Cholesterol synthesis enzyme SC4MOL is fine-tuned by sterols and targeted for degradation by the E3 ligase MARCHF6.

Cholesterol biosynthesis is a highly regulated pathway, with over 20 enzymes controlled at the transcriptional and posttranslational levels. While some enzymes remain stable, increased sterol levels can trigger degradation of several synthesis enzymes via the ubiquitin-proteasome system. Of note, we previously identified four cholesterol synthesis enzymes as substrates for one E3 ubiquitin ligase, membrane-associated RING-CH-type finger 6 (MARCHF6).

The blood vasculature instructs lymphatic patterning in a SOX7-dependent manner.

Despite a growing catalog of secreted factors critical for lymphatic network assembly, little is known about the mechanisms that modulate the expression level of these molecular cues in blood vascular endothelial cells (BECs). Here, we show that a BEC-specific transcription factor, SOX7, plays a crucial role in a non-cell-autonomous manner by modulating the transcription of angiocrine signals to pattern lymphatic vessels. While SOX7 is not expressed in lymphatic endothelial cells (LECs), the conditional loss of SOX7 function in mouse embryos causes a dysmorphic dermal lymphatic phenotype.

A dominant-negative SOX18 mutant disrupts multiple regulatory layers essential to transcription factor activity.

Few genetically dominant mutations involved in human disease have been fully explained at the molecular level. In cases where the mutant gene encodes a transcription factor, the dominant-negative mode of action of the mutant protein is particularly poorly understood. Here, we studied the genome-wide mechanism underlying a dominant-negative form of the SOX18 transcription factor (SOX18RaOp) responsible for both the classical mouse mutant Ragged Opossum and the human genetic disorder Hypotrichosis-lymphedema-telangiectasia-renal defect syndrome.

The cholesterol synthesis enzyme lanosterol 14α-demethylase is post-translationally regulated by the E3 ubiquitin ligase MARCH6.

Cholesterol synthesis is a tightly controlled pathway, with over 20 enzymes involved. Each of these enzymes can be distinctly regulated, helping to fine-tune the production of cholesterol and its functional intermediates. Several enzymes are degraded in response to increased sterol levels, whilst others remain stable.

Cholesterol increases protein levels of the E3 ligase MARCH6 and thereby stimulates protein degradation.

The E3 ligase embrane-ssociated ing--type finger 6 (MARCH6) is a polytopic enzyme bound to the membranes of the endoplasmic reticulum. It controls levels of several known protein substrates, including a key enzyme in cholesterol synthesis, squalene monooxygenase. However, beyond its own autodegradation, little is known about how MARCH6 itself is regulated.

Measuring Activity of Cholesterol Synthesis Enzymes Using Gas Chromatography/Mass Spectrometry.

The development of gas chromatography/mass spectrometry (GC/MS) technology has improved the ease and efficiency with which sterols in biological samples can be analyzed. Its advantages include that it needs only a small amount of sample, a short analysis time, and has enhanced specificity over traditional methods. Furthermore, a major benefit is its nonselective properties, which means that a complete scan of the sample will display the relative abundance of every sterol in the sample.

Manipulating Cholesterol Status Within Cells.

Cellular cholesterol levels are intricately controlled to maintain homeostasis. Here, we describe ways in which cellular cholesterol status can be manipulated for the study of cholesterol homeostasis, including sterol starvation (by culturing cells in lipoprotein-deficient serum and pretreating/treating with the cholesterol-lowering drug, statin) and sterol enrichment (using cholesterol complexed to cyclodextrin, and low-density lipoprotein). We also describe how to prepare lipoprotein-deficient serum and complex cholesterol to cyclodextrin.

DHCR7: A vital enzyme switch between cholesterol and vitamin D production.

The conversion of 7-dehydrocholesterol to cholesterol, the final step of cholesterol synthesis in the Kandutsch-Russell pathway, is catalyzed by the enzyme 7-dehydrocholesterol reductase (DHCR7). Homozygous or compound heterozygous mutations in DHCR7 lead to the developmental disease Smith-Lemli-Opitz syndrome, which can also result in fetal mortality, highlighting the importance of this enzyme in human development and survival. Besides serving as a substrate for DHCR7, 7-dehydrocholesterol is also a precursor of vitamin D via the action of ultraviolet light on the skin.

Phosphorylation regulates activity of 7-dehydrocholesterol reductase (DHCR7), a terminal enzyme of cholesterol synthesis.

Cholesterol is essential for survival, but too much or too little can cause disease. Thus, cholesterol levels must be kept within close margins. 7-dehydrocholesterol reductase (DHCR7) is a terminal enzyme of cholesterol synthesis, and is essential for embryonic development.

Cholesterol-mediated Degradation of 7-Dehydrocholesterol Reductase Switches the Balance from Cholesterol to Vitamin D Synthesis.

