MicroRNA-30a targets BECLIN-1 to inactivate autophagy and sensitizes gastrointestinal stromal tumor cells to imatinib

Gene Expression Regulation and the Signal Transduction of Programmed Cell Death

Cell death is of great significance in maintaining tissue homeostasis and bodily functions. With considerable research coming to the fore, it has been found that programmed cell death presents in multiple modalities in the body, which is not only limited to apoptosis, but also can be divided into autophagy, pyroptosis, ferroptosis, mitotic catastrophe, entosis, netosis, and other ways. Different forms of programmed cell death have disparate or analogous characteristics with each other, and their occurrence is accompanied by multiple signal transduction and the role of a myriad of regulatory factors. In recent years, scholars across the world have carried out considerable in-depth research on programmed cell death, and new forms of cell death are being discovered continually. Concomitantly, the mechanisms of intricate signaling pathways and regulators have been discovered. More critically, cancer cells tend to choose distinct ways to evade cell death, and different tumors adapt to different manners of death. Therefore, targeting the cell death network has been regarded as an effective tumor treatment strategy for a long time. The objective of our paper is to review the signaling pathways and gene regulation in several typical types of programmed cell death and their correlation with cancer.

Is Autophagy Targeting a Valid Adjuvant Strategy in Conjunction with Tyrosine Kinase Inhibitors?

Tyrosine kinase inhibitors (TKIs) represent a relatively large class of small-molecule inhibitors that compete with ATP for the catalytic binding site of tyrosine kinase proteins. While TKIs have demonstrated effectiveness in the treatment of multiple malignancies, including chronic myelogenous leukemia, gastrointestinal tumors, non-small cell lung cancers, and HER2-overexpressing breast cancers, as is almost always the case with anti-neoplastic agents, the development of resistance often imposes a limit on drug efficacy. One common survival response utilized by tumor cells to ensure their survival in response to different stressors, including anti-neoplastic drugs, is that of autophagy. The autophagic machinery in response to TKIs in multiple tumor models has largely been shown to be cytoprotective in nature, although there are a number of cases where autophagy has demonstrated a cytotoxic function. In this review, we provide an overview of the literature examining the role that autophagy plays in response to TKIs in different preclinical tumor model systems in an effort to determine whether autophagy suppression or modulation could be an effective adjuvant strategy to increase efficiency and/or overcome resistance to TKIs.

Insulin-like growth factor 2 targets IGF1R signaling transduction to facilitate metastasis and imatinib resistance in gastrointestinal stromal tumors

BACKGROUND

Gastrointestinal stromal tumors (GISTs) are typical gastrointestinal tract neoplasms. Imatinib is the first-line therapy for GIST patients. Drug resistance limits the long-term effectiveness of imatinib. The regulatory effect of insulin-like growth factor 2 (IGF2) has been confirmed in various cancers and is related to resistance to chemotherapy and a worse prognosis.

AIM

To further investigate the mechanism of IGF2 specific to GISTs.

METHODS

IGF2 was screened and analyzed using Gene Expression Omnibus (GEO: GSE225819) data. After IGF2 knockdown or overexpression by transfection, the phenotypes (proliferation, migration, invasion, apoptosis) of GIST cells were characterized by cell counting kit 8, Transwell, and flow cytometry assays. We used western blotting to evaluate pathway-associated and epithelial-mesenchymal transition (EMT)-associated proteins. We injected transfected cells into nude mice to establish a tumor xenograft model and observed the occurrence and metastasis of GIST.

RESULTS

Data from the GEO indicated that IGF2 expression is high in GISTs, associated with liver metastasis, and closely related to drug resistance. GIST cells with high expression of IGF2 had increased proliferation and migration, invasiveness and EMT. Knockdown of IGF2 significantly inhibited those activities. In addition, OE-IGF2 promoted GIST metastasis in vivo in nude mice. IGF2 activated IGF1R signaling in GIST cells, and IGF2/IGF1R-mediated glycolysis was required for GIST with liver metastasis. GIST cells with IGF2 knockdown were sensitive to imatinib treatment when IGF2 overexpression significantly raised imatinib resistance. Moreover, 2-deoxy-D-glucose (a glycolysis inhibitor) treatment reversed IGF2 overexpression-mediated imatinib resistance in GISTs.

CONCLUSION

IGF2 targeting of IGF1R signaling inhibited metastasis and decreased imatinib resistance by driving glycolysis in GISTs.

The involvement of ROS-regulated programmed cell death in hepatocellular carcinoma

Reactive oxidative species (ROS) is a crucial factor in the regulation of cellular biological activity and function, and aberrant levels of ROS can contribute to the development of a variety of diseases, particularly cancer. Numerous discoveries have affirmed that this process is strongly associated with "programmed cell death (PCD)," which refers to the suicide protection mechanism initiated by cells in response to external stimuli, such as apoptosis, autophagy, ferroptosis, etc. Research has demonstrated that ROS-induced PCD is crucial for the development of hepatocellular carcinoma (HCC). These activities serve a dual function in both facilitating and inhibiting cancer, suggesting the existence of a delicate balance within healthy cells that can be disrupted by the abnormal generation of reactive oxygen species (ROS), thereby influencing the eventual advancement or regression of a tumor. In this review, we summarize how ROS regulates PCD to influence the tumorigenesis and progression of HCC. Studying how ROS-induced PCD affects the progression of HCC at a molecular level can help develop better prevention and treatment methods and facilitate the design of more effective preventative and therapeutic strategies.

miR-622 Increases miR-30a Expression through Inhibition of Hypoxia-Inducible Factor 1α to Improve Metastasis and Chemoresistance in Human Invasive Breast Cancer Cells

Hypoxia-inducible factor 1α (HIF-1α) plays a pivotal role in the survival, metastasis, and response to treatment of solid tumors. Autophagy serves as a mechanism for tumor cells to eliminate misfolded proteins and damaged organelles, thus promoting invasiveness, metastasis, and resistance to treatment under hypoxic conditions. MicroRNA (miRNA) research underscores the significance of these non-coding molecules in regulating cancer-related protein synthesis across diverse contexts. However, there is limited reporting on miRNA-mediated gene expression studies, especially with respect to epithelial-mesenchymal transition (EMT) and autophagy in the context of hypoxic breast cancer. Our study reveals decreased levels of miRNA-622 (miR-622) and miRNA-30a (miR-30a) in invasive breast cancer cells compared to their non-invasive counterparts. Inducing miR-622 suppresses HIF-1α protein expression, subsequently activating miR-30a transcription. This cascade results in reduced invasiveness and migration of breast cancer cells by inhibiting EMT markers, such as Snail, Slug, and vimentin. Furthermore, miR-30a negatively regulates beclin 1, ATG5, and LC3-II and inhibits Akt protein phosphorylation. Consequently, this improves the sensitivity of invasive MDA-MB-231 cells to docetaxel treatment. In conclusion, our study highlights the therapeutic potential of inducing miR-622 to promote miR-30a expression and thus disrupt HIF-1α-associated EMT and autophagy pathways. This innovative strategy presents a promising approach to the treatment of aggressive breast cancer.

