DNA hypomethylation leads to cGAS-induced autoinflammation in the epidermis.

DNA methylation is a fundamental epigenetic modification, important across biological processes. The maintenance methyltransferase DNMT1 is essential for lineage differentiation during development, but its functions in tissue homeostasis are incompletely understood. We show that epidermis-specific DNMT1 deletion severely disrupts epidermal structure and homeostasis, initiating a massive innate immune response and infiltration of immune cells. Mechanistically, DNA hypomethylation in keratinocytes triggered transposon derepression, mitotic defects, and formation of micronuclei. DNA release into the cytosol of DNMT1-deficient keratinocytes activated signaling through cGAS and STING, thus triggering inflammation. Our findings show that disruption of a key epigenetic mark directly impacts immune and tissue homeostasis, and potentially impacts our understanding of autoinflammatory diseases and cancer immunotherapy.

Divergent roles of HDAC1 and HDAC2 in the regulation of epidermal development and tumorigenesis.

The histone deacetylases HDAC1 and HDAC2 remove acetyl moieties from lysine residues of histones and other proteins and are important regulators of gene expression. By deleting different combinations of Hdac1 and Hdac2 alleles in the epidermis, we reveal a dosage-dependent effect of HDAC1/HDAC2 activity on epidermal proliferation and differentiation. Conditional ablation of either HDAC1 or HDAC2 in the epidermis leads to no obvious phenotype due to compensation by the upregulated paralogue. Strikingly, deletion of a single Hdac2 allele in HDAC1 knockout mice results in severe epidermal defects, including alopecia, hyperkeratosis, hyperproliferation and spontaneous tumour formation. These mice display impaired Sin3A co-repressor complex function, increased levels of c-Myc protein, p53 expression and apoptosis in hair follicles (HFs) and misregulation of HF bulge stem cells. Surprisingly, ablation of HDAC1 but not HDAC2 in a skin tumour model leads to accelerated tumour development. Our data reveal a crucial function of HDAC1/HDAC2 in the control of lineage specificity and a novel role of HDAC1 as a tumour suppressor in the epidermis.

p19(ARF) /p14(ARF) controls oncogenic functions of signal transducer and activator of transcription 3 in hepatocellular carcinoma.

UNLABELLED: Signal transducer and activator of transcription 3 (Stat3) is activated in a variety of malignancies, including hepatocellular carcinoma (HCC). Activation of Ras occurs frequently at advanced stages of HCC by aberrant signaling through growth factor receptors or inactivation of effectors negatively regulating Ras signaling. Here, we addressed the role of Stat3 in Ras-dependent HCC progression in the presence and absence of p19(ARF) /p14(ARF) . We show that constitutive active (ca) Stat3 is tumor suppressive in Ras-transformed p19(ARF-/-) hepatocytes, whereas the expression of Stat3 lacking Tyr(705) phosphorylation (U-Stat3) enhances tumor formation. Accordingly, Ras-transformed Stat3(Δhc) /p19(ARF-/-) hepatocytes (lacking Stat3 and p19(ARF) ) showed increased tumor growth, compared to those expressing Stat3, demonstrating a tumor-suppressor activity of Stat3 in cells lacking p19(ARF) . Notably, endogenous expression of p19(ARF) in Ras-transformed hepatocytes conveyed oncogenic Stat3 functions, resulting in augmented or reduced HCC progression after the expression of caStat3 or U-Stat3, respectively. In accord with these data, the knockdown of p14(ARF) (the human homolog of p19(ARF) ) in Hep3B cells was associated with reduced pY-Stat3 levels during tumor growth to circumvent the tumor-suppressive effect of Stat3. Inhibition of Janus kinases (Jaks) revealed that Jak causes pY-Stat3 activation independently of p14(ARF) levels, indicating that p14(ARF) controls the oncogenic function of pY-Stat3 downstream of Jak. CONCLUSION: These data show evidence that p19(ARF) /p14(ARF) determines the pro- or anti-oncogenic activity of U-Stat3 and pY-Stat3 in Ras-dependent HCC progression.

Epithelial-mesenchymal transition in hepatocellular carcinoma.

The transition of epithelial cells to a mesenchymal phenotype is of paramount relevance for embryonic development and adult wound healing. During the past decade, the epithelial-mesenchymal transition (EMT) has been increasingly recognized to occur during the progression of various carcinomas such as hepatocellular carcinoma (HCC). Here, we focus on EMT in both experimental liver models and human HCC, emphasizing the underlying molecular mechanisms which show partial recurrence of embryonic programs such as TGF-beta and Wnt/ beta-catenin signaling, including collaboration with hepatitis viruses. We further discuss the differentiation repertoire of malignant hepatocytes with respect to the potential acquisition of stemness, and the involvement of the mesenchymal to epithelial transition, the reversal of EMT, in cancer dissemination and metastatic colonization. The strong evidence for EMT in HCC patients demands novel strategies in pathological assessments and therapeutic concepts to efficiently combat HCC progression.

A human model of epithelial to mesenchymal transition to monitor drug efficacy in hepatocellular carcinoma progression.

The epithelial to mesenchymal transition (EMT) of malignant hepatocytes is a crucial event in hepatocellular carcinoma (HCC) progression and recurrence. We aimed to establish a human model of EMT to examine drug efficacy and specificity in HCC progression. Human HCC cell populations were characterized by immunofluorescence analysis, migration and invasion assays, array comparative genomic hybridization, whole-genome expression profiling, and promoter methylation. Therapeutic agents clinically used against HCC were examined for efficacy by determination of IC(50) values. We show that liver cancer cell lines exhibited either an epithelial or mesenchymal phenotype of which the latter showed strong migratory and invasive abilities in vitro. The common cellular origin of both cell types indicated that mesenchymal HCC cells have been derived from epithelial hepatocytes through EMT in the HCC patient. Drug exposure of mesenchymal HCC cells showed higher resistance to the targeted therapeutic agents sorafenib and erlotinib as compared to epithelial HCC cells, which were slightly more resistant to cytostatic drugs. Most remarkably, combined treatment with doxorubicin and sorafenib caused increased susceptibility of both HCC cell types resulting in enhanced drug efficacy. Taken together, this EMT model of human HCC allows the identification of molecular mechanisms and the assessment of therapeutic drug efficacy during liver cancer progression in preclinical studies.