Chuandong Fan

Synthesis and structure-activity relationships of novel 1-arylmethyl-3-aryl-1H-pyrazole-5-carbohydrazide hydrazone derivatives as potential agents against A549 lung cancer cells.

A series of novel 1-arylmethyl-3-aryl-1H-pyrazole-5-carbohydrazide hydrazone derivatives were synthesized and the effects of all the compounds on A549 cell growth were investigated. The results showed that all compounds had almost inhibitory effects on the growth of A549 cells. The study on structure-activity relationships and prediction of lipophilicities of compounds showed that compounds with LogP values in the range of 4.12-6.80 had inhibitory effects on the growth of A549 cells, and among of them the hydrazone derived from salicylaldehyde had much more inhibitory effects.

Ubiquitin-dependent Regulation of Phospho-AKT Dynamics by the Ubiquitin E3 Ligase, NEDD4-1, in the Insulin-like Growth Factor-1 Response

Background: After activation by phosphorylation, phospho-AKT (pAKT) is translocated to nucleus. Results: Ubiquitination of pAKT by NEDD4-1 is coupled to AKT activation at the plasma membrane by insulin-like growth factor (IGF)-1, which promotes pAKT nuclear trafficking. Conclusion: NEDD4-1 is an E3 ligase for pAKT specifically involved in pAKT nuclear trafficking in IGF-1 signaling. Significance: AKT activation and proper subcellular localization requires specific E3 ligases in a ligand-specific manner. AKT is a critical effector kinase downstream of the PI3K pathway that regulates a plethora of cellular processes including cell growth, death, differentiation, and migration. Mechanisms underlying activated phospho-AKT (pAKT) translocation to its action sites remain unclear. Here we show that NEDD4-1 is a novel E3 ligase that specifically regulates ubiquitin-dependent trafficking of pAKT in insulin-like growth factor (IGF)-1 signaling. NEDD4-1 physically interacts with AKT and promotes HECT domain-dependent ubiquitination of exogenous and endogenous AKT. NEDD4-1 catalyzes K63-type polyubiquitin chain formation on AKT in vitro. Plasma membrane binding is the key step for AKT ubiquitination by NEDD4-1 in vivo. Ubiquitinated pAKT translocates to perinuclear regions, where it is released into the cytoplasm, imported into the nucleus, or coupled with proteasomal degradation. IGF-1 signaling specifically stimulates NEDD4-1-mediated ubiquitination of pAKT, without altering total AKT ubiquitination. A cancer-derived plasma membrane-philic mutant AKT(E17K) is more effectively ubiquitinated by NEDD4-1 and more efficiently trafficked into the nucleus compared with wild type AKT. This study reveals a novel mechanism by which a specific E3 ligase is required for ubiquitin-dependent control of pAKT dynamics in a ligand-specific manner.

Synthesis and preliminary biological evaluation of novel pyrazolo[1,5-a]pyrazin-4(5H)-one derivatives as potential agents against A549 lung cancer cells.

A series of novel pyrazolo[1,5-a]pyrazin-4(5H)-one derivatives were synthesized by the reaction of ethyl 3-aryl-1-(2-bromoethyl)-1H-pyrazole-5-carboxylate and amine in the general heating condition and microwave-assisted condition. The structures of the compounds were determined by IR, (1)H NMR and mass spectroscopy, in addition, representative single-crystal structures were characterized by using X-ray diffraction analysis. Preliminary biological evaluation showed that the compounds could inhibit the growth of A549 cells in dosage- and time-dependent manners. The study on structure-activity relationships showed that compounds with 4-chlorophenyl group at pyrazole moiety, such as 5-benzyl-2-(4-chlorophenyl)-6,7-dihydropyrazolo[1,5-a]pyrazin-4(5H)-one (3o) had much more inhibitory effects. Compound 3o was the most effective small molecule in inhibiting A549 cell growth and might perform its action through modulating autophagy.

