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Although numerous epigenetic aberrancies accumulate in melanoma, their contribution to initiation and progression remain unclear. The epigenetic mark 5-hydroxymethylcytosine (5hmC), generated through TET-mediated DNA modification, is now referred to as the sixth base of DNA and has recently been reported as a potential biomarker for multiple types of cancer. Loss of 5hmC is an epigenetic hallmark of melanoma, but whether a decrease in 5hmc levels contributes directly to pathogenesis or whether it merely results from disease progression-associated epigenetic remodeling remains to be established. Here, we show that NRAS-driven melanomagenesis in mice is accompanied by an overall decrease in 5hmC and specific 5hmC gains in selected gene bodies. Strikingly, genetic ablation of Tet2 in mice cooperated with oncogenic NRASQ61K to promote melanoma initiation while suppressing specific gains in 5hmC. We conclude that TET2 acts as a barrier to melanoma initiation and progression, partly by promoting 5hmC gains in specific gene bodies. Significance: This work emphasizes the importance of epigenome plasticity in cancer development and highlights the involvement of druggable epigenetic factors in cancer.

Calcineurin is a calcium/calmodulin-regulated phosphatase known for its role in activation of T cells following engagement of the T cell receptor. Calcineurin inhibitors (CNIs) are widely used as immuno-suppressive agents; common adverse effects of CNIs are hypertension and hyperkalemia. While previous studies have implicated activation of the Na-Cl cotransporter (NCC) in the renal distal convoluted tubule (DCT) in this toxicity, the molecular mechanism of this effect is unknown. The renal effects of CNIs mimic the hypertension and hyperkalemia that result from germ-line mutations in with-no-lysine (WNK) kinases and the Kelch-like 3 (KLHL3)-CUL3 ubiquitin ligase complex. WNK4 is an activator of NCC and is degraded by binding to KLHL3 followed by WNK4's ubiquitylation and proteasomal degradation. This binding is prevented by phosphorylation of KLHL3 at serine 433 (KLHL3(S433-P)) via protein kinase C, resulting in increased WNK4 levels and increased NCC activity. Mechanisms mediating KLHL3(S433-P) dephosphorylation have heretofore been unknown. We now demonstrate that calcineurin expressed in DCT is a potent KLHL3(S433-P) phosphatase. In mammalian cells, the calcium ionophore ionomycin, a calcineurin activator, reduces KLHL3(S433-P) levels, and this effect is reversed by the calcineurin inhibitor tacrolimus and by siRNA-mediated knock-down of calcineurin. In vivo, tacrolimus increases levels of KLHL3(S433-P), resulting in increased levels of WNK4, phosphorylated SPAK, and NCC. Moreover, tacrolimus attenuates KLHL3-mediated WNK4 ubiquitylation and degradation, while this effect is absent in KLHL3 with S433A substitution. Additionally, increased extracellular K+ induced calcineurin-dependent dephosphorylation of KLHL3(S433-P). These findings demonstrate that KLHL3(S433-P) is a calcineurin substrate and implicate increased KLHL3 phosphorylation in tacrolimus-induced pathologies.

An important model for axon pathfinding is provided by guidance of embryonic commissural axons from dorsal spinal cord to ventral midline floor plate (FP). FP cells produce a chemoattractive activity, comprised largely of netrin1 (FP-netrin1) and Sonic hedgehog (Shh), that can attract the axons at a distance in vitro. netrin1 is also produced by ventricular zone (VZ) progenitors along the axons' route (VZ-netrin1). Recent studies using region-specific netrin1 deletion suggested that FP-netrin1 is dispensable and VZ-netrin1 sufficient for netrin guidance activity in vivo. We show that removing FP-netrin1 actually causes guidance defects in spinal cord consistent with long-range action (i.e., over hundreds of micrometers), and double mutant analysis supports that FP-netrin1 and Shh collaborate to attract at long range. We further provide evidence that netrin1 may guide via chemotaxis or haptotaxis. These results support the model that netrin1 signals at both short and long range to guide commissural axons in spinal cord.

