Thioredoxin domain-containing protein 9 (TXNDC9) contributes to oxaliplatin resistance through regulation of autophagy-apoptosis in colorectal adenocarcinoma
Introduction
Colorectal cancer (CRC) is the third most common malignancy worldwide [1]. It has become a public health crisis with almost 2 million new cases every year. The mortality rate of CRC is remarkably high and 860,000 CRC-related deaths occurred in 2018 around the world [2]. In China, the incidence of CRC is on the rise and has led to an indisputable societal burden due to the high cost of cancer treatments [3,4]. Therefore, CRC is currently a hot area in scientific research, with great interest in prevention, early cancer screening, and treatment of this severe disease. Chemotherapy drugs used in the treatment of CRC include 5-fluorouracil (5-FU) capecitabine, irinotecan, and oxaliplatin [5]. Oxaliplatin is a third-generation platinum drug and has become a standard for treating colorectal tumors [6]. However, resistance to oxaliplatin-chemotherapy has become a significant cause for treatment failure and CRC-related death. Hence, it is critically important to understand the molecular mechanisms underlying the development of drug resistance to oxaliplatin in order to optimize the chemotherapy.
NF-E2-related factor 2 (Nrf2) pathway, a well-known antioxidant cell signaling pathway, is implicated in many malignant cells [7]. Nrf2/Keap1 signaling was observed in chemo-resistant processes through transcriptional induction of Nrf2 targeted cytoprotective genes, including NADPH, NQO1, and HO1 [8]. These genes are associated with detoxification, energy metabolism, cell differentiation, and autophagy [9]. Autophagy is a cellular catabolic process functioning in degradation of misfolded proteins or damaged cellular components to provide fuel for cells and maintain cellular homeostasis [10,11]. Any disturbance of this cytoprotective process leads to severe health problems such as metabolic disease, neurodegeneration, and many types of cancers [[12], [13], [14], [15]]. An enormous amount of literature supports the emerging role of autophagy in chemoresistance. Evidence in literature reveals that inhibition of autophagy sensitizes many types of cancer cells to chemotherapies [[16], [17], [18]].
Thioredoxin (TXN) domain-containing 9 (TXNDC9), a member of the TXN family, contains the same redox site as TXN. Although its biological functions remain unknown, recent studies implicated that TXNDC9 is critical for cell differentiation and progression of prostate cancer [19]. In addition, TXNDC9 also promotes hepatocellular carcinoma (HCC) development and is correlated with poor prognosis of HCC [20]. However, the biological functions of this protein in CRC, particularly oxaliplatin-related chemoresistance, has yet to be determined.
In this study, we anticipated that TXNDC9 might demonstrate a protective role in oxaliplatin-resistant CRC cells. TXNDC9 was found significantly upregulated when treated with oxaliplatin. Manipulation of TXNDC9 expression largely affects oxaliplatin-induced cell death. Moreover, TXNDC9 regulates the autophagy and apoptosis in response to oxaliplatin treatment in HT29 cells via the Nrf2 pathway. Taken together, our findings explore the biological role of TXNDC9 in oxaliplatin resistance in CRC cells and provide a novel therapeutic target to counteract drug resistance to oxaliplatin.
Section snippets
Cell culture
The colorectal adenocarcinoma cell line HT29 was purchased from American Type Culture Collection (Manassas, VA) and grown in Dulbecco’s Modified Eagle Medium (DMEM) (Invitrogen Life Technologies) containing 10% fetal bovine serum (FBS) (Biomeda) and 1% penicillin-streptomycin-glutamine (Thermo Fisher Scientific) in a humidified incubator with 5% CO2 at 37 °C.
Antibodies and reagents
The following primary antibodies were used in the present study: rabbit anti-cleaved PARP (#5625, 1:1000, Cell Signaling Technology),
Results
Oxaliplatin treatment induces TXNDC9 upregulation and autophagy in CRC cells. TXNDC9 is implicated in cell proliferation in some types of cancers [19,20]. To investigate the involvement of TXNDC9 in cancer cell sensitivity to oxaliplatin, we tested the expression of TXNDC9 post-treatment with oxaliplatin. HT29 cells were exposed to oxaliplatin treatment at different doses for 24 h. Western blot analysis showed that autophagy pathways were significantly evoked in response to oxaliplatin in a
Discussions
CRC is one of the leading causes of malignancy-related deaths [1]. In the last decade, discovery of novel chemotherapy agents have led to a remarkable increase in overall patient survival. However, intrinsic and acquired resistance of tumor cells to chemo-drugs cause treatment failure and tumor recurrence. A growing interest exists in identifying the molecular mechanisms underlying chemotherapy resistance including epigenetic alteration, DNA repair, intracellular detoxification, and autophagy.
Declaration of competing interest
The authors have declared no competing interests.
Acknowledgments
This research was supported by grants from the National Natural Science Foundation of China (No.81770212).
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