The AXL receptor and its activating ligand, growth arrest–specific 6 (GAS6), are important drivers of metastasis and therapeutic resistance in human cancers. Given the critical roles that GAS6 and AXL play in refractory disease, this signaling axis represents an attractive target for therapeutic intervention. However, the strong picomolar binding affinity between GAS6 and AXL and the promiscuity of small molecule inhibitors represent important challenges faced by current anti-AXL therapeutics. Here, we have addressed these obstacles by engineering a second-generation, high-affinity AXL decoy receptor with an apparent affinity of 93 femtomolar to GAS6. Our decoy receptor, MYD1-72, profoundly inhibited disease progression in aggressive preclinical models of human cancers and induced cell killing in leukemia cells. When directly compared with the most advanced anti-AXL small molecules in the clinic, MYD1-72 achieved superior antitumor efficacy while displaying no toxicity. Moreover, we uncovered a relationship between AXL and the cellular response to DNA damage whereby abrogation of AXL signaling leads to accumulation of the DNA-damage markers γH2AX, 53BP1, and RAD51. MYD1-72 exploited this relationship, leading to improvements upon the therapeutic index of current standard-of-care chemotherapies in preclinical models of advanced pancreatic and ovarian cancer.
Mihalis S. Kariolis, Yu Rebecca Miao, Anh Diep, Shannon E. Nash, Monica M. Olcina, Dadi Jiang, Douglas S. Jones II, Shiven Kapur, Irimpan I. Mathews, Albert C. Koong, Erinn B. Rankin, Jennifer R. Cochran, Amato J. Giaccia
Li-Fraumeni syndrome (LFS) is a cancer predisposition disorder caused by germline mutations in
Ping-yuan Wang, Jie Li, Farzana L. Walcott, Ju-Gyeong Kang, Matthew F. Starost, S. Lalith Talagala, Jie Zhuang, Ji-Hoon Park, Rebecca D. Huffstutler, Christina M. Bryla, Phuong L. Mai, Michael Pollak, Christina M. Annunziata, Sharon A. Savage, Antonio Tito Fojo, Paul M. Hwang
Tumor cells gain metastatic capacity through a Golgi phosphoprotein 3–dependent (GOLPH3-dependent) Golgi membrane dispersal process that drives the budding and transport of secretory vesicles. Whether Golgi dispersal underlies the pro-metastatic vesicular trafficking that is associated with epithelial-to-mesenchymal transition (EMT) remains unclear. Here, we have shown that, rather than causing Golgi dispersal, EMT led to the formation of compact Golgi organelles with improved ribbon linking and cisternal stacking. Ectopic expression of the EMT-activating transcription factor ZEB1 stimulated Golgi compaction and relieved microRNA-mediated repression of the Golgi scaffolding protein PAQR11. Depletion of PAQR11 dispersed Golgi organelles and impaired anterograde vesicle transport to the plasma membrane as well as retrograde vesicle tethering to the Golgi. The N-terminal scaffolding domain of PAQR11 was associated with key regulators of Golgi compaction and vesicle transport in pull-down assays and was required to reconstitute Golgi compaction in PAQR11-deficient tumor cells. Finally, high PAQR11 levels were correlated with EMT and shorter survival in human cancers, and PAQR11 was found to be essential for tumor cell migration and metastasis in EMT-driven lung adenocarcinoma models. We conclude that EMT initiates a PAQR11-mediated Golgi compaction process that drives metastasis.
