Targeting the N Terminus of eIF4AI for Inhibition of Its Catalytic Recycling.

DEAD-box ATP-dependent helicases (DEAH/D) are a family of conserved genes predominantly involved in gene expression regulation and RNA processing. As its prototype, eIF4AI is an essential component of the protein translation initiation complex. Utilizing a screening system based on wild-type eIF4AI and its L243G mutant with a changed linker domain, we discovered an eIF4AI inhibitor, sanguinarine (SAN) and used it to study the catalytic mechanism of eIF4AI. Herein, we describe the crystal structure of the eIF4AI-inhibitor complex and demonstrate that the binding site displays certain specificity, which can provide the basis for drug design to target eIF4AI. We report that except for competitive inhibition SAN's possible mechanism of action involves interference with eIF4AI catalytic cycling process by hindering the formation of the closed conformation of eIF4AI. In addition, our results highlight a new targetable site on eIF4AI and confirm eIF4AI as a viable pharmacological target.

Prolyl 4-hydroxylase 2 promotes B-cell lymphoma progression via hydroxylation of Carabin.

B-cell lymphomas are heterogeneous blood disorders with limited therapeutic options, largely because of their propensity to relapse and become refractory to treatments. Carabin, a key suppressor of B-cell receptor signaling and proliferation, is inactivated in B-cell lymphoma by unknown mechanisms. Here, we identify prolyl 4-hydroxylase 2 (P4HA2) as a specific proline hydroxylase of Carabin. Carabin hydroxylation leads to its proteasomal degradation, thereby activating the Ras/extracellular signal-regulated kinase pathway and increasing B-cell lymphoma proliferation. P4HA2 is undetectable in normal B cells but upregulated in the diffuse large B-cell lymphoma (DLBCL), driving Carabin inactivation and lymphoma proliferation. Our results indicate that P4HA2 is a potential prognosis marker for DLBCL and a promising pharmacological target for developing treatment of molecularly stratified B-cell lymphomas.

USP9X controls translation efficiency via deubiquitination of eukaryotic translation initiation factor 4A1.

Controlling translation initiation is an efficient way to regulate gene expression at the post-transcriptional level. However, current knowledge regarding regulatory proteins and their modes of controlling translation initiation is still limited. In this study, we employed tandem affinity purification and mass spectrometry to screen for unknown proteins associated with the translation initiation machinery. Ubiquitin specific peptidase 9, X-linked (USP9X), was identified as a novel binding partner, that interacts with the eukaryotic translation initiation factor 4B (eIF4B) in a mRNA-independent manner. USP9X-deficient cells presented significantly impaired nascent protein synthesis, cap-dependent translation initiation and cellular proliferation. USP9X can selectively alter the translation of pro-oncogenic mRNAs, such as c-Myc and XIAP. Moreover, we found that eIF4A1, which is primarily ubiquitinated at Lys-369, is the substrate of USP9X. USP9X dysfunction increases the ubiquitination of eIF4A1 and enhances its degradation. Our results provide evidence that USP9X is a novel regulator of the translation initiation process via deubiquitination of eIF4A1, which offers new insight in understanding the pivotal role of USP9X in human malignancies and neurodevelopmental disorders.

Screening in larval zebrafish reveals tissue-specific distribution of fifteen fluorescent compounds.

The zebrafish is a prominent vertebrate model for low-cost in vivo whole organism screening. In our recent screening of the distribution patterns of fluorescent compounds in live zebrafish larvae, fifteen compounds with tissue-specific distributions were identified. Several compounds were observed to accumulate in tissues where they were reported to induce side-effects, and compounds with similar structures tended to be enriched in the same tissues, with minor differences. In particular, we found three novel red fluorescent bone-staining dyes: purpurin, lucidin and 3-hydroxy-morindone; purpurin can effectively label bones in both larval and adult zebrafish, as well as in postnatal mice, without significantly affecting bone mass and density. Moreover, two structurally similar chemotherapeutic compounds, doxorubicin and epirubicin, were observed to have distinct distribution preferences in zebrafish. Epirubicin maintained a relatively higher concentration in the liver, and performed better in inhibiting hepatic hyperplasia caused by the over-expression of krasG12V In total, our study suggests that the transparent zebrafish larvae serve as valuable tools for identifying tissue-specific distributions of fluorescent compounds.

Amino Acid Conjugated Anthraquinones from the Marine-Derived Fungus Penicillium sp. SCSIO sof101.

Emodacidamides A-H (1-8), natural products featuring anthraquinone-amino acid conjugates, have been isolated from a marine-derived fungus, Penicillium sp. SCSIO sof101, together with known anthraquinones 9 and 10. The planar structures of 1-8 were elucidated using a combination of NMR spectroscopy and mass spectrometry. The absolute configurations of the amino acid residues were confirmed using Marfey's method and chiral-phase HPLC analyses. Additionally, isolates were evaluated for possible immunomodulatory and cytotoxic activities. Emodacidamides A (1), C (3), D (4), and E (5) inhibited interleukin-2 secretion from Jurkat cells with IC50 values of 4.1, 5.1, 12, and 5.4 µM, respectively.

Cytotoxic rearranged angucycline glycosides from deep sea-derived Streptomyces lusitanus SCSIO LR32.

Two new rearranged linear angucycline glycosides, designated grincamycins G and H (1 and 2), together with three known congers P-1894B (vineomycin A1, 3), saquayamycin B (4) and vineomycin B2 (5), were obtained from marine-derived actinomycete Streptomyces lusitanus SCSIO LR32. The structures of 1 and 2 were elucidated by MS, 1D and 2D NMR techniques. Compounds 2-5 showed significant inhibitory effect on Jurkat T-cell proliferation with IC50 values of 3.0, 0.011, 0.037 and 0.3 µM, respectively.

Developing an Efficient and General Strategy for Immobilization of Small Molecules onto Microarrays Using Isocyanate Chemistry.

Small-molecule microarray (SMM) is an effective platform for identifying lead compounds from large collections of small molecules in drug discovery, and efficient immobilization of molecular compounds is a pre-requisite for the success of such a platform. On an isocyanate functionalized surface, we studied the dependence of immobilization efficiency on chemical residues on molecular compounds, terminal residues on isocyanate functionalized surface, lengths of spacer molecules, and post-printing treatment conditions, and we identified a set of optimized conditions that enable us to immobilize small molecules with significantly improved efficiencies, particularly for those molecules with carboxylic acid residues that are known to have low isocyanate reactivity. We fabricated microarrays of 3375 bioactive compounds on isocyanate functionalized glass slides under these optimized conditions and confirmed that immobilization percentage is over 73%.