RGS2-mediated translational control mediates cancer cell dormancy and tumor relapse
Jaebeom Cho, Hye-Young Min, Ho Jin Lee, Seung Yeob Hyun, Jeong Yeon Sim, Myungkyung Noh, Su Jung Hwang, Shin-Hyung Park, Hye-Jin Boo, Hyo-Jong Lee, Sungyoul Hong, Rang-Woon Park, Young Kee Shin, Mien-Chie Hung, Ho-Young Lee
Jaebeom Cho, Hye-Young Min, Ho Jin Lee, Seung Yeob Hyun, Jeong Yeon Sim, Myungkyung Noh, Su Jung Hwang, Shin-Hyung Park, Hye-Jin Boo, Hyo-Jong Lee, Sungyoul Hong, Rang-Woon Park, Young Kee Shin, Mien-Chie Hung, Ho-Young Lee
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Research Article Cell biology Oncology

RGS2-mediated translational control mediates cancer cell dormancy and tumor relapse

Abstract

Slow-cycling/dormant cancer cells (SCCs) have pivotal roles in driving cancer relapse and drug resistance. A mechanistic explanation for cancer cell dormancy and therapeutic strategies targeting SCCs are necessary to improve patient prognosis, but are limited because of technical challenges to obtaining SCCs. Here, by applying proliferation-sensitive dyes and chemotherapeutics to non–small cell lung cancer (NSCLC) cell lines and patient-derived xenografts, we identified a distinct SCC subpopulation that resembled SCCs in patient tumors. These SCCs displayed major dormancy-like phenotypes and high survival capacity under hostile microenvironments through transcriptional upregulation of regulator of G protein signaling 2 (RGS2). Database analysis revealed RGS2 as a biomarker of retarded proliferation and poor prognosis in NSCLC. We showed that RGS2 caused prolonged translational arrest in SCCs through persistent eukaryotic initiation factor 2 (eIF2α) phosphorylation via proteasome-mediated degradation of activating transcription factor 4 (ATF4). Translational activation through RGS2 antagonism or the use of phosphodiesterase 5 inhibitors, including sildenafil (Viagra), promoted ER stress–induced apoptosis in SCCs in vitro and in vivo under stressed conditions, such as those induced by chemotherapy. Our results suggest that a low-dose chemotherapy and translation-instigating pharmacological intervention in combination is an effective strategy to prevent tumor progression in NSCLC patients after rigorous chemotherapy.

Authors

Jaebeom Cho, Hye-Young Min, Ho Jin Lee, Seung Yeob Hyun, Jeong Yeon Sim, Myungkyung Noh, Su Jung Hwang, Shin-Hyung Park, Hye-Jin Boo, Hyo-Jong Lee, Sungyoul Hong, Rang-Woon Park, Young Kee Shin, Mien-Chie Hung, Ho-Young Lee

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Figure 6

Regulation of ATF4 protein stability by RGS2 via interaction in SCCs.

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Regulation of ATF4 protein stability by RGS2 via interaction in SCCs. (A...
(A and B) Changes in the expression of ATF4, phosphorylated eIF2α, and ATF4 target genes in H460/PcR-shRGS2 compared with H460/PcR-shEV (A) and in H460-RGS2 compared with H460-EV (B), as determined by immunoblotting and real-time PCR. (C) ATF4 mRNA expression in SCCs compared with the corresponding ACCs, in H460/PcR-shRGS2 compared with H460/PcR-shEV and in H460-RGS2 compared with H460-EV was analyzed by real-time PCR. (D) Regulation of de novo ATF4 protein synthesis in H460-EV and H460-RGS2 cells was determined by autoradiography using 35S-labeled ATF4 immunoprecipitants. Immunoblotting result is representative of triplicates. (E) Changes in ATF4 protein stability regulated by RGS2 were determined by immunoblotting using lysates from cells treated with cycloheximide (CHX; 100 μg/mL) for the indicated time periods. Immunoblotting result is representative of triplicates. (F) ATF4 ubiquitination in SCCs compared with ACCs and in cells with modulated RGS2 expression was determined by immunoprecipitation of ATF4 and subsequent immunoblotting for ubiquitin. (G) The endogenous interaction between RGS2 and ATF4 was determined by coimmunoprecipitation assay in H460/PcR cells treated with MG132 (10 μM for 4 hours). (H) The interaction between ectopic RGS2 and endogenous ATF4 was determined by coimmunoprecipitation assay in H460 cells treated with or without MG132 (10 μM, 4 hours). (I) Diagrams showing the full-length (FL) and mutant recombinant RGS2 proteins. (J) The interaction between ATF4 and FL or mutant RGS2 proteins was determined by pulldown assay. (K) Regulation of protein translation by overexpression of FL or mutant RGS2 proteins. The data are presented as the mean ± SD. n = 3 for A–E; n = 6 for K. *P < 0.05, **P < 0.01, and ***P < 0.001, as determined by a 2-tailed Student’s t test (A–E) and 1-way ANOVA with Dunnett’s post hoc test (K).