CRISPR-Cas9 based knockout of S100A8 in mammary epithelial cells enhances cell proliferation and triggers oncogenic transformation via the PI3K-Akt pathway: Insights from a deep proteomic analysis.

S100A8 is a calcium-binding protein with multiple functions, including being a chemoattractant for phagocytes and playing a key role in the inflammatory response. Its expression has been shown to influence epithelial-mesenchymal transition (EMT) and metastasis in colorectal cancer. However, the role of S100A8 in cell proliferation and differentiation remains unknown. In this study, we used the CRISPR-Cas9 system to knock out S100A8 in healthy mammary epithelial cells and investigated the resulting changes in proteome profiling and signaling pathways. Our results showed that S100A8 knockout led to an increase in cell proliferation and migration, reduced cell-cell adhesion, and increased apoptosis compared to wildtype cells. Proteomics data indicated that S100A8 significantly affects cell cycle progression, cell proliferation, and cell survival through the PI3K-Akt pathway. Furthermore, our findings suggest that S100A8 function is associated with Pten expression, a negative regulator of the PI3K-Akt pathway. These results indicate that S100A8 dysregulation in healthy cells can lead to altered cellular physiology and higher proliferation, similar to cancerous growth. Therefore, maintaining S100A8 expression is critical for preserving healthy cell physiology. This study provides novel insights into the role of S100A8 in cell proliferation and differentiation and its potential relevance to cancer biology. SIGNIFICANCE: The study suggests that maintaining S100A8 expression is critical for preserving healthy cell physiology, and dysregulation of S100A8 in healthy cells can lead to altered cellular physiology and higher proliferation, similar to cancerous growth. Therefore, targeting the PI3K-Akt pathway or regulating Pten expression, a negative regulator of the PI3K-Akt pathway, may be potential strategies for cancer treatment by controlling S100A8 dysregulation. Additionally, S100A8 and S100A9 have been shown to promote metastasis of breast carcinoma by forming a metastatic milieu. However, the differential expression of S100A8 in tumors and its dual effects of antitumor and protumor make the relationship between S100A8 and tumors complicated. Currently, most research focuses on the function of S100A8 as a secretory protein in the microenvironment of tumors, and its function inside healthy cells without forming dimers remains unclear. Furthermore, the study provides insight into the role of S100A8 in cell proliferation and differentiation, which may have implications for other diseases beyond cancer. The functional role of S100A8 in normal mammary epithelial cells remains completely uncertain. Therefore, the objective of this study is to investigate the function of S100A8 on proliferation in mammary epithelial cells after its deletion and to elucidate the underlying proteins involved in downstream signaling. Our findings indicate that the deletion of S100A8 leads to excessive proliferation in normal mammary epithelial cells, reduces apoptosis, and affects cell-cell adhesion molecules required for cellular communication, resulting in a cancer-like phenotype.