Inhibitor of Differentiation-1 Sustains Mutant KRAS-Driven Progression, Maintenance, and Metastasis of Lung Adenocarcinoma via Regulation of a FOSL1 Network

The prognostic impact of pathogenic stromal cell-associated genes in lung adenocarcinoma

BACKGROUND

Lung adenocarcinoma (LUAD) stands as the most prevalent subtype among lung cancers. Interactions between stromal and cancer cells influence tumor growth, invasion, and metastasis. However, the regulatory mechanisms of stromal cells in the lung adenocarcinoma tumor microenvironment remain unclear. This study seeks to elucidate the regulatory connections among critical pathogenic genes and their associated expression variations within distinct stromal cell subtypes.

METHOD

Analysis and investigation were conducted on a total of 114,019 single-cell RNA data and 346 The Cancer Genome Atlas (TCGA) LUAD-related samples using bioinformatics and statistical algorithms. Differential gene expression analysis was performed for tumor samples and controls, followed by Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Differential genes between stromal cells and other cell clusters were identified and intersected with the differential genes from TCGA. We employed a combination of LASSO regression and multivariable Cox regression to identify the ultimate set of pathogenic gene. Survival models were trained to predict the relationship between patient survival and these pathogenic genes. Analysis of transcription factor (TF) cell specificity and pseudotime trajectories within stromal cell subpopulations revealed that vascular endothelial cells (ECs) and matrix cancer-associated fibroblasts (CAFs) are key in regulation of the prognosis-associated genes CAV2, COL1A1, TIMP1, ETS2, AKAP12, ID1 and COL1A2.

RESULTS

Seven pathogenic genes associated with LUAD in stromal cells were identified and used to develop a survival model. High expression of these genes is linked to a greater risk of poor survival. Stromal cells were categorized into eight subtypes and one unannotated cluster. Mesothelial cells, vascular endothelial cells (ECs), and matrix cancer-associated fibroblasts (CAFs) showed cell-specific regulation of the pathogenic genes.

CONCLUSIONS

The seven disease-causing genes in vascular ECs and matrix CAFs can be used to detect the survival status of LUAD patients, providing new directions for future targeted drug design.

Evolving landscape of treatments targeting the microenvironment of liver metastases in non-small cell lung cancer

ABSTRACT

Liver metastases (LMs) are common in lung cancer. Despite substantial advances in diagnosis and treatment, the survival rate of patients with LM remains low as the immune-suppressive microenvironment of the liver allows tumor cells to evade the immune system. The impact of LMs on the outcomes of immune checkpoint inhibitors in patients with solid tumors has been the main focus of recent translational and clinical research. Growing evidence indicates that the hepatic microenvironment delivers paracrine and autocrine signals from non-parenchymal and parenchymal cells. Overall, these microenvironments create pre- and post-metastatic conditions for the progression of LMs. Herein, we reviewed the epidemiology, physiology, pathology and immunology, of LMs associated with non-small cell lung cancer and the role and potential targets of the liver microenvironment in LM in each phase of metastasis. Additionally, we reviewed the current treatment strategies and challenges that should be overcome in preclinical and clinical investigations. These approaches target liver elements as the basis for future clinical trials, including combinatorial interventions reported to resolve hepatic immune suppression, such as immunotherapy plus chemotherapy, immunotherapy plus radiotherapy, immunotherapy plus anti-angiogenesis therapy, and surgical resection.

Trametinib sensitizes KRAS-mutant lung adenocarcinoma tumors to PD-1/PD-L1 axis blockade via Id1 downregulation

BACKGROUND

The identification of novel therapeutic strategies to overcome resistance to the MEK inhibitor trametinib in mutant KRAS lung adenocarcinoma (LUAD) is a challenge. This study analyzes the effects of trametinib on Id1 protein, a key factor involved in the KRAS oncogenic pathway, and investigates the role of Id1 in the acquired resistance to trametinib as well as the synergistic anticancer effect of trametinib combined with immunotherapy in KRAS-mutant LUAD.

