The SUMO-targeted ubiquitin ligase RNF4 localizes to etoposide-exposed mitotic chromosomes: Implication for a novel DNA damage response during mitosis

RNF4, a SUMO-targeted ubiquitin ligase (STUbL), localizes to the nucleus and functions in the DNA damage response during interphase of the cell cycle. RNF4 also exists in cells undergoing mitosis, where its regulation and function remain poorly understood. Here we showed that administration of etoposide, an anticancer DNA topoisomerase II poison, to mitotic human cervical cancer HeLa cells induced SUMO-2/3-dependent localization of RNF4 to chromosomes. The FK2 antibody signals, indicative of poly/multi-ubiquitin assembly, were detected on etoposide-exposed mitotic chromosomes, whereas the signals were negligible in cells depleted for RNF4 by RNA interference. This suggests that RNF4 functions as a STUbL in the etoposide-induced damage response during mitosis. Indeed, RNF4-depletion sensitized mitotic HeLa cells to etoposide and increased cells with micronuclei. These results indicate the importance of the RNF4-mediated STUbL pathway during mitosis for the maintenance of chromosome integrity and further implicate RNF4 as a target for topo II poison-based therapy for cancer patients.     

Augmentation of drug-induced cell death by ER protein BRI3BP

To determine the contribution of the endoplasmic reticulum (ER) to cell fate decision, we focused on BRI3-binding protein (BRI3BP) residing in this organelle. BRI3BP, when overexpressed, augmented the apoptosis of human embryonic kidney 293T cells challenged with drugs including the anti-cancer agent etoposide. In contrast, the knockdown of BRI3BP reduced the drug-triggered apoptosis. BRI3BP overexpression enhanced both mitochondrial cytochrome c release and caspase-3 activity in etoposide-treated cells. In response to etoposide, the ER reorganized into irregularly shaped lamellae in mock-transfected cells, whereas in BRI3BP-overexpressing cells, such reorganization was not observed. These observations suggest that BRI3BP is involved in the structural dynamics of the ER and affects mitochondrial viability. Taken together, BRI3BP, widely expressed in animal cell types, seems to possess a pro-apoptotic property and can potentiate drug-induced apoptosis.     

鬼臼素衍生物Vp—16和Vm—26合成副产物之结构和机理研究

本文报导了以4′-去甲表鬼臼素-4-β-D-葡萄糖甙分别与二甲醇缩乙醛和噻吩甲醛反应合成抗肿瘤药物依托泊甙(Vp-16)和替尼泊甙(Vm-26)中得到的两个主要副产物Vp-x和Vm-x的结构鉴定,并对其反应机理进行了探讨。     

Patterns of treatment failure for PD-(L)1 refractory extensive-stage small cell lung cancer in continued PD-(L)1 treatment

BackgroundAlthough immunotherapy greatly extends overall survival (OS) of patients with extensive-stage small cell lung cancer (ES-SCLC), a number of patients develop immunotherapy resistance (IR). Patterns of failure in ES-SCLC are not clarified. Our study aims to explore the clinical pattern of IR and prognostic factors for these patients.MethodsThe study was conducted from 117 ES-SCLC patients with immunotherapy between 2018 and 2022. Chi-square tests and Fishers' exact tests was used to explore failure patterns in different populations. Survival analyses of different progression patterns and subsequent treatment regimens were conducted by Kaplan–Meier curves and log-rank test.Results86 (73.5%) patients experienced IR. The patients with smoking (never smoker vs. current or ex-smoker, 59.5 % vs. 81.3%, P = 0.010), liver metastasis (extrahepatic metastasis vs. intrahepatic metastasis, 73.6 % vs. 90.9%, P = 0.050), and distant metastasis status (no distant metastasis vs. distant metastasis, 39.1 % vs. 81.9%, P<0.001) were associated with IR rates. Liver progression had a lower incidence in 1st line immunotherapy (1st line vs. ≥2nd lines, 14.0 % vs. 41.7%, P = 0.004) and a higher incidence in multiple progression (multiple progression vs. Oligo-progression, 39.4 % vs. 17.0%, P = 0.021). Cranial (41.7 % vs. 16.1%, P = 0.012) and distant lymph node (16.7 % vs. 3.2%, P = 0.049) progression were the main failure model for acquired IR in comparison to primary IR. Patients with new lesion progression only (17.73 vs. 9.17 months, P = 0.013) and non-hepatic progression (14.23 vs. 11.67 months, P = 0.042) had a longer OS. Patients in cross-line immunotherapy after IR had a favourable prognosis (17.07 vs. 11.93 months, P = 0.007).ConclusionThe most common failure pattern of immunotherapy for ES-SCLC was lung and regional lymph node progression. Brain and liver progression were the most common extra thoracic failure sites for 1st line and 2nd and more lines immunotherapy, respectively. There was a higher probability of primary IR in 2 lines and above immunotherapy. Patients with new only progression site and cross-line rechallenge immunotherapy had a better prognosis.     

Substrate specificities of family 1 UGTs gained by domain swapping

Family 1 glycosyltransferases are a group of enzymes known to embrace a large range of different substrates. This study devises a method to enhance the range of substrates even further by combining domains from different glycosyltransferases to gain improved substrate specificity and catalytic efficiency. Chimeric glycosyltransferases were made by combining domains from seven different family 1 glycosyltransferases, UGT71C1, UGT71C2, UGT71E1, UGT85C1, UGT85B1, UGT88B1 and UGT94B1. Twenty different chimeric glycosyltransferases were formed of which twelve were shown to be catalytically active. The chimeric enzymes of Arabidopsis thaliana UGT71C1 and UGT71C2 showed major changes in acceptor substrate specificity and were able to glycosylate etoposide significantly better than the parental UGT71C1 and UGT71C2 enzymes, with K_cat and efficiency coefficients 3.0 and 2.6 times higher, respectively. Chimeric glycosyltransferases of UGT71C1 combined with Stevia rebaudiana UGT71E1, also afforded enzymes with high catalytic efficiency, even though the two enzymes only display 38% amino acid sequence identity. These chimeras show a significantly altered regiospecificity towards especially trans-resveratrol, enabling the production of trans-resveratrol-β-4′-O-glucoside (resveratroloside). The study demonstrates that it is possible to obtain improved catalytic properties by combining domains from both closely as well as more distantly related glycosyltransferases. The substrate specificity gained by the chimeras is difficult to predict because factors determining the acceptor specificity reside in the N- terminal as well as the C-terminal domains.