Cholesterol is detrimental to human health in excess but is also essential for normal embryogenesis. Hence, enzymes involved in its synthesis possess many layers of regulation to achieve balanced cholesterol levels. 7-Dehydrocholesterol reductase (DHCR7) is the terminal enzyme of cholesterol synthesis in the Kandutsch-Russell pathway, converting 7-dehydrocholesterol (7DHC) to cholesterol.

Oxysterols: Old Tale, New Twists.

Oxysterols have long been known for their important role in cholesterol homeostasis, where they are involved in both transcriptional and posttranscriptional mechanisms for controlling cholesterol levels. However, they are increasingly associated with a wide variety of other, sometimes surprising cell functions. They are activators of the Hedgehog pathway (important in embryogenesis), and they act as ligands for a growing list of receptors, including some that are of importance to the immune system.

Navigating the Shallows and Rapids of Cholesterol Synthesis Downstream of HMGCR.

Cholesterol is vital for human life, but its levels must be tightly regulated. Too little cholesterol leads to developmental disorders, but too much is widely appreciated as contributing to heart disease. Levels are regulated through the coordinated control of cholesterol synthesis, uptake and efflux.

The terminal enzymes of cholesterol synthesis, DHCR24 and DHCR7, interact physically and functionally.

Cholesterol is essential to human health, and its levels are tightly regulated by a balance of synthesis, uptake, and efflux. Cholesterol synthesis requires the actions of more than twenty enzymes to reach the final product, through two alternate pathways. Here we describe a physical and functional interaction between the two terminal enzymes.

Squalene mono-oxygenase, a key enzyme in cholesterol synthesis, is stabilized by unsaturated fatty acids.

SM (squalene mono-oxygenase) catalyses the first oxygenation step in cholesterol synthesis, immediately before the formation of the steroid backbone at lanosterol. SM is an important control point in the pathway, and is regulated at the post-translational level by accelerated cholesterol-dependent ubiquitination and proteasomal degradation, which is associated with the accumulation of squalene. Using model cell systems, we report that SM is stabilized by unsaturated fatty acids.

Signaling regulates activity of DHCR24, the final enzyme in cholesterol synthesis.

The role of signaling in regulating cholesterol homeostasis is gradually becoming more widely recognized. Here, we explored how kinases and phosphorylation sites regulate the activity of the enzyme involved in the final step of cholesterol synthesis, 3β-hydroxysterol Δ24-reductase (DHCR24). Many factors are known to regulate DHCR24 transcriptionally, but little is known about its posttranslational regulation.

The role of signalling in cellular cholesterol homeostasis.

Cholesterol is a vital lipid and performs diverse functions on a whole body and cellular level. However, excess cellular cholesterol is toxic, and thus, elegant mechanisms have evolved to tightly regulate this important lipid. The regulation of cholesterol homeostasis is an area of intense research, and the role that signalling plays is gradually becoming more widely recognised.

Protein tyrosine phosphatase inhibition down-regulates ligand-induced ABCA1 expression.

Objective: ATP-binding cassette transporter (ABC)-A1 is an important protein of cholesterol homoeostasis and atherosclerosis as it is the major lipid transporter responsible for the export of cholesterol from cells. Many studies have examined kinase regulation of ABCA1 expression. In contrast, very little is known about whether dephosphorylation events play a role in ABCA1 expression.

Cholesterol through the looking glass: ability of its enantiomer also to elicit homeostatic responses.

How cholesterol is sensed to maintain homeostasis has been explained by direct binding to a specific protein, Scap, or through altering the physical properties of the membrane. The enantiomer of cholesterol (ent-cholesterol) is a valuable tool in distinguishing between these two models because it shares nonspecific membrane effects with native cholesterol (nat-cholesterol), but not specific binding interactions. This is the first study to compare ent- and nat-cholesterol directly on major molecular parameters of cholesterol homeostasis.

Akt acutely activates the cholesterogenic transcription factor SREBP-2.

Akt is an essential protein kinase for cell growth, proliferation, and survival. Perturbed Akt regulation is associated with a number of human diseases, such as cancer and diabetes. Recently, evidence has emerged that Akt is involved in the regulation of the sterol-regulatory element binding proteins, which are master transcriptional regulators of lipid metabolism.

Akt phosphorylates Sec24: new clues into the regulation of ER-to-Golgi trafficking.

Regulation of protein transport within the early secretory pathway is a relatively unexplored area. Here, we propose a new player in the control of protein transport from the endoplasmic reticulum (ER) to the Golgi. Akt is an important signaling kinase whose functioning is perturbed in diseases such as cancer and diabetes.

The Akt-SREBP nexus: cell signaling meets lipid metabolism.

Phosphatidylinositol 3'-kinase (PI3K) and Akt are signaling kinases involved in cell survival and proliferation. Recent evidence suggests that PI3K/Akt activates the sterol-regulatory element-binding proteins (SREBPs), master transcriptional regulators of lipid metabolism. The precise molecular mechanisms are controversial and differ between SREBP isoforms; proposed mechanisms include increased trafficking and processing of SREBP, reduced degradation, and involvement of the downstream signaling hub, mammalian target of rapamycin complex 1 (mTORC1).