METHODS

We evaluated the effects of trametinib on KRAS-mutant LUAD by Western blot, RNA-seq and different syngeneic mouse models. Genetic modulation of Id1 expression was performed in KRAS-mutant LUAD cells by lentiviral or retroviral transductions of specific vectors. Cell viability was assessed by cell proliferation and colony formation assays. PD-L1 expression and apoptosis were measured by flow cytometry. The anti-tumor efficacy of the combined treatment with trametinib and PD-1 blockade was investigated in KRAS-mutant LUAD mouse models, and the effects on the tumor immune infiltrate were analyzed by flow cytometry and immunohistochemistry.

RESULTS

We found that trametinib activates the proteasome-ubiquitin system to downregulate Id1 in KRAS-mutant LUAD tumors. Moreover, we found that Id1 plays a major role in the acquired resistance to trametinib treatment in KRAS-mutant LUAD cells. Using two preclinical syngeneic KRAS-mutant LUAD mouse models, we found that trametinib synergizes with PD-1/PD-L1 blockade to hamper lung cancer progression and increase survival. This anti-tumor activity depended on trametinib-mediated Id1 reduction and was associated with a less immunosuppressive tumor microenvironment and increased PD-L1 expression on tumor cells.

CONCLUSIONS

Our data demonstrate that Id1 expression is involved in the resistance to trametinib and in the synergistic effect of trametinib with anti-PD-1 therapy in KRAS-mutant LUAD tumors. These findings suggest a potential therapeutic approach for immunotherapy-refractory KRAS-mutant lung cancers.

Pathway-driven analysis of synthetic lethal interactions in cancer using perturbation screens

Synthetic lethality offers a promising approach for developing effective therapeutic interventions in cancer when direct targeting of driver genes is impractical. In this study, we comprehensively analyzed large-scale CRISPR, shRNA, and PRISM screens to identify potential synthetic lethal (SL) interactions in pan-cancer and 12 individual cancer types, using a new computational framework that leverages the biological function and signaling pathway information of key driver genes to mitigate the confounding effects of background genetic alterations in different cancer cell lines. This approach has successfully identified several putative SL interactions, including KRAS-MAP3K2 and APC-TCF7L2 in pan cancer, and CCND1-METTL1, TP53-FRS3, SMO-MDM2, and CCNE1-MTOR in liver, blood, skin, and gastric cancers, respectively. In addition, we proposed several FDA-approved cancer-targeted drugs for various cancer types through PRISM drug screens, such as cabazitaxel for VHL-mutated kidney cancer and alectinib for lung cancer with NRAS or KRAS mutations. Leveraging pathway information can enhance the concordance of shRNA and CRISPR screens and provide clinically relevant findings such as the potential efficacy of dasatinib, an inhibitor of SRC, for colorectal cancer patients with mutations in the WNT signaling pathway. These analyses revealed that taking signaling pathway information into account results in the identification of more promising SL interactions.

A novel [89Zr]-anti-PD-1-PET-CT to assess response to PD-1/PD-L1 blockade in lung cancer

Background

Harnessing the anti-tumor immune system response by targeting the program cell death protein (PD-1) and program cell death ligand protein (PD-L1) axis has been a major breakthrough in non-small cell lung cancer (NSCLC) therapy. Nonetheless, conventional imaging tools cannot accurately assess response in immunotherapy-treated patients. Using a lung cancer syngeneic mouse model responder to immunotherapy, we aimed to demonstrate that [89Zr]-anti-PD-1 immuno-PET is a safe and feasible imaging modality to assess the response to PD-1/PD-L1 blockade in NSCLC.

Materials and methods

A syngeneic mouse model responder to anti-PD-1 therapy was used. Tumor growth and response to PD-1 blockade were monitored by conventional 2-deoxy-2-[18F]fluoro-D-glucose ([18F]-FDG) PET scans. Additionally, tumor lymphocyte infiltration was analyzed by the use of an [89Zr]-labeled anti-PD-1 antibody and measured as 89Zr tumor uptake.

