Figure 6. HMG-CoA reductase activity and cholesterol content of cells expressing ORP2.

(A) Effect of ORP2 overexpression on cellular HMG-CoA reductase activity. The three ORP2/HeLa cell lines (identified below the panel) were cultured for 42 h in lipoprotein-deficient medium in the absence (white bars) or presence (black bars) of 1 μg/ml doxycycline, after which HMG-CoA reductase activity was assayed as described in the Experimental section. The results are shown as d.p.m. [¹⁴C]mevalonic acid lactone/mg of protein during a 90 min reaction (mean±S.E.M.; n=3, **P<0.01, t test). (B) Effect of ORP2 overexpression on the cellular content of total, free and esterified cholesterol. After the incubation of inducible HeLa cells in normal serum-containing medium for 42 h in the absence (white bars) or presence (black bars) of 1 μg/ml doxycycline, the amounts of total and free cholesterol (CH) were measured from cell extracts with enzymatic methods. The amount of CEs was determined by subtracting FC from TC. (C) Cholesterol amounts were similarly measured from cells cultured in 5% LPDS in the presence or absence of 1 μg/ml doxycycline. The results in (B and C) are representative of three measurements for three cell lines and are shown as μg of cholesterol/mg of protein (mean±S.E.M.; n=9, *P<0.05, t test).