Xiaochao Tan, Priyam Banerjee, Hou-Fu Guo, Stephen Ireland, Daniela Pankova, Young-ho Ahn, Irodotos Michail Nikolaidis, Xin Liu, Yanbin Zhao, Yongming Xue, Alan R. Burns, Jonathon Roybal, Don L. Gibbons, Tomasz Zal, Chad J. Creighton, Daniel Ungar, Yanzhuang Wang, Jonathan M. Kurie
Mutations and deletions in components of ubiquitin ligase complexes that lead to alterations in protein turnover are important mechanisms in driving tumorigenesis. Here we describe an alternative mechanism involving upregulation of the microRNA miR-424 that leads to impaired ubiquitination and degradation of oncogenic transcription factors in prostate cancers. We found that miR-424 targets the E3 ubiquitin ligase COP1 and identified STAT3 as a key substrate of COP1 in promoting tumorigenic and cancer stem-like properties in prostate epithelial cells. Altered protein turnover due to impaired COP1 function led to accumulation and enhanced basal and cytokine-induced activity of STAT3. We further determined that loss of the ETS factor ESE3/EHF is the initial event that triggers the deregulation of the miR-424/COP1/STAT3 axis. COP1 silencing and STAT3 activation were effectively reverted by blocking of miR-424, suggesting a possible strategy to attack this key node of tumorigenesis in ESE3/EHF–deficient tumors. These results establish miR-424 as an oncogenic effector linked to noncanonical activation of STAT3 and as a potential therapeutic target.
Cecilia Dallavalle, Domenico Albino, Gianluca Civenni, Jessica Merulla, Paola Ostano, Maurizia Mello-Grand, Simona Rossi, Marco Losa, Gioacchino D’Ambrosio, Fausto Sessa, George N. Thalmann, Ramon Garcia-Escudero, Andrea Zitella, Giovanna Chiorino, Carlo V. Catapano, Giuseppina M. Carbone
Hematopoietic stem and progenitor cells (HSPCs) reside in the bone marrow. Stress signals from cancer and other conditions promote HSPC mobilization into circulation and subsequent homing to tissue microenvironments. HSPC infiltration into tissue microenvironments can influence disease progression; notably, in cancer, HSPCs encourage tumor growth. Here we have uncovered a mutually exclusive distribution of EPHB4 receptors in bone marrow sinusoids and ephrin B2 ligands in hematopoietic cells. We determined that signaling interactions between EPHB4 and ephrin B2 control HSPC mobilization from the bone marrow. In mice, blockade of the EPHB4/ephrin B2 signaling pathway reduced mobilization of HSPCs and other myeloid cells to the circulation. EPHB4/ephrin B2 blockade also reduced HSPC infiltration into tumors as well as tumor progression in murine models of melanoma and mammary cancer. These results identify EPHB4/ephrin B2 signaling as critical to HSPC mobilization from bone marrow and provide a potential strategy for reducing cancer progression by targeting the bone marrow.
Hyeongil Kwak, Ombretta Salvucci, Roberto Weigert, Jorge L. Martinez-Torrecuadrada, Mark Henkemeyer, Michael G. Poulos, Jason M. Butler, Giovanna Tosato
Natural killer (NK) cells can have potent antileukemic activity following haplo-mismatched, T cell–depleted stem cell transplantations for the treatment of acute myeloid leukemia (AML), but they are not successful in eradicating de novo AML. Here, we have used a mouse model of de novo AML to elucidate the mechanisms by which AML evades NK cell surveillance. NK cells in leukemic mice displayed a marked reduction in the cytolytic granules perforin and granzyme B. Further, as AML progressed, we noted the selective loss of an immature subset of NK cells in leukemic mice and in AML patients. This absence was not due to elimination by cell death or selective reduction in proliferation, but rather to the result of a block in NK cell differentiation. Indeed, NK cells from leukemic mice and humans with AML showed lower levels of TBET and EOMES, transcription factors that are critical for terminal NK cell differentiation. Further, the microRNA miR-29b, a regulator of T-bet and EOMES, was elevated in leukemic NK cells. Finally, deletion of miR-29b in NK cells reversed the depletion of this NK cell subset in leukemic mice. These results indicate that leukemic evasion of NK cell surveillance occurs through miR-mediated dysregulation of lymphocyte development, representing an additional mechanism of immune escape in cancer.