Results

Conventional [18F]-FDG-PET scans failed to detect the antitumor activity exerted by anti-PD-1 therapy. However, [89Zr]-anti-PD-1 uptake was substantially higher in mice that responded to PD-1 blockade. The analysis of tumor-infiltrating immune cell populations and interleukins demonstrated an increased anti-tumor effect elicited by activation of effector immune cells in PD-1-responder mice. Interestingly, a positive correlation between [89Zr]-anti-PD-1 uptake and the proportion of tumor-infiltrating lymphocytes (TILs) was found (Cor = 0.8; p = 0.001).

Conclusion

Our data may support the clinical implementation of immuno-PET as a promising novel imaging tool to predict and assess the response of PD-1/PD-L1 inhibitors in patients with NSCLC.

The Fra-1/AP-1 Oncoprotein: From the "Undruggable" Transcription Factor to Therapeutic Targeting

The genetic and epigenetic changes affecting transcription factors, coactivators, and chromatin modifiers are key determinants of the hallmarks of cancer. The acquired dependence on oncogenic transcriptional regulators, representing a major determinant of cancer cell vulnerability, points to transcription factors as ideal therapeutic targets. However, given the unavailability of catalytic activities or binding pockets for small-molecule inhibitors, transcription factors are generally regarded as undruggable proteins. Among components of the AP-1 complex, the FOS-family transcription factor Fra-1, encoded by FOSL1, has emerged as a prominent therapeutic target. Fra-1 is overexpressed in most solid tumors, in response to the BRAF-MAPK, Wnt-beta-catenin, Hippo-YAP, IL-6-Stat3, and other major oncogenic pathways. In vitro functional analyses, validated in onco-mouse models and corroborated by prognostic correlations, show that Fra-1-containing dimers control tumor growth and disease progression. Fra-1 participates in key mechanisms of cancer cell invasion, Epithelial-to-Mesenchymal Transition, and metastatic spreading, by driving the expression of EMT-inducing transcription factors, cytokines, and microRNAs. Here we survey various strategies aimed at inhibiting tumor growth, metastatic dissemination, and drug resistance by interfering with Fra-1 expression, stability, and transcriptional activity. We summarize several tools aimed at the design and tumor-specific delivery of Fra-1/AP-1-specific drugs. Along with RNA-based therapeutics targeting the FOSL1 gene, its mRNA, or cognate regulatory circRNAs, we will examine the exploitation of blocking peptides, small molecule inhibitors, and innovative Fra-1 protein degraders. We also consider the possible caveats concerning Fra-1 inhibition in specific therapeutic contexts. Finally, we discuss a recent suicide gene therapy-based approach, aimed at selectively killing the Fra-1-overexpressing neoplastic cells.

ERK inhibitor ASN007 effectively overcomes acquired resistance to EGFR inhibitor in non-small cell lung cancer

The emergence of acquired resistance limits the long-term efficacy of EGFR tyrosine kinase inhibitors (EGFR TKIs). Thus, development of effective strategies to overcome resistance to EGFR TKI is urgently needed. Multiple mechanisms to reactivate ERK signaling have been successfully demonstrated in acquired resistance models. We found that in EGFR mutant non-small cell lung cancer (NSCLC) patients, acquired resistance to EGFR TKIs was accompanied by increased activation of ERK. Increased ERK activation was also found in in vitro models of acquired EGFR TKI resistance. ASN007 is a potent selective ERK1/2 inhibitor with promising antitumor activity in cancers with BRAF and RAS mutations. ASN007 treatment impeded tumor cell growth and the cell cycle in EGFR TKI-resistant cells. In addition, combination treatment with ASN007 and EGFR TKIs significantly decreased the survival of resistant cells, enhanced induction of apoptosis, and effectively inhibited the growth of erlotinib-resistant xenografts, providing the preclinical rationale for testing combinations of ASN007 and EGFR TKIs in EGFR-mutated NSCLC patients. This study emphasizes the importance of targeting ERK signaling in maintaining the long-term benefits of EGFR TKIs by overcoming acquired resistance.

