative signals, where it recruits the histone acetyltransferase GCN5 to bind and regulate local gene acetylation and expression. We demonstrate that PIN1-mediated localization of MYC to the nuclear pore regulates MYC target genes responsive to mitogen stimulation that are involved in proliferation and migration pathways. These changes are also present at the chromatin level, with an increase in open regulatory elements in response to stimulation that is PIN1-dependent and associated with MYC chromatin binding. Taken together, our study indicates that post-translational modification of MYC controls its spatial activity to optimally regulate gene expression in response to extrinsic signals in normal and diseased states.

GPR124 regulates microtubule assembly, mitotic progression, and glioblastoma cell proliferation.

GPR124 is involved in embryonic development and remains expressed by select organs. The importance of GPR124 during development suggests that its aberrant expression might participate in tumor growth. Here we show that both increases and decreases in GPR124 expression in glioblastoma cells reduce cell proliferation by differentially altering the duration mitotic progression. Using mass spectrometry-based proteomics, we discovered that GPR124 interacts with ch-TOG, a known regulator of both microtubule (MT)-plus-end assembly and mitotic progression. Accordingly, changes in GPR124 expression and ch-TOG similarly affect MT assembly measured by real-time microscopy in cells. Our study describes a novel molecular interaction involving GPR124 and ch-TOG at the plasma membrane that controls glioblastoma cell proliferation by modifying MT assembly rates and controlling the progression of distinct phases of mitosis.

Dynamic mass redistribution reveals diverging importance of PDZ-ligands for G protein-coupled receptor pharmacodynamics.

G protein-coupled receptors (GPCRs) are essential membrane proteins that facilitate cell-to-cell communication and co-ordinate physiological processes. At least 30 human GPCRs contain a Type I PSD-95/DLG/Zo-1 (PDZ) ligand in their distal C-terminal domain; this four amino acid motif of X-[S/T]-X-[φ] sequence facilitates interactions with PDZ domain-containing proteins. Because PDZ protein interactions have profound effects on GPCR ligand pharmacology, cellular localization, signal-transduction effector coupling and duration of activity, we analyzed the importance of Type I PDZ ligands for the function of 23 full-length and PDZ-ligand truncated (ΔPDZ) human GPCRs in cultured human cells. SNAP-epitope tag polyacrylamide gel electrophoresis revealed most Type I PDZ GPCRs exist as both monomers and multimers; removal of the PDZ ligand played minimal role in multimer formation. Additionally, SNAP-cell surface staining indicated removal of the PDZ ligand had minimal effects on plasma membrane localization for most GPCRs examined. Label-free dynamic mass redistribution functional responses, however, revealed diverging effects of the PDZ ligand. While no clear trend was observed across all GPCRs tested or even within receptor families, a subset of GPCRs displayed diminished agonist efficacy in the absence of a PDZ ligand (i.e. HT2RB, ADRB1), whereas others demonstrated enhanced agonist efficacies (i.e. LPAR2, SSTR5). These results demonstrate the utility of label-free functional assays to tease apart the contributions of conserved protein interaction domains for GPCR signal-transduction coupling in cultured cells.

Alkylindole-sensitive receptors modulate microglial cell migration and proliferation.

