Nuclear hormone receptors regulate diverse metabolic pathways and the orphan nuclear receptor LRH-1 (NR5A2) regulates bile acid biosynthesis1,2. Structural studies have identified phospholipids as potential LRH-1 ligands3–5, but their functional relevance is unclear. Here we show that an unusual phosphatidylcholine species with two saturated 12 carbon fatty acid acyl side chains (dilauroyl phosphatidylcholine, DLPC) is an LRH-1 agonist ligand in vitro. DLPC treatment induces bile acid biosynthetic enzymes in mouse liver, increases bile acid levels, and lowers hepatic triglycerides and serum glucose. DLPC treatment also decreases hepatic steatosis and improves glucose homeostasis in two mouse models of insulin resistance. Both the antidiabetic and lipotropic effects are lost in liver specific Lrh-1 knockouts. These findings identify an LRH-1 dependent phosphatidylcholine signaling pathway that regulates bile acid metabolism and glucose homeostasis.

SUMMARY SCF ubiquitin ligase assembly is regulated by the interplay of substrate binding, reversible Nedd8 conjugation on Cul1, and the F-box protein (FBP) exchange factors Cand1 and Cand2. Detailed investigations into SCF assembly and function in reconstituted systems and Cand1,2 knockout cells informed the development of a mathematical model for how dynamical assembly of SCF complexes is controlled, and how this cycle is coupled to degradation of an SCF substrate. Simulations predicted an unanticipated hypersensitivity of Cand1/2-deficient cells to FBP expression levels, which was experimentally validated. Together, these and prior observations lead us to propose the adaptive exchange hypothesis, which posits that regulation of the koff of an FBP from SCF by the actions of substrate, Nedd8, and Cand1 molds the cellular repertoire of SCF complexes, and that the plasticity afforded by this exchange mechanism may enable large variations in FBP expression during development and in FBP gene number during evolution.

Chronic endoplasmic reticulum (ER) stress results in toxicity that contributes to multiple human disorders. We report a stress resolution pathway initiated by the nuclear receptor LRH-1 that is independent of known unfolded protein response (UPR) pathways. Like mice lacking primary UPR components, hepatic Lrh-1-null mice cannot resolve ER stress, despite a functional UPR. In response to ER stress, LRH-1 induces expression of the kinase Plk3, which phosphorylates and activates the transcription factor ATF2. Plk3-null mice also cannot resolve ER stress, and restoring Plk3 expression in Lrh-1-null cells rescues ER stress resolution. Reduced or heightened ATF2 activity also sensitizes or desensitizes cells to ER stress, respectively. LRH-1 agonist treatment increases ER stress resistance and decreases cell death. We conclude that LRH-1 initiates a novel pathway of ER stress resolution that is independent of the UPR, yet equivalently required. Targeting LRH-1 may be beneficial in human disorders associated with chronic ER stress.DOI: http://dx.doi.org/10.7554/eLife.01694.001

Glutamine synthetase (GS) plays an essential role in metabolism by catalyzing the synthesis of glutamine from glutamate and ammonia. Our recent study showed that CRBN, a direct protein target for the teratogenic and antitumor activities of immunomodulatory drugs such as thalidomide, lenalidomide, and pomalidomide, recognizes an acetyl degron of GS, resulting in ubiquitylation and degradation of GS in response to glutamine. Here, we report that valosin-containing protein (VCP)/p97 promotes the degradation of ubiquitylated GS, resulting in its accumulation in cells with compromised p97 function. Notably, p97 is also required for the degradation of all four known CRBN neo-substrates [Ikaros family zinc finger proteins 1 (IKZF1) and 3 (IKZF3), casein kinase 1α (CK1α), and the translation termination factor GSPT1] whose ubiquitylation is induced by immunomodulatory drugs. Together, these data point to an unexpectedly intimate relationship between the E3 ubiquitin ligase CRL4 CRBN and p97 pathways.lutamine plays important roles in many cellular processes, including oxidative metabolism and ATP generation, biosynthesis of proteins, lipids, and nucleic acids, and cell growth and proliferation through the regulation of the mTOR signaling pathway, translation, and autophagy (1, 2). In mammals, it is the most abundant amino acid in plasma with a concentration of 0.5-0.9 mM (3), accounting for ∼20% of its free amino acid pool. Glutamine synthetase (GS) is the only enzyme that is capable of de novo synthesis of glutamine and also functions to detoxify glutamate and ammonia, depending on tissue localization. Skeletal muscles and lungs are major sites of glutamine synthesis, whereas cells of the gut and the immune system, such as lymphocytes and macrophages, consume large amounts of glutamine in plasma (4). GS protects neurons against excitotoxicity by converting glutamate into glutamine in brain, detoxifies ammonia in liver, and maintains physiologic pH in kidney (5). In an attempt to investigate the role of GS in development, He et al. generated GS-knockout mice and reported that GS is essential in early embryogenesis, because deletion of the murine GLUL gene causes lethality at the blastocyst stage (embryonic day 3.5) (6). Interestingly, mouse ES cells maintain pluripotency and proliferate when grown in the absence of exogenous glutamine (7). However, inhibition of GS with the small molecule methionine sulfoximine (MSO) is sufficient to block the proliferation of ES cells in glutamine-free medium (7). In humans, congenital systemic glutamine deficiency caused by homozygous GS mutations results in multiorgan failure and neonatal death (8).Recent studies highlight the importance of glutamine metabolism in metabolic reprogramming, because many tumor cells display "glutamine addiction" (9). Activation of oncogenes such as MYC, KRAS, and HIF1α and/or loss of tumor suppressor genes including p53 can directly mediate the reprogramming of glutamine metabolism by selectively activating their downstream signaling or metabolic pathway...

Protein quality control (PQC) plays an important role in stemming neurodegenerative diseases and is essential for the growth of some cancers. Valosin-containing protein (VCP)/p97 plays a pivotal role in multiple PQC pathways by interacting with numerous adaptors that link VCP to specific PQC pathways and substrates and influence the post-translational modification state of substrates. However, our poor understanding of the specificity and architecture of the adaptors, and the dynamic properties of their interactions with VCP hinders our understanding of fundamental features of PQC and how modulation of VCP activity can best be exploited therapeutically. In this study we use multiple mass spectrometry-based proteomic approaches combined with biophysical studies to characterize the interaction of adaptors with VCP. Our results reveal that most VCP-adaptor interactions are characterized by rapid dynamics that in some cases are modulated by the VCP inhibitor NMS873. These findings have significant implications for both the regulation of VCP function and the impact of VCP inhibition on different VCP-adaptor complexes.