Emerging noncoding RNAs contained in extracellular vesicles: rising stars as biomarkers in lung cancer liquid biopsy

Lung cancer has a high morbidity and mortality rate, and affected patients have a poor prognosis and low survival. The therapeutic approaches for lung cancer treatment, including surgery, radiotherapy, and chemotherapy, are not completely effective, due to late diagnosis. Although the identification of genetic drivers has contributed to the improvement of lung cancer clinical management, the discovery of new diagnostic and prognostic tools remains a critical issue. Liquid biopsy (LB) represents a minimally invasive approach and practical alternative source to investigate tumor-derived alterations and to facilitate the selection of targeted therapies. LB allows for the testing of different analytes such as circulating tumor cells, extracellular vesicles (EVs), tumor-educated platelets, and cell-free nucleic acids including DNAs, RNAs, and noncoding RNAs (ncRNAs). Several regulatory factors control the key cellular oncogenic pathways involved in cancers. ncRNAs have a wide range of regulatory effects in lung cancers. This review focuses on emerging regulatory ncRNAs, freely circulating in body fluids or shuttled by EVs, such as circular-RNAs, small nucleolar-RNAs, small nuclear-RNAs, and piwi-RNAs, as new biomarkers for early detection, prognosis, and monitoring of therapeutic strategy of lung cancer treatment.

Advances in deubiquitinating enzymes in lung adenocarcinoma

The process of ubiquitination and deubiquitination is widely present in the human body's protein reactions and plays versatile roles in multiple diseases. Deubiquitinating enzymes (DUBs) are significant regulators of this process, which cleave the ubiquitin (Ub) moiety from various substrates and maintain protein stability. Lung adenocarcinoma (LUAD) is the most common type of non-small cell lung cancer (NSCLC) and remains refractory to treatment. To elucidate the mechanism of LUAD and advance new therapeutic targets, we review the latest research progress on DUBs in LUAD. We summarize the biological capabilities of these DUBs and further highlight those DUBs that may serve as anticancer target candidates for precision treatment. We also discuss deubiquitinase inhibitors, which are expected to play a role in targeted LUAD therapy.

SMAD4 represses FOSL1 expression and pancreatic cancer metastatic colonization

Metastasis is a complex and poorly understood process. In pancreatic cancer, loss of the transforming growth factor (TGF)-β/BMP effector SMAD4 is correlated with changes in altered histopathological transitions, metastatic disease, and poor prognosis. In this study, we use isogenic cancer cell lines to identify SMAD4 regulated genes that contribute to the development of metastatic colonization. We perform an in vivo screen identifying FOSL1 as both a SMAD4 target and sufficient to drive colonization to the lung. The targeting of these genes early in treatment may provide a therapeutic benefit.

Id1 and PD-1 Combined Blockade Impairs Tumor Growth and Survival of KRAS-mutant Lung Cancer by Stimulating PD-L1 Expression and Tumor Infiltrating CD8+ T Cells

Simple Summary

Lung adenocarcinoma is the most frequent lung cancer subtype. Many of those adenocarcinomas of the lung are driven by the KRAS gene. Although immunotherapy has significantly improved the clinical outcomes of patients with lung adenocarcinomas, many patients do not benefit from that therapeutic strategy. Id1 is a protein involved in immunosuppression. Here we aimed to test whether a combined blockade of Id1 and PD-1 is able to improve outcomes of mice models with KRAS-driven lung adenocarcinoma.