AutophagyNet: high-resolution data source for the analysis of autophagy and its regulation

Macroautophagy/autophagy is a highly-conserved catabolic procss eliminating dysfunctional cellular components and invading pathogens. Autophagy malfunction contributes to disorders such as cancer, neurodegenerative and inflammatory diseases. Understanding autophagy regulation in health and disease has been the focus of the last decades. We previously provided an integrated database for autophagy research, the Autophagy Regulatory Network (ARN). For the last eight years, this resource has been used by thousands of users. Here, we present a new and upgraded resource, AutophagyNet. It builds on the previous database but contains major improvements to address user feedback and novel needs due to the advancement in omics data availability. AutophagyNet contains updated interaction curation and integration of over 280,000 experimentally verified interactions between core autophagy proteins and their protein, transcriptional and post-transcriptional regulators as well as their potential upstream pathway connections. AutophagyNet provides annotations for each core protein about their role: 1) in different types of autophagy (mitophagy, xenophagy, etc.); 2) in distinct stages of autophagy (initiation, expansion, termination, etc.); 3) with subcellular and tissue-specific localization. These annotations can be used to filter the dataset, providing customizable download options tailored to the user's needs. The resource is available in various file formats (e.g. CSV, BioPAX and PSI-MI), and data can be analyzed and visualized directly in Cytoscape. The multi-layered regulation of autophagy can be analyzed by combining AutophagyNet with tissue- or cell type-specific (multi-)omics datasets (e.g. transcriptomic or proteomic data). The resource is publicly accessible at http://autophagynet.org.Abbreviations: ARN: Autophagy Regulatory Network; ATG: autophagy related; BCR: B cell receptor pathway; BECN1: beclin 1; GABARAP: GABA type A receptor-associated protein; IIP: innate immune pathway; LIR: LC3-interacting region; lncRNA: long non-coding RNA; MAP1LC3B: microtubule associated protein 1 light chain 3 beta; miRNA: microRNA; NHR: nuclear hormone receptor; PTM: post-translational modification; RTK: receptor tyrosine kinase; TCR: T cell receptor; TLR: toll like receptor.

Clostridioides difficile PCR ribotypes 001 and 084 can trigger autophagy process in human intestinal Caco-2 cells

Autophagy is a homeostatic process that can promote cell survival or death. However, the exact role of autophagy in Clostridioides difficile infection (CDI) is still not precisely elucidated. Here, we investigate the role of distinct C. difficile ribotypes (RTs) in autophagy induction using Caco-2 cells. The expression analysis of autophagy-associated genes and related miRNAs were examined following treatment of Caco-2 cells with C. difficile after 4 and 8 h using RT-qPCR. Toxin production was assessed using enzyme-linked immunosorbent assay (ELISA). Immunofluorescence analysis was performed to detect MAP1LC3B/LC3B, followed by an autophagic flux analysis. C. difficile significantly reduced the viability of Caco-2 cells in comparison with untreated cells. Elevated levels of LC3-II and SQSTM1/p62 by C. difficile RT001 and RT084 in the presence of E64d/leupeptin confirmed the induction of autophagy activity. Similarly, the immunofluorescence analysis demonstrated that C. difficile RT001 and RT084 significantly increased the amount of LC3-positive structures in Caco-2 cells. The induction of autophagy was further demonstrated by increased levels of LC3B, ULK1, ATG12, PIK3C3/VPS34, BECN1 (beclin 1), ATG5, and ATG16L1 transcripts and reduced levels of AKT and MTOR gene expression. The expression levels of MIR21 and MIR30B, microRNAs that suppress autophagy, were differentially affected by C. difficile. In conclusion, the present work revealed that C. difficile bacteria can induce autophagy through both toxin-dependent and -independent mechanisms. Also, our results suggest the potential role of other C. difficile virulence factors in autophagy modulation using intestinal cells in vitro.

Targeting autophagy and beyond: Deconvoluting the complexity of Beclin-1 from biological function to cancer therapy

Beclin-1 is the firstly-identified mammalian protein of the autophagy machinery, which functions as a molecular scaffold for the assembly of PI3KC3 (class III phosphatidylinositol 3 kinase) complex, thus controlling autophagy induction and other cellular trafficking events. Notably, there is mounting evidence establishing the implications of Beclin-1 in diverse tumorigenesis processes, including tumor suppression and progression as well as resistance to cancer therapeutics and CSC (cancer stem-like cell) maintenance. More importantly, Beclin-1 has been confirmed as a potential target for the treatment of multiple cancers. In this review, we provide a comprehensive survey of the structure, functions, and regulations of Beclin-1, and we discuss recent advances in understanding the controversial roles of Beclin-1 in oncology. Moreover, we focus on summarizing the targeted Beclin-1-regulating strategies in cancer therapy, providing novel insights into a promising strategy for regulating Beclin-1 to improve cancer therapeutics in the future.

Regulatory miRNAs in cancer cell recovery from therapy exposure and its implications as a novel therapeutic strategy for preventing disease recurrence

The desired outcome of cancer therapies is the eradication of disease. This can be achieved when therapy exposure leads to therapy-induced cancer cell death as the dominant outcome. Theoretically, a permanent therapy-induced growth arrest could also contribute to a complete response, which has the potential to lead to remission. However, preclinical models have shown that therapy-induced growth arrest is not always durable, as recovering cancer cell populations can contribute to the recurrence of cancer. Significant research efforts have been expended to develop strategies focusing on the prevention of recurrence. Recovery of cells from therapy exposure can occur as a result of several cell stress adaptations. These include cytoprotective autophagy, cellular quiescence, a reversable form of senescence, and the suppression of apoptosis and necroptosis. It is well documented that microRNAs regulate the response of cancer cells to anti-cancer therapies, making targeting microRNAs therapeutically a viable strategy to sensitization and the prevention of recovery. We propose that the use of microRNA-targeting therapies in prolonged sequence, that is, a significant period after initial therapy exposure, could reduce toxicity from the standard combination strategy, and could exploit new epigenetic states essential for cancer cells to recover from therapy exposure. In a step toward supporting this strategy, we survey the available scientific literature to identify microRNAs which could be targeted in sequence to eliminate residual cancer cell populations that were arrested as a result of therapy exposure. It is our hope that by successfully identifying microRNAs which could be targeted in sequence we can prevent disease recurrence.