Bethany L. Mundy-Bosse, Steven D. Scoville, Li Chen, Kathleen McConnell, Hsiaoyin C. Mao, Elshafa H. Ahmed, Nicholas Zorko, Sophia Harvey, Jordan Cole, Xiaoli Zhang, Stefan Costinean, Carlo M. Croce, Karilyn Larkin, John C. Byrd, Sumithira Vasu, William Blum, Jianhua Yu, Aharon G. Freud, Michael A. Caligiuri
The rising success of cancer immunotherapy has produced immense interest in defining the clinical contexts that may benefit from this therapeutic approach. To this end, there is a need to ascertain how the therapeutic modulation of intrinsic cancer cell programs influences the anticancer immune response. For example, the role of autophagy as a tumor cell survival and metabolic fitness pathway is being therapeutically targeted in ongoing clinical trials that combine cancer therapies with antimalarial drugs for the treatment of a broad spectrum of cancers, many of which will likely benefit from immunotherapy. However, our current understanding of the interplay between autophagy and the immune response remains incomplete. Here, we have evaluated how autophagy inhibition impacts the antitumor immune response in immune-competent mouse models of melanoma and mammary cancer. We observed equivalent levels of T cell infiltration and function within autophagy-competent and -deficient tumors, even upon treatment with the anthracycline chemotherapeutic doxorubicin. Similarly, we found equivalent T cell responses upon systemic treatment of tumor-bearing mice with antimalarial drugs. Our findings demonstrate that antitumor adaptive immunity is not adversely impaired by autophagy inhibition in these models, allowing for the future possibility of combining autophagy inhibitors with immunotherapy in certain clinical contexts.
Hanna Starobinets, Jordan Ye, Miranda Broz, Kevin Barry, Juliet Goldsmith, Timothy Marsh, Fanya Rostker, Matthew Krummel, Jayanta Debnath
Interactions between multiple myeloma (MM) cells and the BM microenvironment play a critical role in bortezomib (BTZ) resistance. However, the mechanisms involved in these interactions are not completely understood. We previously showed that expression of CYP26 in BM stromal cells maintains a retinoic acid–low (RA-low) microenvironment that prevents the differentiation of normal and malignant hematopoietic cells. Since a low secretory B cell phenotype is associated with BTZ resistance in MM and retinoid signaling promotes plasma cell differentiation and Ig production, we investigated whether stromal expression of the cytochrome P450 monooxygenase CYP26 modulates BTZ sensitivity in the BM niche. CYP26-mediated inactivation of RA within the BM microenvironment prevented plasma cell differentiation and promoted a B cell–like, BTZ-resistant phenotype in human MM cells that were cocultured on BM stroma. Moreover, paracrine Hedgehog secretion by MM cells upregulated stromal CYP26 and further reinforced a protective microenvironment. These results suggest that crosstalk between Hedgehog and retinoid signaling modulates BTZ sensitivity in the BM niche. Targeting these pathological interactions holds promise for eliminating minimal residual disease in MM.
Salvador Alonso, Daniela Hernandez, Yu-ting Chang, Christian D. Gocke, Megan McCray, Ravi Varadhan, William H. Matsui, Richard J. Jones, Gabriel Ghiaur
A vast number of cancer genes are transcription factors that drive tumorigenesis as oncogenic fusion proteins. Although the direct targeting of transcription factors remains challenging, therapies aimed at oncogenic fusion proteins are attractive as potential treatments for cancer. There is particular interest in targeting the oncogenic PAX3-FOXO1 fusion transcription factor, which induces alveolar rhabdomyosarcoma (aRMS), an aggressive cancer of skeletal muscle cells for which patient outcomes remain dismal. In this work, we have defined the interactome of PAX3-FOXO1 and screened 60 candidate interactors using siRNA-mediated depletion to identify candidates that affect fusion protein activity in aRMS cells. We report that chromodomain helicase DNA binding protein 4 (CHD4), an ATP-dependent chromatin remodeler, acts as crucial coregulator of PAX3-FOXO1 activity. CHD4 interacts with PAX3-FOXO1 via short DNA fragments. Together, they bind to regulatory regions of PAX3-FOXO1 target genes. Gene expression analysis suggested that CHD4 coregulatory activity is essential for a subset of PAX3-FOXO1 target genes. Depletion of CHD4 reduced cell viability of fusion-positive but not of fusion-negative RMS in vitro, which resembled loss of PAX3-FOXO1. It also caused specific regression of fusion-positive xenograft tumors in vivo. Therefore, this work identifies CHD4 as an epigenetic coregulator of PAX3-FOXO1 activity, providing rational evidence for CHD4 as a potential therapeutic target in aRMS.
