The circMYBL2-Encoded p185 Protein Suppresses Colorectal Cancer Progression by Inhibiting Serine Biosynthesis.

Circular RNAs are a class of covalently closed single-stranded loop RNAs that have been implicated to play a functional role in almost all types of cancers. Previous studies have revealed that circMYBL2 acts as a tumor-promoting circular RNA. In this study, we found that circMYBL2 in colorectal cancer encodes a 185-amino acid protein, p185. Functionally, circMYBL2-encoded p185 suppressed the growth and aggressiveness of colorectal cancer cells in vitro and in vivo. Mechanistically, p185 counteracted ubiquitin C-terminal hydrolase L3 (UCHL3)-mediated deubiquitination of phosphoglycerate dehydrogenase (PHGDH) by competitively binding to the C1 domain of UCHL3, resulting in PHGDH degradation and a subsequent reduction in serine and glycine biosynthesis. These data revealed that the circMYBL2-encoded p185 isoform serves as a tumor suppressor to inhibit the progression of colorectal cancer by reducing serine biosynthesis. Significance: A p185 protein encoded by circMYBL2 functions as a tumor suppressor that inhibits the progression of colorectal cancer by increasing the degradation of PHGDH to reduce serine biosynthesis.

ESRP1-driven alternative splicing of CLSTN1 inhibits the metastasis of gastric cancer.

Tumor metastasis severely limits the prognosis of gastric cancer patients. RNA-binding proteins (RBPs) are crucial in tumor metastasis, yet there is limited research into their involvement in gastric cancer. Here, we found that ESRP1, a RBP specific in epithelial cells, is important in regulating the metastasis of gastric cancer cells. ESRP1 is negatively correlated with distant metastasis and lymph node metastasis in gastric cancer patients. And we demonstrated that ESRP1 inhibit migration and invasion of gastric cancer in vitro and in vivo. Mechanistically, ESRP1 promotes exon 11 alternative splicing of CLSTN1 pre-mRNA. The post-splicing short CLSTN1 stabilizes the Ecadherin/ß-catenin binding structure, and promotes ß-catenin protein ubiquitination and degradation, thereby inhibiting the migration and invasion of gastric cancer cells. Our study highlights the role of ESRP1 in regulating metastasis of gastric cancer and extends its mechanism. These results provide a possibility for ESRP1 and CLSTN1 to become therapeutic targets for metastasis of gastric cancer.

Combination of PARP inhibitor and CDK4/6 inhibitor modulates cGAS/STING-dependent therapy-induced senescence and provides "one-two punch" opportunity with anti-PD-L1 therapy in colorectal cancer.

Although PARP inhibitor (PARPi) has been proven to be a promising anticancer drug in cancer patients harboring BRCA1/2 mutation, it provides limited clinical benefit in colorectal cancer patients with a low prevalence of BRCA1/2 mutations. In our study, we found PARPi talazoparib significantly induced cellular senescence via inhibiting p53 ubiquitination and activating p21. Furthermore, CDK4/6i palbociclib amplified this therapy-induced senescence (TIS) in vitro and in vivo. Mechanistically, talazoparib and palbociclib combination induced senescence-associated secretory phenotype (SASP), and characterization of SASP components revealed type I interferon (IFN)-related mediators, which were amplified by cGAS/STING signaling. More importantly, RNA sequencing data indicated that combination therapy activated T cell signatures and combination treatment transformed the tumor microenvironment (TME) into a more antitumor state with increased CD8 T cells and natural killer (NK) cells and decreased macrophages and granulocytic myeloid-derived suppressor cells (G-MDSCs). Moreover, clearance of the TIS cells by αPD-L1 promoted survival in immunocompetent mouse colorectal cancer models. Collectively, we elucidated the synergistic antitumor and immunomodulatory mechanisms of the talazoparib-palbociclib combination. Further combination with PD-L1 antibody might be a promising "one-two punch" therapeutic strategy for colorectal cancer patients.

Using Transcriptional Signatures to Find Cancer Drivers with LURE.

