Loss of CDC4/FBXW7 in gastric carcinoma

Analysis of biopsies of gastric cancer, intestinal and diffuse, and non-atrophic gastritis: an overview of loss of heterozygosity in Mexican patients

This study analyzed the loss of heterozygosity (LOH) effect on gastric cancer (GC) tumor samples from 21 Mexican patients, including diffuse (DGC) and intestinal (IGC) subtypes, as well as non-atrophic gastritis (NAG, control). Whole-genome high-density arrays were performed, and LOH regions were identified among the tissue samples. The differences in affected chromosomes were established among groups, with chromosomes 6 and 8 primarily affected in DGC and chromosomes 3, 16, and 17 in IGC. Functional pathway analysis revealed involvement in cancer-associated processes, such as signal transduction, immune response, and cellular metabolism. Five LOH-genes (IRAK1, IKBKG, PAK3, TKTL1, PRPS1) shared between GC and NAG suggest an early role in carcinogenesis. Specific genes were highlighted for Hallmarks of Cancer NAG-related genes (PTPRJ and NDUFS) were linked to cell proliferation and growth; IGC genes (GNAI2, RHOA, MAPKAPK3, MST1R) to genomic instability, metastasis, and arrest of cell death; and DGC genes to energy metabolism and immune evasion. These findings emphasize the role of LOH in GC pathogenesis and underscore the need for further research to understand LOH-affected genes and their diagnostic or evolution potential in cancer management. Portions of this text were previously published as part of a preprint (https://www.medrxiv.org/content/10.1101/2024.07.29.24311063v1).

Isoform alterations in the ubiquitination machinery impacting gastrointestinal malignancies

The advancement of RNAseq and isoform-specific expression platforms has led to the understanding that isoform changes can alter molecular signaling to promote tumorigenesis. An active area in cancer research is uncovering the roles of ubiquitination on spliceosome assembly contributing to transcript diversity and expression of alternative isoforms. However, the effects of isoform changes on functionality of ubiquitination machineries (E1, E2, E3, E4, and deubiquitinating (DUB) enzymes) influencing onco- and tumor suppressor protein stabilities is currently understudied. Characterizing these changes could be instrumental in improving cancer outcomes via the identification of novel biomarkers and targetable signaling pathways. In this review, we focus on highlighting reported examples of direct, protein-coded isoform variation of ubiquitination enzymes influencing cancer development and progression in gastrointestinal (GI) malignancies. We have used a semi-automated system for identifying relevant literature and applied established systems for isoform categorization and functional classification to help structure literature findings. The results are a comprehensive snapshot of known isoform changes that are significant to GI cancers, and a framework for readers to use to address isoform variation in their own research. One of the key findings is the potential influence that isoforms of the ubiquitination machinery have on oncoprotein stability.

Pan-cancer analysis of FBXW family with potential implications in prognosis and immune infiltration

Background

The F-box and WD repeat domain containing (FBXW) family of SCF E3 complexes has 10 members that are responsible for ubiquitination and degradation of substrate proteins involved in cell cycle regulation and tumorigenesis. Among them, FBXW1 (also called b-TrCP1/BTRC) and FBXW7 are the central proteins in this category. However, there is still a lack of elaborate exploration of the contribution of FBXW family members, especially FBXW1 and FBXW7, in various tumor types.

Methods

In this present study, we preliminarily analyzed the genetic structure characteristics of the FBXW family, and systematically investigated their expression patterns and clinical correlations based on the TCGA pan-cancer data. Survival analysis of FBXWs was also conducted through the Kaplan-Meier method. In addition, we assessed their immune infiltration level through immune-related algorithms like Timer and xCell.

Results

There were obvious genetic heterogeneity and different clinical traits in FBXW family members. Moreover, we found that FBXW family genes may be useful in predicting prognosis and therapeutic efficacy using survival analysis. In addition, the immune infiltration of FBXW family was also clearly illustrated in this study. The results showed these genes were closely involved in immune components such as immune score, immune subtypes, tumor-infiltrating lymphocytes and immune checkpoints. Notedly, FBXW1 as an oncogene and FBXW7 as a tumor suppressor gene also show opposite relationships on immune cells.