Tumor-Suppressive and Immunomodulating Activity of miR-30a-3p and miR-30e-3p in HNSCC Cells and Tumoroids

Head and neck squamous cell carcinomas (HNSCCs) are heterogeneous tumors, well known for their frequent relapsing nature. To counter recurrence, biomarkers for early diagnosis, prognosis, or treatment response prediction are urgently needed. miRNAs can profoundly impact normal physiology and enhance oncogenesis. Among all of the miRNAs, the miR-30 family is frequently downregulated in HNSCC. Here, we determined how levels of the 3p passenger strands of miR-30a and miR-30e affect tumor behavior and clarified their functional role in LA-HNSCC. In a retrospective study, levels of miR-30a-3p and miR-30e-3p were determined in 110 patients and correlated to overall survival, locoregional relapse, and distant metastasis. miR-30a/e-3p were expressed in HNSCC cell lines and HNSCC patient-derived tumoroids (PDTs) to investigate their effect on tumor cells and their microenvironment. Both miRNAs were found to have a prognosis value since low miR-30a/e-3p expression correlates to adverse prognosis and reduces overall survival. Low expression of miR-30a/e-3p is associated with a shorter time until locoregional relapse and a shorter time until metastasis, respectively. miR-30a/e-3p expression downregulates both TGF-βR1 and BMPR2 and attenuates the survival and motility of HNSCC. Results were confirmed in PDTs. Finally, secretomes of miR-30a/e-3p-transfected HNSCC activate M1-type macrophages, which exert stronger phagocytic activities toward tumor cells. miR-30a/e-3p expression can discriminate subgroups of LA-HNSCC patients with different prognosis, making them good candidates as prognostic biomarkers. Furthermore, by targeting members of the TGF-β family and generating an immune-permissive microenvironment, they may emerge as an alternative to anti-TGF-β drugs to use in combination with immune checkpoint inhibitors.

The multifaceted landscape behind imatinib resistance in gastrointestinal stromal tumors (GISTs): A lesson from ripretinib

Gastrointestinal stromal tumors (GISTs) are rare mesenchymal sarcomas and the gold-standard treatment is represented by tyrosine kinase inhibitors (TKIs). Unfortunately, first-line treatment with the TKI imatinib usually promotes partial response or stable disease rather than a complete response, and resistance appears in most patients. Adaptive mechanisms are immediately relevant at the beginning of imatinib therapy, and they may represent the reason behind the low complete response rates observed in GISTs. Concurrently, resistant subclones can silently continue to grow or emerge de novo, becoming the most representative populations. Therefore, a slow evolution of the primary tumor gradually occurs during imatinib treatment, enriching heterogeneous imatinib resistant clonal subpopulations. The identification of secondary KIT/PDGFRA mutations in resistant GISTs prompted the development of novel multi-targeted TKIs, leading to the approval of sunitinib, regorafenib, and ripretinib. Although ripretinib has broad anti-KIT and -PDGFRA activity, it failed to overcome sunitinib as second-line treatment, suggesting that imatinib resistance is more multifaceted than initially thought. The present review summarizes several biological aspects suggesting that heterogeneous adaptive and resistance mechanisms can also be driven by KIT or PDGFRA downstream mediators, alternative kinases, as well as ncRNAs, which are not targeted by any TKI, including ripretinib. This may explain the modest effect observed with ripretinib and all anti-GIST agents in patients.

Autophagy as a self-digestion signal in human cancers: Regulation by microRNAs in affecting carcinogenesis and therapy response

Autophagy is defined as a "self-digestion" signal, and it is a cell death mechanism its primary function is degrading toxic agents and aged organelles to ensure homeostasis in cells. The basic leve ls of autophagy are found in cells, and when its levels exceed to standard threshold, cell death induction is observed. Autophagy dysregulation in cancer has been well-documented, and regulation of this pathway by epigenetic factors, especially microRNAs (miRNAs), is interesting and noteworthy. miRNAs are considered short endogenous RNAs that do not encode functional proteins, and they are essential regulators of cell death pathways such as apoptosis, necroptosis, and autophagy. Accumulating data has revealed miRNA dysregulation (upregulation or downregulation) during tumor progression, and their therapeutic manipulation provides new insight into cancer therapy. miRNA/autophagy axis in human cancers has been investigated an exciting point is the dual function of both autophagy and miRNAs as oncogenic and onco-suppressor factors. The stimulation of pro-survival autophagy by miRNAs can increase the survival rate of tumor cells and mediates cancer metastasis via EMT inductionFurthermore, pro-death autophagy induction by miRNAs has a negative impact on the viability of tumor cells and decreases their survival rate. The miRNA/autophagy axis functions beyond regulating the growth and invasion of tumor cells, and they can also affect drug resistance and radio-resistance. These subjects are covered in the current review regarding the new updates provided by recent experiments.

MicroRNAs in the Pathogenesis, Prognostication and Prediction of Treatment Resistance in Soft Tissue Sarcomas

Soft tissue sarcomas are highly aggressive malignant neoplasms of mesenchymal origin, accounting for less than 1% of adult cancers, but comprising over 20% of paediatric solid tumours. In locally advanced, unresectable, or metastatic disease, outcomes from even the first line of systemic treatment are invariably poor. MicroRNAs (miRNAs), which are short non-coding RNA molecules, target and modulate multiple dysregulated target genes and/or signalling pathways within cancer cells. Accordingly, miRNAs demonstrate great promise for their utility in diagnosing, prognosticating and improving treatment for soft tissue sarcomas. This review aims to provide an updated discussion on the known roles of specific miRNAs in the pathogenesis of sarcomas, and their potential use in prognosticating outcomes and prediction of therapeutic resistance.