Regulation of Mdm2 protein stability and the p53 response by NEDD4-1 E3 ligase

Mdm2 is a critical negative regulator of the tumor suppressor protein p53. Mdm2 is an E3 ligase whose overexpression leads to functional inactivation of p53. Mdm2 protein stability is regulated by several mechanisms including RING (Really Interesting New Gene) domain-mediated autoubiquitination. Here we report biochemical identification of NEDD4-1 as an E3 ligase for Mdm2 that contributes to the regulation of Mdm2 protein stability in cells. NEDD4-1 was identified from Jurkat cytosolic fractions using an enzyme-dead Mdm2 mutant protein as a substrate for in vitro E3 ligase assays. We show that lysates from Nedd4-1 knockout (KO) mouse embryonic fibroblasts (MEFs) have significantly diminished E3 ligase activity toward Mdm2 compared with lysates from wild-type (WT) MEFs. Recombinant NEDD4-1 promotes Mdm2 ubiquitination in vitro in a concentration- and time-dependent manner. In cells, NEDD4-1 physically interacts with Mdm2 via the RING domain of Mdm2. Overexpression of NEDD4-1, but not an enzyme-dead NEDD4-1CS mutant, increases ubiquitination of Mdm2. NEDD4-1 catalyzes the formation of K63-type polyubiquitin chains on Mdm2 that are distinct from K48-type polyubiquitination chains mediated by the Mdm2/MdmX complex. Importantly, K63-type polyubiquitination by NEDD4-1 competes with K48-type polyubiquitination on Mdm2 in cells. As a result, NEDD4-1-mediated ubiquitination stabilizes Mdm2. NEDD4-1 knockdown reduces the t1/2 (half-life) of endogenous Mdm2 from 20 to 12 min in U2OS cells. Nedd4-1 KO MEFs manifest increased p53 levels and activity, a more robust DNA damage response and increased G1 arrest compared with WT MEFs. Similarly, NEDD4-1 knockdown in WT-p53-bearing cells increases basal p53 levels and activity in an Mdm2-dependent manner, causes stronger p53 responses to DNA damage and results in p53-dependent growth inhibition compared with corresponding NEDD4-1-proficient control cells. This study identifies NEDD4-1 as a novel component of the p53/Mdm2 regulatory feedback loop that controls p53 activity during stress responses.

FL118 Induces p53-Dependent Senescence in Colorectal Cancer Cells by Promoting Degradation of MdmX

Anticancer agent FL118 was recently identified in screening of small-molecule inhibitors of human survivin expression. Although FL118 is a camptothecin analogue, its antitumor potency is much superior to other FDA-approved camptothecin analogues (irinotecan and topotecan). The mechanism of action (MOA) underlying the antitumor effects of FL118 remains to be fully elucidated. Here, we report that FL118 activates tumor suppressor p53 as a novel MOA in p53 wild-type cancer cells. Our studies show that this MOA involves an induction of proteasomal degradation of MdmX, a critical negative regulator of p53, in a manner largely independent of ATM-dependent DNA damage signaling pathway but dependent on E3-competent Mdm2. FL118 inhibits p53 polyubiquitination and monoubiquitination by Mdm2-MdmX E3 complex in cells and in cell-free systems. In contrast, FL118 stimulates Mdm2-mediated MdmX ubiquitination. Coimmunoprecipitation revealed that FL118 slightly decreases Mdm2-p53 interactions and moderately increases Mdm2-MdmX interactions, suggesting a change of targeting specificity of Mdm2-MdmX E3 complex from p53 to MdmX, resulting in accelerated MdmX degradation. As a result, p53 ubiquitination by Mdm2-MdmX E3 complex is reduced, which in turn activates p53 signaling. Activation of the p53 pathway by FL118 induces p53-dependent senescence in colorectal cancer cells. However, in the absence of p53 or in the presence of MdmX overexpression, FL118 promotes p53-independent apoptosis. These two distinct cellular consequences collectively contribute to the potent effects of FL118 to inhibit clonogenic potential of colon cancer cells. This study identifies a potential application of FL118 as an MdmX inhibitor for targeted therapies.

Homo-trimerization is essential for the transcription factor function of Myrf for oligodendrocyte differentiation

Abstract Myrf is a key transcription factor for oligodendrocyte differentiation and central nervous system myelination. We and others have previously shown that Myrf is generated as a membrane protein in the endoplasmic reticulum (ER), and that it undergoes auto-processing to release its N-terminal fragment from the ER, which enters the nucleus to work as a transcription factor. These previous studies allow a glimpse into the unusual complexity behind the biogenesis and function of the transcription factor domain of Myrf. Here, we report that Myrf N-terminal fragments assemble into stable homo-trimers before ER release. Consequently, Myrf N-terminal fragments are released from the ER only as homo-trimers. Our re-analysis of a previous genetic screening result in Caenorhabditis elegans shows that homo-trimerization is essential for the biological functions of Myrf N-terminal fragment, and that the region adjacent to the DNA-binding domain is pivotal to its homo-trimerization. Further, our computational analysis uncovered a novel homo-trimeric DNA motif that mediates the homo-trimeric DNA binding of Myrf N-terminal fragments. Importantly, we found that homo-trimerization defines the DNA binding specificity of Myrf N-terminal fragments. In sum, our study elucidates the molecular mechanism governing the biogenesis and function of Myrf N-terminal fragments and its physiological significance.

