Lipid droplets (LDs) are organelles found in most types of cells in the tissues of vertebrates, invertebrates, and plants, as well as in bacteria and yeast. They differ from other organelles in binding a unique complement of proteins and lacking an aqueous core but share aspects of protein trafficking with secretory membrane compartments. In this minireview, we focus on recent evidence supporting an endoplasmic reticulum origin for LD formation and discuss recent findings regarding LD maturation and fusion.
"In the late phase of adipocyte differentiation, PLIN2 expression gradually declines and is replaced by PLIN1 in mature adipocytes . PLIN2 primarily localizes to the surface of LDs as do PLIN1, whereas PLIN3 is stable in the cytoplasm and relocates to nascent LDs upon increased TAG synthesis . "
"3. Regulation of Lipolysis via the Coordinated Action of Lipases and Cofactors The discovery of perilipin 1 provided proof of cofactors which exist in the cytoplasm and on the lipid droplet surface . Perilipin 1 is the founding member of the perilipin, adipophilin, and TIP47 family (referred to as the PAT/perilipin family protein) of lipid droplet-coated proteins  and is expressed mostly in white adipose tissue, where it coats lipid droplets, and in steroidogenic tissue . Perilipin 1 has as many as six phosphorylation sites (Ser81, Ser222, Ser276, Ser433, Ser492, and Ser517) in adipocytes by PKA    . "
[Show abstract][Hide abstract] ABSTRACT: Physical exercise accelerates the mobilization of free fatty acids from white adipocytes to provide fuel for energy. This happens in several tissues and helps to regulate a whole-body state of metabolism. Under these conditions, the hydrolysis of triacylglycerol (TG) that is found in white adipocytes is known to be augmented via the activation of these lipolytic events, which is referred to as the “lipolytic cascade.” Indeed, evidence has shown that the lipolytic responses in white adipocytes are upregulated by continuous exercise training (ET) through the adaptive changes in molecules that constitute the lipolytic cascade. During the past few decades, many lipolysis-related molecules have been identified. Of note, the discovery of a new lipase, known as adipose triglyceride lipase, has redefined the existing concepts of the hormone-sensitive lipase-dependent hydrolysis of TG in white adipocytes. This review outlines the alterations in the lipolytic molecules of white adipocytes that result from ET, which includes the molecular regulation of TG lipases through the lipolytic cascade.
Journal of obesity 05/2015; 2015:1-10. DOI:10.1155/2015/473430
"FAs can act as signalling molecules and can modulate major growth and metabolic pathways in the cell by acting as ligands for peroxisome proliferator-activated receptors (PPARs)   , by modulating liver X receptor (LXR) and sterol regulatory element-binding protein 1 (SREBP-1) transcription factor activities  , and even by binding to G protein coupledreceptors and activating growth and survival signalling cascades, such as the PI3K pathway  . However, FAs display a plethora of indirect signalling and metabolic effects as well, since they can be remodelled into membrane phospholipids, catabolised through mitochondrial FA oxidation or esterified into triacylglycerols (TAGs), which are stored in lipid droplets (LDs) in the cytosol of most cells, including cancer cells   . Several enzymes critical for the regulation of FA availability in the cell through synthesis, such as fatty acid synthase (FAS), acetyl-CoA carboxylase (ACC) and stearoyl-CoA desaturase-1 (SCD-1)  , and through lipolysis, such as monoacylglycerol lipase (MAGL)  , have been clearly associated with cancer. "
[Show abstract][Hide abstract] ABSTRACT: Secreted phospholipases A2 (sPLA2s) hydrolyse cell and lipoprotein phospholipid membranes to release free fatty acids and lysophospholipids, and can also bind to specific proteins. Several sPLA2s have been associated with various cancers, including prostate, colon, gastric, lung and breast cancers, yet, their role is controversial and seems to be dependent on the cancer type, the local microenvironment and the enzyme studied. There is strong evidence that the expression of some sPLA2s, most notably the group IIA, III and X enzymes, is dysregulated in various malignant tissues, where, as described in a number of in vitro and in vivo studies using mouse models and according to correlations between sPLA2 expression and patient survival, a particular enzyme may exert either a pro- or an anti-tumourigenic role. It is becoming clear that there are multiple, context-dependent mechanisms of action of sPLA2s in different cancers. First, the role of sPLA2s in cancer has traditionally been associated with their enzymatic activity and ability to participate in the release of potent biologically active lipid mediators, in particular arachidonic acid-derived eicosanoids, which promote tumourigenesis by stimulating cell proliferation and cell survival, by abrogating apoptosis and by increasing local inflammation and angiogenesis. Second, several biological effects of sPLA2s were found to be independent of sPLA2 enzymatic activity, arguing for a receptor-mediated mechanism of action. Finally, recent studies have implicated sPLA2s in the regulation of basal lipid metabolism, opening a new window to the understanding of the diverse roles of sPLA2s in cancer. In this short review, we highlight the newest findings on the biological roles of sPLA2s in cancer, with emphasis on their diverse mechanisms of action.
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