Epigenetic and post-translational modifications in autophagy: biological functions and therapeutic targets

Autophagy is a conserved lysosomal degradation pathway where cellular components are dynamically degraded and re-processed to maintain physical homeostasis. However, the physiological effect of autophagy appears to be multifaced. On the one hand, autophagy functions as a cytoprotective mechanism, protecting against multiple diseases, especially tumor, cardiovascular disorders, and neurodegenerative and infectious disease. Conversely, autophagy may also play a detrimental role via pro-survival effects on cancer cells or cell-killing effects on normal body cells. During disorder onset and progression, the expression levels of autophagy-related regulators and proteins encoded by autophagy-related genes (ATGs) are abnormally regulated, giving rise to imbalanced autophagy flux. However, the detailed mechanisms and molecular events of this process are quite complex. Epigenetic, including DNA methylation, histone modifications and miRNAs, and post-translational modifications, including ubiquitination, phosphorylation and acetylation, precisely manipulate gene expression and protein function, and are strongly correlated with the occurrence and development of multiple diseases. There is substantial evidence that autophagy-relevant regulators and machineries are subjected to epigenetic and post-translational modulation, resulting in alterations in autophagy levels, which subsequently induces disease or affects the therapeutic effectiveness to agents. In this review, we focus on the regulatory mechanisms mediated by epigenetic and post-translational modifications in disease-related autophagy to unveil potential therapeutic targets. In addition, the effect of autophagy on the therapeutic effectiveness of epigenetic drugs or drugs targeting post-translational modification have also been discussed, providing insights into the combination with autophagy activators or inhibitors in the treatment of clinical diseases.

Cryptosporidium parvum regulates HCT-8 cell autophagy to facilitate survival via inhibiting miR-26a and promoting miR-30a expression

BACKGROUND

Cryptosporidium parvum is an important zoonotic parasite, which not only causes economic losses in animal husbandry but also harms human health. Due to the lack of effective measures for prevention and treatment, it is important to understand the pathogenesis and survival mechanism of C. parvum. Autophagy is an important mechanism of host cells against parasite infection through key regulatory factors such as microRNAs and MAPK pathways. However, the regulatory effect of C. parvum on autophagy has not been reported. Here, we demonstrated that C. parvum manipulated autophagy through host cellular miR-26a, miR-30a, ERK signaling and P38 signaling for parasite survival.

METHODS

The expression of Beclin1, p62, LC3, ERK and P38 was detected using western blotting in HCT-8 cells infected with C. parvum as well as treated with miR-26a-mimic, miR-30a-mimic, miR-26a-mimic or miR-30a-inhibitor post C. parvum infection. The qPCR was used to detect the expression of miR-26a and miR-30a and the number of C. parvum in HCT-8 cells. Besides, the accumulation of autophagosomes was examined using immunofluorescence.

RESULTS

The expression of Beclin1 and p62 was increased, whereas LC3 expression was increased initially at 0-8 h but decreased at 12 h and then increased again in C. parvum-infected cells. C. parvum inhibited miR-26a-mimic-induced miR-26a but promoted miR-30a-mimic-induced miR-30a expression. Suppressing miR-30a resulted in increased expression of LC3 and Beclin1. However, upregulation of miR-26a reduced ERK/P38 phosphorylation, and inhibiting ERK/P38 signaling promoted Beclin1 and LC3 while reducing p62 expression. Treatment with miR-26a-mimic, autophagy inducer or ERK/P38 signaling inhibitors reduced but treatment with autophagy inhibitor or miR-30a-mimic increased parasite number.

CONCLUSIONS

The study found that C. parvum could regulate autophagy by inhibiting miR-26a and promoting miR-30a expression to facilitate the proliferation of parasites. These results revealed a new mechanism for the interaction of C. parvum with host cells.

Multi-omics characterization of autophagy-related molecular features for therapeutic targeting of autophagy

Autophagy is a major contributor to anti-cancer therapy resistance. Many efforts have been made to understand and overcome autophagy-mediated therapy resistance, but these efforts have been unsuccessful in clinical applications. In this study, we establish an autophagy signature to estimate tumor autophagy status. We then classify approximately 10,000 tumor samples across 33 cancer types from The Cancer Genome Atlas into autophagy score-high and autophagy score-low groups. We characterize the associations between multi-dimensional molecular features and tumor autophagy, and further analyse the effects of autophagy status on drug response. In contrast to the conventional view that the induction of autophagy serves as a key resistance mechanism during cancer therapy, our analysis reveals that autophagy induction may also sensitize cancer cells to anti-cancer drugs. We further experimentally validate this phenomenon for several anti-cancer drugs in vitro and in vivo, and reveal that autophagy inducers potentially sensitizes tumor cells to etoposide through downregulating the expression level of DDIT4. Our study provides a comprehensive landscape of molecular alterations associated with tumor autophagy and highlights an opportunity to leverage multi-omics analysis to utilize multiple drug sensitivity induced by autophagy.

AMBRA1 and its role as a target for anticancer therapy

The activating molecule in Beclin1-regulated autophagy protein 1 (AMBRA1) is an intrinsically disordered protein that regulates the survival and death of cancer cells by modulating autophagy. Although the roles of autophagy in cancer are controversial and context-dependent, inhibition of autophagy under some circumstances can be a useful strategy for cancer therapy. As AMBRA1 is a pivotal autophagy-associated protein, targeting AMBRA1 similarly may be an underlying strategy for cancer therapy. Emerging evidence indicates that AMBRA1 can also inhibit cancer formation, maintenance, and progression by regulating c-MYC and cyclins, which are frequently deregulated in human cancer cells. Therefore, AMBRA1 is at the crossroad of autophagy, tumorigenesis, proliferation, and cell cycle. In this review, we focus on discussing the mechanisms of AMBRA1 in autophagy, mitophagy, and apoptosis, and particularly the roles of AMBRA1 in tumorigenesis and targeted therapy.