Abstract

The use of PD-1/PD-L1 checkpoint inhibitors in advanced NSCLC is associated with longer survival. However, many patients do not benefit from PD-1/PD-L1 blockade, largely because of immunosuppression. New immunotherapy-based combinations are under investigation in an attempt to improve outcomes. Id1 (inhibitor of differentiation 1) is involved in immunosuppression. In this study, we explored the potential synergistic effect of the combination of Id1 inhibition and pharmacological PD-L1 blockade in three different syngeneic murine KRAS-mutant lung adenocarcinoma models. TCGA analysis demonstrated a negative and statistically significant correlation between PD-L1 and Id1 expression levels. This observation was confirmed in vitro in human and murine KRAS-driven lung cancer cell lines. In vivo experiments in KRAS-mutant syngeneic and metastatic murine lung adenocarcinoma models showed that the combined blockade targeting Id1 and PD-1 was more effective than each treatment alone in terms of tumor growth impairment and overall survival improvement. Mechanistically, multiplex quantification of CD3⁺/CD4⁺/CD8⁺ T cells and flow cytometry analysis showed that combined therapy favors tumor infiltration by CD8⁺ T cells, whilst in vivo CD8⁺ T cell depletion led to tumor growth restoration. Co-culture assays using CD8⁺ cells and tumor cells showed that T cells present a higher antitumor effect when tumor cells lack Id1 expression. These findings highlight that Id1 blockade may contribute to a significant immune enhancement of antitumor efficacy of PD-1 inhibitors by increasing PD-L1 expression and harnessing tumor infiltration of CD8⁺ T lymphocytes.

DNF: A differential network flow method to identify rewiring drivers for gene regulatory networks

Differential network analysis has become an important approach in identifying driver genes in development and disease. However, most studies capture only local features of the underlying gene-regulatory network topology. These approaches are vulnerable to noise and other changes which mask driver-gene activity. Therefore, methods are urgently needed which can separate the impact of true regulatory elements from stochastic changes and downstream effects. We propose the differential network flow (DNF) method to identify key regulators of progression in development or disease. Given the network representation of consecutive biological states, DNF quantifies the essentiality of each node by differences in the distribution of network flow, which are capable of capturing comprehensive topological differences from local to global feature domains. DNF achieves more accurate driver-gene identification than other state-of-the-art methods when applied to four human datasets from The Cancer Genome Atlas and three single-cell RNA-seq datasets of murine neural and hematopoietic differentiation. Furthermore, we predict key regulators of crosstalk between separate networks underlying both neuronal differentiation and the progression of neurodegenerative disease, among which APP is predicted as a driver gene of neural stem cell differentiation. Our method is a new approach for quantifying the essentiality of genes across networks of different biological states.

Dysregulated Kras/YY1/ZNF322A/Shh transcriptional axis enhances neo-angiogenesis to promote lung cancer progression

Angiogenesis enhances cancer metastasis and progression, however, the roles of transcription regulation in angiogenesis are not fully defined. ZNF322A is an oncogenic zinc-finger transcription factor. Here, we demonstrate a new mechanism of Kras mutation-driven ZNF322A transcriptional activation and elucidate the interplay between ZNF322A and its upstream transcriptional regulators and downstream transcriptional targets in promoting neo-angiogenesis.

Methods: Luciferase activity, RT-qPCR and ChIP-qPCR assays were used to examine transcription regulation in cell models. In vitro and in vivo angiogenesis assays were conducted. Immunohistochemistry, Kaplan-Meier method and multivariate Cox regression assays were performed to examine the clinical correlation in tumor specimens from lung cancer patients.

Results: We validated that Yin Yang 1 (YY1) upregulated ZNF322A expression through targeting its promoter in the context of Kras mutation. Reconstitution experiments by knocking down YY1 under Kras^G13V activation decreased Kras^G13V-promoted cancer cell migration, proliferation and ZNF322A promoter activity. Knockdown of YY1 or ZNF322A attenuated angiogenesis in vitro and in vivo. Notably, we validated that ZNF322A upregulated the expression of sonic hedgehog (Shh) gene which encodes a secreted factor that activates pro-angiogenic responses in endothelial cells. Clinically, ZNF322A protein expression positively correlated with Shh and CD31, an endothelial cell marker, in 133 lung cancer patient samples determined using immunohistochemistry analysis. Notably, patients with concordantly high expression of ZNF322A, Shh and CD31 correlated with poor prognosis.

