INTERNATIONAL CONGRESS OF
CancerGenetics
LncRNA NEAT1 remodels chromatin to promote the 5-Fu resistance by maintaining colorectal cancer stemness
-
fatemeh,1,* farideh,2
- Introduction: Colorectal cancer (CRC) is the third leading cause of all-cancer-related death1. The treatment of CRC is mainly through surgery and drugs. 5-fluorouracil (5-Fu) is an effective drug for colorectal cancer2. So studying the mechanism of 5-Fu resistance may be a key factor in improving colorectal cancer survival3. At present, more and more studies showed that cancer stem cells have the ability of self-renewal and partial differentiation4–7. They have some mechanisms to escape from damages caused by drugs, such as high drug transporter expression, efficient DNA repair, quiescence, and apoptotic block8. Thus, cancer stem cells are regarded as a main contributor of chemoresistance9–12. LncRNAs are defined as RNA polymerase II transcripts longer than 200 nucleotides in length with limited coding potential13,14. NEAT1 is an essential component of nuclear paraspeckles and can participate in transcriptional regulation15. Studies had shown that lncRNA NEAT1 acted as a scaffold and recruited the chromosome modification enzyme EZH2 to silence target-specific genes, thereby promoting β-catenin nuclear transport and promoting the occurrence of gliomas16. In triple-negative breast cancer, lncRNA NEAT1 confered the oncogenic role through modulating chemoresistance and cancer stemness17. However, the biological role of NEAT1 on CRC cell 5-Fu chemoresistance remains poorly understood. In present study, we want to investigate the role of NEAT1 in CRC chemoresistance and reveal the way NEAT1 affect the resistance to 5-Fu.
- Methods: All the human CRC tissues and paratumor normal tissues were collected in the Department of Colorectal Cancer Surgery, the Second Affiliated Hospital of Harbin Medical University. After surgical debulking, patients have undergone XELOX or mFOLFOX6 regimen therapy. Informed consent was obtained from the patients before sample collection in accordance with institutional guidelines. Recurrence was monitored by imaging examination systems (Chest X-ray and CT), gastrointestinal endoscopy with biopsy, and telephone follow-up. In order to obtain two independent cohorts for mutual verification, cohort A was collected from January 2012 to September 2012 and cohort B was collected from January 2014 to September 2014. The expression of NEAT1 was evaluated in cohort A and cohort B. The prognostic significance of NEAT1 was evaluated in cohort B. Patients were pathologically and clinically diagnosed with colorectal cancer. This study was carried out under the permission of the Clinical Research Ethics Committees of the Second Affiliated Hospital of Harbin Medical University.
- Results: To study the role of NEAT1 in CRC, we first detected its expression in CRC tissues and normal tissues in The Cancer Genome Atlas (TCGA) datasets. TCGA shown elevated NEAT1 levels in human CRC tissue relatived to normal tissue (Fig. (Fig.1A).1A). Next, Kaplan–Meier analysis was used to determine whether NEAT1 expression levels in the CRC tissues were associated with clinical patient outcome. Survival analysis of the TCGA cohort revealed that a higher NEAT1 level was associated with poor disease-free survival (DFS) in CRC patients (Fig. (Fig.1B).1B). Next, we measured NEAT1 levels in 66 pairs of normal tissues and tumor tissues of CRC patients without recurrence, and 16 pairs of normal tissues and tumor tissues of CRC patients with recurrence by qRT-PCR. As shown in Fig. Fig.1C,1C, the expression level of NEAT1 in tumor tissues of most patients is significantly higher than that of normal tissues. And we can see that the expression level of NEAT1 in tumor tissues of patients with recurrence is higher than that of patients without recurrence (Fig. (Fig.1D),1D), whose clinical characteristics were shown in Supplemental Table 1. Next, we used another cohort B (55 pairs of normal tissues and tumor tissues of CRC patients without recurrence, and 27 pairs of normal tissues and tumor tissues of CRC patients with recurrence) of our center to validate the results of cohort A, and the results were consistent (Supplemental Table 2 and Fig. Fig.1E).1E). Then we evaluated the prognostic significance of NEAT1 in cohort B. Patients in the NEAT1-high-expression group showed a shorter recurrent free survival (RFS) than those in the NEAT1-low-expression group (P = 0.01, Fig. Fig.1F).1F). This suggests that NEAT1 may play a role in CRC recurrence.
- Conclusion: Colorectal cancer is the leading cause of cancer deaths worldwide, and 5-Fu based chemotherapy has been widely used to treat different types of cancer including CRC. Understanding the mechanisms of resistance in CRC is imperative to improve the survival. In recent years, studies have shown that NEAT1 was associated with resistance to chemotherapy in hepatocellular carcinoma24, endometrial cancer25 and others. Moreover, the effects of NEAT1 and cancer stem cells in breast cancer have also been reported17. In this study, we observed that NEAT1 was highly expressed in colorectal cancer tissues from patients with recurrence and was also associated with poor recurrence-free survival. Thus, NEAT1 may be related to patients’ drug resistance and recurrence. To elucidate the underlying mechanism, further research revealed that downregulation of NEAT1 significantly inhibited the growth of CRC cell lines and reduced the sensitivity to 5-Fu. At present, more and more studies have shown that cancer stem cells can evade the damage of chemotherapy drugs through some mechanisms8. We speculated that NEAT1 may mediate drug resistance by regulating the stemness of CRC. Further research showed that the activity of ALDH1 and CD133 was decreased by downregulating the expression of NEAT1 in colorectal cancer cell lines. Next, we found that downregulation of NEAT1 decreased the expression of stemness factors, such as SOX2, NANOG, c-Myc, and OCT4. In summary, knockdown of NEAT1 could reduce the expression of stemness factors to inhibit CSC properties of colorectal cancer cells. NEAT1 is a component of nuclear paraspeckle, so we speculated that knockdown of NEAT1 may affect chromatin remodeling. Studies have shown that NEAT1 can be used as a scaffold to participate in the chromatin remodeling of glioma cells, promote the increase of the trimethylation level of the promoter of downstream genes, and then promote its expression16. In our study, we found that NEAT1 increased H3K27ac by affecting chromatin remodeling and led to an increase in acetylation levels of ALDH1 and c-Myc promoter regions, which increased their expression and thus enhanced the stemness of colorectal cancer cells. In summary, our work demonstrated that NEAT1 was associated with 5-Fu resistance in CRC patients, suggesting that NEAT1 may affect 5-Fu resistance in colon cancer cells by affecting cancer cell stem. In addition to its biological importance, our work may be related to the clinical management of CRC patients. Our data raise an important clinical question: Are conventional chemotherapy regimens, including 5-Fu, suitable for CRC patients with high NEAT1 expression? Alternatively, we suggest that traditional chemotherapy be combined with drugs that target tumor stem cells to treat CRC patients with high levels of NEAT1.
- Keywords: Cancer stem cells, Oncogenes, Cancer stem cells, Oncogenes