Ligands targeting G protein-coupled receptors (GPCR) expressed by microglia have been shown to regulate distinct components of their activation process, including cell proliferation, migration and differentiation into M1 or M2 phenotypes. Cannabinoids, including the active component of the Cannabis plant, tetrahydrocannabinol (THC), and the synthetic alkylindole (AI) compound, WIN55212-2 (WIN-2), activate two molecularly identified GPCRs: CB1 and CB2 . Previous studies reported that WIN-2 activates an additional unknown GPCR that is not activated by plant-derived cannabinoids, and evidence indicates that microglia express these receptors. Detailed studies on the role of AI-sensitive receptors in microglial cell activation were difficult as no selective pharmacological tools were available. Here, three newly-developed AI analogues allowed us to determine if microglia express AI-sensitive receptors and if so, study how they regulate the microglial cell activation process. We found that mouse microglia in primary culture express functional AI-sensitive receptors as measured by radioligand binding and changes in intracellular cAMP levels, and that these receptors control both basal and ATP-stimulated migration. AI analogues inhibit cell proliferation stimulated by macrophage-colony stimulating factor (M-CSF) without affecting basal cell proliferation. Remarkably, AI analogues do not control the expression of effector proteins characteristic of M1 or M2 phenotypes; yet activating microglia with M1 and M2 cytokines reduces the microglial response to AI analogues. Our results suggest that microglia express functional AI-sensitive receptors that control select components of their activation process. Agonists of these novel targets might represent a novel class of therapeutics to influence the microglial cell activation process.

Downregulation of cannabinoid receptor 1 from neuropeptide Y interneurons in the basal ganglia of patients with Huntington's disease and mouse models.

Cannabinoid receptor 1 (CB(1) receptor) controls several neuronal functions, including neurotransmitter release, synaptic plasticity, gene expression and neuronal viability. Downregulation of CB(1) expression in the basal ganglia of patients with Huntington's disease (HD) and animal models represents one of the earliest molecular events induced by mutant huntingtin (mHtt). This early disruption of neuronal CB(1) signaling is thought to contribute to HD symptoms and neurodegeneration. Here we determined whether CB(1) downregulation measured in patients with HD and mouse models was ubiquitous or restricted to specific striatal neuronal subpopulations. Using unbiased semi-quantitative immunohistochemistry, we confirmed previous studies showing that CB(1) expression is downregulated in medium spiny neurons of the indirect pathway, and found that CB(1) is also downregulated in neuropeptide Y (NPY)/neuronal nitric oxide synthase (nNOS)-expressing interneurons while remaining unchanged in parvalbumin- and calretinin-expressing interneurons. CB(1) downregulation in striatal NPY/nNOS-expressing interneurons occurs in R6/2 mice, Hdh(Q150/Q150) mice and the caudate nucleus of patients with HD. In R6/2 mice, CB(1) downregulation in NPY/nNOS-expressing interneurons correlates with diffuse expression of mHtt in the soma. This downregulation also occludes the ability of cannabinoid agonists to activate the pro-survival signaling molecule cAMP response element-binding protein in NPY/nNOS-expressing interneurons. Loss of CB(1) signaling in NPY/nNOS-expressing interneurons could contribute to the impairment of basal ganglia functions linked to HD.

Quantitative trait loci affecting phenotypic variation in the vacuolated lens mouse mutant, a multigenic mouse model of neural tube defects.

The vacuolated lens (vl) mouse mutant arose spontaneously on the C3H/HeSn background and exhibits neural tube defects (NTDs), congenital cataract, and occasionally a white belly spot. We previously reported that 1) the vl phenotypes are due to a mutation in an orphan G protein-coupled receptor (GPCR), Gpr161; 2) the penetrance of the vl NTD and cataract phenotypes are affected by genetic background, allowing three unlinked quantitative trait loci (QTL) to be mapped (modifiers of vacuolated lens, Modvl1-3); and 3) phenotype-based bioinformatics followed by genetic and molecular analysis identified a lens-specific transcription factor that contributes to the cataract-modifying effect of Modvl3. We now extend this analysis in three ways. First, using the Gpr161 mutation to unequivocally identify mutant adults and embryos, we determined that approximately 50% of vl/vl NTD-affected embryos die during development. Second, the MOLF/Ei genetic background suppresses this embryonic lethality but increases the incidence of the adult belly spot phenotype. Additional QTL analysis was performed, and two novel modifiers were mapped [Modvl4, logarithm of odds ratio (LOD) 4.4; Modvl5, LOD 5.0]. Third, phenotype-based bioinformatics identified candidate genes for these modifiers including two GPCRs that cause NTD or skin/pigmentation defects (Modvl4: Frizzled homolog 6; Modvl5: Melanocortin 5 receptor). Because GPCRs form oligomeric complexes, these genes were resequenced and nonsynonymous coding variants were identified. Bioinformatics and protein modeling suggest that these variants may be functional. Our studies further establish vl as a multigenic mouse model for NTDs and identify additional QTL that interact with Gpr161 to regulate neurulation.