Conclusions: These findings highlight the mechanism by which dysregulation of Kras/YY1/ZNF322/Shh transcriptional axis enhances neo-angiogenesis and cancer progression in lung cancer. Therapeutic strategies that target Kras/YY1/ZNF322A/Shh signaling axis may provide new insight on targeted therapy for lung cancer patients.

Xanthohumol targets the ERK1/2‑Fra1 signaling axis to reduce cyclin D1 expression and inhibit non‑small cell lung cancer

High expression of cyclin D1 has a crucial role in the maintenance of unlimited cell growth in human cancer cells. The present study indicated that cyclin D1 was overexpressed in human non-small cell lung cancer (NSCLC) tumor tissues and cell lines. Knockout of cyclin D1 suppressed NSCLC cell growth, colony formation and in vivo tumor growth. Of note, the natural product xanthohumol (Xanth) inhibited NSCLC cells via the downregulation of cyclin D1. A further mechanistic study revealed that Xanth suppressed ERK1/2 signaling and reduced the protein levels of FOS-related antigen 1 (Fra1), which eventually inhibited the transcriptional activity of activator protein-1 and decreased the mRNA level of cyclin D1. Furthermore, suppression of ERK1/2 impaired Fra1 phosphorylation and enhanced Xanth-induced Fra1 ubiquitination and degradation. In addition, the S265D mutation compromised Xanth-induced Fra1 degradation. Finally, the in vivo anti-tumor effect of Xanth was validated in a xenograft mouse model. In summary, the present results indicated that targeting ERK1/2-Fra1-cyclin D1 signaling is a promising anti-tumor strategy for NSCLC treatment.

EGFR-PKM2 signaling promotes the metastatic potential of nasopharyngeal carcinoma through induction of FOSL1 and ANTXR2

Nasopharyngeal carcinoma (NPC) is notorious for its aggressiveness and high metastatic potential. NPC patients with distant metastasis have a particularly poor prognosis; however, evaluating metastatic potential by expression profiles of primary tumors is challenging. This study aimed to investigate the association between activation of epidermal growth factor receptor (EGFR) signaling and NPC metastasis and the underlying mechanisms. We found an association between EGFR protein overexpression and intense EGFR immunostaining in NPC samples with advanced tumor node metastasis stage, clinical stage, and distant metastasis in NPC patients. Exogenous EGF stimulates NPC mobility and invasiveness in vitro. Activation of EGFR signaling prompted PKM2 translocation to the nucleus. Silencing either EGFR or PKM2 attenuates NPC cell aggressiveness in vitro and in vivo. Blocking EGFR signaling with cetuximab suppressed NPC cell invasiveness in vitro and metastatic potential in vivo. Comprehensive analyses of transcriptome profiles indicated that the EGFR-PKM2 axis activates a number of novel metastasis promoters, including F3, FOSL1, EPHA2, ANTXR2, and AKR1C2. Finally, we found that the metastasis-promoting function of the EGFR-PKM2 axis is dependent on nuclear PKM2 regulation of the transcription of metastasis-related genes, including FOSL1 and ANTXR2. Our study indicates that EGFR-PKM2 signaling promotes NPC cell invasion and metastasis through induction of FOSL1 and ANTXR2 and identifies EGFR as a promising biomarker for predicting the risk of distant metastasis.

