RLIP76 and Cancer

Abstract

RLIP76 is a multifunctional membrane protein that transports glutathione conjugates of electrophilic compounds and other xenobiotics including chemotherapy agents out of cells. The protein is overexpressed in lung carcinomas, ovarian carcinomas, and melanomas. The protein also binds Ral and participates in mitotic spindle function, clathrin-dependent endocytosis, and triggers GTPase-activating protein activity. It is found throughout the cell, in membrane, cytosol, and the nucleus, and is known to shift between these compartments in response to stress. Loss of RLIP76 by antibody or antisense therapy is associated with increased sensitivity to radiation and chemotherapy. Conversely, liposomally delivered RLIP may treat poisoning and wounds.

Fig. 1

A, generation of 4-hydroxynonenal from linoleic acid, a polyunsaturated fatty acid. A free hydroxyl radical abstracts H and makes a lipid radical. Oxygen addition produces a peroxyl radical. Peroxycyclization follows, and then dioxetane fragmentation occurs. H extraction from PUFA then generates 4-hydroxynonenal. B, GSH is composed of glutamic acid, cysteine, and glycine with a γ-glutamyl linkage. Bound to glutathione-S-transferases, the thiol group is deprotonated by an adjacent tyrosine. GS-E reacts with 4-hydroxynonenal to form an intermediate. This intermediate reacts with water to seize a proton and release a negatively charged hydroxyl ion. The enol then rearranges through the ketoenol tautomerism to the aldehyde. The aldehyde unders oxo-cyclo tautomerism and forms the cyclic 5 – membered hemiacetal form. This GS-E is a substrate for RLIP76.

Fig. 2

A, schema of RLIP76 ATPase – dependent efflux of GSH conjugates with electrophiles. E, electrophile. B, RLIP76 is a 655 amino acid protein with ATP binding sites at residues 69 to 74 and 418 to 425. The membrane-binding domain is from residues 154 to 219. The NH₂ terminus has an AP2 binding domain. The middle domain has the Rho/Rac GAP function. The Ral binding domain and POB1/cdc2 binding domain are the first half and second half of the COOH terminus region, respectively (25).