Maria Böhm, Marco Wachtel, Joana G. Marques, Natalie Streiff, Dominik Laubscher, Paolo Nanni, Kamel Mamchaoui, Raffaella Santoro, Beat W. Schäfer
Different tumor microenvironments (TMEs) induce stromal cell plasticity that affects tumorigenesis. The impact of TME-dependent heterogeneity of tumor endothelial cells (TECs) on tumorigenesis is unclear. Here, we isolated pure TECs from human colorectal carcinomas (CRCs) that exhibited TMEs with either improved (Th1-TME CRCs) or worse clinical prognosis (control-TME CRCs). Transcriptome analyses identified markedly different gene clusters that reflected the tumorigenic and angiogenic activities of the respective TMEs. The gene encoding the matricellular protein SPARCL1 was most strongly upregulated in Th1-TME TECs. It was also highly expressed in ECs in healthy colon tissues and Th1-TME CRCs but low in control-TME CRCs. In vitro, SPARCL1 expression was induced in confluent, quiescent ECs and functionally contributed to EC quiescence by inhibiting proliferation, migration, and sprouting, whereas siRNA-mediated knockdown increased sprouting. In human CRC tissues and mouse models, vessels with SPARCL1 expression were larger and more densely covered by mural cells. SPARCL1 secretion from quiescent ECs inhibited mural cell migration, which likely led to stabilized mural cell coverage of mature vessels. Together, these findings demonstrate TME-dependent intertumoral TEC heterogeneity in CRC. They further indicate that TEC heterogeneity is regulated by SPARCL1, which promotes the cell quiescence and vessel homeostasis contributing to the favorable prognoses associated with Th1-TME CRCs.
Elisabeth Naschberger, Andrea Liebl, Vera S. Schellerer, Manuela Schütz, Nathalie Britzen-Laurent, Patrick Kölbel, Ute Schaal, Lisa Haep, Daniela Regensburger, Thomas Wittmann, Ludger Klein-Hitpass, Tilman T. Rau, Barbara Dietel, Valérie S. Méniel, Alan R. Clarke, Susanne Merkel, Roland S. Croner, Werner Hohenberger, Michael Stürzl
Carcinoma cells can acquire increased motility and invasiveness through epithelial-to-mesenchymal transition (EMT). However, the significance of EMT in cancer metastasis has been controversial, and the exact fates and functions of EMT cancer cells in vivo remain inadequately understood. Here, we tracked epithelial cancer cells that underwent inducible or spontaneous EMT in various tumor transplantation models. Unlike epithelial cells, the majority of EMT cancer cells were specifically located in the perivascular space and closely associated with blood vessels. EMT markedly activated multiple pericyte markers in carcinoma cells, in particular PDGFR-β and N-cadherin, which enabled EMT cells to be chemoattracted towards and physically interact with endothelium. In tumor xenografts generated from carcinoma cells that were prone to spontaneous EMT, a substantial fraction of the pericytes associated with tumor vasculature were derived from EMT cancer cells. Depletion of such EMT cells in transplanted tumors diminished pericyte coverage, impaired vascular integrity, and attenuated tumor growth. These findings suggest that EMT confers key pericyte attributes on cancer cells. The resulting EMT cells phenotypically and functionally resemble pericytes and are indispensable for vascular stabilization and sustained tumor growth. This study thus proposes a previously unrecognized role for EMT in cancer.
