Figure 3

PI3K-activator IGF-I rapidly downregulates mRNA levels of ER and ER target genes. (a) MCF-7 breast cancer cells were starved in SFM and then incubated with IGF-I (100 ng/ml, 8 nM) for 3 or 24 hours. RNA was isolated, and ER mRNA levels were measured with QRT-PCR (± SEM). (b) MCF-7 cells were incubated with an increasing dose of IGF-I, and ER mRNA levels were measured as in part (a). (c) ER levels in MCF-7 cells incubated with (+) or without (-) cycloheximide and stimulated with or without IGF-I (100 ng/ml) for 3 hours. (d) In two additional cell lines (ZR75-1 and BT483), expression levels of ER and ER target genes (PR and CAV1) after IGF-I treatment (100 ng/ml for 3 hours). All comparisons shown here between IGF-I (100 ng/ml) and control (± SD) were significant, with P ≤ 0.05.