HIV-1 viral protein R (Vpr) induction of apoptosis and cell cycle arrest in multidrug-resistant colorectal cancer cells

Abstract

Abstract. Colorectal cancer is a significant health problem, and the advanced stages of the disease have a low response rate to chemotherapy and easily acquire chemoresistance. HIV-1 viral protein R (Vpr) has been shown to possess inhibitory effects on various malignant cells in vivo and in vitro. In this study, an Ad-Vpr construct was used to infect the multidrug-resistant human colorectal cancer HCT-8/5-FU(MDR) cell line in vitro for cell viability, apoptosis, gene expression and gene activity using the MTT, flow cytometry, immunoblotting and gel shift assays, respectively. The data showed that Ad-Vpr significantly reduced HCT-8/5-FU(MDR) cell viability in a dose-and time-dependent manner. Ad-Vpr infection promoted HCT-8/5-FU(MDR) cells to undergo apoptosis and to arrest at the G2 phase of the cell cycle. The G2 cell cycle protein Cyclin B1 accumulated in the cells after Ad-Vpr infection. Furthermore, Ad-Vpr induced activation of caspase-3 and -9, but not caspase-8, in HCT-8/5-FU(MDR) cells. Ad-Vpr suppressed expression of the Bcl-xl protein, but upregulated Bax expression and cytochrome c release from the mitochondria in HCT-8/5-FU(MDR) cells. Ad-Vpr infection also resulted in a time-dependent decrease in nuclear translocation of NF-κB/p65 protein and p65 DNA-binding activity in HCT-8/5-FU(MDR) cells. The data from the current study provide mechanistic insights into understanding the molecular basis and utility of Ad-Vpr as a novel anticancer agent for multidrug resistance in human colorectal cancer. IntroductionColorectal cancer is a significant health problem in the world, and is the third most common cancer in women and the fourth most common in men. More than half a million patients with colorectal cancer die of the disease annually worldwide (1,2). To date, surgical intervention is the most effective tool to cure colorectal cancer, whereas chemotherapy is another important means to treat colorectal cancer, especially for advanced staged disease. In those patients, chemotherapy appears to be the only therapeutic modality and offers some benefit. For chemotherapy, 5-fluorouracil (5-FU)-based regimens are the most common choice for patients. The combination of 5-FU with irinotecan and oxaliplatin has significantly improved the response rate of colorectal cancer patients. Additionally, combination regimens of 5-FU with irinotecan have been evaluated as the first-line therapeutic selection for advanced colorectal cancer with a response rate of 30-50% and an overall survival of 14-20 months (3,4). However, the response rate for these advanced targeted therapies and third-generation chemotherapies remains low (5). The reason may be due to innate and acquired chemoresistance (6) of colorectal cancer, which often leads to relapse and poor patient prognosis. Thus, a more aggressive and effective therapy to control colorectal cancer is imperative.To this end, our research focuses on the viral protein R (Vpr), which is an accessory protein and plays an important role in the regulation of nuclear import of the HIV-1 ...