No abstract

It has been established that the acute phase protein, Serum amyloid A (SAA), which is usually synthesized by the liver, is also synthesized by cancer cells and cancer-associated cells in the tumor microenvironment. SAA also activates modulators of autophagy, such as the PI3K/Akt and MAPK signaling pathways. However, the role of SAA in autophagy in breast cancer still remains to be elucidated. The aim of this study was to investigate the role of SAA in the regulation of signaling pathways and autophagy in in vitro and in vivo models of breast cancer. The MDA-MB-231 and MCF7 cell lines were transiently transfected to overexpress SAA1. A tumor-bearing SAA1/2 knockout mouse model was also utilized in this study. SAA1 overexpression activated ERK signaling in the MDA-MB-231 cells, downregulated the PI3K pathway protein, PKB/Akt, in the MCF7 cell line, while SAA1/2 knockout also inhibited Akt. Furthermore, SAA1 overexpression in vitro downregulated autophagy, while the expression of SQSTM1/p62 was increased in the MCF7 cells, and SAA1/2 knockout induced autophagy in vivo. SAA overexpression in the MDA-MB-231 and MCF7 cells resulted in an increase in cell viability and increased the expression of the proliferation marker, MCM2, in the MCF7 cells. Furthermore, knockout of SAA1/2 resulted in an altered inflammatory profile, evident in the decrease of plasma IL-1β, IL-6 and IL-10, while increasing the plasma levels of MCP-1 and TNF-α. Lastly, SAA1/2 knockout promoted resistance to apoptosis and necrosis through the regulation of autophagy. SAA thus regulates autophagy in breast cancer cells to promote tumorigenesis.

Background Past research has identified the family of Serum Amyloid A (SAA) proteins to be intricately involved in inflammatory signaling and various disease pathologies. In cancer patients, SAA proteins have been reported to be upregulated in blood and tumor tissue, correlating in many instances with disease progression. However, the exact role of SAA proteins in cancer pathology remains to be fully elucidated. We, therefore, investigated systemic SAA1 and SAA2 (SAA1/2) in modulating the inflammasome, cell cycle, apoptosis, and epithelial-to-mesenchymal transition (EMT). Methods Breast cancer allografts were established in wild-type mice (WT), and mice lacking the SAA1/2 orthologs (SAADKO). Subsequently, tumor volume was monitored, species survival determined, the inflammatory profiles of mice assessed with a multiplex assay, and tumor molecular biology and histology characterized with western blotting and H&E histological staining. Results WT tumor-bearing mice had increased levels of plasma SAA compared to WT control mice, while SAADKO control and tumor-bearing mice presented with lower levels of SAA in their plasma. SAADKO tumor-bearing mice also displayed significantly lower concentrations of the systemic inflammatory markers, IL-1β, IL-6, and IL-10 compared to WT tumor-bearing mice. Tumors from SAADKO mice overall had lower levels of SAA compared to tumors from WT mice, decreased apoptotic (cytochrome c, caspases 9/3, PARP), and inflammasome (NFκB, caspase 1, NLRP3) signaling, with little to no tumor necrosis. Conclusions We show that systemic SAA1/2 promotes the activation of the NLRP3 inflammasome in breast cancer tumors and the generation of pro-inflammatory cytokines, which promotes apoptosis and tumor necrosis. Based on these findings, we hypothesize that SAA1/2-mediated necrosis is due to NLRP3-mediated pore formation in membranes, while apoptosis signaling is likely mediated via the TIF-IA-NF-κB-apoptosis axis.