The orphan receptor GPR125 (ADGRA3) belongs to subgroup III of the adhesion G protein−coupled receptor (aGPCR) family. aGPCRs, also known as class B2 GPCRs, share basic structural and functional properties with other GPCRs. Many of them couple to G proteins and activate G protein−dependent and −independent signaling pathways, but little is known about aGPCR internalization and β-arrestin recruitment. GPR125 was originally described as a spermatogonial stem cell marker and studied for its role in Wnt signaling and cell polarity. Here, using cell-based assays and confocal microscopy, we show that GPR125 is expressed on the cell surface and undergoes constitutive endocytosis in a β-arrestin−independent, but clathrin-dependent manner, as indicated by colocalization with transferrin receptor 1, an early endosome marker. These data support that the constitutive internalization of GPR125 contributes to its biological functions by controlling receptor surface expression and accessibility for ligands. Our study sheds light on a new property of aGPCRs, namely internalization; a property described to be important for signal propagation, signal termination, and desensitization of class A (rhodopsin-like) and B1 (VIP/secretin) GPCRs.
Tumorigenesis is increasingly considered to rely on subclones of cells poised to undergo an epithelial to mesenchymal transition (EMT) program. We and others have provided evidence, however, that the tumorigenesis of human breast cancer is not always restricted to typical EMT cells but is also somewhat paradoxically conveyed by subclones of apparently differentiated, non-EMT cells. Here we characterize such non-EMT-like and EMT-like subclones. Through a loss-of-function screen we found that a member of the E3 ubiquitin ligase complexes, FBXO11, specifically fuels tumor formation of a non-EMT-like clone by restraining the p53/p21 pathway. Interestingly, in the related EMT-like clone, FBXO11 operates through the BCL2 pathway with little or no impact on tumorigenesis. These data command caution in attempts to assess tumorigenesis prospectively based on EMT profiling, and they emphasize the importance of next generation subtyping of tumors, that is at the level of clonal composition.Electronic supplementary materialThe online version of this article (10.1186/s12943-018-0918-6) contains supplementary material, which is available to authorized users.
Introduction: Breast cancer is the most frequent cancer among women worldwide, and the aggressive subtype triple-negative breast cancer (TNBC) comprises 15% of breast cancer cases. Taxanes are a key component of the (neo)adjuvant treatment for TNBC; however, taxane resistance develops in one in five neoadjuvant or adjuvant taxane-treated patients. Resistance to anticancer drugs represents the main cause of cancer-related deaths. Thus, resensitization of taxane-resistant cancer cells constitutes a highly unmet medical need. Materials and Methods: SCO-101 is a modulator of the Volume Regulated Anion Channel (VRAC) complex. It is an oral drug and has previously passed 4 phase I clinical trials where it demonstrated excellent PK (T1/2=15 hours) and only limited toxicity. In this study we used an isogenic pair of parental (sensitive) and docetaxel (taxane)-resistant MDA-MB-231 human TNBC cells (Hansen et al.,Tumor Biol 2015:36:4327-38). Cell viability in vitro during 72h or 120h exposure to SCO-101 and/or docetaxel was addressed by MTT and Presto blue assays and cell counting. Potential targets for SCO-101 were investigated by transient knockdown of LRRC8a (obligatory component of VRAC) followed by cell viability assay, and by studying Pgp-mediated substrate efflux. Results: In parental MDA-MB-231 cells, SCO-101 and docetaxel each had a dose-dependent effect on cell viability and no combinatorial effects were observed between the drugs. When exposing docetaxel-resistant cells to the combination of SCO-101 and docetaxel, a significant inhibitory effect on cell viability compared to either drug alone was observed, suggesting an additive or synergistic effect between these two drugs with SCO-101 resensitizing the resistant cells to docetaxel. By knockdown of LRRC8a no differences in the response to SCO-101 and/or docetaxel were observed, suggesting that the anticancer effects of SCO-101 are not dependent on this obligatory VRAC component. Alternatively, preliminary experimental interrogation of the Pgp drug efflux pump suggests that SCO-101 affects this well-known docetaxel resistance mechanism. Conclusion and Future Perspectives: These preclinical studies demonstrate that SCO-101 sensitizes docetaxel-resistant breast cancer cells to docetaxel through a mechanism not dependent on LRRC8a expression. Currently, xenotransplant models of mice are being established to examine the in vivo inhibitory effects of SCO-101 on tumor growth. Additionally, we are preparing a clinical phase II study enrolling metastatic TNBC patients who have failed prior docetaxel treatment. These patients will be reexposed to the combination of docetaxel and SCO-101. End-point will be objective response rate according to RECIST 1.1. Citation Format: Sofie O. Bagger, Jørgen Drejer, Nils Brünner, Signe L. Nielsen, Palle Christoffersen, Jan Stenvang. Sensitization of docetaxel-resistant breast cancer cells to docetaxel by the VRAC modulator SCO-101 [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A144.
On the front cover: The cover image, submitted by Mette et al., is from the original article “Arrestin‐independent constitutive endocytosis of GPR125/ADGRA3,” https://doi.org/10.1111/nyas.14263.
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