Similarly, although in response to PDGF, in HCC cells exposed to PDGFRβ-targeted siRNA (HCC-siRNA-PDGFRβ), rapamycin (50 ng/ml for 6 h) did not up-regulate phosphorylation of AKT and ERK prominently (Fig. 2B), suggesting that PDGFRβ-dependent feedback loop may play an important role in rapamycin-induced AKT and ERK phosphorylation in HCC. Here, PDGFRB is linked to hepatocellular carcinoma.