Components of the cytosolic and released virtosomes from stimulated and non-stimulated human lymphocytes.

Abstract Aim: This work intends to analyse the structure and the composition of virtosomes and their role.

Background: Virtosomes are newly synthesized DNA-RNA-lipoprotein complexes released from living cells in a regulated and energy-dependent manner.

Methods: Virtosome fractions were isolated by ultracentrifugation from human lymphocytes cytoplasm and from culture medium before and after stimulation with phitoemoagglutinin (PHA).

Intranuclear sphingomyelin is associated with transcriptionally active chromatin and plays a role in nuclear integrity.

Background Information: Sphingomyelin is one of the major phospholipids in the cell nucleus. However, its intranuclear distribution with regard to different functional nuclear domains as well as its possible involvement in the nuclear functional architecture remains to be elucidated.

Results: We carried out an ultrastructural cytochemical study of the intranuclear distribution of SM (sphingomyelin) using an in situ binding assay of neutral SMase (sphingomyelinase) conjugated to colloidal gold particles.

Identification and characterization of a novel peptide interacting with cAMP-responsive elements binding and cAMP-responsive elements modulator in mouse liver.

Background/aims: Transcription factors coupled to cyclic adenosine mono phosphate (cAMP) signalling in the cAMP-responsive elements binding (CREB)/ATF family constitute a family of activators or repressors that bind to cAMP-responsive promoter elements (CREs) in the regulatory regions of cAMP-inducible genes. A role for CREB/ATF family has been advocated in the control of hepatocellular carcinoma progression. CREB appears to be activated by the X protein of hepatitis B virus, which links to the unphosphorylated form of CREB and activates transcription, thus obviating an otherwise indispensable Ser-133 phosphorylation.

Effect of 1alpha,25-dihydroxyvitamin D3 in embryonic hippocampal cells.

Although the role of 1alpha,25-dihydroxyvitamin D3 in calcium homeostasis of bone tissue is clear, evidence of the involvement of vitamin D3 in the central nervous system functions is increasing. In fact, vitamin D3 regulates vitamin D receptor and nerve growth factor expression, modulates brain development, and reverses experimental autoimmune encephalomyelitis. Only few studies, however, address vitamin D3 effect on embryonic hippocampal cell differentiation.

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.

HOPS is an essential constituent of centrosome assembly.

Centrosomes direct microtubule organization during cell division. Aberrant number of centrosomes results from alteration of its components and leads to abnormal mitoses and chromosome instability. HOPS is a newly discovered protein isolated during liver regeneration, implicated in cell proliferation.

Phosphatidylcholine/sphingomyelin metabolism crosstalk inside the nucleus.

It is known that phospholipids represent a minor component of chromatin. It has been highlighted recently that these lipids are metabolized directly inside the nucleus, thanks to the presence of enzymes related to their metabolism, such as neutral sphingomyelinase, sphingomyelin synthase, reverse sphingomyelin synthase and phosphatidylcholine-specific phospholipase C. The chromatin enzymatic activities change during cell proliferation, differentiation and/or apoptosis, independently from the enzyme activities present in nuclear membrane, microsomes or cell membranes.

Signal transducer and activator of transcription 3 and sphingomyelin metabolism in intranuclear complex during cell proliferation.

An "intranuclear complex" characterized by the presence of a new synthesised double-strand RNA stabilized by sphingomyelin and cholesterol has been recently isolated from hepatocyte nuclei. In the present research the existence of STAT3 in the intranuclear complex and its behaviour in relation to cyclin D and sphingomyelin metabolism during liver regeneration were studied with the aim to see if the sphingomyelinase could have a role in cell proliferation. Our data demonstrate that the transcription factor is present in the intranuclear complex either as unphosphorylated or phosphorylated monomeric form.

Sphingomyelin-cholesterol and double stranded RNA relationship in the intranuclear complex.

The nuclear double-stranded RNA can be exported to the cytoplasm leading to the incorporation alternative aminoacids into the translated protein, can be retained to the nucleus playing a role on quality control nuclear function or can engaged by vigilin complex initiating the heterochromatin function. In the nucleus this RNA is associated to the protein, a small amount of DNA, sphingomyelin, phosphatidylcholine, and enzymes related to sphingomyelin metabolism such as sphingomyelinase and sphingomyelin-synthase constituting an intranuclear complex. Our data show an association between cholesterol and sphingomyelin that could play a role in double strand formation after RNA synthesis since [3H]-uridine incorporation demonstrates that nuclear double stranded RNA is new-synthesized.

