Alteration of cholesterol distribution at the plasma membrane of cancer cells: From evidence to pathophysiological implication and promising therapy strategy

Abstract

Cholesterol-enriched domains are nowadays proposed to contribute to cancer cell proliferation, survival, death and invasion, with important implications in tumor progression. They could therefore represent promising targets for new anticancer treatment. However, although diverse strategies have been developed over the years from directly targeting cholesterol membrane content/distribution to adjusting sterol intake, all approaches present more or less substantial limitations. Those data emphasize the need to optimize current strategies, to develop new specific cholesterol-targeting anticancer drugs and/or to combine them with additional strategies targeting other lipids than cholesterol. Those objectives can only be achieved if we first decipher (i) the mechanisms that govern the formation and deformation of the different types of cholesterol-enriched domains and their interplay in healthy cells; (ii) the mechanisms behind domain deregulation in cancer; (iii) the potential generalization of observations in different types of cancer; and (iv) the specificity of some alterations in cancer vs. non-cancer cells as promising strategy for anticancer therapy. In this review, we will discuss the current knowledge on the homeostasis, roles and membrane distribution of cholesterol in non-tumorigenic cells. We will then integrate documented alterations of cholesterol distribution in domains at the surface of cancer cells and the mechanisms behind their contribution in cancer processes. We shall finally provide an overview on the potential strategies developed to target those cholesterol-enriched domains in cancer therapy.

Keywords: anticancer therapy; apoptosis; cancer; caveolae; cell migration; cell proliferation; lipid rafts; submicrometric domains.

FIGURE 1

Physiological homeostasis, roles and cellular/membrane distribution of cholesterol. (A) Stages of chol homeostasis involving de novo synthesis, import, export, esterification and storage. (B,C) Pleiotropic actions of chol. (D) Differential levels of heterogeneity of membrane chol distribution in cells. PM, plasma membrane. See the Section 2 of the text for further details.

FIGURE 2

Importance of cholesterol for membrane biophysical properties and heterogeneity. (A,B) Membrane chol content modulates membrane thickness (A) and rigidity (B), two membrane biophysical properties. (C) Membrane chol is a key component of lipid rafts, caveolae and submicrometric domains. Those different types of domains can be modified in abundance, size, stability, stiffness and contents in cancer cells but data are sparse and effects sometimes divergent. ≠, alteration vs. non-tumorigenic cells; ?, unknown. (D) Surface chol and PS contents have been proposed to be increased in cancer cells as compared to non-tumorigenic cells. See the Section 3 of the text for further details.

FIGURE 3

Specific increase of surface cholesterol content, submicrometric cholesterol-enriched domain abundance and membrane stiffness on malignant breast cancer cells. (A,B) Specific increase of dorsal chol and distribution in submicrometric domains (arrowheads) at the surface of the malignant MCF-10CAIa cells. X–Z reconstructions of confocal images of normal MCF-10A, pre-malignant MCF-10AT and malignant MCF-10CAIa cell lines plated on glass coverslips, labeled at 4 °C with the mCherry-Theta toxin fragment specific to endogenous chol (A) and quantified for the Theta dorsal fluorescence (fluo.) intensity (B). (C,D) Evidence for submicrometric chol-enriched domains at the dorsal face of malignant MCF-10CAIa cells by two complementary chol-specific probes, i.e., endogenous chol decoration by mCherry-Theta toxin fragment (Theta) (as in A,B) and PM insertion of TopFluor-Chol (TF-Chol). Yellow arrowheads, colocalization. (E) Specific stiffening of chol-enriched domains with respect to non-adhesive areas on malignant MCF-10CAIa cells. (A–D) Adapted from Maja et al., 2022; (E) Adapted from Dumitru et al., 2020. See the Section 3.4 of the text for further details.

FIGURE 4

Contribution of rafts and submicrometric cholesterol-enriched domains in cancer. (A) Rafts recruit and cluster proteins involved in proliferation, survival, adhesion, migration and apoptosis. Binding of growth factors induce phosphorylation (P) and activation of tyrosine kinase receptors (RTKs) recruited in raft, which then activate downstream signaling cascades like the phosphatidylinositol 3-kinase (PI3K)/AKT and MAPK pathway promoting cell proliferation and survival. Domains also promote adhesion and migration of cancer cells by recruitment of integrins and displacement of the cell surface adhesion receptor CD44 to non-raft membrane areas. Fas/CD95 death receptors cluster in rafts to recruit the adaptor molecule Fas-associated death domain (FADD) which activates the caspase-mediated pro-apoptotic signaling pathway. PIP2, phosphatidylinositol (4,5)-bisphosphate; PIP3, phosphatidylinositol (3,4,5)-trisphosphate; ECM, extracellular matrix; ERM, Ezrin/Radixin/Moesin; FAK, focal adhesion kinase. (B) Chol-enriched domains participate in membrane deformation either by forming actin-based and proteolytically-active invadopodia or releasing microvesicles (MVs). MMPs, matrix metalloproteinases. (C) Rafts mediate recognition between cells. The antigen presented at the surface of the antigen presenting cell (APC) by the major histocompatibility complex (MHC) class II is recognized by the T cell receptors (TCR) clustered in rafts and induce T cell activation. See the Section 4 of the text for further details.

FIGURE 5

Potential strategies to target cholesterol content and membrane domains enriched in cholesterol as anti-cancer therapy. Several strategies have been proposed over the years, including inhibition of chol synthesis in the endoplasmic reticulum (ER; A) or targeting plasma membrane (PM) chol (B-F). Nevertheless, more investigation is needed to understand the mechanism behind as well as the potential benefit as anticancer drugs for patients. (A) Statins inhibit the 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR) that catalyzes the conversion of HMG-CoA to mevalonate. (B) Methyl-β-cyclodextrin (mβCD) extracts membrane chol and thereby impairs chol-enriched domain organization and integrity. (C) Saponins can disrupt chol-enriched domains and induce membrane pore formation. (D) Edelfosine interacts with lipid rafts and induces the recruitment and clustering of Fas/CD95 death receptors. (E) Plant β-sitosterol has been proposed to modify the composition and stability of lipid rafts. (F) The fish oil-derived polyunsaturated fatty acid (PUFA) docosahexaenoic acid (DHA) modifies lipid raft composition, size and clustering capacities. See the Section 5 of the text for further details.