Anitha K. Shenoy, Yue Jin, Huacheng Luo, Ming Tang, Christine Pampo, Rong Shao, Dietmar W. Siemann, Lizi Wu, Coy D. Heldermon, Brian K. Law, Lung-Ji Chang, Jianrong Lu
Tumor-associated macrophages (TAMs) can influence ovarian cancer growth, migration, and metastasis, but the detailed mechanisms underlying ovarian cancer metastasis remain unclear. Here, we have shown a strong correlation between TAM-associated spheroids and the clinical pathology of ovarian cancer. Further, we have determined that TAMs promote spheroid formation and tumor growth at early stages of transcoelomic metastasis in an established mouse model for epithelial ovarian cancer. M2 macrophage–like TAMs were localized in the center of spheroids and secreted EGF, which upregulated αMβ2 integrin on TAMs and ICAM-1 on tumor cells to promote association between tumor cells and TAM. Moreover, EGF secreted by TAMs activated EGFR on tumor cells, which in turn upregulated VEGF/VEGFR signaling in surrounding tumor cells to support tumor cell proliferation and migration. Pharmacological blockade of EGFR or antibody neutralization of ICAM-1 in TAMs blunted spheroid formation and ovarian cancer progression in mouse models. These findings suggest that EGF secreted from TAMs plays a critical role in promoting early transcoelomic metastasis of ovarian cancer. As transcoelomic metastasis is also associated with many other cancers, such as pancreatic and colon cancers, our findings uncover a mechanism for TAM-mediated spheroid formation and provide a potential target for the treatment of ovarian cancer and other transcoelomic metastatic cancers.
Mingzhu Yin, Xia Li, Shu Tan, Huanjiao Jenny Zhou, Weidong Ji, Stefania Bellone, Xiaocao Xu, Haifeng Zhang, Alessandro D. Santin, Ge Lou, Wang Min
The intratumoral microenvironment, or stroma, is of major importance in the pathobiology of pancreatic ductal adenocarcinoma (PDA), and specific conditions in the stroma may promote increased cancer aggressiveness. We hypothesized that this heterogeneous and evolving compartment drastically influences tumor cell abilities, which in turn influences PDA aggressiveness through crosstalk that is mediated by extracellular vesicles (EVs). Here, we have analyzed the PDA proteomic stromal signature and identified a contribution of the annexin A6/LDL receptor-related protein 1/thrombospondin 1 (ANXA6/LRP1/TSP1) complex in tumor cell crosstalk. Formation of the ANXA6/LRP1/TSP1 complex was restricted to cancer-associated fibroblasts (CAFs) and required physiopathologic culture conditions that improved tumor cell survival and migration. Increased PDA aggressiveness was dependent on tumor cell–mediated uptake of CAF-derived ANXA6+ EVs carrying the ANXA6/LRP1/TSP1 complex. Depletion of ANXA6 in CAFs impaired complex formation and subsequently impaired PDA and metastasis occurrence, while injection of CAF-derived ANXA6+ EVs enhanced tumorigenesis. We found that the presence of ANXA6+ EVs in serum was restricted to PDA patients and represents a potential biomarker for PDA grade. These findings suggest that CAF–tumor cell crosstalk supported by ANXA6+ EVs is predictive of PDA aggressiveness, highlighting a therapeutic target and potential biomarker for PDA.
