Identification of the receptor tyrosine kinases (RTKs)-oriented functional targets of miR-206 by an antibody-based protein array

A low-molecular-weight compound exerts anticancer activity against breast and lung cancers by disrupting EGFR/Eps8 complex formation

BACKGROUND

Epidermal growth factor receptor (EGFR) and epidermal growth factor receptor pathway substrate 8 (Eps8) have been widely reported to be expressed in various tumors. Eps8 is an important active kinase substrate of EGFR that directly binds to the juxtamembrane (JXM) domain of EGFR to form an EGFR/Eps8 complex. The EGFR/Eps8 complex is involved in regulating cancer progression and might be an ideal target for antitumor therapy. This study focused on the screening of small-molecule inhibitors that target the EGFR/Eps8 complex in breast cancer and non-small cell lung cancer (NSCLC).

METHODS

In silico virtual screening was used to identify small-molecule EGFR/Eps8 complex inhibitors. These compounds were screened for the inhibition of A549 and BT549 cell viability. The direct interaction between EGFR and Eps8 was measured using coimmunoprecipitation (CoIP) and JXM domain replacement assays. The antitumor effects of the inhibitors were analyzed in cancer cells and xenograft models. An acute toxicity study of EE02 was performed in a mouse model. In addition, the effect of the EE02 inhibitor on the protein expression of elements downstream of the EGFR/Eps8 complex was determined by western blotting and protein chip assays.

RESULTS

In this study of nearly 390,000 compounds screened by virtual database screening, the top 29 compounds were identified as candidate small-molecule EGFR/Eps8 complex inhibitors and evaluated by using cell-based assays. The compound EE02 was identified as the best match to our selection criteria. Further investigation demonstrated that EE02 directly bound to the JXM domain of EGFR and disrupted EGFR/Eps8 complex formation. EE02 selectively suppressed growth and induced apoptosis in EGFR-positive and Eps8-positive breast cancer and NSCLC cells. More importantly, the PI3K/Akt/mTOR and MAPK/Erk pathways downstream of the EGFR/Eps8 complex were suppressed by EE02. In addition, the suppressive effect of EE02 on tumor growth in vivo was comparable to that of erlotinib at the same dose.

CONCLUSIONS

We identified EE02 as an EGFR/Eps8 complex inhibitor that demonstrated promising antitumor effects in breast cancer and NSCLC. Our data suggest that the EGFR/Eps8 complex offers a novel cancer drug target.

The oncomir face of microRNA-206: A permanent miR-206 transfection study

MiR-206 is a remarkable miRNA because it functions as a suppressor miRNA in rhabdomyosarcoma while at the same time, as previously showed, it can act as an oncomiRNA in SMARCB1 immunonegative soft tissue sarcomas. The aim of this study was to investigate the effect of miR-206 on its several target genes in various human tumorous and normal cell lines. In the current work, we created miR-206-overexpressing cell lines (HT-1080, Caco2, iASC, and SS-iASC) using permanent transfection. mRNA expression of the target genes of miR-206 (SMARCB1, ACTL6A, CCND1, POLA1, NOTCH3, MET, and G6PD) and SMARCB1 protein expression were examined with quantitative real-time polymerase chain reaction, immunoblotting, immunocytochemistry, and flow cytometry. MiRNA inhibition was used to validate our results. We found a diverse silencing effect of miR-206 on its target genes. While an overall tendency of downregulation was noted, expression profiles of individual cell lines showed large variability. Only CCND1 and MET were consistently downregulated. MiR-206 had an antiproliferative effect on a normal human fibroblast cell line. A strong silencing effect of SMARCB1 in miR-206 transfected SS-iASC was most likely caused by the synergic influence of the SS18-SSX1 fusion protein and miR-206. In the same cell line, a moderate decrease of SMARCB1 protein expression could be observed with immunocytochemistry and flow cytometry. In the most comprehensive analysis of miR-206 effects so far, a modest but significant downregulation of miR-206 targets on the mRNA level was confirmed across all cell lines. However, the variability of the effect shows that the action of this miRNA is largely cell context-dependent. Our results also support the conception that the oncomiR effect of miR-206 on SMARCB1 plays an important but not exclusive role in SMARCB1 immunonegative soft tissue sarcomas so it can be considered important in planning the targeted therapy of these tumors in the future. Impact statement Mir-206 is a very unique microRNA because it can act as a suppressor miRNA or as an oncomiRNA depending on the tumor tissue. In SMARCB1 negative soft tissue sarcomas miR-206 is overexpressed, so thus in epithelioid and synovial sarcomas it functions as an oncomiRNA. MiR-206 has diverse silencing effects on its target genes. We found that the action of miR-206 is largely cell context dependent. The oncomiR role of miR-206 is crucial but not exclusive in SMARCB1 negative soft tissue sarcomas and miR-206 has an antiproliferative effect on a normal human fibroblast cell line. Expressions of miR-206 targets observed in tumors can only be reproduced in the corresponding tumorous cell lines. This is the first study which examined the permanent effect of miR-206 on its target genes in normal, tumor, and genetically engineered cell lines.

Tiny giants of gene regulation: experimental strategies for microRNA functional studies

The discovery over two decades ago of short regulatory microRNAs (miRNAs) has led to the inception of a vast biomedical research field dedicated to understanding these powerful orchestrators of gene expression. Here we aim to provide a comprehensive overview of the methods and techniques underpinning the experimental pipeline employed for exploratory miRNA studies in animals. Some of the greatest challenges in this field have been uncovering the identity of miRNA-target interactions and deciphering their significance with regard to particular physiological or pathological processes. These endeavors relied almost exclusively on the development of powerful research tools encompassing novel bioinformatics pipelines, high-throughput target identification platforms, and functional target validation methodologies. Thus, in an unparalleled manner, the biomedical technology revolution unceasingly enhanced and refined our ability to dissect miRNA regulatory networks and understand their roles in vivo in the context of cells and organisms. Recurring motifs of target recognition have led to the creation of a large number of multifactorial bioinformatics analysis platforms, which have proved instrumental in guiding experimental miRNA studies. Subsequently, the need for discovery of miRNA-target binding events in vivo drove the emergence of a slew of high-throughput multiplex strategies, which now provide a viable prospect for elucidating genome-wide miRNA-target binding maps in a variety of cell types and tissues. Finally, deciphering the functional relevance of miRNA post-transcriptional gene silencing under physiological conditions, prompted the evolution of a host of technologies enabling systemic manipulation of miRNA homeostasis as well as high-precision interference with their direct, endogenous targets. For further resources related to this article, please visit the WIREs website.