Background & objectives In gastrointestinal stromal tumour (GIST), not only genetic abnormalities are responsible for adverse clinical events, but epigenetic modifications also play a crucial role. MicroRNA (miRNA) dysregulation plays a significant role in carcinogenesis as miRNAs serve as natural silencer for their targets. Our study aimed to explore the miRNAs expression and its association with molecular and histopathological characteristics of GIST. Methods Fifty GIST samples, including 45 formalin fixed paraffin embedded (FFPE) and fresh tissues were included. Peripheral non-tumour tissues were used as controls. All the cases were confirmed using immunohistochemistry. RNA was extracted using miRNA-specific kit, and the expression was performed using RT-qPCR. The data were evaluated using AriaMx software version 1.5 (Agilent, US). MiRNAs expression was analyzed by using the relative quantification method (ΔΔCT). Results miR-221, miR-222, miR-494 and miR-34a showed significant down-regulation in tumours relative to non-tumour tissues. The expression levels of these miRNAs were significantly down-regulated in c-KIT (proto-oncogene encoding the tyrosine kinase transmembrane receptor)-positive tumours compared to c-KIT-negative. Further analysis revealed that reduced expression was associated with spindle subtypes and gastric localization. However, there was no significant correlation with other histological features. Additionally, miR-221/222, and miR-494 were down-regulated in most of the KIT exon 11 mutant subtypes, while miRNA-34a was associated with platelet derived growth factor receptor alpha (PDGFRA) mutations. Interpretation & conclusions The present study showed that the down-regulation of these miRNAs may help better molecular classification and characterization of GISTs. Our results offer new insight into the association between miRNAs and histological features, enabling a more thorough understanding of GISTs at the molecular level.

Receptor tyrosine kinases (RTKs) are widely expressed transmembrane proteins that act as receptors for growth factors and other extracellular signalling molecules. Upon ligand binding, RTKs activate intracellular signalling cascades, and as such are involved in a broad variety of cellular functions including differentiation, proliferation, migration, invasion, angiogenesis, and survival under physiological as well as pathological conditions. Aberrant RTK activation can lead to benign proliferative conditions as well as to various forms of cancer. Indeed, more than 70% of the known oncogene and proto-oncogene transcripts involved in cancer code for RTKs. Consequently, these receptors are broadly studied as targets in the treatment of different tumours, and a large variety of small-molecule tyrosine kinase inhibitors (TKIs) are approved for therapy. In most cases, patients develop resistance to the TKIs within a short time. MicroRNAs are short (18-22 nucleotides) non-protein-coding RNAs that fine-tune cell homeostasis by controlling gene expression at the post-transcriptional level. Deregulation of microRNAs is common in many cancers, and increasing evidence exists for an important role of microRNAs in the development of resistance to therapies, including TKIs. In this review we focus on the role of microRNAs in mediating resistance to small-molecule TKIs in solid tumours.

Gain-of-function mutations and overexpression of KIT are characteristic features of gastrointestinal stromal tumor (GIST). Dysregulation in miRNA expression may lead to KIT overexpression and tumorigenesis.

miRNA microarray analysis and real-time PCR were used to determine the miRNA expression profiles in a cohort of 69 clinical samples including 50 CD117IHC+/KITmutation GISTs and 19 CD117IHC-/wild-type GISTs. GO enrichment and KEGG pathway analyses were performed to reveal the predicted targets of the dysregulated miRNAs. Of the dysregulated miRNAs whose expression was inversely correlated with that of KIT miRNAs were predicted by bioinformatics analysis and confirmed by luciferase reporter assay. Cell counting kit-8 (CCK-8) and flow cytometry were used to measure the cell proliferation, cycle arrest and apoptosis. Wound healing and transwell assays were used to evaluate migration and invasion. A xenograft BALB/c nude mouse model was applied to investigate the tumorigenesis in vivo. Western blot and qRT-PCR were used to investigate the protein and mRNA levels of KIT and its downstream effectors including ERK, AKT and STAT3.

Of the six miRNAs whose expression was inversely correlated with that of KIT, we found that miR-148b-3p was significantly downregulated in the CD117IHC+/KITmutation GIST cohort. This miRNA was subsequently found to inhibit proliferation, migration and invasion of GIST882 cells. Mechanistically, miR-148b-3p was shown to regulate KIT expression through directly binding to the 3'-UTR of the KIT mRNA. Restoration of miR-148b-3p expression in GIST882 cells led to reduced expression of KIT and the downstream effectors proteins ERK, AKT and STAT3. However, overexpression of KIT reversed the inhibitory effect of miR-148b-3p on cell proliferation, migration and invasion. Furthermore, we found that reduced miR-148b-3p expression correlated with poor overall survival (OS) and disease-free survival (DFS) in GIST patients.

miR-148b-3p functions as an important regulator of KIT expression and a potential prognostic biomarker for GISTs.

HOTAIR, a long non-coding RNA (lncRNA), plays a crucial role in tumor initiation and metastasis by interacting with the PRC2 complex and the modulation of its target genes. The role of HOTAIR in gastrointestinal stromal tumors (GISTs) is remains unclear. Herein we investigate the mechanism of HOTAIR in the genesis and promotion of GISTs. The expression of HOTAIR was found to be higher in surgically resected high-risk GISTs than that in low- and intermediate-risk GISTs. Using GIST-T1 and GIST882 cells, we demonstrated that HOTAIR repressed apoptosis, was associated with cell cycle progression, and controlled the invasion and migration of GIST cells. Using a gene expression microarray and lists of HOTAIR-associated candidate genes, we suggested that protocadherin 10 (PCDH10) is a key molecule. PCDH10 expression was significantly decreased in GIST-T1 and GIST882 cells, possibly as a consequence of hypermethylation. We observed that HOTAIR induced PCDH10 methylation in a SUZ12-dependent manner. In this study, we found that the malignant character of GISTs was initiated and amplified by PCDH10 in a process regulated by HOTAIR. In summary, our findings imply that PCDH10 and HOTAIR may be useful markers of disease progression and therapeutic targets.