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R347 --> Ceramide are central intermediates of sphingolipid metabolism, mediating cell proliferation, mitochondrial apoptosis, and intracellular trafficking. Ceramide regulates diverse physiological and pathological reactions in part through inverting topology of certain transmembrane proteins. This topological inversion is achieved through Regulated Alternative Translocation (RAT), which reverses the direction by which membrane proteins are translocated across the endoplasmic reticulum during translation. We previously reported that RAT of transmembrane 4 L6 subfamily member 20 (TM4SF20) induced by ceramide converts the topology of TM4SF20. As a result, TM4SF20 with the different topology triggers proteolytic activation of a transcription factor called cAMP responsive element binding protein 3‐like 1 (CREB3L1), which in turn activates transcription of genes that inhibit cell proliferation. However, it remains unclear how ceramide levels are sensed in cells to trigger the ceramide‐induced signaling reactions including RAT. Here we describe a chemoproteomic strategy that uses photo‐activatable and clickable short chain ceramide (pac‐C7‐Cer) in combination with stable isotope labeling by amino acids in cell culture (SILAC)‐based mass spectrometry to perform a proteome‐wide identification of ceramide‐binding proteins directly in living cells. This approach yields 24 ceramide‐binding proteins repeated in three independent experiments. Among these proteins, we determine that translocating chain associated membrane protein 1 (TRAM1), an ER translocon‐associated proteins, and TRAM2, a protein known to be involved in RAT of TM4SF20, are specific ceramide‐binding proteins. We address that interrupting the binding of TRAM proteins to ceramide derived from pac‐C7‐Cer by inhibiting the conversion of short chain ceramide to long chain ceramide will also inactivate RAT of TM4SF20 induced by C6‐ceramide. Furthermore, we demonstrate that B13, by serving as a competitive inhibitor that blocked binding of ceramide to TRAM proteins prevented ceramide‐induced RAT of TM4SF20. It suggests that TRAM proteins might be the ceramide sensor involved in RAT regulation. Above all, this study supports a role of TRAM proteins in RAT regulation induced by ceramide and provides a molecular framework for understanding of global cellular function exerted by sphingolipids interacting proteins. [ABSTRACT FROM AUTHOR]

The direct synthesis of benzimidazoles from 2-nitroaniline and ethanol over Cu-Pd/γ-Al2O3 catalysts has the advantages of requiring easily available starting materials, having high efficiency, and a simple procedure. The modification by Mg of the Cu-Pd/γ-Al2O3 catalyst could improve the catalytic activity significantly. The addition of Mg to the Cu-Pd/γ-Al2O3 catalyst could maintain and promote the formation of CuPd alloy active sites. Meanwhile, the basicity of the support was enhanced appropriately by Mg, which generated more basic sites (Al-Oδ−) to accelerate the dehydrogenation of alcohol and increased the rate of the whole coupled reaction. The 2-nitroaniline was completely converted over Cu-Pd/(Mg)γ-Al2O3 after reacting for six hours, and the yield of 2-methylbenzimidazole was 98.8%. The results of this work provide a simple method to develop a more efficient catalyst for the "alcohol-dehydrogenation, hydrogen transfer and hydrogenation" coupled reaction system. [ABSTRACT FROM AUTHOR]

Transmembrane protein 52B (TMEM52B), a newly identified tumor-related gene, has been reported to regulate various tumors, yet its role in nasopharyngeal carcinoma (NPC) remains unclear. Transcriptomic analysis of NPC cell lines reveals frequent overexpression of TMEM52B, and immunohistochemical results show that TMEM52B is associated with advanced tumor stage, recurrence, and decreased survival time. Depleting TMEM52B inhibits the proliferation, migration, invasion, and oncogenesis of NPC cells in vivo. TMEM52B encodes two isoforms, TMEM52B-P18 and TMEM52B-P20, differing in their N-terminals. While both isoforms exhibit similar pro-oncogenic roles and contribute to drug resistance in NPC, TMEM52B-P20 differentially promotes metastasis. This functional discrepancy may be attributed to their distinct subcellular localization; TMEM52B-P18 is confined to the cytoplasm, while TMEM52B-P20 is found both at the cell membrane and in the cytoplasm. Mechanistically, cytoplasmic TMEM52B enhances AKT phosphorylation by interacting with phosphoglycerate kinase 1 (PGK1), fostering NPC growth and metastasis. Meanwhile, membrane-localized TMEM52B-P20 promotes E-cadherin ubiquitination and degradation by facilitating its interaction with the E3 ubiquitin ligase NEDD4, further driving NPC metastasis. In conclusion, the TMEM52B-P18 and TMEM52B-P20 isoforms promote the metastasis of NPC cells through different mechanisms. Drugs targeting these TMEM52B isoforms may offer therapeutic benefits to cancer patients with varying degrees of metastasis., (© 2024 The Author(s). Advanced Science published by Wiley‐VCH GmbH.)