Argonaute 2 modulates EGFR-RAS signaling to promote mutant HRAS and NRAS-driven malignancies.

Activating mutations in RAS GTPases drive nearly 30% of all human cancers. Our prior work described an essential role for Argonaute 2 (AGO2), of the RNA-induced silencing complex, in mutant KRAS-driven cancers. Here, we identified a novel endogenous interaction between AGO2 and RAS in both wild-type (WT) and mutant HRAS/NRAS cells. This interaction was regulated through EGFR-mediated phosphorylation of Y393-AGO2, and utilizing molecular dynamic simulation, we identified a conformational change in pY393-AGO2 protein structure leading to disruption of the RAS binding site. Knockdown of AGO2 led to a profound decrease in proliferation of mutant HRAS/NRAS-driven cell lines but not WT RAS cells. These cells demonstrated oncogene-induced senescence (OIS) as evidenced by ß-galactosidase staining and induction of multiple downstream senescence effectors. Mechanistically, we discovered that the senescent phenotype was mediated via induction of reactive oxygen species. Intriguingly, we further identified that loss of AGO2 promoted a novel feed forward pathway leading to inhibition of the PTP1B phosphatase and activation of EGFR-MAPK signaling, consequently resulting in OIS. Taken together, our study demonstrates that the EGFR-AGO2-RAS signaling axis is essential for maintaining mutant HRAS and NRAS-driven malignancies.

Biochemical characterization of the interaction between KRAS and Argonaute 2.

Oncogenic mutations in KRAS result in a constitutively active, GTP-bound form that in turn activates many proliferative pathways. However, because of its compact and simple architecture, directly targeting KRAS with small molecule drugs has been challenging. Another approach is to identify targetable proteins that interact with KRAS. Argonaute 2 (AGO2) was recently identified as a protein that facilitates RAS-driven oncogenesis. Whereas previous studies described the in vivo effect of AGO2 on cancer progression in cells harboring mutated KRAS, here we sought to examine their direct interaction using purified proteins. We show that full length AGO2 co-immunoprecipitates with KRAS using purified components, however, a complex between FL AGO2 and KRAS could not be isolated. We also generated a smaller N-terminal fragment of AGO2 (NtAGO2) which is believed to represent the primary binding site of KRAS. A complex with NtAGO2 could be detected via ion-mobility mass spectrometry and size exclusion chromatography. However, the data suggest that the interaction of KRAS with purified AGO2 (NtAGO2 or FL AGO2) is weak and likely requires additional cellular components or proteo-forms of AGO2 that are not readily available in our purified assay systems. Future studies are needed to determine what conformation or modifications of AGO2 are necessary to enrich KRAS association and regulate its activities.

An essential role for Argonaute 2 in EGFR-KRAS signaling in pancreatic cancer development.

Both KRAS and EGFR are essential mediators of pancreatic cancer development and interact with Argonaute 2 (AGO2) to perturb its function. Here, in a mouse model of mutant KRAS-driven pancreatic cancer, loss of AGO2 allows precursor lesion (PanIN) formation yet prevents progression to pancreatic ductal adenocarcinoma (PDAC). Precursor lesions with AGO2 ablation undergo oncogene-induced senescence with altered microRNA expression and EGFR/RAS signaling, bypassed by loss of p53. In mouse and human pancreatic tissues, PDAC progression is associated with increased plasma membrane localization of RAS/AGO2. Furthermore, phosphorylation of AGO2Y393 disrupts both the wild-type and oncogenic KRAS-AGO2 interaction, albeit under different conditions. ARS-1620 (G12C-specific inhibitor) disrupts the KRASG12C-AGO2 interaction, suggesting that the interaction is targetable. Altogether, our study supports a biphasic model of pancreatic cancer development: an AGO2-independent early phase of PanIN formation reliant on EGFR-RAS signaling, and an AGO2-dependent phase wherein the mutant KRAS-AGO2 interaction is critical for PDAC progression.

