ABSTRACT
Ribosome assembly factor URB1 is essential for ribosome biogenesis. However, its latent role in cancer remains unclear. Analysis of The Cancer Genome Atlas database and clinical tissue microarray staining showed that URB1 expression was upregulated in colorectal cancer (CRC) and prominently related to clinicopathological characteristics. Silencing of URB1 hampered human CRC cell proliferation and growth in vitro and in vivo. Microarray screening, ingenuity pathway analysis, and JASPAR assessment indicated that activating transcription factor 4 (ATF4) and X-box binding protein 1 (XBP1) are potential downstream targets of URB1 and could transcriptionally interact through direct binding. Silencing of URB1 significantly decreased ATF4 and cyclin A2 (CCNA2) expression in vivo and in vitro. Restoration of ATF4 effectively reversed the malignant proliferation phenotype of URB1-silenced CRC cells. Dual-luciferase reporter and ChIP assays indicated that XBP1 transcriptionally activated ATF4 by binding with its promoter region. X-box binding protein 1 colocalized with ATF4 in the nuclei of RKO cells, and ATF4 mRNA expression was positively regulated by XBP1. This study shows that URB1 contributes to oncogenesis and CRC growth through XBP1-mediated transcriptional activation of ATF4. Therefore, URB1 could be a potential therapeutic target for CRC.
Subject(s)
Activating Transcription Factor 4/genetics , Cell Proliferation/genetics , Colorectal Neoplasms/genetics , Nuclear Proteins/genetics , Ribosomes/genetics , Transcriptional Activation/genetics , Cell Line, Tumor , Cell Transformation, Neoplastic/genetics , Colorectal Neoplasms/pathology , Female , Gene Expression Regulation, Neoplastic/genetics , HCT116 Cells , Humans , Male , Middle Aged , Signal Transduction/genetics , Up-Regulation/genetics , X-Box Binding Protein 1/geneticsABSTRACT
Mammalian target of rapamycin complex 1 (mTORC1) is evolutionally conserved and frequently activated in various tumors, including colorectal cancer (CRC). It has been reported that the ribosome assembly factor Urb1 acts downstream of mTORC1/raptor signaling and contributes to digestive organ development in zebrafish. Previously, we highlighted that URB1 was overexpressed in CRC. Here, we assessed the mTORC1/regulatory associated protein with mTOR (RAPTOR)-URB1 axis in CRC tumorigenesis. We found that RAPTOR was overexpressed in CRC tissues and cell lines, was a favorable predictor in patients with CRC, and positively correlated with URB1. Silencing of RAPTOR suppressed CRC cell proliferation and migration and induced cell cycle arrest and apoptosis in vitro and inhibited xenograft growth in vivo. Moreover, ectopic overexpression of RAPTOR exerted an inverse biological phenotype. Knockdown of RAPTOR quenched mTORC1 activity and reduced the expression of URB1 and cyclinA2 (CCNA2). In contrast, overexpression of RAPTOR activated mTORC1 and upregulated URB1 and CCNA2. Furthermore, URB1 and CCNA2 expression were also impeded by rapamycin, which is a specific inhibitor of mTORC1. Thus, RAPTOR promoted CRC proliferation, migration, and cell cycle progression by inducing mTORC1 signaling and transcriptional activation of both URB1 and CCNA2. Taken together, we concluded that RAPTOR has the potential to serve as a novel biomarker and therapeutic target for CRC.
Subject(s)
Biomarkers, Tumor/metabolism , Colorectal Neoplasms/genetics , Mechanistic Target of Rapamycin Complex 1/metabolism , Nuclear Proteins/genetics , Regulatory-Associated Protein of mTOR/metabolism , Animals , Apoptosis/drug effects , Apoptosis/genetics , Biomarkers, Tumor/genetics , Carcinogenesis/drug effects , Carcinogenesis/genetics , Cell Line, Tumor , Cell Proliferation/drug effects , Cell Proliferation/genetics , Colon/pathology , Colon/surgery , Colorectal Neoplasms/diagnosis , Colorectal Neoplasms/mortality , Colorectal Neoplasms/surgery , Cyclin A2/genetics , Female , Gene Expression Regulation, Neoplastic/drug effects , Gene Knockdown Techniques , Humans , Kaplan-Meier Estimate , Male , Mechanistic Target of Rapamycin Complex 1/antagonists & inhibitors , Mice , Middle Aged , Rectum/pathology , Rectum/surgery , Signal Transduction/drug effects , Signal Transduction/genetics , Sirolimus/pharmacology , Up-Regulation/drug effects , Xenograft Model Antitumor AssaysABSTRACT
PURPOSE: The aim of this meta-analysis was to compare high inferior mesenteric artery (IMA) ligation (HL) with low IMA ligation (LL) for the treatment of colorectal cancer and to evaluate the lymph node yield, survival benefit, and safety of these surgeries. METHODS: PubMed, Embase, Cochrane Library, Web of Science, and China Biomedical Literature Database (CBM) were systematically searched for relevant articles that compared HL and LL for sigmoid or rectal cancer. We calculated the odds ratio (OR) with 95% confidence intervals (CIs) for dichotomous outcomes and the weighted mean difference (WMD) for continuous outcomes. RESULTS: In total, 30 studies were included in this analysis. There were significantly higher odds of anastomotic leakage and urethral dysfunction in patients treated with HL compared to those treated with LL (OR = 1.29; 95% CI = 1.08 to 1.55; OR = 2.45; 95% CI = 1.39 to 4.33, respectively). There were no significant differences between the groups in terms of the total number of harvested lymph nodes, the number of harvested lymph nodes around root of the IMA, local recurrence rate, and operation time. Further, no statistically significant group differences in 5-year overall survival rates and 5-year disease-free survival rates were detected among all patients nor among subgroups of stage II patients and stage III patients, respectively. CONCLUSIONS: LL can achieve equivalent lymph node yield to HL, and both procedures have similar survival benefits. However, LL is associated with a lower incidence of leakage and urethral dysfunction. Thus, LL is recommended for colorectal cancer surgery.
