Cholesterol, but not its esters, triggers programmed cell death in human erythroleukemia K562 cells

Abstract

Cholesterol, its biosynthetic precursors and the cholesterol-lowering drug compactin were able to inhibit the growth of human erythroleukemia K562 cells. Compactin, farnesyldiphosphate and cholesterol were cytotoxic by the induction of apoptosis (programmed cell death, PCD). Compactin doubled the number of apoptotic cells compared to control numbers, whereas farnesyldiphosphate and cholesterol led to a fivefold increase in PCD over the control levels. At variance with cholesterol, cholesterol esters did not affect K562 cell viability and apoptotic body formation, regardless of chain length and degree of saturation. Compactin and farnesyldiphosphate reduced the membrane cholesterol content, thus increasing membrane fluidity. Conversely, cholesterol treatment reduced the membrane fluidity by increasing cholesterol content in the lipid bilayer. Unlike farnesyldiphosphate, the other cholesterol precursors and cholesterol esters were ineffective in increasing the cholesterol content and, thereby, the fluidity of cell membranes. Compactin and cholesterol precursors, apart from farnesyldiphosphate, did not affect the amount of the farnesylated proteins Ras and lamin B in the cytosolic and the membrane fractions of K562 cell extracts, whereas farnesyldiphosphate reduced the content of both proteins in both fractions. The level of lamin B in K562 cytosol and membranes was also reduced by cholesterol treatment, which did not significantly affect the amount of Ras. These findings highlight the role of cholesterol in promoting PCD.Keywords : apoptosis ; cholesterol ; lamin B ; membrane ; Ras.Apoptosis (programmed cell death, PCD) is a genetically syl anchor, belongs to a superfamily containing more than 50 small GTPases (Peeper et al., 1997). Ras is implicated in cell controlled process, which counteracts mitosis in regulating cell number (Kerr et al., 1972). Several cell-death pathways are trig-growth control and, therefore, associated with several human cancers. Lamin B, a 67-kDa farnesylated protein, has a structural gered by membrane receptors and are executed through membrane-derived lipid messengers (Hale et al., 1996; Skowronski role in nuclear membranes (Hancock, 1993; Gibbs et al., 1994).Lamin B is cleaved by caspases (Kumar and Lavin, 1996) in the et al., 1996). Recently, we have reported profound changes in the cell membrane composition of human erythroleukemia K562 pathway of Fas-mediated PCD (Greidinger et al., 1996; Peter et al., 1996). Thus, a perturbation of cholesterol biosynthesis can cells forced into apoptosis by treatment with transforming growth factor β1, alone or in combination with cisplatin (Mac-be expected to affect the cells by altering the membrane cholesterol content (that is, membrane properties) and/or the level of carrone et al., 1996). These changes at the membrane level might be the basis for specific recognition and elimination of farnesylated proteins (that is, regulation of cell proliferation).Inhibitors of cholesterol biosynthesis, such as lovastatin and apoptotic cells by macrophage...

Increased atherosclerosis in LDL receptor–null mice lacking ACAT1 in macrophages

“…The TUNEL-stained cells did not stain with antisera that recognizes either macrophage or smooth muscle cell antigens (not shown). However, we presume that the TUNEL-stained cells were macrophages because these cells were markedly reduced in the ACAT1 -/-recipients and ACAT1 deficiency causes macrophage death in vitro (36)(37)(38).…”

“…Because in vitro studies have demonstrated that cholesterol toxicity associated with ACAT inhibition can cause cell death in macrophages (36)(37)(38), we examined the extent of apoptosis and necrosis in arterial lesions by TUNEL staining of aortic cross sections from study animals. The proportion of TUNEL-stained cells was threefold higher in ACAT1 -/-recipient mice than in controls (18% vs. 52%, P = 0.037), indicating that necrotic and apoptotic cell death contributed to the diminished numbers of macrophages in lesions ( Figure 3, c and d).…”

“…The cholesterol clefts typical of advanced lesions contain free cholesterol crystals, which may also serve as nucleation sites for calcification (41). Cholesterol crystals can also form intracellularly (42) and have been shown to induce macrophage cell toxicity and death (36)(37)(38), thus contributing to the expansion of the atheroma lipid core (43). It is likely that choles- Serum cholesterol levels were determined using Sigma Kit no.…”

Blocking protein geranylgeranylation is essential for lovastatin-induced apoptosis of human acute myeloid leukemia cells

“…29 In contrast, inhibition of cholesterol biosynthesis by squalene epoxidase inhibitors TU-2078 and NB-598 prevents apoptosis in L6 myoblasts 30 and cholesterol itself induces apoptosis in human erythroleukemia K562 cells. 31 Taken together, the relationship between the inhibition of cholesterol end products and cell death appears to be dependent on the intracellular cholesterol content rather than other end products in the mevalonate pathway, as shown in a study using a neuronal cell system and a HMG-CoA reductase inhibitor. 32 In the present study, four metabolites of cholesterol synthesis, cholesterol, squalene, lanosterol and desmosterol, were supplemented in cell cultures treated with lovastatin.…”

A simple and rapid method to measure cholesterol binding to P450s and other proteins

“…Cholesterol also serves as a regulator of gene transcription, protein degradation, and enzyme activity and has been implicated in programmed cell death (1,2). Moreover, the role of cholesterol in signal transduction is being increasingly recognized (3).…”