Disruption of cellular cholesterol transport and homeostasis as a novel mechanism of action of membrane-targeted alkylphospholipid analogues.
OBJECTIVE
Alkylphospholipid (APL) analogues constitute a new class of synthetic anti-tumour agents that act directly on cell membranes. We have previously demonstrated that hexadecylphosphocholine (HePC) alters intracellular cholesterol traffic and metabolism in HepG2 cells. We now extended our studies to analyse the effects of other clinically relevant APLs, such as edelfosine, erucylphosphocholine and perifosine on intracellular cholesterol homeostasis.


METHODS
Using radiolabelled substrates we determined the effect of APLs on cholesterol metabolism and cholesterol traffic from the plasma membrane to the endoplasmic reticulum (ER). Protein levels and gene expression of the main proteins involved in cholesterol homeostasis were analysed by Western blot and RT-PCR respectively. Membrane raft and non-raft fractions were isolated from HepG2 cells by a detergent-free method.


RESULTS
All APLs inhibited the transport of cholesterol from the plasma membrane to the ER, which induced a significant cholesterogenic response in HepG2 cells. This response involved an increased gene expression and higher levels of several proteins related to the biosynthesis and the receptor-mediated uptake of cholesterol. Cell exposure to the APL-representative HePC enhanced the content of cholesterol mainly in the membrane raft fractions, compared with the untreated cells.


CONCLUSIONS
Membrane-targeted APLs exhibited a novel and common mechanism of action, through disruption of cholesterol homeostasis, which in turn affected specific lipid microdomains of cellular membranes.
Carrasco
María P
MP
Department of Biochemistry and Molecular Biology I, University of Granada, Spain. mpazcj@ugr.es <mpazcj@ugr.es>
Jiménez-López
José M
JM
Ríos-Marco
Pablo
P
Segovia
Josefa L
JL
Marco
Carmen
C
D000970:Antineoplastic Agents / Q000494:pharmacology; D001692:Biological Transport; D015153:Blotting, Western; D006528:Carcinoma, Hepatocellular / Q000188:drug therapy / Q000378:metabolism; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000187:drug effects; D002784:Cholesterol / Q000378:metabolism*; D016503:Drug Delivery Systems; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006706:Homeostasis / Q000187:drug effects; D006801:Humans; D008113:Liver Neoplasms / Q000188:drug therapy / Q000378:metabolism; D021962:Membrane Microdomains; D010742:Phospholipid Ethers / Q000494:pharmacology*; D010767:Phosphorylcholine / Q000031:analogs & derivatives* / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction
D000970:Antineoplastic Agents; D010742:Phospholipid Ethers; D010767:Phosphorylcholine; C075010:erucylphosphocholine; C026659:edelfosine; C105905:perifosine; D002784:Cholesterol