Crystal structure of inhibitor-bound human MSPL that can activate high pathogenic avian influenza.

Infection of certain influenza viruses is triggered when its HA is cleaved by host cell proteases such as proprotein convertases and type II transmembrane serine proteases (TTSP). HA with a monobasic motif is cleaved by trypsin-like proteases, including TMPRSS2 and HAT, whereas the multibasic motif found in high pathogenicity avian influenza HA is cleaved by furin, PC5/6, or MSPL. MSPL belongs to the TMPRSS family and preferentially cleaves [R/K]-K-K-R↓ sequences. Here, we solved the crystal structure of the extracellular region of human MSPL in complex with an irreversible substrate-analog inhibitor. The structure revealed three domains clustered around the C-terminal α-helix of the SPD. The inhibitor structure and its putative model show that the P1-Arg inserts into the S1 pocket, whereas the P2-Lys and P4-Arg interacts with the Asp/Glu-rich 99-loop that is unique to MSPL. Based on the structure of MSPL, we also constructed a homology model of TMPRSS2, which is essential for the activation of the SARS-CoV-2 spike protein and infection. The model may provide the structural insight for the drug development for COVID-19.

A series of novel indazole derivatives of Sirt 1 activator as osteogenic regulators.

A series of indazole derivatives were identified as Sirt 1 activators though high-throughput screening. Optimization of each substituent on the indazole ring led to the identification of compound 13. Compound 13 appeared to give the best Sirt 1 activity of the compounds tested and also showed osteogenesis activity in a cell assay. Sirt 1 activators are therefore potential candidates for the treatment of osteoporosis.

Ski co-repressor complexes maintain the basal repressed state of the TGF-beta target gene, SMAD7, via HDAC3 and PRMT5.

The products encoded by ski and its related gene, sno, (Ski and Sno) act as transcriptional co-repressors and interact with other co-repressors such as N-CoR/SMRT and mSin3A. Ski and Sno mediate transcriptional repression by various repressors, including Mad, Rb and Gli3. Ski/Sno also suppress transcription induced by multiple activators, such as Smads and c-Myb. In particular, the inhibition of TGF-beta-induced transcription by binding to Smads is correlated with the oncogenic activity of Ski and Sno. However, the molecular mechanism by which Ski and Sno mediate transcriptional repression remains unknown. In this study, we report the purification and characterization of Ski complexes. The Ski complexes purified from HeLa cells contained histone deacetylase 3 (HDAC3) and protein arginine methyltransferase 5 (PRMT5), in addition to multiple Smad proteins (Smad2, Smad3 and Smad4). Chromatin immunoprecipitation assays indicated that these components of the Ski complexes were localized on the SMAD7 gene promoter, which is the TGF-beta target gene, in TGF-beta-untreated HepG2 cells. Knockdown of these components using siRNA led to up-regulation of SMAD7 mRNA. These results indicate that Ski complexes serve to maintain a TGF-beta-responsive promoter at a repressed basal level via the activities of histone deacetylase and histone arginine methyltransferase.

A novel nucleolar protein, PAPA-1, induces growth arrest as a result of cell cycle arrest at the G1 phase.

We have identified a novel nucleolar protein, PAP-1-associated protein-1 (PAPA-1), after screening the interacting proteins with Pim-1-associated protein-1 (PAP-1), a protein that is a phosphorylation target of Pim-1 kinase. PAPA-1 comprises 345 amino acids with a basic amino-acid cluster. PAPA-1 was found to be localized in the nucleolus in transfected HeLa cells, and the lysine/histidine cluster was essential for nucleolar localization of PAPA-1. PAPA-1 protein and mRNA expression decreased upon serum restimulation of starvation-synchronized cells, which displayed maximum level of PAPA-1 expression at G0 and early G1 phase of the cell cycle. Ectopic expression of PAPA-1 induced growth suppression of cells, and the effect was dependent on its nucleolar localization in established HeLa cell lines that inducibly express PAPA-1 or its deletion mutant under the control of a tetracycline-inducible promoter. Furthermore, when PAPA-1-inducible HeLa cells were synchronized by thymidine, colcemid or mimosine, and then PAPA-1 was expressed, the proportion of cells at the G1 phase was obviously increased. These results suggest that PAPA-1 induces growth and cell cycle arrests at the G1 phase of the cell cycle.