01, and 6.4 ± 1 in Pkd2cKO mice treated with 60 mg/kg/daily, P < 0.01) (Fig. 1C). Consistent with the increase in liver cysts, the liver/body weight ratio of Pkd2cKO mice was also significantly higher in sorafenib-treated animals (Pkd2cKO vehicles: 0.058 versus 0.0762 in mice treated with 20 mg/kg/day, P < 0.01, and 0.079 in mice treated with 60 mg/kg/day, P < 0.01) (Supporting Fig. 1). Previous studies have shown that the growth of liver cysts is dependent upon an increased

proliferation and a decreased apoptosis of cystic cholangiocytes.7, 8, 21 Consistent with the increased volume of liver cysts, the immunohistochemical expression of Ki67, a nuclear antigen present BVD-523 in vitro only in the nuclei of proliferating cells,22 was significantly selleck inhibitor increased in mice treated with sorafenib (Pkd2cKO vehicles: 6.8 ± 1% versus 11 ± 2% in Pkd2cKO mice treated with 20 mg/kg/day, P < 0.01, and 10.5 ± 2.1 in Pkd2cKO mice treated with 60 mg/kg/day, P < 0.01) (Fig. 2A). Apoptosis was assessed by measuring the immunohistochemical expression of CC3.7, 8 The number of CC3-positive cells in the liver cyst epithelium was significantly decreased in mice treated with sorafenib (Supporting Fig. 2) (Pkd2cKO vehicles: 11.0 ± 0.8% versus 8.2 ± 0.8% in Pkd2cKO mice treated with 20 mg/kg/day, P < 0.01, and 7.9 ± 0.7 in Pkd2cKO mice treated with 60 mg/kg/day; P <

0.01). These data suggest that sorafenib increases liver cyst growth through increased cell proliferation and decreased apoptosis in the liver cystic epithelium. Cyst proliferation in Pkd2cKO mice is sustained by a PKA-dependent Raf/MEK/ERK1/2 pathway.7 ERK1/2 is downstream of Raf and therefore should be inhibited by sorafenib. On the contrary,

the expression of phosphorylated ERK1/2 (pERK1/2) was significantly increased in cholangiocytes lining the cysts in mice treated with sorafenib, with respect to untreated Pkd2cKO mice (Pkd2cKO vehicles: 3 ± 0.7% versus 4.9 ± 1.1% in Pkd2cKO mice treated with 20 mg/kg/day, P < 0.01, and 5.2 ± 1 in Pkd2cKO mice treated with 60 mg/kg/day; P < 0.01) (Fig. 2B). No differences in the percentage of pERK1/2 positive hepatocytes were observed (Pkd2cKO vehicles: 2.2 ± 0.8% versus 2.8 ± 0.97% in Pkd2cKO mice treated with 20 mg/kg/day, P value not significant). These data suggest that increased proliferation in cystic Selleck Lonafarnib cells in sorafenib-treated Pkd2cKO mice is a consequence of increased ERK1/2 signaling. In apparent contrast to our in vivo data, Yamaguchi et al.23 reported that sorafenib inhibits ERK1/2 activation and cell proliferation in kidney cells isolated from cysts of ADPKD patients. To clarify whether sorafenib has inhibitory effects on isolated PC2-defective cholangiocytes, we measured cell proliferation (by MTS and BrdU assays) and the levels of phosphorylated ERK1/2 in cholangiocytes isolated from normal controls and from liver cyst epithelial cells of Pkd2cKO mice, as described.