Using computerized video time-lapse microscopy, we studied early cellular events during carcinogen-induced transformation of C3H10T1/2 cells. Multinucleate/polyploid giant cells (MN/PGs) formed due to DNA damage are thought to die via mitotic catastrophe. Before they die, some MN/PGs undergo a novel type of cell division, termed neosis, characterized by karyokinesis via nuclear budding followed by asymmetric, intracellular cytokinesis, producing several small mononuclear cells, termed the Raju cells, with extended mitotic life span (MLS). Mitotic derivatives of Raju cells give rise to transformed cell lines, inherit genomic instability, display a phenotype and transcriptome different from the neosis mother cell, and anchorage-independent growth. Neosis of MN/PGs also precedes spontaneous transformation of p53 -/-mouse cells. Rodent neotic clones, and primary and metastatic human tumor cells undergo spontaneous or induced secondary/ tertiary neosis. Neosis seems to extend the MLS of cells under conditions of genetic duress not favoring mitosis. It precedes tumorigenesis, occurs several times during tumor progression, yielding tumor-initiating Raju cells and introducing tumor cell heterogeneity subject to natural selection during tumor progression. Events during neosis, and its relevance to origin of established cell lines, multistep carcinogenesis, cancer stem cells, and therapeutic advantages of anti-neotic agents (neosicides) are discussed.

Excess lipid induced metabolic disorders are one of the major existing challenges for the society. Among many different causes of lipid disorders, overproduction and compromised catabolism of triacylglycerol-rich very low density lipoproteins (VLDL) have become increasingly prevalent leading to hyperlipidemia worldwide. This review provides the latest understanding in different aspects of VLDL assembly process, including structure-function relationships within apoB, mutations in APOB causing hypobetalipoproteinemia, significance of modulating microsomal triglyceride-transfer protein activity in VLDL assembly, alterations of VLDL assembly by different fatty acid species, and hepatic proteins involved in vesicular trafficking, and cytosolic lipid droplet metabolism that contribute to VLDL assembly. The role of lipoprotein receptors and exchangeable apolipoproteins that promote or diminish VLDL assembly and secretion is discussed. New understanding on dysregulated insulin signaling as a consequence of excessive triacylglycerol-rich VLDL in the plasma is also presented. It is hoped that a comprehensive view of protein and lipid factors that contribute to molecular and cellular events associated with VLDL assembly and secretion will assist in the identification of pharmaceutical targets to reduce disease complications related to hyperlipidemia.

This article is available online at http://www.jlr.org secretion under lipid-rich conditions. J. Lipid Res. 2010. 51: 150-161. Supplementary key words triacylglycerol • hypotriglyceridemia • hypertriglyceridemia • microsomal triglyceride transfer protein • hepatocyteApolipoprotein (apo) C-III is a small exchangeable apolipoprotein (79 amino acids) that is synthesized mainly in the liver and intestine from the APOA5-APOA4-APOC3-APOA1 gene locus and is secreted into the plasma as a component of VLDL and HDL ( 1 ). Elevated plasma apoC-III concentration is commonly observed in human subjects with insulin resistance and central obesity and is positively correlated with plasma triacylglycerol (TAG) concentrations in hypertriglyceridemia subjects ( 2, 3 ). Early studies have shown that mutations within the APOA4-APOC3-APOA1 gene locus were associated with patients of premature atherosclerosis ( 4, 5 ). However, the close proximity of apoA-IV, apoC-III, and apoA-I encoded within this gene cluster makes it diffi cult to ascertain the contribution of apoC-III defi ciency per se to the development of atherosclerosis. Recently, a genome-wide association study has discovered an apoC-III null allele (R19×) in Lancaster Amish population and shown that individuals heterozygous of the R19× allele have a favorable plasma lipid proAbstract Apolipoprotein (apo) C-III plays a regulatory role in VLDL lipolysis and clearance. In this study, we determined a potential intracellular role of apoC-III in hepatic VLDL assembly and secretion. Stable expression of recombinant apoC-III in McA-RH7777 cells resulted in increased secretion effi ciency of VLDL-associated triacylglycerol (TAG) and apoB-100 in a gene-dosage-dependent manner. The stimulatory effect of apoC-III on TAG secretion was manifested only when cells were cultured under lipid-rich (i.e., media supplemented with exogenous oleate) but not lipid-poor conditions. The stimulated TAG secretion was accompanied by increased secretion of apoB-100 and apoB-48 as VLDL 1 . Expression of apoC-III also increased mRNA and activity of microsomal triglyceride transfer protein (MTP). Pulse-chase experiments showed that apoC-III expression promoted VLDL 1 secretion even under conditions where the MTP activity was inhibited immediately after the formation of lipid-poor apoB-100 particles, suggesting an involvement of apoC-III in the second-step VLDL assembly process. Consistent with this notion, the newly synthesized apoC-III was predominantly associated with TAG within the microsomal lumen that resembled lipid precursors of VLDL. Introducing an Ala23-to-Thr mutation into apoC-III, a naturally occurring mutation originally identifi ed in two Mayan Indian subjects with hypotriglyceridemia, abolished the ability of apoC-III to stimulate VLDL secretion from transfected cells. Thus, expression of apoC-III in McA-RH7777 cells enhances hepatic TAG-rich VLDL assembly and secretion under lipid-rich conditions. -Sundaram, M.,

