Characterization of naturally occurring pentacyclic triterpenes as novel inhibitors of deubiquitinating protease USP7 with anticancer activity in vitro.

Deubiquitinating protease USP7 is a promising therapeutic target for cancer treatment, and interest in developing USP7 inhibitors has greatly increased. In the present study, we reported a series of natural pentacyclic triterpenes with USP7 inhibitory activity in vitro. Among them, both the ursane triterpenes and oleanane triterpenes were more active than the lupine triterpenes, whereas ursolic acid was the most potent with IC50 of 7.0±1.5 µmol/L. Molecular docking studies showed that ursolic acid might occupy the ubiquitin binding pocket of USP7, with the 17-carboxyl group and 3-hydroxyl group playing a vital role in the USP7-ursolic acid interaction. Using the cellular thermal shift assay, we demonstrated that ursolic acid interacted with USP7 in RPMI8226 human myeloma cells. Ursolic acid dose-dependently inhibited the proliferation of the myeloma cells with IC50 of 6.56 µmol/L, accompanied by reductions in USP7 substrates such as MDM2, UHRF1 and DNMT1. Overexpression of USP7 partially, but significantly attenuated ursolic acid-induced cell death as well as downregulation of MDM2, UHRF1 and DNMT1. In conclusion, we demonstrate for the first time that pentacyclic triterpenes represent a novel scaffold for developing USP7 inhibitors and that USP7 inhibition contributes to the anti-cancer effect of ursolic acid.

Complete mitochondrial genome of the Wuhua three-yellow chicken (Gallus gallus domesticus).

Wuhua three-yellow chicken is a native breed of Guangdong Province in China. The complete mitochondrial DNA (mtDNA) genome presented here was the first assemble of Wuhua three-yellow chicken, which was determined through the polymerase chain reaction-based method. The complete mitogenome was 16,784 bp in length, with the nucleotide composition of 30.29% for A, 23.75% for T, 32.48% for C and 13.48% for G, and exhibited the typical mitochondrial structure, including 2 rRNA genes, 13 protein-coding genes, 22 tRNA genes and a non-coding control region.

Targeting truncated retinoid X receptor-α by CF31 induces TNF-α-dependent apoptosis.

A truncated version of retinoid X receptor-α, tRXR-α, promotes cancer cell survival by activating the phosphoinositide 3-kinase (PI3K)/AKT pathway. However, targeting the tRXR-α-mediated survival pathway for cancer treatment remains to be explored. We report here our identification of a new natural product molecule, CF31, a xanthone isolated from Cratoxylum formosum ssp. pruniflorum, and the biologic evaluation of its regulation of the tRXR-α-mediated PI3K/AKT pathway. CF31 binds RXR-α and its binding results in inhibition of RXR-α transactivation. Through RXR-α mutational analysis and computational studies, we show that Arg316 of RXR-α, known to form salt bridges with certain RXR-α ligands, such as 9-cis-retinoic acid (9-cis-RA), is not required for the antagonist effect of CF31, showing a distinct binding mode. Evaluation of several CF31 analogs suggests that the antagonist effect is mainly attributed to an interference with Leu451 of helix H12 in RXR-α. CF31 is a potent inhibitor of AKT activation in various cancer cell lines. When combined with TNF-α, it suppresses TNF-α activation of AKT by inhibiting TNF-α-induced tRXR-α interaction with the p85α regulatory subunit of PI3K. CF31 inhibition of TNF-α activation of AKT also results in TNF-α-dependent activation of caspase-8 and apoptosis. Together, our results show that CF31 is an effective converter of TNF-α signaling from survival to death by targeting tRXR-α in a unique mode and suggest that identification of a natural product that targets an RXR-mediated cell survival pathway that regulates PI3K/AKT may offer a new therapeutic strategy to kill cancer cells.

Xanthone and benzophenone glycosides from the stems of Cratoxylum formosum ssp. pruniflorum.

Two new xanthone glycosides, namely pruniflorosides A and B (1, 2), a new benzophenone glycoside, prunifloroside C (3), and a new xanthone, pruniflorone S (4) were isolated from the stems of Cratoxylum formosum ssp. pruniflorum, along with six known xanthones (5-10). Their structures were determined on the basis of extensive spectroscopic analysis. In addition, their retinoid X receptor α (RXRα) transcriptional activities were evaluated in vitro.

Bioactive xanthones from the stems of Cratoxylum formosum ssp. pruniflorum.

Six new compounds, pruniflorones M-R (1-6), together with 19 known compounds (7-25) were isolated from the stems of Cratoxylum formosum ssp. pruniflorum. The structures of the new compounds were established on the basis of extensive spectroscopic data interpretation. In addition, their RXRalpha transcriptional activities were evaluated using an in vitro assay.

Oncogenic potential of retinoic acid receptor-gamma in hepatocellular carcinoma.

Retinoic acid receptors (RAR; alpha, beta, and gamma), members of the nuclear receptor superfamily, mediate the pleiotropic effects of the vitamin A metabolite retinoic acid (RA) and derivatives (retinoids) in normal and cancer cells. Abnormal expression and function of RARs are often involved in the growth and development of cancer. However, the underlying molecular mechanisms remain largely elusive. Here, we report that levels of RARgamma were significantly elevated in tumor tissues from a majority of human hepatocellular carcinoma (HCC) and in HCC cell lines. Overexpression of RARgamma promoted colony formation by HCC cells in vitro and the growth of HCC xenografts in animals. In HepG2 cells, transfection of RARgamma enhanced, whereas downregulation of RARgamma expression by siRNA approach impaired, the effect of RA on inducing the expression of alpha-fetoprotein, a protein marker of hepatocarcinogenesis. In studying the possible mechanism by which overexpression of RARgamma contributed to liver cancer cell growth and transformation, we observed that RARgamma resided mainly in the cytoplasm of HCC cells, interacting with the p85alpha regulatory subunit of phosphatidylinositol 3-kinase (PI3K). The interaction between RARgamma and p85alpha resulted in activation of Akt and NF-kappaB, critical regulators of the growth and survival of cancer cells. Together, our results show that overexpression of RARgamma plays a role in the growth of HCC cells through nongenomic activation of the PI3K/Akt and NF-kappaB signaling pathways.