Conclusion

Our results provided valuable strategies to guide the therapeutic orientation concerning the role of FBXW family genes in cancer.

Manifold role of ubiquitin in Helicobacter pylori infection and gastric cancer

Infection with H. pylori induces a strong host cellular response represented by induction of a set of molecular signaling pathways, expression of proinflammatory cytokines and changes in proliferation. Chronic infection and inflammation accompanied by secretory dysfunction can result in the development of gastric metaplasia and gastric cancer. Currently, it has been determined that the regulation of many cellular processes involves ubiquitinylation of molecular effectors. The binding of ubiquitin allows the substrate to undergo a change in function, to interact within multimolecular signaling complexes and/or to be degraded. Dysregulation of the ubiquitinylation machinery contributes to several pathologies, including cancer. It is not understood in detail how H. pylori impacts the ubiquitinylation of host substrate proteins. The aim of this review is to summarize the existing literature in this field, with an emphasis on the role of E3 ubiquitin ligases in host cell homeodynamics, gastric pathophysiology and gastric cancer.

Roles of E3 ubiquitin ligases in gastric cancer carcinogenesis and their effects on cisplatin resistance

Although gastric cancer (GC) is one of the most common cancers with high incidence and mortality rates, its pathogenesis is still not elucidated. GC carcinogenesis is complicated and involved in the activation of oncoproteins and inactivation of tumor suppressors. The ubiquitin-proteasome system (UPS) is crucial for protein degradation and regulation of physiological and pathological processes. E3 ubiquitin ligases are pivotal enzymes in UPS, containing various subfamily proteins. Previous studies report that some E3 ligases, including SKP2, CUL1, and MDM2, act as oncoproteins in GC carcinogenesis. On the other hand, FBXW7, FBXL5, FBXO31, RNF43, and RNF180 exert as tumor suppressors in GC carcinogenesis. Moreover, E3 ligases modulate cell growth, cell apoptosis, and cell cycle; thus, it is complicated to confer cisplatin resistance/sensitivity in GC cells. The intrinsic and acquired cisplatin resistance limits its clinical application against GC. In this review, we explore oncogenic and tumor suppressive roles of E3 ligases in GC carcinogenesis and focus on the effects of E3 ligases on cisplatin resistance in GC cells, which will provide novel therapeutic targets for GC therapy, especially for cisplatin-resistant patients.

Functional roles of E3 ubiquitin ligases in gastric cancer

To date, >650 E3 ubiquitin ligases have been described in humans, including >600 really interesting new genes (RINGs), 28 homologous to E6-associated protein C-terminus (HECTs) and several RING-in-between-RINGs. They are considered key regulators and therapeutic targets of many types of human cancers, including gastric cancer (GC). Among them, some RING and HECT E3 ligases are closely related to the proliferation, infiltration and prognosis of GC. During the past few years, abnormal expressions and functions of many E3 ligases have been identified in GC. However, the functional roles of E3 ligases in GC have not been fully elucidated. The present article focuses on the functional roles of E3 ligases related to the proteasome in GC. In this comprehensive review, the latest research progress on E3 ligases involved in GC and elaborate their structure, classification, functional roles and therapeutic value in GC was summarized. Finally, 30 E3 ligases that serve essential roles in regulating the development of GC were described. Some of these ligases may serve as oncogenes or tumor suppressors in GC, whereas the pathological mechanism of others needs further study; for example, constitutive photomorphogenic 1. In conclusion, the present review demonstrated that E3 ligases are crucial tumor regulatory factors and potential therapeutic targets in GC. Therefore, more studies should focus on the therapeutic targeting of E3 ligases in GC.