ST-11: A New Brain-Penetrant Microtubule-Destabilizing Agent with Therapeutic Potential for Glioblastoma Multiforme.

Glioblastoma multiforme is a devastating and intractable type of cancer. Current antineoplastic drugs do not improve the median survival of patients diagnosed with glioblastoma multiforme beyond 14 to 15 months, in part because the blood-brain barrier is generally impermeable to many therapeutic agents. Drugs that target microtubules (MT) have shown remarkable efficacy in a variety of cancers, yet their use as glioblastoma multiforme treatments has also been hindered by the scarcity of brain-penetrant MT-targeting compounds. We have discovered a new alkylindole compound, ST-11, that acts directly on MTs and rapidly attenuates their rate of assembly. Accordingly, ST-11 arrests glioblastoma multiforme cells in prometaphase and triggers apoptosis. In vivo analyses reveal that unlike current antitubulin agents, ST-11 readily crosses the blood-brain barrier. Further investigation in a syngeneic orthotopic mouse model of glioblastoma multiforme shows that ST-11 activates caspase-3 in tumors to reduce tumor volume without overt toxicity. Thus, ST-11 represents the first member of a new class of brain-penetrant antitubulin therapeutic agents. Mol Cancer Ther; 15(9); 2018-29. ©2016 AACR.

ABHD6 blockade exerts antiepileptic activity in PTZ-induced seizures and in spontaneous seizures in R6/2 mice.

The serine hydrolase α/ß-hydrolase domain 6 (ABHD6) hydrolyzes the most abundant endocannabinoid (eCB) in the brain, 2-arachidonoylglycerol (2-AG), and controls its availability at cannabinoid receptors. We show that ABHD6 inhibition decreases pentylenetetrazole (PTZ)-induced generalized tonic-clonic and myoclonic seizure incidence and severity. This effect is retained in Cnr1(-/-) or Cnr2(-/-) mice, but blocked by addition of a subconvulsive dose of picrotoxin, suggesting the involvement of GABAA receptors. ABHD6 inhibition also blocked spontaneous seizures in R6/2 mice, a genetic model of juvenile Huntington's disease known to exhibit dysregulated eCB signaling. ABHD6 blockade retained its antiepileptic activity over chronic dosing and was not associated with psychomotor or cognitive effects. While the etiology of seizures in R6/2 mice remains unsolved, involvement of the hippocampus is suggested by interictal epileptic discharges, increased expression of vGLUT1 but not vGAT, and reduced Neuropeptide Y (NPY) expression. We conclude that ABHD6 inhibition may represent a novel antiepileptic strategy.

CACNA1H mutations in autism spectrum disorders.

Autism spectrum disorders (ASD) are neurodevelopmental conditions characterized by impaired social interaction, communication skills, and restricted and repetitive behavior. The genetic causes for autism are largely unknown. Previous studies implicate CACNA1C (L-type Ca(V)1.2) calcium channel mutations in a disorder associated with autism (Timothy syndrome). Here, we identify missense mutations in the calcium channel gene CACNA1H (T-type Ca(V)3.2) in 6 of 461 individuals with ASD. These mutations are located in conserved and functionally relevant domains and are absent in 480 ethnically matched controls (p = 0.014, Fisher's exact test). Non-segregation within the pedigrees between the mutations and the ASD phenotype clearly suggest that the mutations alone are not responsible for the condition. However, functional analysis shows that all these mutations significantly reduce Ca(V)3.2 channel activity and thus could affect neuronal function and potentially brain development. We conclude that the identified mutations could contribute to the development of the ASD phenotype.