Phosphatidate phosphatase-1 (PAP-1) converts phosphatidate to diacylglycerol and plays a key role in the biosynthesis of phospholipids and triacylglycerol (TAG). PAP-1 activity is encoded by members of the lipin family, including lipin-1 (1a and 1b), -2, and -3. We determined the effect of lipin-1 expression on the assembly and secretion of very low density lipoproteins (VLDL) using McA-RH7777 cells. Expression of lipin-1a or -1b increased the synthesis and secretion of [ 3 H]glycerol-labeled lipids under either basal-or oleate-supplemented conditions. In the presence of oleate, the increased TAG secretion was mainly associated with VLDL 1 (S f . 100) and VLDL 2 (S f 20-100). Expression of lipin-1a or -1b increased secretion efficiency and decreased intracellular degradation of [35 S]apolipoprotein B-100 (apoB100). Knockdown of lipin-1 using specific short interfering RNA decreased secretion of [ 3 H]glycerolipids and [ 35 S]apoB100 even though total PAP-1 activity was not decreased, owing to the presence of lipin-2 and -3 in the cells. Deletion of the nuclear localization signal sequences within lipin-1a not only abolished nuclear localization but also resulted in impaired association with microsomal membranes. Cells expressing the cytosolic lipin-1a mutant failed to promote

Glucocorticoids (GCs) increase hepatic phosphatidate phosphatase (PAP1) activity. This is important in enhancing the liver's capacity for storing fatty acids as triacylglycerols (TAGs) that can be used subsequently for b-oxidation or VLDL secretion. PAP1 catalyzes the conversion of phosphatidate to diacylglycerol, a key substrate for TAG and phospholipid biosynthesis. PAP1 enzymes in liver include lipin-1A and -1B (alternatively spliced isoforms) and two distinct gene products, lipin-2 and lipin-3. We determined the mechanisms by which the composite PAP1 activity is regulated using rat and mouse hepatocytes. Levels of lipin-1A and -1B mRNA were increased by dexamethasone (dex; a synthetic GC), and this resulted in increased lipin-1 synthesis, protein levels, and PAP1 activity. The stimulatory effect of dex on lipin-1 expression was enhanced by glucagon or cAMP and antagonized by insulin. Lipin-2 and lipin-3 mRNA were not increased by dex/cAMP, indicating that increased PAP1 activity is attributable specifically to enhanced lipin-1 expression.This work provides the first evidence for the differential regulation of lipin activities. Selective lipin-1 expression explains the GC and cAMP effects on increased hepatic PAP1 activity, which occurs in hepatic steatosis during starvation, diabetes, stress, and ethanol