Sphingolipids play a very important role in cell membrane formation, signal transduction, and plasma lipoprotein metabolism, all of which may well have an impact on the development of atherosclerosis. To investigate the relationship between sphingolipid metabolism and atherosclerosis, we utilized myriocin to inhibit mouse serine palmitoyl-CoA transferase (SPT), the key enzyme for sphingolipid biosynthesis. We injected 8-week-old apoE-deficient mice with myriocin (0.3 mg/ kg/every other day, intraperitoneal) for 60 days. On a chow diet, myriocin treatment caused a significant decrease (50%) in liver SPT activity (p < 0.001), significant decreases in plasma sphingomyelin, ceramide, and sphingosine-1-phosphate levels (54, 32, and 73%, respectively) (p < 0.0001), and a significant increase in plasma phosphatidylcholine levels (91%) (p < 0.0001). Plasma total cholesterol and triglyceride levels demonstrated no significant changes, but there was a significant decrease in atherosclerotic lesion area (42% in root and 36% in en face assays) (p < 0.01). On a high fat diet, myriocin treatment caused marked decreases in plasma sphingomyelin, ceramide, and sphingosine-1-phosphate levels (59, 66, and 81%, respectively) (p < 0.0001), and a marked increase in plasma phosphatidylcholine levels (100%) (p < 0.0001). Total cholesterol and triglyceride demonstrated no significant changes, but there was a significant decrease in atherosclerotic lesion area (39% in root and 37% in en face assays) (p < 0.01). These results indicate that, apart from cholesterol levels, sphingolipids have an effect on atherosclerotic development and that SPT has proatherogenic properties. Thus, inhibition of SPT activity could be an alternative treatment for atherosclerosis.Sphingolipids have many biological functions, including cell membrane formation, signal transduction, and lipid metabolism, and all of these may be related to the development of atherosclerosis. Serine palmitoyl-CoA transferase (SPT) 1 is the rate-limiting enzyme in the biosynthesis of sphingolipids (1). It has long been known that SPT plays an important role in the metabolism of sphingolipids, but its role in other lipid metabolisms and atherosclerosis has not been unequivocally determined. When SPT activity is increased in rat liver (2) and lung (3), sphingolipid formation is likewise increased. The activity of SPT is heightened in the aortas of rabbits fed a high cholesterol diet (4). Two candidate cDNAs for yeast SPT, termed LCB1 and LCB2, have been cloned (5, 6), and the translated sequences indicate that their gene products have a 21% amino acid sequence identity (6). The lack of SPT activity in a yeast strain defective in LCB1 or LCB2, together with the protein similarity data, suggest that the two genes encode subunits of SPT (6). Mouse and human LCB1 and LCB2 cDNA homologues have also been cloned (7,8). In mouse, the two mRNAs have the same tissue distribution (lung, kidney Ͼ brain Ͼ cartilage, skin Ͼ heart Ͼ liver Ͼ muscle), and the ratio of the amounts of the two transcri...

P-glycoprotein (P-gp) is a major factor in multidrug resistance (MDR) which is a serious obstacle in chemotherapy. P-gp has also been implicated in causing apoptosis of tumor cells, which was shown to be another important mechanism of MDR recently. To study the influence of P-gp in tumor cell apoptosis, K562/A cells (P-gp+) and K562/S cells (P-gp−) were subjected to doxorubicin (Dox), serum withdrawal, or independent co-incubation with multiple P-gp inhibitors, including valspodar (PSC833), verapamil (Ver) and H108 to induce apoptosis. Apoptosis was simultaneously detected by apoptotic rate, cell cycle by flow cytometry and cysteine aspartic acid-specific protease 3 (caspase 3) activity by immunoassay. Cytotoxicity and apoptosis induced by PSC833 were evaluated through an MTT method and apoptosis rate, and cell cycle combined with caspase 3 activity, respectively. The results show that K562/A cells are more resistant to apoptosis and cell cycle arrest than K562/S cells after treatment with Dox or serum deprivation. The apoptosis of K562/A cells increased after co-incubation with each of the inhibitors of P-gp. OPEN ACCESSMolecules 2014, 19 13062 P-gp inhibitors also enhanced cell cycle arrest in K562/A cell. PSC833 most strikingly decreased viability and led to apoptosis and S phase arrest of cell cycle in K562/A cells. Our study demonstrates that P-gp inhibits the apoptosis of tumor cells in addition to participating in the efflux of intracellular chemotherapy drugs. The results of the caspase 3 activity assay also suggest that the role of P-gp in apoptosis avoidance is caspase-related.

Pro-protein convertase-2 (PC2) and carboxypeptidase-E (CPE) proteins are two major members of the pro-protein convertases that involve in the maturation of protein precursor. By using PC2 activity, immunocytochemistry (ICC) and Western blot method, PC2, CPE and preproNPY protein expression levels were compared among mature retina tissue, RGC-5 cells and its differentiated cells, or brain cortex tissue, NS20Y tumor cells and its differentiated cells, or mature breast tissue, breast tumor cell RM1 and breast adenocarcinoma tissue. The experimental results indicated that the differentiated cells or tissues had higher or highest PC2 activity. In the comparative experiments, more PC2 protein expression in the mature tissues and more CPE and preproNPY protein expression in the tumor cells or tumor tissue were observed, but no expression of preproNPY protein was observed in the mature tissues. Compared with NS20Y or RGC-5 undifferentiated cells, its differentiated cells showed less proPC2, more proCPE and more preproNPY protein expressions. The results demonstrated that the mature tissues showed stronger PC2/CPE-mediated pro-protein processing ability than the tumor cells or tissue. The results also showed that the artificial differentiation of RGC-5 or NS20Y cells was different from maturation of its corresponding normal tissue.