Advances in the research of the mechanism of secondary resistance to imatinib in gastrointestinal stromal tumors

Gastrointestinal stromal tumors (GISTs) are the most common mesenchymal tumors of the gastrointestinal tract. At present, surgery is the first-line treatment for primary resectable GISTs; however, the recurrence rate is high. Imatinib mesylate (IM) is an effective first-line drug used for the treatment of unresectable or metastatic recurrent GISTs. More than 80% of patients with GISTs show significantly improved 5-year survival after treatment; however, approximately 50% of patients develop drug resistance after 2 years of IM treatment. Therefore, an in-depth research is urgently needed to reveal the mechanisms of secondary resistance to IM in patients with GISTs and to develop new therapeutic targets and regimens to improve their long-term prognoses. In this review, research on the mechanisms of secondary resistance to IM conducted in the last 5 years is discussed and summarized from the aspects of abnormal energy metabolism, gene mutations, non-coding RNA, and key proteins. Studies have shown that different drug-resistance mechanism networks are closely linked and interconnected. However, the influence of these drug-resistance mechanisms has not been compared. The combined inhibition of drug-resistance mechanisms with IM therapy and the combined inhibition of multiple drug-resistance mechanisms are expected to become new therapeutic options in the treatment of GISTs. In addition, implementing individualized therapies based on the identification of resistance mechanisms will provide new adjuvant treatment options for patients with IM-resistant GISTs, thereby delaying the progression of GISTs. Previous studies provide theoretical support for solving the problems of drug-resistance mechanisms. However, most studies on drug-resistance mechanisms are still in the research stage. Further clinical studies are needed to confirm the safety and efficacy of the inhibition of drug-resistance mechanisms as a potential therapeutic target.

All-trans retinoic acid-mediated miR-30a up-regulation suppresses autophagy and sensitizes gastric cancer cells to cisplatin

AIMS

The potential of all-trans retinoic acid (ATRA) in regulating some microRNAs (miRNAs) involved in multiple cancer-related pathways, including resistance to chemotherapeutics, may be a valuable idea for overcoming the CDDP resistance of GC cells.

MAIN METHODS

Treatment of gastric AGS and MKN-45 cells with CDDP enriched the CDDP surviving cells (CDDP-SCs). The abilities of chemoresistance to CDDP drug, migration, either apoptosis or cell cycle distribution, spheroid body formation and changes at miRNA and protein levels were evaluated in vitro by MTT assay, colony formation assay, flow cytometry, tumor spheres culture, qRT-PCR and western blot assay in CDDP-SCs and ATRA-treated CDDP-SCs cells, respectively.

KEY FINDINGS

CDDP-based chemotherapy significantly reduced microRNA-30a (miR-30a) levels in GC cells. We also observed elevated autophagy activity in cancer cells that possess stem cell-like properties with overexpressed specific stem cell markers. Our extended study suggested that the reduction of miR-30a by CDDP treatment, is the possible underlying mechanism of enhanced autophagic activity, as demonstrated by enhancing autophagy-related protein beclin 1 and LC3-II/LC-I ratio. The addition of ATRA in the culture medium of GC cells increased the expression of miR-30a, and disturbed characteristic CSC-like properties. Additional studies revealed that the increased expression of miR-30a declined the expression level of its target gene, beclin 1, and beclin 1-mediated autophagy. This leads to promoted CDDP-induced GC cell apoptosis and G2/M cell cycle arrest.

SIGNIFICANCE

Overall, miR-30a/autophagy signaling has a critical role in regulating the chemoresistance of GC cells that ATRA could modulate.

Molecular Mechanisms of Autophagy in Cancer Development, Progression, and Therapy

Autophagy is an evolutionarily conserved and tightly regulated process that plays an important role in maintaining cellular homeostasis. It involves regulation of various genes that function to degrade unnecessary or dysfunctional cellular components, and to recycle metabolic substrates. Autophagy is modulated by many factors, such as nutritional status, energy level, hypoxic conditions, endoplasmic reticulum stress, hormonal stimulation and drugs, and these factors can regulate autophagy both upstream and downstream of the pathway. In cancer, autophagy acts as a double-edged sword depending on the tissue type and stage of tumorigenesis. On the one hand, autophagy promotes tumor progression in advanced stages by stimulating tumor growth. On the other hand, autophagy inhibits tumor development in the early stages by enhancing its tumor suppressor activity. Moreover, autophagy drives resistance to anticancer therapy, even though in some tumor types, its activation induces lethal effects on cancer cells. In this review, we summarize the biological mechanisms of autophagy and its dual role in cancer. In addition, we report the current understanding of autophagy in some cancer types with markedly high incidence and/or lethality, and the existing therapeutic strategies targeting autophagy for the treatment of cancer.

Exploring the role of non-coding RNAs in autophagy

As a self-degradative mechanism, macroautophagy/autophagy has a role in the maintenance of energy homeostasis during critical periods in the development of cells. It also controls cellular damage through the eradication of damaged proteins and organelles. This process is accomplished by tens of ATG (autophagy-related) proteins. Recent studies have shown the involvement of non-coding RNAs in the regulation of autophagy. These transcripts mostly modulate the expression of ATG genes. Both long non-coding RNAs (lncRNAs) and microRNAs (miRNAs) have been shown to modulate the autophagy mechanism. Levels of several lncRNAs and miRNAs are altered in this process. In the present review, we discuss the role of lncRNAs and miRNAs in the regulation of autophagy in diverse contexts such as cancer, deep vein thrombosis, spinal cord injury, diabetes and its complications, acute myocardial infarction, osteoarthritis, pre-eclampsia and epilepsy.Abbreviations: AMI: acute myocardial infarction; ATG: autophagy-related; lncRNA: long non-coding RNA; miRNA: microRNA.

The Role of Non-Coding RNAs in Autophagy During Carcinogenesis

Macroautophagy (autophagy herein) is a cellular stress response and a survival pathway involved in self-renewal and quality control processes to maintain cellular homeostasis. The alteration of autophagy has been implicated in numerous diseases such as cancer where it plays a dual role. Autophagy serves as a tumor suppressor in the early phases of cancer formation with the restoration of homeostasis and eliminating cellular altered constituents, yet in later phases, autophagy may support and/or facilitate tumor growth, metastasis and may contribute to treatment resistance. Key components of autophagy interact with either pro- and anti-apoptotic factors regulating the proximity of tumor cells to apoptotic cliff promoting cell survival. Autophagy is regulated by key cell signaling pathways such as Akt (protein kinase B, PKB), mammalian target of rapamycin (mTOR) and AMP-activated protein kinase (AMPK) involved in cell survival and metabolism. The expression of critical members of upstream cell signaling, as well as those directly involved in the autophagic and apoptotic machineries are regulated by microRNAs (miRNAs) and long non-coding RNAs (lncRNAs). Consequently, non-coding RNAs play a relevant role in carcinogenesis and treatment response in cancer. The review is an update of the current knowledge in the regulation by miRNA and lncRNA of the autophagic components and their functional impact to provide an integrated and comprehensive regulatory network of autophagy in cancer.

