Hepatocellular carcinoma (HCC) is a rising worldwide cause of cancer mortality, making the elucidation of its underlying mechanisms an urgent priority. The liver is unique in its response to injury, simultaneously undergoing regeneration and fibrosis. HCC occurs in the context of these two divergent responses, leading to distinctive pathways of carcinogenesis. In this review, we highlight pathways of liver tumorigenesis that depend upon, or are enhanced by fibrosis. Activated hepatic stellate cells drive fibrogenesis, changing the composition of the extracellular matrix. Matrix quantity and stiffness also increase, providing a reservoir for bound growth factors. In addition to promoting angiogenesis, these factors may enhance the survival of both pre-neoplastic hepatocytes and activated hepatic stellate cells. Fibrotic changes also modulate the activity of inflammatory cells in the liver, reducing the activity of natural killer and natural killer T cells that normally contribute to tumor surveillance. These pathways synergize with inflammatory signals, including telomerase reactivation and reactive oxygen species release, ultimately resulting in cancer. Clarifying fibrosis-dependent tumorigenic mechanisms will help rationalize antifibrotic therapies as a strategy to prevent and treat HCC.

Objective-We used an informatics approach to identify and validate genes whose expression is unique to hepatic stellate cells, and assessed the prognostic capability of their expression in cirrhosis.Design-We defined a hepatic stellate cell gene signature by comparing stellate, immune, and hepatic transcriptome profiles. We then created a prognostic index using a combination of hepatic stellate cell signature expression and clinical variables, using overall survival as the primary clinical outcome. This signature was derived in a retrospective-prospective cohort of hepatitis Crelated early-stage cirrhosis (prognostic index derivation set), and validated in an independent retrospective cohort of post-resection HCC patients (n=82, prognostic index validation set). We then examined association between hepatic stellate cell signature expression and decompensation, hepatocellular carcinoma (HCC) incidence, and progression of Child-Pugh class as additional outcomes in the prognostic index derivation set, and HCC recurrence as an additional outcome in the validation set. We tested whether hepatic stellate cell signature expression is predictive of Results-The 122-gene hepatic stellate cell signature consists of genes encoding extracellular matrix proteins and developmental factors, and correlates with the extent of fibrosis in human, mouse, and rat datasets. The hepatic stellate cell signature contains several cell surface genes previously established as stellate cell-specific, as well as PCDH7, a novel protocadherin stellate cell surface marker. Importantly, association of clinical prognostic variables with overall survival (c-index: 0.66, 95% CI: 0.59-0.74) was improved by adding the hepatic stellate cell signature (cindex: 0.70, 95%CI: 0.62-0.78); we used these results to define a prognostic index in the derivation set. In the validation set, the same prognostic index was associated with overall survival Conclusion-This work highlights the unique transcriptional niche of stellate cells, and identifies potential stellate cell targets for tracking, targeting, and isolation. Hepatic stellate cell signature expression may identify HCV cirrhosis or post resection HCC patients with poor prognosis.

