Sterols and inhibitors of sterol transport modulate the degradation and secretion of macrophage ApoE: requirement for the C-terminal domain

Macrophage-derived apoE, produced in the vessel wall, may have important ef fects during atherogenesis. The production of apoE by macrophages can be re gulated at a transcriptional level by cellular differentiation state, cytok ines and sterol loading. In addition, there are post-transcriptional and po st-translational loci for regulation. We have recently identified an interm ediate density cell membrane fraction in which the degradation of apoE call be modulated by sterols. Suppressing degradation of apoE in this fraction by pre-incubating cells in sterols led to enhanced apoE secretion, in this report we demonstrate that the suppressive effect of sterols on the degrada tion of newly synthesized apoE in this fraction depends on the presence on its C-terminal domain, by studying a macrophage cell line transfected to ex press a mutant form of apoE in which amino acids beyond amino acid 202 were deleted. In addition, two modulators of cellular sterol transport, progest erone and U1866A, inhibited the degradation of full-length apoE. In contras t, incubation of cells in the acyl CoA:cholesterol acyltransferase inhibito r S58035 did not influence apoE degradation. As would be predicted based on the results of degradation assays, U1866A, but not S58035, increased the s ecretion of apoE from a cell line transfected to constitutively express ful l-length apoE cDNA. The effect of U1866A on apoE degradation, like the effe ct of sterol, required the presence of the apoE C-terminal domain. Our resu lts indicate that alteration of intracellular sterol homeostasis by preincu bation in sterols or by drugs that modify the subcellular transport of ster ol, modulates the susceptibility of apoE to degradation and that this modul ation requires the presence of C-terminal lipid binding domains. (C) 2000 E lsevier Science B.V. All rights reserved.