Adeno-Associated Virus-Mediated Knockdown of Agmatinase Attenuates Inflammation and Tumorigenesis in a Mouse Model of Colitis-Associated Colorectal Cancer

Abstract

Agmatinase (AGMAT) is an enzyme that hydrolyzes agmatine to putrescine and urea. In this study, we explored the functions of AGMAT in colorectal cancer (CRC). By performing gain-of-function and loss-of-function experiments, we investigated the roles of AGMAT in proliferation, cell cycle progression, and apoptosis of CRC cells. We also established a colitis-associated colorectal cancer model by challenging mice with azoxymethane (AOM) and dextran sodium sulfate (DSS), and we subsequently silenced AGMAT expression in mice by adeno-associated virus 9 (AAV9)-mediated delivery of short hairpin RNA (shRNA). In vitro experiments showed that overexpression of AGMAT accelerated the proliferation and inhibited the apoptosis of CRC cells, and AGMAT knockdown exhibited the opposite effects. Interestingly, the oncogenic transcription factor, c-Myc, could bind to the AGMAT promoter and transcriptionally increase AGMAT expression in CRC cells. Additionally, c-Myc and AGMAT were upregulated in the colon of AOM/DSS-treated mice, and AGMAT silencing significantly mitigated colitis in AOM/DSS-treated mice, as evidenced by the increased colon length, attenuated crypt damage, and reduced levels of inflammatory indicators (myeloperoxidase, interleukin-6, tumor necrosis factor-α, inducible nitric oxide synthase, and phosphorylated p65) in colon tissues. Notably, AGMAT silencing decreased both the number and size of tumors, reduced expression of proliferating cell nuclear antigen, and inhibited phosphorylation of protein kinase B (AKT) and extracellular signal-regulated kinase in the colon of AOM/DSS-treated mice. Overall, we determined that AGMAT facilitates tumor progression in CRC. Our findings will be helpful in the search for potential therapeutic targets for CRC.