The lncRNA landscape of breast cancer reveals a role for DSCAM-AS1 in breast cancer progression.

Molecular classification of cancers into subtypes has resulted in an advance in our understanding of tumour biology and treatment response across multiple tumour types. However, to date, cancer profiling has largely focused on protein-coding genes, which comprise <1% of the genome. Here we leverage a compendium of 58,648 long noncoding RNAs (lncRNAs) to subtype 947 breast cancer samples. We show that lncRNA-based profiling categorizes breast tumours by their known molecular subtypes in breast cancer. We identify a cohort of breast cancer-associated and oestrogen-regulated lncRNAs, and investigate the role of the top prioritized oestrogen receptor (ER)-regulated lncRNA, DSCAM-AS1. We demonstrate that DSCAM-AS1 mediates tumour progression and tamoxifen resistance and identify hnRNPL as an interacting protein involved in the mechanism of DSCAM-AS1 action. By highlighting the role of DSCAM-AS1 in breast cancer biology and treatment resistance, this study provides insight into the potential clinical implications of lncRNAs in breast cancer.

Eradicating acute myeloid leukemia in a Mll(PTD/wt):Flt3(ITD/wt) murine model: a path to novel therapeutic approaches for human disease.

The coexpression of the MLL partial tandem duplication (PTD) and the FLT3 internal tandem duplication (ITD) mutations associate with a poor outcome in cytogenetically normal acute myeloid leukemia (AML). In mice, a double knock-in (dKI) of Mll(PTD/wt) and Flt3(ITD/wt) mutations induces spontaneous AML with an increase in DNA methyltransferases (Dnmt1, 3a, and 3b) and global DNA methylation index, thereby recapitulating its human AML counterpart. We determined that a regulator of Dnmts, miR-29b, is downregulated in bone marrow of dKI AML mice. Bortezomib exerted a dose-dependent increase in miR-29b expression in AML blasts ex vivo, followed by decreased Dnmts, reduced proliferation, and increased apoptosis. In vivo, bortezomib was not active against dKI AML, yet liposomal-encapsulated bortezomib, as a single agent, reversed downregulation of miR-29b in vivo and induced a long-term (90-day) disease-free remission in 80% of dKI AML mice that exhibited high leukemic burden at the start of therapy, yet showed no signs of relapse at autopsy. Taken together, these data support that liposomal bortezomib, as a single agent, eradicates Mll(PTD/wt):Flt3(ITD/wt) AML in mouse and may represent a powerful and potentially curative approach to high-risk human disease.

Mll partial tandem duplication and Flt3 internal tandem duplication in a double knock-in mouse recapitulates features of counterpart human acute myeloid leukemias.

The MLL-partial tandem duplication (PTD) associates with high-risk cytogenetically normal acute myeloid leukemia (AML). Concurrent presence of FLT3-internal tandem duplication (ITD) is observed in 25% of patients with MLL-PTD AML. However, mice expressing either Mll-PTD or Flt3-ITD do not develop AML, suggesting that 2 mutations are necessary for the AML phenotype. Thus, we generated a mouse expressing both Mll-PTD and Flt3-ITD. Mll(PTD/WT):Flt3(ITD/WT) mice developed acute leukemia with 100% penetrance, at a median of 49 weeks. As in human MLL-PTD and/or the FLT3-ITD AML, mouse blasts exhibited normal cytogenetics, decreased Mll-WT-to-Mll-PTD ratio, loss of the Flt3-WT allele, and increased total Flt3. Highlighting the adverse impact of FLT3-ITD dosage on patient survival, mice with homozygous Flt3-ITD alleles, Mll(PTD/WT):Flt3(ITD/ITD), demonstrated a nearly 30-week reduction in latency to overt AML. Here we demonstrate, for the first time, that Mll-PTD contributes to leukemogenesis as a gain-of-function mutation and describe a novel murine model closely recapitulating human AML.