Detection of basal expression levels of CCR7, IGF-1R, c- Myc , CDK-4, and let-7a in seven breast cancer cell lines. (a-b) Let-7a expression levels in breast cancer cells, detected with Northern blot analysis (NB)(a) and real-time RT-PCR(b). U6 and RNU6B were used as a normalization control. (c) Detection of protein expression levels of CCR7, IGF-1R, c-Myc, and CDK-4 by using Western blot analysis. β-actin was used as a normalization control.