Sphingomyelin synthase 1 activity is regulated by the BCR-ABL oncogene.

Sphingomyelin synthase (SMS) produces sphingomyelin while consuming ceramide (a negative regulator of cell proliferation) and forming diacylglycerol (DAG) (a mitogenic factor). Therefore, enhanced SMS activity could favor cell proliferation. To examine if dysregulated SMS contributes to leukemogenesis, we measured SMS activity in several leukemic cell lines and found that it is highly elevated in K562 chronic myelogenous leukemia (CML) cells.

Thyroid cell growth: sphingomyelin metabolism as non-invasive marker for cell damage acquired during spaceflight.

Prolonged spaceflights are known to elicit changes in human cardiovascular, musculoskeletal, and nervous systems, whose functions are regulated by the thyroid gland. It is known that sphingomyelin metabolism is involved in apoptosis (programmed cell death) of thyroid cells induced by UVC radiation, but at present no data exists with regard to this phenomenon, which occurs during space missions. The aim of this study was to analyze, for the first time, the effect of spaceflight on the enzymes of sphingomyelin metabolism, sphingomyelinase, and sphingomyelin synthase, and to determine whether the ratio between the two enzymes might be used as a possible marker for thyroid activity during space missions.

Nuclear phosphatidylcholine and sphingomyelin metabolism of thyroid cells changes during stratospheric balloon flight.

Nuclear sphingomyelin and phosphatidylcholine metabolism is involved in the response to ultraviolet radiation treatment in different ways related to the physiological state of cells. To evaluate the effects of low levels of radiation from the stratosphere on thyroid cells, proliferating and quiescent FRTL-5 cells were flown in a stratospheric balloon (BIRBA mission). After recovery, the activity of neutral sphingomyelinase, phosphatidylcholine-specific phospholipase C, sphingomyelin synthase, and reverse sphingomyelin synthase was assayed in purified nuclei and the nuclei-free fraction.

Nuclear lipid microdomains regulate cell function.

The lipids present in the nuclei play different roles in relation to their localization. They are composed by high levels of phosphatidylcholine and sphingomyelin strongly linked with cholesterol. The nuclear lipid composition shows many modifications during cell life due to the presence and activity of some specific enzymes such as sphingomyelinase, sphingomyelin-synthase, reverse sphingomyelin-synthase and phosphatidylcholine-specific phospholipase C.

App1: an antiphagocytic protein that binds to complement receptors 3 and 2.

In previous studies, we showed that the pathogenic fungus Cryptococcus neoformans (Cn) produces a specific and unique protein called antiphagocytic protein 1 (App1), which inhibits phagocytosis of Cn by alveolar macrophages (AMs). Phagocytosis of Cn by AMs occurs mainly through a complement- or Ab-mediated mechanism. Among AM receptors, complement receptor 3 (CR3) and FcRgamma are the most common receptors involved in the phagocytic process.

Lipid microdomains in cell nucleus.

It is known that nuclear lipids play a role in proliferation, differentiation, and apoptotic process. Cellular nuclei contain high levels of phosphatidylcholine and sphingomyelin, which are partially linked with cholesterol and proteins to form lipid-protein complexes. These lipids are also associated with transcription factors and newly synthesized RNA but, up to date, their organization is still unknown.

Suppression of sphingomyelin synthase 1 by small interference RNA is associated with enhanced ceramide production and apoptosis after photodamage.

We have shown that overexpression of SMS1, an enzyme that converts de novo ceramide into sphingomyelin, is accompanied by attenuated ceramide response and apoptotic resistance after photodamage with the photosensitizer Pc 4 (photodynamic therapy; PDT). To test whether SMS1 overexpression-related effects after PDT can be reversed, in this study SMS1 was downregulated in Jurkat T lymphoma/leukemia cells using small inhibitory RNA (siRNA) for SMS1. Compared to scrambled (control) siRNA-transfectants, in SMS1 siRNA-transfected cells the activity of SMS at rest was downregulated with concomitant decrease in sphingomyelin mass.

Sphingomyelin synthases regulate production of diacylglycerol at the Golgi.

SMS [SM (sphingomyelin) synthase] is a class of enzymes that produces SM by transferring a phosphocholine moiety on to ceramide. PC (phosphatidylcholine) is believed to be the phosphocholine donor of the reaction with consequent production of DAG (diacylglycerol), an important bioactive lipid. In the present study, by modulating SMS1 and SMS2 expression, the role of these enzymes on the elusive regulation of DAG was investigated.

Atf2 transcription factor binds to the APP1 promoter in Cryptococcus neoformans: stimulatory effect of diacylglycerol.

The fungus Cryptococcus neoformans is an environmental human pathogen which enters the lung via the respiratory tract and produces a unique protein, called antiphagocytic protein 1 (App1), that protects it from phagocytosis by macrophages. In previous studies, we proposed genetic evidences that transcription of APP1 is controlled by the enzymatic reaction catalyzed by inositol phosphorylceramide synthase 1 (Ipc1) via the production of diacylglycerol through the activating transcription factor 2 (Atf2). We investigated here the mechanism by which Atf2 binds to the APP1 promoter in vitro and in vivo.

New insights on the use of desipramine as an inhibitor for acid ceramidase.

Treatment of different cancer cell lines with desipramine induced a time- and dose-dependent downregulation of acid ceramidase. Desipramine's effect on acid ceramidase appeared specific for amphiphilic agents (desipramine, chlorpromazine, and chloroquine) but not other lysomotropic agents such as ammonium chloride and bafilomycin A1, and was not transcriptionally regulated. The cathepsin B/L inhibitor, CA074ME, but not the cathepsin D inhibitor, pepstatin A, blocked desipramine's effect on acid ceramidase.

Microvillar membrane microdomains exist at physiological temperature. Role of galectin-4 as lipid raft stabilizer revealed by "superrafts".

Lipid rafts (glycosphingolipid/cholesterol-enriched membrane microdomains) have been isolated as low temperature, detergent-resistant membranes from many cell types, but despite their presumed importance as lateral sorting and signaling platforms, fundamental questions persist concerning raft function and even existence in vivo. The nonionic detergent Brij 98 was used to isolate lipid rafts from microvillar membrane vesicles of intestinal brush borders at physiological temperature to compare with rafts, obtained by "conventional" extraction using Triton X-100 at low temperature. Microvillar rafts prepared by the two protocols were morphologically different but had essentially similar profiles of protein- and lipid components, showing that raft microdomains do exist at 37 degrees C and are not "low temperature artifacts.