We study in this paper the radiative corrections to chiral magnetic current at both zero and nonzero temperature. Our motivation is a radiative correction to the matrix element of the anomalous Ward identity in massless QED stemming from a three-loop diagram where the two photons coming from the one-loop anomalous triangle are rescattered. Through the interplay between the Ward identity and the infrared subtlety of the fermion loop integral, we are able to reproduce the corrections known in literature in a simpler approach and obtain its contribution to the chiral magnetic current at zero temperature. At a nonzero temperature, the infrared subtlety disappeared in a static magnetic field and the three-loop diagram does not contribute to the chiral magnetic current any more. The generalization to all orders of the massless QED and the QCD corrections is discussed.

BACKGROUND: Homeostatic plasticity in mesolimbic dopamine ( DA) neurons plays an essential role in mediating resilience to social stress. Recent evidence implicates an association between stress resilience and projections from the locus coeruleus ( LC) to the ventral tegmental area (VTA) ( LC/VTA) DA system. However, the precise circuitry and molecular mechanisms of the homeostatic plasticity in mesolimbic DA neurons mediated by the LC/VTA circuitry, and its role in conferring resilience to social defeat stress, have not been described. METHODS: In a well-established chronic social defeat stress model of depression, using projection-specific electrophysiological recordings and optogenetic, pharmacological, and molecular profiling techniques, we investigated the functional role and molecular basis of an LC/VTA circuit in conferring resilience to social defeat stress. RESULTS: We found that LC neurons projecting to the VTA exhibit enhanced firing activity in resilient, but not susceptible, mice. Optogenetically mimicking this firing adaptation in susceptible mice reverses their depressionrelated behaviors, and induces reversal of cellular hyperactivity and homeostatic plasticity in VTA DA neurons projecting to the nucleus accumbens. Circuit-specific molecular profiling studies reveal that alpha(1)-and beta(3)-adrenergic receptors are highly expressed in VTA/nucleus accumbens DA neurons. Pharmacologically activating these receptors induces similar proresilient effects at the ion channel and cellular and behavioral levels, whereas antagonizing these receptors blocks the proresilient effect of optogenetic activation of LC/VTA circuit neurons in susceptible mice. CONCLUSIONS: These findings reveal a key role of the LC/VTA circuit in mediating homeostatic plasticity in stress resilience and reveal alpha(1)-and beta(3)-adrenergic receptors as new molecular targets for therapeutically promoting resilience.

In the past 25 years, genetic and biochemical analyses of ribosome assembly in yeast have identified most of the factors that participate in this complex pathway and have generated models for the mechanisms driving the assembly. More recently, the publication of numerous cryo-electron microscopy structures of yeast ribosome assembly intermediates has provided near-atomic resolution snapshots of ribosome precursor particles. Satisfyingly, these structural data support the genetic and biochemical models and provide additional mechanistic insight into ribosome assembly. In this Review, we discuss the mechanisms of assembly of the yeast small ribosomal subunit and large ribosomal subunit in the nucleolus, nucleus and cytoplasm. Particular emphasis is placed on concepts such as the mechanisms of RNA compaction, the functions of molecular switches and molecular mimicry, the irreversibility of assembly checkpoints and the roles of structural and functional proofreading of pre-ribosomal particles.

Tight junction is a cell adhesion apparatus functioning as barrier and/or channel in the paracellular spaces of epithelia. Claudin is the major component of tight junction and polymerizes to form tight junction strands with various morphologies that may correlate with their functions. Here we present the crystal structure of mammalian claudin-3 at 3.6 angstrom resolution. The third transmembrane helix of claudin-3 is clearly bent compared with that of other subtypes. Structural analysis of additional two mutants with a single mutation representing other subtypes in the third helix indicates that this helix takes a bent or straight structure depending on the residue. The presence or absence of the helix bending changes the positions of residues related to claudin-claudin interactions and affects the morphology and adhesiveness of the tight junction strands. These results evoke a model for tight junction strand formation with different morphologies - straight or curvy strands - observed in native epithelia.