Noncoding RNAs in Drug Resistance of Gastrointestinal Stromal Tumor

Gastrointestinal stromal tumor (GIST) is the most common mesenchymal tumor in the gastrointestinal tracts and a model for the targeted therapy of solid tumors because of the oncogenic driver mutations in KIT and PDGDRA genes, which could be effectively inhibited by the very first targeted agent, imatinib mesylate. Most of the GIST patients could benefit a lot from the targeted treatment of this receptor tyrosine kinase inhibitor. However, more than 50% of the patients developed resistance within 2 years after imatinib administration, limiting the long-term effect of imatinib. Noncoding RNAs (ncRNAs), the non-protein coding transcripts of human, were demonstrated to play pivotal roles in the resistance of various chemotherapy drugs. In this review, we summarized the mechanisms of how ncRNAs functioning on the drug resistance in GIST. During the drug resistance of GIST, there were five regulating mechanisms where the functions of ncRNAs concentrated: oxidative phosphorylation, autophagy, apoptosis, drug target changes, and some signaling pathways. Also, these effects of ncRNAs in drug resistance were divided into two aspects. How ncRNAs regulate drug resistance in GIST was further summarized according to ncRNA types, different drugs and categories of resistance. Moreover, clinical applications of these ncRNAs in GIST chemotherapies concentrated on the prognostic biomarkers and novel therapeutic targets.

MicroRNA miR-30a inhibits cisplatin resistance in ovarian cancer cells through autophagy

We study whether microRNA miR-30a inhibits the autophagy through transforming growth factor (TGF)-β/Smad4 to generate cisplatin (DDP) resistance in ovarian cancer cells. The expression of miR-30a, Smad4, and TGF-β was detected in the serum of ovarian cancer patients and DDP-resistant cell lines (A2780) by quantitative real-time polymerase chain reaction (qRT-PCR). Computational search and western blotting were used to demonstrate the downstream target of miR-30a in ovarian cancer cells. Cell viability was measured with CCK8 assay. Apoptosis and autophagy of ovarian cancer cells were analyzed by flow cytometry and transmission electron microscopy, and the expressions of Beclin1 and LC3II protein were detected by western blotting. Expression of miR-30a was significantly decreased, while expressions of TGF-β and Smad4 mRNA were increased in serum of ovarian cancer patients after DDP chemotherapy as well as in DDP-resistant cells. Activation of autophagy contributed to DDP-resistance cells. Moreover, Bioinformatics software predicted Smad4 to be a target of miR-30a. Overexpression of miR-30a decreased the expression of Smad4 and TGF-β. Additionally, miR-30a-overexpressing inhibited DDP-induce autophagy and promoted DDP-resistant cell apoptosis. In conclusion, miR-30a mediates DDP resistance in ovarian cancer by inhibiting autophagy via the TGF-β/Smad4 pathway.

Regulation of autophagy by miRNAs in human diseases

Autophagy is a homeostatic process designed to eliminate dysfunctional and aging organelles and misfolded proteins through a well-concerted pathway, starting with forming a double-membrane vesicle and culminating in the lysosomal degradation of the cargo enclosed inside the mature vesicle. As a vital sentry of cellular health, autophagy is regulated in every human disease condition and is an essential target for non-coding RNAs like microRNAs (miRNAs). miRNAs are short oligonucleotides that specifically bind to the 3'-untranslated region (UTR) of target mRNAs, thus leading to mRNA silencing, degradation, or translation blockage. This review summarizes the recent findings regarding the regulation of autophagy and autophagy-related genes by different miRNAs in various pathological conditions, including cancer, kidney and liver disorders, neurodegeneration, cardiovascular disorders, infectious diseases, aging-related conditions, and inflammation-related diseases. As miRNAs are being identified as prime regulators of autophagy in human disease, pharmacological molecules and traditional medicines targeting these miRNAs are also being tested in disease models, thus initiating a new series of therapeutic interventions targeting autophagy.

MicroRNA expression profiling of sea perch brain cells reveals the roles of microRNAs in autophagy induced by RGNNV infection

Nervous necrosis virus (NNV) is one of the most destructive fish viruses and affects more than 120 marine and freshwater teleost species. However, the pathogenesis of NNV has not been made clear. MicroRNAs (miRNAs) play important roles in the regulation of viral infection. To understand the roles and regulation patterns of miRNAs in NNV infection, high-throughput sequencing was carried out in Lateolabrax japonicus brain (LJB) cells with or without red-spotted grouper NNV (RGNNV) infection at 12 and 24 hr. Here, we identified 59 known and 61 novel differentially expressed miRNAs (DE miRNAs) between mock and RGNNV-infected LJB cells. KEGG pathway analysis showed that the target genes of DE miRNAs were significantly enriched in immune-related signalling pathways, such as autophagy, mitophagy and TGF-beta signalling pathways. The expression patterns of four DE miRNAs (lja-miR-145, lja-miR-182, lja-miR-183 and lja-miR-187) were verified by qRT-PCR both in vivo and in vitro. We found that lja-miR-145 promoted RGNNV proliferation, while lja-miR-183 suppressed RGNNV proliferation. Furthermore, lja-miR-145 facilitated RGNNV-induced autophagy activation, whereas lja-miR-183 repressed autophagy in LJB cells as measured by LC3B-II/I and p62 protein levels. All these results indicate the involvement of lja-miR-145 and lja-miR-183 in RGNNV-induced autophagy. In conclusion, this study provides evidence for the important roles of miRNAs in NNV infection and a basis for uncovering the molecular regulation mechanism of NNV-induced autophagy.

