Figure 3
Expression of IP 3 Rs isoforms and their regulation by E 2 . (A) MCF-7 cells express the three IP3R isoforms. (a) Western blotting allowed the specific detection in MCF-7 microsomes (50 μg proteins/lane) of IP3R1, IP3R2 and IP3R3. Representative blots for 7 to 8 independent experiments are shown. Whereas E2 had no effect on the expression level of IP3R1 (left panel) and IP3R2 (middle panel), E2 increased the expression of IP3R3 (right panel, P < 0.05). This effect of E2 involves an estrogen receptor-dependent intracellular pathway since it was antagonized by the specific anti-estrogen ICI-182,780 (1 μM, b). (B) Statistical analysis of the effect of E2 on the expression level of the 3 types of IP3Rs (a) and of the inhibitory effect of ICI-182,780 on E2-induced stimulation of IP3R3 expression (b). In the presence or absence of ICI-182,780, the expression level of IP3R3 is not significantly different (113.4 ± 21.9 vs. 100.0 ± 18.2% in control conditions, n = 6).