Cancer genome projects have produced multidimensional datasets on thousands of samples. Yet, depending on the tumor type, 5-50% of samples have no known driving event. We introduce a semi-supervised method called Learning UnRealized Events (LURE) that uses a progressive label learning framework and minimum spanning analysis to predict cancer drivers based on their altered samples sharing a gene expression signature with the samples of a known event. We demonstrate the utility of the method on the TCGA Pan-Cancer Atlas dataset for which it produced a high-confidence result relating 59 new connections to 18 known mutation events including alterations in the same gene, family, and pathway. We give examples of predicted drivers involved in TP53, telomere maintenance, and MAPK/RTK signaling pathways. LURE identifies connections between genes with no known prior relationship, some of which may offer clues for targeting specific forms of cancer. Code and Supplemental Material are available on the LURE website: https://sysbiowiki.soe.ucsc.edu/lure.

The DNA Endonuclease Mus81 Regulates ZEB1 Expression and Serves as a Target of BET4 Inhibitors in Gastric Cancer.

DNA replication and repair proteins play an important role in cancer initiation and progression by affecting genomic instability. The DNA endonuclease Mus81 is a DNA structure-specific endonuclease, which has been implicated in DNA replication and repair. In this study, we found that Mus81 promotes gastric metastasis by controlling the transcription of ZEB1, a master regulator of the epithelial-mesenchymal transition (EMT). Our results revealed that Mus81 is highly expressed in gastric cancer samples from patients and cell lines compared with their normal counterparts. Particularly, Mus81 expression positively correlated with ZEB1 expression and Mus81 overexpression was significantly associated with higher incidence of lymph node metastasis in patients. Furthermore, Mus81 promoted migration of gastric cancer cells both in vitro and in vivo We conducted a drug screen using a collection of preclinical and FDA-approved drugs and found that the BRD4 inhibitor AZD5153 inhibited the expression of Mus81 and ZEB1 by regulating the epigenetic factor Sirt5. As expected, AZD5153 treatment significantly reduced the migration of gastric cancer cells overexpressing Mus81 in vitro and in vivo Collectively, we show that Mus81 is a regulator of ZEB1 and promotes metastasis in gastric cancer. Importantly, we demonstrate that the BRD4 inhibitor AZD5153 can potentially be used as an effective antimetastasis drug because of its effect on Mus81.

Identification of a 5­microRNA signature and hub miRNA­mRNA interactions associated with pancreatic cancer.

miRNA­gene axes have been reported to serve an important role in the carcinogenesis of pancreatic cancer (PC). The aim of the present study was to systematically identity the microRNA signature and hub molecules, as well as hub miRNA­gene axes, and to explore the potential biomarkers and mechanisms associated with the carcinogenesis of PC. Eleven microRNA profile datasets were obtained from the National Center for Biotechnology Information (NCBI) Gene Expression Omnibus (GEO) and ArrayExpress databases, and a meta­analysis was performed to identify the differentially expressed miRNAs (DEMs) between tumor tissue and normal tissue. Subsequently, a diagnostic regression model was constructed to identify PC based on The Cancer Genome Atlas (TCGA) miRNA sequence data by using the least absolute shrinkage and selection operator (LASSO) method. In addition, GSE41368 was downloaded, and a weighted gene co­expression network analysis (WGCNA) was performed to obtain the gene module associated with carcinogenesis by using the TCGAbiolinks and WGCNA packages, respectively. Finally, miRNA­gene networks were constructed and visualized using Cytoscape software, followed by Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses based on the Database for Annotation, Visualization, and Integrated Discovery (DAVID). A total of 14 DEMs were identified, and a 5­microRNA­based score generated by the LASSO regression model provided a high accuracy for identifying PC [area under the curve (AUC)=0.918]. In addition, 44 miRNA­mRNA interactions were constructed, and 4 hub genes were screened on the basis of the above bioinformatic tools and databases. Furthermore, 14 biological process (BP) functions and 6 KEGG pathways were identified according to gene set enrichment analysis (GSEA). In summary, the present study applied integrated bioinformatics approaches to generate a holistic view of PC, thereby providing a basis for further clinical application of the 5­miRNA signature and the identified hub molecules, as well as the miRNA­gene axes, which could serve as diagnostic markers and potential treatment targets.