STYX/FBXW7 axis participates in the development of endometrial cancer cell via Notch-mTOR signaling pathway

Endometrial cancer (EC) is the most common gynecologic malignancy in world. It has been reported that the mutation rate of FBXW7 is frequent in EC, but the specific functions of FBXW7 remain unknown in EC. In the present study, we revealed the role and mechanism of FBXW7 in EC cells. Compared with adjacent nontumor tissues, the FBXW7 expression level was lower in EC tissues. However, the level of STYX was in contrast with the expression of FBXW7 in EC tissues. And STYX interacted with FBXW7 and then down-regulated its expression level in EC. Over-expression of FBXW7 inhibited cell proliferation and facilitated apoptosis in EC cells, whereas silencing FBXW7 acted an opposite effect on EC cells. And the process of FBXW7 participated the proliferation and apoptosis in EC was regulated by STYX. FBXW7 suppressed the expression of Notch pathway related protein, and further inhibited the phosphorylation of mTOR. In addition, we also found that mTOR activitor (MHY1485) and Notch activator (Jagged-1) reversed the effect of over-expressing FBXW7 on cell proliferation and cell apoptosis. And Notch inhibitor (DAPT) counteracted the impact of over-expressing STYX on cell proliferation and cell apoptosis. Collectively, the present study verified that STYX inhibited the expression level of FBXW7 in EC, and then promoted cell proliferation but suppressed apoptosis through Notch-mTOR signaling pathway, which promoted carcinogenesis and progression of EC.

High expression of TRIM36 is associated with radiosensitivity in gastric cancer

Radiotherapy is one of the main adjuvant treatments for gastric cancer (GC) that can effectively reduce local recurrence and improve survival rates. However, radiotherapy may result in cytotoxicity and not benefit all patients. This highlights the requirement for identifying potential radiosensitivity genes in GC. The current study investigated the association between tripartite motif containing 36 (TRIM36) status and the prognosis of patients with GC receiving radiotherapy. A total of 371 patients with GC were selected from The Cancer Genome Atlas and randomly divided into test and the validation groups. The results revealed that TRIM36 expression was not associated with the overall survival (OS) rate. Patients who received radiotherapy with high TRIM36 expression had an improved OS rate compared with patients who did not receive radiotherapy in the test group, as demonstrated by univariate analysis [hazard ratio (HR), 0.062; 95% confidence interval (CI), 0.008–0.462; P=0.007] and multivariate analysis (HR, 0.095; 95% CI, 0.012–0.748; P=0.025). In the validation group, patients with high TRIM36 expression had decreased mortality risk when they received radiotherapy compared with patients who did not receive radiotherapy, as determined by univariate analysis (HR, 0.190; 95% CI, 0.067–0.540; P=0.002) and multivariate analysis (HR, 0.075; 95% CI, 0.020–0.276; P<0.001). However, for patients with low expression, no significant difference was identified in the overall survival rates between the radiotherapy and non-radiotherapy groups. Chi-squared analysis revealed that the expression status of TRIM36 was an independent factor and was not associated with clinicopathological factors. The results indicated that patients with high TRIM36 expression receiving radiotherapy exhibited an improved OS rate. TRIM36 may therefore be an important factor affecting the clinical prognosis of patients with GC receiving radiotherapy and may be considered as a potential radiosensitivity gene signature.

FBXW7 in Cancer: What Has Been Unraveled Thus Far?

: The FBXW7 (F-box with 7 tandem WD40) protein encoded by the gene FBXW7 is one of the crucial components of ubiquitin ligase called Skp1-Cullin1-F-box (SCF) complex that aids in the degradation of many oncoproteins via the ubiquitin-proteasome system (UPS) thus regulating cellular growth. FBXW7 is considered as a potent tumor suppressor as most of its target substrates can function as potential growth promoters, including c-Myc, Notch, cyclin E, c-JUN, and KLF5. Its regulators include p53, C/EBP-δ, Numb, microRNAs, Pin 1, Hes-5, BMI1, Ebp2. Mounting evidence has indicated the involvement of aberrant expression of FBXW7 for tumorigenesis. Moreover, numerous studies have also shown its role in cancer cell chemosensitization, thereby demonstrating the importance of FBXW7 in the development of curative cancer therapy. This comprehensive review emphasizes on the targets, functions, regulators and expression of FBXW7 in different cancers and its involvement in sensitizing cancer cells to chemotherapeutic drugs.