The nuclear oncoprotein Fra-1: a transcription factor knocking on therapeutic applications' door

Among the FOS-related members of the AP-1 dimeric complex, the transcription factor Fra-1, encoded by FOSL1, is crucially involved in human tumor progression and metastasis, thus representing a promising therapeutic target. Here we review the state of the art and discuss the emerging topics and perspectives on FOSL1 and its gene product. First, we summarize the present knowledge on the FOSL1 transcriptional and epigenetic controls, driving Fra-1 accumulation in a variety of human solid tumors. We also present a model on the regulatory interactions between Fra-1, p53, and miRNAs. Then, we outline the multiple roles of Fra-1 posttranslational modifications and transactivation mechanisms of select Fra-1 target genes. In addition to summarizing the Fra-1-dependent gene networks controlling proliferation, survival, and epithelial-mesenchymal transitions (EMT) in multiple cancer cell types, we highlight the roles played by Fra-1 in nonneoplastic cell populations recruited to the tumor microenvironment, and in mouse models of tumorigenesis. Next, we review the prognostic power of the Fra-1-associated gene signatures, and envisage potential strategies aimed at Fra-1 therapeutic inhibition. Finally, we discuss several recent reports showing the emerging roles of Fra-1 in the mechanisms of both resistance and addiction to targeted therapies.

Expression and function of FRA1 protein in tumors

AP-1 is a dimeric complex that is composed of JUN, FOS, ATF and MAF protein families. FOS-related antigen 1 (FRA1) which encoded by FOSL1 gene, belongs to the FOS protein family, and mainly forms an AP-1 complex with the protein of the JUN family to exert an effect. Regulation of FRA1 occurs at levels of transcription and post-translational modification, and phosphorylation is the major post-translational modification. FRA1 is mainly regulated by the mitogen-activated protein kinases signaling pathway and is degraded by ubiquitin-independent proteasomes. FRA1 can affect biological functions, such as tumor proliferation, differentiation, invasion and apoptosis. Studies have demonstrated that FRA1 is abnormally expressed in many tumors and plays a relevant role, but the specific condition varies from the target organs. FRA1 is overexpressed in breast cancer, lung cancer, colorectal cancer, prostate cancer, nasopharyngeal cancer, thyroid cancer and other tumors. However, the expression of FRA1 is decreased in cervical cancer, and the expression of FRA1 in ovarian cancer and oral squamous cell carcinoma is still controversial. In this review, we present a detailed description of the regulatory factors and functions of FRA1, also, the expression of FRA1 in various tumors and its function in relative tumor.

Restoration of mutant K-Ras repressed miR-199b inhibits K-Ras mutant non-small cell lung cancer progression

BACKGROUND

miRNAs play crucial role in the progression of K-Ras-mutated nonsmall cell lung cancer (NSCLC). However, most studies have focused on miRNAs that target K-Ras. Here, we investigated miRNAs regulated by mutant K-Ras and their functions.

METHODS

miRNAs regulated by mutant K-Ras were screened using miRNA arrays. miR-199b expression levels were measured by qRT-PCR. The protein expression levels were measured using Western blot and immunohistochemistry. The effects of miR-199b on NSCLC were examined both in vitro and in vivo by overexpressing or inhibiting miR-199b. DNA methylation was measured by bisulfite sequencing.

RESULTS

An inverse correlation was observed between K-Ras mutation status and miR-199b levels in NSCLC specimens and cell lines. The inhibition of miR-199b stimulated NSCLC growth and metastasis, while restoration of miR-199b suppressed K-Ras mutation-driven lung tumorigenesis as well as K-Ras-mutated NSCLC growth and metastasis. miR-199b inactivated ERK and Akt pathways by targeting K-Ras, KSR2, PIK3R1, Akt1, and Rheb1. Furthermore, we determined that mutant K-Ras inhibits miR-199b expression by increasing miR-199b promoter methylation.

CONCLUSION

Our findings suggest that mutant K-Ras plays an oncogenic role through downregulating miR-199b in NSCLC and that overexpression of miR-199b is a novel strategy for the treatment of K-Ras-mutated NSCLC.