Salmonella protein AvrA Promotes Chronic Infection Through MDM2
Medicine and Health Sciences
Background: Recent studies indicated that chronic Salmonella infection contributes to increased risk of human colon cancer. In our previous studies, we found that Salmonella type III secretion effector protein AvrA can induce colon cancer by activating the wnt/ β-catenin pathway. Here, we examined the mechanism of DNA damage and repair by AvrA in the context of Salmonella infectivity. We hypothesize that AvrA downregulates P53 through MDM2, inhibiting apoptosis and allowing Salmonella to establish chronic infection. Methods: We used Salmonella infected human colon epithelial HCT116 cells in vitro and a Salmonella infected mouse model in vivo. The Salmonella strains used included wild type Salmonella (WT), AvrA knockout Salmonella (AvrA-), AvrA overexpression Salmonella (AvrA+), and a Salmonella mutant strain Phopc (Phopc). Western Blot (WB) analysis of proteins in the MDM2/P53 pathway was performed at multiple time points. Tangential markers of virulence included weight loss, fecal Salmonella content, and invasion of Salmonella to other tissues. Results: In human HCT116 cells infected with Salmonella for 8 hours, MDM2, LB1, and RAD51 were significantly higher in the WT and AvrA+ groups compared to the AvrA- group, while P53 was lower. Colon tissue from mice infected with Salmonella for 8 hours showed a similar trend observed in vivo. In colon tissue from mice infected with Salmonella for 11 days, MDM2 expression remained high in the WT and AvrA+ groups compared to the AvrA- group, but P53 expression was presumably recovered through the known ATM/CHK pathway, indicating that AvrA mainly influenced cell-survival in the short-term to allow establishment of chronic infection. ArvA- mice infected for 10 days had lower Salmonella liver translocation and fecal CFU than WT or AvrA+ infected mice, indicating that AvrA promoted intracellular survival, growth, and spread. AvrAinfected mice lost more weight than AvrA+ infected mice, however WT infected mice lost more weight than both groups. This project is ongoing; there are additional 11-day infection mouse samples to WB and the cell culture infection will be repeated before quantifying the WB data. Conclusion: Our study demonstrates that Salmonella effector protein AvrA negatively regulates P53 through MDM2, decreasing the virulence of Salmonella and promoting translocation and chronic infection. Our study provides new insight into the bacterial regulation of DNA damage in host-bacterial interactions. Acknowledgements: This work was performed with Dr. Lang Zha in the lab of Dr. Jun Sun at the University of Illinois at Chicago.
Copyright 2019 all authors
Xia, Eric OMS-2 and Zha, Lang, "Salmonella protein AvrA Promotes Chronic Infection Through MDM2" (2019). MU-COM Research Day. 112.