SCFFBW7-mediated degradation of Brg1 suppresses gastric cancer metastasis

Brg1/SMARCA4 serves as the ATPase and the helicase catalytic subunit for the multi-component SWI/SNF chromatin remodeling complex, which plays a pivotal role in governing chromatin structure and gene transcription. However, the upstream signaling pathways regulating Brg1 protein stability and its physiological contribution to carcinogenesis remain largely elusive. Here we report that Brg1 is a bona fide ubiquitin substrate of SCF^FBW7. We reveal that CK1δ phosphorylates Brg1 at Ser31/Ser35 residues to facilitate the binding of Brg1 to FBW7, leading to ubiquitination-mediated degradation. In keeping with a tumor suppressive role of FBW7 in human gastric cancer, we find an inverse correlation between FBW7 and Brg1 expression in human gastric cancer clinical samples. Mechanistically, we find that stabilization of Brg1 in gastric cancer cells suppresses E-cadherin expression, subsequently promoting gastric cancer metastasis. Hence, this previously unknown FBW7/Brg1 signaling axis provides the molecular basis and the rationale to target Brg1 in FBW7-compromised human gastric cancers.

FBXW7: a critical tumor suppressor of human cancers

The ubiquitin-proteasome system (UPS) is involved in multiple aspects of cellular processes, such as cell cycle progression, cellular differentiation, and survival (Davis RJ et al., Cancer Cell 26:455-64, 2014; Skaar JR et al., Nat Rev Drug Discov 13:889-903, 2014; Nakayama KI and Nakayama K, Nat Rev Cancer 6:369-81, 2006). F-box and WD repeat domain containing 7 (FBXW7), also known as Sel10, hCDC4 or hAgo, is a member of the F-box protein family, which functions as the substrate recognition component of the SCF E3 ubiquitin ligase. FBXW7 is a critical tumor suppressor and one of the most commonly deregulated ubiquitin-proteasome system proteins in human cancer. FBXW7 controls proteasome-mediated degradation of oncoproteins such as cyclin E, c-Myc, Mcl-1, mTOR, Jun, Notch and AURKA. Consistent with the tumor suppressor role of FBXW7, it is located at chromosome 4q32, a genomic region deleted in more than 30% of all human cancers (Spruck CH et al., Cancer Res 62:4535-9, 2002). Genetic profiles of human cancers based on high-throughput sequencing have revealed that FBXW7 is frequently mutated in human cancers. In addition to genetic mutations, other mechanisms involving microRNA, long non-coding RNA, and specific oncogenic signaling pathways can inactivate FBXW7 functions in cancer cells. In the following sections, we will discuss the regulation of FBXW7, its role in oncogenesis, and the clinical implications and prognostic value of loss of function of FBXW7 in human cancers.

Fbxw7 haploinsufficiency loses its protection against DNA damage and accelerates MNU-induced gastric carcinogenesis

Fbxw7, a subunit of the SCF E3 ubiquitin ligase, recognizes oncoprotein substrates and leads to their proteasomal degradation. Fbxw7 acts as a tumor suppressor via inducing apoptosis and growth arrest in various kinds of tumors. To clarify the initiating role in gastric carcinogenesis as well as the histologic characterization of tumor in Fbxw7 allele haploinsufficient mice, we generated Fbxw7 heterozygous knockout mice (Fbxw7^+/−) and treated them with chemical carcinogen N-methyl-N-nitrosourea (MNU) at 5–6 weeks of age. We also treated mouse embryo fibroblasts (MEFs) from Fbxw7^+/− and Fbxw7^+/+ mice with MNU and examined cell DNA damage via comet assay. The protein expression of Fbxw7 and its substrate c-Myc from mouse tumors, as well as human tumors sampled from six patients, were detected by Western blot. As results, the tumor incidence was obviously higher in Fbxw7^+/− mice (13/20) than in Fbxw7^+/+ mice (6/20) after 35-week observation. Intestinal metaplasia (P = 0.013) and dysplasia (P = 0.036) were more severe in Fbxw7^+/− mice than in Fbxw7^+/+ mice. The repair potential of DNA damage was suppressed in MEFs from Fbxw7^+/− mice after MNU exposure. Increased c-Myc expression was accompanied by decreased Fbxw7 protein expression in tumor tissues from mouse and patients. In conclusion, Fbxw7 haploinsufficiency increased the risk of gastric carcinogenesis induced by MNU, which is associated with the accumulation of DNA damage as well as c-Myc oncoprotein.