The histone variant macroH2A generally associates with transcriptionally inert chromatin; however, the factors that regulate its chromatin incorporation remain elusive. Here, we identify the SWI/SNF helicase ATRX (a-thalassemia/ MR, X-linked) as a novel macroH2A-interacting protein.Unlike its role in assisting H3.3 chromatin deposition, ATRX acts as a negative regulator of macroH2A's chromatin association. In human erythroleukemic cells deficient for ATRX, macroH2A accumulates at the HBA gene cluster on the subtelomere of chromosome 16, coinciding with the loss of a-globin expression. Collectively, our results implicate deregulation of macroH2A's distribution as a contributing factor to the a-thalassemia phenotype of ATRX syndrome. The replacement of canonical histones with histone variants contributes to the dynamic nature of chromatin.Due to amino acid differences and, in turn, unique posttranslational modifications, histone variants can alter nucleosome structure, stability, and binding of effector proteins. Histone variants have unique genomic localization patterns, and thus specialized roles such as regulating gene expression or chromosome segregation during cell division . Therefore, the differential genomic incorporation of histone variants directly impacts critical cellular functions.The histone variant macroH2A (mH2A) is a vertebratespecific member of the H2A family and is unusual due to the presence of a C-terminal macro domain (Pehrson and Fried 1992). Two different genes encode mH2A1 and mH2A2 (H2AFY and H2AFY2, respectively), and two splice forms of mH2A1 exist: mH2A1.1 and mH2A1.2 (Costanzi and Pehrson 2001). mH2A is abundant in heterochromatin, including senescence-associated heterochromatic foci (SAHF) and the inactivated X chromosome (Xi) (Costanzi and Pehrson 1998;Zhang et al. 2005). In vitro studies suggest that the macro domain sterically hinders access of transcription factors to DNA, while mH2A's L1 loop produces inflexible nucleosomes (Angelov et al. 2003;Chakravarthy et al. 2005).Our group has recently demonstrated a role for mH2A isoforms in suppressing melanoma progression, and others have linked mH2A expression or its splice patterns to breast and lung cancer (Sporn et al. 2009;Kapoor et al. 2010;Novikov et al. 2011). However, the factors that regulate the association of mH2A with chromatin remain obscure. Therefore, identifying regulators of the incorporation of histone variants at distinct genomic loci is key to understanding how chromatin domains are established and maintained and how these may go awry in disease.A second group of factors contributing to chromatin dynamics are ATP-dependent chromatin remodeling complexes that rearrange or mobilize nucleosomes. Deregulation of members of the SWI/SNF family is implicated in various cancers and mental retardation (MR) syndromes, including ATRX (a-thalassemia/MR, X-linked), (Wilson and Roberts 2011). Mutations in ATRX, predominantly found in the H3K9me3-binding ADD (ATRX-DNMT3-DNMT3L) and/or helicase domains, are associated with ATRX sy...

BackgroundConsiderable evidence indicates that heparan sulfate is essential for the development of tissues consisting of branching ducts and tubules. However, there are few examples where specific sulfate residues regulate a specific stage in the formation of such tissues.Methodology/Principal FindingsWe examined the role of heparan sulfation in mammary gland branching morphogenesis, lactation and lobuloalveolar development by inactivation of heparan sulfate GlcNAc N-deacetylase/N-sulfotransferase genes (Ndst) in mammary epithelial cells using the Cre-loxP system. Ndst1 deficiency resulted in an overall reduction in glucosamine N-sulfation and decreased binding of FGF to mammary epithelial cells in vitro and in vivo. Mammary epithelia lacking Ndst1 underwent branching morphogenesis, filling the gland with ductal tissue by sexual maturity to the same extent as wildtype epithelia. However, lobuloalveolar expansion did not occur in Ndst1-deficient animals, resulting in insufficient milk production to nurture newly born pups. Lactational differentiation of isolated mammary epithelial cells occurred appropriately via stat5 activation, further supporting the notion that the lack of milk production was due to lack of expansion of the lobuloalveoli.Conclusions/SignificanceThese findings demonstrate a selective, highly penetrant, cell autonomous effect of Ndst1-mediated sulfation on lobuloalveolar development.

Background Hepatic stellate cells (HSCs) activate during injury to orchestrate the liver’s inflammatory and fibrogenic responses. A critical feature of HSC activation is the rapid induction of β-PDGFR, which drives cellular fibrogenesis and proliferation; in contrast, normal liver has minimal β-PDGFR expression. While the role of β-PDGFR is well established in liver injury, its expression and contribution during liver regeneration are unknown. The aim of this study is to determine whether β-PDGFR is induced during liver regeneration following partial hepatectomy (pHx), and to define its contribution to the regenerative response. Methods Control mice or animals with HSC-specific β-PDGFR-depletion underwent two-thirds pHx followed by assessment of hepatocyte proliferation and expression of β-PDGFR. RNA-sequencing from whole liver tissue of both groups after pHx was used to uncover pathways regulated by β-PDGFR signaling in HSCs. Results β-PDGFR expression on HSCs was upregulated within 24 hours (h) following pHx in control mice, whereas absence of β-PDGFR blunted the expansion of HSCs. Mice lacking β-PDGFR displayed prolonged increases of transaminase levels within 72 h following pHx. Hepatocyte proliferation was impaired within the first 24 h based on Ki-67 and PCNA expression in β-PDGFR-deficient mice. This was associated with dysregulated growth in the β-PDGFR-deficient mice based on RNAseq with pathway analysis, and real time quantitative PCR, which demonstrated reduced expression of Hgf, Igfbp1, Mapk and Il-6. Conclusions β-PDGFR is induced in HSCs following surgical pHx and its deletion in HSCs leads to prolonged liver injury. However, there is no significant difference in liver regeneration.