Julie Leca, Sébastien Martinez, Sophie Lac, Jérémy Nigri, Véronique Secq, Marion Rubis, Christian Bressy, Arnauld Sergé, Marie-Noelle Lavaut, Nelson Dusetti, Céline Loncle, Julie Roques, Daniel Pietrasz, Corinne Bousquet, Stéphane Garcia, Samuel Granjeaud, Mehdi Ouaissi, Jean Baptiste Bachet, Christine Brun, Juan L. Iovanna, Pascale Zimmermann, Sophie Vasseur, Richard Tomasini
Radioiodide (RAI) therapy of thyroid cancer exploits the relatively selective ability of thyroid cells to transport and accumulate iodide. Iodide uptake requires expression of critical genes that are involved in various steps of thyroid hormone biosynthesis. ERK signaling, which is markedly increased in thyroid cancer cells driven by oncogenic
James Nagarajah, Mina Le, Jeffrey A. Knauf, Giuseppe Ferrandino, Cristina Montero-Conde, Nagavarakishore Pillarsetty, Alexander Bolaender, Christopher Irwin, Gnana Prakasam Krishnamoorthy, Mahesh Saqcena, Steven M. Larson, Alan L. Ho, Venkatraman Seshan, Nobuya Ishii, Nancy Carrasco, Neal Rosen, Wolfgang A. Weber, James A. Fagin
Transcriptional reactivation of telomerase reverse transcriptase (TERT) reconstitutes telomerase activity in the majority of human cancers. Here, we found that ectopic TERT expression increases cell proliferation, while acute reductions in TERT levels lead to a dramatic loss of proliferation without any change in telomere length, suggesting that the effects of TERT could be telomere independent. We observed that TERT determines the growth rate of cancer cells by directly regulating global protein synthesis independently of its catalytic activity. Genome-wide TERT binding across 5 cancer cell lines and 2 embryonic stem cell lines revealed that endogenous TERT, driven by mutant promoters or oncogenes, directly associates with the RNA polymerase III (pol III) subunit RPC32 and enhances its recruitment to chromatin, resulting in increased RNA pol III occupancy and tRNA expression in cancers. TERT-deficient mice displayed marked delays in polyomavirus middle T oncogene–induced (PyMT-induced) mammary tumorigenesis, increased survival, and reductions in tRNA levels. Ectopic expression of either RPC32 or TERT restored tRNA levels and proliferation defects in TERT-depleted cells. Finally, we determined that levels of TERT and tRNA correlated in breast and liver cancer samples. Together, these data suggest the existence of a unifying mechanism by which TERT enhances translation in cells to regulate cancer cell proliferation.
Ekta Khattar, Pavanish Kumar, Chia Yi Liu, Semih Can Akıncılar, Anandhkumar Raju, Manikandan Lakshmanan, Julien Jean Pierre Maury, Yu Qiang, Shang Li, Ern Yu Tan, Kam M. Hui, Ming Shi, Yuin Han Loh, Vinay Tergaonkar
Triple-negative breast cancer (TNBC) includes basal-like and claudin-low subtypes for which no specific treatment is currently available. Although the retinoblastoma tumor-suppressor gene (
Robert A. Jones, Tyler J. Robinson, Jeff C. Liu, Mariusz Shrestha, Veronique Voisin, YoungJun Ju, Philip E.D. Chung, Giovanna Pellecchia, Victoria L. Fell, SooIn Bae, Lakshmi Muthuswamy, Alessandro Datti, Sean E. Egan, Zhe Jiang, Gustavo Leone, Gary D. Bader, Aaron Schimmer, Eldad Zacksenhaus
Adil I. Daud, Kimberly Loo, Mariela L. Pauli, Robert Sanchez-Rodriguez, Priscila Munoz Sandoval, Keyon Taravati, Katy Tsai, Adi Nosrati, Lorenzo Nardo, Michael D. Alvarado, Alain P. Algazi, Miguel H. Pampaloni, Iryna V. Lobach, Jimmy Hwang, Robert H. Pierce, Iris K. Gratz, Matthew F. Krummel, Michael D. Rosenblum