MicroRNA-32 promotes cell proliferation, migration and suppresses apoptosis in breast cancer cells by targeting FBXW7

Background

MicroRNAs are a class of small non-coding RNAs that are involved in many important physiological and pathological processes by regulating gene expression negatively. The purpose of this study was to investigate the effect of miR-32 on cell proliferation, migration and apoptosis and to determine the functional connection between miR-32 and FBXW7 in breast cancer.

Methods

In this study, quantitative RT-PCR was used to evaluate the expression levels of miR-32 in 27 breast cancer tissues, adjacent normal breast tissues and human breast cancer cell lines. The biological functions of miR-32 in MCF-7 breast cancer cells were determined by cell proliferation, apoptosis assays and wound-healing assays. In addition, the regulation of FBXW7 by miR-32 was assessed by qRT-PCR, Western blot and luciferase reporter assays.

Results

MiR-32 was frequently overexpressed in breast cancer tissue samples and cell lines as was demonstrated by qRT-PCR. Moreover, the up-regulation of miR-32 suppressed apoptosis and promoted proliferation and migration, whereas down-regulation of miR-32 showed an opposite effect. Dual-luciferase reporter assays showed that miR-32 binds to the 3′-untranslated region of FBXW7, suggesting that FBXW7 is a direct target of miR-32. Western blot analysis showed that over-expression of miR-32 reduced FBXW7 protein level. Furthermore, an inverse correlation was found between the expressions of miR-32 and FBXW7 mRNA levels in breast cancer tissues. Knockdown of FBXW7 promoted proliferation and motility and suppressed apoptosis in MCF-7 cells.

Conclusions

Taken together, the present study suggests that miR-32 promotes proliferation and motility and suppresses apoptosis of breast cancer cells through targeting FBXW7.

Fbxw7 Tumor Suppressor: A Vital Regulator Contributes to Human Tumorigenesis

Rapidly accumulating data indicate that F-box/WD repeat-containing protein 7 (Fbxw7) is one of the most frequently mutated genes in human cancers and regulates a network of crucial oncoproteins. These studies have generated important new insights into tumorigenesis and may soon enable therapies targeting the Fbxw7 pathway. We searched PubMed, Embase, and ISI Web of Science databases (1973-2015, especially recent 5 years) for articles published in the English language using the key words "Fbxw7," "Fbw7," "hCDC4," and "Sel-10," and we reviewed recent developments in the search for Fbxw7. Fbxw7 coordinates the ubiquitin-dependent proteolysis of several critical cellular regulators, thereby controlling essential processes, such as cell cycle, differentiation, and apoptosis. Fbxw7 contains 3 isoforms (Fbxw7α, Fbxw7β, and Fbxw7γ), and they are differently regulated in subtract recognition. Besides those, Fbxw7 activity is controlled at different levels, resulting in specific and tunable regulation of the abundance and activity of its substrates in a variety of human solid tumor types, including glioma malignancy, nasopharyngeal carcinoma, osteosarcoma, melanoma as well as colorectal, lung, breast, gastric, liver, pancreatic, renal, prostate, endometrial, and esophageal cancers. Fbxw7 is strongly associated with tumorigenesis, and the mechanisms and consequences of Fbxw7 deregulation in cancers may soon enable the development of novel therapeutic approaches.

