Cholesterol promotes both head group visibility and clustering of PI(4,5)P₂driving unconventional secretion of Fibroblast Growth Factor 2

Abstract

Fibroblast Growth Factor 2 (FGF2) is a cell survival factor involved in tumor-induced angiogenesis. FGF2 is secreted through an unconventional secretory pathway based upon direct protein translocation across the plasma membrane. Here we demonstrate that both PI(4,5)P2-dependent FGF2 recruitment at the inner plasma membrane leaflet and FGF2 membrane translocation into the extracellular space are positively modulated by cholesterol in living cells. We further reveal cholesterol to enhance FGF2 binding to PI(4,5)P2-containing lipid bilayers in a fully reconstituted system. Based on extensive atomistic molecular dynamics simulations and membrane tension experiments, we propose cholesterol to modulate FGF2 binding to PI(4,5)P2 by (i) increasing head group visibility of PI(4,5)P2 on the membrane surface, (ii) increasing avidity by cholesterol-induced clustering of PI(4,5)P2 molecules triggering FGF2 oligomerization and (iii) increasing membrane tension facilitating the formation of lipidic membrane pores. Our findings have general implications for phosphoinositide-dependent protein recruitment to membranes and explain the highly selective targeting of FGF2 towards the plasma membrane, the subcellular site of FGF2 membrane translocation during unconventional secretion of FGF2.

Bilayer-Embedded Lipid Droplets Coated with Perilipin-2 Display a Pancake Shape

“…From the independently measured angles α and θ and the measured surface tensions values γ LB and γ LD (see Table 1), we could verify that these values satisfy Equation (2), as plotted in Figure 2D. It results that the measured pancake shapes correspond to an equilibrium wetting morphology, and the reduction of the insertion angle with increasing cholesterol concentration appears to be a consequence of increased bilayer tension as a function of increasing cholesterol concentration, which is consistent with some literature [32,33]. It also indicates that ADRP proteins qualitatively change the surface properties of bilayerembedded LDs, as they do not exhibit a lens-like shape but a pancake shape (see Figure 2).…”

Phospholipids Diffusion on the Surface of Model Lipid Droplets

“…Schematic representation is provide for cholesterol and DOPC. properties of the plasma membrane and thus, it is interesting to investigate the case of a lipid monolayer enriched with Chol. It is known that Chol increases both the bilayer tension and the bilayer fluidity, at least at low temperatures [50,51, 52]. The measured surface tension for a DOPC monolayer with 10 % Chol is ≈1.7 mN/m, while the surface tension of a DOPE monolayer with 10 % Chol is ≈2.5 mN/m, i.e.…”

A Role for Liquid-Ordered Plasma Membrane Nanodomains Coordinating the Unconventional Secretory Pathway of Fibroblast Growth Factor 2?

“…Several lines of evidence support the idea of a subpopulation of liquid-ordered membrane domains enriched in cholesterol and PI(4,5)P 2 as platforms that host the machinery mediating FGF2 membrane translocation. First, in a recent study, cholesterol is demonstrated to be a critical factor affecting the ability of FGF2 to get recruited to membranes in a PI(4,5)P 2 -dependent manner with high binding strength and fast kinetics (Lolicato et al, 2021). The physiological relevance of this phenomenon could be confirmed in intact cells with increased levels of cholesterol resulting in higher efficiencies of FGF2 transport into the extracellular space.…”

“…Second, in the presence of increased levels of cholesterol, PI(4,5)P 2 was found to cluster forming trimers and tetramers. This, in turn, causes an increase in avidity, explaining faster binding kinetics and an enhanced binding strength of FGF2 toward PI(4,5)P 2 (Lolicato et al, 2021). The observed effects of cholesterol could also be directly relevant for the subsequent oligomerization of FGF2.…”