Increased expression of zinc finger E-box binding homeobox 1 (ZEB1) is associated with tumor grade and metastasis in lung cancer, likely due to its role as a transcription factor in epithelial-to-mesenchymal transition (EMT). Here, we modeled malignant transformation in human bronchial epithelial cells (HBECs) and determined that EMT and ZEB1 expression are early, critical events in lung cancer pathogenesis. Specific oncogenic mutations in TP53 and KRAS were required for HBECs to engage EMT machinery in response to microenvironmental (serum/TGF-β) or oncogenetic (MYC) factors. Both TGF-β– and MYC-induced EMT required ZEB1, but engaged distinct TGF-β–dependent and vitamin D receptor–dependent (VDR-dependent) pathways, respectively. Functionally, we found that ZEB1 causally promotes malignant progression of HBECs and tumorigenicity, invasion, and metastases in non–small cell lung cancer (NSCLC) lines. Mechanistically, ZEB1 expression in HBECs directly repressed epithelial splicing regulatory protein 1 (ESRP1), leading to increased expression of a mesenchymal splice variant of CD44 and a more invasive phenotype. In addition,
Jill E. Larsen, Vaishnavi Nathan, Jihan K. Osborne, Rebecca K. Farrow, Dhruba Deb, James P. Sullivan, Patrick D. Dospoy, Alexander Augustyn, Suzie K. Hight, Mitsuo Sato, Luc Girard, Carmen Behrens, Ignacio I. Wistuba, Adi F. Gazdar, Nicholas K. Hayward, John D. Minna
Diffuse large B cell lymphomas (DLBCLs) arise from proliferating B cells transiting different stages of the germinal center reaction. In activated B cell DLBCLs (ABC-DLBCLs), a class of DLBCLs that respond poorly to current therapies, chromosomal translocations and amplification lead to constitutive expression of the B cell lymphoma 6 (
Mariano G. Cardenas, Wenbo Yu, Wendy Beguelin, Matthew R. Teater, Huimin Geng, Rebecca L. Goldstein, Erin Oswald, Katerina Hatzi, Shao-Ning Yang, Joanna Cohen, Rita Shaknovich, Kenno Vanommeslaeghe, Huimin Cheng, Dongdong Liang, Hyo Je Cho, Joshua Abbott, Wayne Tam, Wei Du, John P. Leonard, Olivier Elemento, Leandro Cerchietti, Tomasz Cierpicki, Fengtian Xue, Alexander D. MacKerell Jr., Ari M. Melnick
Genomic studies have linked mTORC1 pathway–activating mutations with exceptional response to treatment with allosteric inhibitors of mTORC1 called rapalogs. Rapalogs are approved for selected cancer types, including kidney and breast cancers. Here, we used sequencing data from 22 human kidney cancer cases to identify the activating mechanisms conferred by mTOR mutations observed in human cancers and advance precision therapeutics. mTOR mutations that clustered in focal adhesion kinase targeting domain (FAT) and kinase domains enhanced mTORC1 kinase activity, decreased nutrient reliance, and increased cell size. We identified 3 distinct mechanisms of hyperactivation, including reduced binding to DEP domain–containing MTOR-interacting protein (DEPTOR), resistance to regulatory associated protein of mTOR–mediated (RAPTOR-mediated) suppression, and altered kinase kinetics. Of the 28 mTOR double mutants, activating mutations could be divided into 6 complementation groups, resulting in synergistic Rag- and Ras homolog enriched in brain–independent (RHEB-independent) mTORC1 activation. mTOR mutants were resistant to DNA damage–inducible transcript 1–mediated (REDD1-mediated) inhibition, confirming that activating mutations can bypass the negative feedback pathway formed between HIF1 and mTORC1 in the absence of von Hippel–Lindau (VHL) tumor suppressor expression. Moreover, VHL-deficient cells that expressed activating mTOR mutants grew tumors that were sensitive to rapamycin treatment. These data may explain the high incidence of mTOR mutations observed in clear cell kidney cancer, where VHL loss and HIF activation is pathognomonic. Our study provides mechanistic and therapeutic insights concerning mTOR mutations in human diseases.
Jianing Xu, Can G. Pham, Steven K. Albanese, Yiyu Dong, Toshinao Oyama, Chung-Han Lee, Vanessa Rodrik-Outmezguine, Zhan Yao, Song Han, David Chen, Daniel L. Parton, John D. Chodera, Neal Rosen, Emily H. Cheng, James J. Hsieh