The role of cullin proteins in gastric cancer

The cullin proteins are a family of scaffolding proteins that associate with RING proteins and ubiquitin E3 ligases and mediate substrate-receptor bindings. Thus, cullin proteins regulate the specificity of ubiquitin targeting in the regulation of proteins involved in various cellular processes, including proliferation, differentiation, and apoptosis. There are seven cullin proteins that have been identified in eukaryotes: CUL1, CUL2, CUL3, CUL4A, CUL4B, CUL5, and CUL7/p53-associated parkin-like cytoplasmic protein. All of these proteins contain a conserved cullin homology domain that binds to RING box proteins. Cullin-RING ubiquitin ligase complexes are activated upon post-translational modification by neural precursor cell-expressed, developmentally downregulated protein 8. The aberrant expression of several cullin proteins has been implicated in many cancers though the significance in gastric cancer has been less well investigated. This review provides the first systematic discussion of the associations between all members of the cullin protein family and gastric cancer. Functional and regulatory mechanisms of cullin proteins in gastric carcinoma progression are also summarized along with a discussion concerning future research areas. Accumulating evidence suggests a critical role of cullin proteins in tumorigenesis, and a better understanding of the function of these individual cullin proteins and their targets will help identify potential biomarkers and therapeutic targets.

Dysregulation of ubiquitin ligases in cancer

Ubiquitin ligases (UBLs) are critical components of the ubiquitin proteasome system (UPS), which governs fundamental processes regulating normal cellular homeostasis, metabolism, and cell cycle in response to external stress signals and DNA damage. Among multiple steps of the UPS system required to regulate protein ubiquitination and stability, UBLs define specificity, as they recognize and interact with substrates in a temporally- and spatially-regulated manner. Such interactions are required for substrate modification by ubiquitin chains, which marks proteins for recognition and degradation by the proteasome or alters their subcellular localization or assembly into functional complexes. UBLs are often deregulated in cancer, altering substrate availability or activity in a manner that can promote cellular transformation. Such deregulation can occur at the epigenetic, genomic, or post-translational levels. Alterations in UBL can be used to predict their contributions, affecting tumor suppressors or oncogenes in select tumors. Better understanding of mechanisms underlying UBL expression and activities is expected to drive the development of next generation modulators that can serve as novel therapeutic modalities. This review summarizes our current understanding of UBL deregulation in cancer and highlights novel opportunities for therapeutic interventions.

Copy number variation in CCND1 gene is implicated in the pathogenesis of sporadic parathyroid carcinoma

BACKGROUND

The molecular bases for parathyroid carcinomas present in conjunction with sporadic primary hyperparathyroidism are not fully elucidated. Gene copy number variations (CNVs) play an important role in tumorigenesis. The aim of the current study was to explore whether the CNVs of specific tumor-associated genes are involved in parathyroid carcinogenesis.

METHODS

A multiplex ligation-dependent probe amplification method was used to compare differences in copy number in 39 common tumor-associated genes among 7 patients with parathyroid carcinoma and 14 age- and sex-matched subjects with parathyroid adenoma.

RESULTS

It was shown that amplification of CCND1, a gene encoding cyclin D1, was more prevalent in parathyroid carcinomas than in adenomas (71 vs. 21 %, p = 0.056). This result was confirmed quantitatively by real-time polymerase chain reaction. Expression of CCND1 mRNA level was significantly higher in carcinomas than in adenomas (p = 0.003). Western blot and immunohistochemical analysis also demonstrated higher expression of CCND1 in carcinoma specimens than in adenoma samples.

CONCLUSIONS

It is thus inferred that gain in copy number of CCND1 is implicated in the molecular pathogenesis of parathyroid carcinoma.

