The ectopic FOF1 ATP synthase of rat liver is modulated in acute cholestasis by the inhibitor protein IF1

Rat liver plasma membranes contain F_OF₁ complexes (ecto-F_OF₁) displaying a similar molecular weight to the mitochondrial F_OF₁ ATP synthase, as evidenced by Blue Native PAGE. Their ATPase activity was stably reduced in short-term extra-hepatic cholestasis. Immunoblotting and immunoprecipitation analyses demonstrated that the reduction in activity was not due to a decreased expression of ecto-F_OF₁ complexes, but to an increased level of an inhibitory protein, ecto-IF₁, bound to ecto-F_OF₁. Since cholestasis down regulates the hepatic uptake of HDL-cholesterol, and ecto-F_OF₁ has been shown to mediate SR-BI-independent hepatic uptake of HDL-cholesterol, these findings provide support to the hypothesis that ecto-F_OF₁ contributes to the fine control of reverse cholesterol transport, in parallel with SR-BI. No activity change of the mitochondrial F_OF₁ ATP synthase (m-F_OF₁), or any variation of its association with m-IF₁ was observed in cholestasis, indicating that ecto-IF₁ expression level is modulated independently from that of ecto-F_OF₁, m-IF₁ and m-F_OF₁.