Description: Two new C 22 -steroidal lactone glycosides, ypsilactosides A ( 1 ) and B ( 2 ), were isolated from the EtOH extract of the whole plant of Ypsilandra thibetica. Their structures were established as (3 β ,5 α ,16 β ,20 S )-3,16-dihydroxy-6-oxopregnane-20-carboxylic acid γ -lactone 3-( β - D -glucopyranoside) ( 1 ) and (3 β ,16 β )-3,16-dihydroxypregna-5,20-diene-20-carboxylic acid γ -lactone 3-{ O - α - L -rhamnopyranosyl-(1→4)- O - α - L -rhamnopyranosyl-(1→4)- O -[ α - L -rhamnopyranosyl-(1→2)]- β - D -glucopyranoside} ( 2 ) on the basis of extensive spectroscopic analyses and chemical degradations.

Description: Chronic hepatitis B virus (HBV) infection remains a major health problem worldwide. The covalently closed circular DNA (cccDNA) minichromosome, which serves as the template for the transcription of viral RNAs, plays a key role in viral persistence. While accumulating evidence suggests that cccDNA transcription is regulated by epigenetic machinery, particularly the acetylation of cccDNA-bound histone 3 (H3) and H4, the potential contributions of histone methylation and related host factors remain obscured. Here, by screening a series of methyltransferases and demethylases, we identified protein arginine methyltransferase 5 (PRMT5) as an effective restrictor of HBV transcription and replication. In the cell culture-based models for HBV infection and the liver tissues of patients with chronic HBV infection, we found that symmetric dimethylation of arginine 3 on H4 (H4R3me2s) on cccDNAwas a repressive marker of cccDNA transcription and was regulated by PRMT5 depending on its methyltransferase domain. Moreover, PRMT5-triggered H4R3me2s on the cccDNA minichromosome involved an interaction with the HBV core protein and the Brg1-based hSWI/SNF chromatin remodeler, which resulted in the downregulation of the binding of RNA Pol II to cccDNA. In addition to the inhibitory effect on cccDNA transcription, PRMT5 inhibited HBV core particle DNA production independent of its methyltransferase activity. Further study revealed that PRMT5 interfered with pre-genomic RNA (pgRNA) encapsidation by preventing its interaction with viral polymerase protein through binding to the RT-RH region of polymerase which is crucial for the polymerase-pgRNA interaction. Conclusion : PRMT5 restricts HBV replication via two-part mechanisms including epigenetic suppression of cccDNA transcription and interference with pgRNA encapsidation. These findings improve the understanding of epigenetic regulation of HBV transcription and host-HBV interaction, thus provide new insights into targeted therapeutic intervention. This article is protected by copyright. All rights reserved.

Description: Mesenchymal stem cells (MSCs) have potential applications in regenerative medicine and tissue engineering as well as being potential carriers for tumour therapy. However, the safety of using MSCs in tumours is unknown. Herein, we analyse malignant transformation of MSCs in the tumour microenvironment. Rat bone marrow MSCs were cultured with malignant rat glioma C6 cells without direct cell–cell contact. After 7 days, the cells were assessed for transformation using flow cytometry, real-time quantitative PCR, immunofluorescence and chromosomal analysis. In addition, wild-type (WT) p53, mutant p53 and mdm2 was determined using Western blotting. Almost all MSCs became phenotypically malignant cells, with significantly decreased WT p53 expression and increased expression of mutant p53 and mdm2, along with an aneuploid karyotype. To evaluate tumorigenesis in vivo , the MSCs indirect co-cultured with C6 cells for 7 days were transplanted subcutaneously into immuno-deficient mice. The cells developed into a large tumour at the injection site within 8 weeks, with systemic symptoms including cachexia and scoliosis. Pathological and cytological analysis revealed poorly differentiated pleomorphic cells with a dense vascular network and aggressive invasion into the adjacent muscle. These data demonstrate that MSCs became malignant cancer cells when exposed to the tumour microenvironment and suggest that factors released from the cancer cells have a critical role in the malignant transformation of MSCs. Copyright © 2012 John Wiley & Sons, Ltd.