MicroRNA-25 promotes gastric cancer proliferation, invasion, and migration by directly targeting F-box and WD-40 Domain Protein 7, FBXW7

Increasing evidence shows that abnormal microRNA (miRNA) expression is involved in tumorigenesis. MiR-25 was previously reported to act as tumor suppressor or oncogene in diverse cancers. However, their expression, function, and mechanism in gastric cancer (GC) are not well known. Here, we show that miR-25 was overexpressed in primary tumor tissues of GC patients and was significantly correlated with a more aggressive phenotype of GC in patients. MiR-25 inhibition significantly decreased the proliferation, invasion, and migration of GC cells in vitro. Furthermore, miR-25 repressed F-box and WD-40 domain protein 7 (FBXW7) expression by directly binding to 3-untranslated region (UTR) of FBXW7, and the inverse correlation was observed between the expressions of miR-25 and FBXW7 mRNA in primary GC tissues. Moreover, the restoration of FBXW7 led to suppressed proliferation, invasion, and migration of GC cells. In vivo, miR-25 promotes tumor growth of GC. Taken together, miR-25 promotes GC progression by directly downregulating FBXW7 expression and may be employed as a novel prognostic marker and therapeutic target of GC.

Role of E3 ubiquitin ligases in gastric cancer

E3 ubiquitin ligases have an important role in carcinogenesis and include a large family of proteins that catalyze the ubiquitination of many protein substrates for targeted degradation by the 26S proteasome. So far, E3 ubiquitin ligases have been reported to have a role in a variety of biological processes including cell cycle regulation, cell proliferation, and apoptosis. Recently, several kinds of E3 ubiquitin ligases were demonstrated to be generally highly expressed in gastric cancer (GC) tissues and to contribute to carcinogenesis. In this review, we summarize the current knowledge and information about the clinical significance of E3 ubiquitin ligases in GC. Bortezomib, a proteasome inhibitor, encouraged the evaluation of other components of the ubiquitin proteasome system for pharmaceutical intervention. The clinical value of novel treatment strategies targeting aberrant E3 ubiquitin ligases for GC are discussed in the review.

An evolutionarily conserved synthetic lethal interaction network identifies FEN1 as a broad-spectrum target for anticancer therapeutic development

Harnessing genetic differences between cancerous and noncancerous cells offers a strategy for the development of new therapies. Extrapolating from yeast genetic interaction data, we used cultured human cells and siRNA to construct and evaluate a synthetic lethal interaction network comprised of chromosome instability (CIN) genes that are frequently mutated in colorectal cancer. A small number of genes in this network were found to have synthetic lethal interactions with a large number of cancer CIN genes; these genes are thus attractive targets for anticancer therapeutic development. The protein product of one highly connected gene, the flap endonuclease FEN1, was used as a target for small-molecule inhibitor screening using a newly developed fluorescence-based assay for enzyme activity. Thirteen initial hits identified through in vitro biochemical screening were tested in cells, and it was found that two compounds could selectively inhibit the proliferation of cultured cancer cells carrying inactivating mutations in CDC4, a gene frequently mutated in a variety of cancers. Inhibition of flap endonuclease activity was also found to recapitulate a genetic interaction between FEN1 and MRE11A, another gene frequently mutated in colorectal cancers, and to lead to increased endogenous DNA damage. These chemical-genetic interactions in mammalian cells validate evolutionarily conserved synthetic lethal interactions and demonstrate that a cross-species candidate gene approach is successful in identifying small-molecule inhibitors that prove effective in a cell-based cancer model.

MicroRNA-223 functions as an oncogene in human gastric cancer by targeting FBXW7/hCdc4

AIMS

The aim of this study was (a) to determine the role of micro-223 (miR-223) in gastric cancer and (b) to elucidate its regulatory mechanism on the FBXW7/hCdc4 gene.

MATERIALS AND METHODS

Artificial miR-223 and control oligonucleotide was transfected into gastric cancer cell line SGC7901 by using Lipofectamine2000. Apoptosis of miR-223 group and control group cells was analyzed by flow cytometry, and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-tetrazolium bromide and colony formation assays were performed to detect the cell viability, to survey migration of miR-223 group and control group cells; scratch wound-healing motility assays, Transwell Assay, and Western blot test were performed to measure the variance of hFBXW7. Luciferase Reporter Assay, which was done by pLUC-hFBXW7 WT-3'-UTR co-transfected with pLMP-hsa-miR-223 or pLMP plasmid (as control) into HEK293T cells, used to detect whether hFBXW7 is a direct target gene of miR-223. Gastric cancer cell line SGC7901 transfected with miR-223 or control oligonucleotide was resuspended in ECM gel and then was injected into the flank of nude mice, 4 weeks later, the nude mice were euthanized. The tumors were excised then were measured and weighted. SYBR-Green I-based real-time RT-PCR study was used to detect the level of miR-223 in 22 gastric cancer tissue and corresponding gastric mucosa tissues. Immunohistochemical method was applied to detect the protein of hFBXW7.

