Using the albumin promoter to drive Cre expression has resulted in hepatocyte-specific deletion of Phb1. However, at 3 weeks of age the deletion was not complete. This is consistent with known efficiency of the albumin-Cre transgene as reported by Postic and Magnuson,20 which was 40% immediately after birth, 60% at 1 week, and 75% at 3 weeks. Deletion

of liver-specific Phb1 resulted in striking liver injury very early on. Because the proportion of homozygotes (KO) is much lower than the expected 18.8% (25% chance from Phb1lox/lox and 75% from Alb-Cre+, or 0.25 × 0.75 = 0.188) based on Mendelian genetics, we suspect there is fetal wastage. This is plausible as albumin can be expressed very early during mouse development,

stage 7 to 8 somites.20 In yeast, it is known that PHB1 and PHB2 are interdependent.3 Thus, loss of one results in the loss of the find more other. Whether this is also true in higher organisms was unclear. Our results show that this is also true in mammalian liver as PHB2 was also reduced (although to a lesser degree) when PHB1 was markedly see more reduced. Many of the liver-specific Phb1 KO mice died before weaning and at only 3 weeks of age there is biochemical and histological evidence of marked liver injury. Histologically, the liver is characterized by necrosis and inflammation at 3 weeks. There is also increased apoptosis, which progressed as the mice grew to 14 weeks. Consistent with its known role as a mitochondrial chaperone, marked reduction in PHB1 resulted in abnormal mitochondrial morphology and oxidative stress. There is also increased proliferation, as indicated by PCNA staining. Interestingly, as early as 3 weeks of age, there is already increased staining for OV-6 and GSTP, oval cell and preneoplastic markers, respectively. By 14 weeks, dysplastic hepatic nodules were

evident microscopically and by 20 weeks, all mice have multiple hepatic nodules on gross examination. By 35 to 46 weeks, more than one-third of the mice developed multifocal HCC. Because increased proliferation and stem cell expansion observed in the livers of the KO mice may be due to a compensatory response medchemexpress to injury, we examined the effect of acute reduction in PHB1 on cell proliferation in nontransformed AML12 cells. Acute loss of PHB1 in a nontransformed hepatocyte resulted in increased proliferation whereas overexpression of PHB1 resulted in the opposite. Although PHB1 expression also tended to have a similar effect in Huh-7 cells, changes were not statistically significant. Taken together, these observations would support a role for PHB1 as a tumor suppressor, at least in normal hepatocytes. It is possible that the effect of PHB1 on growth is different in normal versus malignant hepatocytes as many signaling pathways are altered in cancer. This is an area that will require further investigation.