Knockdown of lncRNA HIF1A-AS2 increases drug sensitivity of SCLC cells in association with autophagy

The aim of this study was to determine the effect of lncRNA HIF1A-AS2 on autophagy-associated drug resistance in small cell lung cancer (SCLC) cells. The expression of HIF1A-AS2 was silenced by siRNA in doxorubicin-sensitive H69 and doxorubicin-resistant H69AR cells. Then, cytotoxicity, apoptosis and autophagy analyses were carried out in the normoxic and CoCl₂-induced hypoxic environment. The effect of HIF1A-AS2 on the expression levels of genes, which are associated with drug resistance and autophagy, was determinated by qRT-PCR analysis. The levels of MRP1, HIF-1α and Beclin-1 were analyzed by western blot method. Knockdown of HIF1A-AS2 increased doxorubicin sensitivity of SCLC cells and decreased autophagy. Knockdown of HIF1A-AS2 has also affected the expression of several genes that will increase drug sensitivity and inhibit autophagy in both cell lines. The levels of HIF-1α and Beclin-1 were decreased in both cell lines by knockdown of HIF1A-AS2. MRP1 expression was decrease in H69AR cells. In addition, CoCl₂-induced hypoxic environment decreased in doxorubicin sensitivity of H69 cells, and knockdown of HIF1A-AS2 reversed this effect of hypoxia. Knockdown of HIF1A-AS2 increased drug sensitivity of SCLC cells in relation to autophagy. Therefore, hypoxia-HIF1A-AS2-autophagy interaction is thought to be determinative in drug sensitivity of these cells.

Hydroxychloroquine (HCQ) Modulates Autophagy and Oxidative DNA Damage Stress in Hepatocellular Carcinoma to Overcome Sorafenib Resistance via TLR9/SOD1/hsa-miR-30a-5p/Beclin-1 Axis

Sorafenib is used for treating advanced hepatocellular carcinoma (HCC), but some patients acquire sorafenib resistance. We investigated the mechanisms underlying acquired sorafenib resistance in HCC cells and targeted them to re-sensitize them to sorafenib. In silico analysis indicated that toll-like receptor (TLR)-9 was significantly overexpressed, and that miRNA (hsa-miR-30a-5p) was downregulated in sorafenib-resistant HCC cells, which modulated HCC cell proliferation, oxidative stress, and apoptosis. TLR9 overexpression increased HCC cell proliferation, whereas TLR9 inhibition from hydroxychloroquine (HCQ) decreased HCC cell proliferation, tumor growth, oxidative stress marker (SOD1), and the formation of autophagosome bodies (reduced ATG5 and Beclin-1 expression). Moreover, HCQ treatment reduced epithelial-mesenchymal transition, leading to decreased clonogenicity, migratory ability, and invasiveness. HCQ targeted and reduced the self-renewal capacity phenotype by inhibiting tumorsphere generation. Both in vitro and in vivo results demonstrated the synergistic effect of the HCQ-sorafenib combination on sorafenib-resistant HCC (Huh7-SR) cells, increasing their sensitivity to treatment by modulating TLR9, autophagy (ATG5 and Beclin-1), oxidative stress (SOD1), and apoptosis (c-caspase3) expression and thus overcoming the drug resistance. This study's findings indicate that TLR9 overexpression occurs in sorafenib-resistant HCC cells and that its downregulation aids HCC suppression. Moreover, HCQ treatment significantly increases sorafenib's effect on sorafenib-resistant HCC cells.

LncRNA-HOTAIR activates autophagy and promotes the imatinib resistance of gastrointestinal stromal tumor cells through a mechanism involving the miR-130a/ATG2B pathway

Gastrointestinal stromal tumors (GISTs) are common neoplasms of the gastrointestinal tract that can be treated successfully using C-kit target therapy and surgery; however, imatinib chemoresistance is a major barrier to success in therapy. The present study aimed to discover alternative pathways in imatinib-resistant GISTs. Long noncoding RNAs (lncRNAs) are newly discovered regulators of chemoresistance. Previously, we showed that the lncRNA HOTAIR was upregulated in recurrent GISTs. In this study, we analyzed differentially expressed lncRNAs after imatinib treatment and found that HOTAIR displayed the largest increase. The distribution of HOTAIR in GISTs was shifted from nucleus to cytoplasm after imatinib treatments. The expression of HOTAIR was validated as related to drug sensitivity through Cell Counting Kit-8 assays. Moreover, HOTAIR was associated strongly with cell autophagy and regulated drug sensitivity via autophagy. Mechanistically, HOTAIR correlated negatively with miRNA-130a in GISTs. The downregulation of miRNA-130a reversed HOTAIR-small interfering RNA-induced suppression of autophagy and imatinib sensitivity. We identified autophagy-related protein 2 homolog B (ATG2B) as a downstream target of miR-130a and HOTAIR. ATG2B downregulation reversed the effect of pEX-3-HOTAIR/miR-130a inhibitor on imatinib sensitivity. Finally, HOTAIR was shown to influence the autophagy and imatinib sensitivity of GIST cells in mouse tumor models. Our results suggested that HOTAIR targets the ATG2B inhibitor miR-130a to upregulate the level of cell autophagy so that promotes the imatinib resistance in GISTs.

Cytotoxicity mechanisms of plumbagin in drug-resistant tongue squamous cell carcinoma

OBJECTIVES

To evaluate the inhibitory effect and mechanism of plumbagin (PLB) against drug-resistant tongue squamous cell carcinoma (TSCC), and whether its antitumour effect is not affected by tumour drug resistance.

METHODS

TSCC sensitive CAL27 cells and drug-resistant CAL27/RE cells were used to study the cytotoxicity and mechanism of PLB in vitro, including CCK-8 analysis, colony formation, DAPI staining, flow cytometry assay, transmission electron microscopy, western blotting assay, autophagy, apoptosis and ROS fluorescent probes. BALB/c nude mice xenograft models were used to study the growth inhibitory effect of PLB in vivo.

KEY FINDINGS

The results showed that the cell viability and proliferation inhibition and apoptosis induction abilities of PLB on drug-resistant cells were more obvious than that on sensitive cells. And PLB induced protective autophagy in TSCC cells. Mechanistically, PLB induced apoptosis and autophagy by generating reactive oxygen species to mediate JNK and AKT/mTOR pathways. Finally, the growth inhibitory effect of PLB against drug-resistant TSCC was also confirmed in vivo.

CONCLUSIONS

PLB will be a promising anticancer agent to overcome drug-resistant TSCC without being affected by its drug resistance properties.