RESULTS

Gastric cancer cell line SGC7901, transfected with miR-223, showed significant reduction in cellular apoptosis and increased proliferation and invasion in vitro. Similar results were found in tumorigenesis assays performed in nude mice. Moreover, 19 of 22 cancer tissue samples highly expressed miR-223, when compared with patient-matched normal gastric mucosa. Specifically, patients with lymph node metastasis or metastatic disease (M1) at an advanced pathological stage showed significantly higher expression of miR-223. FBXW7/hCdc4 protein (FBW7) levels in gastric cancer cases were inversely correlated with miR-223 expression. Overexpression of miR-223 in gastric cancer cell lines decreased FBW7 expression at the translational level and decreased FBXW7/hCdc4-driven luciferase-reporter activity.

CONCLUSION

In summary, the data indicated that miR-223 targets FBXW7/hCdc4 expression at the post-transcriptional level and appears to regulate cellular apoptosis, proliferation, and invasion in gastric cancer. MiR-223 may serve as a novel therapeutic target in gastric cancer.

Low frequency of HER2 amplification and overexpression in early onset gastric cancer

Background

The recent ToGA trial results indicated that trastuzumab is a new, effective, and well-tolerated treatment for HER2-positive gastric cancer (GC). Although GC mainly affects older patients, fewer than 10% of GC patients are considered early-onset (EOGC) (presenting at the age of 45 years or younger). These EOGC show different clinicopathological and molecular profiles compared to late onset GC suggesting that they represent a separate entity within gastric carcinogenesis. In light of potential trastuzumab benefit, subpopulations of GC such as EOGC (versus late onset) should be evaluated for their frequency of amplification and overexpression using currently available techniques.

Methods

Tissue microarray (TMA) blocks of 108 early onset GC and 91 late onset GC were stained by immunohistochemistry (IHC, Hercep test, DAKO) and chromogenic in situ hybridization (CISH, SPoT-Light, Invitrogen).

Results

Overall, we found only 5% HER2 high level amplification and 3% HER2 3+ overexpression (6/199). In addition, 8 patients (4%) showed a low level CISH amplification and 9 patients (4.5%) showed a 2+ IHC score. IHC and CISH showed 92% concordance and CISH showed less heterogeneity than IHC. In 2/199 cases (1%), IHC showed clinically relevant heterogeneity between TMA cores, but all cases with focal IHC 3+ expression were uniformly CISH high level amplified. Early onset GCs showed a significantly lower frequency of HER2 amplification (2%) and overexpression (0%) than late onset GCs (8% and 7% respectively) (p = 0.085 and p = 0.008 respectively). Proximal GC had more HER2 amplification (9% versus 3%) and overexpression (7% versus 2%) than distal tumours although this difference was not significant (p = 0.181 and p = 0.182 respectively). HER2 CISH showed more high level amplification in the intestinal type (7%, 16% if low-level included) compared to the mixed (5%, 5% if low-level included) and diffuse type (3%, 4% if low-level included) GCs (p = 0.029). A similar association was seen for HER2 IHC and histologic type (p = 0.008). Logistic regression indicated a significant association between HER2 expression and age, which remained significant when adjusted for both location and histological type.

Conclusions

Even focal HER2 overexpression in GC points to uniform HER2 amplification by CISH. We show for the first time that early onset GC has a lower frequency of HER2 amplification and overexpression than late onset GC, and confirm that intestinal type GC shows the highest rate of HER2 amplification and overexpression.