The RNA helicase DHX9 establishes nucleolar heterochromatin, and this activity is required for embryonic stem cell differentiation.

Long non-coding RNAs (lncRNAs) have been implicated in the regulation of chromatin conformation and epigenetic patterns. lncRNA expression levels are widely taken as an indicator for functional properties. However, the role of RNA processing in modulating distinct features of the same lncRNA is less understood. The establishment of heterochromatin at rRNA genes depends on the processing of IGS-rRNA into pRNA, a reaction that is impaired in embryonic stem cells (ESCs) and activated only upon differentiation. The production of mature pRNA is essential since it guides the repressor TIP5 to rRNA genes, and IGS-rRNA abolishes this process. Through screening for IGS-rRNA-binding proteins, we here identify the RNA helicase DHX9 as a regulator of pRNA processing. DHX9 binds to rRNA genes only upon ESC differentiation and its activity guides TIP5 to rRNA genes and establishes heterochromatin. Remarkably, ESCs depleted of DHX9 are unable to differentiate and this phenotype is reverted by the addition of pRNA, whereas providing IGS-rRNA and pRNA mutants deficient for TIP5 binding are not sufficient. Our results reveal insights into lncRNA biogenesis during development and support a model in which the state of rRNA gene chromatin is part of the regulatory network that controls exit from pluripotency and initiation of differentiation pathways.

The ubiquitin ligase Uhrf2 is a master regulator of cholesterol biosynthesis and is essential for liver regeneration.

Fibroblast growth factors (FGFs) are key regulators of the remarkable regenerative capacity of the liver. Mice lacking FGF receptors 1 and 2 (Fgfr1 and Fgfr2) in hepatocytes are hypersensitive to cytotoxic injury during liver regeneration. Using these mice as a model for impaired liver regeneration, we identified a critical role for the ubiquitin ligase Uhrf2 in protecting hepatocytes from bile acid accumulation during liver regeneration. During regeneration after partial hepatectomy, Uhrf2 expression increased in an FGFR-dependent manner, and Uhrf2 was more abundant in the nuclei of liver cells in control mice compared with FGFR-deficient mice. Hepatocyte-specific Uhrf2 knockout or nanoparticle-mediated Uhrf2 knockdown caused extensive liver necrosis and impaired hepatocyte proliferation after partial hepatectomy, resulting in liver failure. In cultured hepatocytes, Uhrf2 interacted with several chromatin remodeling proteins and suppressed the expression of cholesterol biosynthesis genes. In vivo, the loss of Uhrf2 resulted in cholesterol and bile acid accumulation in the liver during regeneration. Treatment with a bile acid scavenger rescued the necrotic phenotype, hepatocyte proliferation, and the regenerative capacity of the liver in Uhrf2-deficient mice subjected to partial hepatectomy. Our results identify Uhrf2 as a key target of FGF signaling in hepatocytes and its essential function in liver regeneration and highlight the importance of epigenetic metabolic regulation in this process.

The treatment of multiple myeloma using vincristine, carmustine, melphalan, cyclophosphamide, and prednisone (VBMCP) alternating with high-dose cyclophosphamide and alpha(2)beta interferon versus VBMCP: results of a phase III Eastern Cooperative Oncology Group Study E5A93.

BACKGROUND: A randomized controlled trial tested the hypothesis that aggressive initial therapy using high-dose cyclophosphamide (HiCy) and alpha(2)beta interferon (IFN) may be superior to standard combination alkylating agent regimens in the treatment of newly diagnosed myeloma. METHODS: This Eastern Cooperative Oncology Group trial evaluated 268 previously untreated patients with active multiple myeloma randomized to vincristine, carmustine, melphalan, cyclophosphamide, and prednisone (VBMCP) or VBMCP plus HiCy and recombinant IFN. RESULTS: The overall objective response was 62% in the VBMCP regimen and 68% in the VBMCP + HiCy + IFN group. The near complete response and complete response rates were 8.1% and 8.9%, respectively. Progression-free survival was 22.1 and 25.3 months, respectively. The median overall survival was 37.1 months for patients treated with VBMCP and 41.3 months for those treated with VBMCP + HiCy + IFN (P = .38). The 5-year overall survival rates were not significantly different between the 2 arms: 26.4% and 33%, respectively. Lethal toxicities occurred in 15 patients, including 10 from infection, but there was no significant difference in lethal toxicities between the 2 regimens. CONCLUSIONS: The study showed no significant benefit with the addition of HiCy and IFN to VBMCP.