Nuclear sphingomyelin pathway in serum deprivation-induced apoptosis of embryonic hippocampal cells.

Sphingomyelin (SM) cycle has been involved in the regulation of proliferation, differentiation, and apoptosis. Increases in ceramide have been found after a larger number of apoptotic stimuli including cytokines, cytotoxic drugs, and environmental stresses. Accumulating evidence suggest that the subcellular localization of ceramide generation is a critical factor in determining the cellular behavior.

HOPS: a novel cAMP-dependent shuttling protein involved in protein synthesis regulation.

The liver has the ability to autonomously regulate growth and mass. Following partial hepatectomy, hormones, growth factors, cytokines and their coupled signal transduction pathways have been implicated in hepatocyte proliferation. To understand the mechanisms responsible for the proliferative response, we studied liver regeneration by characterization of novel genes that are activated in residual hepatocytes.

Nuclear sphingomyelin-synthase and protein kinase C delta in melanoma cells.

The aim of this research is to study the influence of protein kinase C delta on the nuclear phospholipids metabolism. Murine and human melanoma cells, in which overexpression of protein kinase delta was induced, were used. After purification of the nuclei, the phosphatidylcholine-dependent phospholipase C, sphingomyelin-synthase, and sphingomyelinase activities were measured.

Plasmalogens in rat liver chromatin: new molecules involved in cell proliferation.

A minor component of chromatin, the phospholipid fraction, changes during cell cycle as result of the activation of intranuclear lipid metabolism enzymes including phosphatidylcholine-dependent phospholipase C activity. It is known that this enzyme may be activated by phosphatidylcholine plasmalogen (Plg). Until now, there has been little evidences for the presence of Plgs inside the nucleus.

Involvement of nuclear phosphatidylinositol-dependent phospholipases C in cell cycle progression during rat liver regeneration.

Nuclear lipid metabolism is involved in the regulation of cell proliferation. Modulation of the expression and activity of nuclear PI-phospholipase C (PI-PLC) has been reported during liver regeneration after partial hepatectomy, although it has not been determined whether different PLC isoforms play specific roles in the regulation of cell cycle progression. Here, we report evidence that the increased activity of nuclear PLCs in regenerating rat liver occurs before the peak of DNA replication and involves the enzyme activity associated to the chromatin and not that associated to the nuclear membrane.

Reverse sphingomyelin-synthase in rat liver chromatin.

The chromatin phospholipid fraction is enriched in sphingomyelin content which changes during cell maturation and proliferation. Recently, we have demonstrated that the sphingomyelin variations can be due to chromatin neutral sphingomyelinase and sphingomyelin-synthase activities which differ in pH and K(m) optima from those present in nuclear membranes. The sphingomyelin can be used also as a source of phosphorylcholine for phosphatidylcholine synthesis by reverse sphingomyelin-synthase.

A possible role of cholesterol-sphingomyelin/phosphatidylcholine in nuclear matrix during rat liver regeneration.

Background/aims: Phospholipids and cholesterol in chromatin have been previously demonstrated. The lipid fraction changes during cell proliferation in relation to activation of enzymes of phospholipid metabolism. The aim of the present work is to clarify if chromatin lipids may derive or not from nuclear matrix and if they have different roles.

lal-1: a differentially expressed novel gene during proliferation in liver regeneration and in hepatoma cells.

Background: During liver regeneration, 95% of the resting hepatocytes enter in G1/S phase of the cell cycle. A number of hormones, growth factors and cytokines were identified that activate signal transduction pathways playing a primary role in hepatocyte proliferation. A wide and representative cDNA library containing 1.

The presence and the role of chromatin cholesterol in rat liver regeneration.

Background/aims: It has been shown that cholesterol is necessary in early G1 phase during cell duplication. In the present research we have studied the presence of cholesterol in the hepatocyte chromatin lipid fraction and its behaviour in liver regeneration.

Methods: Hepatocyte nuclei and chromatin were isolated from normal and regenerating rat liver.