The Macro-Autophagy-Related Protein Beclin-1 Immunohistochemical Expression Correlates With Tumor Cell Type and Clinical Behavior of Uveal Melanoma

Uveal melanoma, in spite of its rarity, represents the most common primitive intraocular malignant neoplasm of the adults; it affects choroid, ciliary bodied and iris and remains clinically silent for a long time, being accidentally discovered by routine ophthalmic exams. Prognosis of uveal melanoma is poor and frequently characterized by liver metastases, within 10-15 years from diagnosis. Autophagy is a multi-step catabolic process by which cells remove damaged organelles and proteins and recycle nutrients. It has been hypothesized that in early stages of tumorigenesis autophagy has a tumor suppressor role while, in more advanced stages, it may represent a survival mechanism of neoplastic cells in response to stress. Several proteins related to autophagy cascade have been investigated in numerous subtypes of human cancer, with overall controversal results. In this paper we studied the immunohistochemical expression of 3 autophagy related proteins (Beclin-1, p62 and ATG7) in a cohort of 85 primary uveal melanoma treated by primary enucleation (39 with metastasis and 46 non metastatic) and correlated their expression with clinico-pathological parameters and blood vascular microvessel density, in order to investigate the potential prognostic role of autophagy in this rare neoplasm. We found that high immunohistochemical levels of Beclin-1 correlated with a lower risk of metastasis and higher disease-free survival times, indicating a positive prognostic role for Beclin-1 in uveal melanoma. No statistically significative differences regarding the expression of ATG7 and p62 between metastatic and non metastatic patients was detected.

circCUL2 regulates gastric cancer malignant transformation and cisplatin resistance by modulating autophagy activation via miR-142-3p/ROCK2

Background

Circular RNAs (circRNAs) are a class of noncoding RNAs (ncRNAs) and can modulate gene expression by binding to miRNAs; further, circRNAs have been shown to participate in several pathological processes. However, the expression and biological function of circCUL2 in gastric cancer (GC) remains largely unknown.

Methods

circRNA microarrays and quantitative real-time PCR (qRT-PCR) were used to identify differentially expressed circRNAs in GC tissues and cell lines. circCUL2 knockdown and overexpression were performed to indicate the functional role of circCUL2 in vitro and in vivo. The expression and regulation of circCUL2, miR-142-3p and ROCK2 were evaluated using fluorescence in situ hybridization (FISH), dual-luciferase assays, RNA pull-down assays, RNA immunoprecipitation (RIP) and rescue experiments. Furthermore, the regulation of cisplatin sensitivity and autophagy by circCUL2/miR-142-3p/ROCK2 was demonstrated by cellular apoptosis assays, western blot, immunofluorescence and transmission electron microscopy analyses.

Results

The level of circCUL2, which is stable and cytoplasmically localized, was significantly reduced in GC tissues and cells. Overexpressed circCUL2 inhibited malignant transformation in vitro and tumorigenicity in vivo. In the AGS and SGC-7901 cell lines, circCUL2 sponged miR-142-3p to regulate ROCK2, thus modulating tumor progression. Furthermore, in the AGS/DDP and SGC-7901/DDP cell lines, circCUL2 regulated cisplatin sensitivity through miR-142-3p/ROCK2-mediated autophagy activation.

Conclusion

circCUL2 may function as a tumor suppressor and regulator of cisplatin sensitivity through miR-142-3p/ROCK2-mediated autophagy activation, which could be a key mechanism and therapeutic target for GC.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s12943-020-01270-x.

MicroRNA-mediated autophagy regulation in cancer therapy: The role in chemoresistance/chemosensitivity

Chemoresistance has doubled the effort needed to reach an effective treatment for cancer. Now, scientists should consider molecular pathways and mechanisms involved in chemoresistance to overcome cancer. Autophagy is a "self-digestion" mechanism in which potentially toxic and aged organelles and macromolecules are degraded. Increasing evidence has shown that autophagy possesses dual role in cancer cells (onco-suppressor or oncogene). So, it is vital to identify its role in cancer progression and malignancy. MicroRNAs (miRs) are epigenetic factors capable of modulation of autophagy in cancer cells. In the current review, we emphasize on the relationship between miRs and autophagy in cancer chemotherapy. Besides, we discuss upstream mediators of miR/autophagy axis in cancer chemotherapy including long non-coding RNAs, circular RNAs, Nrf2 c-Myc, and HIF-1α. At the final section, we provide a discussion about how anti-tumor compounds affect miR/autophagy axis in ensuring chemosensitivity. These topics are described in this review to show how autophagy inhibition/induction can lead to chemosensitivity/chemoresistance, and miRs are considered as key players in these discussions.

Therapeutic Potential of PI3K/AKT/mTOR Pathway in Gastrointestinal Stromal Tumors: Rationale and Progress

Simple Summary

Most gastrointestinal stromal tumors (GISTs) arise due to gain-of-function mutations of KIT and PDGFRA, encoding the receptor tyrosine kinase (RTK). The introduction of the RTK inhibitor imatinib has significantly improved the management of GISTs; however, drug resistance remains a challenge. Constitutive autophosphorylation of RTKs is associated with the activation of the PI3K/AKT/mTOR pathway. Especially, this pathway plays a pivotal role in mRNA translation initiation, directly regulated by eukaryotic initiation factors (eIFs). This review highlights the progress for targeting PI3K/AKT/mTOR-dependent mechanisms in GISTs and explores the relationship between mTOR downstream eIFs and the development of GISTs, which may be a promising future therapeutic target for this tumor entity.

Abstract

Gastrointestinal stromal tumor (GIST) originates from interstitial cells of Cajal (ICCs) in the myenteric plexus of the gastrointestinal tract. Most GISTs arise due to mutations of KIT and PDGFRA gene activation, encoding the receptor tyrosine kinase (RTK). The clinical use of the RTK inhibitor imatinib has significantly improved the management of GIST patients; however, imatinib resistance remains a challenge. The phosphatidylinositol 3-kinase (PI3K)/protein kinase B (AKT)/mammalian target of rapamycin (mTOR) pathway is a critical survival pathway for cell proliferation, apoptosis, autophagy and translation in neoplasms. Constitutive autophosphorylation of RTKs has an impact on the activation of the PI3K/AKT/mTOR pathway. In several preclinical and early-stage clinical trials PI3K/AKT/mTOR signaling inhibition has been considered as a promising targeted therapy strategy for GISTs. Various inhibitory drugs targeting different parts of the PI3K/AKT/mTOR pathway are currently being investigated in phase Ι and phase ΙΙ clinical trials. This review highlights the progress for PI3K/AKT/mTOR-dependent mechanisms in GISTs, and explores the relationship between mTOR downstream signals, in particular, eukaryotic initiation factors (eIFs) and the development of GISTs, which may be instrumental for identifying novel therapeutic targets.