Localization of a Domain in Apolipoprotein E with both Cytostatic and Cytotoxic Activity

Abstract

Apoliprotein E (apoE) is a potent suppressor of interleukin 2- (IL2-) dependent T lymphocyte proliferation. In this study, we have used a range of monomeric and dimeric peptides encompassing amino acids 130-169 in human apoE to locate a region with both cytostatic and cytotoxic effects on IL2-dependent T lymphocytes. Monomeric peptides representing residues 130-149 or 130-155 inhibited the proliferation of the cells without causing loss of cell viability. However, cytostasis by a peptide representing the extended 130-169 domain or dimeric peptides of amino acids 141-155 or 141-149 was accompanied by potent cytotoxic activity. These results suggest that residues 141-149, which include the overlap between the functional peptides, are responsible for cytostasis and cytotoxicity. Complete ablation of both activities by the polyanionic agent heparin highlighted the important contribution of the positively charged amino acids in the 141-149 region to peptide bioactivity. Furthermore, the bioactive apoE peptides also had a relatively high helical content, suggesting that alpha-helical content is necessary for bioactivity. Cytotoxic apoE peptides were characterized by a high density of polar face positively charged residues together with a high nonpolar face hydrophobicity. This conclusion is supported by the reduced hydrophobicity and polar face positive charge density of the significantly less active E2(130-169) peptide. The cytotoxic apoE peptides are structurally similar to previously characterized class L lytic peptides. They do not, however, exert their cytotoxic activity by destabilizing membrane bilayers as is the case with the class L peptides, as evidenced by their minimal hemolytic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotoxicity of the 22 kDa Thrombin-Cleavage Fragment of Apolipoprotein E and Related Synthetic Peptides Is Receptor-Mediated

“…Cytotoxicity of apoE peptides has been demonstrated previously with lymphocyte cultures (Clay et al, 1995). Neuritedegenerative effects of these peptides were subsequently demonstrated with explant cultures of chick sympathetic neurons (Crutcher et al, 1994).…”

“…However, these peptides are not toxic to all cells. For example, high concentrations of peptide E (141-155) 2 failed to cause lysis of erythrocytes (Clay et al, 1995), and non-neuronal cells within cultures of sympathetic explants appear to be relatively resistant (Crutcher et al, 1994), suggesting that toxicity involves specific interaction of the apoE peptides with the cell membrane.…”

“…However, the mechanism underlying these toxic effects, including the question of whether the effects are mediated by specific receptors, is unknown. The cytotoxic apoE peptides and the 22 kDa thrombin fragment include residues 141-155, which reside within the receptor-binding region of apoE (residues 140 -160) Weisgraber et al, 1983;Lalazar et al, 1988), as well as the overlapping high-affinity heparin-binding region (residues 142-147) (Weisgraber et al, 1986), suggesting that these regions are important for cytotoxicity (Clay et al, 1995). The present investigation was performed to determine whether any of the cell surface molecules that have been shown previously to mediate the uptake of apoE lipoproteins are implicated in the neurotoxicity of the synthetic peptides or N-terminal thrombin-cleavage fragment of apoE.…”

“…Therefore, initial experiments were performed to determine whether the apoE peptides would also result in the death of dissociated neurons in culture. Synthetic peptides, prepared as described previously (Clay et al, 1995), were added to dissociated embryonic chick sympathetic neurons that had been in culture for 24 hr. The cells were exposed for 20 hr to different concentrations of each of three toxic apoE peptides, E (141-149) 2 , E (141-155) 2 , or E 130 -169 , or to peptides that have been found previously to be inactive in other assays.…”

N-methyl-d-aspartate receptor inhibition by an apolipoprotein E-derived peptide relies on low-density lipoprotein receptor-associated protein

“…Further, apoE [133][134][135][136][137][138][139][140][141][142][143][144][145][146][147][148][149] initiates signaling in murine macrophages, similar to intact apoE, and functions in this regard via the LRP (Misra et al, 2001). Lastly, apoE [130][131][132][133][134][135][136][137][138][139][140][141][142][143][144][145][146][147][148][149] and apoE inhibit-interleukin-2-dependent Tlymphocyte proliferation, similar to intact apoE (Clay et al, 1995).…”