Wee1 inhibition can suppress tumor proliferation and sensitize p53 mutant colonic cancer cells to the anticancer effect of irinotecan.

Wee1 is an oncogenic nuclear kinase, which can regulate the cell cycle as a crucial G2M checkpoint. Overexpression of Wee1 can be observed in various cancer types, which may lead to a poor prognosis, but the potential therapeutic value of Wee1 in colorectal cancer has not been fully studied. In the present study, the role of Wee1 in colonic cancer was investigated. Wee1 inhibition by small interfering RNA was demonstrated to significantly restrain cancer cell proliferation and sensitize the p53 mutant colonic cancer cell lines HT29 and SW480 to the effect of treatment with ionizing radiation. The anticancer effect of the Wee1 inhibitor MK1775 was investigated in these two colonic cancer cell lines. MK1775 was demonstrated to induce significant DNA damage, suppress cell viability and induce apoptosis. In addition, MK1775 sensitized HT29 and SW480 cells to the effect of irinotecan. Annexin V/propidium iodide staining demonstrated that combination therapy can induce increased apoptosis compared with MK1775 or irinotecan monotherapy. The results of western blot analysis also indicated increased expression of the DNA damage marker histone H2AX, and apoptosis­associated protein cleaved caspase 3, in HT29 and SW480 cells. In conclusion, the present study indicated that Wee1 may be a valuable target for treatment of p53 mutant colonic cancer.

Dissect the Dynamic Molecular Circuits of Cell Cycle Control through Network Evolution Model.

The molecular circuits of cell cycle control serve as a key hub to integrate from endogenous and environmental signals into a robust biological decision driving cell growth and division. Dysfunctional cell cycle control is highlighted in a wide spectrum of human cancers. More importantly the mainstay anticancer treatment such as radiation therapy and chemotherapy targets the hallmark of uncontrolled cell proliferation in cancer cells by causing DNA damage, cell cycle arrest, and cell death. Given the functional importance of cell cycle control, the regulatory mechanisms that drive the cell division have been extensively investigated in a huge number of studies by conventional single-gene approaches. However the complexity of cell cycle control renders a significant barrier to understand its function at a network level. In this study, we used mathematical modeling through modern graph theory and differential equation systems. We believe our network evolution model can help us understand the dynamic cell cycle control in tumor evolution and optimizing dosing schedules for radiation therapy and chemotherapy targeting cell cycle.

Chk1 inhibition potentiates the therapeutic efficacy of PARP inhibitor BMN673 in gastric cancer.

Globally, gastric cancer is the second leading cause of cancer deaths because of the lack of effective treatments for patients with advanced tumors when curative surgery is not possible. Thus, there is an urgent need to identify molecular targets in gastric cancer that can be used for developing novel therapies and prolonging patient survival. Checkpoint kinase 1 (Chk1) is a crucial regulator of cell cycle transition in DNA damage response (DDR). In our study, we report that Chk1 plays an important role in promoting gastric cancer cell survival and growth, which serves as an effective therapeutic target in gastric cancer. First, Chk1 ablation by small interfering RNA could significantly inhibit cell proliferation and sensitize the effects of ionizing radiation (IR) treatment in both p53 wild type gastric cancer cell line AGS, and p53 mutant cell line MKN1. Secondly, we tested the anticancer effects of Chk1 chemical inhibitor LY2606368, which is a novel Chk1/2 targeted drug undergoing clinical trials in many malignant diseases. We found that LY2606368 can induce DNA damage, and remarkably suppress cancer proliferation and induce apoptosis in AGS and MKN1 cells. Moreover, we identified that LY2606368 can significantly inhibit homologous recombination (HR) mediated DNA repair and thus showed marked synergistic anticancer effect in combination with poly (ADP-ribose) polymerase 1 (PARP1) inhibitor BMN673 in both in vitro studies and in vivo experiments using a gastric cancer PDx model. The synergy between LY2606368 and PARP1 was likely caused by impaired the G2M checkpoint due to LY2606368 treatment, which forced mitotic entry and cell death in the presence of BMN673. In conclusion, we propose that Chk1 is a valued target for gastric cancer treatment, especially Chk1 inhibitor combined with PARP inhibitor may be a more effective therapeutic strategy in gastric cancer.