No abstract

The exosome functions in the degradation of diverse RNA species, yet how it is negatively regulated remains largely unknown. Here, we show that NRDE2 forms a 1:1 complex with MTR4, a nuclear exosome cofactor critical for exosome recruitment, via a conserved MTR4-interacting domain (MID). Unexpectedly, NRDE2 mainly localizes in nuclear speckles, where it inhibits MTR4 recruitment and RNA degradation, and thereby ensures efficient mRNA nuclear export. Structural and biochemical data revealed that NRDE2 interacts with MTR4's key residues, locks MTR4 in a closed conformation, and inhibits MTR4 interaction with the exosome as well as proteins important for MTR4 recruitment, such as the cap-binding complex (CBC) and ZFC3H1. Functionally, MID deletion results in the loss of self-renewal of mouse embryonic stem cells. Together, our data pinpoint NRDE2 as a nuclear exosome negative regulator that ensures mRNA stability and nuclear export.

Nuclear speckles (NSs) serve as splicing factor storage sites. In this study, we unexpectedly found that many endogenous intronless mRNAs, which do not undergo splicing, associate with NSs. These associations do not require transcription, polyadenylation, or the polyA tail. Rather, exonic splicing enhancers present in intronless mRNAs and their binding partners, SR proteins, promote intronless mRNA localization to NSs. Significantly, speckle targeting of mRNAs promotes the recruitment of the TREX export complex and their TREX-dependent nuclear export. Furthermore, TREX, which accumulates in NSs, is required for releasing intronless mRNAs from NSs, whereas NXF1, which is mainly detected at nuclear pores, is not. Upon NXF1 depletion, the TREX protein UAP56 loses speckle concentration but coaccumulates with intronless mRNAs and polyA RNAs in the nucleoplasm, and these RNAs are trapped in NSs upon UAP56 codepletion. We propose that the export-competent messenger RNP assembly mainly occurs in NSs for intronless mRNAs and that entering NSs serves as a quality control step in mRNA export.

The RNA‐binding protein ALYREF plays key roles in nuclear export and also 3′‐end processing of polyadenylated mRNAs, but whether such regulation also extends to non‐polyadenylated RNAs is unknown. Replication‐dependent (RD)‐histone mRNAs are not polyadenylated, but instead end in a stem‐loop (SL) structure. Here, we demonstrate that ALYREF prevalently binds a region next to the SL on RD‐histone mRNAs. SL‐binding protein (SLBP) directly interacts with ALYREF and promotes its recruitment. ALYREF promotes histone pre‐mRNA 3′‐end processing by facilitating U7‐snRNP recruitment through physical interaction with the U7‐snRNP‐specific component Lsm11. Furthermore, ALYREF, together with other components of the TREX complex, enhances histone mRNA export. Moreover, we show that 3′‐end processing promotes ALYREF recruitment and histone mRNA export. Together, our results point to an important role of ALYREF in coordinating 3′‐end processing and nuclear export of non‐polyadenylated mRNAs.

A20 (TNFAIP3), known to inhibit NF-κB function by deubiquitinating-specific NF-κB signaling molecules, has been found in many cell types of the immune system. Recent findings suggest that A20 is essential for the development and functional performance of dendritic cell, B cell, T cell and macrophage. A number of studies further demonstrate that these cells are crucial in the pathogenesis of autoimmune diseases, such as type 1 diabetes, systemic lupus erythematosus, inflammatory bowel disease, ankylosing arthritis, Sjögren's syndrome and rheumatoid arthritis. In this article, we focus on the recent advances on the roles of A20 in autoimmune diseases and discuss the therapeutic significance of these new findings.

An ew procedure on palladium-catalyzedc arbonylative cyclization of N-(2-pyridyl)sulfonyl (N-SO 2 Py)-2iodoanilines with terminal alkenes has been developed for the rapid construction of dihydroquinolin-4(1H)-ones caffolds. Enabled by the chelatingg roup and using benzene-1,3,5-triyl triformate (TFBen) as the CO source, both aromatic and aliphatic alkenes were smoothly transformed into the corresponding 2,3-dihydroquinolin-4(1H)-ones in good yields with excellent regioselectivities. Notably,t he reaction of aromatic alkenes produces 2-aryl-2,3-dihydroquinolin-4(1H)-ones, while 3-alkyl-2,3-dihydroquinolin-4(1H)-ones were obtained when aliphatic alkenes were used. This protocol has been appliedi nt he synthesiso f antitumora gent A as well. Scheme3.Removal of the N-SO 2 Py directing group. Scheme4.Synthesis of the antitumoragent A. Scheme5.Preliminarymechanistic studies. Scheme6.Plausible mechanism.

Controlling proper RNA pool for nuclear export is important for accurate gene expression. ZFC3H1 is a key controller that not only facilitates nuclear exosomal degradation, but also retains its bound polyadenylated RNAs in the nucleus upon exosome inactivation. However, how ZFC3H1 retains RNAs and how its roles in RNA retention and degradation are related remain largely unclear. Here, we found that upon degradation inhibition, ZFC3H1 forms nuclear condensates to prevent RNA trafficking to nuclear speckles (NSs) where many RNAs gain export competence. Systematic mapping of ZFC3H1 revealed that it utilizes distinct domains for condensation and RNA degradation. Interestingly, ZFC3H1 condensation activity is required for preventing RNA trafficking to NSs, but not for RNA degradation. Considering that no apparent ZFC3H1 condensates are formed in normal cells, our study suggests that nuclear RNA degradation and retention are two independent mechanisms with different preference for controlling proper export RNA pool—degradation is preferred in normal cells, and condensation retention is activated upon degradation inhibition.

An efficient [3 + 2] cycloaddition of 3-ylideneoxindoles with in situ generated CFHCHN for the syntheses of spirooxindoles has been developed. This methodology gives access to a range of relatively complex spirooxindoles featuring a CFH group and three contiguous stereogenic centers in up to 84% yield and 99 : 1 trans/cis.