Histochem Cell Biol (2008) 129:735–749 predisposed to development of thioacetamide-induced liver Wbrosis (Strnad et al. 2008). Ablations of diVerent K8/K18 phosphorylation sites usually led to a somewhat milder phenotype which became apparent in stress situations, but not under basal conditions (Ku et al. 2007). For example, K18 S52A variant resulted in increased sensitivity to micro- cystin-LR-induced liver injury, whereas K8 S73A mice were predisposed to Fas-induced liver apoptosis (Ku et al. 1998; Ku and Omary 2006). The ablation of K18 S33 phos- phorylation site, which regulates the binding to 14-3-3 pro- teins, caused limited mitotic arrest and accumulation of abnormal mitotic Wgures after partial hepatectomy (Ku et al. 2002a). In contrast, mice lacking K19 did not have an obvious liver phenotype (Tao et al. 2003), but surprisingly exhibited skeletal myopathy (Stone et al. 2007). GFAP/vimentin- knockouts displayed compromised astrocytic function with attenuated reactive gliosis, but no obvious alteration in the in vitro activation of hepatic stellate cells despite the lack of IF network (Geerts et al. 2001; Pekny and Pekna 2004). However, in vivo studies are needed to conclusively address the Wbrogenic potency of these transgenic mice. Keratin variants in liver disease The large body of evidence from animal studies showing the importance of K8/K18 for liver homeostasis led to a search for keratin mutations in patients with liver diseases. Several K8/K18 variants were found to associate with the development of cryptogenic liver disease (Ku et al. 2001). In subsequent studies, K8/K18 were shown to represent susceptibility genes for development of end-stage liver dis- ease of multiple etiologies (Ku et al. 2003a, 2005). In par- ticular, biologically signiWcant K8/K18 variants were found in 44 of 467 liver explants (12.4%), but only in 11 out of 349 analyzed blood bank donors, which were used as a con- trol group (P < 0.0001, prevalence OR3.8; 95% CI = 2.1– 7). Furthermore, K8/K18 variants associate with liver Wbro- sis progression in patients with chronic hepatitis C (Strnad et al. 2006). K8 R340H represents the most common amino acid altering K8/K18 variant and it is the only one, which was signiWcantly associated with development of end-stage liver disease (Ku et al. 2005). Larger studies are needed to analyze the pathological signiWcance of the other less com- mon K8/K18 variants (Ku et al. 2007). In contrast to human association studies, experiments in K8/K18-deWcient mice were shown to predispose mainly to acute liver injury (Ku et al. 2007). To address this issue, we recently analyzed a large cohort of patients with acute liver failure (ALF). K8/K18 variants were signiWcantly more fre- quent in total ALF patient cohort (46/345; 13.3%) and in 739 patients with acetaminophen-induced ALF (21/169; 12.4%) when compared to blood bank donors (11/349; 3.7%; P < 0.002 for both comparisons). Among the single poly- morphisms, the K8 R340H variant was found at signiW- cantly higher frequencies in the whole ALF cohort as well as in the acetaminophen-induced ALF subgroup (frequency 6.6 and 7.1%, respectively vs. 3.1% in the control group; P < 0.03 for both comparisons). In addition, transgenic mice over-expressing K8 R340 variants displayed aug- mented acetaminophen-induced liver toxicity. In conclu- sion, K8/K18 are also susceptibility genes for development of ALF and K8/K18 variants may predispose to drug- induced liver injury (Strnad et al., unpublished data). Up to date, only one published study analyzed the poly- morphisms in K19 gene and found no association between K19 variants and inXammatory bowel disease (Tao et al. 2007). Interestingly, we recently observed K19 G17S vari- ant in three out of 190 patients with primary biliary cirrho- sis, but none was found in control blood bank donors (200 samples; Zhong et al., unpublished data). However, larger studies are needed to address the importance of K19 in bili- ary diseases. The human K8/K18 variants described above do not cause a particular liver disease per se, they just pose a risk factor for its development. This is diVerent from the situa- tion in stratiWed epithelia, where keratin mutations result in several monogenic keratin diseases (Lane and McLean 2004; Omary et al. 2004). This discrepancy may be caused either by the intrinsic diVerence between keratins of simple and stratiWed epithelia (Hutton et al. 1998) or by the diVer- ent localization of the variants within the protein backbone. To that end, disease-causing keratin mutations in stratiWed epithelia are clustered in the highly conserved helix initia- tion and termination motif, whereas K8/K18 disease-pre- disposing variants are observed in more variable domains (Owens and Lane 2004; Omary et al. 2004; Ku et al. 2007). The disturbance in cytoprotective function of keratins is the likely mechanisms by which K8 and K18 variants pre- dispose to liver disorders. For example, K8/K18 are anti- apoptotic proteins and this ability is hampered in keratin- deWcient animals (Oshima 2002; Ku and Omary 2006; Mar- ceau et al. 2007; Ku et al. 2007). The ways of interaction between keratins and apoptosis are manifold. K8/K18 bind to several apoptotic proteins and type I keratins are estab- lished caspase substrates (Oshima 2002; Green et al. 2005; Marceau et al. 2007). In addition, K8/K18 serve as physio- logic kinase substrates in vitro and in transgenic mice and an ablation of the K8 S73 phosphorylation site or introduc- tion of the naturally occurring K8 G61C variant leads to increased apoptosis through increased phosphorylation of pro-apoptotic proteins (Ku et al. 2002b; Ku and Omary 2006). The keratin-mediated anti-apoptotic function may be highly relevant given the importance of apoptosis in liver 123