SIP/CacyBP promotes autophagy by regulating levels of BRUCE/Apollon, which stimulates LC3-I degradation.

BRUCE/Apollon is a membrane-associated inhibitor of apoptosis protein that is essential for viability and has ubiquitin-conjugating activity. On initiation of apoptosis, the ubiquitin ligase Nrdp1/RNF41 promotes proteasomal degradation of BRUCE. Here we demonstrate that BRUCE together with the proteasome activator PA28γ causes proteasomal degradation of LC3-I and thus inhibits autophagy. LC3-I on the phagophore membrane is conjugated to phosphatidylethanolamine to form LC3-II, which is required for the formation of autophagosomes and selective recruitment of substrates. SIP/CacyBP is a ubiquitination-related protein that is highly expressed in neurons and various tumors. Under normal conditions, SIP inhibits the ubiquitination and degradation of BRUCE, probably by blocking the binding of Nrdp1 to BRUCE. On DNA damage by topoisomerase inhibitors, Nrdp1 causes monoubiquitination of SIP and thus promotes apoptosis. However, on starvation, SIP together with Rab8 enhances the translocation of BRUCE into the recycling endosome, formation of autophagosomes, and degradation of BRUCE by optineurin-mediated autophagy. Accordingly, deletion of SIP in cultured cells reduces the autophagic degradation of damaged mitochondria and cytosolic protein aggregates. Thus, by stimulating proteasomal degradation of LC3-I, BRUCE also inhibits autophagy. Conversely, SIP promotes autophagy by blocking BRUCE-dependent degradation of LC3-I and by enhancing autophagosome formation and autophagic destruction of BRUCE. These actions of BRUCE and SIP represent mechanisms that link the regulation of autophagy and apoptosis under different conditions.

Ubiquitin Ligase Nrdp1 Controls Autophagy-Associated Acrosome Biogenesis and Mitochondrial Arrangement during Spermiogenesis.

Autophagy is critical to acrosome biogenesis and mitochondrial quality control, but the underlying mechanisms remain unclear. The ubiquitin ligase Nrdp1/RNF41 promotes ubiquitination of the mitophagy-associated Parkin and interacts with the pro-autophagic protein SIP/CacyBP. Here, we report that global deletion of Nrdp1 leads to formation of the round-headed sperm and male infertility by disrupting autophagy. Quantitative proteome analyses demonstrated that the expression of many proteins associated with mitochondria, lysosomes, and acrosomes was dysregulated in either spermatids or sperm of the Nrdp1-deficient mice. Deletion of Nrdp1 increased the levels of Parkin but decreased the levels of SIP, the mitochondrial fission protein Drp1 and the mitochondrial protein Tim23 in sperm, accompanied by the inhibition of autophagy, the impairment of acrosome biogenesis and the disruption of mitochondrial arrangement in sperm. Thus, our results uncover an essential role of Nrdp1 in spermiogenesis and male fertility by promoting autophagy, providing important clues to cope with the related male reproductive diseases.

Proteasome activator PA200 maintains stability of histone marks during transcription and aging.

The epigenetic inheritance relies on stability of histone marks, but various diseases, including aging-related disorders, are usually associated with alterations of histone marks. Whether and how the proteasome is responsible for maintaining the histone marks during transcription and aging remain unclear. The core histones can be degraded by the atypical proteasome, which contains the proteasome activator PA200, in an acetylation-dependent manner during somatic DNA damage response and spermiogenesis. Methods: By utilizing a substitute of methionine to label proteins metabolically, we analyzed histone degradation genome-wide by sequencing the DNA fragments following pulse-chase assays. The genome-wide RNA-sequencing analysis was performed to analyze transcription and chromatin-immunoprecipitation (ChIP)-sequencing was used for analyses of histone marks. The experimental models included gene-manipulated cells (including both mouse and yeast), mouse liver, and mice. Results: Degradation of H4 or the transcription-coupled histone variant H3.3 could be suppressed by deletion of PA200 or its yeast ortholog Blm10. The histone deacetylase inhibitor accelerated the degradation rates of H3, while the mutations of the putative acetyl-lysine-binding region of PA200 abolished histone degradation in the G1-arrested cells. Deletion of PA200 dramatically altered deposition of the active transcriptional hallmarks (H3K4me3 and H3K56ac) and transcription, especially during cellular aging. Furthermore, deletion of PA200 or Blm10 accelerated cellular aging. Notably, the PA200-deficient mice displayed a range of aging-related deteriorations, including immune malfunction, anxiety-like behavior and shorter lifespan. Conclusion: PA200 promotes the transcription-coupled degradation of the core histones, and plays an important role in maintaining the stability of histone marks during transcription and aging.

High-Temperature Reversible Phase-Transition Behavior, Switchable Dielectric and Second Harmonic Generation Response of Two Homochiral Crown Ether Clathrates.

Crowning achievement: Two homochiral crown ether clathrates were synthesized which undergo high-temperature reversible phase transition. In addition, second harmonic generation (SHG) responses and abnormal dielectric property further confirm the reversible phase transitions and symmetry breaking behaviors of the structures.