Mdm2 Splice isoforms regulate the p53/Mdm2/Mdm4 regulatory circuit via RING domain-mediated ubiquitination of p53 and Mdm4

ABSTRACT p53 is regulated by heterodimer E3 ligase Mdm2-Mdm4 via RING domain interaction. Mdm2 transcripts undergo alternative splicing, and Mdm2 splice isoforms are increased in cancer and induced by DNA damage. Although 2 major Mdm2 splice isoforms that do not bind to p53 were reported to impact the p53 pathway, the underlying biochemical mechanisms were not understood. Here, we show that these Mdm2 splice isoforms ubiquitinate Mdm2 and Mdm4 in vivo and regulate the activity of Mdm2-Mdm4 E3 complex in cells. The Mdm2 isoforms are capable of promoting p53 ubiquitination in the absence of Mdm2 or Mdm4. The 2 isoforms stimulate Mdm2 or Mdm4 activity for p53 ubiquitination in vivo and promote degradation of p53 and Mdm4 in cells. However, the Mdm2 isoforms have opposing effects on the steady-state p53 levels depending on the stoichiometric ratios of Mdm2, Mdm4 and the isoforms, causing either decreased or increased p53 levels in cells. Our data indicate that the Mdm2 splice isoforms can act as independent E3 ligases for p53 when Mdm2 and Mdm4 are absent, form potent heterodimer E3 ligases with either Mdm2 or Mdm4 for targeting p53 degradation, or act as inhibitory regulators of Mdm2-Mdm4 E3 ligase activity by downregulating Mdm4. These findings suggest that Mdm2 splice isoforms may play critical roles in the regulatory loop of p53/Mdm2-Mdm4 via a RING domain-mediated biochemical mechanism.

The Thoc1 Encoded Ribonucleoprotein Is a Substrate for the NEDD4-1 E3 Ubiquitin Protein Ligase

Ribonucleoprotein (RNP) complexes form around nascent RNA during transcription to facilitate proper transcriptional elongation, RNA processing, and nuclear export. RNPs are highly heterogeneous, and different types of RNPs tend to package functionally related transcripts. These observations have inspired the hypothesis that RNP mediated mechanisms help specify coordinated gene expression. This hypothesis is supported by the observation that mutations in RNP components can cause defects in specific developmental pathways. How RNP biogenesis itself is regulated, however, is not well understood. The evolutionarily conserved THO RNP complex functions early during transcription to package nascent transcripts and facilitate subsequent RNP biogenesis. THO deficiency compromises transcriptional elongation as well as RNP mediated events like 3′ end formation and nuclear export for some transcripts. Using molecularly manipulated cells and in vitro reconstituted biochemical reactions, we demonstrate that the essential THO protein component encoded by the Thoc1 gene is poly-ubiquitinated by the NEDD4-1 E3 ubiquitin ligase. Poly-ubiquitinated pThoc1 is degraded by the proteasome. These results indicate THO activity is regulated by the ubiquitin-proteasome pathway, and that this regulation is evolutionarily conserved between yeast and mammals. Manipulation of NEDD4-1 levels has modest effects on Thoc1 protein levels under steady state conditions, but destabilization of Thoc1 protein upon treatment with a transcriptional elongation inhibitor is dependent on NEDD4-1. This suggests NEDD4-1 functions in conjunction with other post-translational mechanisms to regulate Thoc1 protein and THO activity.

A synthesized butyrolactone derivative in combination with chloroquine can inhibit cancer cell growth and lysosome vacuolation induced by chloroquine in A549 lung cancer cells

3BDO in combination with chloroquine could elevate the Na+,K+-ATPase activity and decrease the expression of long non-coding RNA TGFB2-OT1. Therefore, the combination inhibited the cell growth and lysosomal vacuolation.

Abstract 5157: Ubiquitin-dependent regulation of AKT by NEDD4-1.

Several E3 ligases have been reported to regulate AKT stability and activation through ubiquitination. We found that NEDD4-1 is a novel E3 ligase involved in ubiquitin-dependent regulation of AKT. NEDD4-1 physically interacts with AKT and mediates AKT ubiquitination in vitro and in vivo. NEDD4-1 catalyzes K63-type polyubiquitin chain formation on AKT in an in vitro ubiquitination assay. AKT ubiquitination by NEDD4-1 in vivo requires plasma membrane binding but not phosphorylation of AKT. Ubiquitination of AKT or pAKT by NEDD4-1 promotes AKT nucleus-oriented translocation. IGF-1 signaling stimulates NEDD4-1-mediated ubiquitination of pAKT but not total AKT. A cancer-derived plasma membrane-philic mutant AKT(E17K) is more effectively ubiquitinated by NEDD4-1 and more efficiently trafficked into the nucleus compared with AKT. This study revealed a novel function of AKT ubiquitination by NEDD4-1 in its nuclear trafficking, a step that contributes to AKT activation process in IGF-1 response. Citation Format: Xinjiang Wang, Chuan-Dong Fan, Michelle A. Lum, Chao Xu, Jennifer D. Black. Ubiquitin-dependent regulation of AKT by NEDD4-1. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5157. doi:10.1158/1538-7445.AM2013-5157